CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
Peripheral Nervous System (PNS)
OBJECTIVES:
1.
Outline the major divisions of the nervous system.
2.
Discuss how the organs of the central nervous system (CNS) are protected in terms of
bones, membranes and fluid.
3.
Name the three meninges and discuss the differences between how they are structured
around the brain and spinal cord.
4.
Name the space that lies between two of the meninges surrounding both the brain and
spinal cord, and name the fluid that fills this space.
5.
Name the additional space that is found around the spinal cord, and name the fluid that
fills this space.
6.
Define the term meningitis.
7.
Discuss the external structure of the spinal cord in terms of its length, start, end, number
of segments, and enlarged areas.
8.
Name the terminal point of the spinal cord, the term used for how the remaining spinal
nerves appear, and the point at which they terminate.
9.
Fully discuss the cross-sectional anatomy of the spinal cord.
10.
Name the cells that line the central canal and identify the fluid that fills the central canal.
11.
Distinguish between a "horn" and a "column" in the spinal cord.
12.
Explain which portion of the spinal cord is the location for the major nerve tracts, and
discuss their significance.
13.
Compare and contrast ascending and descending tracts.
14.
Discuss the general characteristics of nerve tracts.
15.
Discuss the features located on the periphery of the spinal cord in cross-section.
16.
Define the term ganglion and discuss the specificities of a dorsal root ganglion.
17.
Define the term nerve pathway.
18.
List and discuss the components in a reflex arc.
19.
Discuss the significance of reflex arcs.
20.
Fully discuss the three-fold function of the nervous system.
A.
In the first sentence, name the three functions of the nervous system.
B.
Then write a paragraph discussing how and where a nerve impulse begins and
name the components of a nerve pathway.
C.
Then draw a simple nerve pathway that involves three neurons (with cell parts
labeled), and track (on your diagram) the transmission of a nerve impulse
throughout this pathway.
D.
Finally, fully discuss how the nerve impulse begins, how it travels through each
neuron, how it is transmitted between neurons, and finally, how it is transmitted to
the effector.
21.
Name and locate the three major regions of the brain.
22.
Discuss the structure of the cerebrum in terms of its size, two major divisions, surface
appearance, major grooves, and lobal divisions.
23.
Identify the composition of the bulk of the cerebrum.
24.
Define the term cerebral cortex and discuss its composition and significance.
25.
Compare the major functional areas (sensory and motor) of the cerebral cortex in terms of
location and function (a diagram may help here).
26.
Explain what is meant by an association area of the cerebral cortex and name a few
association traits.
27.
Name the term referring to the measurement of brain activity.
28.
Explain what is meant by hemisphere dominance, and name the hemisphere that is
dominant in most people.
29.
Define the term basal ganglia and explain their location and function.
30.
Name the interconnected cavities within the cerebrum and brain stem and identify the
fluid that fills these spaces and name the cells that line these spaces.
31.
Name the specialized capillaries that secrete CSF and denote their location on a diagram.
32.
Trace a drop of CSF from where it is secreted to where it is reabsorbed back into the
blood stream.
33.
Define the terms arachnoid granulations and dural sinuses.
34.
Discuss the functions of CSF.
35.
Discuss the two important areas of gray matter within the diencephalon, in terms of
location and function.
36.
Identify the three major parts of the brain stem.
37.
Discuss the midbrain in terms of its location, composition and function.
38.
Name the location of the pneumotaxic area of the respiratory center.
39.
Discuss the importance of the medulla (oblongata).
40.
Briefly explain the significance of the limbic system and reticular formation.
41.
Locate the cerebellum on a diagram, and discuss its structure and function.
42.
Discuss the general structure of a nerve.
43.
Distinguish between a mixed, sensory, and motor nerve.
44.
Name the twelve pairs of cranial nerves, designate them by Roman numeral, discuss their
function, and designate them as sensory, motor, or mixed.
45.
Discuss the characteristics of spinal nerves in terms of number, coverings, and
composition.
46.
Discuss how a spinal nerve is distributed.
47.
Define the term nerve plexus and explain its significance.
48.
Name the four major nerve plexuses and briefly discuss the areas that each innervates.
49.
Compare the somatic and autonomic divisions of the NS in terms of motor neurons
involved, the presence or absence of ganglia, neurotransmitter type, and effector type.
50.
Describe the general function of the ANS.
51.
Name the two major divisions of the ANS, and describe their general function.
52.
Compare the length of a preganglionic and postganglionic neuron in the sympathetic and
parasympathetic division of the ANS.
53.
Define the term ganglion, and compare the location of sympathetic and parasympathetic
ganglia.
54.
Explain why sympathetic ganglia are called chain ganglia.
55.
Compare the origin of a sympathetic preganglionic neuron with a parasympathetic
preganglionic neuron.
56.
Describe the structures around the spinal cord (i.e. dorsal root, ventral root, spinal nerve,
white ramus communicans, gray ramus communicans, paravertebral (chain) ganglia, and
prevertebral ganglia.)
57.
Explain the general preganglionic sympathetic pathway traveled by a nerve impulse to
the paravertebral (chain) ganglia.
58.
Explain the three different routes that a nerve impulse above may take from the
paravertebral ganglia (i.e. It may synapse with the postganglionic neuron either ...)
59.
Distinguish between cholinergic and adrenergic fibers (axons).
60.
Define the term receptor.
61.
Describe the two types of cholinergic and adrenergic receptors.
62.
Compare and contrast the two divisions of the ANS in terms of their name, general
function, origin of preganglionic fiber, length of preganglionic fiber, location of ganglia,
and type of neurotransmitter secreted by the postganglionic fiber.
I.
PROTECTION OF THE CNS
The brain and spinal cord are protected (surrounded) by bones, membranes, and fluid.
A.
Bones
1.
The brain is encased by eight skull bones (i.e. cranium; name the eight
bones);
2.
The spinal cord is encased by 26 bones that make up the vertebral column
B.
Meninges
The membranes around the brain and spinal cord are called "meninges"; three
distinct layers.
1.
Brain: See Figure 11.1, page 367.
o
o
o
o
o
o
o
a.
Dura mater ("white" in Fig 11.1):
outermost membrane that is attached to the inner
periosteum of the skull;
tough, white fibrous CT;
contains many blood vessels & nerves;
Note: DM splits into two layers where it encloses the dural
sinuses (that collect venous blood from the brain).
b.
Arachnoid Mater ("violet" in Fig 11.1):
middle layer;
thin net-like membrane.
Beneath the arachnoid mater lies a wide space called the
sub-arachnoid space.
This space is filled with cerebrospinal fluid (CSF) and
serves as a cushion for the brain.
o
o
o
o
*
c.
Pia Mater ("salmon" in Fig 11.1):
inner layer that clings to brain surface;
very thin delicate CT;
many nerves & blood vessels = nourishment;
dips into grooves & contours.
See blue boxes on page 368 concerning subdural hematoma & meningitis.
2.
a.
b.
c.
Spinal cord: See Fig 11.2, page 368.
Note that the dura mater is not attached to bone of the vertebra (as
in the brain where it is attached to the skull).
The space between the dura mater and the bone is called the
epidural space and is filled with loose CT and fat.
CSF fills the subarachnoid space and central canal.
I.
PROTECTION OF THE CNS
C.
Ventricles and Cerebrospinal Fluid (CSF)
1.
In addition to filling the subarachnoid space, CSF
fills the ventricles (interconnected cavities) within the cerebral
hemispheres and brain stem. See Figure 11.3, page 369.
2.
The Ventricles:
a.
are continuous with central canal of spinal cord;
b.
are filled with cerebrospinal fluid (CSF)
c.
are lined by ependymal cells (remember this
neuroglial cell in CNS?)
3.
Secretion and Circulation of CSF See
Figure
11.4, page 370.
a.
CSF is secreted by specialized capillaries in
choroid plexuses into the lateral ventricles (ventricles 1 & 2);
b.
CSF circulates down into the 3rd & then
4th ventricle and then into either:
o
the central canal of spinal cord;
o
the subarachnoid space of meninges.
c.
CSF is reabsorbed back into the bloodstream
through arachnoid granulations that project into dural sinuses.
d.
CSF movement is aided by cilia of
ependymal cells.
4.
CSF
a. Total volume in above spaces = 150 mL.
o
About 1 liter is secreted daily to replenish the circulating
150 ml every 3-4 hours.
b. Functions:
o
mechanical protection (i.e. cushion);
o
chemical protection (i.e. ions, hormones);
*
See CA 11.1, page 371 concerning CSF pressure.
II.
THE SPINAL CORD
The spinal cord is a nerve column that passes downward from brain into the vertebral
canal. Recall that it is part of the CNS. Spinal nerves extend to/from the spinal cord and
are part of the PNS.
A.
B.
Structure of the Spinal Cord: Longitudinal
See Fig 11.5, page 372.
1.
Length = about 17 inches;
a.
Start = foramen magnum;
b.
End = tapers to point (conus medullaris) and terminates near the
intervertebral disc that separates the 1st - 2nd lumbar (L1-L2)
vertebra.
2.
Contains 31 segments (and therefore gives rise to 31 pairs of spinal
nerves).
3.
Note cervical and lumbar enlargements.
4.
Note cauda equina (“horse’s tail”) in which the lower lumbar and sacral
nerves travel downward (i.e. lower spinal nerves must “chase” their points
of exit).
5.
Note filum terminale that represents distal portion of the tail (pia mater).
Structure of the Spinal Cord: Cross-Sectional
See Figure 11.6, page 373.
A cross-section of the spinal cord resembles a butterfly with its wings outspread
(gray matter) surrounded by white matter.
1.
Gray matter or "butterfly" = bundles of (interneuron) cell bodies:
a.
b.
c.
2.
posterior (dorsal) horns,
lateral horns, and
anterior (ventral) horns.
Note location of:
a.
central canal (lined by ependymal cells),
b.
gray commissure,
c.
anterior median fissure,
d.
posterior median sulcus.
II.
THE SPINAL CORD
B.
Structure of the Spinal Cord: Cross-Sectional
3.
White matter = myelinated (interneuron) axons:
a.
Locations:
o
posterior (dorsal) funiculi or white column,
o
lateral funiculi or white column, and
o
anterior (ventral) funiculi or white column.
4.
Other Important Features:
a.
ventral root;
b.
dorsal root;
o
dorsal root ganglion (DRG).
1.
Ganglion = a bundle of cell bodies outside the CNS;
2.
DRG contains the cell bodies of sensory (afferent)
neurons bringing impulses to the CNS.
c.
The fusion of the dorsal and ventral roots designates the beginning
of the spinal nerve which then passes through its intervertebral
foramen.
5.
Summary sketch:
II.
THE SPINAL CORD
C.
Functions of the Spinal Cord
Nerve Pathway = the route traveled by a nerve impulse through the nervous
system.
1.
Reflex arc = the simplest demonstration of a nerve pathway
See Figure 11.7, page 374.
a.
b.
c.
involves 2-3 neurons;
involuntary response;
does not involve the brain;
d.
Examples include:
o
o
o
o
2.
knee-jerk or patellar reflex (Fig 11.8, page 374)
withdrawal (Fig 11.9, page 375 & Fig 11.10, page 376)
sneezing
blinking
Components of a Reflex arc:
See Table 11.2, page 375.
a.
b.
c.
d.
e.
3.
A receptor, which reacts to a stimulus;
A sensory neuron, that conducts the afferent (sensory) impulses to
the CNS;
The integration center, consisting of one to several synapses in the
CNS;
A motor neuron, that conducts the efferent (motor) impulses from
the CNS to an effector;
An effector, the muscle fibers or gland that respond to the motor
impulse by contracting or secreting a hormone.
Uses of Reflexes: See Clinical Application 11.2, page 377.
a.
b.
to insure proper transmission of a NI from sensory receptor to
effector;
to prevent tissue damage.
II.
THE SPINAL CORD
D.
Ascending and Descending Tracts
1.
The white matter of the spinal cord represents the location
of our major nerve pathways called "nerve tracts".
a.
b.
E.
provide a 2-way system of communication:
See Figures 11.11, 11.13, pages 377-379 and Table 11.3, page 379.
o
In general, ascending tracts are located in the posterior
(dorsal) columns and conduct sensory (afferent) impulses
from body parts to brain;
o
In general, descending tracts are located in the anterior
(ventral) columns and conduct motor (efferent) impulses
from brain to effectors.

General characteristics of nerve tracts:
1.
Most cross over;
2.
Most consist of 2-3 successive neurons;
3.
Most exhibit somatotropy (i.e. tracts
from/to upper body are located on outside,
tracts from/to lower body on inside);
All pathways are paired (right and left).
Spinal Cord Injuries. See Clinical Application 11.3, page 380.
III.
BRAIN
A.
Brain Development
1.
Embryonic neural tube expands and hollows cranially.
2.
Three vesicles develop that split and become four adult ventricles.
3.
The walls of the three vesicles become certain adult brain areas
a.
b.
c.
Forebrain = Cerebrum, basal nuclei, and diencephalons
Midbrain = Midbrain
Hindbrain = pons, medulla oblongata, and cerebellum
The brain is the largest and most complex portion of the nervous system. It occupies the
cranial cavity and is composed of one hundred billion multipolar neurons. The brain
oversees the function of the entire body and also provides characteristics like personality.
The brain is composed of 4 major portions, including the cerebrum, cerebellum,
diencephalon and brain stem.
See Figure 11.15, page 382 and reference plate 76, page 968.
B.
Structure of the Cerebrum
1.
Cerebrum = the largest portion of the brain, which is
divided into two cerebral hemispheres.
a.
b.
c.
d.
Hemispheres are connected by a deep bridge of nerve fibers called
the corpus callosum;
Surface ridges are called convolutions* (gyri);
Each hemisphere is divided into lobes, which are named for
the bones that cover them including frontal, parietal,
temporal, and occipital lobes.
See Fig 11.16, page 383.
Convolutions are separated by two types of grooves:
o
o
*
sulci = shallow groove;
1.
central sulcus (frontal/parietal)
2.
lateral sulcus (temporal/others)
fissure = deep groove;
1.
longitudinal fissure separates the two cerebral
hemispheres.
2.
transverse fissure (cerebrum/cerebellum)
See blue box on page 384 concerning a disorder called
lissencephaly ("smooth brain").
III.
BRAIN
B.
Structure of the Cerebrum
1.
Cerebrum
e.
Composition:
o
Bulk of cerebrum is white matter.
*
o
C.
nerve
fibers
(by
Cerebral cortex or the outer portion of cerebrum is
composed of gray matter.
*
o
bundles of myelinated
oligodendrocyte);
bundles of neuron cell bodies.
Sketch:
Functions of the Cerebrum
1.
Functional Regions of the Cerebral cortex
See Fig 11.17, page 385.
Responsible for all conscious behavior by containing
three kinds of functional areas, which include motor, sensory and
association areas:
a.
Motor Areas are located in the frontal cortex:
o
Primary motor cortex
1.
initiates all voluntary muscle movements;
2.
located
in the gyrus just anterior to the central sulcus
(precentral gyrus).
o
Broca's area
1.
motor speech area;
2.
located
in left frontal lobe, above temporal lobe;
III.
BRAIN
C.
Functions of the Cerebrum
1.
Functional Regions of the Cerebral cortex
b.
Sensory Areas are concerned with
conscious awareness of sensations and are located in the parietal,
occipital, and temporal cortex.
o
Primary somatosensory cortex
1.
receives information from general receptors (i.e.
temperature, touch, pressure, & pain).
2.
located in postcentral gyrus of parietal cortex;
o
Visual (Cortex) Area
1.
receives incoming information from vision
receptors (in eye);
2.
located in occipital cortex.
o
Auditory (Cortex) Area
1.
receives incoming information from hearing
receptors (in ear);
2.
located in temporal cortex.
o
Gustatory cortex Not Pictured on page 385.
1.
receives incoming information from taste receptors
in taste buds;
2.
located
in
parietal cortex just above the temporal lobe.
o
o

c.
Association Areas of cerebral cortex
General:
1.
include areas that are not directly involved in motor
or sensory function.
2.
are involved in many traits.
3.
are usually interconnected.
4.
involve all four lobes.
Association traits include:
1.
analyzing & interpreting sensory experiences;
2.
help provide
memory, reasoning, verbalizing, judgment and
emotions.
See Table 11.5, page 387, Functions of Cerebral Lobes.
III.
BRAIN
C.
Functions of the Cerebrum
1.
Functional Regions of the Cerebral cortex
d.
e.
2.
Hemisphere Dominance (Brain Lateralization)
o
Most basic functions (sensory & motor) are equally
controlled by both left & right hemispheres (remember
communication exists through corpus callosum).
o
However, for some association functions, one hemisphere
has greater control over language-related activities
including speech, writing, reading, mathematics and logic.
1.
This hemisphere is considered the "dominant
hemisphere".
a.
In most people, the left hemisphere is
dominant.
b.
The other hemisphere (non-dominant)
controls orientation in space, art and musical
appreciation and emotions.
Memory
Memory is the consequence of learning. Whereas learning is the
acquisition of new knowledge, memory is the persistence of that
learning, with the ability to access it at a later time.
o
Two types of memory:
See page 387 & 388.
1.
Short Term
2.
Long Term.
Basal Nuclei
c.
See Fig 11.19, page 389.
a.
masses of gray matter located deep within
the white matter of the cerebral hemispheres.
b.
serve as relay stations for outgoing motor
impulses from the brain.
(i.e. from primary motor cortex in frontal
cortex to basal ganglia and then through brain stem, down spinal
cord, etc.)
Release dopamine, which inhibits excess movements
*
See Clinical Application 11.5, page 390, Parkinson's disease.
III.
BRAIN
D.
Diencephalon:
1.
2.
See Fig 11.15, page 382 & Fig 11.21, page 392.
includes two important areas of gray matter:
a.
Thalamus
central relay station for incoming sensory impulses (except smell),
that directs the impulse to the appropriate area of the cerebral
cortex for interpretation;
b.
Hypothalamus
o
main visceral control center of the body (i.e. regulates
homeostasis).
a.
heart rate & blood pressure;
b.
body temperature;
c.
water & electrolyte balance;
d.
control of hunger & body weight;
e.
control of digestive movements & secretions;
f.
regulation of sleep-wake cycles;
g.
control of endocrine system functioning.
Limbic System = involved in Emotional response
a.
also includes structures in the frontal and
temporal cortex, basal nuclei, and deep nuclei;
b.
controls emotional experience and expression;
c.
can modify the way a person acts;
d.
produces feelings of fear, anger, pleasure, and sorrow;
e.
recognizes life threatening upsets in a
person's physical or psychological condition and counters them;
f.
involved in sense of smell.
III.
BRAIN
E.
Brain Stem: See Fig 11.20, page 389, and Fig 11.21, page 392.
The brain stem is composed of three major parts that include the midbrain,
pons, and medulla oblongata. The brain stem serves as a pathway for fiber
tracts running to (sensory impulses) and from (motor impulses) the cerebrum and
is the sight where many cranial nerves (PNS) arise.
1.
Midbrain
a.
located between diencephalon and
pons
b.
Corpora quadrigemina = 4 dome-like
protrusions on the dorsal midbrain surface (remember you saw
these in lab when you separated the cerebrum from cerebellum!);
c.
gray matter within white matter;
d.
acts in reflex actions (visual and
auditory);
e.
also contains areas associated with
reticular formation.
2.
Pons
a.
bulging portion of brain stem;
b.
"bridge" or pathway of conduction tracts;
c.
location of pneumotaxic area (regulation of
breathing rate) of respiratory center;
d.
also contains areas associated with reticular formation.
3.
Medulla (Oblongata)
a.
inferior portion of brain stem, which blends
into the spinal cord at its base;
b.
contains an autonomic reflex center
involved in maintaining homeostasis of important visceral organs.
o
Cardiac center adjusts force and rate of heart contraction;
o
Vasomotor center regulates blood pressure by acting on
smooth muscle in the walls of peripheral arterioles (i.e.
vasoconstriction = bp increase; vasodilation = bp decrease)
o
Respiratory center = controls the depth and rhythm of
breathing.
o
Additional centers regulate involuntary activities such as
vomiting, hiccuping, swallowing, coughing, and sneezing.)
4.
Reticular Formation
Fig 11.21, page 392
controls brains
inhibited = sleep, alcohol, tranquilizers
5.
See
alertness;
Types of Sleep
a.
Slow wave (90min) overall decrease in reticular formation activity
b.
III.
Rapid eye movement sleep (REM) certain areas of brain are active
o
responsible for dreaming
o
lasts 15 minutes
o
alternates with slow wave
THE BRAIN
F.
Cerebellum See Fig 11.22, page 394.
1.
large, cauliflower-like structure located dorsally to the pons and
medulla and inferiorly to the occipital lobe of the cerebrum (separated by
transverse fissure);
2.
note pattern of white matter (within gray matter) = "arbor vitae";
3.
coordinates
all
voluntary
muscle
movements
(subconsciously); skilled movements, posture, equilibrium (i.e. balance).
G.
Brain Function Summary Table: See Table 11.7, page 395.
Brain Part
Cerebrum
Specific Portion
Primary Motor Cortex
Broca’s Area
Primary
Somatosensory
Cortex
Visual Cortex
Auditory Cortex
Gustatory Cortex
Association Areas
Basal Nuclei
Diencephalon
Thalamus
Hypothalamus
Brain Stem
Midbrain
Pons
Medulla (Oblongata)
Location/ Characteristics
Functions
Cerebellum
I.
PNS INTRODUCTION
The peripheral nervous system (PNS) consists of nerves that extend to and from the CNS
organs. In other words, the PNS includes the cranial nerves and spinal nerves. The PNS
connects all body parts to the brain and/or spinal cord.
The PNS is divided into a sensory and motor branch, and the motor branch of the PNS is
further subdivided into a somatic nervous system (from CNS to skin and skeletal
muscles) and autonomic nervous system (from CNS to smooth muscle, cardiac muscle
and endocrine glands).
II.
STRUCTURE OF PERIPHERAL NERVES
See Fig 11.23, page 397 & Fig 11.24, page 398.
A.
A nerve is a cord-like bundle of axons wrapped in CT.
B.
Structure of a Nerve:
a.
b.
c.
III.
1.
Three types of CT wrappings (similar to muscle):
endoneurium around each axon (and myelin);
perineurium around each fascicle (bundle) of axons;
epineurium around each nerve.
NERVE FIBER CLASSIFICATION
A.
Mixed Nerves
1.
Nerves that carry impulses both to and from the CNS;
2.
contain both sensory and motor axons;
3.
most common; 2-way communication.
B.
Sensory (afferent) Nerves
1.
Nerves that only carry sensory impulses toward the CNS;
2.
rare (only three pairs of cranial nerves).
C.
Motor (efferent) Nerves
1.
Nerves that only carry motor impulses away from CNS;
2.
rare (only five pairs of cranial nerves).
IV.
CRANIAL NERVES
See Fig 11.25, page 399 and Table 11.9, page 402.
A.
12 pairs
1.
2 pairs to/from forebrain,
2.
10 pairs to/from brain stem;
B.
designated by Roman numerals:
I.
Olfactory = sense of smell; sensory only.
II.
Optic = sense of vision; sensory only.
III.
Oculomotor = innervates eye muscles; motor only.
IV.
Trochlear = innervates eye muscles; motor only.
V.
Trigeminal = largest; sensory from face; motor to chewing muscles; mixed.*
VI.
Abducens = innervates eye muscles; motor only.
VII.
Facial = innervates muscles of facial expression; sensory taste;
mixed.
VIII.
Vestibulocochlear = sense of hearing and equilibrium; sensory only.
IX.
Glossopharyngeal = moves tongue and pharynx muscles; mixed.
X.
Vagus = innervates visceral smooth muscle; mixed; See Fig 11.28, page 401.
XI.
Accessory = innervates neck muscles; motor only.
XII.
Hypoglossal = moves tongue; motor only.
C.
Memorize by using one of many mnemonic devices:
One example is: "Oh, Oh, Oh, To Touch And Feel Very Good Velvet AH!"
See www.medicalmnemonics.com for more.
*
See green box on page 400 concerning trigeminal neuralgia.
IV.
CRANIAL NERVES
D.
Numeral
Summary Table (Keyed at the end of this outline)
Name
Function
Sensory, Motor, or
Mixed Nerve
V.
SPINAL NERVES: See Figure 11.29, page 403.
A.
B.
Introduction
1.
Recall that a spinal nerve is formed from the fusion of a dorsal and ventral
root. Then the spinal nerve passes through its intervertebral foramen.
2.
Spinal nerves are associated with the spinal cord and are named for the
region of the spinal cord from which they arise.
General Characteristics:
1.
a.
b.
c.
d.
e.
2.
C.
31 pairs:
C1 - C8
T1 - T12
L1 - L5
S1 - S5
Co
Composition = all mixed nerves.
Distribution of Spinal Nerves
A short distance after passing through its intervertebral foramen, a spinal nerve
branches into several branches:
See Fig 11.31, page 405.
1.
2.
3.
A posterior branch (dorsal ramus)
A large anterior branch (i.e. ventral ramus)
Branches to paravertebral (autonomic) ganglia = rami communicans
V.
SPINAL NERVES: See Figure 11.29, page 403.
D.
Nerve plexus
1.
Definition = a branching network (of the anterior branches) of spinal
nerves.
a.
2.
See Figure 11.32, page 406.
The nerves do not extend directly to the body part they innervate,
instead they form networks.
present in all spinal nerves except T2 - T12:
a.
b.
c.
d.
cervical plexus; neck muscles and diaphragm (breathing)
brachial plexus; upper limb
lumbar plexus; anterior and medial thigh
sacral plexus; posterior lower limb, leg
3.
Each resulting branch of the plexus contains the fibers from several spinal
nerves;
4.
Fibers from each spinal nerve are carried to the body periphery via several
different routes or branches.
Therefore, damage to one spinal segment cannot completely paralyze any
limb muscle.
See Clinical Application 11.7, page 408 concerning spinal nerve injuries.
E.
Intercostal Nerves
1.
2.
Nerves T2-T11 run in intercostal spaces
Supply skin (sensory) and muscles (motor) in the surrounding area
I.
GENERAL CHARACTERISTICS
The Autonomic Nervous System (ANS) regulates the action of smooth muscles, cardiac
muscle, and some glands. In other words, the ANS regulates involuntary (automatic;
unconscious) actions. There are two major divisions of the ANS. The parasympathetic
division functions under normal conditions (to maintain homeostasis), and the
sympathetic division of the ANS functions under stress.
II.
AUTONOMIC NERVE FIBERS: See Figure 11.35, page 409.
A.
B.
C.
Somatic (Fig 11.35b):
1.
one motor neuron;
2.
no ganglia;
3.
NT = acetylcholine (ACh); excitatory;
4.
Effector = skeletal muscles.
ANS (fig 11.35a):
1.
two motor neurons;
2.
synapse between neurons occur within a ganglion;
3.
effectors = smooth muscle, cardiac muscle, glands.
4.
Two Divisions:
a.
Parasympathetic:
o
1st neuron (preganglionic) = long;
o
2nd neuron (postganglionic) = short.
o
NT of postganglionic fiber = ACh.
b.
Sympathetic:
o
1st neuron (preganglionic) = short;
o
2nd neuron (postganglionic) = long.
o
NT of postganglionic fiber = norepinephrine..
LOCATION OF ANS GANGLIA:
1.
Definition: A ganglion is a collection of neuron cell bodies outside
the CNS.
2.
Parasympathetic ganglia are located at or near the effector.
See Fig 11.39, page 413.
3.
Sympathetic ganglia are located on either side of the spinal cord
(chain ganglia; sympathetic trunk), and are far from their effector.
See Fig 11.38, page 412.
4.
Pre-ganglionic neuron
a.
Origination:
o
Parasympathetic arise from the Craniosacral regions of
the brain & spinal cord.
o
Sympathetic arise from the Thoracolumbar regions of the
spinal cord.
b.
Length of axon (or pre-ganglionic fiber):
o
Parasympathetic = long.
o
Sympathetic = short.
III.
ANATOMY OF THE ANS:
See Fig 11.37, page 410.
A.
Sympathetic (Thoracolumbar) Division See Fig 11.38, page 412
1.
T1 - L2;
2.
General Pathway is complex!!!!
a.
preganglionic neuron from spinal cord;
b.
out through white ramus communicans to enter an adjoining
c.
paravertebral (chain) ganglion forming part of the sympathetic
trunk (chain).
3.
Once a preganglionic axon reaches a paravertebral ganglion, one of three
things can happen:
a.
It can synapse with a postganglionic neuron
within the same ganglion = synapse in a paravertebral chain
ganglion at same level.
The postganglionic neuron passes through the gray ramus
communicans and out the ventral ramus leading to its effector
(blood vessel, skin).
b.
It can ascend or descend within the sympathetic chain to synapse
in another paravertebral ganglion = synapse in a paravertebral
chain ganglion at a different level.
The postganglionic neuron passes through gray ramus
communicans.
c.
It can pass through the ganglion to prevertebral (collateral)
ganglion (via Splanchnic Nerve)
Therefore synapse occurs within the prevertebral ganglion and the
postsynaptic neuron extends to effector (abdominal organ).
B.
Parasympathetic ANS
See Fig 11.39, page 413
1.
Long preganglionic fibers; much simpler.
2.
Preganglionic fibers follow blood vessels to ganglia in or near wall of
effector
IV.
PHYSIOLOGY OF THE ANS
A.
B.
Autonomic Neurotransmitters
1.
ACh is released by cholinergic fibers (axons);
2.
Norepinephrine is released by adrenergic fibers (axons).
Actions of Autonomic Neurotransmitters
A receptor is present in the cell membrane of an effector and recognizes its NT,
allowing for a response to occur within the effector.
1.
Cholinergic receptors bind ACh; two types:
a.
nicotinic are always stimulatory.
b.
muscarinic may be stimulatory or inhibitory.
See Fig 11.40, page 414.
2.
3.
Adrenergic receptors bind norepinephrine; two types:
a.
alpha (α ) are usually stimulatory.
b.
beta ( β ) are usually inhibitory.
Effects of Autonomic Stimulation on Various Effectors:
See Table 11.10, page 414.
C,
Control of Autonomic Activity
1.
overall CNS controls ANS
a.
medulla oblongata = cardiac, vasomotor, and respiratory functions
b.
hypothalamus = visceral control including renal and digestive
c.
limbic system = controls physiology of emotions
V.
ANS Summary Table (Keyed at the end of this outline)
Branch of ANS
General
Function
Origin of Preganglionic
fiber
Length of
Preganglionic fiber
Location of Ganglia
NT secreted by postganglionic
fiber
VI.
LIFE SPAN CHANGES
As the nervous system ages, cells are lost, which over time, lead to slowed functioning.
A.
B.
C.
D.
E.
VII.
Apoptosis of brain neurons begins before birth.
Neuron loss among brain regions is not uniform.
In adults, the number of cerebral cortex dendrites has declined, leading to slower
neurotransmission.
Risk of falling increases as balance decreases.
Sleep problems are common in the elderly.
Clinical Terms Related to the Nervous System
See pages 416-417.
CHAPTER 11: NERVOUS SYSTEM II: DIVISIONS OF THE NERVOUS SYSTEM
Peripheral Nervous System (PNS)
Summary Table for Cranial Nerves
Numeral
Name
Function
Sensory, Motor, or
Mixed Nerve
I
OLFACTORY
OLFACTION/SMELL
SENSORY
II
OPTIC
VISION
SENSORY
III
OCULOMOTOR
MOVE EYE
MOTOR
IV
TROCHLEAR
MOVE EYE
MOTOR
V
TRIGEMINAL
CHEWING/MASTICATION
AND SENSORY FROM
FACE
MIXED
VI
ABDUCENS
MOVE EYE
MOTOR
VII
FACIAL
FACIAL EXPRESSION
MIXED
VIII
VESTIBULOCOCHLEAR
HEARING AND
EQUILIBRIUM
SENSORY
IX
GLOSSOPHARYNGEAL
MOVE MUSCLES OF
TONGUE AND PHARYNX
MIXED
X
VAGUS
INNERVATE VISCERAL
SMOOTH MUSCLE
MIXED
XI
ACCESSORY
MOVE NECK MUSCLES
MOTOR
XII
HYPOGLOSSAL
MOVE TONGUE
MOTOR
ANS Summary Table
Branch of ANS
PARASYMPATHETIC
SYMPATHETIC
General
Function
maintain homeostasis
to survive stressful or “fight
or flight” situations
Origin of Preganglionic
fiber
from cranial region of brain or
sacral region of spinal cord
from thoracic or lumbar
region of spinal cord
Length of
Preganglionic fiber
Long
short
Location of Ganglia
at or near effector
alongside spinal cord
NT secreted by postganglionic
fiber
acetylcholine
norepinephrine
Chapter 11: Nervous System II
I. Introduction
A. Introduction
1. The central nervous system consists of the brain and spinal cord.
2. The brain is the largest and most complex part of the nervous system
3. The brain includes two cerebral hemispheres, the diencephalon, the brainstem,
and the cerebellum.
4. The brainstem connects the brain and spinal cord and allows two-way
communication between them.
5. The spinal cord provides two-way communication between the central nervous
system and the peripheral nervous system.
6. The brain lies within the cranial cavity of the skull and the spinal cord
occupies the vertebral canal.
7. Meninges are located between the bone and the soft tissues of the nervous
system and protect the brain and spinal cord.
II. Meninges
A. The meninges have three layers.
B. The outermost layer is the dura mater and is composed of tough, white, dense
connective tissue.
C. Dural sinuses are channels in dura mater.
D. Denticulate ligaments are bands of pia mater that attach spinal cord to dura mater.
E. The epidural space is between the dural sheath and the bony walls and contains blood
vessels.
F. The arachnoid mater is thin, weblike membrane that lacks blood vessels and is located
between the dura and pia maters.
G. The subarachnoid space is between the arachnoid and pia maters and contains a fluid
called cerebrospinal fluid.
H. The pia mater is very thin and contains many nerves and blood vessels.
I. The pia matter is attached to the surfaces of the brain and spinal cord.
III. Ventricles and Cerebrospinal Fluid
A. Introduction
1. Ventricles are interconnected cavities and are located within the cerebral
hemispheres and brain stem.
2. The ventricles are continuous with the central canal of the spinal cord
and are filled with cerebrospinal fluid.
3. The largest ventricles are the lateral ventricles which are located in the cerebral
hemispheres.
4. The third ventricle is located in the midline of the brain beneath the corpus
callosum.
5. The fourth ventricle is located in the brainstem just in front of the cerebellum.
6. The cerebral aqueduct is a connection between the third and fourth ventricles.
7. The choroids plexus is specialized mass of capillaries and functions to secrete
cerebrospinal fluid.
8. Most of the cerebrospinal fluid arises in the lateral ventricles
and circulates into the third ventricle, fourth ventricle, the central canal of the
spinal cord, and the subarachnoid space.
9. Cerebrospinal fluid is continuously absorbed into the blood.
10. Arachnoid granulations are tiny, fingerlike structures that project from the
subarachnoid space into the dural sinuses.
11. Cerebrospinal fluid is different from blood in that it contains a greater
concentration of sodium and lesser concentrations of glucose and potassium.
12. The functions of cerebrospinal fluid are to help maintain a stable ionic
concentration in the CNS, and provides a pathway to the blood for wastes.
13. Because cerebrospinal fluid completely surrounds the brain and spinal cord, it
protects them by absorbing forces that might otherwise jar and damage them.
IV. Spinal Cord
A. Introduction
1. The spinal cord is continuous with the brain and extends through downward
through the vertebral canal.
2. The spinal cord begins at the level of the foramen magnum and terminates near
the intervertebral disc that separates the first and second lumbar vertebrae.
B. Structure of the Spinal Cord
1. The spinal cord consists of thirty-one segments, each of which gives rise to a
pair of spinal nerves.
2. The two enlargements of the spinal cord are the cervical enlargement and the
lumbar enlargement.
3. The cervical enlargement supplies nerves to the upper limbs.
4. The lumbar enlargement supplies nerves to the lower limbs.
5. The conus medullaris is the tapered end of the spinal cord.
6. The filum terminale is a thin cord of connective tissue that anchors the spinal
cord to the upper surface of the coccyx.
7. The cauda equina is a group of spinal nerves below the conus medullaris.
8. Two grooves that extend the length of the spinal cord are the anterior median
fissure and a posterior median sulcus.
9. In a cross section of the spinal cord, white matter surrounds gray matter.
10. Each side of the gray matter is divided into the following three horns:
posterior horn, anterior horn, and lateral horn.
11. Motor neurons are located in the anterior horns.
12. The gray commissure is a horizontal bar of gray matter in the middle of the
spinal cord.
13. The central canal is a canal running through the center of the gray
commissure down the entire length of the spinal cord.
14. Three regions of the white matter are posterior funiculi, anterior funiculi, and
lateral funiculi.
15. Nerve tracts are groups of myelinated nerve fibers in the CNS.
C. Functions of the Spinal Cord
1. Reflex Arcs
a. Reflex arcs carry out reflexes.
b. A reflex arc begins with a receptor at the end of the dendrites of a
sensory neuron.
c. The sensory neuron leads to several interneurons which serve as a
processing center.
d. The interneurons communicate with motor neurons whose fibers pass
to effectors.
e. Spinal reflexes are reflexes whose arcs pass through the spinal cord.
2. Reflex Behavior
a. Reflexes are automatic, subconscious responses to changes within or
outside the body.
b. Reflexes function to maintain homeostasis by controlling many
involuntary processes such as heart rate, breathing rate, etc.
c. The knee-jerk reflex is an example of a simple monosynaptic reflex
because it only uses two neurons.
d. The knee-jerk reflex is initiated by striking the patellar tendon.
e. When the tendon is struck, the quadriceps muscle is pulled.
f. When the muscle is pulled, stretch receptors are stimulated.
g. The receptors generate a nervous impulse that enters the spinal cord on
an axon; the axon synapses with a motor neuron.
h. The axon of the motor neuron synapses with the quadriceps muscle and
the muscle responds by contracting.
i. The knee-jerk reflex helps maintain posture.
j. The withdrawal reflex occurs when a person touches something painful.
k. In the withdrawal reflex, muscles on the affected side contract and the
flexor muscles on the unaffected side are inhibited.
l. The extensor muscles on the unaffected side contract, helping to support
the body weight that has been shifted.
m. A crossed extensor reflex is due to interneuron pathways within the
reflex center of the spinal cord that allow sensory impulses arriving on one
side of the cord to pass across to the other side and produce an opposite
effect.
n. A withdrawal reflex protects because it prevents or limits tissue
damage when a body part touches something potentially harmful.
3. Ascending and Descending Tracts
a. Ascending tracts conduct sensory impulses to the brain.
b. Descending tracts conduct motor impulses away from the brain.
c. The names that identify nerve tracts often reflect the origin and
termination of the tract.
d. Four major ascending tracts of the spinal cord are fasciculus gracilis,
fasciculus cuneatus, spinothalamic tracts, and spinocerebellar tracts.
e. The fasciculus gracilis and fasciculus cuneatus are located in posterior
funiculi.
f. The fibers of fasciculus gracilis and fasciculus cuneatus conduct
sensory impulses associated with the senses of touch, pressure, and body
movement from skin, muscles, tendons, and joints to the brain.
g. The spinothalamic tracts are located in lateral and anterior funiculi.
h. The lateral spinothalamic tracts conduct impulses from various body
regions to the brain and five rise to sensation of pain and temperature.
i. The anterior spinothalamic tracts impulses are interpreted as touch and
pressure.
j. Spinocerebellar tracts are located in lateral funiculi.
k. Impulses on the spinocerebellar tracts originate in the muscles of the
lower limbs and trunk and travel to the cerebellum.
l. Three major descending tracts of the spinal cord are corticospinal tracts,
reticulospinal tracts, and reubrospinal tracts.
m. Corticospinal tracts are located in lateral and anterior funiculi.
n. The corticospinal tracts conduct motor impulses associated with
voluntary movements from the brain to skeletal muscles.
o. The pyramidal tracts are the corticospinal tracts and the extrapyramidal
tracts are all other descending spinal tracts.
p. Reticulospinal tracts are located in lateral and anterior funiculi.
q. Motor impulses of the reticulospinal tracts control muscular tone and
activity of sweat glands.
r. Rubrospinal tracts are located in lateral funiculi.
s. Rubrospinal tracts carry motor impulses that coordinate muscles and
control posture.
V. Brain
A. Introduction
1. The brain contains nerve centers associated with sensory
functions.
and is responsible for sensations and perceptions.
2. The other functions of the brain include control of motor
functions and higher mental functions such as memory; it also
provides characteristics such as personality.
B. Brain Development
1. The brain begins as a neural tube.
2. The portion of the neural tube that becomes the brain has the following three
major cavities: forebrain, midbrain, and hidbrain.
3. The forebrain divides into the telencephalon and the diencephalon.
4. The hindbrain partially divides into the metencephalon and myelencephalon.
5. The wall of the anterior potion of the forebrain gives rise to the cerebrum and
basal nuclei.
6. The posterior portion of the forebrain gives rise to the diencephalon.
7. The midbrain is called midbrain in the adult and the hindbrain gives rise to the
cerebellum, pons, and medulla oblongata.
C. Structure of the Cerebrum
1. The cerebrum is the largest part of the adult brain.
2. The cerebrum consists of two hemispheres.
3. The corpus callosum is a bridge of nerve fibers that connects the two cerebral
hemispheres.
4. Convolutions are ridges.
5. Sulci are grooves between ridges.
6. A fissure is a deep groove.
7. The longitudinal fissure separates the left and right cerebral hemispheres.
8. The transverse fissure separates the cerebrum from the cerebellum.
9. The 5 lobes of the cerebral hemispheres are frontal, parietal, occipital,
temporal and insular.
10. The most anterior lobe is the frontal.
11. The frontal lobe is bordered posteriorly by the central sulcus and inferiorly by
a lateral sulcus.
12. The parietal lobe is separated from the frontal lobe by the central sulcus.
13. The temporal lobe lies inferior to the frontal and parietal lobes and is
separated from them by the lateral sulcus.
14. The most posterior lobe is the occipital lobe.
15. The tentorium cerebelli is an extension of the dura mater between the
occipital lobe and cerebellum.
16. The insula is located deep within the lateral fissure.
17. The cerebral cortex is an outer, thin layer of gray matter and contains nearly
75% of all the neuron cell bodies in the nervous system
18. Just beneath the cerebral cortex is white matter.
D. Functions of the Cerebrum
1. Functional Regions of the Cortex
a. The cerebral cortex is divided into the following three major sections: motor, sensory, and
association areas.
2. Motor Areas
a. The primary motor areas are located in the frontal lobes just in front of
the central sulcus and in the anterior wall of this sulcus.
b. Impulses transmitted from the primary motor are responsible for fine
movements in skeletal muscles.
c. Broca’s area is located just anterior to the primary motor cortex and
superior to the lateral sulcus and is responsible for coordinating complex
muscular movements of the mouth, tongue, and larynx for speech.
d. Broca’s area is usually found in the left hemisphere.
e. The frontal eye field is located above Broca’s area and is responsible
for controlling voluntary movements of the eyes and eyelids.
3. Sensory Areas
a. Sensory areas interpret impulses from sensory receptors.
b. Sensations on the skin are interpreted in the anterior portions of the
parietal lobes along the central sulcus.
c. Visual sensations are interpreted in the occipital lobe.
d. Auditory sensations are interpreted in the temporal lobe.
e. Taste sensations are interpreted in the bases of the central sulci along
the lateral sulci.
f. Like motor fibers, sensory fibers cross over in the spinal cord or
brainstem.
4. Association Areas
a. Association areas are regions of the cerebral cortex that are not
primarily sensory or motor in function.
b. Association areas analyze and interpret sensory experiences and help
provide memory, reasoning, verbalizing, judgment, and emotions.
c. The association areas of the frontal lobe provide higher intellectual
processes.
d. The prefrontal areas control emotional behavior and produce awareness
of the possible consequences of behavior.
e. The parietal lobes have association areas that help interpret sensory
information and aid in understanding speech and choosing word to express
thoughts and feeling.
f. The association areas of the temporal lobes interpret complex sensory
experiences, such as those needed to understand speech and to read.
g. The association areas of the occipital lobes are important for analyzing
visual patterns and combining visual images with other sensory
experiences.
h. The general interpretative area is located where the parietal, temporal,
and occipital association areas join and functions to make it possible for a
person to recognize words and arrange them to express a thought, and to
read and understand ideas presented in writing.
5. Hemisphere Dominance
a. In over 90% of the population, the left hemisphere is dominant.
b. The dominant hemisphere controls language-related activities of
speech, writing, and reading. Is also controls complex intellectual
functions requiring verbal, analytical, and computational skills.
c. The nondominant hemisphere controls nonverbal functions, such as
motor tasks that require orientation of the body in space, understanding
and interpreting musical patterns and visual experiences. It also controls
emotional intuitive through processes.
d. Nerve fibers of the corpus callosum enable the dominant hemisphere
to control the motor cortex of the nondominant hemisphere.
6. Memory
a. Memory is the consequence of learning.
b. Two types of memory are short-term and long-term.
c. Short-term memories are electrical in nature.
d. When the electrical impulse of a short-term memory ceases, the
memory goes away.
e. Long-term memory changes the structure or function of neurons in
ways that enhance synaptic transmission.
f. Memory consolidation is the way the brain encodes memories and how
short-term memories are converted to long-term memories.
E. Basal Nuclei
1. The basal nuclei are masses of gray matter located deep within
the cerebral hemispheres and are called caudate nucleus, the
putamen, and globus pallidus.
2. The basal nuclei relay motor impulses originating in the cerebral cortex and
passing into the brainstem and spinal cord.
3. The basal nuclei produce most of the dopamine in the nervous system.
4. Impulses from the basal nuclei function to control muscular activities.
F. Diencephalon
1. The diencephalon is located between the cerebral hemispheres and above the
brainstem.
2. The various parts of the diencephalon are thalamus, hypothalamus, optic tracts,
the infundibulum, posterior pituitary bland, mammillary bodies and the pineal
gland.
3. The thalamus is a selective gateway for sensory impulses ascending from other
parts of the nervous system to the cerebral cortex.
4. The thalamus receives most sensory impulses and channels them to
appropriate parts of the cortex for interpretation.
5. The hypothalamus regulates heart rate, arterial blood pressure, body
temperature, water and electrolyte balance, control of hunger and body weight,
control of movements and glandular secretions of the stomach and intestine,
produces hormones, and controls sleep and wakefulness.
6. The limbic system consists of portions of the cerebral cortex, thalamus,
hypothalamus, basal nuclei, and other deep nuclei and controls emotional
experience and expression and can modify the way a person acts.
G. Brain Stem
1. Introduction
a. The brain stem connects the brain and spinal cord.
b. The brain stem consists of the midbrain, pons, and medulla oblongata.
c. Nuclei of the brain stem are masses of gray matter.
2. Midbrain
a. The midbrain is between the diencephalon and the pons.
b. The cerebral aqueduct is a connection between the third ventricle and
fourth ventricle.
c. Corpora quadrigemina are two pairs of rounded knobs on the superior
surface of the midbrain.
d. The superior colliculi contain centers for visual reflexes.
e. The inferior colliculi contain centers for auditory reflexes.
f. The red nucleus is at the center of the midbrain and is important for
controlling reflexes that maintain posture.
3. Pons
a. The pons is located on the underside of the brainstem between the
midbrain and medulla oblongata.
b. The dorsal portion of the pons largely consists of fibers that relay
impulses to and from the medulla oblongata and the cerebrum.
c. The ventral portion consists of fibers that relay impulses from the
cerebrum to centers within the cerebellum.
d. Several nuclei of the pons relay sensory information to higher brain
centers.
e. The pons also regulates rate and depth of breathing.
4. Medulla Oblongata
a. The medulla oblongata is located between the spinal cord and pons.
b. The olive of the medulla oblongata is a bulge where bundles of fibers
originate and pass to the cerebellum.
c. The visceral activities controlled by the medulla oblongata are heart
rate, vasoconstriction, vasodilation, and breathing.
d. Nonvital reflexes regulated by the medulla oblongata are coughing,
sneezing, swallowing, and vomiting.
5. Reticular Formation
a. The reticular formation is a complex network of fibers that extend throughout the brainstem
and diencephalon and connects with centers of the hypothalamus,
cerebrum, cerebellum, and basal nuclei.
b. The reticular formation activates the cerebral cortex into a state of
wakefulness.
c. Decreased activity of the reticular formation results in sleep.
d. The reticular formation also filters incoming sensory impulses.
e. The reticular formation also regulates motor activities so that various
skeletal muscles move together evenly, and it inhibits or enhances certain
spinal reflexes.
6. Types of Sleep
a. The two types of sleep are slow wave and rapid eye movement.
b. Slow-wave sleep occurs when a person is very tired and it reflects
decreasing activity of the reticular formation.
c. Slow-wave sleep is accompanied by reduced blood pressure and
respiratory rate.
d. REM sleep is the type of sleep in which dreaming occurs and heart rate
and respiratory rates are irregular.
H. Cerebellum
1. The cerebellum is located inferior to the occipital lobes of the cerebrum and
posterior to the pons and medulla oblongata.
2. The falx cerebelli is a layer of dura mater that partially separates the
cerebellar hemispheres.
3. The vermis is a structure that connects the cerebellar hemispheres at the
midline.
4. The cerebellar cortex is an outer, thin layer of gray matter.
5. The arbor vitae is a treelike pattern of white matter in the cerebellum.
6. The largest and most important nucleus of the cerebellum is the dentate
nucleus.
7. Cerebellar peduncles are nerve tracts.
8. Inferior peduncles bring sensory information concerning the actual position of
body parts such as limbs and joints to the cerebellum.
9. The middle peduncles transmit impulses from the cerebral cortex about the
desired position of body parts to the cerebellum.
10. The superior peduncles sends correcting impulses to the midbrain.
11. Overall, the cerebellum functions to integrate sensory information concerning
the position of body parts and coordinated skeletal muscle activity and maintains
posture
VII. Peripheral Nervous System
A. Introduction
1. The peripheral nervous system consists of nerves that branch from the central
nervous system.
2. The somatic nervous system consists of the cranial and spinal nerve fibers that
connect the DNS to the skin and skeletal muscles.
3. The autonomic nervous system consists of fibers that connect the CNS to
viscera and various glands
B. Structure of Peripheral Nerves
1. A peripheral nerve consists of connective tissue surrounding bundles of nerve
fibers.
2. Epineurium is the outermost layer of connective tissue of a nerve.
3. Perineurium is a sleeve of connective tissue that surrounds a nerve fascicle.
4. Endoneurium is loose connective tissue that surrounds individual nerve fibers.
C. Nerve Fiber Classification
1. Sensory nerves are nerves that conduct impulses into the brain or spinal cord.
2. Motor nerves are nerves that conduct impulses to muscles or glands
3. Mixed nerves are nerves that include both sensory fibers and motor fibers.
4. Cranial nerves are nerves that originate from the brain.
5. Spinal nerves are nerves that originate from the spinal cord.
6. General somatic efferent fibers carry motor impulses outward from the brain or
spinal cord to skeletal muscles and stimulate them to contract.
7. General visceral efferent fibers carry motor impulses outward from the brain or
spinal cord to various smooth muscles and glands associated with internal organs,
causing certain muscles to contract or glands to secrete.
8. General somatic afferent fibers carry sensory impulses inward to the brain or
spinal cord from receptors in the skin and skeletal muscles.
9. General visceral afferent fibers carry sensory impulses to the central nervous
system from blood vessels and internal organs.
10. Special somatic efferent fibers carry motor impulses outward from the brain
to the muscles used in chewing, swallowing, speaking, and forming facial
expressions.
11. Special visceral afferent fibers carry sensory impulses inward to the brain
from the olfactory and taste receptors.
12. Special somatic afferent fibers carry sensory impulses inward to the brain
from the receptors of sight, hearing, and equilibrium.
D. Cranial Nerves
1. Cranial nerves arise from the underside of the brain.
2. Cranial nerves are designated by roman numerals or names.
3. The olfactory nerve functions to transmit sensory impulses associated with
smell.
4. The optic nerve functions to transmit sensory impulses associated with sight.
5. The oculomotor nerve functions to transmit impulses to muscles that arise the
eyelids, move the eyes, and adjust the amount of light entering the eyes, and focus
the lenses. It also transmits sensory impulses associated with proprioceptors.
6. The trochlear nerve functions to transmit impulses to muscles that move the
eyes. It also transmits sensory impulses associated with proprioceptors.
7. The three divisions of the trigeminal nerve are ophthalmic, maxillary, and
mandibular.
8. The ophthalmic division functions to transmit sensory impulses from the
surface of the eyes, tear glands, scalp, forehead, and upper eyelids.
9. The maxillary division functions to transmit impulses from the upper teeth,
upper gum, upper lip, lining of the palate, and skin of the face.
10. The mandibular division functions to transmit sensory impulse from the
scalp, skin of the jaw, lower teeth, lower gum, and lower lip. It al transmits motor
impulses to muscles of mastication and to muscles in the floor of the mouth.
11. The abducens nerve functions to transmit motor impulses to muscles that
move the eyes. It also transmits sensory impulses associated with proprioceptors.
12. The facial nerve functions to transmit sensory impulses associated with taste
receptors of the anterior tongue. It also transmits motor impulse to muscles of
facial expression, tear gland, and salivary glands.
13. The two branches of the vestibulocochlear nerve are the vestibular branch and
the cochlear branch.
14. The vestibular branch functions to transmit sensory impulses associated with
the sense of equilibrium.
15. The cochlear branch functions to transmit sensory impulses associated with
hearing.
16. The glossopharyngeal nerve functions to transmit sensory impulses for the
pharynx, tonsils, posterior tongue, and carotid arteries. It also transmits motor
impulses to salivary glands and to muscles of the pharynx used in swallowing.
17. The vagus nerve functions to transmit motor impulses to muscles associated
with speech and swallowing, and to viscera of the thorax and abdomen. It also
transmits sensory impulses from the pharynx, larynx, esophagus, and viscera of
the thorax and abdomen.
18. The branches of the accessory nerve are the cranial branch and spinal branch.
19. The cranial branch functions to transmit motor impulses to muscles of the
soft palate, pharynx, and larynx.
20. The spinal branch functions to transmit motor impulses to muscles of the
neck and back.
21. The hypoglossal nerve functions to transmit motor impulses to muscles that
move the tongue.
E. Spinal Nerves
1. Introduction
a. There are thirty-one pairs of spinal nerves.
b. All spinal nerves are mixed nerves and they provide two –way
communication between the spinal cord and parts of the upper and lower
limbs, neck and trunk.
c. There are 8 pairs of cervical nerves.
d. There are 12 pairs of thoracic nerves.
e. There are 5 pairs of lumbar nerves.
f. There are 5 pairs of sacral nerves.
g. There is 1 pair of coccygeal nerves.
h. The adult spinal cord ends at the level of the first or second lumbar
vertebrae.
i. The cauda equina is a collection of spinal nerves at the end of the spinal
cord.
j. Each spinal nerve emerges from the cord by roots.
k. The dorsal root ganglion contains the cell bodies of the sensory neurons
whose dendrites conduct impulses from the peripheral body parts.
l. The axons of neurons in dorsal root ganglia extend through the dorsal
root.
m. A dermatome is an area of skin that the sensory nerve fibers of a
particular spinal nerve innervate.
n. The ventral root consists of axons from the motor neurons whose cell
bodies are located within the gray matter of the cord.
o. A ventral root and dorsal root unite to form a spinal nerve.
p. A meningeal branch of a spinal nerve supplies the meninges and blood
vessels of the spinal cord, as well as the intervertebral ligaments and the
vertebrae.
q. A posterior branch of a spinal nerve supplies the muscles and skin of
the back.
r. An anterior branch of a spinal nerve supplies muscles and skin on the
front and sides of the trunk and limbs.
s. A visceral branch of a spinal nerve supplies viscera.
t. A plexus is a complex network of anterior branches of spinal nerves.
u. In a plexus, fibers of various spinal nerves are sorted and recombined,
so fibers associated with a particular peripheral body part reach it in the
same nerve, even though the fibers originate from different spinal nerves.
2. Cervical Plexuses
a. The cervical plexus is located deep in the neck on either side.
b. The cervical plexus is formed by the anterior branches of the first four
cervical nerves.
c. Fibers from the cervical plexus supply the muscles and skin of the neck
and contribute to the phrenic nerve.
d. The phrenic nerve conducts impulses to the diaphragm.
3. Brachial Plexuses
a. The brachial plexus is located deep within the shoulders between the
neck and axillae.
b. The brachial plexus is formed by the anterior branches of the lower
four cervical nerves and the first thoracic nerve.
c. The major branches emerging from the brachial plexus are the
musculocutaneous, ulnar, median, radial, and axillary.
d. The musculocutaneous nerves supply muscles of the arms on the
anterior sides and the skin of the forearms.
e. The ulnar nerves supply muscles of the forearms and hands and the
skin of the hands.
f. The radial nerves supply muscles of the arms on the posterior sides and
the skin of the forearms and hands.
g. The median nerves supply muscles of the forearms and muscles and
skin of the hands.
h. The axillary nerves supply muscles and skin of the superior, lateral, and
posterior regions of the arm.
4. Lumbosacral Plexuses
a. The lumbosacral plexus is located in the lumbar and pelvic regions.
b. The lumbosacral plexus is formed by anterior branches of the last
thoracic nerve and lumbar, sacral , and coccygeal nerves.
c. The major branches of the lumbosacral plexus are obturator, femoral,
and sciatic nerves.
d. The obturator nerves supply the adductor muscles of the thighs.
e. The femoral nerves supply motor impulses to muscles of the thighs and
legs and receive sensory impulses from the skin of the thighs and legs.
f. The sciatic nerves supply muscles and skin the thighs, legs, and feet.
g. The common peroneal nerves supply muscles and skin of the thighs,
legs, and feet.
h. The anterior branches of thoracic spinal nerves do not form plexuses;
instead these branches become intercostal nerves that supply motor
impulses to the intercostal muscles and the upper abdominal wall muscles.
VIII. Autonomic Nervous System
A. Introduction
1. The autonomic nervous system controls visceral activities by regulating the
actions of smooth muscles, cardiac muscles, and various glands.
2. The autonomic nervous system functions without conscious effort.
B. General Characteristics
1. The two divisions of the autonomic nervous system are sympathetic and
parasympathetic.
2. The sympathetic division prepares the body for energy-expending, stressful, or
emergency situations.
3. The parasympathetic division is most active during ordinary, restful
conditions.
C. Autonomic Nerve Fibers
1. All nerve fibers of the autonomic nervous system are motor fibers.
2. In the autonomic system, motor pathways include two neurons.
3. A preganglionic fiber is an axon of a preganglionic neuron.
4. A postganglionic fiber is an axon of a postganglionic neuron.
5. A preganglionic fiber synapses with a postganglionic neuron.
6. A postganglionic fiber synapses with an effector, such as a gland.
D. Sympathetic Division
1. In the sympathetic division, the preganglionic fibers originate from neurons
within the lateral horns of the spinal cord. These neurons are in the thoracic and
lumbar regions of the spinal cord.
2. In the sympathetic division, the preganglionic fibers leave the spinal nerves
through white rami and enter sympathetic ganglia.
3. Paravertebral ganglia are located in chains along the sides of the vertebral
column.
4. The sympathetic trunks are Paravertebral ganglia and the fibers that connect
the ganglia.
5. The collateral ganglia are located within the abdomen, closely associated with
certain large blood vessels.
6. Typically a preganglionic axon of the sympathetic nervous system will
synapse with several other neurons within a sympathetic ganglion.
7. In the sympathetic division, the postganglionic fibers extend out from the
sympathetic ganglia to visceral effectors.
8. Gray rami are branches that contain unmyelinated postganglionic axons.
E. Parasympathetic Division
1. The preganglionic fibers of the parasympathetic division arise from neurons in
the midbrain, pons, medulla oblongata, and sacral region of the spinal cord.
2. The preganglionic fibers of the parasympathetic division lead to ganglia that
are located near or within various organs.
3. The short postganlionic fibers of the parasympathetic division lead to specific
muscles or glands within visceral organs.
4. Parasympathetic preganglionic fibers are usually myelinated and the
postganglionic fibers are usually unmyelinated.
F. Autonomic Neurotransmitters
1.
The preganglionic fibers of the sympathetic and
parasympathetic divisions secrete acetylcholine and are called
cholinergic.
2. The parasympathetic postganglionic fibers are cholinergic fibers.
3. Most sympathetic postganglionic fibers secrete norepinephrine and are called
adrenergic.
4. The different postganglionic neurotransmitters are responsible for the different
effects that the sympathetic and parasympathetic divisions have on organs.
5. Sympathetic tone is a state of constant partial contraction of smooth muscles in
the wall of blood vessels caused by sympathetic innervation.
G. Actions of Autonomic Neurotransmitters
1. The actions of autonomic neurotransmitters result from their binding to protein
receptors in the membrane of effector cells.
2. Two types of cholinergic receptors are muscarinic and nicotinic.
3. Muscarinic receptors are located in the membranes of effector cells at the ends
of all postganglionic parasympathetic nerve fibers and at the ends of the
cholinergic sympathetic fibers.
4. Nicotinic receptors are located in the synapses between the preganglionic and
postganglionic neurons of the parasympathetic and sympathetic pathways.
5. Responses from muscarinic receptors are excitatory and slow.
6. Responses from nicotinic receptors are excitatory and rapid.
7. The two major types of adrenergic receptors are alpha and beta receptors.
8. Acetylcholinesterase decomposes acetylcholine.
H. Control of Autonomic Activity
1. The autonomic nervous system is largely controlled by the brain and spinal
cord.
2. The limbic system and cerebral cortex control the autonomic nervous system
during emotional stress.
IX. Life-Span Changes
A. Apoptosis is a form of programmed cell death and first
occurs during development.
B. By age thirty, the die-off of neurons accelerates.
C. Over an average lifetime, the brain shrinks by about 10%.
D. With aging, the numbers of dendritic branches and amounts of neurotransmitters
decrease.
E. Noticeable signs of a normally aging nervous system include fading memory and
slowed responses and reflexes.
F. Decline in function of the sympathetic nervous system may cause transient drops in
blood pressure.
G. Changes in sleep patterns reflect the functioning of the reticular activating system.