THE
NERVOUS
SYSTEM
http://www.youtube.com/watch?v=YRwPMICvbT4
I. Introduction
A.Functions of N.S.
1.Sensory input
2.Integration
3.Homeostasis
4.Mental activity
5.Control of
skeletal muscles
I. Introduction
B. Divisions of the N.S.
Central N.S.
Brain
Peripheral N.S.
Spinal Cord Efferent Afferent
Autonomic
Parasympathetic
Somatic
Sympathetic
I. Introduction
B. Divisions of the N.S.
Central N.S.
Peripheral N.S.
Brain Spinal Cord Made of 12 cranial
nerves & 31 spinal
No potential for
nerves
regeneration
PNS
A.Afferent (sensory) division
carries messages toward
CNS.
B. Efferent (motor) division
carries messages away from
CNS toward muscles & glands
(somatic).
Sympathetic NS
Fight or Flight
• Dilates pupils
• Reduces saliva,
mucus, peristalsis,
intestinal motility,
urine secretion
• Increases heart
rate, glycogen to
glucose conversion
Parasympathetic NS
Digest & Rest
• Constricts pupils
• Reduces heart
rate
• Increases mucus
production, gastric
juice production,
digestion, urine
production,
intestinal tract
motility,
peristalsis
II. Histology of the N.S.
2 types of cells: neurons & support cells (neuroglia)
A.Neurons –
1. Are excitable, irritable,
& conductive.
– nerve cells
– functional unit of n.s.
Neurons are not nerves!
Nerves are bundles of PNS fibers held together by
several layers of connective tissue
A. Neurons
2. Structure.
a. Cell body
b. Dendrites
receive
incoming
signals
towards
cell
body
A. Neurons
2. Structure
c. Axons
transmit
signals
away
from cell
body
2. Structure
c. Axons
• Myelin Sheath membrane
"insulation"
around axons
• Nodes of Ranvier
- gaps between
myelin
2. Structure
c. Axons
• Nissil bodies rough endoplasmic
reticulum... Lots of
protein synthesis
• Synaptic vesicles stores
neurotransmitter at
axon terminal
Structural Classification of Neurons
Regeneration
A. Neurons do not reproduce themselves, but they can
regenerate new parts sometimes.
B. If a neuron is cut through a myelinated axon, the
proximal portion may survive if the cell body is not
damaged.
C. The distal portion will die (degenerate).
Macrophages move into the area and remove debris.
D. Neuron cell body reorganizes its Nissl bodies to
provide proteins necessary for axon growth.
E. The Schwann cells form a regeneration tube that
helps guide the axon to its proper destination.
Regeneration
F. New fiber will eventually fill the myelin sheath and
innervate the muscle. Growth occurs at 3-5 mm/day.
(1 mm = 0.04 inch)
G. In the CNS, this repair is unlikely because the
neurons lack the neurilemma necessary to form the
regeneration tube. Also, the astrocytes quickly fill
the damaged area forming scar tissue. Most CNS
injuries cause permanent damage.
Regeneration
H. Crushing and bruising can also damage nerve fibers
resulting in paralysis. Inflammation of the injury site
damages more fibers. Early treatment with
methyprednisolone reduces inflammation and
decreases severity of injury. It must be given within
8 hours to be effective.
http://www.youtube.com/watch?v=kxVMog4PkYo
II. Histology of the N.S.
B. Neuroglia – nonexcitable; help &
support neurons
OF THE CNS
1.Astrocytes - "nurse" cells;
nourish & protect neurons;
form blood brain barrier
2.Oligodendrocytes - form
myelin in CNS
II. Histology of the N.S.
B. Neuroglia – nonexcitable; help &
support neurons
OF THE CNS
3.Microglia - provide immune
protection in CNS.
4.Ependymal cells –circulate
cerebrospinal fluid
II. Histology of the N.S.
B.Neuroglia – OF THE PNS
5.Schwann Cells - form myelin
in peripheral nerves
6.Satellite Cells – surround
and support neurons of the
ganglia
C. Nerves and Ganglia
1.Nerves
a.bundles of nerve cell axons
and/or dendrites in
periphery of body.
b.Functional classification
• Sensory (afferent) nerves
carry incoming signals
from sense receptors
towards CNS.
C. Nerves and Ganglia
1.Nerves
b. Functional classification
• Motor (efferent) nerves –
carry outgoing (away from
CNS) signals to muscle &
glands.
• Interneurons nerves –
connect motor and sensory
neurons
C. Nerves and Ganglia
2.Ganglia.
Ganglia are bundles of
nerve cell bodies in
periphery of body.
II. Histology of the N.S.
D.Gray & White Matter
1.White Matter
• Made of mylinated
processes
2.Gray Matter
• Unmylinated processes and
cell bodies
II. Histology of the N.S.
D.Gray & White Matter
3. Location
Spinal cord
gray
matter
forms H in
center
surrounded
by white
matter
II. Histology of the N.S.
D.Gray & White Matter
3. Location
Brain central white
matter with a
superficial gray
matter covering
III. Neurophysiology
A.Membrane Properties
1. Neurons must be able to transmit their
excitable response that started either in
the dendrites or the nerve cell body down
through the axon.
2. When at rest, the neuron has more +
charges outside the cell membrane than inside.
3. This electric imbalance called the resting
membrane potential or simply stated the
Resting potential is the difference b/w the 2
sides of the neuron’s membrane when the cell
is not conducting an impulse
Resting Potential
A. Membrane Properties
3. Resting Potential ion distribution
• Lg # Na+ outside; K+ inside
A. Membrane Properties
4. Changes in ion distribution cause
Stimulation of membrane
Opens ion channels (pores)
• When this occurs it is called an
Action Potential or simply stated
an Action potential is the electrical
signal that rapidly travels along the axon
of neurons causing changes in ion
distribution.
III. Neurophysiology
B. Action Potentials
1.Are a specialized kind of
electric signal generated
only by neurons and muscle
cells
2.are self-propagating
3.are all-or-none events.
III. Neurophysiology
C. Action Potentials have 3 Phases
1.Depolarization
• Rapid (1 msec)
• sodium channels open, Na+
rush in
III. Neurophysiology
C. Action Potentials have 3 Phases
1.Depolarization
•Ends in an overshoot
(i.e. brief period of time
inside of cell is more
positive than outside)
III. Neurophysiology
C. Action Potentials have 3 Phases
2.Repolarization
• Na+ channels close
• K+ channels open and K+
rushes out
III. Neurophysiology
C. Action Potentials have 3 Phases
2.Repolarization
• overshoots the
resting point
III. Neurophysiology
C. Action Potentials have 3 Phases
3.Undershoot Phase
• Membrane is hyperpolarized
back to the resting potential
• K+ channels close
• Na+/K+ pump reestablishes
the resting potential
• 3 Na+ moved for 2 K+
Na+ / K+ Pump
Reestablishes Resting
Potential
III. Neurophysiology
D. Nerve Impulse
1. Impulse conduction
• Unmyelinated fibers conduct
impulse over entire membrane
surface.
• Myelinated fibers conduct
impulse from node to node
2. Action potential spreads down the
fiber to adjacent areas of
membrane
http://www.youtube.com/watch?v=FR4S1BqdFG4
How the neurons work with the brain
III. Neurophysiology
E.All or None Response
1.If the nerve fiber responds to
the impulse, it responds
completely
2.Greater intensity of
stimulation triggers more
impulses per second, not
stronger impulses
IV. The Synapse
A.Defined
The junction (cleft) between 2
neurons
IV. The Synapse
B.Synaptic Transmission
1. The process by which the impulse
is transmitted across the synaptic
cleft
IV. The Synapse
B.Synaptic
Transmission
2. Steps
• Impulse reaches
the synaptic
knobs of axon
• synaptic vesicles
release
neurotransmitter
into the cleft
IV. The Synapse
C.Kinds of Neurotransmitters
1. Acetylcholine (ACh)
• Made from acetic acid
2. Biogenic Amines
• Made from amino acids
• Include:
dopamine,
epinephrine (adrenaline),
norepinephrine (noradrenaline),
Serotonin and histamine
C. Kinds of Neurotransmitters
3. Amino Acids
4. Peptides (includes endorphins)
5. ATP
6. Nitric Oxide (NO)
7. Carbon monoxide (CO)
Nicotine mimics acetylcholine but can block function by
producing sustained depolarization
V. The Reflex Arc
A.The Pathway
1.Receptors
2.Sensory Neuron
3.CNS Integration
Center
4.Motor Neuron
5.Effector
B. Reflexes
1.Are rapid,
automatic
responses
to stimuli
2.A specific
stimulus
produces
the same
motor
response
VI. The Brain
A.The Cerebrum
1. Function
a.Thinking and
consciousness
b.Willed movements
c.Memory
d.Vision
e.Hearing
f.Sensory perception
g.Emotions
h.Speech
A. The Cerebrum
2. General Comments
a. 83% of total weight of brain
b. Paired cerebral hemispheres
A. The Cerebrum
3. Anatomy
a.Lobes Named for bones over
them
•
•
•
•
•
Frontal
Temporal
Parietal
Occipital
Insula
(limbic) –inside lateral sulcus
Occipital Lobe - Responsible for the processing of visual information.
Damage to this area results in partial or complete blindness.
Parietal Lobe - Responsible for the sensation of pain, touch, taste,
temperature, pressure. It is also related with mathematics and logics.
Frontal Lobe - Responsible for the elaboration of thinking, planning,
programming individual needs and emotion.
Temporal Lobe - It is primarily related with auditory sense, allowing the
recognition of specific tones and sound intensity. This area has also a
role in memory and emotion processing.
Limbic Lobe - It is involved in the emotional and sexual aspects of
behavior and in the processing of memory.
A. The Cerebrum
3. Anatomy
b. Fissures
Deep grooves
• Longitudinal (median, between
cerebral hemispheres)
• Transverse (between cerebrum and
cerebellum)
c.Sulci (sulcus singular)
Shallow grooves
• Central: between frontal/parietal
• Parieto-occipital
• Lateral: between temporal/frontal/
parietal
A. The Cerebrum
3. Anatomy
b. Gyri (gyrus singular)
Elevated ridges of tissue
• Precentral (anterior to central sulcus)
• Postcentral (posterior to central sulcus)
c.Basic Regions
Cortex
• Outer layer
• Gray Matter
White Matter – internal
Basal Nuclei
• Islands of gray matter inside white
matter
Memorize parts of Brain Song
http://www.youtube.com/watch?v=v
YwOtTMUz0c
VI. The Brain
B.The Diencephalon
1. Consists of
a.Thalamus
b.Hypothalamus
c.Epithalamus
VI. The Brain
B.The Diencephalon
2. Thalamus
a.“Gateway of the
Cerebral Cortex”
for afferent (sensory)
fibers especially touch &
taste
b.Relay station for sensory
and motor impulses
VI. The Brain
B.The Diencephalon
3. Hypothalamus
a.Autonomic control center
b.Main visceral control center
of the body
c.Involved in regulation of
•
•
•
•
Body temperature
Water balance and thirst
Food intake and metabolism
Sleep and wake cycles
VI. The Brain
B.The Diencephalon
3. Hypothalamus
c.Involved in regulation of
d.Endocrine functions
• Regulates pituitary
Produces releasing and
inhibiting hormones
• Produces hormones
• Antidiuretic hormone (ADH)
• Oxytocin
B.The Diencephalon
3. Hypothalamus
c.Involved in regulation of
d.Endocrine functions
e.Center for emotional response
and behavior
• Thirst center
• Appetite center
• Sex (sexual arousal) center
• Pain center
• Pleasure center
• Fear & Anger
B.The Diencephalon
4. Epithalamus
a.Forms roof of
3rd ventricle
b.Pineal Gland or
Body
c.Choroid
• Secretes
Plexus
melatonin
• Regulates sleep- • Forms
cerebral
wake cycles and
spinal fluid
moods
VI. The Brain
C. The Brain Stem
1. Midbrain
2. Pons
3. Medulla Oblongata
VI. The Brain
C.The Brain Stem
1. Midbrain
a.Conduction
pathway
between
higher and
lower brain
centers
b.Cranial Nerves
III & IV Oculomotor & Trochlear (eye movement)
VI. The Brain
C.The Brain Stem
2. Pons
a.Conduction
pathway
between
higher and
lower brain
centers
Cranial Nerves V – VII
b.Regulates c.
Trigeminal, Abducens, & Facial
sensory & chewing; rolls eye laterally; &
breathing Facefacial
expression & taste
C.The Brain Stem
3. Medulla
a.Autonomic reflex center for
body homeostasis
b.Centers
•
•
•
•
•
•
•
•
Cardiac
Vasomotor
Respiratory
Vomiting
Hiccupping
Swallowing
Cranial Nerves VIII – XII
Coughing c.
Vestibulocochlear, Glossopharyngeal,Vagus,Accessory,&Hypoglossal
swallow & taste; GI activity & Heart activity; acts on
Sneezing Hearing;sternocleidomastoid
& trapezius muscles; & control tong
movement & sensory impulses
VI. The Brain
D.Cerebellum
1. Assists in
maintaining
• Balance
• Posture
• Equilibrium
2. Coordinates skeletal
muscle
VI. The Brain
E. Functional Brain
Systems
1. Limbic System
• Our emotional or
affective (feelings)
brain
• Includes
hypothalamus and
parts of the
cerebrum
VI. The Brain
E. Functional Brain Systems
2. The Reticular Formation
• Involved in arousal of the
brain
• Filters the flood of sensory
input (99% filtered out)
– Filters out repetitive, familiar
or weak signals
– Passes on unussual, strong, or
significant signals
VI. The Brain
E. Functional Brain Systems
2. The Reticular Formation
• Involved in arousal of the
brain
• Filters the flood of sensory
input (99% filtered out)
– Filters out repetitive, familiar
or weak signals
– Passes on unussual, strong, or
significant signals
VI. Parts of the Brain & How
they work
E. http://educationportal.com/academy/lesson/pa
rts-of-the-brain.html
VI. The Brain
E.Functional Brain Systems
3. The Ventricles
Cavities
within the
brain
through
which
cerebralspinal fluid
flows
Demo of Sheep Brain
Dissection & Id it’s parts
http://www.youtube.com/watch?v=y
7gEWzPqm94
VII. The Spinal Cord
A.Function – involved with
1. Sensory
pathways to
brain
2. Motor
pathways to
body
3. Spinal cord
reflexes
VII. The Spinal Cord
B. Gray Matter at center of cord
1.Dorsal (posterior) horns = cell
bodies of the sensory neurons
2.Ventral (anterior) horns = cell
bodies of the motor neurons
VII. The Spinal Cord
B. Gray Matter at center of cord
3.Lateral horns = cell bodies of
preganglionic neurons of the
autonomic nervous system
VII. The Spinal Cord
B. Gray Matter at center of cord
4.Gray commisure = connects the
lateral halves of gray matter
VII. The Spinal Cord
C. Spinal Cord Injuries
1.Flaccid Paralysis
a.occurs when there is damage
to lower motor neurons
(i.e. anterior horns of gray
matter)
b.results in a total loss of
muscle tone and atrophy of
the muscle tissue
VII. The Spinal Cord
C. Spinal Cord Injuries
1.Spastic Paralysis
a.occurs when there is damage
to upper motor neurons
b.results in increased muscle
tone, due to reduced
inhibition of, but no voluntary
control over, skeletal muscle
VIII. CNS Protective Structures
A.Skull and Vertebral
Column
1.Cranial Bones (8)
2.Vertebral Column (33)
VIII. CNS Protective Structures
B.Meninges
1.three, thin
membranes that
completely cover the
brain and the spinal
cord.
2.Spinal fluid flows in the space
between two of the
membranes.
3.Include the dura, arachnoid,
pia
VIII. CNS Protective Structures
B.Meninges
3.Dura Matter
a.Outer layer
b.In the skull,
a double
layered
– outer layer = periosteal layer
attached to periosteium of
skull
– inner layer = meningeal layer is
outermost brain covering
Meninges in the Brain
VIII. CNS Protective Structures
A.Skull and Vertebral Column
B.Meninges
3.Dura Mater
c.In vertebral column
– Only a single layer
4.Arachnoid mater- middle
layer
5.Pia mater - inner layer
VIII. CNS Protective Structures
A.Skull and Vertebral Column
B.Meninges
C.Spaces between the meninges
1.Epidural
Above the dura
Only in spinal column
2.Subdural
Between dura and arachanoid
3.Subarachnoid
Between arachanoid and pia
VIII. CNS Protective Structures
D. Ventricles
1.fluid filled cavities in
the brain
2.Include:
a.1st & 2nd or Lateral Ventricle: in
the cerebral hemispheres, just above
the epithalmus.
b.Third ventricle: in diencephalon
c.4th ventricle: between the Pons &
Cerebellum
d.Cerebral Aquaduct: connects the 3rd
to the 4th ventricles.
VIII. CNS Protective Structures
D. Ventricles
3. Contain tufts of vascular
tissue called the choroid
plexus which
a.Produce cerebral spinal fluid &
b.Allows CSF to flow from ventricles to
surface of brain and then is return to
the blood.
VIII. CNS Protective Structures
E. Cerebral Spinal Fluid
1.Nourishes brain and spinal cord
2.Gives buoyancy to brain
Prevents brain from being
crushed by its own weight
3.Produced in choroid plexuses
• volume = 150 mL (1/2 cup)
• Replaced every 3-4 hrs
arachanoid
F. Blood Brain Barrier
1.Is the relative impermeability
of brain capillaries
Due to tight
junctions, and
endothelial
lining of blood
vessels in
brain
F. Blood Brain Barrier
Prevents passage
of proteins,
blood borne
metabolic wastes
(urea, creatine),
some toxins,
most drugs
Allows passage of nutrients: glucose,
essential amino acids, some
electrolytes
VIII. CNS Protective Structures
F. Blood Brain Barrier
3.Protects brain
against
fluctuations in
– Hormones
– Ions
– Nutrients
– Toxic
substances
HIV
VIII. CNS Disorders
A.Meningitis
1.Infection of the CSF
– Viral:
less dangerous
– Bacterial:
can lead to brain damage,
hearing loss, learning
disabilities, death
2.Infection of the CSF
– Causes inflamation of the
meninges
VIII. CNS Protective Structures
A.Meningitis
3.Symptoms
– High fever
– Stiff neck
– Intolerance for light
VIII. CNS Protective Structures
B. Encephalitis
1.Inflamation of brain tissue and
surrounding meninges
2.Cause – viral infections
3.Outcome
– Destruction of gray matter
– Can be fatal
C. Alzheimer Disease
1. Accumulation of plaque and
tangles in brain
2. Cause – unknown
VIII. CNS Protective Structures
D.Parkinson
1.characterized by a decrease in
spontaneous movements, gait
difficulty, postural instability,
rigidity and tremor
2.Cause the degeneration of the
neurons producing dopamine
Dissecting a Human Brain
http://www.youtube.com/watch?v
=OMqWRlxo1oQ
IX. CRANIAL AND SPINAL NERVES
A.Cranial Nerves
1.Visible on ventral surface
2.12 pair
IX. CRANIAL AND SPINAL NERVES
A.Cranial Nerves
2. 12 Pair
I. Olfactory: smell
II. Optic: vision
III.Oculomotor: eye movement
pupil dilation
IV.Trochlear: eye movement
V. Trigeminal: chewing;
somatosensory (pain touch)
for head
A. Cranial Nerves
2. 12 pair
VI. Abducens: eye movement-lateral
VII. Facial Nerve: taste, facial
expressions, somatosensory
from ear
VIII.Vestibulocochlear: hearing
and balance
IX. Glossopharyngeal: taste,
swallowing, sematosensory
from tongue
A. Cranial Nerves
2. 12 pair
X. Vegas: GI & Heart activity;
sensory, motor, autonomic
functions of viscera
XI.Spinal Accessory: head
movement
XII.Hypoglossal: tongue muscles
Here is a mnemonic:
On Old Olympus Towering Top A Famous
Vocal German Viewed Some Hops.
IX. CRANIAL AND SPINAL NERVES
B. Spinal Nerves – 31 pair
(1) Cervical
(2) Thoracic
(3) Lumbar
(4) Sacral
(5) Coccygeal
(6) Sciatic
(7) Lumbar plexus
(8) Intercostal
(9) Brachial plexus
(10) Cervical plexus
IX. CRANIAL AND SPINAL NERVES
B. Spinal Nerves – 31 pair
A nerve
plexus is a
network of
interwoven
nerves.
Recall
Divisions of the N.S.
Central N.S.
Brain
Peripheral N.S.
Spinal Cord Efferent Afferent
Autonomic
Parasympathetic
Somatic
Sympathetic
X. THE PERIPHERAL NS
CNS
PNS
X. THE PERIPHERAL NS
A. Afferent vs Efferent
X. THE PERIPHERAL NS
A. Afferent vs Efferent
1.Afferent NS
a.Sensory neurons.
Proprioceptors: sensitive to
position and movement
b.Pick up stimulus and carry it
toward the CNS
X. THE PERIPHERAL NS
A. Afferent vs Efferent
2.Efferent NS
a.Motor neurons
b.Carry response impulses from
the CNS to the effector
X. THE PERIPHERAL NS
A. Afferent vs Efferent
3. Disorders of Afferent &
Efferent systems
a.Myasthenia Gravis: immune
system attacks Ach; leads to
muscle weakness and fatigue
b.Multiple sclerosis: loss of
myelin sheath of motor and
sensory neurons; leads to
limb weakness, tremors,
vision disorders, vertigo
X. THE PERIPHERAL NS
B. Somatic vs Autonomic NS
1.Somatic
a.Controls skeletal muscles.
b.Can be conscious or subconscious
c.Has a single neuron between CNS
and effector
X. THE PERIPHERAL NS
B. Divisions of the Efferent NS
2. Autonomic
a.Controls smooth muscles of viscera
and glands
b.Is subconscious
c.Has 2 neurons b/w CNS & effector
X. THE PERIPHERAL NS
B. Divisions of the Efferent NS
2. Autonomic
c.Has two neurons between CNS
and effector
– Preganglionic neurons
 Originate in spinal cord
– Ganglion neurons
 Nerve cell bodies
– Neurons in effector
X. THE PERIPHERAL NS
C. Sympathetic and Parasympathetic
1. Sympathetic
a.“Fight or Flight”
b.Consists of
– Preganglionic neurons
– 2+ Ganglionic neurons
– Specialized neurons in adrenal
gland (secretes hormone
controlling production of Ach)
XI. Pain Perception
A. Gate Control Theory
1.Without any stimulation, both large
and small nerve fibers are quiet
and the inhibitory interneuron (I)
blocks the signal in the projection
neuron (P) that connects to the
brain. The "gate is closed" and
therefore NO PAIN
XI. Pain Perception
A. Gate Control Theory
2.With non-painful stimulation, large
nerve fibers are activated
primarily. This activates the
projection neuron (P), BUT it ALSO
activates the inhibitory interneuron
(I) which then BLOCKS the signal
in the projection neuron (P) that
connects to the brain. The "gate is
closed" and therefore NO PAIN.
XI. Pain Perception
A. Gate Control Theory
3.With pain stimulation, small nerve
fibers become active. They
activate the projection neurons (P)
and BLOCK the inhibitory
interneuron (I). Because activity of
the inhibitory interneuron is
blocked, it CANNOT block the
output of the projection neuron
that connects with the brain. The
"gate is open", therefore, PAIN!!
I = "Inhibitory Interneuron"; P = "Projection Neuron"
- = inhibition (blocking); + = excitation (activation)
XI. Pain Perception
B. Controlling Pain
1.Aspirin: acts mostly in PNS;
reduces inflammation
2.Morphine: acts in CNS to block
pain messages
3.Acupuncture:
stimulates large
diameter fibers
that inhibit pain
(closes the gate)
Sheep Brain Dissection
http://www.youtube.com/watch?v=hHl1PslMc8M