The Spinal Cord (CNS) and Peripheral Nervous System
 Spinal Cord (CNS)
• Meninges and Injections/Punctures
• Tracts and Information Pathways
• Spinal nerves
• Medical conditions: Spinal cord injury, shingles
 Peripheral Nervous System
• Structure of a Nerve and Its Wrappings
• The Twelve Cranial Nerves
• Reflexes: Monosynaptic and Polysynaptic
• Branches of the Peripheral System
o
Comparison between autonomic and somatic
 Sympathetic division
 Parasymphathetic division
• Developmental Aspects of the Nervous System
Spinal Cord
 Extends from the medulla
oblongata to the region of T12
 Below L2 is the cauda equina (a
collection of spinal nerves)
C7
 Enlargements occur in the cervical
and lumbar regions
 31 pairs of spinal nerves branch off
it
 Meninges follow cord all the way
to the spinal hiatus of the sacrum
at L2
Figure 7.18
Lumbar Puncture vs. Epidural Space Injection
1
2
3
Lumbar puncture for CSF below L2 in
larger subarachnoid space
Epidural injection (steroids,
anaesthetic) into epidural space
Spinal Cord Anatomy
 Exterior white mater – conduction tracts (axons) – is myelinated
 Internal gray matter - mostly cell bodies, is unmyelinated
•
Dorsal (posterior) horns (mostly association/interneurons)
•
Anterior (ventral) horns (motor nerves of somatic system)
 Central canal filled with cerebrospinal fluid
The Spinal Cord (CNS) and Peripheral Nervous System
 Spinal Cord (CNS)
• Meninges and Injections/Punctures
• Tracts and Information Pathways
• Spinal nerves
• Medical conditions: Spinal cord injury, shingles
 Peripheral Nervous System
• Structure of a Nerve and Its Wrappings
• The Twelve Cranial Nerves
• Reflexes: Monosynaptic and Polysynaptic
• Branches of the Peripheral System
o
Comparison between autonomic and somatic
 Sympathetic division
 Parasymphathetic division
• Developmental Aspects of the Nervous System
What’s in the Gray Matter of the Spinal Cord?
Dorsal root (sensory)
Dorsal root ganglion
Dorsal horn (interneurons)
Somatic
sensory
neuron
Visceral
sensory
neuron
Visceral
motor
neuron
Somatic
motor neuron
Spinal nerve
Ventral root
(motor)
Ventral horn
(motor neurons)
Interneurons receiving input from somatic sensory neurons
Interneurons receiving input from visceral sensory neurons
Visceral motor (autonomic) neurons
Somatic motor neurons
Figure 12.32
White Matter: Spinal Cord Information Pathways
 Dorsal columns carry only
ascending/afferent sensory tracts
Dorsal/posterior
 Lateral and anterior columns carry
both
• Ascending/afferent sensory
tracts
• Descending/efferent motor
tracts
 Pathways are composed of 2-3
neurons in a chain or relay
 Pathways cross from one side of the
CNS to the other (decussate)
 Ascending fibers add on laterally in
cord as they join - they “map” in the
tract based on where they enter or
exit (somatotopy)
Ventral/anterior
Ascending/Afferent
Sensory Tracts only in
posterior columns
Ascending/ Afferent
Sensory) AND
Descending/Efferent
Motor) Tracts in
lateral and anterior
columns
Three Ascending Pathways to Somatosensory Cortex
Spinocerebellar tracts
Conveys information about
muscle or tendon stretch. Do
not contribute to conscious
sensation. In lateral columns.
Dorsal column-medial
lemniscal pathway
Precise, “straight-through”
transmission of inputs from
single, localized body surface
receptors. In dorsal columns.
Anterolateral
(spinothalmic) pathways
Transmission of pain,
temperature, and coarse
touch. In anterior-ventral and
lateral columns.
Descending Pathways and Tracts
Direct pyramidal pathways
stimulate skeletal muscles
Indirect (Extrapyramidal system), e.g.
the rubrospinal tract
The Spinal Cord (CNS) and Peripheral Nervous System
 Spinal Cord (CNS)
• Meninges and Injections/Punctures
• Tracts and Information Pathways
• Spinal nerves
• Medical conditions: Spinal cord injury, shingles
 Peripheral Nervous System
• Structure of a Nerve and Its Wrappings
• The Twelve Cranial Nerves
• Reflexes: Monosynaptic and Polysynaptic
• Branches of the Peripheral System
o
Comparison between autonomic and somatic
 Sympathetic division
 Parasymphathetic division
• Developmental Aspects of the Nervous System
Spinal Nerves
 There is a pair of spinal
nerves at the level of each
vertebrae (8 cervical, 12
thoracic, 5 lumbar, 5
sacral, 1 coccygeal) = a
total of 31 pairs
 Spinal nerves are formed
by the combination of the
ventral and dorsal roots
of the spinal cord
 Spinal nerves are named
for the region from which
they arise
Nerve C8 emerges
Below vertebra C7
Anatomy of Spinal Nerves
 Spinal nerves divide soon after
leaving the spinal cord
• Dorsal ramus – serves the skin
and muscles of the posterior
trunk
• Ventral ramus – forms a
complex of networks (plexus)
for the anterior part of the body
spinal
nerve
posterior
anterior
The Spinal Cord (CNS) and Peripheral Nervous System
 Spinal Cord (CNS)
• Meninges and Injections/Punctures
• Tracts and Information Pathways
• Spinal nerves
• Medical conditions: spinal cord injury, shingles
 Peripheral Nervous System
• Structure of a Nerve and Its Wrappings
• The Twelve Cranial Nerves
• Reflexes: Monosynaptic and Polysynaptic
• Branches of the Peripheral System
o
Comparison between autonomic and somatic
 Sympathetic division
 Parasymphathetic division
• Developmental Aspects of the Nervous System
Areas of the Skin Served By Single Spinal Nerves
 Dermatomes
• Used to diagnose spinal
cord injury
• Pain in a particular skin
area reflects trouble in a
specific spinal nerve and
spinal location
• Can help to locate the site
of damage in the spinal
cord
• Most dermatomes overlap,
so destruction of a single
spinal nerve will not cause
complete numbness
Shingles (Herpes zoster) is a viral infection of sensory neurons to the skin
 Scaly, painful blisters
confined to a narrow
strip of skin on one side
of the body trunk
 Infects sensory skin
neurons
 Caused by latent
infection (resurgence)
of chicken pox virus
when immune system is
weakened as an adult
 Mostly in people over
50.
The Spinal Cord (CNS) and Peripheral Nervous System
 Spinal Cord (CNS)
• Meninges and Injections/Punctures
• Tracts and Information Pathways
• Spinal nerves
• Medical conditions: Spinal cord injury, shingles
 Peripheral Nervous System
• Structure of a Nerve and Its Wrappings
• The Twelve Cranial Nerves
• Reflexes: Monosynaptic and Polysynaptic
• Branches of the Peripheral System
o
Comparison between autonomic and somatic
 Sympathetic division
 Parasymphathetic division
• Developmental Aspects of the Nervous System
Peripheral Nervous System (The PNS)
one neuron (nerve fiber)
 Nerves and ganglia outside the central
nervous system
 Nerve = bundle of neuron fibers
 Neuron fibers are bundled by
connective tissue; one fiber = 1 axon
or cell
 Endoneurium surrounds each fiber,
just outside of Schwann cells
 Groups of fibers are bound into
fascicles by perineurium
 Fascicles are bound together by
epineurium
Classification of Nerves
 Mixed nerves – both sensory and motor fibers
present in the nerve
 Afferent (sensory) nerves – carry impulses
toward the CNS
 Efferent (motor) nerves – carry impulses
away from the CNS
The Twelve Cranial Nerves (I-V)
I Olfactory nerve – purely sensory for smell; ask
patient to identify oil of cloves and vanilla
II Optic nerve – purely sensory for vision;
observe eye, test patient with eye chart
III Oculomotor nerve – mostly motor fibers to
eye muscles, some proprioreceptive afferents;
examine pupil size and reflex, ability to follow
objects with the eye
IV Trochlear – mostly motor fibers to extrinsic
eye muscles; test patient’s ability to follow
objects with eye
V Trigeminal nerve – 3 divisions:
•
Opthalmic (tested by corneal reflex)
carrying sensory for skin of anterior
scalp, eyelid, nose
•
Maxillary (tested with pain, touch
temperature using safety pin) carrying
sensory from nasal cavity, palate, upper
lip, cheek
•
Mandibular (test by teeth clenching,
move jaw) carrying sensory from lower
teeth, masseter, temporalis
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The Twelve Cranial Nerves (Vi-XIII)
VI Abducens nerve – motor fibers to eye muscles
(lateral rectus); test by having patient follow
object side-to-side
VII Facial nerve – sensory for taste; motor fibers
to the face (test with ability to taste sweet salt,
sour, bitter and close eyes, smile, whistle, make
tears); five major branches: temporal,
zygomatic, buccal, mandibular, cervical
VIII Vestibulocochlear nerve – sensory for
balance (semicircular canals) and hearing; test
with air and bone conduction with tuning fork
IX Glossopharyngeal nerve – sensory for taste and
touch, pressure, pain from posterior tongue;
motor fibers to the swallowing muscles in
pharynx; test for gag and swallowing reflex,
cough, taste, uvula position
X Vagus nerves – sensory (including aortic arch
baroreceptors, respiration) and motor fibers for
pharynx, larynx, and viscera (heart rate,
breathing, digestive activity); test by gag,
swallowing reflexes
XI Accessory nerve – mostly motor fibers to neck
and upper back (trapezius, sternocleidomastoid);
test for head rotation strength and shrugging
against resistance
XII Hypoglossal nerve – mostly motor fibers to
tongue allowing food manipulation; test by
tongue protraction and retraction)
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The Spinal Cord (CNS) and Peripheral Nervous System
 Spinal Cord (CNS)
• Meninges and Injections/Punctures
• Tracts and Information Pathways
• Spinal nerves
• Medical conditions: Spinal cord injury, shingles
 Peripheral Nervous System
• Structure of a Nerve and Its Wrappings
• The Twelve Cranial Nerves
• Reflexes: Monosynaptic and Polysynaptic
• Branches of the Peripheral System
o
Comparison between autonomic and somatic
 Sympathetic division
 Parasymphathetic division
• Developmental Aspects of the Nervous System
Reflexes
 Classification by Acquisition
• Inborn (intrinsic) reflex: a rapid, involuntary, predictable motor response
to a stimulus
o
E.g. withdrawing your arm when fingers burned
• Learned (acquired) reflexes result from practice or repetition
o
Example: driving skills, knitting
 Classification by Function
• Somatic (drives skeletal muscle)
• Autonomic/visceral if activates visceral effectors in glands or smooth and
cardiac muscle
 Classification by Number of Synapses
• Monosynaptic - e.g. any stretch reflex like knee-jerk reflex
• Polysynaptic - e.g.
o
Golgi tendon reflex causing muscle relaxation and lengthening
o
Flexor/withdrawal reflexes causing flexion of muscles to pull limb away
o
Crossed-extensor reflexes casuing withdrawal and opposing extensor activity
like sudden pain in the foot and shifting of weight
Basic Reflex Arc
Stimulus
Skin
1 Receptor
Interneuron
2 Sensory neuron
3 Integration center
4 Motor neuron
5 Effector
Spinal cord
(in cross section)
Figure 13.14
Stretch Reflexes are Monosynaptic Pathways Triggered By Muscle Stretching
Stretched muscle spindles initiate a stretch reflex,causing contraction of the stretched muscle
and inhibition of its antagonist.
The events by which muscle stretch is damped
Sensory
neuron
Cell body of
sensory neuron
Initial stimulus
(muscle stretch)
Spinal cord
Muscle spindle
Antagonist muscle
Figure 13.17 (1 of 2), step1
Stretch Reflexes are Monosynaptic Pathways Triggered By Muscle Stretching
Stretched muscle spindles initiate a stretch reflex,causing contraction of the stretched muscle
and inhibition of its antagonist.
The events by which muscle stretch is damped
1 When muscle spindles are activated
by stretch, the associated sensory
neurons (blue) transmit afferent impulses
at higher frequency to the spinal cord.
Sensory
neuron
Cell body of
sensory neuron
Initial stimulus
(muscle stretch)
Spinal cord
Muscle spindle
Antagonist muscle
Figure 13.17 (1 of 2), step1
Stretched muscle spindles initiate a stretch reflex,
causing contraction of the stretched muscle and
inhibition of its antagonist.
The events by which muscle stretch is damped
1 When muscle spindles are activated
2 The sensory neurons synapse directly with alpha
motor neurons (red), which excite extrafusal fibers
by stretch, the associated sensory
of the stretched muscle. Afferent fibers also
neurons (blue) transmit afferent impulses synapse with interneurons (green) that inhibit motor
at higher frequency to the spinal cord.
neurons (purple) controlling antagonistic muscles.
Sensory
neuron
Cell body of
sensory neuron
Initial stimulus
(muscle stretch)
Spinal cord
Muscle spindle
Antagonist muscle
Figure 13.17 (1 of 2), step 2
Stretched muscle spindles initiate a stretch reflex,
causing contraction of the stretched muscle and
inhibition of its antagonist.
The events by which muscle stretch is damped
1 When muscle spindles are activated
2 The sensory neurons synapse directly with alpha
motor neurons (red), which excite extrafusal fibers
by stretch, the associated sensory
of the stretched muscle. Afferent fibers also
neurons (blue) transmit afferent impulses synapse with interneurons (green) that inhibit motor
at higher frequency to the spinal cord.
neurons (purple) controlling antagonistic muscles.
Sensory
neuron
Cell body of
sensory neuron
Initial stimulus
(muscle stretch)
Spinal cord
Muscle spindle
Antagonist muscle
3a Efferent impulses of alpha motor neurons
cause the stretched muscle to contract,
which resists or reverses the stretch.
Figure 13.17 (1 of 2), step 3a
Stretched muscle spindles initiate a stretch reflex,
causing contraction of the stretched muscle and
inhibition of its antagonist.
The events by which muscle stretch is damped
1 When muscle spindles are activated
2 The sensory neurons synapse directly with alpha
motor neurons (red), which excite extrafusal fibers
by stretch, the associated sensory
of the stretched muscle. Afferent fibers also
neurons (blue) transmit afferent impulses synapse with interneurons (green) that inhibit motor
at higher frequency to the spinal cord.
neurons (purple) controlling antagonistic muscles.
Sensory
neuron
Cell body of
sensory neuron
Initial stimulus
(muscle stretch)
Spinal cord
Muscle spindle
Antagonist muscle
3a Efferent impulses of alpha motor neurons
3b Efferent impulses of alpha motor
cause the stretched muscle to contract,
which resists or reverses the stretch.
neurons to antagonist muscles are
reduced (reciprocal inhibition).
Figure 13.17 (1 of 2), step 3b
The patellar (knee-jerk) reflex—a specific example of a stretch reflex
2
Quadriceps
(extensors)
1
3a
3b
3b
Patella
Muscle
spindle
Spinal cord
(L2–L4)
Hamstrings
(flexors)
Patellar
ligament
1 Tapping the patellar ligament excites
muscle spindles in the quadriceps.
2 Afferent impulses (blue) travel to the
spinal cord, where synapses occur with
motor neurons and interneurons.
3a The motor neurons (red) send
+
–
Excitatory synapse
Inhibitory synapse
activating impulses to the quadriceps
causing it to contract, extending the
knee.
3b The interneurons (green) make
inhibitory synapses with ventral horn
neurons (purple) that prevent the
antagonist muscles (hamstrings) from
resisting the contraction of the
quadriceps.
Figure 13.17 (2 of 2)
Golgi Tendon Reflex: A Polysynaptic Reflex
1 Quadriceps strongly
2 Afferent fibers synapse
contracts. Golgi tendon
organs are activated.
with interneurons in the
spinal cord.
Interneurons
Quadriceps
(extensors)
Spinal cord
Golgi
tendon
organ
Hamstrings
(flexors)
+ Excitatory synapse
– Inhibitory synapse
3a Efferent impulses
3b Efferent
to muscle with
stretched tendon are
damped. Muscle
relaxes, reducing
tension.
impulses to
antagonist
muscle cause
it to contract.
Figure 13.18
Crossed Extensor Reflex: A Polysynaptic Reflex
+ Excitatory synapse
– Inhibitory synapse
Interneurons
Efferent
fibers
Afferent
fiber
Efferent
fibers
Extensor
inhibited
Flexor
stimulated
Site of stimulus: a noxious
stimulus causes a flexor
reflex on the same side,
withdrawing that limb.
Flexor
inhibited
Extensor
stimulated
Arm
movements
Figure 13.19
Site of reciprocal
activation: At the
same time, the
extensor muscles
on the opposite
side are activated.
The Spinal Cord (CNS) and Peripheral Nervous System
 Spinal Cord (CNS)
• Meninges and Injections/Punctures
• Tracts and Information Pathways
• Spinal nerves
• Medical conditions: Spinal cord injury, shingles
 Peripheral Nervous System
• Structure of a Nerve and Its Wrappings
• The Twelve Cranial Nerves
• Reflexes: Monosynaptic and Polysynaptic
• Branches of the Peripheral System
o
Comparison between autonomic and somatic
 Sympathetic division
 Parasymphathetic division
• Developmental Aspects of the Nervous System
Autonomic Nervous System
 The involuntary branch of
the nervous system
 Consists of only motor
nerves
 Innervate smooth and
cardiac muscle and glands
 Make adjustments to
ensure optimal support for
body activities
 Operate via subconscious
control
 Divided into two divisions
• Sympathetic division
• Parasympathetic
division
Skin,
muscle, and
joint
sensors
visceral
sensory
fibers
(visceral
afferents)
and
reflexes
Visceral
organ
sensors
inhibitory
stimulatory
Efferent Pathways
 Somatic nervous system
• A, thick, heavily myelinated somatic motor fiber
makes up each pathway from the CNS to the
muscle
 ANS pathway is a two-neuron chain
1. Preganglionic neuron (in CNS) has a thin, lightly
myelinated preganglionic axon
2. Ganglionic neuron in autonomic ganglion has an
unmyelinated postganglionic axon that extends to
the effector organ
Differences Between Somatic and Autonomic Nervous Systems
Somatic
Autonomic
one motor neuron,
always stimulatory
preganglionic and postganglionic nerves
Effector organs
skeletal muscle
smooth muscle, cardiac muscle, and
glands
Nerurotransmitters
always uses acetylcholine
Nerves
(two neurons connected end to end);
stimulatory and inhibitory types
uses ACh in pre-ganglionic
neurons; either ACh or
norepinephrine in post-ganglionic
fibers
Comparison of Somatic and Autonomic Nervous Systems
Closer to spinal
cord than target
Closer to target
than spinal cord
Anatomy of the Sympathetic Division
 Originates from T1 through L2
 Short pre-ganglionic neuron
and long postganglionic
neuron transmit impulses
from CNS to the effector
 Ganglia are closer to the
spinal cord than the target
 Norepinephrine and
epinephrine are
neurotransmitters to the
effector organs
Anatomy of the Parasympathetic Division
 Originates from the brain
stem (cranial nerves
III,VII, IX, X) and S1
through S4
 Long pre-ganglionic
neuron and short
postganglionic neuron
transmit impulses from
CNS to the effector
 Terminal ganglia are at
the effector organs
(closer to target than
spinal cord)
 Always uses acetylcholine
as a neurotransmitter
Autonomic Functioning
 Sympathetic – “fight-or-flight”
• Response to unusual stimulus
• Takes over to increase
activities
• Remember as the “E” division
= exercise, excitement,
emergency, and embarrassment
 Parasympathetic –
housekeeping activites
• Conserves energy
• Maintains daily necessary
body functions
• Remember as the “D”
division - digestion,
defecation, and diuresis
Sympathetic and Parasympathetic Compared
Sympathetic Division 14.2
Parasympathetic Division 14.6
Neurotransmitters and Receptor Types
 Cholinergic fibers release the neurotransmitter acetylcholine (Ach)
• All ANS preganglionic axons
• All parasympathetic postganglionic axons
• Post synaptic membranes have cholinergic receptors
 Adrenergic fibers release the neurotransmitter norepinephrine (NE)
• Most sympathetic postganglionic axons
• Post synaptic membranes have adrenergic receptors
o Two general class types
 Alpha (), e.g. 1: constricts blood vessels & sphincter, dilates pupils
 Beta (), e.g. 1: increases heart rate, stimulates renin release (BP)
2: inhibitory; dilates blood vessels and bronchioles,
relaxes smooth muscle walls of GI tract, bladder, uterus
The Spinal Cord (CNS) and Peripheral Nervous System
 Spinal Cord (CNS)
• Meninges and Injections/Punctures
• Tracts and Information Pathways
• Spinal nerves
• Medical conditions: Spinal cord injury, shingles
 Peripheral Nervous System
• Structure of a Nerve and Its Wrappings
• The Twelve Cranial Nerves
• Reflexes: Monosynaptic and Polysynaptic
• Branches of the Peripheral System
o
Comparison between autonomic and somatic
 Sympathetic division
 Parasymphathetic division
• Developmental Aspects of the Nervous System
Interactions of the Autonomic Divisions
 Most visceral organs have dual innervation
 Dynamic antagonism allows for precise
control of visceral activity
• Sympathetic division increases heart and
respiratory rates, and inhibits digestion
and elimination
• Parasympathetic division decreases heart
and respiratory rates, and allows for
digestion and the discarding of wastes
Four Steps of Regeneration of Peripheral Nerves
Axon becomes fragmented at injury site
Macrophages clean off the dead axon
distal to the injury
Axon sprouts or filaments grow through a
regeneration tube formed by Schwann cells
Axon regenerated and a new myelin sheath
forms
Developmental Aspects of Fetal Nervous System
 Measles (rubella)
 Lack of oxygen
 Radiation and drugs
 Lack of folic acid
 Premature birth problems
Aging of the Brain and Nervous System
 No more neurons are formed
after birth, but growth and
maturation continues for
several years; brain atrophies in
old age
 Loss of sympathetic nervous
activity and slowing of
vasoconstriction (e.g.
headrushes, dizziness)
Enlargement of the subarachnoid space (left) and loss of white matter (right)
 Circulatory problems
 Dry eyes, constipation
 Need for regular checkups
when elderly
Shrinkage of hippocampus (left) and enlargement of ventricles (right)
The Spinal Cord (CNS) and Peripheral Nervous System
 Spinal Cord (CNS)
•
Meninges and Injections/Punctures
•
Tracts and Information Pathways
•
Spinal nerves
•
Medical conditions: Spinal cord injury, shingles
 Peripheral Nervous System
•
Structure of a Nerve and Its Wrappings
•
The Twelve Cranial Nerves
•
Reflexes: Monosynaptic and Polysynaptic
•
Branches of the Peripheral System
o
Comparison between autonomic and somatic
 Sympathetic division
 Parasymphathetic division
•
Developmental Aspects of the Nervous System