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PowerPoint® Lecture Slides prepared by Vince Austin, University of Kentucky
Spinal Cord – Part I
Human Anatomy & Physiology, Sixth Edition
Elaine N. Marieb
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
12b
Spinal Cord
 CNS tissue is enclosed within the vertebral column from the
foramen magnum to L1
 Provides two-way communication to and from the brain
 Protected by bone, meninges, and CSF
 Epidural space – space between the vertebrae and the dural
sheath (dura mater) filled with fat and a network of veins
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Principal Parts
Principal Parts
1. 42-45 cm in length; 2.5 cm wide
2. cervical enlargement - C4:T1 supply upper limbs
3. lumbar enlargement - T9:T12 supply lower limbs
4. conus medullaris - tapers off to end at L1-L2
5. filum terminale - pia mater anchors cord to coccyx
6. cauda equina - (horse tail) nerves below L2
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Spinal Cord
Figure 12.28a
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Things to NOTE about the Spinal Cord
1. Cord itself ends at L1-L2 vertebrae
2. Lower nerves dangle down in the cauda equina
3. There are 31 pairs of spinal nerves
4. spinal segment - gives rise to one spinal nerve
5. C1-C7 spinal nerves project ABOVE C1-C7 vertebrae
6. C8 spinal nerve projects below C7 vertebra
7. T1-S5 spinal nerves project BELOW T1-S5 vertebrae
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Grey Matter areas vs. White Matter areas
1. grey matter - nerve cell bodies motor & interneurons
2. white matter - myelinated axons of motor & sensory
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Cross-Sectional Anatomy of the Spinal Cord
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Figure 12.30a
Regions in the Grey Matter - H shaped center
1. grey commissure - cross bar of the H
2. central canal - hole in the center
3. anterior (ventral) horns
4. posterior (dorsal) horns
5. lateral (intermediate) horns (T, L, S only)
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Gray Matter and Spinal Roots
Figure 12.30b
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Gray Matter: Organization
 Dorsal half – sensory roots and ganglia
 Ventral half – motor roots
 Dorsal and ventral roots fuse laterally to form spinal nerves
 Four zones are evident within the gray matter – somatic
sensory (SS), visceral sensory (VS), visceral motor (VM),
and somatic motor (SM)
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Gray Matter: Organization
Figure 12.31
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PowerPoint® Lecture Slides prepared by Vince Austin, University of Kentucky
Spinal Nerves
Human Anatomy & Physiology, Sixth Edition
Elaine N. Marieb
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
13b
Spinal Nerves
 Thirty-one pairs of mixed nerves arise from the spinal cord
and supply all parts of the body except the head
 They are named according to their point of issue
 8 cervical (C1-C8)
 12 thoracic (T1-T12)
 5 lumbar (L1-L5)
 5 sacral (S1-S5)
 1 coccygeal (C0)
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Spinal Nerves
Figure 13.6
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Spinal Nerves: Roots
 Each spinal nerve connects to the spinal cord via two medial
roots
 Each root forms a series of rootlets that attach to the spinal
cord
 Ventral roots arise from the anterior horn and contain
motor (efferent) fibers
 Dorsal roots arise from sensory neurons in the dorsal root
ganglion and contain sensory (afferent) fibers
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Spinal Nerves: Roots
Figure 13.7a
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Nerve Plexuses
 All ventral rami except T2-T12 form interlacing nerve
networks called plexuses
 Plexuses are found in the cervical, brachial, lumbar, and
sacral regions
 Each resulting branch of a plexus contains fibers from
several spinal nerves
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Nerve Plexuses
 Fibers travel to the periphery via several different routes
 Each muscle receives a nerve supply from more than one
spinal nerve
 Damage to one spinal segment cannot completely paralyze a
muscle
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Spinal Nerve Innervation: Back, Anterolateral
Thorax, and Abdominal Wall
 The back is innervated by dorsal rami via several branches
 The thorax is innervated by ventral rami T1-T12 as
intercostal nerves
 Intercostal nerves supply muscles of the ribs, anterolateral
thorax, and abdominal wall
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Spinal Nerve Innervation: Back, Anterolateral
Thorax, and Abdominal Wall
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Figure 13.7b
Cervical Plexus
 The cervical plexus is formed by ventral rami of
C1-C4
 Most branches are cutaneous nerves of the neck, ear, back of
head, and shoulders
 The most important nerve of this plexus is the phrenic
nerve - the major motor and sensory nerve of the diaphragm
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Cervical Plexus
Figure 13.8
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Brachial Plexus
 Formed by C5-C8 and T1 (C4 and T2 may also contribute to
this plexus in some people)
 It gives rise to the nerves that innervate the upper limb
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Brachial Plexus
There are four major branches of this plexus
 Roots – five ventral rami (C5-T1)
 Trunks – upper, middle, and lower, which form divisions
 Divisions – anterior and posterior serve the front and
back of the limb
 Cords – lateral, medial, and posterior fiber bundles
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Brachial Plexus
Figure 13.9a
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Brachial Plexus: Nerves
 Axillary – innervates the deltoid and teres minor
 Musculocutaneous – sends fibers to the biceps brachii and
brachialis
 Median – branches to most of the flexor muscles of arm
 Ulnar – supplies the flexor carpi ulnaris and part of the
flexor digitorum profundus
 Radial – innervates essentially all extensor muscles
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Brachial Plexus: Distribution of Nerves
Figure 13.9c
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Brachial Plexus: Nerves
Figure 13.9b
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Lumbar Plexus
 Arises from L1-L4 and innervates the thigh, abdominal wall,
and related muscles
 The major nerves are the femoral and the obturator
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Lumbar Plexus
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Figure 13.10
Sacral Plexus
 Arises from L4-S4 and serves the buttock, lower limb, pelvic
structures, and the related sacral areas
 The major nerve is the sciatic, the longest and thickest nerve
of the body
 The sciatic is actually composed of two nerves: the tibial
and the common fibular nerves
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Sacral Plexus
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Figure 13.11
Dermatomes
 A dermatome is the area of skin innervated by the cutaneous
branches of a single spinal nerve
 All spinal nerves except C1 participate in dermatomes
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Dermatomes
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Figure 13.12
PowerPoint® Lecture Slides prepared by Vince Austin, University of Kentucky
Spinal Cord – Part II
Human Anatomy & Physiology, Sixth Edition
Elaine N. Marieb
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
12b
White Matter in the Spinal Cord
 Fibers run in three directions – ascending, descending, and
transversely
 Divided into three funiculi (columns) – posterior, lateral,
and anterior
 Each funiculus contains several fiber tracks
 Fiber tract names reveal their origin and destination
 Fiber tracts are composed of axons with similar functions
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White Matter: Pathway Generalizations
 Pathways decussate (cross to contralateral side of body)
 Most consist of two or three neurons in the pathway
 Most exhibit somatotopy (precise spatial relationships)
 Pathways are paired (one on each side of the spinal cord or
brain)
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Ascending (Sensory) Tracts
Figure 12.32
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Ascending Tracts
TRACT
FUNCTION
1. anterior (ventral) spinothalamic
- touch and pressure to thalamus
2. lateral spinothalamic tract
- pain & temperature to thalamus
3. fasciculus gracilis & cuneatus
- touch, 2-pt. discrimination
conscious proprioception,
stereognosis, weight
discrimination, vibration
4. posterior spinocerebellar
- subconscious proprioception
5. anterior spinocerebellar
- subconscious proprioception
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Nonspecific Ascending Pathway
 Nonspecific
pathway for pain,
temperature, and
crude touch within
the lateral
spinothalamic
tract
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Figure 12.33b
Descending (Motor) Pathways
 Motor pathways involve two neurons (upper motor
neuron and lower motor neuron)
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Descending (Motor) Tracts
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Descending (Motor) Pathways
TRACTS
FUNCTIONS
1. lateral & anterior corticospinal
motor output from cortex motor
to cells of ant. horn
2. rubrospinal
motor from midbrain to anterior
horn for precise movement
3. tectospinal
motor from midbrain to anterior
horn; movements in response to
audiovisual/cutaneous stimuli
4. vestibulospinal
motor from medulla to anterior
horn; coordination/balance
5. lateral reticulospinal
motor from medulla to anterior
horn; inhibit extensor reflexes
6. medial reticulospinal
motor from pons to anterior horn;
facilitate extensor reflexes
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The Direct (Pyramidal) Motor System
 Direct pathways originate with the pyramidal neurons in
the precentral gyri
 Impulses are sent through the corticospinal tracts and
synapse in the anterior horn
 Stimulation of anterior horn neurons activates skeletal
muscles
 Parts of the direct pathway, called corticobulbar tracts,
innervate cranial nerve nuclei
 The direct pathway regulates fast and fine (skilled)
movements
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The Direct (Pyramidal) System
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Figure 12.34a
Indirect (Extrapyramidal) Motor System
 Includes the brain stem, motor nuclei, and all motor
pathways not part of the pyramidal system
 This system includes the rubrospinal, vestibulospinal,
reticulospinal, and tectospinal tracts
 These motor pathways are complex and multisynaptic, and
regulate:
 Axial muscles that maintain balance and posture
 Muscles controlling coarse movements of the proximal
portions of limbs
 Head, neck, and eye movement
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Indirect (Extrapyramidal) System
Figure 12.34b
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Extrapyramidal (Multineuronal) Pathways
 Reticulospinal tracts – maintain balance
 Rubrospinal tracts – control flexor muscles
 Superior colliculi and tectospinal tracts mediate head
movements
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White Matter: Pathway Generalizations
Figure 12.32
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Spinal Cord Trauma: Paralysis
 Paralysis – loss of motor function
 Flaccid paralysis – severe damage to the ventral root or
anterior horn cells
 Lower motor neurons are damaged and impulses do not
reach muscles
 There is no voluntary or involuntary control of muscles
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Spinal Cord Trauma: Paralysis
 Spastic paralysis – only upper motor neurons of the primary
motor cortex are damaged
 Spinal neurons remain intact and muscles are stimulated
irregularly
 There is no voluntary control of muscles
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Spinal Cord Trauma: Transection
 Cross sectioning of the spinal cord at any level results in
total motor and sensory loss in regions inferior to the cut
 Paraplegia – transection between T1 and L1
 Quadriplegia – transection in the cervical region
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Poliomyelitis
 Destruction of the anterior horn motor neurons by the
poliovirus
 Early symptoms – fever, headache, muscle pain and
weakness, and loss of somatic reflexes
 Vaccines are available and can prevent infection
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Amyotrophic Lateral Sclerosis (ALS)
 Lou Gehrig’s disease – neuromuscular condition involving
destruction of anterior horn motor neurons and fibers of the
pyramidal tract
 Symptoms – loss of the ability to speak, swallow, and
breathe
 Death occurs within five years
 Linked to malfunctioning genes for glutamate transporter
and/or superoxide dismutase
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