Download Lecture 9

I.
Anatomy
II.
Physiology
Spinal
Cord
1
The Spinal Cord & Spinal Nerves

Together with brain forms the CNS

Functions
1. spinal cord reflexes
2. integration (summation of inhibitory and
excitatory) nerve impulses
3. highway for upward and downward travel of
sensory and motor information
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I.
II.
Anatomy
1.
Protective Structures
2.
External
3.
Internal
4.
Spinal Nerves
a.
Covering
b.
Distribution
c.
Dermatomes
Physiology
Spinal
Cord
3
Spinal Cord Protection
1. vertebral column
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Structures Covering the Spinal Cord
2.
Membrane
A. Dura mater - dense
irregular CT tube

Subdural space filled
with interstitial fluid
B. Arachnoid = spider web of
collagen fibers
A. Subarachnoid space =
CSF
C. Pia mater

thin layer covers BV

denticulate ligs hold in
place
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External Anatomy of Spinal Cord

Flattened cylinder

16-18 Inches long &
3/4 inch diameter

In adult ends at L2

In newborn ends at L4

Growth of cord stops at age 5
1.
Cervical enlargement

2.
upper limbs
Lumbar enlargement

lower limbs
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Inferior End of Spinal Cord
1.
Conus medullaris

2.
3.
Filum terminale

thread-like extension of pia
mater

stabilizes spinal cord in
canal
Caudae equinae (horse’s tail)

4.
cone-shaped end of spinal
cord
Conus
medullaris
dorsal & ventral roots of
lowest spinal nerves
Spinal segment

area of cord from which
each pair of spinal nerves
arises
Filum
terminale
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Spinal Cord & Spinal Nerves

Spinal nerves begin as
roots
Posterior
Root
(Sensory)
1. Dorsal or posterior root
is incoming sensory fibers

dorsal root ganglion
(swelling) = cell bodies
of sensory nerves
2. Ventral or anterior root
is outgoing motor fibers
Anterior
Root
(Motor)
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Gray Matter of the Spinal Cord
 Central canal continuous with
4th ventricle of brain
 Gray matter is shaped like the
letter H or a butterfly
 contains neuron cell bodies,
unmyelinated axons &
dendrites
 paired dorsal and ventral gray
horns
 lateral horns only present in
thoracic spinal cord
 gray commissure crosses the
midline
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White Matter of the Spinal Cord
 White matter covers gray
matter
 Anterior median fissure
deeper than Posterior
median sulcus
 Anterior, Lateral and
Posterior White Columns
contain axons that form
ascending & descending
tracts
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Spinal Nerves

31 Pairs of spinal nerves

Named & numbered by the
cord level of their origin

1.
8 pairs of cervical nerves
(C1 to C8)
2.
12 pairs of thoracic nerves
(T1 to T12)
3.
5 pairs of lumbar nerves
(L1 to L5)
4.
5 pairs of sacral nerves
(S1 to S5)
5.
1 pair of coccygeal nerves
Mixed sensory & motor nerves
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A Nerve Plexus
 Joining of ventral rami of
spinal nerves to form nerve
networks or plexuses
 Found in neck, arm, low
back & sacral regions
 No plexus in thoracic region
 intercostal nn. innervate
intercostal spaces
 T7 to T12 supply
abdominal wall as well
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Cervical Plexus
 Ventral rami of spinal
nerves (C1 to C5)
 Supplies parts of head,
neck & shoulders
 Phrenic nerve (C3-C5)
keeps diaphragm alive
 Damage to cord above
C3 causes respiratory
arrest
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Phrenic Nerve
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Brachial Plexus
 Ventral rami from C5 to T1
 Supplies shoulder & upper limb
 Passes superior to 1st rib &
under clavicle
 Axillary n. = deltoid & teres m.
 Musculocutaneous n. = elbow
flexors
 Radial n. = shoulder & elbow
extensors
 Median & ulnar nn. = flexors
of wrist & hand
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Branches off Brachial Plexus
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Lumbar Plexus
 Ventral rami of L1 to L4
 Supplies abdominal wall,
external genitals &
anterior/medial thigh
 Injury to femoral nerve
causes inability to extend
leg & loss of sensation in
thigh
 Injury to obturator nerve
causes paralysis of thigh
adductors
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Branches of Lumbar Plexus
 Notice: Femoral and
Obturator nerves
 Found anterior and medial
to hip joint
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Sacral Plexus
 Ventral rami of L4-L5 & S1-S4
 Anterior to the sacrum
 Supplies buttocks, perineum &
part of lower limb
 Sciatic nerve = L4 to S3 supplies
post thigh & all below knee
 Peroneal nerve injury
produces foot drop or
numbness
 Tibial nerve injury produces
calcaneovalgus (loss of
function on anterior leg &
dorsum of foot)
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Branches of Sacral Plexus
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Sciatic Nerve Branches
 Notice: Common Peroneal
nerve and Tibial nerve
behind the knee
 Notice: Sciatica pain
extends from the buttock
down the leg to the foot
 may be sign of herniated
disc
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Dermatomes & Myotomes
 Each spinal nerve contains both
sensory & motor nerve fibers
 Dermatome
 area of skin supplied by one
spinal nerve
 overlap prevents loss of
sensation if one damaged
 sensory anesthesia requires 3
spinal nerves to be blocked
 Skin on face supplied by Cranial
Nerve V
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I.
Anatomy
II.
Physiology
1.
Tracts
2.
Reflexes
a.
Stretch
b.
Tendon
c.
Flexor
d.
Crossed Extensor
Spinal
Cord
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Tracts of the Spinal Cord

Function of tracts
1. highway for sensory & motor information
2. sensory tracts ascend
3. motor tracts descend

Naming of tracts

indicates position & direction of signal

example = anterior spinothalamic tract

impulses travel from spinal cord towards brain
(thalamus)

found in anterior part of spinal cord
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Location of Tracts inside Cord
Motor tracts
Sensory tracts
pyramidal tract (corticospinal)
spinothalamic tract
extrapyramidal tract
posterior column
spinocerebellar
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Function of Spinal Tracts
two-point discrimination,
pressure and vibration
pain, temperature, deep
pressure
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Function of Spinal Tracts
voluntary
movements,
posture & muscle
tone, equilibrium
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Spinal Reflexes
 Automatic response to change in environment
 Integration center for spinal reflexes is gray matter of spinal
cord
 Examples
 somatic reflexes result in skeletal muscle contraction
 autonomic (visceral) reflexes involve smooth & cardiac
muscle and glands.
 heart rate, respiration, digestion, urination, etc
 Note: cranial reflexes involve cranial nerves
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Reflex Arc

Specific nerve impulse pathway

5 components of reflex arc

1.
receptor
2.
sensory neuron
3.
integrating center
4.
motor neuron
5.
effector
4 important somatic spinal
reflexes
1.
stretch,
2.
tendon,
3.
flexor(withdrawal)
4.
crossed extensor reflexes
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Illustration of the Stretch Reflex
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Illustration of Tendon Reflex
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Flexor (withdrawal) Reflex
 Step on tack (pain fibers
send signal to spinal cord)
 Interneurons branch to
different spinal cord
segments
 Motor fibers in several
segments are activated
 More than one muscle
group activated to lift foot
off of tack
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Crossed Extensor Reflex
 Lifting left foot requires
extension of right leg to
maintain one’s balance
 Pain signals cross to
opposite spinal cord
 Contralateral extensor
muscles are stimulated by
interneurons to hold up the
body weight
 Reciprocal innervation when extensors contract
flexors relax, etc
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