Transcript Chapter 13
Chapter 13
The Spinal Cord & Spinal Nerves
Together with brain forms the CNS
Functions
spinal cord reflexes
integration (summation of inhibitory and
excitatory) nerve impulses
highway for upward and downward travel of
sensory and motor information
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Spinal Cord Protection
By the vertebral column, meninges, cerebrospinal
fluid, and vertebral ligaments.
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Structures Covering the Spinal Cord
Vertebrae
Epidural space filled with fa
Dura mater
dense irregular CT tube
Subdural space filled with
interstitial fluid
Arachnoid = spider web of
collagen fibers
Subarachnoid space = CSF
Pia mater
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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 a
age 5
Cervical enlargement
upper limbs
Lumbar enlargement
lower limbs
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Inferior End of
Spinal Cord
Conus medullaris
Filum terminale
thread-like extension of pia
mater
stabilizes spinal cord in canal
Caudae equinae (horse’s tail)
cone-shaped end of spinal cord
dorsal & ventral roots of lowest
spinal nerves
Spinal segment
area of cord from which each5
Spinal Cord & Spinal Nerves
Spinal nerves begin as roots
Dorsal or posterior root is incoming sensory fibers
dorsal root ganglion (swelling) = cell bodies of sensory
nerves
Ventral or anterior root is outgoing motor fibers
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Spinal tap or Lumbar Puncture
Technique
long needle into subarachnoid space
safe from L3 to L5
Purpose
sampling CSF for diagnosis
injection of antibiotics, anesthetics or
chemotherapy
measurement of CSF pressure
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Gray Matter of the Spinal Cord
Note: colors in
reverse due to
staining of tissue
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
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White Matter of the Spinal Cord
White matter covers gray matter
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Tracts of the Spinal Cord
Function of tracts
highway for sensory & motor information
sensory tracts ascend
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
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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 nerves12
Reflex Arc
Specific nerve impulse pathway
5 components of reflex arc
receptor
sensory neuron
integrating center
motor neuron
effector
4 important somatic spinal reflexes
stretch, tendon, flexor(withdrawal) & crossed
extensor reflexes
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Stretch Reflex (patellar reflex)
Prevents injury from over stretching because
muscle contracts when it is stretched
Events of stretch reflex
muscle spindle signals stretch of muscle
motor neuron activated & muscle contracts
Brain sets muscle spindle sensitivity as it sets
muscle tone (degree of muscle contraction at
rest)
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Illustration of the Stretch Reflex
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Tendon Reflex
Controls muscle tension by causing muscle
relaxation that prevents tendon damage
Both tendon & muscle are protected
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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
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
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Clinical Considerations
Checking a patient’s reflexes may help to
detect disorders/injury
Plantar flexion reflex -- stroke the lateral
margin of the sole
normal response is curling under the toes
abnormal response or response of children
under 18 months is called Babinski sign
(upward fanning of toes due to incomplete
myelination in child)
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Spinal Nerves
31 Pairs of spinal nerves
Named & numbered by the
cord level of their origin
8 pairs of cervical nerves
(C1 to C8)
12 pairs of thoracic nerves
(T1 to T12)
5 pairs of lumbar nerves
(L1 to L5)
5 pairs of sacral nerves
(S1 to S5)
1 pair of coccygeal nerves
Mixed sensory & motor
nerves
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Branching of Spinal Nerve
Spinal nerves formed from dorsal & ventral
roots
Spinal nerves branch into dorsal & ventral
rami
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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
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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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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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Clinical Correlations
Erb-Duchene palsy
Radial nerve injury
improper deltoid injection
or tight cast
wrist drop
Median nerve injury
waiter’s tip position
fall on shoulder
numb palm & fingers; inability to pronate & flex fingers
Ulnar nerve injury (clawhand)
inability to adduct/abduct fingers,
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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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Sacral Plexus
Ventral rami of L4-L5 & S1S4
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
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function on anterior leg &
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
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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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Dermatomes
Damaged regions of
the spinal cord can be
distinguished by
patterns of numbness
over a dermatome
region
Infusing local
anesthetics or cutting
roots must be done
over 3 adjacent spinal
nerves.
Spinal cord transection
injury that severs the
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Neuritis
inflammation of nerves
caused by injury, vitamin deficiency or poison
Shingles
Disorders
infection of peripheral nerve by chicken pox
virus
causes pain, skin discoloration, line of skin
blisters
Poliomyelitis
viral infection causing motor neuron death and
possible death from cardiac failure or
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respiratory arrest