Transcript Chapter 13

Chapter 13
The Spinal Cord & Spinal Nerves
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Together with brain forms the CNS
Functions
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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
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Vertebrae
Epidural space filled with fa
Dura mater
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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
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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
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upper limbs
Lumbar enlargement
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lower limbs
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Inferior End of
Spinal Cord
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Conus medullaris
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Filum terminale
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thread-like extension of pia
mater
stabilizes spinal cord in canal
Caudae equinae (horse’s tail)
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cone-shaped end of spinal cord
dorsal & ventral roots of lowest
spinal nerves
Spinal segment
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area of cord from which each5
Spinal Cord & Spinal Nerves
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Spinal nerves begin as roots
Dorsal or posterior root is incoming sensory fibers
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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
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Technique
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long needle into subarachnoid space
safe from L3 to L5
Purpose
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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
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Gray matter is shaped like the letter H or a butterfly
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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
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White matter covers gray matter
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Tracts of the Spinal Cord
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Function of tracts
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highway for sensory & motor information
sensory tracts ascend
motor tracts descend
Naming of tracts
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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
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Motor tracts
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Sensory tracts
pyramidal tract (corticospinal) ---spinothalamic tract
extrapyramidal tract
---posterior
column
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Spinal Reflexes
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Automatic response to change in environment
Integration center for spinal reflexes is gray
matter of spinal cord
Examples
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somatic reflexes result in skeletal muscle
contraction
autonomic (visceral) reflexes involve smooth &
cardiac muscle and glands.
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heart rate, respiration, digestion, urination, etc
Note: cranial reflexes involve cranial nerves12
Reflex Arc
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Specific nerve impulse pathway
5 components of reflex arc
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receptor
sensory neuron
integrating center
motor neuron
effector
4 important somatic spinal reflexes
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stretch, tendon, flexor(withdrawal) & crossed
extensor reflexes
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Stretch Reflex (patellar reflex)
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Prevents injury from over stretching because
muscle contracts when it is stretched
Events of stretch reflex
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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
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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
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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
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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
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Checking a patient’s reflexes may help to
detect disorders/injury
Plantar flexion reflex -- stroke the lateral
margin of the sole
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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
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31 Pairs of spinal nerves
Named & numbered by the
cord level of their origin
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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
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Spinal nerves formed from dorsal & ventral
roots
Spinal nerves branch into dorsal & ventral
rami
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A Nerve Plexus
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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
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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
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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
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Erb-Duchene palsy
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Radial nerve injury
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improper deltoid injection
or tight cast
wrist drop
Median nerve injury
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waiter’s tip position
fall on shoulder
numb palm & fingers; inability to pronate & flex fingers
Ulnar nerve injury (clawhand)
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inability to adduct/abduct fingers,
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Lumbar Plexus
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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
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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
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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
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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
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Each spinal nerve contains both sensory &
motor nerve fibers
Dermatome
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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
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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
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injury that severs the
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Neuritis
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inflammation of nerves
caused by injury, vitamin deficiency or poison
Shingles
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Disorders
infection of peripheral nerve by chicken pox
virus
causes pain, skin discoloration, line of skin
blisters
Poliomyelitis
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viral infection causing motor neuron death and
possible death from cardiac failure or
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respiratory arrest