1. 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

2. Spinal Cord Protection
By the vertebral column, meninges, cerebrospinal fluid, and vertebral ligaments.

3. Structures Covering the Spinal Cord
Vertebrae
Epidural space filled with fat
Dura mater
dense irregular CT tube
Subdural space filled with interstitial fluid
Arachnoid = spider web of collagen fibers
Subarachnoid space = CSF
Pia mater
thin layer covers BV
denticulate ligs hold in place

4. 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
Cervical enlargement
upper limbs
Lumbar enlargement
lower limbs

5. Inferior End of Spinal Cord
Conus medullaris
cone-shaped end of spinal cord
Filum terminale
thread-like extension of pia mater
stabilizes spinal cord in canal
Caudae equinae (horse’s tail)
dorsal & ventral roots of lowest spinal nerves
Spinal segment
area of cord from which each pair of spinal nerves arises

6. 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

7. 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

8. 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
gray commissure crosses the midline
Central canal continuous with 4th ventricle of brain

9. 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

10. 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

11. Location of Tracts inside Cord
Motor tracts Sensory tracts
pyramidal tract (corticospinal) ---spinothalamic tract
extrapyramidal tract ---posterior column
---spinocerebellar

12. Function of Spinal Tracts
Spinothalamic tract
pain, temperature, deep pressure & crude touch
Posterior columns
proprioception, discriminative touch, two-point discrimination, pressure and vibration
Direct pathways (corticospinal & corticobulbar)
precise, voluntary movements
Indirect pathways (rubrospinal, vestibulospinal)
programming automatic movements, posture & muscle tone, equilibrium & coordination of visual reflexes

13. 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

14. 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

15. Stretch Reflex (patellar reflex)
Monosynaptic,ipsilateral reflex arc
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)
Reciprocal innervation (polysynaptic- interneuron)
antagonistic muscles relax as part of reflex

16. Illustration of the Stretch Reflex

17. Tendon Reflex
Controls muscle tension by causing muscle relaxation that prevents tendon damage
Golgi tendon organs in tendon
activated by stretching of tendon
inhibitory neuron is stimulated (polysynaptic)
motor neuron is hyperpolarized and muscle relaxes
Both tendon & muscle are protected
Reciprocal innervation (polysynaptic)
causes contraction of ipsilateral muscle group

18. Illustration of Tendon Reflex

19. 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

20. 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

21. 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)

22. 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

23. Connective Tissue Coverings
Endoneurium = wrapping of each nerve fibers
Perineurium = surrounds group of nerve fibers forming a fascicle
Epineurium = covering of entire nerve
dura mater blends into it at intervertebral foramen

24. Endoneurium
Perineurium
Epineurium

25. Branching of Spinal Nerve
Spinal nerves formed from dorsal & ventral roots
Spinal nerves branch into dorsal & ventral rami
dorsal rami supply skin & muscles of back
ventral rami form plexus supply anterior trunk & limbs
meningeal branches supply meninges, vertebrae & BV

26. 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

27. 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

28. Phrenic Nerve

29. 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

30. Branches off Brachial Plexus

31. Clinical Correlations
Erb-Duchene palsy
waiter’s tip position
fall on shoulder
Radial nerve injury
improper deltoid injection or tight cast
wrist drop
Median nerve injury
numb palm & fingers; inability to pronate & flex fingers
Ulnar nerve injury (clawhand)
inability to adduct/abduct fingers, atrophy of interosseus
Long thoracic nerve injury (winged scapula)
paralysis of serratus anterior, can’t abduct above horizontal

32. 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

33. Branches of Lumbar Plexus
Notice: Femoral and Obturator nerves
Found anterior and medial to hip joint

34. 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)

35. Branches of Sacral Plexus
Notice: Sciatic nerve origins

36. 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

37. 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

38. 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 cord loss of sensation& motor control below the injury

39. Disorders Neuritis Shingles Poliomyelitis inflammation of nerves
caused by injury, vitamin deficiency or poison
Shingles
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 respiratory arrest