1. 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

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
Caudae equinae (horse’s tail)
dorsal & ventral roots of lowest spinal nerves

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. 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

9. Reflex Arc Specific nerve impulse pathway 5 components of reflex arc
receptor
sensory neuron
integrating center
motor neuron
effector

10. 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

11. Illustration of the Stretch Reflex

12. 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

13. 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)

14. 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

15. 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

16. Dermatomes
Damaged regions of the spinal cord can be distinguished by patterns of numbness over a dermatome region
Spinal cord transection
injury that severs the cord loss of sensation & motor control below the injury

17. 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