1. Structure of Nerves (including roots and rami and plexuses)
Consist of
Axon bundles/nerve fibers
Schwann cells
Connective tissue
Blood vessels
Endoneurium: surrounds individual neurons
loose CT with capillaries (for neurons)
Perineurium: Surrounds fascicles
blood vessels Epineurium: surrounds the entire nerve
Dense CT

2. Spinal Cord and Spinal Nerves
Chapter 12
Spinal Cord and Spinal Nerves

3. Spinal Cord Functions
carry/transmit sensory and motor impulses between spinal nerves and the brain
in columns/white matter
integration center for spinal reflexes
in gray matter

4. Spinal Cord Extends from foramen magnum to ~L1-L2
Vertebral canal continues length of sacrum
a portion of the vertebral canal is not occupied by the actual spinal cord
creates the opportunity for spinal tap/lumbar puncture (see next side)
Gives rise to 31 pairs of spinal nerves
Exit through intervertebral and sacral foramina

5. Lumbar puncture

6. Spinal Cord Not uniform in diameter Conus medullaris: Cauda equina:
Cervical enlargement:
supplies upper limbs
Lumbar enlargement:
supplies lower limbs
Conus medullaris:
Tapered/pointed inferior end of cord.
Cauda equina:
Roots and nerves extending down vertebral canal below L2 that exit intervertebral and sacral foramina

8. Spinal Nerves Thirty-one pairs of spinal nerves
First pair exit vertebral column between skull and atlas
Exit vertebral canal through intervertebral and sacral foramina
8 pair cervical, 12 pair thoracic, 5 pair lumbar, 5 pair sacral, & coccygeal

10. Rami of spinal nerve (thoracic region): rami branch off the spinal nerve

11. C1 2 3 Cervical 4 nerves 5 6 7 8 T1 Thoracic 9 10 11 12 L1 Lumbar
Sacral
Coccygeal
(a) Posterior view C1 T1 2 3 4 5 6 7 8 9 10 11 12 L1

12. Dermatomal Map
Dermatomal map: skin area supplied with somatic sensory innervation by spinal nerves—general trends

13. Plexuses: intermingling nerves arising from multiple anterior rami

14. Branches of Spinal Nerves
Dorsal/posterior Ramus:
innervate deep muscles of the trunk responsible for movements of the vertebral column and skin near dorsal midline
Ventral/anterior Ramus:
innervates structures anterior and lateral to spinal cord.
Thoracic region: form intercostal nerves that innervate the intercostal muscles and the skin over the thorax
Other regions they form plexuses (intermingling of nerves).
Ventral rami C1-C4= cervical plexus
Ventral rami C5-T1= brachial plexus
Ventral rami of L1-L4= lumbar plexus
Ventral rami of L4-S4= sacral plexus
Ventral rami S4 & S5= coccygeal plexus
12-14 14

16. Plexus

17. Cervical Plexus
C1-C4
Innervates superficial neck structures, skin of neck, posterior portion of head
Selected nerve of cervical plexus
--Phrenic nerve
Innervate diaphragm
Sole motor innervation of diaphragm

18. Brachial Plexus C5-T1 and some from C4 Nerves arising from: Axillary
Radial
Musculocutaneous
Ulnar
Median

19. Lumbar Plexus Lumbar plexus: ventral rami of L1-L4 Selected Nerves:
Femoral
Obturator

20. sacral Plexus Sacral plexus: ventral rami of L4-S4
sometimes considered together because of their close relationship
major nerves exit and enter lower limb
Selected Nerves:
Sciatic
Tibial
Common fibular (peroneal)

21. Cross Section of Spinal Cord

22. Cross Section of Spinal Cord
Gray matter: mostly glial cell, cell bodies, dendrites
Horns
Posterior (dorsal)
sensory neurons enter the cord
Anterior (ventral)
cell bodies of somatic motor neurons
Lateral
associated with ANS—cell bodies of visceral motor neurons
distinct lateral horn not present in all regions of cord

23. Commissures: connections between left and right halves (of CNS)
Gray & White Commisures
Roots: nerves connecting to the cord
Dorsal (posterior) root
Sensory Nerve
contains sensory neurons (unipolar)
Dorsal Root Ganglion: cell bodies of sensory neurons

24. Ventral (anterior) Root motor nerve
axons of motor neurons (multipolar)
Spinal Nerve: Two roots merge to form a spinal nerve
then passes through intervertebral foramen
mixed nerves
axons of both motor and sensory neurons

25. Cross Section of Spinal Cord
White matter: myelinated axons forming nerve tracts
columns (funiculi):
divided into tracts (fasciculi; pathways)
Carry information:
to and from the brain (ascending and descending)
to and from other regions of the spinal cord

26. Figure 16.4
locations of various neurons within spinal cord (e.g., somatic motor, visceral motor [autonomic], somatic sensory) 26 26

27. Pathways through roots and cord

28. Ascending and Descending Tracts/Pathways
= sensory
= motor

29. Specific Ascending Pathways within spinal cord white matter
Anteriolateral System — within anterior and lateral columns
Spinothalamic Tracts: somatic sensory information from cutanous receptors to Thalamus
pain, crude touch, temperature
Dorsal Column System — in dorsal columns
proprioception, fine touch, two point discrimination
Spinocerebellar--periphery of lateral and dorsal columns
proprioception to cerebellum

30. Spinocerebellar--periphery of lateral and dorsal columns
Anteriolateral System —Spinothalamic Tracts: somatic sensory information from cutanous receptors to Thalamus
pain, pressure, crude touch, temperature
Dorsal Column System
proprioception, fine-touch, two point discrimination, pressure
Spinocerebellar--periphery of lateral and dorsal columns
proprioception to cerebellum

32. Descending Pathways through spinal cord white matter
Corticospinal (pyramidal)—within dorsal and anterior columns
voluntary movements
Indirect Pathways
involuntary movement, upright posture, balance, walking, reflexive movements of head and neck in response to visual and auditory stimuli

34. ramus roots plexus “nerves” Spinal nerve
e.g., femoral, median, phrenic, sciatic

36. Spinal Meninges and Protection of cord

37. Cross Section of Spinal Cord

38. Figure 16.2 38 38

39. Meninges & Associated Spaces
Connective tissue membranes surrounding spinal cord and brain
Epidural Space:
Contains blood vessels, areolar CT and fat.
Dura mater:
continuous with epineurium of the spinal nerves
Arachnoid mater: thin and wispy
Subarachnoid space:
Contains CSF and blood vessels within web-like strands of arachnoid tissue
Pia mater:
bound tightly to surface of brain and spinal cord.
filum terminale: anchors spinal cord to coccyx—longitudinal support
denticulate ligaments: attach the spinal cord to the dura mater laterally—lateral support

40. Protection of the Spinal Cord
Physical Protection
Vertebrae
rigid protection
Epidural Space with adipose
padding/cushioning
Meninges
CSF
cushioning
Filum Terminale
longitudinal support
Denticulate Ligaments
lateral support
Chemical Protection
Blood Brain Barrier—blood CNS barrier

41. Somatic Motor and Sensory: --Single sensory neurons carry sensory impulses from the receptor/site of stimulus all the way into the spinal cord. --Single motor neurons carry motor impulses from the spinal cord all the way to the effector muscle

42. Pathways through roots and cord

43. Reflexes
Automatic responses to specific stimuli (do not require conscious thought/processing)
Higher brain centers can influence, suppress, or exaggerate reflex responses
Types:
Learned
Innate (typically homeostatic)
Spinal, integrated in spinal cord
Cranial, integrated in brain

44. Spinal Reflexes
represent some of the most basic nerve pathways and CNS integration
Brain not necessary for spinal reflexes to occur
Although brain can modify (suppress or enhance ) spinal reflexes.
The nerve pathway is called a reflex arc

45. Reflex Arc Components
Electrical Impulse (Action potentials) produced in sensory receptors transmitted to
Sensory neuron. To-
Interneurons—in most cases. To-
Motor neuron. To-
Effector organ which responds with a reflex

46. Stretch/Extensor Reflexes
Monosynaptic:
Two neurons
One synapse
Sensory neuron synapses directly with motor neuron
Stretch Receptor (Muscle spindle):
Sensory neuron
synapse with motor neurons of the spinal cord
Motor neuron innervates muscle that was stretch causing contraction

47. Stretch/Extensor Reflex

48. Withdrawal/Flexor Reflex: Function is to remove a body limb or other part from a painful stimulus.
Polysynaptic:
2+ synapses
3+ neurons
Interneuron(s) between sensory and motor neuron
Variations:
Reciprocal inhibition
causes relaxation of antagonistic extensor muscle when flexor muscle contracts.
Crossed extensor reflex:
when a withdrawal reflex is initiated in one lower limb, the crossed extensor reflex causes extension of opposite lower limb.

49. Withdrawal Reflex

50. Withdrawal Reflex with Reciprocal Inhibition

51. Withdrawal Reflex with Crossed Extensor Reflex

52. Relationship of Brain and Spinal Cord Reflexes
Sensory information goes to brain; e.g., pain.
Descending tracts from brain carry info to reflexes.
Neurotransmitters produce inhibitory or excitatory effects modifying the reflex.

54. PNS Disorders General disorders Anesthesia: loss of sensation
Hyperesthesia: increased sensitivity to pain, pressure, light
Paresthesia: tingling, prickling, burning
Neuralgia: nerve inflammation causing stabbing pain
Sciatica: pain radiating down back of thigh and leg
Infections
Herpes: skin lesions
Shingles or herpes zoster: adult disease of chickenpox, virus latent in peripheral ganglia
Poliomyelitis: infantile paralysis
Anesthetic leprosy: bacterial infection of peripheral nerves
Diptheria: demylenation, motor/sensory decline, resp and heart failure
Genetic and autoimmune disorders
Myasthenia gravis: results in fatigue and muscular weakness due to inadequate ACh receptors