1. Lecture 9: Chapter 13 The Spinal Cord and Spinal Nerves Pages : 421- 450
Lecturer: Dr. Barjis
Room: P313
Phone: (718)

2. Learning Objectives
Discuss the structure and functions of the spinal cord.
Describe the three meningeal layers that surround the CNS.
Describe the major components of a spinal nerve and relate their distribution to their regions of innervation.
Discuss the significance of neuronal pools.
Describe the steps in a neural reflex.
Explain how reflexes interact to produce complicated behaviors.

3. General Organization of the Nervous System
Divisions of the Nervous System
CNS
Brain and spinal cord
In the white matter, axons arranged in tracts and columns
PNS
Remainder of nervous tissue

4. An Introduction to the Anatomical Organization of the Nervous System

5. Gross Anatomy of the Spinal Cord
Adult spinal cord
Localized enlargements provide innervation to limbs
31 segments
each segment has a pair of dorsal roots and a pair of ventral roots
Filum terminale
Conus medularis
Spinal nerves extend off cord
Mixed nerves

6. Gross Anatomy of the Adult Spinal Cord

7. Spinal meninges Provide physical stability and shock absorption
Three layers
Dura mater
Arachnoid
Pia mater

8. Dura mater Covers spinal cord Tapers to coccygeal ligament
Epidural space separates dura mater from walls of vertebral canal

9. The Spinal Cord and Spinal Meninges

10. The Spinal Cord and Spinal Meninges

11. Arachnoid
Interior to dura mater are the subdural space, the arachnoid and the subarachnoid space
Subarachnoid space contains CSF

12. Pia mater Meshwork of elastin and collagen fibers
Innermost meningeal layer
Denticulate ligaments extend from pia mater to dura mater

13. The Cervical Spinal Cord

14. Sectional anatomy of the spinal cord
White matter is myelinated and unmyelinated axons
Gray matter is cell bodies, unmyelinated axons and neuroglia
Projections of gray matter toward outer surface of cord are horns

15. The Sectional Organization of the Spinal Cord

16. The Sectional Organization of the Spinal Cord

17. Horns of spinal cord
Posterior gray horn contains somatic and visceral sensory nuclei
Anterior gray horns deal with somatic motor control
Lateral gray horns contain visceral motor neurons
Gray commissures contain axons that cross from one side to the other

18. White matter Divided into six columns (funiculi) containing tracts
Ascending tracts relay information from the spinal cord to the brain
Descending tracts carry information from the brain to the spinal cord
Animation: Spinal cord dissections (see tutorial)

19. 31 pairs of spinal nerves Nerves consist of: Epineurium Perineurium
Endoneurium

20. A Peripheral Nerve

21. Spinal nerves White ramus (myelinated axons)
Gray ramus (unmyelinated axons that innervate glands and smooth muscle)
Dorsal ramus (sensory and motor innervation to the skin and muscles of the back)
Ventral ramus (supplying ventrolateral body surface, body wall and limbs)
Each pair of nerves monitors one dermatome

22. Peripheral Distribution of Spinal Nerves

23. Peripheral Distribution of Spinal Nerves

24. Dermatomes

25. Nerve plexus Complex interwoven network of nerves Four large plexuses
Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus

26. Peripheral Nerves and Nerve Plexus

27. The Brachial Plexus

28. The Branchial Plexus

29. The Branchial Plexus

30. The Lumbar and Sacral Plexuses

31. The Lumbar and Sacral Plexuses

32. Principles of Functional Organization
General organization
Sensory neurons
Deliver information to CNS
Motor neurons
Distribute commands to peripheral effectors
Interneurons
Interpret information and coordinate responses

33. Neuronal pools Functional group of interconnected neurons
Neural circuit patterns
Divergence
Convergence
Serial processing
Parallel processing
Reverberation

34. The Organization of Neuronal Pools

35. An introduction to reflexes
Reflexes are rapid automatic responses to stimuli
Neural reflex involves sensory fibers to CNS and motor fibers to effectors

36. Reflex arc Wiring of a neural reflex Five steps
Arrival of stimulus and activation of receptor
Activation of sensory neuron
Information processing
Activation of motor neuron
Response by effector

37. Components of a Reflex Arc

38. Reflex classification
According to
development
Site of information processing
Nature of resulting motor response
Complexity of neural circuit

39. Methods of Classifying Reflexes

40. reflex classifications
Innate reflexes
Result from connections that form between neurons during development
Acquired reflexes
Learned, and typically more complex

41. More reflex classifications
Cranial reflexes
Reflexes processed in the brain
Spinal reflexes
Interconnections and processing events occur in the spinal cord

42. still more reflex classifications
Somatic reflexes
Control skeletal muscle
Visceral reflexes (autonomic reflexes)
Control activities of other systems

43. and more reflex classifications
Monosynaptic reflex
Sensory neuron synapses directly on a motor neuron
Polysynaptic reflex
At least one interneuron between sensory afferent and motor efferent
Longer delay between stimulus and response

44. Neural Organization and Simple Reflexes

45. Spinal Reflexes
Range from simple monosynaptic to complex polysynaptic and intersegmental
Many segments interact to form complex response

46. Monosynaptic Reflexes
Stretch reflex automatically monitors skeletal muscle length and tone
Patellar (knee jerk) reflex
Sensory receptors are muscle spindles
Postural reflex maintains upright position

47. Components of the Stretch Reflex

48. The Patellar Reflex

49. Intrafusal Fibers

50. Polysynaptic reflexes
Produce more complicated responses
Tendon reflex
Withdrawal reflexes
Flexor reflex
Crossed extensor reflex

51. The Flexor and Crossed Extensor Reflexes

52. Polysynaptic reflexes
Involve pools of interneurons
Are intersegmental in distribution
Involve reciprocal inhibition
Have reverberating circuits to prolong the motor response
Several reflexes may cooperate to produce a coordinated response

53. Control of spinal reflexes
Brain can facilitate or inhibit motor patterns based in spinal cord
Motor control involves a series of interacting levels
Monosynaptic reflexes are the lowest level
Brain centers that modulate or build on motor patterns are the highest

54. Reinforcement and inhibition
Reinforcement = facilitation that enhances spinal reflexes
Spinal reflexes can also be inhibited
Babinski reflex replaced by planter reflex

55. The Babinski Reflexes

56. You should now be familiar with:
The structure and functions of the spinal cord.
The three meningeal layers that surround the CNS.
The major components of a spinal nerve and their distribution in relation to their regions of innervation.
The significance of neuronal pools.
The steps in a neural reflex.
How reflexes interact to produce complicated behaviors.