1. The Spinal Cord and Spinal Nerves
Chapter 13
The Spinal Cord and Spinal Nerves

2. Functions of the nervous system
Sensory (input):
Light
Sound
Touch
Temperature
Taste
Smell
Internal Chemical
Pressure
Stretch

3. Functions of the nervous system (cont’d)
Integration:
Integration means making sense of sensory input. Analyzing stimuli based on experience, learning, emotion & instinct and reacting in a useful way (you hope).
Motor (output):
The response to the sensory input and subsequent integration. Sending signals to the muscles and other organs of the body instructing them how to respond to the stimuli.

4. Nervous System Organization

5. Overview of Ch 13 & Ch 14

6. The Spinal Cord & Nerves
The spinal cord is part of the Central Nervous System.
The spinal nerves are part of the Peripheral Nervous System.
The lowest level of integration occurs in the spinal cord and peripheral ganglia.

7. Spinal cord: gross anatomy

8. Spinal cord anatomy: the meninges

9. Spinal cord and associated structures

10. Functional arrangement of the spinal cord tissues
More about the specific functions these tracts in Chapter 15.
Functional arrangement of the spinal cord tissues

11. Cross section of the spinal cord

12. White Matter in the Spinal Cord
Fibers run in three directions – ascending, descending, and transversely
Divided into three funiculi (columns) – posterior, lateral, and anterior
Each funiculus contains several fiber tracks
Fiber tract names reveal their origin and destination
Fiber tracts are composed of axons with similar functions

14. Spinal nerves
Thirty-one pairs of mixed nerves arise from the spinal cord and supply all parts of the body except the head
They are named according to their point of issue
8 cervical (C1-C8)
12 thoracic (T1-T12)
5 Lumbar (L1-L5)
5 Sacral (S1-S5)
1 Coccygeal (C0)

15. Spinal nerve structure

16. Spinal Nerve structure
Each axon is also called a “nerve fiber”
These are covered by an endoneurium
The endoneurium is made of areolar c.t.
Fibers are bundled into “fascicles”
These are covered by perineurium
This is an extension of the outer layer of collagen fibers
Nerves are bundles of fascicles
Each nerve is covered by dense irregular tissue of collagen fibers

17. Components of the Peripheral Nervous System
Motor pathways
Leave the spinal cord via the ventral nerve roots.
Have multipolar cell bodies found in the gray matter.
Carry motor impulses to skeletal muscle (somatic pathways) and to glands, smooth muscle, the heart, organs, etc (autonomic pathways).
Are also called efferent pathways.

18. Motor pathways

19. Components of the PNS Sensory Pathways
Enter the cord via the dorsal roots.
Have unipolar cell bodies found in the dorsal root ganglia.
Carry sensory inputs into the CNS via the central processes of their axons. They begin at the general sensory receptors of the skin (somatic sensory) and internal organs (visceral sensory).
Are also known as afferent pathways.
Special sense will be covered in Chapter 17

20. Sensory pathways

21. What’s a damn dermatome?

22. Nerve plexuses

23. Nerve plexuses
Fibers travel to the periphery via several different routes
Each muscle receives a nerve supply from more than one spinal nerve
Damage to one spinal segment cannot completely paralyze a muscle

24. Cervical plexus

25. Summary: Cervical Plexus
Table 13-1

26. Brachial plexus

27. The brachial plexus
Fig a

28. Some common injuries to the brachial plexus Study question: Which nerves are affected here?

29. Summary: Brachial Plexus
Table 13–2 (1 of 2)

30. Summary: Brachial Plexus
Table 13–2 (2 of 2)

31. Lumbar and sacral plexuses

32. Summary: Lumbar and Sacral Plexuses
Table 13-3 (1 of 2)

33. Summary: Lumbar and Sacral Plexuses
Table 13-3 (2 of 2)

34. Lumbar & sacral plexus nerves

35. Neural circuits

36. Neural Circuits
Divergent – spread information from one source to several destinations.
Examples: visual input being processed at a conscious level (the horizon is tilting) and a subconscious level (I adjust my body so that I don’t fall over).
Convergent – multiple sources of input into one neuron.
Examples: conscious – I contract my rectus femoris to step over a pile of dog poop. Unconscious – my rectus femoris automatically contracts as the bus moves

37. Neural Circuits Serial – a series of neurons in a sequence.
Example: Pain pathways
Parallel – Divergence followed by serial.
Example – reflexes that result in a complex series of responses simultaneously
Reverberation – positive feedback loops
Examples – many of the complex processes of the brain.

38. Reflexes Rapid, automatic responses to stimuli.
Can be visceral (e.g. swallowing) or somatic (“knee-jerk”).
Have little variability

40. Components of a reflex arc
Stimulus activates a receptor.
Impulse travels along a sensory pathway.
Integration occurs in an integration center (most often in the CNS)
Impulse then travels by a motor pathway.
An effector responds.

41. 4 Classifications of Reflexes
By early development
By type of motor response
By complexity of neural circuit
By site of information processing

42. Development How reflex was developed: innate reflexes:
basic neural reflexes
formed before birth
acquired reflexes:
rapid, automatic
learned motor patterns

43. Response Nature of resulting motor response: somatic reflexes:
involuntary control of nervous system
superficial reflexes of skin, mucous membranes
stretch reflexes (deep tendon reflexes) e.g., patellar reflex
visceral reflexes (autonomic reflexes):
control systems other than muscular system e.g., glands smooth muscle and cardiac muscle

44. Complexity Complexity of neural circuit: monosynaptic reflex:
sensory neuron synapses directly onto motor neuron
polysynaptic reflex:
at least 1 interneuron between sensory neuron and motor neuron

45. Processing Site of information processing: spinal reflexes:
occurs in spinal cord
cranial reflexes:
occurs in brain

46. Monosynaptic: Stretch reflex

47. Monosynaptic Reflexes
Have least delay between sensory input and motor output:
e.g., stretch reflex (such as patellar reflex)
Completed in 20–40 msec

48. Muscle Spindles The receptors in stretch reflexes
Bundles of small, specialized intrafusal muscle fibers:
innervated by sensory and motor neurons
Surrounded by extrafusal muscle fibers:
which maintain tone and contract muscle

49. Muscle spindles

50. Postural Reflexes Postural reflexes:
stretch reflexes
maintain normal upright posture
Stretched muscle responds by contracting:
automatically maintain balance

51. Polysynaptic Reflexes
More complicated than monosynaptic reflexes
Interneurons control more than 1 muscle group
Produce either EPSPs or IPSPs

52. Polysynaptic: Flexor

53. The Tendon Reflex Prevents skeletal muscles from:
developing too much tension
tearing or breaking tendons
Sensory receptors unlike muscle spindles or proprioceptors

54. Withdrawal Reflexes
Move body part away from stimulus (pain or pressure):
e.g., flexor reflex:
pulls hand away from hot stove
Strength and extent of response:
depends on intensity and location of stimulus

55. Reflex Arcs Ipsilateral reflex arcs: Crossed extensor reflexes:
occur on same side of body as stimulus
stretch, tendon, and withdrawal reflexes
Crossed extensor reflexes:
involves a contralateral reflex arc
occurs on side opposite stimulus

56. The Crossed Extensor Reflex
Figure 13–18

57. 5 General Characteristics of Polysynaptic Reflexes
Involve pools of neurons
Are intersegmental in distribution
Involve reciprocal inhibition
Have reverberating circuits:
which prolong reflexive motor response
Several reflexes cooperate:
to produce coordinated, controlled response

58. The Babinski Reflexes Normal in infants
May indicate CNS damage in adults
The Babinski Reflexes
Figure 13–19

59. Spinal Cord Trauma: Paralysis
Paralysis – loss of motor function
Flaccid paralysis – severe damage to the ventral root or anterior horn cells
Lower motor neurons are damaged and impulses do not reach muscles
There is no voluntary or involuntary control of muscles

60. Spinal Cord Trauma: Paralysis
Spastic paralysis – only upper motor neurons of the primary motor cortex are damaged
Spinal neurons remain intact and muscles are stimulated irregularly
There is no voluntary control of muscles

61. Spinal Cord Trauma: Transection
Cross sectioning of the spinal cord at any level results in total motor and sensory loss in regions inferior to the cut
Paraplegia – transection between T1 and L1
Quadriplegia – transection in the cervical region

62. Spinal cord transection

63. Poliomyelitis
Destruction of the anterior horn motor neurons by the poliovirus
Early symptoms – fever, headache, muscle pain and weakness, and loss of somatic reflexes
Vaccines are available and can prevent infection

64. Some effects of Polio

65. Amyotrophic Lateral Sclerosis (ALS)
Lou Gehrig’s disease – neuromuscular condition involving destruction of anterior horn motor neurons and fibers of the pyramidal tract
Symptoms – loss of the ability to speak, swallow, and breathe
Death often occurs within five years
Linked to malfunctioning genes for glutamate transporter and/or superoxide dismutase

66. Some Famous Victims of ALS
Lou Gehrig
Steven Hawking,
renowned physicist

67. Axonal degeneration of motor neurons evident in lateral corticospinal (pyramidal) pathways, especially in the loss of myelinated fibers of the corticospinal tracts

68. SUMMARY (1 of 7) General organization of nervous system:
CNS, PNS
Gross anatomy of spinal cord:
enlargements, dorsal and ventral roots, filum terminale, conus medullaris

69. SUMMARY (2 of 7) Afferent (sensory) and efferent (motor) fibers
Structures and functions of spinal meninges
Gray matter and horns of spinal cord

70. SUMMARY (3 of 7) White matter and columns (tracts) of spinal cord
3 layers in spinal nerves
Distribution (rami) of spinal nerves:
white, gray, dorsal, ventral

71. SUMMARY (4 of 7) 4 major nerve plexuses:
cervical, brachial, lumbar, sacral
Neuronal pools and neural circuit patterns:
divergence, convergence, serial, parallel, reverberation

72. SUMMARY (5 of 7) Reflexes and reflex arcs Classifications of reflexes:
innate vs. acquired
somatic vs. visceral
cranial vs. spinal
monosynaptic, polysynaptic, or intersegmental

73. SUMMARY (6 of 7) Characteristics of monosynaptic reflexes:
stretch reflex, postural reflex, muscle spindles
Characteristics of polysynaptic reflexes:
tendon, withdrawal, flexor, and crossed extensor reflexes

74. End
Chapter 13