1. Chapter 13: The Spinal Cord, Spinal Nerves, and Spinal Reflexes

2. What are the major components of a spinal nerve?

3. Spinal Nerves
Figure 13–6

4. Organization of Spinal Nerves
Every spinal cord segment:
is connected to a pair of spinal nerves
Every spinal nerve:
is surrounded by 3 connective tissue layers
that support structures and contain blood vessels

5. 3 Connective Tissue Layers
Epineurium:
outermost layer
dense network of collagen fibers
Perineurium:
middle layer
divides nerve into fascicles (axon bundles)
Endoneurium:
inner layer
surrounds individual axons

6. Peripheral Nerves Interconnecting branches of spinal nerves
Surrounded by connective tissue sheaths

7. How does the distribution pattern of spinal nerves relate to the regions they innervate?

8. Peripheral Distribution of Spinal Nerves
form lateral to intervertebral foramen
where dorsal and ventral roots unite
then branch and form pathways to destination

9. Nerve Plexuses Contain no synapses!
For pre-midterm (Summarized in tables in text and lab guide):
Know cord roots (“ventral rami,” actually) that contribute to the plexus
Know the names of the major peripheral nerves that each plexus gives rise to.
3D Rotation of Peripheral Nerves and Nerve Plexuses
PLAY
Figure 13–9

10. The Cervical Plexus
Figure 13–10

11. The Lumbar and Sacral Plexuses
Innervate pelvic girdle and lower limbs
3D Rotation of Lumbar and Sacral Plexuses
PLAY
Figure 13–12a, b

12. The Lumbar and Sacral Plexuses
Figure 13–12c, d

13. Medical Example: Shingles
Post-Viral inflammation of the sensory nerves
Rash follows dermatomes.
Notice it does not cross the midline.

14. Dermatomes Bilateral region of skin
Monitored by specific pair of spinal nerves
Figure 13–8

15. Peripheral Distribution of Spinal Nerves
Sensory fibers
Figure 13–7b

16. Peripheral Distribution of Spinal Nerves
Motor fibers
PLAY
Peripheral Distribution of Spinal Nerves
Figure 13–7a

17. Functional Organization of Neurons
Sensory neurons:
about 10 million
deliver information to CNS
Motor neurons:
about 1/2 million
deliver commands to peripheral effectors

18. Functional Organization of Neurons
Interneurons:
about 20 billion
interpret, plan, and coordinate signals in and out
often organized into functional “neuronal pools”

19. 5 Patterns of Neural Circuits in Neuronal Pools
Divergence:
spreads stimulation to many neurons or neuronal pools in CNS
Figure 13–13a

20. 5 Patterns of Neural Circuits in Neuronal Pools
Convergence:
brings input from many sources to single neuron
Figure 13–13b

21. 5 Patterns of Neural Circuits in Neuronal Pools
Serial processing:
moves information in single line
Figure 13–13c

22. 5 Patterns of Neural Circuits in Neuronal Pools
Parallel processing:
moves same information along several paths simultaneously
Figure 13–13d

23. 5 Patterns of Neural Circuits in Neuronal Pools
Reverberation:
positive feedback mechanism
functions until inhibited
Figure 13–13e

24. Reflexes

25. Development of Reflexes
A reflex is a rapid, predictable motor response to a stimulus.
Innate reflexes are unlearned and involuntary
Acquired reflexes are complex, learned motor patterns

26. Nature of Reflex Responses
Somatic: Reflexes involving skeletal muscles and somatic motor neurons.
Autonomic (visceral) Reflexes controlled by autonomic neurons
Heart rate, respiration, digestion, urination, etc
Spinal reflexes are integrated within the spinal cord gray matter while cranial reflexes are integrated in the brain.
Reflexes may be monosynaptic or polysynaptic

28. Components of a Reflex Arc
1. Activation of a Receptor: site of stimulus
2. Activation of a Sensory Neuron: transmits the afferent impulse to spinal cord (CNS)
3. Information processing at the Integration center: synapses (monosynaptic reflexes) or interneurons (polysynaptic) between the sensory and motor neurons.
In CNS
Spinal reflexes or cranial reflexes

29. Components of a Reflex Arc
4. Activation of a Motor Neuron: transmits the efferent impulse to effector organ
5. Response of a peripheral Effector: Muscle or gland that responds

30. Interneuron

31. Spinal Reflexes 4 important somatic spinal reflexes Stretch Tendon
Flexor(withdrawal)
Crossed extensor reflexes

32. Stretch Reflexes
1. Stretching of the muscle activates a muscle spindle (receptor)
2. An impulse is transmitted by afferent fibers to the spinal cord
3. Motor neurons in the spinal cord cause the stretched muscle to contract
4. The integration area in the spinal cord
Polysynaptic reflex arc to antagonist muscle causing it to to relax (reciprocal innervation)

33. Notice hammer
Stretch Reflex

34. Stretch Reflex Example Patellar Reflex
Tap the patellar tendon
muscle spindle signals stretch of muscle
motor neuron activated & muscle contracts
Quadriceps muscle contracts
Hamstring muscle is inhibited (relaxes)
Reciprocal innervation (polysynaptic- interneuron)
antagonistic muscles relax as part of reflex
Lower leg kicks forward
Demonstrates sensory and motor connections between muscle and spinal cord are intact.

35. Tendon Reflexes
Monitors external tension produced during muscular contraction to prevent tendon damage
Controls muscle tension by causing muscle relaxation
Golgi tendon organs in tendon (sensory receptor)
activated by stretching of tendon
inhibitory neuron is stimulated
motor neuron is hyperpolarized and muscle relaxes
Both tendon & muscle are protected
Reciprocal innervation (polysynaptic)
causes contraction
Martini pg 443 states the receptor is unidentified; this is incorrect.

36. Notice no hammer
Tendon Reflex

37. Flexor Reflex Withdrawal reflex
When pain receptors are activated it causes automatic withdrawal of the threatened body part.

38. Flexor (Withdrawal) Reflex
Is this a monosynaptic or a polysynaptic reflex?
Is this an ipsilateral or a contralateral reflex?

39. Crossed Extensor Reflex
Complex reflex that consists of an ipsilateral withdrawal reflex and a contralateral extensor reflex
This keeps you from falling over, for example if you step on something painful. When you pull your foot back, the other leg responds to hold you up.

40. Crossed Extensor Reflex

41. Superficial Reflexes Elicited by gentle cutaneous stimulation
Important because they involve upper motor pathways (brain) in addition to spinal cord neurons

42. Superficial Reflexes Plantar Reflex
Tests spinal cord from L4 to S2
Indirectly determines if the corticospinal tracts of the brain are working
Draw a blunt object downward along the lateral aspect of the plantar surface (sole of foot)
Normal: Downward flexion (curling) of toes

43. Plantar Reflex
Normal
Abnormal
(Babinski’s)

44. Abnormal Plantar Reflex: Babinski’s Sign
Great toe dorsiflexes (points up) and the smaller toes fan laterally
Happens if the primary motor cortex or corticospinal tract is damaged
Normal in infants up to one year old because their nervous system is not completely myelinated.

45. Preview of the ANS

46. Organization Similarities of SNS and ANS
Figure 16–2

47. Visceral Reflexes Provide automatic motor responses
Can be modified, facilitated, or inhibited by higher centers, especially hypothalamus

48. Visceral Reflexes
Figure 16–11

49. Visceral Reflex Arc
Receptor  Sensory neuron  Processing center interneuron(s)
1 or 2 visceral motor neurons
Pre- and post-synaptic neurons (long reflex)
Just a post-synaptic neuron (short reflex)

50. Long Reflexes
Autonomic equivalents (target visceral effectors) of polysynaptic somatic reflexes
Coordinate activities of the entire organ
Visceral sensory neurons deliver information to CNS along dorsal roots of spinal nerves:
within sensory branches of cranial nerves
within autonomic nerves that innervate visceral effectors

51. Short Reflexes Bypass CNS Involve 1 small part of target organ
Involve sensory neurons and interneurons located within autonomic ganglia
Interneurons synapse on ganglionic neurons
Motor commands distributed by postganglionic fibers
Control simple motor responses with localized effects

52. Case of the Woman with HT
Name the two parts of the ANS
Describe the two major groups of receptors and their subtypes (and their usual ligands.)
Distinguish between receptor stimulation and cell stimulation.
Explain what “specificity” means when we are referring to a ligand’s specificity for receptors.
Provide a background for studying examples of somatic and autonomic reflexes.

53. review

54. Nerve Plexuses Complex, interwoven networks of nerve fibers
Formed from blended fibers of ventral rami of adjacent spinal nerves
Control skeletal muscles of the neck and limbs

55. The 4 Major Plexuses of Ventral Rami
Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus

56. Dorsal and Ventral Rami
Dorsal ramus:
contains somatic and visceral motor fibers
innervates the back
Ventral ramus:
larger branch
innervates ventrolateral structures and limbs
contribute to plexuses

57. Summary: Cervical Plexus
Table 13-1

58. The Cervical Plexus
Figure 13–10

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

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

61. Major Nerves of Brachial Plexus
Musculocutaneous nerve (lateral cord)
Median nerve (lateral and medial cords)
Ulnar nerve (medial cord)
Axillary nerve (posterior cord)
Radial nerve (posterior cord)

62. The Lumbar and Sacral Plexuses
Innervate pelvic girdle and lower limbs
3D Rotation of Lumbar and Sacral Plexuses
PLAY
Figure 13–12a, b

63. The Lumbar and Sacral Plexuses
Figure 13–12c, d

64. The Lumbar Plexus Includes ventral rami of spinal nerves T12–L4
Major nerves:
genitofemoral nerve
lateral femoral cutaneous nerve
femoral nerve

65. The Sacral Plexus Includes ventral rami of spinal nerves L4–S4
Major nerves:
pudendal nerve
sciatic nerve
Branches of sciatic nerve:
fibular nerve
tibial nerve

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

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

68. Medical Example: Poliomyelitis
Polio means gray matter
Virus causes inflammation of the gray matter in the anterior horn motor neurons.
Results in paralysis which could kill a patient if it reaches the respiratory muscles
Patients who recover have permanent weakness or paralysis in parts of the body (usually the legs)

69. Lou Gehrig’s Disease Amyotrophic Lateral Sclerosis
ALS is a genetic disease that causes progressive destruction of anterior horn motor neurons.
Leads to paralysis and death within 5 years.
Stephen Hawking has this disease.

70. Medical Example: Shingles
Post-Viral inflammation of the sensory nerves
Rash follows dermatomes.
Notice it does not cross the midline.

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

72. end