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

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Presentation on theme: "Chapter 13: The Spinal Cord, Spinal Nerves, and Spinal Reflexes."— Presentation transcript:

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

2 What are the major components of a spinal nerve?

3 Figure 13–6 Spinal Nerves

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 Spinal nerves: –form lateral to intervertebral foramen –where dorsal and ventral roots unite –then branch and form pathways to destination

9 Figure 13–9 3D Rotation of Peripheral Nerves and Nerve Plexuses PLAY 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.

10 Figure 13–10 The Cervical Plexus

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

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

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

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

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

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

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 Figure 13–13a 5 Patterns of Neural Circuits in Neuronal Pools 1. Divergence: –spreads stimulation to many neurons or neuronal pools in CNS

20 Figure 13–13b 5 Patterns of Neural Circuits in Neuronal Pools 2. Convergence: –brings input from many sources to single neuron

21 Figure 13–13c 5 Patterns of Neural Circuits in Neuronal Pools 3. Serial processing: –moves information in single line

22 Figure 13–13d 5 Patterns of Neural Circuits in Neuronal Pools 4. Parallel processing: –moves same information along several paths simultaneously

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

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

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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 Stretch Reflex Notice hammer

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 Tendon Reflex Notice no hammer

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 Normal Abnormal (Babinski’s) Plantar Reflex

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 Figure 16–2 Organization Similarities of SNS and ANS

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

48 Figure 16–11 Visceral Reflexes

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 1.Cervical plexus 2.Brachial plexus 3.Lumbar plexus 4.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 Table 13-1 Summary: Cervical Plexus

58 Figure 13–10 The Cervical Plexus

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

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

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

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

64 The Lumbar Plexus Includes ventral rami of spinal nerves T 12 –L 4 Major nerves: –genitofemoral nerve –lateral femoral cutaneous nerve –femoral nerve

65 The Sacral Plexus Includes ventral rami of spinal nerves L 4 –S 4 Major nerves: –pudendal nerve –sciatic nerve Branches of sciatic nerve: –fibular nerve –tibial nerve

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

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

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

72 end


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