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

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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. Figure 13 10 ... – PowerPoint PPT presentation

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


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 136
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
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 139
10
The Cervical Plexus
Figure 1310
11
The Lumbar and Sacral Plexuses
  • Innervate pelvic girdle and lower limbs

3D Rotation of Lumbar and Sacral Plexuses
PLAY
Figure 1312a, b
12
The Lumbar and Sacral Plexuses
Figure 1312c, 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 138
15
Peripheral Distribution of Spinal Nerves
  • Sensory fibers

Figure 137b
16
Peripheral Distribution of Spinal Nerves
  • Motor fibers

Peripheral Distribution of Spinal Nerves
PLAY
Figure 137a
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 1313a
20
5 Patterns of Neural Circuits in Neuronal Pools
  • Convergence
  • brings input from many sources to single neuron

Figure 1313b
21
5 Patterns of Neural Circuits in Neuronal Pools
  • Serial processing
  • moves information in single line

Figure 1313c
22
5 Patterns of Neural Circuits in Neuronal Pools
  • Parallel processing
  • moves same information along several paths
    simultaneously

Figure 1313d
23
5 Patterns of Neural Circuits in Neuronal Pools
  • Reverberation
  • positive feedback mechanism
  • functions until inhibited

Figure 1313e
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

27
(No Transcript)
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 ExamplePatellar 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 ReflexesPlantar 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 (Babinskis)
44
Abnormal Plantar Reflex Babinskis 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 162
47
Visceral Reflexes
  • Provide automatic motor responses
  • Can be modified, facilitated, or inhibited by
    higher centers, especially hypothalamus

48
Visceral Reflexes
Figure 1611
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 ligands 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 1310
59
Summary Brachial Plexus
Table 132 (1 of 2)
60
Summary Brachial Plexus
Table 132 (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 1312a, b
63
The Lumbar and Sacral Plexuses
Figure 1312c, d
64
The Lumbar Plexus
  • Includes ventral rami of spinal nerves T12L4
  • Major nerves
  • genitofemoral nerve
  • lateral femoral cutaneous nerve
  • femoral nerve

65
The Sacral Plexus
  • Includes ventral rami of spinal nerves L4S4
  • 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 Gehrigs 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 1319
72
end
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