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

What are the major
components of a spinal nerve?
Spinal Nerves
Figure 13–6
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
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
Peripheral Nerves
• Interconnecting branches of spinal
nerves
• Surrounded by connective tissue
sheaths
How does the distribution
pattern of spinal nerves relate
to the regions they innervate?
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
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
The Cervical Plexus
Figure 13–10
The Lumbar and Sacral Plexuses
• Innervate pelvic girdle and lower limbs
PLAY
3D Rotation of Lumbar and Sacral
Plexuses
Figure 13–12a, b
The Lumbar and Sacral Plexuses
Figure 13–12c, d
Medical Example: Shingles
• Post-Viral inflammation of the
sensory nerves
• Rash follows dermatomes.
• Notice it does not cross the midline.
Dermatomes
• Bilateral region of skin
• Monitored by specific pair
of spinal nerves
Figure 13–8
Peripheral Distribution
of Spinal Nerves
• Sensory fibers
Figure 13–7b
Peripheral Distribution
of Spinal Nerves
• Motor fibers
PLAY
Peripheral Distribution of Spinal Nerves
Figure 13–7a
Functional Organization
of Neurons
• Sensory neurons:
– about 10 million
– deliver information to CNS
• Motor neurons:
– about 1/2 million
– deliver commands to peripheral effectors
Functional Organization
of Neurons
• Interneurons:
– about 20 billion
– interpret, plan, and coordinate signals in
and out
– often organized into functional “neuronal
pools”
5 Patterns of Neural
Circuits in Neuronal Pools
1. Divergence:
–
spreads stimulation to
many neurons or neuronal
pools in CNS
Figure 13–13a
5 Patterns of Neural
Circuits in Neuronal Pools
2. Convergence:
–
brings input from many
sources to single neuron
Figure 13–13b
5 Patterns of Neural
Circuits in Neuronal Pools
3. Serial processing:
–
moves information in single
line
Figure 13–13c
5 Patterns of Neural
Circuits in Neuronal Pools
4. Parallel processing:
–
moves same information
along several paths
simultaneously
Figure 13–13d
5 Patterns of Neural
Circuits in Neuronal Pools
5. Reverberation:
–
–
positive feedback
mechanism
functions until inhibited
Figure 13–13e
Reflexes
Development of Reflexes
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A reflex is a rapid, predictable motor
response to a stimulus.
Innate reflexes are unlearned and
involuntary
Acquired reflexes are complex,
learned motor patterns
Nature of Reflex Responses
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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
Components of a Reflex Arc
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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.
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In CNS
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Spinal reflexes or cranial reflexes
Components of a Reflex Arc
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4. Activation of a Motor Neuron:
transmits the efferent impulse to
effector organ
5. Response of a peripheral Effector:
Muscle or gland that responds
Interneuron
Spinal Reflexes
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4 important somatic spinal reflexes
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Stretch
Tendon
Flexor(withdrawal)
Crossed extensor reflexes
Stretch Reflexes
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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)
Notice hammer
Stretch Reflex
Stretch Reflex Example
Patellar Reflex
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Tap the patellar tendon
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Quadriceps muscle contracts
Hamstring muscle is inhibited (relaxes)
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muscle spindle signals stretch of muscle
motor neuron activated & muscle contracts
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.
Tendon Reflexes
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Monitors external tension produced during
muscular contraction to prevent tendon damage
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Golgi tendon organs in tendon (sensory receptor)
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Controls muscle tension by causing muscle relaxation
Martini pg 443 states the
activated by stretching of tendon
receptor is unidentified;
inhibitory neuron is stimulated
this is incorrect.
motor neuron is hyperpolarized and muscle relaxes
Both tendon & muscle are protected
Reciprocal innervation (polysynaptic)

causes contraction
Notice no hammer
Tendon Reflex
Flexor Reflex
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Withdrawal reflex
When pain receptors are activated it causes
automatic withdrawal of the threatened
body part.
Flexor
(Withdrawal)
Reflex
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Is this a
monosynaptic or
a polysynaptic
reflex?
Is this an
ipsilateral or a
contralateral
reflex?
Crossed Extensor Reflex
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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.
Crossed
Extensor
Reflex
Superficial Reflexes
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Elicited by gentle cutaneous stimulation
Important because they involve upper
motor pathways (brain) in addition to
spinal cord neurons
Superficial Reflexes
Plantar Reflex
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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
Plantar Reflex
Normal
Abnormal
(Babinski’s)
Abnormal
Plantar Reflex:
Babinski’s Sign
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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.
Preview of the ANS
Organization Similarities
of SNS and ANS
Figure 16–2
Visceral Reflexes
• Provide automatic motor responses
• Can be modified, facilitated, or
inhibited by higher centers, especially
hypothalamus
Visceral Reflexes
Figure 16–11
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.
• review
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
The 4 Major Plexuses
of Ventral Rami
1.
2.
3.
4.
Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus
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
Summary: Cervical Plexus
Table 13-1
The Cervical Plexus
Figure 13–10
Summary: Brachial Plexus
Table 13–2 (1 of 2)
Summary: Brachial Plexus
Table 13–2 (2 of 2)
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)
The Lumbar and Sacral Plexuses
• Innervate pelvic girdle and lower limbs
PLAY
3D Rotation of Lumbar and Sacral
Plexuses
Figure 13–12a, b
The Lumbar and Sacral Plexuses
Figure 13–12c, d
The Lumbar Plexus
• Includes ventral rami of spinal nerves
T12–L4
• Major nerves:
– genitofemoral nerve
– lateral femoral cutaneous nerve
– femoral nerve
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
Summary: Lumbar
and Sacral Plexuses
Table 13-3 (1 of 2)
Summary: Lumbar
and Sacral Plexuses
Table 13-3 (2 of 2)
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)
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.
Medical Example: Shingles
• Post-Viral inflammation of the
sensory nerves
• Rash follows dermatomes.
• Notice it does not cross the
midline.
The Babinski Reflexes
• Normal in infants
• May indicate CNS damage in adults
Figure 13–19
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