Transcript Chapter 12 Notes.ppt

12
The Spinal Cord,
Spinal Nerves,
and Spinal
Reflexes
PowerPoint® Lecture Presentations prepared by
Alexander G. Cheroske
Mesa Community College at Red Mountain
© 2011 Pearson Education, Inc.
Section 1: Functional Organization of the Spinal
Cord
• Central Nervous System organization
• Brain, cranial nerves, cranial reflexes (Chapter 13)
• More complex
• Spinal cord, spinal nerves, spinal reflexes (this
chapter)
• Simpler
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A diagram of a functional perspective for studying the CNS
The Brain
Sensory
receptors
Sensory input
over cranial nerves
Reflex
centers
in brain
Motor output over
cranial nerves
Effectors
Muscles
The Spinal Cord
Glands
Sensory
receptors
Sensory input
over spiral nerves
Reflex
centers
in spinal
cord
Motor output over
spinal nerves
Adipose tissue
Figure 12 Section 1
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Module 12.1: Spinal cord functional anatomy
• Adult spinal cord dimensions
• Length: ~45 cm (18 in.)
• Width: ~14 mm (0.55 in.) maximum
• Superficial anatomy
• Cervical enlargement
• Supplies nerves to shoulder and upper limbs
• Lumbar enlargement
• Supplies nerves to pelvis and lower limbs
• Conus medullaris
• Tapered terminal end inferior to lumbar enlargement
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Module 12.1: Spinal cord functional anatomy
• Superficial anatomy (continued)
• Cauda equina (cauda, tail + equus, horse)
• Long, inferiorly extending dorsal and ventral roots +
filum terminale
• Resembles horse’s tail
• Filum terminale
• Slender thread of connective tissue attaching conus
medullaris to 2nd sacral vertebra
• Provides longitudinal support to spinal cord
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Module 12.1: Spinal cord functional anatomy
• Superficial anatomy (continued)
• 31 pairs of spinal nerves
• Arise from 31 segments of spinal cord
• Identified by adjacent vertebrae
• Cervical nerves
• From vertebrae immediately inferior
• Last vertebrae with this number system is C8
• Thoracic nerves
• From vertebrae immediately superior
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The 31 pairs of spinal nerves
Cervical spinal
nerves
Cervical
enlargement
Posterior median sulcus
Thoracic spinal
nerves
Lumbar enlargement
Conus medullaris
Lumbar
spinal
nerves
Interior tip of spinal cord
Cauda equina
Sacral spinal
nerves
Filum terminale
Coccygeal
nerve (Co1)
Figure 12.1
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Module 12.1: Spinal cord functional anatomy
• Spinal cord anatomy in cross section (continued)
• White matter
• Superficial
• Contains large numbers of myelinated and
unmyelinated axons
• Gray matter
• Surrounds central canal
• Forms butterfly or H shape
• Dominated by cell bodies of neurons, neuroglia, and
unmyelinated axons
• Greater amount in spinal cord segments serving limbs
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Cross sections of three of the spinal cord’s 31 segments
Posterior median sulcus
Dorsal root
Dorsal root ganglion
White matter
Spinal nerve
Gray
matter
Segment C3
Ventral root
Anterior median fissure
White matter
Gray matter
Segment T3
Central
canal
Segment L1
Segment S2
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Figure 12.1
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Module 12.2: Spinal meninges
•
Spinal meninges
•
Series of specialized membranes that provide physical
stability and shock absorption for the spinal cord
• Blood vessels branching within deliver oxygen and nutrients to
spinal cord
•
Are continuous with cranial meninges and connective tissues
surrounding spinal nerves
•
Three layers
1. Dura mater – outermost dense collagen fibers
narrow subdural space separating from arachnoid mater
2.Arachnoid mater – middle contains CSF ( lumbar puncture)
3.Pia mater- innermost Meshwork of elastic and collagen fibers
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A section demonstrating the procedure called a lumbar
puncture or spinal tap
Dura mater
Epidural space
Body of third
lumbar vertebra
Interspinous
ligament
Lumbar puncture
needle with tip in
subarachnoid space
Cauda equina in
subarachnoid
space
Figure 12.2
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Module 12.2: Spinal meninges
•
Epidural space
•
Between dura mater and vertebral canal
•
Contains areolar connective tissue, blood vessels,
and protective adipose tissue
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A posterior view of the dissected spinal cord showing the
basic relationships among the spinal meninges
Gray matter
Pia mater
White matter
Ventral
root
Spinal
nerve
Dorsal
root
Arachnoid mater
Dura mater
Figure 12.2
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A cross-sectional view showing the structures surrounding the spinal
cord and the spaces between the meningeal layers
Cerebrospinal
fluid (CSF)
Anterior
Ventral
root
Spinal meninges
Vertebral body
Spinal cord
Epidural space
Dorsal root ganglion
Pia mater
Arachnoid mater
Dura mater
Dorsal
root
Figure 12.2
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An anterior view of the cervical spinal cord
showing the meninges, supporting ligaments,
and the roots of the spinal nerves
Spinal cord
Anterior median fissure
Pia mater
Denticulate ligaments
Dorsal root
Blood vessels within
the subarachnoid space
Ventral root, formed by
several “rootlets” from
one cervical segment
Arachnoid mater (reflected)
Dura mater (reflected)
Figure 12.2
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A cross section showing most of the anatomical landmarks of the spinal cord
Posterior
median sulcus
Posterior gray
commissure
Structural Organization
of Gray Matter
The projections of gray
matter toward the outer
surface of the spinal cord
are called horns.
Anterior view of
spinal cord
Posterior gray horn
Central canal
Dura mater
Lateral gray horn
Arachnoid
mater (broken)
Anterior gray horn
Pia mater
Dorsal root ganglion
Anterior
median fissure
Anterior gray
commissure
Ventral root
Figure 12.3
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A diagrammatic view of the organization of the gray matter of the spinal cord
Site of a frontal
section that separates
the sensory (posterior,
or dorsal) nuclei from
the motor (anterior,
or ventral) nuclei
Posterior
gray horn
Dorsal
root
ganglion
Functional Organization
of Gray Matter
Gray commissures
Lateral
gray horn
Anterior
gray horn
Somatic
The cell bodies of neurons
in the gray matter of the
spinal cord are organized
into functional groups
called nuclei.
Visceral
Sensory nuclei
Visceral
Motor nuclei
Somatic
Ventral root
Figure 12.3
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Organization of Tracts
in the Posterior White
Column
The organization of the white matter into columns containing tracts
The posterior white
column contains
ascending tracts
providing sensations
from the trunk and limbs.
Leg
Hip
Trunk
Arm
Structural and
Functional
Organization
of White Matter
Posterior white column
Lateral white column
Anterior white column
Flexors/Extensors
Anterior white commissure
Trunk Shoulder Arm
Forearm Hand
In the cervical enlargement, which
contains neurons involved with
sensations and motor control of the
upper limbs, the motor nuclei of the
anterior gray horn are grouped by region,
with motor neurons controlling flexor
muscles medial to those controlling
extensor muscles.
Figure 12.3
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•
Connective tissue layers of a spinal nerve
1. Epineurium
•
Outermost covering of nerve
•
Dense network of collagen fibers
2. Perineurium
•
Middle layer
•
•
Divide nerve into compartments that contain bundles of
axons (fascicles)
Branching blood vessels from epineurium continue on to form
capillaries in endoneurium
3. Endoneurium
•
Innermost layer
•
Delicate connective tissues surrounding individual axons
•
Capillaries here supply axons, Schwann cells, and fibroblasts
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A sectional view of a spinal nerve showing its connective tissue layers
Connective Tissue
Layers of a
Spinal Nerve
Epineurium
Perineurium
Endoneurium
Artery and vein within
the perineurium
Fascicle
Schwann cell
Myelinated axon
Figure 12.4
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Module 12.4: Spinal nerve structure and
distribution
•
Spinal nerve branches
•
Called rami (singular ramus, a branch)
•
Some carry visceral motor fibers of autonomic
nervous system (ANS)
•
In thoracic and upper lumbar segments,
sympathetic division (“fight or flight”) motor fibers
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The branching of a spinal nerve to form rami
Dorsal root
Dorsal root
ganglion
Dorsal ramus
Ventral ramus
Ventral
root
Communicating rami
Autonomic nerve
Sympathetic
ganglion
Figure 12.4
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Module 12.4: Spinal nerve structure and
distribution
•
Dermatome
•
Specific bilateral region of skin surface monitored
by single pair of spinal nerves
•
C1 usually lacks sensory branch to skin
•
•
When present, helps monitor scalp with C2 and C3
Face is monitored by pair of cranial nerves
•
Boundaries between dermatomes overlap
•
Clinically important to determine damage or
infection of spinal nerve or dorsal root ganglion
•
Loss of sensation or signs on skin in dermatome
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Dermatomes, the specific bilateral regions of the skin
surface monitored by a single pair of spinal nerves
Anterior
Posterior
Figure 12.4
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Module 12.4: Spinal nerve structure and
distribution
•
Shingles
•
Viral infection of dorsal root ganglia
•
Caused by varicella-zoster virus
•
Same herpes virus as chickenpox
•
Produces painful rash and blisters on dermatome
served by infected nerves
•
Those who have had chickenpox are more at risk
•
Virus can remain dormant within anterior gray horns
•
Unknown trigger for reactivation
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Figure 12.4
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The cervical, brachial, lumbar, and sacral plexuses (at left), and
the major peripheral nerves of each (at right)
Cervical
plexus
Brachial
plexus
Lesser occipital nerve
Great auricular nerve
Transverse cervical nerve
Supraclavicular nerve
Phrenic nerve
Axillary nerve
Musculocutaneous
nerve
Thoracic nerves
Radial nerve
Lumbar
plexus
Ulnar nerve
Median nerve
Iliohypogastric
nerve
Sacral
plexus
Ilioinguinal
nerve
Genitofemoral
nerve
Femoral nerve
Obturator nerve
Superior gluteal nerve
Inferior gluteal nerve
Pudendal nerve
Saphenous nerve
Sciatic nerve
Figure 12.6
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Module 12.6: Spinal nerve plexuses introduction
and the cervical plexus
•
Cervical plexus
•
Ventral rami of spinal nerves C1–C5
•
Branches innervate
•
Muscles of neck and to control
•
Diaphragmatic muscles (phrenic nerve)
•
Extends into thoracic cavity
•
Skin of neck
•
Skin of superior part of chest
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The cervical plexus, which consists of the ventral rami of spinal
nerves C1–C5, and some of the muscles its branches innervate
Cranial Nerves
Accessory
nerve (XI)
Hypoglossal
nerve (XII)
Lesser occipital
nerve
Great auricular nerve
Nerve Roots of
Cervical Plexus
C1
C2
C3
C4
C5
Geniohyoid muscle
Transverse cervical nerve
Thyrohyoid muscle
Ansa cervicalis
Omohyoid muscle
Supraclavicular
nerves
Clavicle
Phrenic nerve
Sternohyoid muscle
Sternothyroid muscle
Figure 12.6
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Module 12.7: Brachial plexus
•
Brachial plexus
•
Innervates pectoral girdle and upper limb
•
Contributions from ventral rami of nerves C4–T1
•
Clinical importance of cutaneous nerve
• Damage or injury can be precisely localized by testing sensory
function in hand
Animation: Brachial Plexus
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The brachial plexus, which innervates the pectoral girdle
and upper limbs with contributions from the ventral rami
of spinal nerves C4–T1
Trunks of
Brachial Plexus
Dorsal scapular nerve
Suprascapular nerve
Spinal Nerves
Forming Brachial
Plexus
C4 nerve
C5 nerve
C6 nerve
C7 nerve
C8 nerve
T1 nerve
Superior
Middle
Inferior
Musculocutaneous
nerve
Median nerve
Ulnar nerve
Radial nerve
Lateral antebrachial
cutaneous nerve
Superficial branch
of radial nerve
Deep radial nerve
Ulnar nerve
Median nerve
Palmar digital
nerves
Figure 12.7
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The distribution of the cutaneous
nerves of the wrist and hand
Posterior
Anterior
Radial
nerve
Ulnar
nerve
Median
nerve
Figure 12.7
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Module 12.8: Lumbar and sacral plexuses
•
Lumbar and sacral plexuses
•
Arise from lumbar and sacral segments of spinal
cord
•
Innervate pelvic girdle and lower limbs
•
Lumbar plexus
• Innervates mostly anterior and side surfaces
•
Sacral plexus
• Innervates mostly posterior surfaces
• Contains sciatic nerve (longest & largest nerve in body)
Animation: Lumbar Sacral Plexus
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The origins of the spinal
nerves of the sacral plexus
Spinal Nerves
Forming the
Sacral Plexus
Lumbosacral trunk
L4 nerve
L5 nerve
Nerves of the
Sacral Plexus
S1 nerve
Superior gluteal
S2 nerve
Inferior gluteal
S3 nerve
Sciatic
Posterior femoral
cutaneous
Pudendal
S4 nerve
Co1
Sacral plexus, anterior view
Figure 12.8
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A posterior view of the lower limb
showing the distribution of the nerves
of the sacral plexus
Superior gluteal nerve
Inferior gluteal nerve
Pudendal nerve
Posterior femoral
cutaneous nerve
Sciatic nerve
Tibial nerve
Common fibular
nerve
Sural nerve
Figure 12.8
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The dermatomes of the sensory nerves
innervating the ankle and foot
Saphenous
nerve
Sural nerve
Sural
nerve
Saphenous
nerve
Fibular
nerve
Tibial nerve
Fibular nerve
Figure 12.8
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3
An anterior view of the lower trunk
and lower limb showing the
distribution of the nerves of both
the lumbar and sacral plexuses
Iliohypogastric nerve
Ilioinguinal nerve
Genitofemoral nerve
Lateral femoral
cutaneous nerve
Femoral nerve
Obturator nerve
Superior gluteal nerve
Inferior gluteal nerve
Pudendal nerve
Posterior femoral
cutaneous nerve (cut)
Sciatic nerve
Saphenous nerve
Common fibular
nerve
Superficial fibular
nerve
Deep fibular
nerve
Figure 12.8
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Module 12.9: Reflexes
• Reflexes
• Are rapid, automatic responses to specific stimuli
• Show little variability
• Preserve homeostasis by making rapid adjustments in
functions of organs or organ systems
• In neural reflexes:
• Sensory fibers carry information from peripheral receptors to
integration center
• Motor fibers carry motor commands to peripheral effectors
• Reflex arc
• “Wiring” of a single reflex from receptor to effector
Animation: Components of a Reflexive Arc
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Module 12.9: Reflexes
• Example: Simple withdrawal reflex
1. Arrival of stimulus and activation of receptor
•
Receptor is specialized cell or dendrites of sensory
neuron
•
•
Sensitive to:
•
Physical or chemical changes in body
•
Or changes in external environment
Example: pain receptor in hand
2. Activation of sensory neuron
•
Stimulation of dendrites produces graded polarization
leading to action potential
•
Action potential travels through dorsal root to spinal cord
3. Information processing
•
Sensory neuron releases excitatory neurotransmitters at
postsynaptic membrane of interneuron
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Module 12.9: Reflexes
4. Activation of motor neuron
•
Activation of interneuron leads to stimulation of
motor neuron to carry action potential to
periphery
•
Axonal collaterals may relay sensation to other
centers in brain and spinal cord
5. Response of peripheral effector
•
Release of neurotransmitters by synaptic knobs
leads to response by peripheral effector
•
Generally removes or opposes original stimulus
•
•
An example of negative feedback
Example: skeletal muscle contraction moving
hand away from painful sensation
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STEP 2
The Activation of a Sensory
Neuron
The steps in a reflex arc: a simple withdrawal reflex
STEP 1
The Arrival
of a Stimulus
and Activation of
a Receptor
STEP 3
Information
Processing
Dorsal root
ganglion
To higher
centers
REFLEX
ARC
Receptor
Stimulus
Effector
STEP 5
The Response
of a Peripheral
Effector
STEP 4
The Activation
of a Motor
Neuron
Sensory neuron
(stimulated)
Excitatory
interneuron
Motor neuron
(stimulated)
Figure 12.9
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Module 12.9: Reflexes
•
Reflex categories
1. Development
•
Innate reflexes
•
Connections formed between neurons genetically or
developmentally programmed
•
Generally appear in a predictable sequence
•
•
Example: simplest (withdrawal) to complex (suckling)
Acquired reflexes
•
Learned rather than preestablished
•
Enhanced by repetition
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Module 12.9: Reflexes
•
Reflex categories (continued)
2. Nature of response
•
Somatic reflexes
•
Involuntary control of skeletal muscles
•
•
•
Example: withdrawal reflex
Rapid response that can later be supplemented
voluntarily
Visceral reflexes (autonomic reflexes)
•
Control or adjust activities of smooth & cardiac
muscle, glands, and adipose tissues
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Module 12.9: Reflexes
•
Reflex categories (continued)
3. Complexity of circuit
•
•
Polysynaptic reflexes
•
Involve at least one interneuron, one sensory neuron,
and one motor neuron
•
Longer delay between stimulus and response due to
increased number of synapses
•
Produce more complex reflexes
Monosynaptic reflexes
•
Simplest reflex arc involving one sensory and one
motor neuron
•
Faster response time due to only one synapse
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Module 12.9: Reflexes
•
Reflex categories (continued)
4. Processing site
•
Spinal reflexes
•
•
Occur in nuclei of spinal cord
Cranial reflexes
•
Occur in nuclei of brain
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Module 12.10: Monosynaptic reflex
•
Stretch reflex
•
Best-known monosynaptic reflex
•
Provides automatic regulation of skeletal
muscle length
•
Example: patellar reflex
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The patellar reflex, a stretch reflex
and the best-known
monosynaptic reflex
STEP 2
Activation of a
Sensory Neuron
STEP 1
Arrival of the
Stimulus and
Activation of
a Receptor
STEP 3
Information
Processing in
the CNS
Stretch
Spinal cord
REFLEX
ARC
Receptor
(muscle spindle)
Contraction
Response
Effector
STEP 4
Activation of a Motor Neuron
STEP 5
Response of a
Peripheral Effector
KEY
Sensory neuron
(stimulated)
Motor neuron
(stimulated)
Figure 12.10
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Module 12.10: Monosynaptic reflex
•
Postural reflexes
•
Many stretch reflexes that help maintain
upright posture
•
Coordinated activities of opposing muscles to
keep body’s weight over feet
•
Example: leaning forward stretches calf muscle
receptors which stimulate the muscles to
increase tone
•
•
Returns body to upright position
Postural muscles generally have firm muscle
tone and extremely sensitive stretch receptors
•
Allow for very fine, subconscious adjustments
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Module 12.11: Polysynaptic reflexes
•
Polysynaptic reflexes
•
Responsible for automatic actions involved in
complex movements
•
•
Examples: walking and running
May involve sensory and motor responses on
the same side of body or opposite sides
•
Same side: ipsilateral reflexes
•
•
Examples: stretch reflex, withdrawal reflex
Opposite sides: contralateral reflexes
•
Example: crossed extensor reflex
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Module 12.11: Polysynaptic reflexes
•
Withdrawal reflexes
•
Move affected body parts away from stimulus
•
Strongest are triggered by painful stimuli but other
stimuli can initiate
•
Show tremendous versatility because sensory
neurons activate many pools of interneurons
•
•
Intensity and location of stimulus affect:
•
Distribution of effects
•
Strength and character of motor responses
Example: flexor reflex, crossed extensor
reflexes
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Module 12.11: Polysynaptic reflexes
•
Withdrawal reflex example: flexor reflex
•
Grabbing an unexpectedly hot pan causes
pain receptors in hand to be stimulated
•
Sensory neurons activate interneurons in
spinal cord
•
Interneurons
•
Activate motor neurons in anterior gray horn to
contract flexor muscles
•
Activated inhibitory interneurons keep
extensors relaxed
•
= Reciprocal inhibition
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The flexor reflex, a representative withdrawal reflex
Distribution within gray
horns to other segments
of the spinal cord
Painful
stimulus
Flexors
stimulated
Sensory neuron
(stimulated)
Muscles undergoing
reciprocal inhibition
Extensors
inhibited
Excitatory
interneuron
Motor neuron
(stimulated)
Motor neuron
(inhibited)
Inhibitory
interneuron
Figure 12.11
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1
Module 12.11: Polysynaptic reflexes
•
Crossed extensor reflexes
•
Example: stepping on a tack
•
•
Flexor reflex pulls injured foot away
•
Flexor muscles stimulated
•
Extensor muscles inhibited
Crossed extensor reflex straightens uninjured
leg and supports shifting weight
•
Activated by collaterals of excitatory and inhibitory
interneurons
•
Extensor muscles stimulated
•
Flexor muscles inhibited
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The crossed extensor reflex, which involves
a contralateral reflex arc
To motor neurons
in other segments
of the spinal cord
Extensors
inhibited
Flexors
stimulated
Extensors
stimulated
Flexors
inhibited
Sensory neuron
(stimulated)
Excitatory
interneuron
Motor neuron
(stimulated)
Painful
stimulus
Motor neuron
(inhibited)
Inhibitory
interneuron
Figure 12.11
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CLINICAL MODULE 12.12: Brain influences on spinal
reflexes and diagnostics using reflexes
•
Brain influences on spinal reflexes
•
Can facilitate or inhibit motor neurons or
interneurons involved
•
•
Facilitation = reinforcement
Example: voluntary movement to pull apart clasped
hands can reinforce stretch reflexes and increase
response (example: bigger kick after patellar tap)
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CLINICAL MODULE 12.12: Brain influences on spinal
reflexes and diagnostics using reflexes
•
Reflexes used in diagnostic testing
•
Specific examples
•
Babinski reflex
•
Stroking lateral side of sole of foot
•
Positive response: toes fan due to lack of inhibitory control
of reflex response from descending motor pathways
•
•
Normal in infants
•
Can indicate damaged higher centers or descending
tracts in adults
Negative response: toes curl due to development and
normal reflex response
•
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= Plantar reflex
CLINICAL MODULE 12.12: Brain influences on spinal
reflexes and diagnostics using reflexes
•
Reflexes used in diagnostic testing (continued)
•
Specific examples (continued)
•
Abdominal reflex
•
Depends on descending facilitation
•
Light stroking of skin of anterior abdomen produces
reflexive twitch of abdominal muscles
•
Absence of response may indicate damage to descending
tracts
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