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55 part 2.pdf
1. 13-7 Spinal Reflexes
Muscle spindle structure (continued)
Dendrites of sensory neurons wind around central
region of intrafusal fibers.
Sensory neuron axonenters CNS in posterior root
Sensory neurons synapse in spinal cord directly with
motor neurons
.Gammaefferents complete reflex arc by synapsing
back atthe intrafusal fibers
Muscle contracts back to its resting length
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2. Solitary
cel Sensary root
Dorsal root ganglion
Posterior
horn
External besalcells
Descending
-Cornicospinal tract
Intermediate zone
Intemeurons
Antenor hom
LGarmma motor neurg ber
Antenior motor
neurons
Alpha motor neuron
1b ber
alpha motor Motor
endplate
neuron
Gamma motor
Motor roo
Skeletal
musce
neuron
Muscie spindle Goig tandon organ
Figure 55-1. Comections of perpheral sersory tibesand corb
COpna tibers with the nerneurons and anterior motor neuiors of
the spend cord
Figure 55-2. Penpheral sensory fibers
aed anterior motor neurons
innerating skeletal musce
3. In the stretch reflex, the receptor stimulated is
called a
muscle.
The effector isthe
a) Golgi tendon; same
b) muscle spindle; same
c) Golgi tendon;opposite
Stretch Reflex/Myotatic Reflex
d) muscle spindle; opposite
Receptor-
Stretch (muscle
spinde)
REFLEX
ARC
Stimulus
fector
Contrecton
Response
4. Dorsal root ganglion-
Posteriorhom Efferent
Aipe molor
innervation of
Descending
Jibers
skeletal muscles:
intermediate zone-
Garma moor
neuron
Antenior
hom Extrafusal fibers
Gamma motor neuron 1atber
a motor neurons
Alpha motor neuron
1b fiber
Intrafusal fibers-y
Motor end piate
motor neurons
Exmua
musoetbe
Skeletal muscle
Mace spindie Golg tendon organ
sce
Figure 55-2. Perpheral sensory fibers and anterior motor neurons
innervating sieietal muscie
6. Extratusal fibers
Muscle Flower spRy
sensory neurons Gamma
fferent
ersto
intratusal
hbers
Spindle
Aipha motor
neuron to
extrafusa
tbers
Annulospral
sensory neurons
Gamma
efterent
tibers to
ntratusai
bers
Nuciear chan
ber
intrausa
fibers
1) Stretch
Nucear bag
foer
2)Speed of Stretch
7. A weight lifter is straining to lift a 200-kg barbell.
Shortly after he lifts it to chest height, his
muscles appear to relax
and he drops thebarbell
Which reflex has occurred?
a) withdrawal reflex
b) stretch reflex
c) crossed extensor reflex
c)
d) tendon reflex
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8. X Application oftheGolgiTendon OrganJGTps)
Even if the biceps brachii
could somehow generate
enough forceto cul 2000 lbs,
the tendon is not strong
enough to support the
combined weighs,of the bone
and enormous barbel.
Muscles
Absurd
Type Ib afferent
Golgi tendon organ
Collagen
Bone
Tendon
Tear
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10. Motor Motor
Sensory
la
17um
MOTOR NERVES:
14 m 5um 8um5 um alpha-Extrafusalmusclefibers
Gamma-Intrafusal muscle fibers (endportions)
SENSORY NERVES: Central portionof intrafusal muscle
fibers
Extrafusal
fibers
Sheath
Aipha motor
ending
Primary
ending
Intrafusal
fibers
la- Primary ending
I1-Secondary ending
Gamma motor Fluid Secondary
ending
ending cavity
1 cm
Figure 55-3. Muscle spindie, showing its relationship to the large
extrafusal skeletal muscle fibers. Note also both motor and sensory
innervation of the muscle spindle
11. TYPES OF INTRAFUSAL
MUSCLE FIBERS
SENSORY NERVE
ENDING STIMULATED
Dynamic y fiber
(efferent)
Staticy tiber
(efterent)
Group la fiber
(primaryafferent)
Group il fibers
(secondary
afferent)
Piate
ending 1.Nuclearbag Primary nerve
ending
Nuclear bag fiber
(intrafusal muscle)
2. Nuclear chain Primary
ending
Secondary
ending
Nuclear chain fibaor
(intrafusal muscle)
nerve
Trail ending
Figure 55-4. Detals of nere connections from the nuckear bag and
nuciearchainmuscie spindie fibers. (Modifiedfrom Stein RB:Periph
eralcontrol ofmovement. Physiol Rev 54.225, 1974)
nerve
TYPES OF RESPONSES OF MUSCLE
SPINDLES
Static Response
Stretch; if the receptor of the muscle spindle is
stretched slowly
1
2. Dynamic Response
- Rate ofstretch
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12. 13-7 Spinal Reflexes
Postural reflexes
Include both stretch reflexes
(monosynaptic)
and also
complex polysynaptic reflexes
Maintain normal upright posture
Often involve multiple muscle groups (e.g., back and
abdominal muscles)
Maintain firm muscle tone
Extremely sensitive receptors allow constantfine
adjustments to be made as needed
13. 13-7 Spinal Reflexes
Polysynaptic reflexes
More complicated than monosynaptic reflexes
Interneuronscan control multiple muscle groups
Produce either EPSPsor IPSPs, stimulating some
muscles and inhibiting others.
Examples
Tendon reflex
Withdrawal reflexes
Crossed-extensor reflexes
14. 13-7 Spinal Reflexes
The tendon reflex
Prevents skeletal muscles from:
Developing too much tension
Tearing orbreaking tendons
Sensory receptors are Golgi tendon organs
Stimulated when collagen fibers are overstretched
Stimulate inhibitory interneurons in spinal cord
More muscle tension leads to more muscle
inhibition
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15. 13-7 Spinal Reflexes
Withdrawal reflexes
Move body part awayfrom stimulus (pain or pressure)
Example: flexor reflex in limbs; pullshandfrom
hot pan
Strength and extent of response dependson intensity
and location of stimulus
Reciprocal inhibition
Forflexor reflex to work, stretch reflex of antagonistic
(extensor) muscles must be inhibited(reciprocalI
inhibition) by interneurons in spinal cord.
When flexors contract, extensors relax
When extensors contract, flexors relax
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16. Withdrawal Reflex
Distribution within gray matter horns
to other
segments of thespinal cord
Painful
stimulus
Flexors
stimulated
Extensors
inhiblted
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17. You've just touched a hot stove.What type of
reflex did you experience? In what way was your
brain involved in the reflex?
a) cranial;the somatosensory cortex
b) visceral; only tracts that respond to pain
b)
c) complex; all the sensory tracts
d) spinal; it was not involved
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18. 13-7 Spinal Reflexes
Reflex arcs
Ipsilateral reflex arcs
Occur on same side of body as stimulus
Stretch,tendon,andwithdrawalreflexes
Crossed extensor reflexes involve contralateral reflex
arcs
Occur on side opposite stimulus
19. 13-7 Spinal Reflexes
Crossed extensorreflexes
.Coordinated with flexor reflex
Step on something sharp; before flexorreflex can lift
injured foot, crossed extensor reflex straightens
oppositelimb to receive body weight, then flexor reflex
can occur
.Maintained by reverberating circuits
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20. During a withdrawal reflex, the limb on the side
opposite the stimulus
called a
.This response is
a) flexes; stretch reflex
b) adducts; tendon reflex
c) extends; crossed extensor reflex
d) abducts; tendon reflex
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21. aCrossed Extensor Reflex
To motorneurons in other
segments of the spinal cord
Extensors.
inhibited
Flexors
-
Extensors stimulated
stimulated
Flexors inhibited
KEY
Sensoryneuron ----Motor neuron
(stimulated) (inhiblted)
Excitatory
intermeuron
--Inhibltory
interneuron
Motor neuron
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22. 13-8 The Brain Can Alter Spinal Reflexes
Plantar reflex
Normal in adults
Stroke lateral sole, causes reflexive toe-curling
TheBabinski reflex
Normal ininfants
May indicate CNS damage in adults
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23. After injuring her back, 18-year-old Tina exhibits
a positive Babinski reflex. What does this imply
about Tina's injury?
a) possible paraplegia
b) possible damageto sensory tracts to foot
b)
possible damage to ascending tracts in spinal cord
c)
d) possible damage to descending tracts in the spinal cord
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24. After injuring her back, 18-year-old Tina exhibits
apositive Babinski reflex. What does this imply
about Tina's injury?
a) possible paraplegia
b) possible damage to sensory tracts to foot
b)
c) possible damage to ascending tracts in spinal cord
d) possible damage to descending tracts in the spinal
cord
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25. aThe plantar reflex, a
curling of the toes, is
seen in healthy
adults.
bThe Babinski reflex occurs without
descending
inhibition. It is normal in
infants, but pathological
in adults.
