1. Integrative Physiology I: Control of Body Movement13

2. Neural Reflexes

3. Somatic Motor Reflexes
Monosynaptic and polysynaptic somatic motor reflexes
Figure 13-1a

4. Autonomic Reflexes Some visceral reflexes are spinal reflexes
Stimulus
Response
Postganglionic
autonomic
neuron
Preganglionic
CNS
integrating
center
Sensory
Receptor
Target
cell
Autonomic
ganglion
All autonomic reflexes are polysynaptic,
with at least one synapse in the CNS
and another in the autonomic ganglion.
Figure 13-2

5. Skeletal Muscle Reflexes
Proprioceptors are located in skeletal muscle, joint capsules, and ligaments
Proprioceptors carry input sensory neurons to CNS
CNS integrates input signal
Somatic motor neurons carry output signal
Alpha motor neurons
Effectors are contractile skeletal muscle fibers
Examples of proprioceptors
Muscle spindle
Golgi tendon organ
Joint receptors
Are found in capsules and ligaments around joints

6. Proprioceptors
Muscle spindles are sensory receptors in muscle that control muscle tone and prevent injury from overstretching of the muscle. They are found in all muscles and are tonically active, firing increases as the muscle stretches.
Figure 13-3a–b

7. Muscle Spindles
Muscle spindles monitor muscle length and prevent overstretching of the same muscle. The tonic signaling produces muscle tone.
Sensory
neuron
endings
Intrafusal
fibers of
muscle spindle
(a)
Extrafusal muscle
fibers at resting length
Sensory neuron is
tonically active.
Spinal cord integrates
function.
Alpha motor neurons
to extrafusal fibers
receive tonic input
from muscle spindles.
Extrafusal fibers maintain a certain
level of tension
even at rest.
Spinal
cord
Alpha motor 1 2 4 5 3
Figure 13-4a

8. Muscle Spindles
During a stretch reflex increased firing by the sensory neuron increases signaling by the alpha motor neuron causing the muscle to contract.
Figure 13-4b

9. Alpha-Gamma Coactivation***
Gamma motor neurons intervate the ends of intrafusal fibers in muscle spindles and keep the sensory neuron active even when the muscle contracts
Alpha motor
neuron fires.
Stretch on center
of intrafusal fibers
is reduced.
Firing rate of
spindle sensory
neuron decreases.
Muscle contracts.
(a)
If gamma motor axons are cut, the spindle loses activity when muscle contracts.
Muscle shortens
Action potential
Time
Less stretch
on intrafusal
fibers
Muscle
length
Action
potentials of
spindle
sensory
neuron 1 2 3 4
Figure 13-5a

10. Alpha-Gamma Coactivation
When an alpha motor neuron fires the muscle contracts and shortens but the gamma motor neuron will also fire and thus there will be stretching at the spindle fiber to keep the tonic firing.
Alpha motor
neuron fires and
gamma motor
neuron fires.
Muscle contracts.
Stretch on centers
of intrafusal fibers
unchanged. Firing
rate of afferent
neuron remains
constant.
(b)
Alpha-gamma coactivation maintains spindle function when muscle contracts.
Muscle
length
Muscle shortens
Intrafusal fibers do not slacken, so
firing rate remains constant.
Action
potentials of
spindle
sensory
neuron
Time 1 2 3
Figure 13-5b, steps 1–3

11. Proprioceptors
Golgi tendon organs are sensory receptors in muscle that respond to tension changes in the muscle and attempt to prevent injury from excessively strong contractions. When golgi sensory neuron fibers the efferent signal in inhibitory and thus there is a loss in contraction strength
Figure 13-3a, c

12. Muscle Reflexes: response to load and overload

13. Patellar Tendon (Knee Jerk) Reflex
Stimulus:
Tap to tendon
stretches
muscle.
Receptor: Muscle
spindle stretches
and fires.
Afferent path: Action
potential travels through
sensory neuron.
The patellar tendon (knee jerk)
reflex illustrates a
monosynaptic stretch
reflex and reciprocal
inhibition of the
antagonistic muscle.
Figure 13-7

14. Patellar Tendon (Knee Jerk) Reflex
Stimulus:
Tap to tendon
stretches
muscle.
Receptor: Muscle
spindle stretches
and fires.
Afferent path: Action
potential travels through
sensory neuron.
Integrating
center:
Sensory neuron
synapses in
spinal cord.
Efferent path 2: Interneuron
inhibiting somatic motor neuron
Efferent path 1:
Somatic motor neuron
The patellar tendon (knee jerk)
reflex illustrates a
monosynaptic stretch
reflex and reciprocal
inhibition of the
antagonistic muscle.
onto
Figure 13-7

15. Patellar Tendon (Knee Jerk) Reflex
Stimulus:
Tap to tendon
stretches
muscle.
Receptor: Muscle
spindle stretches
and fires.
Afferent path: Action
potential travels through
sensory neuron.
Integrating
center:
Sensory neuron
synapses in
spinal cord.
Efferent path 2: Interneuron
inhibiting somatic motor neuron
Effector 2: Hamstring
muscle
Response: Hamstring
stays relaxed, allowing
extension of leg
(reciprocal inhibition).
Efferent path 1:
Somatic motor neuron
Effector 1: Quadriceps
Response: Quadriceps
contracts, swinging lower
leg forward.
The patellar tendon (knee jerk)
reflex illustrates a
monosynaptic stretch
reflex and reciprocal
inhibition of the
antagonistic muscle.
onto
Figure 13-7

16. Flexion Reflex and the Crossed Extensor Reflex
White
matter
Gray
Spinal
cord
Ascending pathways to brain
Painful stimulus
activates nociceptor.
Primary sensory
neuron enters spinal
cord and diverges.
One collateral activates
ascending pathways for
sensation (pain) and postural
adjustment (shift in center of gravity).
Sensory
neuron
Nociceptor
Painful
stimulus
Spinal cord 1 2 3a
Figure 13-8, steps 1–3a

17. Flexion Reflex and the Crossed Extensor Reflex
White
matter
Gray
Spinal
cord
Ascending pathways to brain
Alpha motor
neurons
Painful stimulus
activates nociceptor.
Primary sensory
neuron enters spinal
cord and diverges.
One collateral activates
ascending pathways for
sensation (pain) and postural
adjustment (shift in center of gravity).
Withdrawal reflex pulls foot away
from painful stimulus.
Sensory
neuron
Nociceptor
Painful
stimulus
Spinal cord 1 2 3a 3b
Extensors
inhibited
Flexors contract,
moving foot
away from
painful
stimulus.
Figure 13-8, steps 1–3b

18. Flexion Reflex and the Crossed Extensor Reflex
White
matter
Gray
Spinal
cord
Ascending pathways to brain
Alpha motor
neurons
Extensors
inhibited
Flexors inhibited
Flexors contract,
moving foot
away from
painful
stimulus.
Extensors contract
as weight shifts to
left leg.
Painful stimulus
activates nociceptor.
Primary sensory
neuron enters spinal
cord and diverges.
One collateral activates
ascending pathways for
sensation (pain) and postural
adjustment (shift in center of gravity).
Withdrawal reflex pulls foot away
from painful stimulus.
Crossed extensor reflex supports
body as weight shifts away from
painful stimulus.
Sensory
neuron
Nociceptor
Painful
stimulus
Spinal cord 1 2 3a 3b 3c
Figure 13-8, steps 1–3c

19. Movement Classification
Three types of movement: Reflex (simplest) voluntary (most complex) Rhythmic (a combination of relex and voluntary).

20. CNS Integrates Movement
Spinal cord integrates spinal reflexes and contains central pattern generators
Brain stem and cerebellum control postural reflexes and hand and eye movements
Cerebral cortex and basal ganglia
Voluntary movement- can become reflexive once well learned
Rhythmic movement is initiated at the cerebrum but maintained by interneurons in the spinal cord

21. Integration of Muscle Reflexes
Reflexes are managed by the spinal cord, cerebellum, and brain stem. They do not require input from the cerebrum. However, sensory input is send to the cerebrum so we aware of what happens.
Figure 13-9

22. CNS Control of Voluntary Movement
Voluntary movement can be planned based on postural reflex information. There are 3 phases, sensory feed back is used in the first two.
Figure 13-10

23. Voluntary Movement
Feedforward reflexes and feedback of information during movement
Figure 13-13

24. Visceral Movement Contraction of cardiac and smooth muscle
Moves material in hollow organs by changing the shape of the organ
Controlled by ANS as a reflex
Some create own action potentials
Muscle can respond to hormones or signaling from neighboring cells through gap junction