Term
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Definition
- Large change in membrane potential
- All or none event
- Signals propagate over long distances (not decremental) |
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Term
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Definition
A reflex is a patterned, involuntary response to a stimulus
The response is graded: strength of the response is proportional to the stimulus. Therefore, the stronger the stimulus, the stronger the response. |
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Term
| how does reflex activity occur? |
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Definition
- Reflex activity occurs through Reflex Arcs
Reflexes can be:
- Monosynaptic – single synapse between afferent and efferent neurons
- Polysynaptic – multiple synapses between the afferent and efferent neurons |
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Term
| 5 Components of a Reflex Arc |
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Definition
1. Transduces a stimulus into an electrical signal, activating an AP in an afferent neuron. (Stimulus to receptor)
2. Propagates AP to the integrator in CNS (receptor to afferent nerve fibers)
3. Spinal cord or higher areas within CNS. Activates efferent neurons. (afferent nerve fibers to integrating center)
4.Propagates AP from integrator to the effector structure/system (integrating center to efferent nerve fibers)
5. Receives the signal which elicits a response (efferent nerve fibers to effector-->response) |
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Term
| Monosynaptic Reflex: Stretch/Myotatic Reflex |
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Definition
Tap deflects tendon, stretching muscle spindle-->
Activates receptor (1)
(Synapse)-->
Excites IA afferents (2)
Enter s spinal column via dorsal root (3)
(Synapse)-->
Excites the efferent α motor neuron (4)
Leaves Spinal Column via ventral root (Synapse)-->
Activates Muscle (5)
-->
Muscle shortens |
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Term
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Definition
- Detects length and rate of stretch of muscle
- Modified muscle fiber (Intrafusal muscle fiber)
- Muscle fibers are called extrafusal muscle fibers
- Encircled by branches from a IA afferent nerve fiber |
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Term
| Hoffman Reflex (H-Reflex) |
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Definition
Electrically induced monosynaptic reflex.
It is the refractory (monosynaptic) reaction of a muscle after an electrical stimulus on sensory fiber in the muscle spindle (nerve). Typically on the tibial nerve. |
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Term
| in lab, what muscle did we directly stimulate, how, and what did we see because of this? |
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Definition
In lab, we directly stimulated the tibial nerve and therefore bypassed the muscle spindle
The tibial nerve has both IA afferents and α motor neurons so we saw 2 types of waves:
H-wave: caused by IA afferent neuron activation of α motor neurons
M-wave: caused by directly activating α motor neurons |
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Term
| how direct stimulation of the tibial nerve causes muscle contraction |
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Definition
Direct stimulation of the Tibial nerve
-->
Excites IA afferents
-->
IA axons make a monosynaptic connection to α motor neuron (efferent neurons)
-->
Activated α motor neuron causes contraction of the muscle |
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Term
| Increasing Stimulus Voltage |
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Definition
- IA afferent fibers have a larger diameter than α motor neurons.
- As you start to increase the voltage magnitude you should see the H-wave first(~30-45 msec after initiation of the stimulus)
- As you continue to increase the voltage the M-wave will appear (~10-20msec after initiation of the stimulus)
- Latency – time period between stimulation and response |
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Term
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Definition
- Renshaw Cell is an Inhibitory interneuron found in the gray matter of the spinal cord
- Branch of the α motor neuron near the cell body synapse and inhibit the α motor neuron it was stimulated by as well as other motor neurons
- Uses Glycine as an inhibitory neurotransmitter
- This single interneuronal, synaptic self-inhibition is called Recurrent inhibition
- increased frequency=increased activation of the renshaw cell= decreased H wave amplitude |
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Term
| Increasing Stimulus Frequency |
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Definition
- At low frequencies, the α motor neuron is able to recover from the recurrent inhibition from the Renshaw cells before the next stimulus
- At higher frequencies, the α motor neuron is not able to recover from recurrent inhibition before the next stimulus
- Causes the α motor neuron to be less responsive to IA afferent stimulation |
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Term
| Vestibular-Occular Reflex |
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Definition
Stimulus
- Inertia and interaction between movement of endolymph and hair cells in response to angular acceleraton
Receptors
- Hair Cells (extension of nerve fibers)
- Kinocilium – tallest hair cell
Positioned toward midline of the head on each side
- Sterocilia – shorter hair cells
Move more than the kinocilium |
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Term
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Definition
- Mechanoreceptors able to detect movement along a particular axis
- One large Kinocilium (tallest)
- Multiple Stereocilia (shorter)
- Each hair cell synapses with the vestibular nerve fibers
- Hair bundles (cilia) are embedded in a gelatinous mass called the cupula
- Cupula and hair cells project into the fluid filling the semicircular canals (Endolymph) |
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Term
| Response to Angular Acceleration |
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Definition
- Hair cells move with endolymph in response to acceleration
- Deceleration – acceleration to the opposite direction
- Bending stereocilia away from the kinocilium hyperpolarizes the hair cell by causing K+ channels to close
- Do not get release of exctiatory transmitter
Example: counterclockwise rotation
Hair cells on the left side will be depolarized because the stereocilia bend toward the kinocilium. Hair cells on the right will be hyperpolarized |
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Term
| Response Portion of the Reflex |
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Definition
Once afferent neurons are activated, the signal is integrated within the brainstem.
Results in activation of motor neurons that innervate the lateral and medial eye muscles.
Response is nystagmus – alternating slow and fast components of eye movement in response to a sudden change in acceleration of the head
In our example
Slow eye movement – direction opposite of the spin
Rapid eye movement – in the direction of the spin
Nystagmus – defined by direction of rapid eye movement
Integration of the relative activity between the sensory afferents coming from the two sides of the head produces the appropriate nystagmus. |
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Term
| What direction are you moving? |
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Definition
Your sensation of moving will also be modulated by input from the vestibular apparatus.
As you accelerate, your body is moving faster than the endolymph, which causes the stereocilia to be bent.
When your speed becomes constant, the endolymph will be moving at the same speed as your body
You will not have the sensation of moving.
As you decelerate, your endolymph will spin faster than your body.
As a result, you will have the sensation of spinning in the opposite direction (because the stereocilia will be bent in the opposite direction). |
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Term
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Definition
| EMG stands for electromyography, which is a device used to record electrical activities produced by skeletal muscle. |
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Term
| Effect of stimulus voltage and magnitude of the EMG |
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Definition
- Overall, increasing stimulus voltage increases magnitude of the EMG
- M-wave: increases and reaches a maximum
- H-wave: increases and reaches a maximum, then decreases due to the activation of the Renshaw cell(which inhibits production of the H-wave) |
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Term
| What is the vestibular system? What are its components? |
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Definition
| the vestibular system is a sensory system that contributes to sense of spatial orientation, movement, and balance. It includes the cochlea (part of the auditory system), the horizontal canal, the posterior canal, the anterior canal, the utricle, the saccule, and the nerve. |
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Term
| Define vestibular nystagmus |
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Definition
| rapid involuntary eye movements triggered by a disruption of the signal pathways between the eyes, inner ear, and the brain. |
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Term
| What eye movements did you observe when the subject is slowly rotated (and the eyes were OPEN)? What influenced these eye movements |
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Definition
The participant was spun in a clockwise direction. The direction of the fast eye movement was clockwise while the direction the slow eye movement was counter clockwise.
Both vestibular and visual systems influenced the eye movement. The vestibular system undergoes both hyperpolarization and depolarization giving the sense of direction. The quick eye snap from the left to the right was due to the visual system overriding the vestibular system allowing the eye to fixate on a specific object. |
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Term
| Explain what happened during rotation of the subject (and the eyes were CLOSED). Explain the mechanism responsible for the subject’s perception of rotation. |
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Definition
The participant was spun in a clockwise direction. The direction of fast eye movement was counter clockwise and the direction of the slow eye movement was clockwise.
Acceleration in the clockwise direction caused the endolymph to moved in the opposite direction/deceleration causing the participant to point the thumbs in the direction of the spin. As soon as the participant achieve a constant velocity the endolymph reached a plateau, which gave the perception of being stopped resulting in thumbs facing up. Once deceleration took place, the endolymph shifted in the direction of the initial spin, which causes the perception of movement in the opposite direction. |
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Term
| What occurs in the hair cells of the vestibular system of the left versus right ear during rotation? |
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Definition
| Depending on the rotation of the spin, each cupula within the semicircular canal will be shifting in a different direction. |
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Term
| What happened when the subject was spun at rapid rotation and the abruptly stopped? WHy did this happen? |
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Definition
- direction of fast eye movement: against the spin
- direction of sloe eye movement: with the spin
- Eyes were twitching left and right but predominantly with fast movement against the spin.
Perception of motion did not equal actual motion.
The fluid (endolymph) in the subject's semicircular canals had caught up to the speed the subject had been rotating in space. When the subject was suddenly stopped, the fluid continued to move.
There was a sudden change in polarization of the hair cells. |
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Term
| Why was the subject able to control nystagmus when spun slowly, but couldn’t when spun quickly? |
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Definition
When the subject is spun slowly, their VOR has time to focus on an image and adjust when it is out of view.
At high speeds, however, the subject's VOR is unable to focus on a particular image so when they are stopped, they see multiple images. |
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