LAB EXAM: Human Reflex Behavior

Question 1

What is a reflex

Answer 1

rapid involuntary response to a stimulus

Question 2

the neural pathway mediating a reflex

Answer 2

a reflex arc

Question 3

a reflex arc consists of a ____ that perceives the stimulus, an ____ neuron that delivers the message to the CNS, and _____ center in the CNS, an ____ neuron that transmits the repsonse to the periphery, and an ____ organ that mediates the response.

Answer 3

a reflex arc consists of a RECEPTOR that perceives the stimulus, an AFFERENT SENSORY neuron that delivers the message to the CNS, an INTEGRATION center in the CNS, an EFFERENT neuron that transmits the response to the periphery, and an EFFECTOR organ that mediates the response.

Question 4

for many reflexes, the integration center is in the ____ ____. Which types of reflexes are an excpetion?

Answer 4

most are in the spinal cord, except the auditory or visual reflexes, which are integrated in the brain.

Question 5

Proprioception

Answer 5

the perception of the position of one’s body parts, especially the limbs, independent of visual input.

Question 6

locations of proprioceptors

Answer 6

skeletal muscles, tendons, joints and inner ear.

Question 7

What is the skeletal muscle proprioceptor and what does it do?

Answer 7

called a muscle spindle. monitors changes in the length of the muscle.

Question 8

how is a reflex elicited?

Answer 8

by tapping on the tendons attached to muscle. the tapping causes the muscle to STRETCH and stimulates the MUSCLE SPINDLE, eliciting a reflex arc.

Question 9

tapping the achilles tendon to elicit a reflex is called the ___ ___, causing the toes to:

Answer 9

plantar flexion. Causes the toes to point downwards.

Question 10

how can a plantar flexion be quantified?

Answer 10

using an EMG electrode attached to the gastrocnemius (Calf) muscle that is coupled to a force transducer in order to respond to depression of the foot.

Question 11

the __ ___ of the force transducer converts mechanical movement into an electrical signal that can be recorded via ___ ___ ___

Answer 11

the STRAIN GAUGE of the force transducer converts mechanical movement into an electrical signal that can be recorded via CATHODE RAY OSCILLOSCOPE

Question 12

When reading the OSCILLOSCOPE, (upper channels) records the :

and the (lower channel) records the:

Answer 12

upper channel records the force of the foot depressing the treadle

lower channel records the electrical activity in the muscle. (EMG)

Question 13

purpose of the preamplifier

Answer 13

attached to the oscilloscope and EMG electrodes and amplifies the small muscle action potentials and reduced background noise so that we can see the EMG signal on the oscilloscope.

Question 14

after eliciting a plantar reflex, which screen on the oscilloscope would have any activity first? what does this indicate?

Answer 14

channel 2 would have activity because there would be an EMG FIRST (spike in electrical activity, muscle action potential), and then a resulting muscular force recording a short while after (muscle contraction) in channel 2, which causes the foot to push down the treadle.

Question 15

What is the reflex time?

Answer 15

the time from the trigger arrowhead to the PEAK of the EMG burst (aka the electrical potential change on LOWER CHANNEL)

Question 16

what does the reflex time represent? Outline the events that happen and the neurons involved that elicit the reflex.

Answer 16

represents the time between the stimulation of stretch receptors (MUSCLE SPINDLE) to the initiation of the muscle action potential by motor nerve endings.

1) a stretch triggered by the tap of the heel activates the muscle spindle
2) the muscle spindle is synapsed with the 1a SENSORY fiber, which gets stimulated and fires an action potential down its axon to the spinal cord (through the dorsal root ganglion), which is PICKED UP BY THE LOWER CHANNEL.

Question 17

what is the total reaction time on the oscilloscope?

Answer 17

the time from the trigger arrowhead to the DOWNWARD force recording. (the time for the foot to depress the treadle).

Question 18

What events occur during the interval between the EMG burst and the plantar flexion? (between the reflex time and the total reaction time)

Answer 18

There is a lag because it takes time for the electrical excitatory signal to transform into phsyical movement. This is called EXCITATION COUPLING

The action potential moving up from the sensory 1A neuron synapses with the alpha motor neuron at the spinal cord, and activates it, triggering an AP in the alpha motor neuron, which is propagated down to the terminals of the alpha motor neuron.

2) the alpha motor neuron is synapsed with the EXTRAFUSAL muscle fibers. The alpha motor neuron released Ach into the synapse and causes an Na+ influx into the extrafusal muscle fibers, depolarizing them.
3) The depolarization of the extrafusal muscle fibers causes voltage gated Ca2+ receptors to open, and Ca2+ that was stored in the SARCOPLASMIC reticulum is released into the fiber.
4) the Ca2+ in the muscle fiber binds to TROPONIN and causes it o move out of the way. tropomyosin also moves, exposing the myosin binding sites on the actin molecuels, allowing the myosin heads to attach to the thin filament
5) ones the myosin heads are able to bind to the actin, contraction can occur.

Excitation coupling (linking a nerve impulse to the shortening of a sarcomere)all takes time, which results in the lag between the EMG (muscle AP) and the actual contraction)

Question 19

discuss spinal cord innervation and show the neurons invovled in the achilles stretch reflex. Explain what a muscle spindle is.

Answer 19

the muscle spindle is the large sensory receptor on the terminal end of the afferent neuron. It synapses with a muscle fiber and is connected to the Sensory 1A neuron.

once a stimulus (tap or stretch) is picked up by the muscle spindle in the INTRAFUSAL FIBERS, it propagates an electrical response through the afferent (sensory 1A) neuron, which goes through the DORSAL ROOT GANGLION into the spinal cord. The achilles relfex is MONOSYNAPTIC and thus the afferent neuron directly synapses with the ALPHA motor neuron. Starting in the spinal cord, the motor neuron gets excited by the sensory neuron, and an AP is propagated to the GASTROCNEMIUS muscle EXTRAFUSAL FIBERS through the release of ACH IN THE SYNAPSE. the Ach released causes an EXCITATION-CONTRACTION COUPLING MECHANISM (ex/ Ca2+ gets released by sarcolemma and moves the troponin-tropomyosin complex to expose the myosin binding sites on the actin heads, allowing for contraction), causing the foot to push down on the tredal and exhibit a measurable force.

Question 20

Most reflexes are polysynaptic, using multiple interneurons to relay info between afferent and efferent neurons. what’re some examples of monosynaptic reflex arcs?

Answer 20

patellar reflex (knee) and achilles reflex.

Question 21

What events occur between the time of the tendon tap and the EMG response? (the reflex time)

Answer 21

1) tap
2) the tap causes a STRETCH, which excites PROPRIORECEPTOR sensory receptors (MUSCLE SPINDLE) in the INTRAFUSAL MUSCLE, which is connected to the sensory neuron.
3) depolarizations from sensory neuron due to intrafusal muscle spindle stimulation elicits an action potential which excites the motor neuron AND initiates the muscle action potential by motor nerve endings (picked up by EMG)

Question 22

Why are stretch receptors so important?

Answer 22

monitor the physical state of various organs and muscles. They keep track of the distension occuring in the colon walls, hearts and lungs, and relay it back to the medulla so that the body can maintain an adequate functional state. Stretch receptors monitor blood pressure and bodily functions.

Stretch reflex is also PROTECTIVE because it monitors any abnormal stretch response. Mitigates bodily damage because the arc is localized in the spinal cord and does not require conscious thought processing which would take longer and thus would sustain more damage.

• Once the muscle overstretches, the response is to compensate for the stretch of the tendon.
• Proprioceptors (muscle spindles) monitor stretch response.

Question 23

Why are reflexes in general and important physiological mechanism in the body?

Answer 23

they are fast reacting mechanisms that allow the body to remove itself from threatening stimuli without requiring processing time from the brain.

Question 24

alpha motor neurons synapse with the ___ ___ and receive inputs from various brain centers. What do these inputs do?

Answer 24

alpha neurosn synapse with the EXTRA FUSALmuscle fibers and receive inputs from various brain centers.

inputs ALTER MEMBRANE VOLTAGE of alpha motorneuron, and thus modulates the motor neurons sensitivity to the muscle spindle excitation (on the afferent neuron) therefore, the afferent neuron does not need to “work that hard” in order to depolarize the motor neuron.

Question 25

2 Methods to alter alpha motor neuron sensitivity

Answer 25

1) jandresseck Manoever

2) voluntary gastronemius muscle contraction or flexion before measuring the achilles reflex

Question 26

What is the Jandressck manoever and how does it modify the ankle jerk reflex?

Answer 26

you get the subject to interlock their fingers and pull outwards. (ISOMETRIC MUSCLE CONTRACTION) Typically, when fiddling with their hands, there is a stronger EMG because you are distracted by another task. There is no difference in time though.

Question 27

What is an isometric muscle contraction?

Answer 27

type of strength training in which the joint angle and muscle length do not change during contraction. Isometrics are done in static positions, rather than being dynamic through a range of motion.

Question 28

How does prior voluntary exertion by planting your foot on the ground as hard as you can affect the achilles reflex?

Answer 28

it shouldn’t. you’re using your quads to exert force on your foot and thus your calf wouldn’t be exerted

Question 29

How does standing on your toes prior to measuring achilles reflex affect it?

Answer 29

the reflex may be weaker because of muscle exertion, constant activation may result in the temporary depletion of calcium stores, ,or may reduce sensitivity of the motor neurons, resulting in a less forceful reflex

Question 30

how does stretching via leg lunge affect the achilles reflex?

Answer 30

it may align the microfilaments better if the lunge was done properly, resulting in a stronger reflex because there is a better opportunity of overlap and forming cross-bridges (bonds between actin and myosin)

Question 31

How do reaction times of voluntary cued responses compare to reflex times?

Answer 31

they are typically longer because it requires more processing times

Question 32

Outline the neurons and steps involved in depressing the treadle in response to a visual stimulus

Answer 32

1) peripheral events such as visual input
2) peripheral PHOTOreceptors take in visual stimuli (light energy), reansforms them into electrical signals by synapsing with the BIPOLAR CELLS and then GANGLION Cells, which converge through the OPTIC NERVE.
3) the electrical signal moves past the OPTIC CHIASM, which separates different parts of the visual stimulus to the left and right hemispheres of the brain, and through the OPTIC TRACT to the LGN in the THALAMUS
4) After moving through the brain stem nuclei (THALAMUS), the signal getting processed in the OCCIPITAL LOBE, and info is also conveyed to the ASSOCIATION CORTEX that allows some recall/more info added to the stimulus (more synapses)
5) the sensory and association areas relay the electrical signal to the premotor and supplementary motor areas, and then relays it to the PRIMARY motor cortex
7) the PRIMARY MOTOR CORTEX, AFFERENT NEURON TERMINALS, and BRAIN STEM NUCLEI all have inputs to the ALPHA motor neuron. Excitation of the alpha motor neuron from the primary motor cortex and inputs trigger its depolarization and action potential down its axon, where it synapses with EXTRAFUSAL muscle and releases Ach, facilitating a contraction by excitation-contraction coupling.

Question 33

When measuring “voluntary” reaction time, what all is encapsulated in the entire time?

Answer 33

the reaction time includes the time required for excitation of a specific sensory receptor, signals to reach the sensory area of the cerebral cortex via a sensory nerve, and for the signals to travel to the motor are and carry a motor impulse to the muscle.

Question 34

What’re some factors that may affect the reaction time of an individual?

Answer 34

age, gender, physical fitness, fatigue, distraction, alcohol, DRUGS, CAFFEINE, personality and emotional factors, and whether the stimulus is auditory or visual.

Question 35

Why may the visual reaction times for voluntary plantar flexion and for catching a ruler vary?

Answer 35

voluntary plantar flexion may take longer to exert because the leg muscle is not only more bulky and larger than moving your fingers, but the sensory and motor neurons may also be longer. THERE IS A DIFFERENCE IN LENGTH OF A PATHWAY. Unlike reflexes, the sensory (visual) info must be processed in the cerebral cortex, and several inputs from the primary motor stimulus, brain stem are needed to induce a motor neuron activity. Because the nerve bundle innervating the calf is further away from the brain stem compared to the motor bundles innervating the hands, it may take longer to relay and process the information necessary to induce a leg reaction.

Question 36

How do mean values of visual/auditory reaction times compare to stretch reflex time?

Answer 36

visual reaction times are longer than stretch refelx times. A sensory reaction time is NO LONGER A REFLEX. It is now a CONCEIOUS RESPONSE to a stimulus, where as a reflex time is UNCONCIOUS.

All sensroy inputs have different response times. Hearing ones may be faster than sensory ones.

Sensory input also takes more time because it is NOT a monosynaptic reflex. Processing of sensory info needs to go through MULTIPLE SYNAPSES and adds LENGTH to the pathway. (because it needs to go to both the sensory cortex and the motor cortex). Therefore, there is a synaptic delay.

Question 37

Sensory inputs will be generally GREATER than ____ms

Answer 37

100ms

Question 38

Adding ___ and ____ to a pathway makes it longer, which is why conscious repsonses take longer than reflex.

Answer 38

LENGTH and SYNAPSES.

Question 39

The ____ fiber are muscle cells inside the muscle and synapses with the ____ Sensory neuron, and the ____ fiber is responsible for contracting, and is synapsed to the ___ ___ __

Answer 39

The INTRAFUSAL fiber are muscle cells inside the muscle and synapses with the 1A Sensory neuron, and the EXTRAFUSAL fiber is responsible for contracting, and is synapsed to the ALPHA motor neuron.

Question 40

Why may touching certain areas elicit a faster response?

Answer 40

Touching the thigh versus touching the face to create a reaction time might elicit different rates because touch info goes through the primary association area and SOMATOSENSORY Regions in the cortex. It must be processed in the corical strucutres, and thus if the subject was touched at a distal point in their body, the sensory neuron must relay the message a longer a distance and possibly have to move through more synapses rather than if the person was touched in a region closer to the somatosensory cortex (ie/ touched on the face).

Touching a person close to the somatosensory regioni in the cortex will elicit a faster response because it takes less time to the action potential to propagate up the SENSORY axon