Human Physiology Lab - Exam 1

isometric exercises

-balancing on tiptoes -doing a plank -holding bench press bar -pushing constantly against a concrete wall

isotonic exercises

-doing a bicep curl -swimming freestyle -running up a hill -pedaling a bicycle on a flat surface

sympathetic nervous system

-relatively long postganglionic fibers -part of the autonomic nervous system that originates from the thoracic and lumber regions -activated in fight or flight -postganglioninc neurotransmitter is commonly norepinephrine

parasympathetic nervous system

-short postganglionic fibers -part of the autonomic nervous system that originates from cranio-sacral -postganglionic neurotransmitter is acetylcholine

Which statement is true of a single motor neuron? 1. It innervates one motor unit. 2. It may innervate a number of motor units.

1. It innervates one motor unit.

Which statement regarding evoked EMG is true? 1. The amplitude of the measured EMG is independent of the number of motor units recruited. 2. There is synchronous excitation of the muscle fibers innervated by the stimulated nerve.

2. There is synchronous excitation of the muscle fibers innervated by the stimulated nerve.

What is the approximate conduction velocity of motor nerves?

50m/s

Unlike the discrete waveform from an ECG, the EMG waveform is irregular. Why is this?

An ECG records electrical activity from the heart. Unlike the heart, skeletal muscle does not contract in a fully synchronized fashion. Instead, an EMG records the unsynchronized electrical activity of many muscle fibers.

When the current reached the following stages, what proportion of fibers in the muscle were contracting? a) at threshold b) at the maximal stimulus c) above the maximal stimulus

At 0 mA no muscle fibers are contraction a. at threshold just a few muscle fibers are being recruited b. by definition the maximal stimulus is seen when 100% of recruitable fibers are contracting c. above maximal stimulus the number of contracting fibers cannot increase

You may observe a change in the skin potential even before the stimulus is delivered. How can you explain this?

Changes in the skin potential may begin to occur even before the stimulus is delivered. This may be due to anticipation of the tap, or a change in sound in the environment that signals that the tap is about to happen. For example, the volunteer may hear a slight movement in the cord the tendon hammer is attached to, or even the sudden absence of sound just before the tap occurs.

The stimulus interval has a profound effect on the contraction force of the muscle. In your own words explain what happened when the muscle was stimulated in rapid succession. At which interval did the volunteer's muscle twitches begin to merge together (summate)?

Depends on data. Basically, if the stimulus interval is shorter than the recovery time for the muscle fibers, the muscle will continue to shorten as each contraction adds to the previous one. This gives rise to a higher force generated than a single stimulus alone.

Do the mean RR intervals differ between quiet and deep breathing? How do the SDs differ? Explain these observations.

Depends on data. The means should stay very similar, but the standard deviation for deep breathing should be greater than for quiet breathing which reflects the greater spread of the data when we breathe deeply.

Mental arithmetic is an excellent distraction compared to other tasks. How did it change the latency of the volunteer's reaction?

Depends on volunteer's reaction time. Typically the latency to a response will be considerably greater with a distraction

What does EMG record?

Electrical activity of the innervated muscle fibers.

From your data, do you think that verbal encouragement or brief rests limited the extent of muscle fatigue?

Encouragement and brief rests have been shown to limit fatigue to some extent during sustained maximal grip forces

A short period of rapid electrical stimuli is used to observe muscle fibers contracting continuously (tetanus). Chemical agents can cause tetanus by interfering with the motor neurons. These agents include a toxin produced by the soil bacterium Clostridium tetani. One of the symptoms of these agents is called "spastic paralysis". Explain in your own words why these agents would have a negative effect on you and your muscles

If the muscles required for breathing were involved, death could follow

Examine the data recorded when the volunteer attempted to maintain a 50% contraction with their eyes shut. Almost all volunteers will show a declining force (pseudo-fatigue) while their eyes are shut that is very similar to actual fatigue. This is not true fatigue because the full 50% force can be exerted easily, as can be seen when the volunteer's eyes are opened again. What explanations can you think of for pseudo-fatigue?

In the absence of information on the actual force produced, the internal sensation of fatigue can predominate and lead to a decline in the force generated

Did you observe a difference between auditory and visual cues? Could this difference really be due to different processing times in the brain?

In theory, the reaction times to auditory stimuli should be faster than those to visual stimuli. Visual and auditory stimuli processed by different parts of the brain with more connections involved in the visual pathway than the auditory pathway. A major difference is the chemical reaction required to convert light into electrical signals which the brain can process. This takes time and happens slower than the conversion of mechanical sound waves in the ear. Alternatively the volunteer may have reacted faster due to subtle cues from the tester.

How can muscle fibers show a range of responses to different levels of stimulation?

Individual twitches in the same fiber can summate.

Define and describe isometric contraction.

Isometric contraction is a muscle contraction where the muscle remains the same length. That is, isometric describes a contraction in which there is no movement of the joint.

Define and describe isotonic contraction.

Isotonic contraction is a muscle contraction where the tension remains the same and movement of a joint occurs. In other words, the contraction strength does not change but the joint angle does.

What is one defining property of a voluntary action that differentiates it from a reflex?

It is performed by choice.

Which describes the phenomenon of "coactivation"?

It is the weaker contraction of the antagonist muscle during the contraction of the agonist muscle.

How can you explain the change in potential across the hand and foot that follows peripheral nerve stimulation?

Peripheral nerve stimulation is conveyed to the brain, which activates the sympathetic nervous system. This leads to stimulation of sweat production. Why does sweat release cause a change in electrical potential across the hand or foot? The sweat glands on the palm and sole are activated by sympathetic stimulation. However, sweat glands on the dorsal, hairy surfaces of the hand and foot are not activated by sympathetic stimulation. Thus the sympathetic nerve activation results in a brief potential differences across the hand and foot.

How do the latencies and amplitudes in the skin of the hand and the foot compare? Explain any differences in the latencies.

Postganglionic sympathetic nerves are C fibers that supply the sweat glands. The C fibers are unmyelinated with slow conduction velocities. Hence there is a characteristic latency or delay between stimulus and response. Was the foot latency greater than the hand latency? This would be expected because nerve impulses travel a greater distance to the foot. Note that the nerve stimulation occurred on the opposite side to the measurements. So, the sweat response is not a result of direct stimulation of nerves supplying the sweat glands.

How many muscle fibers may a single motor neuron innervate?

Several muscle fibers

Describe the volunteer's skin potential response after the startle, gasp, and thump stimuli. How can you explain these findings?

Some tissues are only supplied by one division of the ANS. For example, sweat glands are only supplied by the sympathetic nervous system. As would be expected, stressful stimuli activate the SNS to stimulate sweating. The gasp is a commonly used intervention, it activates the SNS by stimulating stretch receptors in the lung, which send impulses along afferent fibers of the vagus nerve. This activates the sympathetic nervous system, and an increase in heart rate is also seen.

What is the term given to summation of frequent muscle twitches to give maximum contraction?

Tetanus

What does the effect of the Jendrassik maneuver indicate about the neural pathways involved in simple reflexes?

The Jendrassik increases the knee jerk reflex EMG response by decreasing inhibition of the reflex. This indicates that the brain normally sends inhibitory message to lower tendon reflexes. The Jendrassik can also help to reduce your volunteer's conscious inhibition of the reflex.

Explain why the heart rate and finger pulse change during a Valsalva maneuver. Include in your explanation how changes in arterial blood pressure, peripheral resistance, and autonomic nervous activity bring about these responses.

The breathing is restricted which effects blood pressure due to peripheral nerve response. Autonomic nervous response also comes into play with the muscles voluntarily used to keep from breathing out normally.

What happens to pupil diameter when the eye is focused for near vision? What is the advantage of this change in diameter?

The diameter of the pupil is reduced as the iris contracted. The pupil of the eye is actually a hole, surrounded by smooth muscle called the iris. When viewing a near object, the circular muscle of the iris receives increased parasympathetic activation. The muscle contracted and the pupil diameter become smaller. This limits the amount of light entering the eye, which help to focus light from the object onto the retina.

How is acetylcholine removed from the synaptic cleft?

The enzyme acetylcholinesterase hydrolyzes the acetylcholine within the synaptic cleft.

Describe what happens to the heart rate when the volunteer stands after lying down in a relaxed position.

The heart rate increases when the volunteer stands up. This is part of the baroreceptor reflex which acts to restore arterial blood pressure

Describe how the mean reaction times changed across the conditions. Which conditions caused the greatest increase and decrease in the mean reaction times of your volunteer?

The mean reaction times for your volunteer should be different for each condition, with distraction having the largest mean reaction time and auditory cues having the lowest. However, this may not be the case with your data, so describing what you saw is the important thing.

Briefly describe the evolutionary advantage of a withdrawal reflex.

There are obvious survival advantages for animals to be able to rapidly withdraw from a noxious stimulus and move a limb away before further tissue damage occurs. Stabilization of the opposite limb helps to maintain balance.

If your results are different than expected, what do you think caused this disparity?

There are several variable that can affect whether auditory or visual information is processed more quickly. For example, the volunteer may have reacted faster due to cues from the tester. There may be lots of background noise which makes the tap sound harder to hear. There is variation in how quickly humans naturally react to stimuli

Was there greater heart rate variability during quiet breathing or during deep breathing? Explain your findings.

There is greater variation during deep breathing. The increased tidal volume activates stretch receptors in the lungs, which send impulses along afferent fibers of the vagus nerve. This information is processed in the brainstem and the increased sympathetic tone and/or decreased parasympathetic tone is conveyed back to the heart via the thoracic sympathetic nerves or the vagus. This results in an increased heart rate on inspiration. The deeper the breathing, the greater the variations in the heart rate will be during a respiratory cycle.

What happened to the muscle contraction response as the current stimulus increased from 0 mA? What was the smallest current required to produce each of the following? a) a contraction (threshold current) b) the maximum contraction (maximal stimulus)

This will depend on your data. There can be no measurable response at 0 mA. Usually the first twitch begins around 4-6 mA and the maximum contraction force begins around the 12-15 mA range

During sustained skeletal muscle contraction, can you think of three situations that might cause true fatigue?

True physiological fatigue is complex and may be contributed to by both PNS and CNS. Factors that may lead to true fatigue are thought to include: 1. increased levels of certain metabolites can lead to reduced calcium release from the SR and this impair excitation contraction coupling 2. changes to motor complex activity and motor unit activation can contribute to a decline in muscle force 3. glycogen can be depleted by exercise and is needed for aerobic glycolysis to produce ATP, glycogen levels are shown to decline alongside force 4. muscle contraction can compress blood vessel. Adequate blood flow is necessary to supply oxygen to and remove metabolites from active muscle. Without oxygen supply, the cell begins anaerobic respiration, producing metabolites at a faster rate and contributing to the development of muscle fatigue

In skeletal muscle, what is a minimum unit of contraction caused by a single action potential called?

Twitch

Having carried out the activities under different conditions to test reaction times in this lab, what do you think can influence the variability as seen in the experimental method used today?

Variability which is measured by examining the standard deviation of the data can be influenced by: -volunteer error -experimenter error -motivation -distraction -distance from auditory cue

Describe and explain the sequence of events that occur in the cardiovascular system when a person stands after lying down. Include in your explanation comments on venous return, central venous pressure, stroke volume, and peripheral resistance. How do these parameters change?

Veins are distensible, and the veins in the legs dilate when the volunteer stands. Standing causes blood to pool in the legs. Sympathetic input to the heart increases, which increases heart rate and force of contraction. When we stand, the increase in hydrostatic pressure does not make it harder for blood to return to the heart since the circulation is in a closed loop.

What was the response of the pupil in the opposite eye?

When light is shone on one eye, the circular muscle of the iris of the other eye also contracted (consensual light reflex)

How did the EMG trace change when you added weight to the volunteer's arm? Based on the data you collected, what can you infer is happening to the muscles as weight is added?

When more books were added, the recorded activity increased. From the recorded data, it can be inferred that greater motor unit activity is required to generate more force in order to hold the arm in the same position when more book are added.

Describe what happens to the finger pulse when the volunteer stands after lying relaxed.

When the person stands up, there is a decrease in stroke volume, which is seen as a decrease in finger pulse amplitude

Observe your data. When the volunteer performed the Jendrassik maneuver how did the knee-jerk reflex change?

When you're volunteer performed the Jendrassik, the amplitude of the EMG response should increase. However, the latency should be relatively unchanged between the two conditions

In the knee-jerk reflex arc, where does the synapse between a sensory neuron and a motor neuron occur?

Within the spinal cord.

Did this experiment help you decide which of the factors proposed to explain fatigue are important?

You may have noticed that there is a greater decline in your volunteers grip force during the more strenuous contraction compared with the less strenuous contraction. This is with visual feedback present where the volunteer can see the decline and can attempt to correct for it. There is clearly more fatigue occurring during the more strenuous contractions. A decline in central drive will also have affected some of the results.

neuropathy

a term referring to damage of nerves in the peripheral nervous system and can be caused by a variety of disease and conditions and often cause muscle problems

In the parasympathetic system, which of the following is the preganglionic neurotransmitter? a. It is always acetylcholine. b. It is always norepinephrine. c. It varies depending on the function of the nerve.

a. It is always acetylcholine.

In assessing autonomic nervous system function, which of the following is true for heart rate variability (HRV)? a. It's determined by both vagal and sympathetic innervation of the heart. b. It's determined only by vagal innervation of the heart. c. It's unaffected by respiration.

a. It's determined by both vagal and sympathetic innervation of the heart.

In measuring the autonomic nervous system skin potentials, which of the following is true for stimulation of the median nerve? a. Stimulation can be on either side. b. Stimulation must be on the opposite side of the body to where the potentials are measured. c. Stimulation must be on the same side of the body as the potentials are measured.

a. Stimulation can be on either side.

What affects the nerves of the autonomic neuropath?

alteration to normal gastrointestinal function dry skin dizziness or fainting when getting up at night loss of the ability to urinate blurring vision erectile dysfunction

Which of the following best describes a motor unit? a. All the nerve fibers and muscle fibers in a single muscle bundle. b. A single motor neuron and all the muscle fibers that it innervates. c. One muscle fiber and its single nerve fiber. d. The neuron that provides the CNS with information on the state of contraction of the muscle.

b. A single motor neuron and all the muscle fibers that it innervates.

In assessing autonomic nervous system function in a healthy person, which of the following may the Valsalva maneuver result in? a. An appreciable increase in arterial blood pressure. b. An appreciable increase in heart rate. c. An appreciable increase in skin potential.

b. An appreciable increase in heart rate.

In assessing the autonomic nervous system, which of the following is true for skin potentials recorded over the palm and sole of the foot? a. It assesses parasympathetic activity in peripheral nerves. b. It assesses sympathetic activity in peripheral nerves. c. It depends upon the need for the body to lose heat.

b. It assesses sympathetic activity in peripheral nerves.

In assessing autonomic nervous system function in a healthy person, which of the following may occur with a change from a supine to a standing posture? a. A marked fall in systolic blood pressure after 3 minutes. b. A marked increase in systolic blood pressure after 3 minutes. c. Little change in systolic blood pressure after 3 minutes.

c. Little change in systolic blood pressure after 3 minutes.

Which if the following is true for the parasympathetic system? a. Acetylcholine is never involved as a postganglionic neurotransmitter. b. Both neurotransmitters are used. c. Norepinephrine is never involved as a postganglionic neurotransmitter.

c. Norepinephrine is never involved as a postganglionic neurotransmitter.

Which of the following factors could decrease an individual's reaction time? a. Distractions b. Errors c. Fatigue d. Practice

d. Practice

Which of these choices provides a logical description of the stages in a reflex arc? a. (Interneuron), motor neuron, muscle, spinal cord, sensory neuron. b. (Interneuron), sensory neuron, spinal cord, motor neuron, muscle. c. Sensory neuron, (interneuron), spinal cord, muscle, motor neuron. d. Sensory neuron, spinal cord, (interneuron), motor neuron, muscle

d. Sensory neuron, spinal cord, (interneuron), motor neuron, muscle

Which of the following statements regarding the knee-jerk reflex is false? a. It is a monosynaptic reflex. b. The afferent nerve travels from the receptor to the spinal cord. c. The leg extends in response to a hammer tap. d. Visual receptors sense the hammer tap

d. Visual receptors sense the hammer tap

Which statement about muscle contractions is false? a. An action potential in the muscle cell activates contraction by releasing Ca2+ within the muscle. b. A single action potential at the neuromuscular junction is sufficient to cause a muscle to twitch. c. Summation of twitches leads to a graded increase in the tension that can be generated by a single muscle fiber. d. The tension generated by a muscle can be varied by controlling how many of its motor units are active. e. When maximum muscle tension is achieved, no ATP is required to maintain that level of tension.

e. When maximum muscle tension is achieved, no ATP is required to maintain that level of tension.

true or false: every organ or tissue that has a sympathetic innervation also has a parasympathetic innervation

false

A _________ contraction is when your joints do not move and your muscle fibers are kept at a constant length.

isometric

Which of the following factors have been suggested as contributing to muscle fatigue?

loss of central drive, reduction in calcium release in excitation contraction coupling, reduction in muscle blood flow owing to compression of blood vessels

What is the apparent biological advantage of the pupillary light reflex?

protects the retina from too much light falling upon it

circular muscles of the iris

the iris constricts and reduces the aperture of the pupil

radial muscles of the iris

the pupil dilates

The action potential causes the release of calcium ions from ________________ in the muscle cell.

the sarcoplasmic reticulum

The direct light response is when the iris constricts to reduce the pupil aperture and the amount of light entering the eye.

true

true or false: EMGs may be obtained from needle or surface electrode recordings

true

What affects the peripheral neuropath?

weakness in arm muscles loss of sensation in the feet difficulty walking

Why does varying the stimulus strength affect the twitch force?

with stronger stimuli, more nerve fibers are stimulated and therefore more motor units are recruited