Study Questions Lab 8 Nerve

Question 1

Exercise 1 and 2

1. How does the subject’s mean rxn time to visual signals compare to his or her mean rxn time to auditory signals?

Answer 1

The subject’s mean rxn time to visual signals is slightly longer compared to her rxn time to auditory signals, aka it is delayed.

Question 2

Exercise 1 and 2

2. What would cause a longer rxn time to one type of signal as compared to another?

Answer 2

A longer rxn time to 1 type of singal compared to another can be due to anticipatory effect. E.g. There is anticipation that goes with visual stimuli and this causes a slight delay

Question 3

Exercise 1 and 2

3. How do your subject’s mean rxn times compare to those of other subjects?

Answer 3

Our subject’s mean rxn times are generally shorter (less delayed) than that of other subjects.

Question 4

Exercise 1 and 2

4. Do all subjects respond more quickly to the same signal?

Answer 4

all subjects responded quicker to auditory signals.

Question 5

Exercise 3

5. Name and describe the components of a reflex arc?

Answer 5

1. Receptor - a specialized structure at the beginning of a sensory neuron that receives the original stimulus
2. Afferent neuron - the sensory neuron that relays the receptor signal into the brain or spinal cord
3. CNS center - a center in the spinal cord or brain where information is relayed across one or more synapses from the afferent neuron to the efferent neuron.
4. Efferent Neuron - the neuron that transmits information out of the CNS to an effector
5. Effector - smooth, cardiac, skeletal muscle cells or secretory cells (in glands) that ultimately respond to the application of the stimulus to the receptor.

Question 6

Exercise 3

6. Describe how a stretch receptor codes for the amount of stretch?

Answer 6

A muscle spindle (stretch receptor) codes for the rate at which (and degree) the muscle is stretched. Increasing stretch increases the rate of action potential firing from its basal level. This causes a reflex contraction of the muscle.
The larger the stretch, the larger the excitation of muscle spindles (assumption)

Question 7

Exercise 4
7. Compare the avg reflex times of the Achilles and patellar tendon reflexes. What factors contribute to the difference btwn the 2 reflex times?

Answer 7

• The avg reflex times of the Achilles tendon is longer compared to the rxn times of the patellar reflex.
• This is due to
  (i) a shorter distance travelled to the CNS center in spinal cord for patellar reflex
  (ii) radius of axons (increase radius = decrease axial resistance)
  (iii) degree of axon myelination (increases membrane resistance).

Question 8

Exercise 5

8. Is the time of the response from Person B the same for each stimulus by Person A? If not, what could be the reason?

Answer 8

Time of the response for Person B shows some variation for each stimulus from person A (gets faster from trials 3 – 4).

1. This could be due to repeated stimulation of the nerve that increases excitability.
2. Can also be due to amount of rest between trials
3. pre-excitation due to subject gripping the dynamometer tougher.

Question 9

General

10. Describe the relationship btwn conduction velocity and nerve fibre type

Answer 9

1. There are fast and slow nerve fibre types.
2. Nerves that are large in diameter and myelinated will have the fastest conduction velocity (~120m/s). Example would be motoneurons that supply skeletal muscles. Nerves that are small in diameter and unmyelinated will have the slowest conduction velocity (~0.5m/s). Example would be sensory fibres originating in digestive organs.

Question 10

General
11. Describe 4 differences btwn acute physiological effects induced by electromyostimulation as compared to voluntary muscle contraction

Answer 10

1. Motor unit recruitment: During voluntary contraction, motor units are
   recruited in an orderly manner, from small to large. With EMS, greater
   motor units can be recruited before smaller MU’s.

(ii) Muscle strength: EMS limits the optimal spatial recruitment of MUs and
only stimulated the muscle where electrodes are placed. Thus, EMS
doesn’t facilitate intermuscular coordination and less muscle strength.

(iii) Metabolic activation: EMS strongly activates anerobic glycolysis for
energy that results in a faster decline in intracellular pH and earlier fatigue.

(iv) Muscle fatigue: During voluntary contraction, CNS activated smaller
motor units first, then replaces them to avoid fatigue. EMS has no fatigue resistance, it recruits the same motor units throughout simulation.

Question 11

General

12. Define the term “neuromuscular electrical stimulation (NMES)”. Describe 4 clinical uses of NMES.

Answer 11

Neuromuscular electrical simulation (NMES) refers to the electrical stimulation of intact lower motor neuron to activate paralyzed or paretic muscle. This can allow people with paralysis to perform functional tasks, control of respiration, or bladder function. Can also be used for treatment of hemiplegic shoulder pain, spasticity, cardiovascular spasticity, prevention of muscle atrophy, or deep venous thrombosis (DVT).

Question 12

General

13. How do nerve conduction velocities differ by age, gender, and handedness?

Answer 12

NCV differs by age, gender, and handedness: Below age three NCV is
relatively slow and reached normal mean by age five. In adults, there’s a slow
decline in NCV with advancing years. Females tend to have higher NCV (may be due to smaller average height). NVC may be faster in left handed individuals.

Question 13

Exercise 5:

When the patellar tendon is tapped and knee jerk reflex occurs, what is happening to the hamstring muscle group?

Answer 13

During the patellar tendon tap, inhibitory interneurons in the spinal cord will inhibit the alpha motor neuron innervating the hamstrings (antagonistic muscle). This causes hamstrings to relax during the patellar tendon reflex.