This question is a mini-lab concerning human response to stimulus. Follow the pr

Question

This question is a mini-lab concerning human response to stimulus. Follow the procedures outlined below and answer the questions provided in letter a to j.

Mini-Lab Reflex Arcs

Reflex arcs make up the neural circuit that travels through the spinal cord, providing a framework for reflex actions. Simple physical tests are used to check reflexes. In this investigation, you will observe the presence and strength of a number of reflex arcs.

Materials

Rubber reflex hammer or the edge of your hand

Penlight or small flashlight

Part I: Knee Jerk

1. Find a partner. You will act as each other

Explanation / Answer

1.a. knee jerk reflex

Striking the patellar ligament with a reflex hammer just below the patella stretches the muscle spindle in the quadriceps muscle. This produces a signal which travels back to the spinal cord and synapses (without interneurons) at the level of L4 in the spinal cord, completely independent of higher centres. From there, an alpha-motor neuron conducts an efferent impulse back to the quadriceps femoris muscle, triggering contraction. This contraction, coordinated with the relaxation of the antagonistic flexor hamstring muscle causes the leg to kick or move forward. This reflex is a reflex of proprioception which helps in maintaining the posture and balance, allowing to keep one's balance with little effort or conscious thought.

The patellar reflex is a clinical and classic example of the monosynaptic reflex arc. There is no interneuron in the pathway leading to contraction of the quadriceps muscle. Instead the bipolar sensory neuron synapses directly on a motor neuron in the spinal cord. However, there is an inhibitory interneuron used to relax the antagonistic hamstring muscle.

This test of a basic automatic reflex may be influenced by the patient consciously inhibiting or exaggerating the response; the doctor may use the Jendrassik maneuver as a distraction or diversion in order to ensure a more valid reflex test.

Babinski reflex

A reflex movement of the big toe upward instead of downward when the plantar aspect of the foot is stroked, a manoeuvre used to test injury to,or diseases of,the upper motor neurons. a reflex action of the toes,normal during infancybut abnormal after 12 to 18 months of age; after locomotion begins, it is indicative of abnormalities in the motor control pathways leading from the cerebral cortex and is widely used as a diagnostic aid in disorders of the centralnervous system.

It is elicited by a firm stimulus (usually scraping) on the sole of the foot, which results in dorsiflexion of the great toe andfanning of the smaller toes. Normally such a stimulus causes all the toes to bend downward.

Pupillary light reflex

the pupil reacts by constricting or dilating. Constriction of a dilated pupil in response to an increase in light intensity or just a sudden exposure to light and a dilatation of a constricted pupil in response to a decrease in the intensity. is called pupillary reflex.

Activity of the reflex indicates the efficiency of the retina, the optic and oculomotor nerves and the musculature of the iris.

In this case there is contraction of the pupil on exposure of the retina to sudden light.

pupillary reflex involves- any reflex involving the iris, resulting in change in the size of the pupil, occurring in response to various stimuli, e.g. change in illumination or point of fixation, sudden loud noise, or emotional stimulation.

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