17485.Which one of the following pairs of structures distinguishes a nerve cell from other types of cell?
Perikaryon and dendrites
Vacuoles and fibres
Flagellum and medullary sheath
Nucleus and mitochondria
17486.Which one of the following is an example of negative feedback loop in humans?
Constriction of skin blood vessels and contraction of skeletal muscles when it is too cold
Secretion of tears after falling of sand particles into the eyes
Salivation of mouth at the sight of delicious food
Secretion of sweat glands and constriction of skin blood vessels when it is too hot
17488.Unidirectional transmission of a nerve impulse through nerve fibre is due to the fact that:
nerve fibre is insulated by a medullary sheath
sodium pump starts operating only at the cyton and then continues into the nerve fibre
neurotransmitters are released by dendrites and not by axon endings
neurotransmitters are released by the axon endings and not by dendrites
17489.The function of vagus nerve innervating the heart is to
Initiate the heart beat
Reduce the heart beat
Accelerate the heart beat
Maintain constant heart beat
17490.Cornea transplant in humans is almost never rejected. This is because:
It is a non-living layer
Its cells are least penetrable by bacteria
It has no blood supply
It is composed of enucleated cells
17491.When sympathetic nervous system is activated it causes the secretion of
Adrenaline which inhibits the organ
Acetylcholine which stimulates the organ
Adrenaline which stimulates the organ
Acetylcholine which inhibits the organ
17492.Given below is a table comparing the effects of sympathetic and parasympathetic nervous system for four features (a-d). Which one feature is correctly described?
| Feature | Sympathetic Nervous System | Parasympathetic Nervous System |
|---|---|---|
| (a) Salivary gland | Stimulates secretion | Inhibits secretion |
| (b) Pupil of the eye | Dilates | Constricts |
| (c) Heart rate | Decreases | Increases |
| (d) Intestinal peristalsis | Stimulates | Inhibits |
(a)
(b)
(c)
(d)
17493.During the transmission of nerve impulse through a nerve fibre, the potential on the inner side of the plasma membrane has which type of electric charge?
First positive, then negative and continue to be negative
First negative, then positive and again back to negative
First positive, then negative and again back to positive
First negative, then positive and continue to be positive.
17494.Which one of the followings is the largest portion of the brain in humans?
Cerebrum
Cerebellum
Medulla
Pons