The depolarization of the axonal membrane is due to:

1. Influx of sodium ions

2. Efflux of sodium ions

3. Influx of potassium ions

4. Efflux of the potassium ions

Immediately after an action potential has peaked, which cellular gates open?

1. Sodium
2. Chloride
3. Calcium
4. Potassium

The stapes sends its vibrations to 
1. Incus 
2. Round window
3. Tympanic membrane
4. Oval window

In a chemical synapse, when an impulse arrives at the axon terminal, it:
1. leads to the opening of the calcium channels at the post-synaptic membrane.
2. Stimulates the fusion of synaptic vesicles towards the pre-synaptic membrane.
3. causes the binding of the neurotransmitter of its receptors on the post-synaptic neuron.
4. activates the opening of the potassium channels in the axon terminal.

Above the rows of hair cells of Organ of Corti, there is a thin elastic membrane called:
1. Reissner's membrane
2. Basilar membrane
3. Tectorial membrane
4. Tympanic membrane

Receptor sites for neurotransmitters are present on
1. membrances of synaptic vesicles
2. pre-synaptic membrane
3. tips of axons
4. post-synaptic membrane

Good vision depends on adequate intake of carotene rich food.

Select the best option from the following statements.

I. Vitamin-A derivatives are formed from carotene.
II. The photopigments are embedded in the membrane discs of the inner segment.
III. Retinal is a derivative of vitamin-A.
IV. Retinal is a light absorbing part of all the visual photopigments.

(1) (I) and (II)

(2) (I), (III) and (IV)

(3) (I) and (III)

(4) (II), (III) and (IV)

Myelin sheath is produced by
(1) Schwann cells and Oligodendrocytes

(2) Astrocytes and Schwann cells

(3) Oligodendrocytes and Osteoclasts

(4) Osteoclasts and Astrocytes

Choose the correct statement.
(1) Nociceptors respond to changes in pressure

(2) Meissner's corpuscels are thermoreceptors

(3) Photoreceptors in the human eye are depolarised during darkness and become hyperpolarised in response to the stimulus 

(4) Receptors do not produce graded potentials

Photosensitive compound in human eye is made up of
1. opsin and Retinal
2. opsin and Retinol
3. transducin and Retinene
4. guanosine and Retinol