Neural Control and Coordination

Pons – consists of fibre tracts that interconnect different regions of the brain Hypothalamus – contains several groups of neurosecretory cells that secrete hypothalamic hormones Medulla – contains centres that control respiration and gastric secretions Cerebellum – convoluted surface provides additional space for neurons; regulates posture and balance Correct match: A-III, B-IV, C-II, D-I.

Schwann cells form the myelin sheath around axons (A-III); Synaptic knob releases neurotransmitter at the synapse (B-I); Bipolar neurons are found in the retina (C-IV); Multipolar neurons are found in the cerebral cortex (D-II).

Rods and Cones are photoreceptor cells (a-iii); Blind Spot shows absence of photoreceptor cells (b-i); Fovea has densely packed cones (c-ii); Iris is the visible coloured portion of the eye (d-iv).

Statement I correctly describes olfactory receptors in the nose. Statement II incorrectly swaps the names/descriptions of the eyeball's layers: the external layer is actually the sclera (dense connective tissue), and the middle layer is the choroid (thin, pigmented, vascular layer) — the layers given are reversed, so Statement II is false.

The brainstem consists of the midbrain, pons, and medulla oblongata.

Multipolar neurons (one axon, two or more dendrites) are found in the cerebral cortex; bipolar neurons are found in the retina of the eye; myelinated nerve fibres are found in spinal and cranial nerves; unmyelinated nerve fibres are found in the autonomous and somatic neural systems.

The limbic system is the emotional brain. It controls emotions in our body but not movements. So the limbic system is incorrectly paired.

Carotene is the source of retinal, which is involved in the formation of rhodopsin in rod cells. Retinal, a derivative of vitamin A, is the light-absorbing part of all visual photopigments. Photopigments are in the membrane discs of the outer segment, so (b) is incorrect.

A is the retina, the inner layer that contains the photoreceptor cells, rods and cones.
The blind spot has no photoreceptors, and the anterior part of the choroid forms the ciliary body.

A is the receptor on the post-synaptic membrane and C is the synaptic vesicle containing neurotransmitter.
B is the synaptic cleft and D is $Ca^{++}$.

In the resting (polarised) state the inner side of the plasma membrane of the nerve fibre is negatively charged with respect to the outside; the resting potential is about -70 mV.
When a stimulus is applied, the membrane at that site becomes freely permeable to $Na^+$, and $Na^+$ ions rush in.
The polarity is reversed: the inner side becomes positive (about +30 mV). This is depolarisation, and the potential difference is the action potential, which lasts about 1 millisecond.
Immediately afterwards the permeability to $K^+$ increases and $K^+$ ions diffuse out, so the inner side becomes negative again. This is repolarisation; the sodium-potassium pump then restores the original ionic distribution.
The same sequence is repeated at each successive point as the impulse travels along the fibre.
So the potential on the inner side is first negative, then positive and again back to negative.

At rest, the inside of the axon is negative (about –70 mV).
When stimulated, voltage-gated $Na^+$ channels open and $Na^+$ ions rush into the axon, so the inside becomes positive (depolarisation, about +30 mV).
Then the $K^+$ channels open and $K^+$ moves out, restoring the negative potential (repolarisation).
So, as per the answer key, depolarisation involves $Na^+$ moving inside, with $K^+$ moving outside afterwards.

The hypothalamus lies at the base of the thalamus, which is part of the forebrain; it contains centres that control body temperature and the urge for eating and drinking. This row is fully correct.
The Eustachian tube does equalise the pressure on either side of the ear drum, but it connects the middle ear cavity with the pharynx; it is not part of the internal ear.
The cerebellum is part of the hindbrain and maintains balance and posture; respiration and gastric secretions are controlled by the medulla.
The blind spot is the point where the optic nerve leaves the eye and the retinal blood vessels enter it; photoreceptor cells are not present in that region.
Hence the correct match is hypothalamus – forebrain – controls body temperature, urge for eating and drinking.

Alzheimer's disease is a degenerative disorder of the brain marked by progressive loss of memory and of intellectual functions.
It is associated with the degeneration of the cholinergic neurons of the brain and a marked fall in the level of the neurotransmitter acetylcholine.
Deficiency of dopamine is associated with Parkinson's disease.
Hence Alzheimer's disease is associated with the deficiency of acetylcholine.

In a cross section, each loop of the cochlea shows three canals.
The upper canal is the scala vestibuli and the lower canal is the scala tympani; both are filled with perilymph. In the figure both of these outer chambers are labelled A, so A is perilymph.
The middle canal is the scala media (cochlear duct), which is filled with endolymph. It is separated from the scala vestibuli by Reissner's membrane and from the scala tympani by the basilar membrane. This is the part labelled C, so C is endolymph.
The organ of Corti is located on the basilar membrane and contains the sensory hair cells that act as auditory receptors.
Above the rows of hair cells is a thin elastic membrane called the tectorial membrane, labelled B.
The hair cells are sensory cells, not secretory cells, and the fluid in the outer canals is perilymph, not endolymph or serum.
So the correct labelling is A: Perilymph, B: Tectorial membrane, C: Endolymph.

Bowman's glands (olfactory glands) are located in the olfactory epithelium (olfactory mucosa) lining the upper part of the nasal cavity.
They secrete mucus that keeps the olfactory epithelium moist.
Odorous substances dissolve in this mucus and are then detected by the olfactory receptor cells; the secretion also washes the surface clean for fresh stimuli.
They should not be confused with Bowman's capsule, the cup-shaped structure at the proximal end of the uriniferous tubule (nephron) that encloses the glomerulus.
They are not found in the anterior pituitary or in the reproductive system of the cockroach.
So Bowman's glands are located in the olfactory epithelium of our nose.

Bowman's glands (olfactory glands) are found in the olfactory epithelium lining the upper part of the nasal cavity.
They secrete mucus that keeps the olfactory epithelium moist.
Odorous substances dissolve in this mucus before they stimulate the olfactory receptor cells; the secretion also washes the surface clear for new odours.
They should not be confused with Bowman's capsule, the cup-like part of the nephron that surrounds the glomerulus.
The external auditory canal has ceruminous (wax) glands, not Bowman's glands.
So Bowman's glands are found in the olfactory epithelium.

The autonomic nervous system controls the involuntary activities of the internal organs (viscera) and smooth muscles.
Peristalsis of the intestines is a wave of contraction of the smooth muscles of the gut wall; it is regulated by the autonomic nervous system (the parasympathetic system increases it and the sympathetic system decreases it).
The knee-jerk response is a spinal reflex involving skeletal muscle, controlled by the somatic nervous system.
Swallowing begins as a voluntary action of skeletal muscles.
The pupillary reflex also involves autonomic fibres, but the answer accepted by the key is peristalsis.
So the example of the action of the autonomic nervous system is the peristalsis of the intestines.

Parkinson's disease is a degenerative disorder of the brain, marked by tremors, rigidity of the limbs and slowness of movement.
It is caused by the degeneration of the dopamine-producing neurons of the substantia nigra in the midbrain.
These neurons send fibres to the basal ganglia (corpus striatum), which help to control and smooth out body movements.
With the loss of dopamine, this control is disturbed and the characteristic symptoms appear.
The disease is treated with L-dopa, a precursor that is converted into dopamine in the brain.
So the neurotransmitter involved is dopamine.

At rest, the sodium-potassium pump maintains a high concentration of $Na^+$ outside the axon and a high concentration of $K^+$ inside.
Diffusion always moves an ion from higher to lower concentration.
So $Na^+$, being more concentrated outside, would diffuse into the cell.
$K^+$, being more concentrated inside, would diffuse out of the cell (not into it).
Among the given choices, the correct one is that diffusion would drive $Na^+$ into the cell. (At rest the membrane is far less permeable to $Na^+$, which is why this does not happen until an action potential opens sodium channels.)

The vagus nerve (tenth cranial nerve) is a mixed nerve and the main parasympathetic nerve of the body.
It supplies the heart (slows the heart rate), the larynx and pharynx, the lungs, and the gastrointestinal tract (it increases peristalsis and secretion of digestive juices, including pancreatic secretion).
So an injury to the vagus nerve can affect cardiac movements, gastrointestinal movements and pancreatic secretion.
Movements of the tongue are controlled by the hypoglossal nerve (twelfth cranial nerve), not by the vagus.
So injury to the vagus nerve is not likely to affect tongue movements.