Nervous System and Neurons Questions and Answers

Answer: A

The chemical is called a neurotransmitter.

When a nerve impulse reaches the end of a neuron, the neuron releases chemical messengers into the synapse. They cross the gap and bind to receptors on the next cell, passing the signal on. Acetylcholine, dopamine and serotonin are examples.

Synovial fluid lubricates joints. Lymph is the fluid carried in lymphatic vessels. Plasma is the liquid part of blood. None of them carries signals between nerve cells.

Answer: D

The inhibitory neurotransmitter is Gamma amino butyric acid (GABA).

GABA is the main inhibitory neurotransmitter of the brain. It opens chloride channels in the post-synaptic membrane, making the neuron less likely to fire. Drugs such as benzodiazepines work by enhancing its action.

Dopamine and serotonin are modulatory transmitters whose effect can be excitatory or inhibitory depending on the receptor, so neither is the classic inhibitory transmitter. Acetic acid is not a neurotransmitter at all; the transmitter with a similar name is acetylcholine.

Answer: C

The period is 4-5 minutes.

Brain cells depend on a constant supply of oxygen. When circulation stops, cerebral ischaemia begins at once, and after about 4 to 5 minutes without oxygen irreversible brain damage sets in. Clinical death then passes into biological death, and the person cannot be revived.

This is why cardiopulmonary resuscitation must start within the first few minutes. Two or three minutes is still within the window for revival, and 5-6 minutes is beyond the point the key takes as the limit.

Answer: A

Hemiplegia is paralysis of one side of the body.

The prefix hemi- means half: the arm, leg and often the face on one side are paralysed, usually after a stroke or injury in the opposite half of the brain.

Paralysis of both legs is paraplegia, typically from a spinal cord injury below the neck. Inability to speak is aphasia (or mutism), a disorder of language, not of movement. Paralysis of all four limbs is quadriplegia (tetraplegia), and 'complete paralysis of the entire body' is not what hemiplegia means.

Answer: D

They are reflex actions.

A reflex action is an automatic, involuntary response to a stimulus, such as pulling the hand away from a hot object. The impulse travels along a reflex arc through the spinal cord without waiting for the brain to decide, so the response is much faster than a voluntary action and protects the body from harm.

'Sensory' and 'Nervous' are too general: sensory nerves only carry impulses in. Sensory decussation is the crossing of sensory nerve fibres to the opposite side of the brain, an anatomical feature, not a kind of action.

Answer: A

The correct matching is i-b, ii-c, iii-a.

The forebrain, with the cerebrum and thalamus, integrates the activities of the nervous system and is the seat of thinking, memory and voluntary action (b). The midbrain contains the centres for visual and auditory reflexes, such as turning the head towards a sudden sound or light (c). The hindbrain, through the medulla, controls vital activities such as breathing, circulation and digestive reflexes (a).

Every other option gives the vital centres to the forebrain or midbrain.

Answer: C

The nerve is the trochlear nerve (cranial nerve IV).

The trochlear nerve is the only cranial nerve that leaves the back of the brainstem. It emerges from the dorsal midbrain just below the inferior colliculus, crosses to the opposite side and runs forward around the midbrain to supply the superior oblique muscle. It is also the thinnest cranial nerve and has the longest course inside the skull.

The others all emerge from the front or side. The trigeminal nerve leaves the lateral pons, the facial nerve the cerebellopontine angle at the pontomedullary junction, and the abducens nerve the ventral pontomedullary junction.