MLT GlobePhysiology: Nervous system & special senses
68 Physiology MCQs on Nervous system & special senses with answers and explanations.
Why do action potentials travel faster along myelinated axons?
Myelin insulates the axon, so depolarisation occurs only at nodes and the impulse jumps between them. The refractory period prevents backward conduction.
Which statement about a resting neurone is correct?
At rest the inside is about -70 mV relative to outside. K+ is the main intracellular cation, and depolarisation results from Na+ entering the cell.
At a chemical synapse, the transmitter released from the presynaptic terminal:
Transmitters are stored in vesicles, released by exocytosis, diffuse across the cleft and bind specific receptors. They can excite or inhibit.
Pacinian corpuscles, which are onion-like receptors deep in the dermis, respond mainly to:
Pacinian corpuscles are rapidly adapting mechanoreceptors for deep pressure and high-frequency vibration. Pain and temperature use free nerve endings, and Meissner corpuscles sense light touch.
Cranial and spinal nerves, which connect the brain and spinal cord to the rest of the body, form the:
The PNS (cranial and spinal nerves and ganglia) carries signals between the CNS and receptors or effectors. The CNS is the brain and spinal cord.
A student can read clearly up close but sees distant objects blurred, because light focuses in front of the retina. This is:
In myopia (short-sightedness) the image forms in front of the retina and is corrected with concave lenses. In hypermetropia it forms behind the retina.
Which retinal photoreceptors are responsible for colour vision?
Cones, which contain three photopigments sensitive to different wavelengths, mediate colour and sharp daylight vision. Rods serve dim-light vision, and bipolar and amacrine cells are interneurones.
Damage to the hippocampus, amygdala and cingulate gyrus would mostly disturb which functions?
These structures form the limbic system, which governs emotional behaviour, drives and memory. Balance and posture depend on the cerebellum and vestibular system.
A finger touches a hot plate and the hand withdraws. Which order of events is correct?
A reflex arc begins at a receptor, carries impulses inward by sensory (afferent) fibres to the CNS, and outward by motor (efferent) fibres to a muscle or gland.
Which glial cells wrap brain capillaries with end-feet and help form the blood-brain barrier?
Astrocyte end-feet surround capillaries and induce tight junctions in the endothelium. Oligodendrocytes make CNS myelin, microglia are phagocytes, and ependymal cells line ventricles.
When the patellar tendon is tapped, the afferent neurone synapses directly with the motor neurone. Where is this synapse?
Most spinal reflex arcs, including the monosynaptic knee jerk, are integrated in the spinal cord grey matter without needing the brain.
Once threshold is reached, a neurone fires an action potential of fixed size; below threshold, none occurs. This is the:
Action potentials are all-or-none: stimulus strength is coded by frequency, not amplitude. Graded potentials vary in size and can summate.
A patient with a sixth cranial (abducens) nerve palsy cannot move the affected eye outward. Which muscle is paralysed?
The abducens nerve supplies only the lateral rectus, which abducts the eye. The superior oblique is supplied by the trochlear nerve; the other recti by the oculomotor nerve.
Pulling your hand away from a hot object before you consciously feel pain is an example of a:
A reflex is a rapid, automatic, usually protective motor response to a specific stimulus, processed in the spinal cord or brainstem before conscious awareness.
A sudden threat raises heart rate, dilates the pupils and diverts blood to skeletal muscle. This response is driven by the:
These are 'fight or flight' effects of sympathetic activation. The parasympathetic system promotes 'rest and digest' activity.
Weakness in shrugging the shoulders and turning the head against resistance suggests damage to which cranial nerve?
The spinal accessory nerve supplies trapezius (shoulder shrug) and sternocleidomastoid (head turning). The hypoglossal nerve supplies tongue muscles.
A stroke damaging the primary visual cortex affects which lobe of the brain?
The primary visual cortex lies around the calcarine sulcus in the occipital lobe. The temporal lobe processes hearing and the parietal lobe somatic sensation.
The cornea and lens bend incoming light so that it focuses on the:
Refraction by the cornea and lens brings the image into focus on the retina, where photoreceptors lie. The optic disc has no photoreceptors, so it forms the blind spot.
An eye that focuses distant objects sharply on the retina with the ciliary muscle relaxed is described as:
Emmetropia is the normal refractive state. In myopia distant images fall in front of the retina; in hypermetropia behind it; presbyopia is age-related loss of accommodation.
The centres that control breathing, heart rate and blood vessel diameter are located in the:
The medulla contains the respiratory, cardiac and vasomotor 'vital centres'. Damage here, for example from brainstem compression, can quickly be fatal.