Free Receptors MCQs with Answers

1. The receptors of the retina that allow vision in dim light are the

• A. cones
• B. rods
• C. ganglion cells
• D. cells of the blind spot

Explanation: Rods contain the pigment rhodopsin, which is broken down by very low light intensities, and several rods share one sensory neurone so their effects add up, making them extremely sensitive. The price of that pooling is poor detail and no colour discrimination, which is why night vision is grey and blurred. Cones need bright light and give sharp colour vision instead.

2. Visual acuity is greatest at the fovea because it contains

• A. only rods, packed very closely
• B. no photoreceptors at all
• C. densely packed cones, each with its own connection to the optic nerve
• D. the point where the optic nerve leaves the eye

Explanation: At the fovea the cones are crowded together and each has a private line to the brain, so two nearby points of light stimulate two separate pathways and are seen as separate. Rods share connections, which improves sensitivity but destroys detail. The place with no photoreceptors is the blind spot, where the optic nerve leaves, and nothing falling there is seen at all.

3. A receptor is best described as a structure that

• A. detects a change in the environment and converts it into a nerve impulse
• B. carries impulses from the spinal cord to a muscle
• C. produces a hormone in response to a stimulus
• D. connects two sensory neurones together

Explanation: Receptors are transducers: each responds to one kind of stimulus, such as light, sound, pressure or a chemical, and converts that energy into the electrical signal the nervous system can carry. A structure that carries impulses to a muscle is a motor neurone, and a structure that produces a hormone is a gland. The receptor is therefore always the first component of any reflex pathway.

4. Receptors that respond to changes in temperature are called

• A. photoreceptors
• B. thermoreceptors
• C. chemoreceptors
• D. mechanoreceptors

Explanation: Thermoreceptors in the skin and hypothalamus detect heat and cold and feed the thermoregulatory centre. Photoreceptors respond to light, chemoreceptors to chemicals and mechanoreceptors to pressure and touch, so each stimulus has its own receptor family.

5. The structure of the human eye that adjusts the amount of light entering it is the

• A. retina
• B. iris
• C. lens
• D. cornea

Explanation: Muscles of the iris widen or narrow the pupil, letting more light in during darkness and less in bright sun. The lens focuses light and the cornea refracts it, but neither controls the quantity of light entering the eye.

6. Colour vision in bright light is provided by the retinal receptors called

• A. rods
• B. bipolar cells
• C. cones
• D. ganglion cells

Explanation: Cones, concentrated in the fovea, work in bright light and distinguish colours in three types. Rods are far more light sensitive and serve dim vision but give no colour, which is why colours fade at dusk.

7. The sense of balance and the detection of head rotation depend on receptors located in the

• A. cochlea of the inner ear
• B. eardrum
• C. auditory canal
• D. semicircular canals of the inner ear

Explanation: The three semicircular canals, set at right angles, contain fluid that moves when the head turns, stimulating hair cells that report position and rotation. The cochlea, by contrast, converts sound vibrations into nerve impulses.

8. The receptors responsible for the senses of taste and smell are

• A. mechanoreceptors
• B. chemoreceptors
• C. photoreceptors
• D. thermoreceptors

Explanation: Taste buds and the olfactory epithelium respond to dissolved or volatile chemicals, which is the defining feature of chemoreceptors. Both senses feed closely into each other, which is why food seems tasteless when the nose is blocked.

9. The blind spot of the eye is the region where

• A. the optic nerve leaves the retina and no photoreceptors are present
• B. the lens focuses light most sharply
• C. the iris meets the cornea
• D. rods are most densely packed

Explanation: At the optic disc the axons of ganglion cells gather to form the optic nerve, leaving no space for rods or cones, so light falling there is not seen. The point of sharpest vision is the opposite, the fovea.

10. Neurons that carry impulses from receptors towards the central nervous system are called

• A. motor neurons
• B. interneurons
• C. sensory neurons
• D. glial cells

Explanation: Sensory, or afferent, neurons bring information in from receptors, while motor neurons carry commands out to effectors. Interneurons connect the two within the CNS, so direction of travel is the key to naming each type.