Free Reflexes and the Reflex Arc MCQs with Answers

1. The correct sequence of components in a spinal reflex arc is

• A. effector, motor neurone, spinal cord, sensory neurone, receptor
• B. receptor, motor neurone, spinal cord, sensory neurone, effector
• C. receptor, sensory neurone, interneurone in the spinal cord, motor neurone, effector
• D. sensory neurone, receptor, effector, motor neurone, spinal cord

Explanation: The stimulus is detected by the receptor, carried into the spinal cord by the sensory neurone through the dorsal root, passed to a relay neurone and then out along the motor neurone through the ventral root to the muscle or gland that responds. Sensory always means towards the central nervous system and motor always means away from it, which is enough to rule out the reversed options.

2. A reflex action such as withdrawing the hand from a hot object is fast because

• A. the impulses travel through the cerebrum first
• B. only one neurone is involved in the whole pathway
• C. hormones carry the message directly to the muscle
• D. the response is organised in the spinal cord without waiting for the brain

Explanation: The reflex arc is completed at spinal level, so the muscle contracts before the impulses climbing to the brain arrive and the pain is consciously felt, which is what makes the response protective. The brain is informed afterwards and can modify or suppress some reflexes, but it is not needed for the action itself. At least three neurones are involved, and hormones are far too slow for this.

3. In the spinal cord, unlike the cerebrum, the grey matter

• A. lies on the inside and the white matter surrounds it
• B. lies on the outside and the white matter is central
• C. is entirely absent
• D. contains only myelinated fibres

Explanation: The butterfly shaped core of grey matter contains the cell bodies and synapses, while the outer white matter is made of myelinated axons running up and down the cord, and myelin is what makes that region look white. In the brain the arrangement is inverted, with the grey cortex outside. Recognising the pattern is how a spinal cord section is identified under the microscope.

4. Which component of a reflex arc connects the sensory neuron to the motor neuron within the spinal cord?

• A. Receptor
• B. Effector
• C. Muscle fiber
• D. Associative neuron

Explanation: The associative or relay neurone sits in the grey matter of the spinal cord and passes the impulse straight from the sensory to the motor neurone, which is what allows the response to happen before the brain is even informed. The receptor detects the stimulus at the start of the arc and the effector, usually a muscle or gland, produces the response at the end. A muscle fibre is part of the effector rather than a link in the pathway.

5. Which of the following is the correct pathway of nerve impulse?

• A. Receptors to CNS to Effectors
• B. Effectors to Receptors to CNS
• C. CNS to Effectors to Receptors
• D. Effectors to CNS to Receptors

Explanation: A receptor detects the stimulus, a sensory neurone carries the impulse into the central nervous system, and a motor neurone carries the instruction out to the effector that responds. The direction is fixed by the one way nature of the synapse, since transmitter is released on one side only and receptors sit on the other. Any pathway beginning at the effector reverses the whole logic of the reflex.

6. Which type of neurons stimulate muscles to contract in a reflex arc?

• A. Motor neurons
• B. Sensory neurons
• C. Interneurons
• D. Afferent neurons

Explanation: Motor, or efferent, neurones carry impulses away from the central nervous system to the effector, which in this case is a muscle that contracts. Sensory and afferent are two names for the same thing, neurones carrying impulses inwards, which is why both appear as options. Interneurones link the two inside the spinal cord but do not reach the muscle.