Question

If frog's brain is crushed, even then its leg moves on pricking with a pin, it is called as
A. Simple reflex
B. Conditional reflex
C. Neurotransmitter function
D. Autonomic nerve condition

Answer 1

Knee jerk reflex, contraction of the iris diaphragm (i.e., narrowing of the pupil in response to intense light), blinking of the eyes, removal of the hand on the pinprick, sneezing and secretion of saliva at the sight or scent of food are some typical examples of behaviour related to this condition. Even if the brain is crushed, the impulse responsible for this is responsible for leg movement in frogs.

Complete answer: The word ‘reflex action’ refers to a quick, automatic reaction to a stimulus that is unlearned. As compared to voluntary actions, these actions are involuntary and are controlled by the animal's conscious. The knee jerk reflex or the hand withdrawal after the pinprick is a familiar example of reflex action in man. Impulses are transported from the receptor organ to the central nervous system and back to the effector organ by sensory fibres in such actions. A reflex arc is called the direction or the route by which impulses pass from the receptor organ (via the central nervous system). It is considered a cerebral reflex if the governing nucleus of the reflex arc is located in the brain. It is called a spinal reflex if it is found in the spinal cord. Just one sensory neuron and one motor neuron consist of a basic reflex arc (monosynaptic reflex). But in most reflexes, by intermediate (association) neurons of the spinal cord, a sensory neuron impacts many motor neurons. A dynamic reflex arc, or polysynaptic reflexes, forms this. If the brain of the frog is crushed, the leg movement observed is an example of a simple reflex or unconditional reflex, when pricked with a pin. This form of reflex is controlled only by the spinal cord and does not involve the brain. Such examples include sneezing, jerking of the knee, yawning, etc.
So, option A is the correct answer.

Note: The reflex arcs come in two ways:

1. Somatic reflex arc with effector organs located in the structures of the (soma) body, e.g. skeletal muscles.
2. Visceral reflex arcs contain effectors, such as glands or smooth muscles found in the visceral organs.