Tag: coordination in human beings- chemical control

A reflex action is defined as a spontaneous, involuntary, automated, nerve-mediated activity produced at the unconscious level  by stimulating specific receptors. In other words, a reflex action is a sensory impulse, automatically converted into a motor effect with the involvement of the central nervous system. These actions are sudden and automatic and take place even before one can feel the stimulus through the brain. The quick pulling of the hand on touching a hot object is an automated response to stimuli and is controlled and regulated by the spinal cord along with the sensory and motor neurons which connect the receptor and effector organs. Thus, the correct answer is option C.

Reflex actions are involuntary actions that are either performed when learnt or innately performed. A complex reflex action is made up of a polysynaptic pathway, wherein, more than one synaptic junctions are involved. Swallowing of food bolus is a reflex activity that involves a polysynaptic pathway and is under reflexive or involuntary control. This stage of the swallow begins after food which has been masticated has been gathered together in the mouth and formed into a bolus which is passed from the posterior tongue. It is controlled by medulla oblongata.

There are 4 types of spinal reflex action, namely the stretch reflex, the Golgi tendon reflex, the crossed extensor reflex and the withdrawal reflex. The direction of response is opposite in withdrawal reflex action. The withdrawal reflex is also called as flexor withdrawal reflex. It protects the body from damaging stimuli. It is polysynaptic. Hence, it causes the stimulation of sensory, association and motor neurons.  For example, when a person touches a hot iron, he withdraws his hand from it within fraction of seconds. In this, the heat stimulates temperature and danger receptors in the skin, triggering a sensory impulse that travels to the central nervous system. The sensory neuron synapses with interneurons and connects to motor neurons. These motor neurons send motor impulses to the flexors and allows withdrawal.

A person experiences goose bumps in the presence of extremely cold temperatures. Tiny muscles attached to each hair follicle contracts because of the stimulus of cold surroundings. The hair strands stand on the end due to this contraction of muscles. The contracted tiny muscles cause bunching of the skin around hairs, which results in bumps in the goose bumps. The goose bumps are helpful to reduce the heat loss from the body and it is a way of preserving body's heat by causing the hairs on the skin to stand up.