The sensory neurons present in various organs sense the environment and extend the message to the brain. So, it is equivalent to input device of computers. Brain acts as CPU, i.e., Central Processing Unit. The information gathered by sensory neurons is processed by brain and it gives command to the concerned organ to act accordingly. This message is taken or conveyed by motor neurons which act as output devices.

If a person receives a blow on the back, then it will lead in an impairment of cognitive abilities or physical functioning. It can also result in the disturbance of behavioural or emotional functioning. Cervical injuries often lead to quadriplegia (tetraplegia).

The eustachian tube connects the middle ear cavity with the pharynx. It helps in equalising the pressures on either sides of the ear drum. At the pharyngeal opening of the Eustachian tube, is a valve which normally remains closed. The valve opens during yawning, swallowing and during an abrupt change in altitude, when air enters or leaves the tympanic cavity to equalise the pressure of air on the two sides of the tympanic membrane.

Representation of the following parts of eye

A neuron has three main parts

(i) Cell body (ii) Axon (iii) Dendrites

Any stimulus/nerve impulse passes from one neuron to another via axon. This nerve impulse is wave of bioelectric/electrochemical disturbance that passes along neuron during conduction of an excitation.

Transport and release of a neurotransmitter occurs within a synapse. At a chemical synapse, the membranes of the pre- and post-synaptic neurons are separated by a fluid-filled space called synaptic cleft. Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses. The axon terminals contain vesicles filled with these neurotransmitters. When an impulse (action potential) arrives at the axon terminal, it stimulates the movement of the synaptic vesicles towards the membrane, where they fuse with the plasma membrane and release their neurotransmitters in the synaptic cleft. The released neurotransmitters bind to their specific receptors, present on the post-synaptic membrane. This binding opens ion channels allowing the entry of ions which can generate a new action potential in the post-synaptic neuron.