Human Physiology and Anatomy

Receptors that sense the change in atmospheric pressure are classified under mechanoreceptors. Three pressure receptors are namely Pacinian corpuscles, Ruffini endings and Krause end bulbs which are located in skin. This makes option A incorrect. The three semicircular canals lie at right angle to each other in vestibular apparatus of inner ear and are filled with endolymph; this arrangement senses the change in movement (acceleration or deceleration) or position. The mechanism includes movement of cupula in response to movement of endolymph within the canal causing the bending of cilia to generate the nerve impulse. This makes option C correct and option D incorrect. Migratory birds and animals have receptors in their brain which are activated by direction of sunlight and orient their body at certain angle in relation to sun. This makes option B incorrect. Correct answer is C. 

The olfactory nerve is the second cranial nerve which transmits the nerve impulses from olfactory receptors, receptors of sense the smell that are located in nasal epithelium of roof of the nasal cavity, to the brain.

• When sound waves from the environment enter the external ear, they are directed to ear drum (tympanic membrane). 
• The ear drum vibrates on receiving sound waves and the vibrations are sent to oval window through ear ossicles which are malleus, incus and stapes. 
• From the oval window, these vibrations are passed onto fluid of cochlea where waves are generated into lymph due to these vibrations. 
• These waves generate vibrations in the basilar membrane which bend the hair cells and press them against the tectorial membrane.
• This results in the generation of nerve impulses in afferent neurons which are transmitted by afferent fibres to auditory cortex of brain. 
• The impulses are analysed and recognised in brain.

The sensory nervous system and the motor nervous system are a part of the nervous system responsible for the processing of sensory information. A sensory system consists of sensory neurons, neural pathways, and parts of the brain involved in sensory perception.

Immunoglobulin E (IgE) is a type of antibody that has only been found in mammals. IgE is synthesised by plasma cells. It plays an essential role in type I hypersensitivity, which manifests in various allergic diseases, such as allergic asthma, rhinitis etc. It also plays a pivotal role in responses to allergens, such as anaphylactic drugs, bee stings, and antigen preparations used in desensitization immunotherapy.

The thymus gland, despite containing glandular tissue and producing several hormones, is much more closely associated with the immune system than with the endocrine system. The thymus serves a vital role in the training and development of T-lymphocytes or T cells, an extremely important type of white blood cell. T cells defend the body from potentially deadly pathogens such as bacteria, viruses, and fungi. The function of the thymus is to receive immature T cells that are produced in the red bone marrow and train them into functional, mature T cells that attack only foreign cells. T cells first reside within the cortex of the thymus where they come in contact with epithelial cells presenting various antigens. The immature T cells that respond to the antigens corresponding to foreign cells are selected to survive, mature, and migrate to the medulla while the rest die via apoptosis and are cleaned up by macrophages.

(i) Actin is present in thin filament - True

Main function of central nervous system (brain and spinal cord) is to integrate the sensory inputs from internal and external environment as received by sensory neurons and process and finally transmit the nerve impulses to effectors (muscles and glands). Thus, being the centre of processing information, the brain has the maximum number of cell bodies of neurons (the grey matter). Spinal cord provides means of communication between peripheral nerves and brain. Thus, it has H-shaped grey matter (cell bodies of neurons) and white matter else everywhere (the myelinated axons that carry impulses to and from the brain). Since nerves in retina and tongue serve to conduct information along the sensory pathways; they have single axon with highly branched dendrites but no cell bodies. Thus, the correct answer is option A.

Brain cells remain in the beginning stage of interphase of cell reproduction for their life, and never divide, and instead develop by forming new synapses with other neurons. They lack cellular machinery for cell division. So, the correct answer is option A. 

Proteins are an important component and are the building block of each cell and perform various functions like: