Neural Control and Coordination Test - 29

The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. The lens is the transparent part present behind the cornea. The light passes through the transparent structures and the image is formed on the retina. 

A nerve is composed of nerve fiber bundles. A nerve fiber is a threadlike extension of a nerve cell and consists of an axon and myelin sheath (if present) in the nervous system. There are nerve fibers in the central nervous system and peripheral nervous system. A nerve fiber may be myelinated and/or unmyelinated. In the central nervous system (CNS), myelin is produced by oligodendroglia cells.
Muscle tissue is a soft tissue that gives rise to muscles and has ability to contract. 
Bundle sheath cells is a layer of cells in plant leaves and stem that forms a sheath surrounding the vascular bundles.

The cerebrum is the largest part of the human brain and consists of two cerebral hemispheres, which in turn have four lobes- frontal lobe, parietal lobe, occipital lobe and temporal lobe. 

Two neurons are never physically connected to each other and synapse is the gap between two neurons where information from one neuron is transmitted to the next one. The extracellular space between two neurons is known as synaptic cleft which makes option C true. The neuron that transmits the signal is called as presynaptic neuron while the other that receives the signal is known as postsynaptic neuron. Thus, in case of chemical synapse, neurotransmitter is released from presynaptic neuron and is received by post synaptic ones. This makes option A true. The neurotransmitters are stored in synaptic vesicles of axon terminal and are released into the synaptic cleft. This makes option D a false statement and correct answer with respect to the question. Since a single neuron can have many dendrites and a cell body, both of which can synapse with multiple neurons; a single neuron receives multiple excitatory and inhibitory signal which makes option B true. Correct answer is D. 

Sensory neurons receive sensory inputs from the internal and external environment and transmit it to CNS (brain and spinal cord) for processing.  Motor neurons transmit the nerve impulses from CNS to effectors (muscles and glands).  According to the signal, carried by motor nerves to effector organs, the muscles and glands perform their actions (contraction and secretion respectively) and thereby coordinating the metabolic activities. 

The nerve cells stop dividing after the birth of the child. There are no centrosomes in the neurons. Since there are no centrosomes the formation of the spindle apparatus cannot take place. The spindle fibres are necessary for the cell division to take place because they help in the attachment of the chromosomes

The eyeball has three coats namely sclera, choroid and retina. The white and opaque sclera has a ring shaped scleral venous sinus at its junction with cornea which make option D incorrect. Cornea is the transparent window of eye located within otherwise opaque sclera. It has no blood vessels at all which makes option C correct. Choroid is dark pigmented thin vascular layer and is characterized by presence of many blood vessels; option B incorrect. The third layer retina contains rod and cone cells; the blood vessels coming from optic nerve open in retina which makes option A is incorrect. Correct answer is C.

• Reflex action is a sudden and involuntary response to stimuli.  
• Pulling our hands away immediately after touching a hot or cold object is a classic example of a reflex action. 
• In a reflex action, the spinal cord along with the brain stem is responsible for reflex movements.
• A few examples of reflex action are: When light acts as a stimulus, the pupil of the eye changes in size. Sudden jerky withdrawal of hand or leg when pricked by a pin.

So, the correct option is option B.

Sound waves enter the external auditory canal and cause the tympanic membrane to vibrate. These vibrations are amplified by ear ossicles and are transmitted through oval window to basilar membrane. Vibrations of basilar membrane stimulate the hair cells (mechanoreceptors) of the organ of Corti and nerve impulse is carried to brain. Auditory nerve serves to pass the nerve impulse, generated in hair cells, to brain irrespective of the pitch of the sound. 

Sensory nerves receive sensory inputs from the internal and external environment and transmit it to CNS (brain and spinal cord) for processing. Motor nerves transmit the nerve impulses from CNS to effectors (muscles and glands).  Out of 12 cranial nerves, olfactory, optic and vestibulocochlear nerves are exclusive sensory nerves. On the other hand, oculomotor, trochlear, abducens, spinal accessory and hypoglossal nerves are exclusive motor nerves.