C.

both 'a' and 'b'

Ventricles are related to both heart and brain. Mammalian heart is four chambered. The upper two chambers known as right and left auricle and the lower as right and left ventricles. In brain there are four ventricles. Ventricle Ist and II (lateral ventricles) are cavities of two cerebral hemispheres. IIIrd ventricle (diocoel) is cavity of diencephalon and IV ventricle (metacoel) is cavity of medulla oblongata.

C.

Ectoderm

The brain is the centre of the nervous system in all vertebrates and most invertebrate animals. The neural plate of ectoderm forms the brain, spinal cord and nerves.

Axon reflex is a neuron reflex in which an afferent impulse travels along a nerve fibre away from the cell body until it reaches a branching, where it is diverted to an end organ without entering the cell body. It does not involve a complete reflex arc and therefore it is not a true reflex.

Cochlear microphonic is the electrical potential generated in the hair cells of the organ of Corti in response to acoustic stimulation.

C.

Nerve cells

The longest cell in human body is neurons or nerve cells. They are located in the base of spinal cord.