Question

Bipolar neurons occur in
A. Vertebrate embryos
B. Retina of eyes
C. Brain and spinal cord
D. Skeletal muscles

Answer 1

Bipolar neuron is a type of nerve cell that has two extensions, one on the axon side, and one on the dendrite. Many bipolar neurons are specialized sensory neurons for the assimilation of sense. As such, they play a role in sensory pathways for smell, taste, hearing, touch, but mainly sight.

Complete answer: Bipolar neurons are nerve cells, which as the name suggests, have bipolar endings. The cell body is present at the centre and with extensions on both sides of the cell, one at the axon and other at the dendrite. Commonly seen nerve cells are a form of multipolar cells that are capable of having multiple connections, whereas a bipolar cell has only two connections. It primarily transmits signals from the presynaptic end usually connected to a sensory receptor, to the dendrites at the other end. Often found in the retina, bipolar neurons play a role in the sensory pathway and perception of sight. The specific location of these cells is crucial in the perception and transmission of signals from receptors. These cells unlike other neurons pass gradual signals to the brain. There are mainly two types of bipolar cells, on-centre, and off-centre bipolar cells. The off-centre bipolar cells have excitatory synaptic signalling, whereas on-centre cells have inhibitory synaptic signalling. This means that off-center cells send a signal when in the dark and on-centre cells send a signal in the presence of light. Bipolar neurons are also present in the vestibular nerve and play a role in sensory information transmission including, hearing, motion detection, and touch. They are present in the retina of the eyes.
Hence, the correct answer is option B.

Note: Bipolar cells are found in the case of other sensory organs such as the vestibulocochlear nerve, which is responsible for transmitting signals of sound to the brain. Bipolar nerves are also found in skeletal muscles and vertebrates of developing embryos, but only to a certain extent and as the embryo grows, they become specialized and primarily found only in the retina of the eye.