(a) Cochlea:
The coiled portion of the labyrinth is called cochlea. The membranes constituting cochlea, the reissner’s and basilar, divide the surrounding perilymph filled bony labyrinth into an upper scala vestibuli and a lower scala tympani. The space within cochlea called scala media is filled with endolymph. At the base of the cochlea, the scala vestibuli ends at the oval window, while the scala tympani terminates at the round window which opens to the middle ear.
(b) Organ of Corti: The organ of Corti is a structure located on the basilar membrane which contains hair cells that act as auditory receptors. The hair cells are present in rows on the internal side of the organ of Corti. The basal end of the hair cell is in close contact with the afferent nerve fibres. A large number of processes called stereo cilia are projected from the apical part of each hair cell. Above the rows of the hair cells is a thin elastic membrane called tectorial membrane.
(c) Synapse:
A nerve impulse is transmitted from one neuron to another through junctions called synapses. A synapse is formed by the membranes of a pre- synaptic neuron and a post – synaptic neuron, which may or may not be separated by a gap called synaptic cleft. There are two types of synapses, namely, electrical synapses, the membranes of pre and post synaptic neurons are in very close proximity. Electrical current can flow directly from one neuron into the other across these synapses.
Transmission of an impulse across electrical synapses is very similar to impulse conduction along a single axon. Impulse transmission across an electrical synapse is always faster than that across a chemical synapse. At a chemical synapse, the membranes of the pre and post synaptic neurons are separated by a fluid – filled space called synaptic cleft
