Neural Control and Coordination - Elementary structure and function of eye and ear
Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The eye wall consists of three layers: the external Sclera (anteriorly forms the Cornea), the middle Choroid (contains blood vessels and forms the Ciliary body and Iris), and the inner Retina.
The Retina contains two types of photoreceptor cells: Rods (responsible for twilight or scotopic vision) and Cones (responsible for daylight or photopic/color vision).
Photopigments in the eye are composed of (a protein) and (an aldehyde of ). Light induces dissociation of from , changing the membrane permeability and generating action potentials.
The 'Blind Spot' is the region where the optic nerve leaves the eye and photoreceptors are absent. The 'Fovea' is a thinned-out part of the retina containing only cones, providing maximum visual resolution.
The Ear is divided into three sections: External ear (Pinna and Auditory canal), Middle ear (Tympanic membrane and three ossicles: , , and ), and Inner ear (Labyrinth).
The Eustachian tube connects the middle ear cavity with the pharynx and helps in equalizing the pressure on either side of the .
The Cochlea is the coiled portion of the inner ear. The Organ of Corti, located on the Basilar membrane, contains 'hair cells' that serve as auditory receptors.
The Inner ear also contains a complex system called the Vestibular apparatus, composed of three Semicircular canals and the Otolith organ (Saccule and Utricle), which is responsible for maintaining body balance and posture.
Mechanism of Hearing: Sound waves Ear drum Ear ossicles Oval window Cochlear fluid Basilar membrane ripple Bending of hair cells against Tectorial membrane Nerve impulse transmission via Auditory nerve.
📐Formulae
💡Examples
Problem 1:
Explain the chemical basis of the visual impulse when light hits the retina.
Solution:
In the presence of light, the photopigment (e.g., ) undergoes a structural change. The dissociates from the protein. This dissociation causes a change in the structure, which alters the membrane permeability of the photoreceptor cell. This results in potential differences (action potentials) that are transmitted via the bipolar neurons and ganglion cells to the optic nerve and finally to the visual cortex of the brain.
Explanation:
The process is a biochemical transduction where electromagnetic energy (light) is converted into an electrochemical signal.
Problem 2:
What is the specific role of the in the middle ear?
Solution:
The is the smallest bone in the human body. It is attached to the 'Oval Window' () of the cochlea. Its primary function is to transmit sound vibrations from the to the fluid-filled inner ear.
Explanation:
Because the inner ear is fluid-filled, it requires more pressure to move the fluid than to move air. The ear ossicles act as a lever system to increase the force of vibrations.
Problem 3:
Identify the ions responsible for the generation of receptor potentials in the hair cells of the cochlea.
Solution:
The movement of the basilar membrane causes the hair cell stereocilia to bend. This mechanical displacement opens mechanically gated ion channels, allowing an influx of (Potassium) ions from the endolymph into the hair cell, leading to depolarization.
Explanation:
Unlike most neurons where causes depolarization, hair cells in the ear utilize the high concentration of in the endolymph.