Sensory organs(receptors) convert information from the external world into electrical signals in neurons. We will focus on the eyes and ears, which are responsible for vision, hearing, and balance.
Basic Knowledge
Structure of the eye and light reception: cornea(refraction)・lens(thickness changes through the ciliary muscle→accommodation for near and far vision)・iris(adjusts the amount of light through the pupil)・retina(cone cells=bright conditions・color vision, rod cells=dark conditions・black and white)・optic nerve(to the visual cortex of the cerebrum)・macula=fovea(highest resolution)・blind spot(passage of the optic nerve・no photoreceptor cells).
Structure of the ear and reception of sound・balance: outer ear(collection of sound waves)→eardrum(reception of vibrations)→three middle-ear ossicles(malleus・incus・stapes, amplification of vibrations)→inner-ear cochlea(hair cells in the organ of Corti receive sound) and vestibule・semicircular canals(balance・sense of rotation)→auditory nerve(to the auditory cortex of the cerebrum).
When looking at a nearby object, how does the lens change? Also, what is the condition in which this accommodation becomes impossible called?
Answer: When looking at a nearby object, the ciliary muscle contracts, relaxing the suspensory ligaments. The lens becomes thicker, increasing its refractive power, and focuses on the nearby object. The condition in which the elasticity of the lens is lost with age or other causes, so that the lens cannot become sufficiently thick even when the ciliary muscle contracts, is called presbyopia.
- Change in lens thickness=accommodation for near and far vision by the ciliary muscle
- Cones=bright conditions・color vision(3 types of opsin), rods=dark conditions・black and white(rhodopsin)
- Macula(fovea)=location of the highest resolution
- Blind spot=optic-nerve passage・no photoreceptor cells
- Ossicles(malleus・incus・stapes)=amplify sound vibrations
- Hair cells in the organ of Corti of the cochlea=receive sound
- Vestibule・semicircular canals=balance・sense of rotation
Points to Note
① When looking far away: ciliary muscle relaxes→suspensory ligaments become taut→lens becomes thinner. When looking nearby: ciliary muscle contracts→suspensory ligaments relax→lens becomes thicker. ② Cones have three types of color-receptive proteins(opsins)(red・green・blue). ③ The blind spot is normally unnoticed because the brain fills in the missing information.
Practice
- What are the photoreceptor cells in the retina that distinguish colors in bright conditions?
- State the name of the cells in the cochlea of the inner ear that receive sound stimuli.
- State all the structures in the inner ear that receive the senses of balance・rotation.