Adv Biology 1-2

Sensory Receptors Sensory receptors detect stimuli. Mechanoreceptor-detects mechanical energy. Sound, pressure Photoreceptors-detects light.

The Eye The outer layer of the eye is a tough tissue called the sclera. Cornea-layer of tissue in front of the pupil. Iris-colored part of the eye. Light enters through the pupil (opening in the iris). Behind the pupil is the lens (focuses light to create an image). Vitreous humor-fluid in the eye, helps maintain the shape of the eye.

The Eye cont’d The back of the eye is covered in photoreceptors. Fovea-area with the most photoreceptors. Rods-extremely sensitive to light, detect shades of grey. Cones-sensitive to bright light, detect colors. Blind spot-area of the fovea that has no photoreceptors. Where the optic nerve meets the eye.

The Eye cont’d The lens focuses light on the back of the eye to produce an image. For objects close up: The muscles around the lens contract. Ligaments loosen and the lens gets thicker. Hyperopia (farsighted)-trouble focusing on nearby objects. Light rays focus behind the retina. Eye is too short or lens cannot be made thick enough.

The Eye cont’d For objects far away: The muscles around the lens relax. Ligaments tighten, lens stretches and gets thinner. Myopia (nearsighted)-difficulty focusing on far away objects. Light rays focus in front of the retina. Eye is too long or the cornea is too steep. Astigmatism-difficulty focusing light rays on the retina. Lens or cornea is misshapen.

The Eye cont’d The optic nerve relays impulses from the rods and cones directly to the brain. Signals are processed by the occipital lobe of the brain. In the back of the brain, part of the cerebral cortex (handles motor skills, sensory reception, language, math, imagination and personality).

The Ear The outer ear (pinna) funnels sound waves to the auditory canal. Opening in the ear, leads to inner ear. The middle ear is separated from the auditory canal by the tympanic membrane (eardrum).

The Ear cont’d In the middle ear, sound waves vibrate the tympanic membrane. The sound wave is passed through a series of small bones, the hammer, anvil and stirrup.

The Ear cont’d The inner ear is made of fluid-filled channels in the bones of the skull. Vibrations from the stirrup are passed to the cochlea (a coiled tube). Fluid in the cochlea vibrates, stimulating hair cells. Hair cell-mechanoreceptors with cilia; when the cilia move, neurotransmitters are released. Hair cells create an impulse.

The Ear cont’d The impulse travels along the auditory nerve to the temporal lobe. Located along the side of the brain, also a part of the cerebral cortex. Interprets signals from the cochlea as sounds.

The Ear cont’d Next to the cochlea are three semicircular canals, which detect body position and movement. One canal is in the X plane, one in the Y plane, the third in the Z plane.

The Ear cont’d Fluid in the semicircular canals sloshes around as the head moves. Hair cells send signals along the vestibular nerve to the brain. Brain interprets the signals and determines position.