The Nervous System & The Endocrine System: Year 8 Biology Final Exam Summary

1.4 The Senses

Touch and Related Senses
> Different sensory receptros in the body responds to touch, temperature, and pain.

1. Touch
– Human skin contains at least 7 types of sensory receptors, including several that responds to different levels of pressure.
– Stimulation of these receptors creates the sensation of touch.

2. Temperature
– Responds to heat and cold. All over the skin & hypothalamus (senses blood temperature).

3. Pain
– Found throughout the body. Many tissues also have pain receptors that respond to chemicals being released during infection or inflammation.
– The brain does not have pain receptors.

Smell and Taste
> Your sense of taste and smell involve the ability to detect chemicals.
> Sensations of taste and smell are both the result of impulses sent to the brain by chemoreceptors.
> Your sense of smell is capable of producing thousands of different sensations. What we commonly call the "taste" of food and drink is actually smell.
> The sense organs that detect taste are the taste buds – most are at the tongue, but few are found at other locations in the mouth.
> Respons to: salty, bitter, sweet, and sour.
> Recently, a fifth sensation was identified– unami (Japanese word for savory). Strongly stimulated by monosodium glutamate (MSG). Also stimulated by meat & cheese, contain the amino acid glumatate.

Hearing and Balance
> Mechanoreceptors found in parts of your ear transmit impulses at the brain. The brain translates the impulses into sound into sound and information about balance.

Hearing: vibration enter ear through the auditory canal and cause the tympanum/ ear drum to vibrate.
> Three tiny bones: hammer, anvil, stirrup, transmit these vibrations to a membrane called the oval window.
> Vibrations there create pressure waves in the fluid–filled cochlea of the inner ear.
> The cochlea is lined with tiny hair cells that are pushed back and forth by pressure waves.
> The hair cells send nerve impulses to the brain, which processes them as sounds.

Balance: In the inner ear, above your cochlea are three canals.
> The semicircular canal and two sacs behind them monitor the position of your body, especially in your head, in relation to gravity.
> Filled with fluid and lined with hair cells.
> If head changed position, the fluid would also change position, causing the hair cells to bend.
> This send impulses to the brain that enable it to determine body motion and position.

Vision
> Vision occurs when photoreceptors in the eyes transmit impulses to the brain, which translates these impulses into image.

Structure of the Eye
> Cornea: light enters through this tough transparent layer of cells.
> Aqueous humor: then through this chamber filled with fluid.
> Iris: a disk shaped structure, colored part of the eye. Tiny muscles in the iris adjust the size of the pupil to regulate the amount of light that enters the eye.
> Pupil: small opening in the middle of the iris.
> Lens: small muscles attached to it changes its shape, help to adjust focus to see near/ distant objects clearly.
> Vitreous humor: a large chamber filled with a transparent, jellylike fluid.
> Retina: inner layer of eye that contains photoreceptros (rods & cones).
> Choroid: middle layer of eye that is rich in blood vessels.
> Sclera: outer layer of the eye that mantains its shape. Serve as point of attachment for muscles that move the eye.

How You See
> The lens focuses light to the retina, the inner layer of the eye. Photoreceptors are arranged in a layer in the retina. They convert light energy into nerve impulses that are carried to the brain by the optic nerve.
> Two types of photoreceptors:
– Rods: extremely sensitive to light, but do not distinguish different colors, only black and white.
– Cornea: less sensitive than rods, but respond to different colors, producing color vision. Concentrated in the fovea, the site of sharpest vision
> Impulses assembled by complicated layer of interconnected cells leave each eye by the way of the optic nerve.
> No photoreceptors where the optic nerbe passes through the back of the eye, producing a blind spot in part of each image sent to the brain.
> During the processing of nerve impulses, the brain fills the holes of the blind spot with information.

p.s.