The Sensory SystemsPart of Chapter 41 and 42

The Brain- The bodies main processing center- Three major parts

- The cerebrum- The cerebellum- The brain stem

- The Cerebrum- Largest part of the brain- Learning, memory, perception, intellectual functions- Divided into right and left hemispheres- Communicate via the corpus callosum- In generally the right controls the left side of the body and visa

versa.

- most sensory and motor processing occurs in the cerebral cortex, which is the outer most layer.

Cerebellum- Located at the posterior (or back/base) of the brain- Regulates balance, posture, and movementBrain Stem- Base of the brain, a stalk like “stem”- Leads down to the spinal chord- Made up of the midbrain, the pons, and the medulla oblongata- Relay information throughout the CNS- Important in homeostasis (ie, heart rate, body temp, sleep, and

breathing)

Thalamus and hypothalamus- Thalamus

- Site for sensory processing- Relays info to the appropriate areas of the cerebral

cortex- Hypothalamus

- With the MO, regulate vital homeostatic functions like breathing a heart rate

- Also regulates feelings of hunger and thirst- Regulates secretion of hormones

Sensory receptors- specialized neurons that detect stimuli and then convert to electrical signals, that can be interpreted by the brain.

- Types of receptors:- Thermoreceptors: temperature change, in skin- Pain: tissue damage, all tissue (except the brain)- Mechanoreceptors, movement, skin, ears,

muscles- Photoreceptors, light, eyes- Chemoreceptors, chemical, tongue, nose

Processing sensory information- Sensory info is directed to 4 general areas or lobes

- Occipital- Mostly visual processing

- Parietal- Your surroundings, spelling, etc…

- Temporal- Memory and understanding (languages)

- Frontal- Executive functions, planning, problem solving

The eyes- We have great visual acuity.

- Retina: lining on the back inner surface that consists of photoreceptors and neurons.- Two types of receptors, rods (respond to dim light)

and cones (respond to bright light and enable color vision)

- Optic Nerve: exits through the back of eye, runs along base of brain to the thalamus, then relays to OL for processing

The Ears- Your ears convert the energy of sound waves to electrical signals

that can be interpreted by your brain.- Eardrum, also called the tympanic membrane, receives this energy

causing it to vibrate.- 3 small bones behind the eardrum (the middle ear) called the

hammer, anvil, and stirrup, transfer the vibrations to a fluid filled chamber in the inner ear called the cochlea.

- Cochlea is coiled like a snail, with mechanoreceptors called hair cells.

- Different waves (frequencies) cause different parts to vibrate, stimulating different hairs, which generate nerve impulses which travel to the brain stem (via the auditory nerve) where the thalamus relays to the temporal lobe where it is processed.

Semicircular canals: fluid filled chambers in the inner ear that contain hairs, which help you to maintain equilibrium.- Clusters of these hair cells respond to head position

with respect to gravity.- Based on head movement and speed of movement,

signals are sent to the brain so that you can adjust.

Chemical senses- The surface of the tongue contains 2000-5000 taste buds- Each is a cluster of 50-100 taste cells (chemoreceptors) that detect at least

four basic chemical substances.- Sweet (sugars), acids (sour), alkaloids (bitter), and salts (salty)- Each is sensitive to all, but generally most sensitive to just one- Taste cells generate electrical signals that are interpreted by the brain.

- Olfactory receptors: detect odors, located in the roof of the nasal passage.- Chemicals in the air stimulate these, which generate electrical signals

that are interpreted by the brain.- Your sense of smell affects your enjoyment of food.- Hence the holding your nose to eat something that tastes bad…not so

much a legend. When you are sick with a cold and stuffed up, it is much more affective at hiding the taste of food.