The Senses

 Somatic – general senses; located all over the body ◦ Pain ◦ Touch ◦ Pressure ◦ Temperature  Special – associated with one area of the body ◦ Hearing ◦ Sight ◦ Taste ◦ Equilibrium ◦ Smelling

 Chemoreceptors  Pain receptors  Thermoreceptors  Mechanoreceptors  Photoreceptors  Δ chemicals  Tissue damage  Δ temperature  Δ pressure/position  Δ light

 Sensation – Sensory receptors reach threshold and brain becomes aware of a sensory event  Perception – How your brain interprets that sensation  Projection – Cerebral cortex causes the feeling to seem to come from the affected area

 Adaptation – Ability of the nervous system to become less responsive to maintained stimulus. ◦ Do you feel your clothing on your body? ◦ Do you notice any sounds in the room?

 Pg 264  Free nerve endings  Tactile (Meissner’s) corpuscles  Lamellated (Pacinian) corpuscles

 Free nerves that respond to either warm or cold. ◦ Warm: >25 ° C (77 ° F) respond heavily >45 ° C (113 ° F) shut down Near 45 ° C = pain (burning) ◦ Cold: 10 ° C-20 ° C (50 °F -68 ° F) respond heavily <10 ° C (50 ° F) = pain (freezing) ◦ Adapt within about 1 minute of stimulation.

 Free nerve endings – stimulated by tissue damage.  Mechanoreceptors and chemoreceptors can also stimulate pain.  They’re the only type of receptors in viscera that can ilicit a sensation.  Adapt poorly.

 Nerve fibers: ◦ Acute pain fibers  Myelinated  Sharp pain  Quits when stimulation stops ◦ Chronic pain fibers  Unmyelinated  Dull, aching sensation  May continue after stimulation stops

 Awareness occurs when impulses reach the thalamus.  Cerebral cortex determines intensity, location, emotions, motor response.

 Can feel like it’s coming from a different part of the body.  Nerve pathways are similar.

 Smell –  Taste –  Hearing –  Equilibrium –  Sight -

 Both chemoreceptors.  Both must be dissolved in fluid.  Usually associated with one another because we do them at the same time.

 Receptors each respond to different smells, then stimulate an interpretation in the olfactory bulb of the brain.

 Taste buds are located within papillae.  Modified epithelial cells act as receptors.

 Taste hairs portrude from openings called taste pores.  Particles must be dissolved in fluid before they can be tasted.

 Five receptors ◦ Bitter ◦ Sweet ◦ Salty ◦ Sour ◦ Umami  Nerve impulses travel to the medulla oblongata and parietal lobe of the cerebrum.

 Accommodation – adjustment of the lens shape to focus vision ◦ Done by the ciliary muscles and suspensory ligaments.  Distance – lens is more flattened; ciliary muscles tense  Close – lens is more convex; ciliary muscles more relaxed

 Photoreceptors (rods and cones) detect light.  They are projected backward and upside- down onto the retina, then sent to the visual cortex.  The visual cortex interprets the images so they are perceived correctly.

 Perilymph  Membrane  Endolymph  Hair cells

 Hair cells bend causing a nerve impulse.  Nerve impulses travel along the auditory nerve to the auditory cortices of the temporal lobes.

 Static – when you’re still ◦ Both are detected by shifting calcium carbonate grains in the semicircular canals of the inner ear. ◦ Sends messages to the brain, which sends messages back to muscles.  Dynamic – when you’re moving ◦ Stimulates hair cells that send messages to the brain.  Mechanoreceptors and sight can aid in equilibrium.