SENSES Sensory Receptors - detect environmental changes and trigger nerve impulses - somatic senses (touch, pressure, temp, pain) - special senses (smell, taste, vision, equilibrium)

Receptors and Sensations Sensation = feeling that occurs when a brain interprets a sensory impulse Projection = process where the cerebral cortex causes a feeling to stem from a source (eyes, ears) Sensory adaptation = sensory receptors stop sending signals when they are repeatedly stimulated

Somatic Senses 1. Sensory Nerve Fibers - epithelial tissue, pain and pressure 2. Meissner's corpuscles - hairless areas of skin (lips, fingertips) 3. Pacinian corpuscles - deep pressure (tendons, joints) Temperature Senses (warm and cold receptors)

Sense of Pain Visceral Pain - occurs in visceral tissues such as heart, lungs, intestine Referred pain - feels as though it is coming from a different part (heart pain may be felt as pain in arm or shoulder) Acute Pain - originates from skin, usually stops when stimulus stops (needle prick) Chronic Pain - dull aching sensation

Regulation of Pain Inhibitors of Pain (natural brain chemicals can be mimicked by drugs such as morphine) Enkephalins Serotonin Endorphins

Sense of Smell (Olfactory)

Sense of Taste (Gustatory) Sweet Sour Bitter Salty

Sense of Hearing External Ear Auricle (pinna) - outer ear External Auditory Meatus

Middle Ear (tympanic cavity) Eardrum (tympanum) Auditory Ossicles - malleus, incus, stapes - transmit vibrations and amplify the signal Auditory Tube (eustachian tube) - connects the middle ear to the throat - helps maintain air pressure

Inner Ear Labyrinth - communicating chambers and tubes Osseous Labyrinth and Membranous Labyrinth Perilymph and Endolymph (fluids within the labyrinth) Semicircular Canals - sense of equilibrium Cochlea - sense or hearing Organ of Corti - contains hearing receptors, hair cells detect vibrations

Inner Ear: Cochlea Inside the cochlea are special neurons called HAIR CELLS The stapes is attached to the OVAL WINDOW, and vibrations cause the perilymph to vibrate; the hair cells here transmit this vibration. Therefore the HAIR CELLS in this region are receptors for HEARING.

Steps in Hearing 1. Sound waves enter external auditory meatus 2. Eardrum vibrates 3. Auditory ossicles (malleus, incus, stapes) amplify vibrations 4. Stapes hits oval window and transmits vibrations to cochlea

5. Organs of corti contain receptor cells (hair cells) that deform from vibrations 6. Impulses sent to the vestibulocochlear nerve 7. Auditory cortex of the temporal lobe interprets sensory impulses 8. (Round window dissipates vibrations within the cochlea)

Sense of Equilibrium Static Equilibrium - sense the position of the head, maintain stability and posture Dynamic Equilibrium (semicircular canals) - balance the head during sudden movement Cerebellum - interprets impulses from the semicircular canals and maintains overall balance and stability

The eye is in the orbit of the skull for protection. Within the orbit are 6 extrinsic eye muscles, which move the eye. There are 4 cranial nerves: Optic (II), Occulomotor (III), Trochlear (IV), and Abducens (VI). People of Asian descent have an EPICANTHIC FOLD in the upper eyelid; no functional difference. The Eye

Visual Accessory Organs Eyelid Conjuctiva Lacrimal Gland Extrinsic Muscles

Eyelid Covers and protects the eye, thin skin Skin will not protect you from intense radiation, that’s why we use special goggles in a tanning bed

CONJUNCTIVA is like a covering around the eye and under the eyelids. PINK EYE (layman’s term), known as CONJUNCTIVITIS (from bacteria, very contagious). Conjunctiva

LACRIMAL GLANDS are the largest set. They are on the superior lateral eyelid and they produce tears, which drain into the nasal cavity via the LACRIMAL DUCT. The function is to moisten and lubricate the eye surface, and it has enzymes to kill bacteria (which thrive in warm, moist conditions). Glands

Outer Tunic Cornea - transparent, focuses light rays Sclera – continuation of cornea, going toward the back of the eye (white of the eye) Optic Nerve – exits at the optic disk and transmits visual information from the eye to the brain.

Middle Tunic Choroid Coat – contains blood vessels Ciliary Body – holds the lens in place Lens – focusing Iris – colored portion of the eye Aqueous humor – liquid surrounding the lens Pupil – opening for light to enter

Inner Tunic Retina - visual receptor cells Fovea Centralis - region of the sharpest vision (aka, macula) Optic Disc – where nerve fibers leave the eye, creating the blind spot Vitreous Humor – supports internal parts, fluid

Retina The retina is on top of the choroid layer. The retina is made up of PHOTORECEPTORS, which are sensors for light.

Light Refraction Light bends around objects Images viewed by the eye are upside down

Clouding of the lens leads to a clinical condition known as CATARACTS. Treatment is to remove the lens and replace it with a plastic one (which is not flexible either). If the lens yellows, you can’t see the color blue. After surgery, can see blue again. Problems

The function is to constrict or dilate the pupil (opening) to allow light in. Therefore, it regulates the amount of light passing to the visual receptors of the eye. If there is a lot of pigment, eye is brown; a medium amount = green, small amount = blue, no pigment = pink (albino). Iris

FLOATERS are when a capillary breaks and cells break off. Floaters don’t actually move, the eye just tries to track them.

The region where the optic nerve and blood vessels goes in and out of the eye has no photoreceptors = BLIND SPOT. Hold your hands out at 45° and that’s the location of the blind spot. You can still see your hands because the other eye sees it. Close your right eye and look for your right hand and you’ll find the blind spot. Blind Spot

HYPEROPIA (far-sighted) eyes are too short MYOPIA (nearsighted) eyes are too long

ASTIGMATISM ASTIGMATISM is when the cornea has an irregular shape. Part of the field of view is out of focus. They eyeball changes shape until age 24.