UNIT 5: Nervous System Senses

Somatic Senses Somatic senses are associated with receptors in the skin, muscles, joints, and viscera (organs of the body) Include senses of touch, pressure, temperature, & pain

EXAMPLES ONLY: FYI Type of stimulus Name of the nerve receptor Cold Krause’s end bulbs Warmth Ruffini’s end organ Touch Meissner’s corpuscle Deep pressure Pacinian corpuscle Pain (free nerve ending)(no special name) Encapsulated receptors

Receptors may also exhibit a characteristic known as adaptation Means that the frequency of the receptor potential decreases over time in response to a continuous stimulus Axon sends fewer impulses, therefore the intensity of the sensation decreases Ex. Feeling your clothes on your skin

Olfaction (Smell) and Gustation (Taste) Our senses of smell and taste are closely related Both play a role in food selection because we smell food at the same time we taste it Receptors for both smell and taste are chemoreceptors Sense chemicals that dissolve in fluids

Sense of Taste (Gustation) Taste buds are the sense organs that respond to gustatory stimuli Taste buds are located on small elevated projections on the tongue called papillae About 10,000 on your tongue, 1,000 on the roof of mouth

Each taste bud contains specialized gustatory cells Tiny cilia-like gustatory hairs extend from each gustatory cell into an opening called a taste pore Taste occurs when the gustatory hairs (chemoreceptors) are stimulated by chemicals in the saliva

Taste buds will respond to chemicals for sweet, sour, salty, bitter, and umami (MSG) All taste buds will respond to each chemical to some degree, but respond most effectively to one of the four The tastes we perceive are from a mixture of the four and our sense of smell Our taste buds may also sense a 6th taste: metallic, alkaline

Sense of Smell (Olfaction) Olfactory receptors are also chemoreceptors Olfactory cells have cilia extending into nasal mucosa Lines nasal cavity and septum Smell occurs when enough odorant molecules stimulate a receptor and trigger an action potential

We have over 400 types of olfactory receptors which sense different odorant molecules With a few hundred types of olfactory receptors we are also able to sense thousands of smells Odorant molecules will bind in different patterns to receptors which the brain interprets as different smells

More Smell Info The olfactory receptors are located high in the nasal cavity so a person may have to sniff forcefully to smell light odors We also will “adapt” to smells Smells may seem to become less intense Video link: 3 min, is shows smell; 7.5 min. in shows taste

Sense of Hearing: The Ear The ear has two sensory functions Sense of Hearing and Balance Structure of the Ear The ear is divided into three parts: the external ear, the middle ear, and the inner ear

External Ear Consists of three parts Auricle (pinna)- flap on the side of the head External Auditory Meatus- ear canal, which leads from the auricle into the ear canal Modified sweat glands secrete cerumen (ear wax) Tympanic Membrane (eardrum)- stretches across the inner end of the auditory canal, separating it from the middle ear

Middle Ear (Tympanic Cavity) Auditory Ossicles- Malleus, incus, stapes 3 very small bones named for their shape (hammer, anvil, stirrup); amplify sound Several openings into the inner ear responsible for passing sound vibrations Ex: Oval Window, opening into the auditory (Eustachian) tube

Auditory (Eustachian) Tube- composed partly of bone and partly of cartilage Extends from the middle ear cavity into the throat Helps to equalize pressure between the middle and outer ear and prevents membrane rupture; occurs when you yawn or swallow

Has structures that help to produce both hearing and balance Inner Ear Has structures that help to produce both hearing and balance cochlea (hearing), vestibule (balance), semicircular canals (balance)

Sense of Hearing Sound occurs from vibrations that travel through the ear and move fluid in the cochlea cochlea means “snail” Fluid then stimulates hair cells in the Organ of Corti Organ of Corti- contains the hearing receptors attached to hair cells

Hearing Test Hearing Test 2

Sound transduction animation Pathway of Sound Waves Sound waves enter outer ear & vibrate tympanic membrane this causes the malleus to move the incus  the incus moves the stapes  this bone sitting in the oval window causes fluid in the cochlea to move  the fluid moves the basilar membrane which stimulates the hair cells of the Organ of Corti Sound transduction animation

Sense of Balance or Equilibrium This sense is really two senses using two different sense organs within the ear Vestibule (static) and Semicircular Canals (dynamic)

Vestibule: STATIC EQUILIBRIUM (FYI)

Semicircular Canals: DYNAMIC EQUILIBRIUM (FYI)

Vision: The eye is the sense organ for vision and converts light into electrical impulses

Structure of the Eye Approximately 5/6 of the eye lies within the bony protection of the orbit, leaving only the small anterior surface exposed 3 layers of tissues make up the eyeball: sclera, choroid, and the retina Outermost layer: Sclera becomes the cornea in front Middle layer: Choroid becomes the iris in front

Retina- incomplete innermost layer of the eyeball Has no anterior portion Optic disk: “blind spot” Retina also contains photoreceptor neurons: rods and cones More rods than cones Cones are densely packed in the fovea centralis No rods in the fovea

The Process of Seeing For vision to occur, an image is focused on the retina to stimulate rods and cones, and the resulting nerve impulses must be conducted to the visual areas in the cerebral cortex to be interpreted Animation!

Light bends in eye fluid Click picture for animation Light bends in eye fluid Lens actively bends light to focus an image on the retina

The Role of Photopigments Both rods and cones contain photopigments, which are light-sensitive compounds In the presence of lights, photopigments undergo structural changes which trigger an impulse (action potential) for the brain to interpret Rods: much more sensitive to light  help you see when there is less light Cones: detect color

ROD PHOTOPIGMENTS: RHODOPSIN retinol + opsin protein

Vitamin A is necessary to make photopigments in rod cells

GLASSES

Labels: Sclera/cornea, choroid/iris, retina Lens Aqueous humor Vitreous humor Pupil Blind spot Optic nerve Fovea

Other cool other things about the eye: Pupil dilation/constriction Function of aqueous humor “floaters” going into dark theatre eyes need to adjust (bleaching)