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 Type of stimulus receptor  Cold  Warmth  Touch  Deep pressure  Pain (free nerve ending)(no special name)

Name of the nerve receptor Krause’s end bulbs Ruffini’s end organ Meissner’s corpuscle Pacinian corpuscle

Receptors may also exhibit a characteristic known as adaptation •Means that the ____________________________________________ 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 Sense of Taste (Gustation) & Smell (Olfaction)  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 ______________________________ – ____________________________________________________________ TASTE: • Taste buds are the sense organs that respond to gustatory stimuli •

Chemoreceptors that respond to chemicals broken down from food in the saliva

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Taste buds are small elevated projections on the tongue called ________________ – About__________________________________________

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Each taste bud contains specialized gustatory cells – _____________________________________ extend from each gustatory cell into an opening called a ______________________

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Taste occurs when the ____________________________________________ in the saliva

Taste buds will respond to ________________________________________________ – 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 _______________________ ____________________________________________

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Our taste buds may also sense a 5th taste: metallic, alkaline, umami (MSG)

SMELL: •Olfactory receptors are also ____________________________________ • Olfactory cells have cilia extending into nasal mucosa -Lines nasal cavity and septum • Smell occurs when enough _______________________________________________ and _____________________________________________________ •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 ___________________________________ 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

Sense of Hearing: The Ear •The ear has two sensory functions –Sense of _____________________ and ______________________ –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 1. _______________________ (pina)- flap on the side of the head 2. _________________________________- ear canal, which leads from the auricle into the ear canal •Modified sweat glands secrete cerumen (ear wax) 3. _________________________________ (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 (___________________________________) –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 ______________________________ between the middle and outer ear and prevents membrane rupture; occurs when you yawn or swallow

Inner Ear •Complex system of communicating chambers & tubes •Has structures that help to produce both hearing and balance –____________________ (hearing), ____________________ (balance), ____________ _____________________ (balance)

Sense of Hearing • Sound occurs from ______________________________________________________ ____________________________________________________________________  cochlea means “snail”  Fluid then stimulates hair cells in the Organ of Corti  Organ of Corti- contains the ____________________________________

Pathway of Sound Waves Sound waves enter outer ear & vibrate _______________________________ this causes the _____________to move the _____________ the incus moves the _____________ this bone sitting in the oval window ____________________________________to move  the fluid moves the basilar membrane which _________________________________________of the Organ of Corti

Sense of Balance or Equilibrium •This sense is really two senses using two different sense organs within the ear –Vestibule (static) FYI  Sense the position of the head; maintains stability & posture when the head and body are still •

–Semicircular Canals (dynamic) FYI  When the head or body suddenly move or rotate; Detect motion & aid in maintaining balance

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: _____________, _____________, and the _____________

 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: _____________________________ –Retina also contains ____________________________________: 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 ________________________________________________________ __________________________, and the resulting nerve impulses must be conducted to the visual areas in the cerebral cortex to be interpreted • 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 ________________________, 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: _____________________________  help you see when there is less light •Cones: ________________________ • Vitamin A is necessary to make photopigments in eye cells (during embryonic development)