hole’s essentials of human anatomy &...

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Chapter 10

Hole’s Essentials of HumanAnatomy & Physiology

David ShierJackie ButlerRicki Lewis

Created by Dr. Melissa Eisenhauer Head Athletic Trainer/Assistant Professor

Trevecca Nazarene UniversityAmended by John Crocker

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Chapter 10

Somatic and Special Senses

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Introduction A. Sensory receptors detect changes in the environmentB. Stimulate neurons to send nerve impulses to the brain.C. Sensations are formed based on the sensory input

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Receptors and Sensations A. Each receptor is more sensitive to a specific kind of

environmental change and less sensitive to othersB. Types of Receptors

1. Five general types:a) Chemoreceptors detect changes in chemical concentrationb) Pain receptors detect tissue damage c) Thermoreceptors detect temperature differences d) Mechanoreceptors detect changes in pressure or

movement e) Photoreceptors

1) In the eyes 2) Detect light energy

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A. Sensations 1. Sensations are feelings that occur when the brain

interprets sensory impulses.2. Projection sends the sensation from the CNS to its

point of origina) Simultaneous to sensation formationb) Allows pinpointing of area of stimulation

B. Sensory Adaptation1. When stimuli are constant sensory impulses are sent

at rates decreasing to zero2. Prevents sensory overload from static ‘background’

stimuli

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Somatic SensesA. Receptors associated with the skin, muscles, joints, and

viscera make up the somatic senses.B. Touch and Pressure Senses

1. Free nerve endings a) Sensory nerve fibers in the epithelial tissues b) Associated with touch and pressure

2. Meissner's corpuscles (Tactile corpuscles) a) Two or more nerve fibers surrounded by flattened

connective tissue sheathsb) Abundant in hairless areas that are very sensitive to touch

3. Pacinian corpuscles 1. large structures of connective tissue and cells resembling

an onion2. function to detect deep pressure

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A. Temperature Senses 1. Warm receptors

a) Work best within a range of temperaturesb) Adapt quicklyc) Temperatures near 45o C stimulate pain receptors

2. Cold receptors a) Work best within a range of temperaturesb) Adapt quicklyc) Temperatures below 10o C stimulate pain receptors and

produce a freezing sensation

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A. Sense of Pain 1. Pain receptors consist of free nerve endings that are

stimulated when tissues are damaged2. Little or no adaptation3. Many stimuli affect pain receptors such as chemicals

and oxygen deprivation4. Visceral pain receptors are the only receptors in the

viscera that produce sensationsa) Respond differently than surface tissuesb) Referred pain can occur because of the common nerve

pathways leading from skin and internal organs

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1. Pain Nerve Fibersa) Acute pain fibers

1) Thin, myelinated fibers 2) Carry impulses rapidly to CNS3) Cease when the stimulus stops.

b) Chronic pain fibers 1) Thin, unmyelinated fibers 2) Conduct impulses slowly 3) Continue sending impulses after the stimulus stops

c) Impulses processed in the gray matter of the dorsal horn of the spinal cord

d) Impulses are conducted to the 1) Thalamus2) Hypothalamus3) cerebral cortex

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1. Regulation of Pain Impulses a) Awareness of pain begins with the impulse reaching the

thalamusb) The cerebral cortex judges the intensity and location of

the pain and determines emotional and motor responsec) Areas of gray matter in the brain stem regulate the flow of

pain impulses from the spinal cord d) The brain stem can trigger the release of enkephalins and

serotonin, which inhibit the release of pain impulses in the spinal cord

e) Endorphins released by the hypothalamus and pituitary provide naturally suppress pain (similar to morphine)

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Special Senses A. The special senses are associated with relatively large

and complex structures located in the headB. These include:

1. Smell2. Taste3. Hearing4. Static equilibrium5. Dynamic equilibrium6. Sight

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Sense of Smell A. Olfactory Receptors

1. Olfactory receptors are chemoreceptors2. The senses of smell and taste operate together to aid

in food selection

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A. Olfactory Organs 1. Olfactory organs

a) located in the upper nasal cavityb) olfactory receptors c) epithelial supporting cells

2. Receptor cells a) bipolar neurons b) hair-like cilia covering the dendrites project into the nasal

cavity

3. Chemicals that enter the nasal cavity must dissolve into the watery fluid surrounding the cilia to be detected

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A. Olfactory Nerve Pathways1. When olfactory receptors are stimulated, their fibers

synapse with neurons in the olfactory bulbs lying on either side of the crista galli.

2. Sensory impulses are first analyzed in the olfactory bulbs

3. Then travel along olfactory tracts to the limbic system

4. Then finally to the olfactory cortex within the temporal lobes

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A. Olfactory Stimulation 1. Scientists are uncertain of how olfactory reception

operates 2. It is thought that each odor stimulates a set of

specific protein receptors in cell membranes3. The brain interprets different receptor

combinations as an olfactory code4. Olfactory receptors adapt quickly but selectively

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Sense of TasteA. Taste buds are the organs of taste B. located within papillae of the tongue and scattered

throughout the mouth and pharynx

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A. Taste Receptors 1. Taste cells (gustatory cells)

a) Modified epithelial cells that function as receptorsb) Contain taste hairs

1) Protrude from openings called taste pores 2) Sensitive to taste

2. Chemicals must be dissolved in water (saliva) in order to be tasted

3. Taste probably involves specific membrane protein receptors that bind with specific chemicals in food

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1. Five types of taste cells:a) Sweet receptors plentiful near the tip of the tongueb) Sour receptors occurring along the lateral edges of the

tonguec) Salt receptors abundant in the tip and upper portion of

the tongued) Bitter receptors are at the back of the tonguee) Umami receptors responds to certain amino acid

derivatives such as monosodium glutamate (MSG)

2. Taste buds may be responsive to at least two taste sensations but one is likely to dominate

3. Taste receptors adapt rapidly

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A. Taste Nerve Pathways1. Taste impulses travel on the facial, glossopharyngeal,

and vagus nerves 2. To the medulla oblongata 3. Then to the gustatory cortex of the cerebrum

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Sense of HearingA. The ear has external, middle, and inner sections B. Provides the senses of hearing and equilibriumC. External Ear

1. The auricle collects sound 2. Sound travels down the external auditory meatus

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A. Middle Ear1. Begins with the tympanic membrane2. Tympanic cavity (an air-filled space) houses the

auditory ossiclesa) Malleusb) Incusc) Stapes

3. The tympanic membrane vibrates the malleus, which vibrates the incus, then the stapes

4. The stapes vibrates the fluid inside the oval window of the inner ear

5. Auditory ossicles both transmit and amplify sound waves

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Figure 10.7

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A. Auditory Tube (eustachian tube)1. Connects the middle ear to the throat 2. Helps maintain equal air pressure on both sides

of the eardrum B. Inner Ear

1. Membranous labyrinth inside osseous labyrinth2. Perilymph fills the space between the labyrinths 3. Endolymph is inside the membranous labyrinth4. The cochlea houses the organ of hearing 5. The semicircular canals function in equilibrium.

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1. Scala vestibulia) Upper compartment within the cochleab) Oval window

2. Scala tympani a) Lower compartmentb) Round window

3. Cochlear duct a) Lies between these two compartments b) Separated from the scala vestibuli by the vestibular membranec) Separated from the scala tympani by the basilar membrane

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1. The Organ of Corti a) Receptors called hair cells lie on the basilar membrane b) Hair cells extend into the endolymph of the cochlear duct

2. Tectorial membrane a) Lies above the hair cells b) Touches the tips of the stereocilia

3. Vibrations in the fluid of the inner ear a) Cause the hair cells to bend resulting in an influx of Ca2+

b) This causes the release of a neurotransmitter from vesicles c) Which stimulate the ends of nearby sensory neurons

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A. Auditory Nerve Pathways1. Nerve fibers carry impulses to the auditory cortices

of the temporal lobes where they are interpreted

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Sense of EquilibriumA. Static equilibrium

1. Maintains stability when the head and body are still2. Organs located

a) Within the vestibule (a bony chamber) of the inner earb) Inside the utricle and saccule (expansions of the

membranous labyrinth).

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1. A macula, consisting of hair cells and supporting cells, lies inside the utricle and saccule

2. Hair cells contact gelatinous material holding otoliths

3. Gravity causes the gelatin and otoliths to shift, bending hair cells generating a nerve impulse

4. Impulses travel to the brain via the vestibular branch of the vestibulocochlear nerve, indicating the position of the head

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A. Dynamic Equilibrium1. Maintains balance when the head and body suddenly

move and rotate2. The three semicircular canals

a) Detect motion of the headb) Aid in balance during sudden movementc) Canals lie at right angles to each other

3. Cristae ampullarisa) Located in the ampulla of each semicircular canalb) Hair cells extend into a dome-shaped gelatinous cupulac) Rapid turning of the head or body generates impulses as

the cupula and hair cells bend4. Propriopceptors (Mechanoreceptors) associated with

joints and changes detected by the eyes aid in maintaining equilibrium

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Sense of SightA. Visual Accessory Organs

1. The eyelid a) Protects the eye from foreign objects b) Made up of the thinnest skin of the body c) Lined with conjunctiva

2. The lacrimal apparatus a) Produces tears

1) lubricate and cleanse the eye2) contain an antibacterial enzyme

b) Two small ducts drain tears into the nasal cavity

3. The extrinsic muscles a) attach to the sclera b) move the eye in all directions

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A. Structure of the Eye 1. The eye is a fluid-filled hollow sphere with three

distinct layers, or tunics. 2. The Outer Tunic

a) Fibrousb) Transparent cornea at the front of the eyec) White sclera of the anterior eyed) The optic nerve and blood vessels pierce the sclera at the

posterior of the eye

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1. The Middle Tunica) The vascular tunic includes:

1) The choroid coat a. vascular and darkly pigmentedb. Nourishes other tissues of the eyec. Keeps the inside of the eye dark

2) The ciliary bodya. forms a ring around the front of the eye b. contains ciliary muscles and suspensory ligamentsc. hold the lens in position and change its shape

(focus)d. The ability of the lens to adjust shape to facilitate

focusing is called accommodation

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1) The iris1) a thin, smooth muscle2) has a circular set of and a radial set of muscle

fibers3) hole in its center4) adjusts the amount of light entering the pupil

2) The anterior cavity1) The anterior chamber (between the cornea and iris) 2) the posterior chamber (between the iris and vitreous

body and housing the lens)3) Filled with aqueous humor4) The aqueous humor circulates from one chamber

to the other through the pupil

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1. The Inner Tunica) Covers the back side of the eye to the ciliary bodyb) Consists of the retina which contains photoreceptorsc) In the center of the retina is the macula lutea

1) the fovea centralis in its center2) the point of sharpest vision in the retina

d) the optic disk1) Medial to the fovea centralis2) where nerve fibers leave the eye 3) a blind spot

e) The large cavity of the eye is filled with vitreous humor

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A. Light Refraction1. Light waves must bend to be focused, 2. This bending of light called refraction3. Both the cornea and lens refract light waves to

focus them on the retina 4. The two humors also refract entering light, though

to a lesser degree

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A. Visual Receptors1. Rods

a) Elongatedb) Function in dim lightc) More sensitive to lightd) Produce colorless vision

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1. Conesa) Blunt cone-shapedb) Function in bright light c) Provide sharp imagesd) Enable color visione) The fovea centralis

1) contains the highest concentration of cones 2) proportion of cones decreases with distance from

fovea centralis3) To see something in detail, a person moves the eyes

so the image falls on the fovea centralis

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A. Visual Pigments1. The light-sensitive pigment in rods is rhodopsin

a) In the presence of it light breaks down into: a) Opsin, a clear protein b) Retinal, a yellowish substance synthesized from

vitamin Ab) Decomposition of rhodopsin

a) Activates an enzyme b) The enzyme initiates changes in the rod cell

membranec) This generates a nerve impulse

c) Nerve impulses travel away from the retina and are interpreted as vision

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1. Three light-sensitive pigments in conesa) Are composed of retinal and opsin proteins

1) Erythrolabe - sensitive to red2) Clorolabe - sensitive to green3) Cyanolabe - sensitive to blue

b) The color perceived depends upon which sets of cones the light stimulates1) If all three sets are stimulated, the color is white2) If none are stimulated, the color is black

c) Decomposition and nerve impulses occur as in rods

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A. Visual Nerve Pathways1. The axons of ganglion cells leave the eyes to form

the optic nervesoptic nerves2. Fibers from the medial half of the retina cross over

in the optic chiasmaoptic chiasma3. Impulses are transmitted to the thalamus and then

to the visual cortex of the occipital lobe

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