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Chapter 12 Notes
1. Types of Sensory Receptors:
thermo, photo, chemo, pain and mechanoreceptors
Types of mechanoreceptors (respond to mechanical forces)
Proprioceptors: sense changes in tension and length of muscles and
tendons; example, stretch receptors
Stretch receptors: in lungs, muscles, tendons
Golgi tendon: in tendons close to muscles; detect changes in
muscle tension; maintains posture;
prevents muscle from being pulled from the insertion (can inhibit
muscle contraction)
Muscle spindles: in skeletal muscles near tendons; detect changes
in muscle length; maintain a desired location of a limb;
(can cause contraction of a muscle when muscle has lengthened)
2. Sensations
A sensation is when the brain becomes aware of the sensory impulse.
Projection: process in which the brain projects the sensation back to the apparent
source.
Sensory adaptation: the ability to ignore unimportant stimuli
(Olfactory and taste receptors adapt quickly; pain receptors do not.)
3. Touch and Pressure Senses
3 kinds of touch and pressure receptors areas follows:
Lamellated (Pacinian) corpuscles; in subcutaneous tissue, ligaments and
tendons; detect heavy pressure and vibrations
Meissner’s corpuscles: in hairless part of skin and lips; detect fine touch
Free nerve endings: in epithelial tissue; responsible for sensation of itch
Fullness after eating a meal is due to both lamellated corpuscles and free nerve
endings.
4. Pain Nerve Pathways
2 main types of pain fibers:
Acute: thin, myelinated; rapid conduction (up to 30 m/sec)
Chronic: thin and unmyelinated; conduct impulses slowly (up to 2 m/sec)
Awareness of pain results when pain impulses reach the thalamus.
Referred pain: pain that seems to come from another pat of the body because
different pain impulses are conducted along the same nerve pathway
See page 446. A person having a heart attack may experience pain in the medial
part of the left upper limb and left shoulder.
SPECIAL SENSES
Smell:
Odorant molecules reach the olfactory receptors in the nasal cavity where
they bind to receptor cells. The nerve impulses travel along the olfactory
nerve and synapse with neurons in the olfactory bulbs and then travel
along the olfactory tracts to the limbic system of the brain, deep within the
temporal lobes.
Taste:
Papillae are tiny elevations of the tongue that are associated with taste
buds.
Taste cells act as receptors.
Taste hairs are microvilli that protrude from the taste cells.
Taste cells function for 1 to 3 days and are replaced.
70-85% of flavor comes from the sense of smell.
The 3 cranial nerves that carry taste sensations are facial (VII),
glossopharyngeal (IX), and vagus (X).
Cranial nerves conduct taste sensations to the medulla oblongata and then
the thalamus.
The gustatory cortex is located within the parietal lobe of the cerebrum.
Hearing:
Outer ear—pinna or auricle
Bones of middle ear: malleus, incus, stapes
Muscles of middle ear: stapedius and tensor tympani
Oval window—opening in wall of tympanic cavity
Organ of Corti—upper surface of basilar membrane; contains 16,000
hearing receptor cells
The tectorial membrane is like a roof over the receptor cells.
Different frequencies move different parts of the basilar membrane.
A particular sound frequency causes hairs of receptor cells to bend.
Impulses travel to the medulla first; then through midbrain to the
thalamus; and then to the temporal lobes of the cerebrum where they are
interpreted.
Auditory tube—eustachian tube; connects middle ear to throat
Labyrinth of inner ear: cochlea, semicircular canals, vestibule (between
cochlea and semicircular canals)
The semicircular canals contain the ampulla, crista ampullaris, and
cupula
The cerebellum interprets the impulses from the semicircular canals.
Sight:
Outer tunic: sclera and cornea
Middle tunic:
choroid coat—contains blood vessels and pigment
ciliary body—made of ciliary muscles and processes
When ciliary muscles relax, suspensory ligaments become taut and the
lens becomes thin. When ciliary muscles relax, suspensory ligaments
become relaxed, and the lens becomes thick.
iris—contains circular and radial muscles
Inner tunic:
retina—contains special receptor cells called rods and cones
Rods are more sensitive to light and provide vision in dim light.
Located on the retina—
macula lutea: yellowish; in the center
fovea centralis: depression in the center of the macula lutea where
sharpest vision is produced
optic disc: where nerve fibers leave the eye and become parts of
the optic nerve
The image is upside down and reversed on the retina.
Lacrimal refers to tears.
What are cataracts? Lens or its capsule becomes cloudy
What are floaters? Crystals in the vitreous humor casting shadows on the
retina
What is glaucoma? Too much aqueous humor
The lobe of the brain where visual impulses are interpreted is the
occipital.
Stereoscopic vision depends on vision with 2 eyes. It allows us to
perceive distance, depth, height, and width.
A convex lens converges light rays.
A concave lens diverges light rays.
If farsighted, corrected by convex lens.
If nearsighted, corrected by concave lens.