Chapter 9 - The Sensory System

What receptors would the brain send signals to when seeing and smelling a flower?

visual and olfactory receptors

sensory receptor(s) categories: based on stimuli

• mechanoreceptors

• thermoreceptors

• pain receptors

• chemoreceptors

• photoreceptors

Mechanoreceptors =

changes in pressure or body movement (also in the inner ear)

thermoreceptors =

changes in external/internal temperature

pain receptors =

damage or oxygen deprivation to the tissues

chemoreceptors =

changes in the chemical concentration of substances (tastebuds, receptors in the nose)

photoreceptors =

stimulated by light energy (only in the eye)

process of sensory receptors

receptor potentials begin with stimulus → action potential in sensory neuron → to brain → brain integrates data from various sensory receptors in order to perceive whatever caused the stimulation

general sensory receptors can be categorized into three types:

proprioceptors, cutaneous receptors, and pain receptors

what are proprioceptors?

mechanoreceptors involved in reflex actions that maintain muscle tone (the body’s equilibrium and posture)

what are the two forms of proprioceptors?

muscle spindles and golgi tendon organs

muscle spindles?

proprioceptor that detects how far a muscle or tendon can stretch

golgi tendon organs?

proprioceptor that senses changes in the muscle tension

what is the role of proprioceptors in reflex actions?

the muscle is prevented from contracting too forcefully, which could possibly injure both muscle and tendon

What are cutaneous receptors?

sensory receptors that make skin sensitive to touch, pressure, pain, and temperature

where are cutaneous receptors found in the skin?

deepest layer of epidermis and the entire dermis layer

pain receptors are also called?

nociceptors

how do visceral nociceptors react in response to a heart attack?

they create crushing pain when blood supply to the heart is reduced

what is referred pain?

pain perceived as having come from a different area other than it’s actual origin

why does referred pain occur?

becasue the somatic pain nociceptors travel in the same spinal cord pathway as the internal visceral nociceptors; brain cannot distinguish between the two

what is a receptor for fine touch?

Meissner corpuscles

senses of taste and smell use what kind of receptors?

chemoreceptors

where are the sensory receptors located for sense of taste?

taste buds

what are the 5 primary types of taste?

sweet, sour, salty, bitter, and umami (savory)

how the brain receives taste information

taste bud opens at pore → microvilli project through taste pore → causes brain to distinguish between type of taste → nerve signals are generated and sent to the brain to interpret them as tastes

What are olfactory cells and where are the located?

located high in the roof of the nasal cavity - modified neurons that bear receptor proteins for odor molecules (smell)

How the brain receives odor information

olfactory bulb → olfactory tract → cerebral cortex (olfactory area) of temporal lobe

what is a uncinate fit?

olfactory hallucination in which the brain tricks someone into smelling odors that have no cause (usually unpleasant) - could be a cause of epilepsy

how do senses of taste and smell work together?

directly linked to the limbic system, which explains why these senses are closely linked to emotions and memories

which taste buds would have to be most sensitive in order to enable someone to taste a poison and reject it?

bitter taste receptors

accessory organs of the eye include:

1. the eyebrows, eyelids, and eyelashes

2. lacrimal apparatus (produces tears)

3. extrinsic muscles that move the eye

function of eyebrows

shade the eyes from the sun and prevent perspiration or debris on the forehead from falling into the eye

function of eyelids/eyelashes

continuation of skin, can trap out debris from entering the eyes. sebaceous glands in each to lubricate the eye

inflammation of the sebaceous gland?

sty

what is conjunctiva?

mucous membrane that lines the inner surface of eyelids and continues over the surface of the eyeball EXCEPT over the cornea

what is a lacrimal apparatus?

consists of the lacrimal gland and sac with its ducts (produces tears)

what are extrinsic muscles?

muscle that anchors and moves the eye; originates from the bony orbit and inserts by tendons to the outer layer of the eyeball

first pair of extrinsic muscles:

Superior rectus - rolls eye upward

inferior rectus - rolls eye downward

second pair of extrinsic muscles:

lateral rectus - turns eye outward, away from midline

medial rectus - turns eye inward, toward midline

third pair of extrinsic muscles:

superior oblique - rotates eye counterclockwise

inferior oblique - rotates eye clockwise

Oculomotor (CN III)

supplies the superior, inferior, and medial rectus muscles as well as the inferior oblique muscle

trochlear (CN IV)

directs the superior oblique muscle

abducens (CN VI)

innervates the lateral rectus muscle

cranial nerves and their motor units

smallest in the body; a single motor axon serves only about 10 muscle fibers allowing eyeball movements to be very precise

A&P of the eye

• elongated sphere about 2.5 cm in diameter

• has 3 layers/coats (sclera, choroid, retina)

• only retina contains photoreceptors for light energy

sclera

protects and supports the eyeball; tough outermost connective tissue layer

cornea

refracts (blends) light rays

choroid

absorbs stray light; blood vessel layer

ciliary body

holds lens in place

ciliary muscle

changes the shape of the lens for near/far vision (accommodation)

iris

regulates entrance of light into retina

pupil

admits light into retina; opening in iris

rods

receptors for black and white, dim-light vision; peripheral vision

cones

receptors for color vision; bright-light vision

fovea centralis

makes acute vision possible; largest concentration of cone cells

optic nerve

transmits visual signals to brain

lens

refracts (blends) and focuses light rays

suspensory ligaments

transmits light rays; supports anterior compartment

vitreous humor

transmits light rays; supports posterior compartment

accommodation in the eye

the lens of the eye must change shape as you view distant and then near objects

what happens when a person’s eyeball is too long or short?

may need corrective lenses to focus the image on retina

when does a lens usually start to degrade?

after age of 40; elasticity becomes less able to accommodate

function of photoreceptors?

convert light into electrical signals, enabling vision (using cones and rods)

function of the retina

contains 3 layers of neurons

• deepest = rod and cone cells

• middle= bipolar cells

• inner= ganglion cells

retina has

• 150 million rod cells

• 6 million cone cells

• 1 million ganglion cells

what is a blind spot in the eye?

area where the optic nerve passes through the retina and where vision is not possible due to the lack of rod and cone cells

process of the retina to the visual cortex

retina → optic nerve → optic chiasma → optic tracts → visual area of the brain

what is a cataract?

opaqueness of the lens, making it incapable of transmitting light

what is glaucoma?

increasing loss of field of vision, caused by blockage of the ducts that drain the aqueous humor, creating pressure buildup and nerve damage

what is macular degeneration (MD)

disruption of the macula lutea (central part of the retina) causing blurred vision

what is diabetic retinopathy?

noninflammatory retinal disorder caused by chronic, uncontrolled diabetes; can cause blindness

the posterior compartment of the eye is filled with _____?

vitreous humor

what are the 2 sensory functions of the ear?

hearing and equilibrium (balance)

where are the sensory receptors for hearing and balance located in the ear?

inner ear - each consisting of hair cells with stereocilia (long microvilli) that respond to pressure or body movement

What does the outer ear consist of?

pinna and external auditory canal

what is pinna?

picks up sound waves (funnel-like structure)

what is the auditory canal?

tube in the outer ear that leads to the tympanic membrane

what do the modified sweat glands in the ear do?

secrete cerumen (earwax) that helps guard the ear against the entrance of foreign materials

what does the middle ear consist of?

malleus, incus, and stapes

where does the middle ear begin?

at the tympanic membrane (eardrum)

what are ossicles?

the tiny bones in the middle ear

what is the malleus (hammer)?

conducts vibrations; first of the three ossicles - from the tympanic membrane to the oval window of the inner ear

what is the incus (anvil)?

conducts vibrations; middle of the three ossicles

what is the stapes (stirrup)?

conducts vibrations; last of the three ossicles

what does the inner ear consist of?

semicircular canals, vestibule, and cochlea

mechanoreceptors for hearing are located here:

the spiral organ (organ of corti) - within the endolymph-filled cochlear duct

What is presbyopia?

condition that occurs with age and it caused by loss of lens elasticity = defective accommodation and inability to focus sharply for near vision