In general, how do all sensory receptors work?
neurons are stimulated, info is sent to brain, cerebral cortex integrates info, forms perception
What is the difference between sensation and perception?
sensation - awareness of the stimuli
perception - interpreting the stimuli
How do we form perceptions?
neurons are stimulated, info is sent to brain, cerebral cortex integrates info, forms perception
What is the largest sense organ of the body?
skin
What do we mean by a threshold? Do receptors respond to only one stimulus?
- with enough stimulation the nerve fires
* receptors can respond to multiple stimuli
What are exteroceptive senses?
respond to stimuli arising outside the body
What are interoceptive senses?
respond to stimuli arising in internal viscera and blood vessels
What are proprioceptive senses?
respond to stretch in skeletal muscles, tendons, joints, ligaments, and CT coverings of bones and muscles (informs brain of one’s movement)
What do we mean when we speak of simple receptors?
- modified dendritic endings of sensory neurons
* found throughout body and monitor most types of general sensory info
Is the cerebral cortex the only place where information is processed?
no
How is information processed?
3 levels:
1) receptor level (sensory receptors)
2) circuit level (processing in ascending pathways)
3) perceptual level (processing in cortical sensory areas)
What is meant by a graded potential or receptor potential?
- graded potential: a ligand opens a ligand-gated channel in the dendrites, allowing ions to enter (or exit) the cell
- receptor (generator) potential: a type of graded potential, is the transmembrane potential difference produced by activation of a sensory receptor
What is transduction?
the conversion of a sensory stimulus from one form to another
What are generator potentials?
stationary depolarization of a receptor that occurs in response to a stimulus and is graded according to its intensity and that results in an action potential when the appropriate threshold is reached
What is sensory adaptation?
reduction in sensitivity to a stimulus after constant exposure to it
What is the difference between phasic and tonic receptors?
phasic - fast adapting (mainly to report changes)
tonic - sustained response w/ little or no adaptation
How is information processed at the perceptual level? What is frequency encoding?
information is processed in cerebral cortex // means by which the central nervous system, limited by the all-or-none properties of nerve impulse conduction, is able to convey information about varying intensity of signals
What sense organs help us feel touch and pressure? What are their receptor cells?
skin // mechanoreceptors
How do we sense different temperatures?
thermoreceptors in skin
What are the receptors for pain? What stimuli can cause pain?
nociceptors detect damage from mechanical, electrical, thermal, or chemical energy
What is substance P?
neurotransmitter involved in the synaptic transmission of pain and other nerve impulses
Do pain receptors adapt? Why is this good?
pain receptors adapt little, if at all (if adapted, protection from pain would be lost and would become useless)
What is the difference between pain threshold and pain tolerance?
all people have the same threshold (perceived pain at the same stimulus intensity), not all people have the same tolerance (how well you handle pain)
What can change a person’s pain tolerance?
age, chronic pain, cultural/psychological factors
What sensations do we get from our viscera?
pain receptors (nociceptors) are the only receptors in the viscera that produce sensations
What is referred pain?
pain that feel like it is coming from somewhere else in the body
What is phantom pain?
pain that comes from a limb that has been amputated
What are the two types of pain fibers and how do they differ?
acute pain fibers: thin, myelinated, conducts up to 30m/s, sharp/localized pain, seldom continues after stimulus stops
chronic pain fibers: thin, unmyelinated, conducts up to 2m/s, dull/aching/widespread pain, may continue after stimulus stops
Hope do ascending and descending fingers modulate pain or cause analgesia?
ascending: block pain transmission in spinal cord
descending: release norepinephrine or serotonin, which suppress pain or activate enkephalin releasing neurons
Hope does aspirin function in pain relief?
inhibits the synthesis of prostaglandins
What do muscle spindles sense? What reflexes do they cause?
sense of stretching of the muscle and cause contraction to maintain position
What do Golgi tendon organs sense? What reflexes do they cause?
sense of change in muscle tension and inhibits relaxation and prevents damage to the tendon
What do nociceptors detect?
respond to damage from mechanical, electrical, thermal, or chemical energy
What do thermoreceptors detect?
respond to changes in temperature
What do mechanorecptors detect?
respond to mechanical forces (fluid movement or pressure)
What do photoreceptors detect?
respond to light
What do chemoreceptors detect?
respond to chemical concentration of various substances
What do osmoreceptors detect?
respond to concentration of chemicals (osmotic pressure)
Which one of the types of receptors functions in the sense of taste?
chemoreceptors (same as smell)
Which one of the types of receptors functions in the sense of smell?
chemoreceptors (same as taste)
Which one of the types of receptors functions in the sense of hearing and equilibrium?
mechanoreceptors
Which one of the types of receptors functions in the sense of vision?
photoreceptors
The senses of smell and taste have nerve fibers that run through the limbic system. What effect does this have?
taste is 80% smell
Of the four types of body tissues, which type of cells form the receptors for the sense of smell? Where are these receptors located?
(bipolar neurons) olfactory epithelium is found in the superior nasal concha and nasal septum
Describe the olfactory mucosa.
located in upper region of nasal cavity, mucus protects the olfactory epithelium and allows odors to dissolve so that can be detected, contains sensory fibers (trigeminal nerve) which play a role in initiation of reflexes like sneezing
What role does the mucus play in the sense of smell? Where does it come from?
chemicals are dissolved in mucus to stimulate the receptor, epithelial supporting cells produce the mucus
How do we recognize thousands of different odors?
a combination of primary scents allow us to recognize thousands of different odors
Are olfactory receptors replaced during a person’s lifetime? Why is this unusual? How long do these receptors live?
receptors last 30-60 days (they are replaced), unusual bc they are neurons and neurons are not usually replaced
What happens to our sense of smell as we get older?
due to a gradual loss of receptors, sense of smell declines bc receptors are replaced more slowly as we age
What bony structure do the olfactory fibers pass through on their way to the olfactory bulb?
cribriform plate
How quickly does the sense of smell adapt?
olfactory cells adapt very rapidly
What can you tell me about the threshold for the sense of smell?
it is a very low threshold, especially to certain odors
What are the five primary taste sensations? Which has the lowest threshold? Why is this protective?
sweet, sour, bitter, salty, umami
bitter is lowest threshold
If we can only detect five tastes, why do foods taste so different from each other?
a combination of smell and tastes change the way we perceive tastes
Where are the receptors for taste located?
mostly on the tongue / some located on soft palate, cheeks, pharynx, epiglottis
Of the four types of tissues, which of the type of cells form the receptors for the sense of taste?
taste receptor cells = epithelial cells
Describe the structure of a taste bud. Are the gustatory receptors primary or secondary receptors?
on top of fungiform papillae, can have receptors for all primary tastes // secondary receptors
How does each of the five tastes cause depolarization of the receptors?
salty = Na+ influx (direct depolarization) sour = H+ (by opening cation channels) sweet/bitter/umami = coupled to unique G-protein gustducin
What cranial nerves transmit our sense of taste?
facial (XII) and glossopharyngeal (IX) taste buds to medulla
vagus (X) pharynx/epiglottis to medulla
What are the three main divisions of the ear?
outer, middle, inner
What structures make up the outer ear? What glands do we find here?
auricle (pinna, lobule, helix)
glands: sebaceous, ceruminous make earwax
What is the primary function of the outer ear?
auricle funnels sound to auditory canal and pass through to the eardrum
What is the structure of the tympanic membrane? What does it do?
thin, translucent CT membrane
detects sound waves, vibrates to middle ear bones
What structures make up the middle ear?
tympanic antrum, auditory tube, auditory ossicles, two muscles
Besides the eardrum and oval window, to what other structures (areas) does the middle ear connect? Why are these important?
mastoid antrum allows it to communicate with the cells of the mastoid bone
What is the function of the middle ear? Name the 3 ossicles in order.
transform sound waves into mechanical vibrations that stimulates the inner ear
(malleus, incus, stapes)
What do we call an infection of the middle ear?
(otitis media) middle ear infection
What are the muscles found in the middle ear and what is their function?
tensor tympani / stapedius muscle
function: they contract and pull the bones together to dampen loud noises (aka: tympanic reflex)
Describe the bony and membranous labyrinths of the inner ear.
bony: channels worming through the bones of the inner ear (filled with perilymph)
membranous: series of membranous sacs and ducts within the bony labyrinth and following its contours (filled with endolymph)
What are the three main divisions of the labyrinths? Which is involved in hearing?
vestibule, semicircular canals, cochlea*
*involved in hearing
What labyrinth is involved in static equilibrium? Dynamic equilibrium?
Static - vestibule
Dynamic - semicircular canals
Describe the structure of the cochlea. Where do we find perilymph? Endolymph?
snail shaped with 3 compartments: scala vestibuli/tympani/media
perilymph: scala vestibuli/tympani
endolymph: membranous labyrinth
What type of tissue makes up the receptors found in the organ of Corti?
epithelial tissue
Trace the path of sound waves from the outer ear to the cochlear branch of crucial nerve VIII and describe how transduction takes place in the organ of Corti.
canal to tympanic membrane, incus/stapes transmit vibrations to oval window, vibrations travel through perilymph to scala vestibuli to scala tympani in cochlea creating waves in fluid, basilar membrane moves causing Organ of Corti to transmit movement to tectorial membrane, outer hairs bend stimulating Organ of Corti to send message through the cochlear nerve, nerve exits auditory tube to cranial nerve VIII (vestibulocochlear nerve), message sent to brain and interpreted
Why does which way the hair cells are bent make a difference? Some fibers from each ear cross over to the opposite cerebral hemisphere. Why?
hair cells bent toward kinocilium = increases frequency of APs
hair cells bent away kinocilium = decreases frequency of APs
spatial correlation between cells in the sensory organ and specific locations in the primary auditory cortex
What is the function of the round window?
allow movement of fluid into the cochlea leading to the movement of hair cells»_space; hearing
How do we hear high sounds differently from low sounds? Soft and loud?
specific hair cells that vibrate and bend give us sense of pitch
number of hair cells that bend give us sense of loud/soft
What is the range of human hearing?
20–20,000 hertz
How do otoliths help maintain static equilibrium? Where are they located?
motions of the head cause the otoliths to pull on the hair cells, stimulating the vestibular nerve, which signals the position of the head with respect to the rest of the body
How do the maculae of the utricle and saccule function?
maculae of utricle = sensitive to horizontal acceleration
maculae of saccule = sensitive to vertical acceleration
(both otoliths, they pulls on hair cells)
What part of the inner ear helps sense dynamic equilibrium? How does it function?
semicircular canals help sense dynamic equilibrium
(when your head moves around, the liquid inside the semicircular canals sloshes around and moves the tiny hairs that line each canal)
What is nystagmus and why does it occur after we spin a chair?
nystagmus: strange, uncontrollable eye movements occurring during/after rotation
fluid in SCC continues to move after spinning causing eyes to track movement
What are the four layers of the eyelid? What two muscles are found here?
skin, muscle, CT, conjunctiva
orbicularis oculi, levator palpebrae superioris
What are eyelashes and eyebrows for?
eyebrows: shade eyes from light, protects from sweat
eyelashes: shade from sun, very good dust catchers
(camels have longest eyelashes)
Where is the lacrimal gland and what does it do?
releases saline solution called lacrimal secretion (tears)
Where do tears go when they leave your eyes? Would the activation of the sympathetic or parasympathetic nervous system produce tears?
[lacrimal puncta, lacrimal canaliculi, lacrimal sac, nasolacrimal duct, inferior nasal meatus]
parasympathetic nervous system
What are the six extrinsic eyes muscles and how does each one move the eyeball?
lateral rectus: outward medial rectus: inward superior rectus: upward inferior rectus: downward superior oblique: downward and medially inferior oblique: upward and laterally
What cranial nerve innervate which extrinsic eye muscle?
lateral rectus - abducens
superior oblique - trochlear
the rest - oculomotor
What is strabismus? What is phoria?
strabismus - cross eyed; eye rotates medially/laterally
phoria - weakness of eye muscles
What are the three layers of the eyeball? What structures are in each layer?
fibrous - cornea, sclera
neural - choroid, ciliary body, iris
inner (retina) - retina
Do you find blood vessels in the fibrous tunic?
nope it is avascular
Why is the cornea clear?
so light can pass through it to the retina
What are the two main functions of the ciliary body?
make aqueous humor / accommodation of the eye
How do muscles of the ciliary body and the lens work together to allow you to see close objects?
ciliary body contracts, shortening fibers, causing lens to become rounder
How and where is aqueous humor produced?
ciliary body is produced in the ciliary body and drains continuously
Where does aqueous humor drain?
into the scleral venous sinus
What happens if too much aqueous humor is produced or if too little drains?
glaucoma
Why is the lens of the eye clear?
is aids in focusing light on the retina
What are crystallins?
transparent, precisely folded proteins that form the body of the lens
What is a cataract?
clouding of the lens
What does the iris do?
responsible for controlling the diameter and size of the pupil
What happens when the iris receives stimulation from the sympathetic nervous system?
pupillary dilation (dim light)
What happens when the iris receives stimulation from the parasympathetic nervous system?
pupillary constriction (low light)
What is the pupil?
round, central opening in iris allowing light to enter the eye
Describe the structure of the retina. (pg. 74)
light-sensitive layer of nerve tissue lining the inner surface of the eye
Where are the photoreceptors located in relationship to incoming light?
w
What are the two types of photoreceptors?
rods and cones
What is the fovea centralis and why is it important?
it is a pit in the center of the macula lutae containing cones compacted closely together // allows light to pass almost directly to the photoreceptors enhancing acuity
Which receptors allow you to see in dim light and to sense fast moving objects?
rods
Which receptors allow you to see colors and to have a good visual acuity?
cones
What about the cones’ relationship with the bipolar and ganglion cells allows for fine discrimination?
one cone to one ganglion cell (1:1 ratio)
What part of your eye sees 20/20?
fovea centralis
What does 20/20 or 20/200 mean?
20/20 = normal visual acuity measured at 20 feet 20/200 = good vision can see at 200 feet what bad vision can see at 20 feet
What do you find in the posterior cavity?
vitreous humor
Why is examination of the interior of the eye important in a medical examination of a patient?
retina is the only place you can see blood vessels clearly // can see circulation helpful for diagnostic purposes
How does your eye focus if you have emmetropia?
good, normal vision; 20/20
How does your eye focus if you have myopia?
nearsightedness (distant objects focus in front of retina) // concave corrective lenses
How does your eye focus if you have hyperopia?
farsightedness (near objects focus behind the retina) // convex corrective lenses
How does your eye focus if you have astigmatism?
light does not focus to a single point on the eye
What is a diopter?
the inverse of a focal length
What are the two parts of any photopigment?
opsin
retinal
How do the photopigments work?
unstable pigments that undergo a chemical change when they absorb light
What are you photoreceptors doing in the dark?
Na+ and Ca+ channels are help open by cGMP, inflow of Na+ triggers continual release of glutamate (neurotransmitter; inhibitory - prevents bipolar cells from firing by hyperpolarizing them
What happens when light hits your photoreceptors?
bent retinal (from Vitamin A) straightens out and no longer fits into the opsin (bleaching), opsin activates a G-protein that initiates the production of phosphodiesterase which breaks down cGMP, receptor hyperpolarizes, stopping the release of inhibitory neurotransmitter, this decrease in inhibition allows the bipolar cells to fire
How do photoreceptors differ from most nerve cells?
light activation causes a graded change in membrane potential and a corresponding change in the rate of transmitter release onto postsynaptic neurons
Trace the path of impulses from the photoreceptors to the occipital cortex. (pg. 76)
retina, optic nerves, optic chiasm, optic tract, lateral geniculate nucleus, optic radiations, visual cortex
Why is it important that some fibers from each eye go to both cerebral hemispheres? What does this allow us to do?
depth perception via stereopsis
What is the most common form of color blindness? What chromosome carries this information?
red-green; X chromosome
