what are the classes of general sensory receptors?
- nocicetors: respond to pain
- mechanoreceptors: respond to touch (tactile), pressure (baroreceptors) and body position (proprioceptors)
what is the difference between general and special senses?
- general receptors are distributed throughout the body and relatively simple in structure
- specialized senses are concentrated within specialized structures located in the head
what are the special senses?
- olfaction (smell)
- gustation (taste)
- equilibrium (balance)
what is in the olfactory epithelium?
- olfactory receptor cells, supporting cells, and stem cells
- lines the nasal cavity
where does the axons of the olfactory epithelium go to?
they are bundled and pass through cribriform palte of the ethmoid bone and into olfactory bulb
where does the olfactory tracts extend to?
the olfactory cortex of the cerebrum, the hypothalamus, and the limbic system
what is the only sense that is not routed through the thalamus?
where are olfactory receptor cells derived from?
- neurons with chemical receptors called odorant-binding proteins on the cilia
- olfactory receptor cells are the only neurons in the nervous system exposed directly to the external environment
- olfactory glands are deeper and secrete mucus
what happens when odorant attaches to olfactory receptor?
- shape of the receptor protein is altered, leading to G protein activation
- diffrent odorants are detected by different combinations of receptors and thus have different receptor codes
- the immense number of potential receptor combinations is how we can smell more than 10,000 different odorants
what is the role of vomeronasal organ?
- detect pheromones, odorless chemical messengers that carry inforamtion between individuals of the same species
- pheromones influence our attraction to others, cause women to ovulate simultaneously
- the vomeronasal organ's sensory neurons act on a different signaling pathway than that of the main olfactory system's sensory neurons
where are gustatory receptors found?
in the gustatory cells of the taste buds, which are found on the sides of the circumvallate papillae
what do gustatory cells have that extend through the taste pore?
microvilli (taste hairs)
what are the primary taste sensations?
sweet, sour, bitter, salty, and umami
what are the different types of papillae?
- fungiform papillae: present mostly at the apex of the tongue as well as at the sides
- foliate papillae: ridges and grooves towards the posterior part of the tongue found at the lateral borders
- circumvallate papillae: arranged in a circular shaped row at the back of the oral part of the tongue (10 to 14 on most people)
what is the purpose of taste hairs?
- respond to chemicals in solution and trigger a change in the membrane potential of the taste cells
- ex. salt receptor triggered by Na+ entry through salt gated channel, action potential travels down membrane, releasing NT to sensory neuron
what are supertasters?
- 10x more taste buds than non-tasters
- very sensitive to bitter, sugar tastes
- hypothesis-at high risk of fetal damage by ingesting toxins (alkaloids) selected for women with sensitive taste
- 25% of population
who are the nontasters?
- 25% of population
- few taste buds
- poorer sense of taste than average
- liek the taste of bitter foods
- prefer lots of salt/sugar on food
what are the layers in the wall of the eye?
- fibrous layer: outermost, containing the sclera and cornea, provides mechanical support, attachment sites for muscles, and assits with focusing
- vascular layer: middle layer containing the choroid, the iris and the ciliary body. Provides route for blood/nutrients for the eye, regulates light entering eye, secrete aqueous humor, controls focusing
- inner layer (neural tunic): retina, absorbs light passing through eye and performs preliminary processing and integration of visual info
The eye is divided into which two cavities?
- anterior cavity (with anterior and posterior chambers): is filled with aqueous humor produced by ciliary processes
- posterior cavity: filled with jellylike vitreous humor
what is the sclera and the cornea?
sclera is the white of the eye and the transparent cornea allos light to enter the eye
what is the function of the iris?
it has pupillary muscles that change the size of the pupil, the window into the eye
what is the function of the ciliary body?
consists of ciliary muscle, ciliary processes, and suspensory ligaments, which adjusts the shape of the lens for focusing
where does the light travel through before reaching the retina?
corneau, aqueous humor, lens and vitreous humor
what does the pupillary dilator muscle do?
- extend radially away from the edge of the pupil.
- Contraction of these muscles enlarges the pupil
- low light, far objects, excitement/fear
what are the pupillary constrictor muscles?
- form a series of concentric circles around the pupil
- when these sphincter muscles contract, the diameter of the pupil decreases
- excess light, near objects, focus light for reading
where is the lens? what does it do?
- posterior to cornea and is held in place by suspensory ligaments
- cells of the lens are wrapped in concetric circle and elastic fibers make lens spherical
- light is bent or refracted as it enters the cornea and lens
- light rays converge on retina at focal point
how does the shape of the lens reflect ciliary muscle?
- for close vision: ciliary muscle contracted, lens rounded
- for distant vision: ciliary muscle relaxed, lens flattened
what is the relationship between the distance of the light source and focal point distance?
- the closer the light source, the longer the focal distance
- the rounder the lens the shorter the focal distance
If the eyeball is too deep or the resting curvature of the lens is too great, then
- the image of a distant object is projected in front of the retina
- myopia is corrected with a diverging, concave lens
If the eyeball is too shallow or the lens is too flat, then
- the ciliary muscle must contract to focus even a distant object on the retina
- hyperopi is corrected with a converging convex lens
what are the two layers in the retina?
- pigmented part, which absorbs light
- neutral part contains the photoreceptors (rods and cones)
- also contains supportive cells, neurons and blood vessels
what is the difference between rods and cones?
- rods are used in dim light and are found on the periphery of retina surface
- cones are used in bright light and detect color. Found in the macula, the center of which is the fovea, fovea centralis
what are photoreceptors closest to?
choroids, rather than near the posterior cavity (virtreous chamber)
what do rods and cones synapse with?
bipolar cells, which synapse with ganglion cells (axons leave the back of the eye through the optic disc)
how does rods respond to photons?
- responds both to presence or absense of photons regardless of wavelength
- very sensitive, therefore effective in dim light
what are the different types of cones needed for accurate color detection?
- blue, green, and red
- contain pigments sensitive to specific wavelengths of light
- less sensitive, therefore function only in bright light
what is the structure of the photoreceptors
- outer segment: contains hundreds to thousands of flattened discs
- -contains visual pigments that absorb photons and initate photoreception
- -made of compound rhodopsin that contains opsin and retinal
- -retinal is the same in rods and cones, opsin is different
- inner segment: contains organelles, synapses with bipolar cells
bleaching and regeneration of visual pigments
- alters rate of NT release into synapse with bipolar cell
- for rod or cone to be able to respond to light again, the opsin and retinal must recombine
what is color blindness?
- occurs when one or more types of cone is not functioning or is missing
- protanopia: complete absense of red retinal photoreceptors (red appears dark)
- deuteranopia: green retinal photoreceptors are absent, moderately affecting red-green hue discrimination
- tritanopia: two cone pigments present and a total absence of blue retinal receptors
what is astigmatism?
- irregular or toric curvature of the cornea or lens
- vision is blurred due to the inability of the optics of the eye to focus a point object into a sharp focus image on the retina
what is a cataract?
clouding that develops in the crystalline lens of the eye, varying in degree from slight to complete opacity an obstructing the passage of light
results in loss of vision in the center of the visual field (the mascula) becuase of damage to the retina. It occurs in dry and wet forms
- eye disease in which the optic nerve is damaged due to increased fluid pressure in the eye
- aqueous humor in the anterior cavity of the eye is always being made behind the iris. It leaves the eye through channels in the front of the eye in an area called the anterior chamber angle, or simply the angle
describe the different parts of the ear
- external ear: visible portion, collects sound waves
- middle ear: chamber with structures that amplify sound waves
- internal ear: contains sensory organs for hearing and equilibrium
The middle ear (tympanic cavity)
contains auditory tube, which allows for pressure equalization on either side of eardrum and ossicles
what does the auditory ossicles (bones) connect?
- tympanic membrane to internal ear
- -malleus attaches to eardrum
- -incus attaches malleus to innermost bone
- -stapes has a base that nearly fills the oval window into the internal ear
what are the structures in the internal ear
- sensory structures protected by bony labyrinth
- -contains fluid perilymph between bony and membranous labyrinths
- inside the bony labyrinth is membranous labyrinth
- -tubes that follow contours of bony labyrinth, filled with fluid endolymph
what are the different bony and membranous labyrinths?
- semicircular canals
what is the vestibule
contains membranous sacs (saccule and utricle) with receptors for gravity and linear acceleration
what is semicircular canals
contain membranous semicircular ducts with receptors for rotational acceleration
what are cochlea?
contains membranous cochlear duct as well as sensory receptors for hearing (in spiral organ)
what are hair cells
- sensory receptors in interal ear
- surrounded by supporting cells
- synapse with dendrites of sensory neurons
- free surface covered with stereocilia
- movement of sterocilia alters NT release
- bending sterocilia in one direction stimulates cell; in the other direction, inhibits cell
what does the semicircular ducts contain?
- an ampulla, which contains the sensory receptors called crista ampullaris
- sensory receptors respond to rotational movements fo the head
- when the head rotates, endolymph pushes against the cristae and actives hair cells (embedded in gelatinous cupula)
what is the vestibular complex?
- receptors in the utricle and saccule respond to gravity and linear acceleration
- hair cells clustered in maculae project into the gelatinous membrane with otoliths (CaCO3)
what determines stimulus in ear?
- frequency of waves determines the pitch (speed; cycles/sec)
- amplitude determines the loudness (force; decibels)
what is the pathway of sound?
- sound waves vibrate the tympanic membrane
- tympanic membrane vibrates the ossicles
- ossicles convert sound energy to air pressure pulses
- pressure pulses travel through perilymph of cochlea stimulating hair cells along the cochlear spiral
how is energy reflected?
- when a sound wave is transferred from a low-impedance medium (air) to one of high impedance (perilymph)
- sounds are amplified in the middle ear to compensate for the resistance to movement in the fluid within the cochlea
what is the stiletto effect?
surface area ratio of ear drum to stapes about 20:1; energy moves to smaller surface
describe the spiral organ of corti
- pressure waves enter the scala and then cross the vestibular membrane passing into the cochlear duct
- waves corss the basilar membrane, stimulating the receptors of the spiral organ and pass into the second scalar tube
- finally the pressure waves reach the membranous round window where the vibrations transfer the energy into the auditory canal.
what does the tectorial membrane do?
- hair cell stereocilla project into tectorial membrane, attached to wall of cochlear duct
- waves strike basilar membrane, moving it up and down
- hair cells are pushed against tectorial membrane, bending stereocilia (can produce either excitatory or inhibiroty potentials)
what are the basilar fibers like at the entrance and at the end of the cochlear duct?
- short and stiff at entrance
- long and loose at apex
how is pitch and volume determined in the cochlea?
- pitch (frequency) determined by which part of cochlear duct is stimulated
- volume (intensity) determined by how many hair cells are activated at that site
describe how sound travels
- 1. sound waves arrive at tympanic membrane
- 2. movmeent of the tympanic membrane causes displacement of the auditory ossicles
- 3. movement of the stapes at the oval window est. pressure waves int eh perilymph of the scala vestibuli
- 4. the pressure waves distort the basilar membrane on their way to the round window of the scala tympani
- 5. vibrations of the basilar membrane causes vibration of hair cells against the tectorial membrane
- 6. information about the region and the intensity of stimulation is relayed to CNS over the cochlear branch of cranial nerve
what is neural deafness
- regular exposure to greater than 90 decibels
- greater than 120 is pain threshold
- the hair cells can't repair or be replaced by stem cells after damage
what is conduction deafness?
- as we age, the joints between the inner ear ossicles stiffen, resulting in decreased conduction of sound waves to the cochlea
- can be compensated by hearing aids