Lecture 10 Flashcards
Chemoreceptors
Sense chemicals in the environment or blood (think taste, smell)
Photoreceptors
Sense light
Thermoreceptors
Respond to heat and cold
Mechanoreceptors
Stimulated by mechanical deformation of the receptor (includes touch and hearing)
Nocioreceptors
Pain receptors, depolarize in response to stimuli from tissue damage
Proprioreceptors
Provide sense of body position and allow fine control of skeletal muscles, tendons, and joints
Cutaneous receptors
Skin receptors, include touch/pressure, heat and cold, and pain receptors
Special senses
Receptors that mediate vision, hearing, taste, smell, equilibrium
Exteroceptors
Respond to stimuli from outside the body including cutaneous receptors and special senses
Interoceptors
Respond to internal stimuli, they monitor blood pressure, pH, oxygen, found in organs
Phasic receptors
Respond with a burst of activity when stimulus is first applied but quickly adapt to stimulus and reduce response
May have another burst when stimulus removed to provide on/off info, allow for sensory adaptation and alert us to changes in environment
Tonic receptors
Maintain a high firing rate as long as the stimulus is applied, example is pain, slow adapting
Four types of stimulus energy transduced by sensory receptors
Chemical, light, thermal, mechanical
Receptor/generator potentials
Sensory stimuli produce this type of depolarization, similar to EPSPs
Pressure on pacinian corpuscle
Touch on pacinian corpuscle produces generator potential, if pressure is increased the magnitude of the generator potential increases until threshold is met and an action potential occurs
Generator potential for phasic receptors
This includes pacinian corpuscles, if pressure is maintained the generator potential will diminish
Generator potential for tonic receptors
Increased intensity leads to increased frequency of action potentials after threshold is reached
Pruritis
Itch sensation
Receptive field
Area of skin that changes the firing rate of a neuron when stimulated
More receptors = smaller receptive field = greater acuity (example: finger tips)
Less receptors = larger receptive field = less acuity (example: backs of legs)
Lateral inhibition (touch)
Allows us to feel a single touch with well defined borders when a blunt object touches the skin
Receptors where touch is strongest are stimulated most and they inhibit those around them
*CNS
Five categories of taste
Sweet, salty, umami, bitter, sour
Salty taste receptor
Na+ enters the taste cell and depolarizes it
Sour taste receptor
H+ enters cell and depolarizes it
Sweet and umami taste receptors
Sugar or glutamate binds receptor activating G- proteins/second messengers to close K+ channels
Bitter taste receptors
Quinine binds to receptor, activates G-protein/ 2nd messenger to release Ca2+ into the cell
Sensitive to low concentrations as protective response
Gustducins
G-proteins involved in taste
Olfaction receptors
Located in olfactory epithelium of nasal cavity, bipolar neurons with ciliated dendrites
Smell process
Receptor proteins in cilia bind to odors
Damaged olfactory receptors
Basal stem cells replace receptors damaged by the environment every 1-2 months, rare area of adult neurogenesis
Vestibular apparatus
Provides a sense of equilibrium, orientation with respect to gravity, located in inner ear
Vestibular apparatus components
2 otolith organs: utricle (for horizontal acceleration) and saccule (for vertical acceleration)
3 semicircular canals for rotational acceleration
Perilymph
Fluid between bony and membranous labyrinth
Endolymph
Fluid within the membranous labyrinth, extracellular with very high K+ concentration which produces depolarization in receptor hair cells
Sound measurements
Frequency or pitch measured in hertz
Intensity or loudness measured in decibels (amplitude of wave)
Scala vestibuli
Upper chamber of cochlea filled with perilymph
Scala tympani
Lower chamber filled with perilymph
Scala media/cochlear duct
Middle chamber filled with endolymph
Helicotrema
Connects scala vestibuli to scala tympani at apex of cochlea
Sound waves
Displace vestibular and basilar membranes, different sound frequencies produce maximum vibration at different areas of the basilar membrane
Low-frequency sound
Travels further down cochlea to apex
Higher frequency
Sound closer to base of cochlea
Inner hair cells
One row running the length of the basilar membrane, relay sound to brain cranial nerve 8)can’t hear without
Outer hair coik
3 rows, innovated by motor neurons, shorten when depolarized and elongate when hyperpolarized, cochlear amplifiers
Hearing process
Sound waves enter the scala media vibrating the tectorial membrane bending stereocilia opening K+ channels facing endolymph, cell depolarizes, cells release glutamate onto sensory neurons and K+ returns to perilymph at base of stereocilia
Loudness of sound
The greater the amount of basilar membrane displacement and bending of secreocilia the more glutamate released producing a greater receptor potential, higher frequency of potentials, and louder perceived sound
Pitch discrimination
Neurons that originate in hair cells where membrane displacement is greatest will be stimulated the most allowing us to determine pitch
Conduction deafness
Transmission of sound waves through the outer and middle ear to the oval window is impaired
Hearing all frequencies impaired, hearing aids
Multiple causes: build up of ear wax, water in middle ear (Ottis media), eardrum damage, overgrowth of bone in middle ear (osteosclerosis)
Sensorineural/perceptive deafness
Nerve impulses not conducted from the cochlea to the auditory cortex in the brain
Impairs hearing particular frequencies, cochlear implants
Cause: damaged hair cells (loud noises)
Prebycusis
Age-related hearing impairment
Pathway of light through the eye
Cornea → anterior chamber → pupil → lens → vitreous → retina → absorbed by choroid
Aqueous humor
Nourishes lens and cornea, drains back into blood, improper drainage can cause glaucoma
Greatest refraction
Occurs at air-cornea interface
Distant vision
20+ feet, ciliary muscle relaxes, suspensory ligaments pulled/stretched, lens flatters
Close vision
Ciliary muscle contracts, suspensory ligaments relax, lens thickens and rounds up
Visual acuity
Sharpness of vision, depends on resolving power (ability to distinguish between two close objects)
Myopia
Nearsightedness, far images are focused in front of retina instead of on it, can be caused by elongated eye, concave lenses fix it
Hyperopia
Farsightedness, for images brought into focus behind the retina, due to short eyeball, convex senses
Astigmatism
Asymmetry of cornea and or lens curvatures, cylindrical lenses
Optic disc
Blind spot where retinal ganglion cell axons gather at a point and exit the eye as the optic nerve, lacks photoreceptors Also where blood vessels enter and exit
Bleaching reaction
Rhodopsin in rods dissociates into retinal and opsin when light is absorbed
Retinal is in 11-cis form shifts to all-trans after bleaching
Occurs in pigment epithelial lens
Dark adaptation
Sensitivity to light is low when going into the dark from the light due to fewer rhodopsin molecules this adaptation increases photo receptor sensitivity partially from more rhodopsin
In the dark
Na+ channels of photoreceptors always open, photoreceptors are depolarized, bipolar cells inhibited, ganglion cells inhibited
In the light
Na+ channels on photoreceptors closed, photoreceptor membrane hyperpolarized, bipolar and ganglion cells activated
Fovea centralis
Point in the retina where vision is best, within the macula lutea, this is because it only contains cones and no other retinal lagers so light falls directly on cones
Cones in this area have 1:1 ratio with ganglion cells, sensitivity to low right is poorest here
Macular degeneration
Degeneration of macula and fovea, leading cause of blindness in the US, loss of retinal pigment epithelium in this region
Temporal portion of retinas
Does not cross sides, but info from nasal portion does
Right visual field carried to left thalamus
