Chapter 10 Flashcards
What are examples of sensory receptors?
- dendritic endings of neurons
- specialized endings of neurons or non-neuronal cells
What are chemoreceptors?
can sense chemical stimuli
What are photoreceptors?
sense light
What are thermoreceptors?
responds to temperature changes
What are mechanoreceptors?
responds to deformation of their cell membrane
What are nocireceptors?
respond to intense stimuli by signaling pain
What are proprioceptors?
signal positional information of body parts
Where are general/cutaneous receptors?
near an epithelial surface
Where are special sense receptors?
part of a sensory organ
What do general receptors respond to?
touch, pressure, temperature, pain
What are examples of sepcial sense receptors?
hearing, sight, equilibrium
What are tonic receptors?
respond at constant rate as long as stimulus is applied
- pain
What are phasic receptors?
respond with burst of activity but quickly reduce firing rate to constant stimulation (adaptation)
- smell
- touch
What is the law of specific nerve energies?
stimulation of sensory fiber evokes only the sensation of its modality
- adequate stimulus = normal (requires least energy to activate its receptor
What is another potential that is similar to generator potential?
sensory receptor equivalent of EPSPs
When are generator potentials produced?
in response to adequate stimulus
After threshold is reached, what is action potential frequency proportional to?
amplitude of generator potential
How does generator potential work in phasic receptors?
it adapts to a constant stimulus and quickly diminishes in amplitude
How does generator potential work in tonic receptors?
it doesn’t adapt to a constant stimulus
What are exteroceptors?
respond to chemicals in external environment
What are interoceptors?
respond to chemicals in internal environment
What do taste receptors sense?
sweet, sour, salty, bitter, umami (amino acids)
What are taste receptor cells?
modified epithelial cells
How many taste receptor cells are in each taste bud?
50-100 cells
How do we taste salty and sour?
Na+ and H+ go through ion channels
- do not bind to receptors
How do we taste sweet and bitter?
act through g-proteins
- bind to receptors
Where are smell receptors?
located in olfactory epithelium at the top of the nose
What is in the olfactory apparatus? What are their functions?
1) receptor cells: bipolar neurons that send axons to olfactory bulb
2) supporting cells: detoxifying enzymes
3) basal cells: stem cells that produce new receptor cells every 1-2 months
How do odor molecules work?
bind to receptors
- act through g-proteins
What is the purpose of the vestibular apparatus?
provides sense of equilibrium
- orientation to gravity
What forms the inner ear?
vestibular apparatus and cochlea
What is in the vestibular apparatus?
otolith organs
- utricle
- saccule
semicircular canals
Where are sensory structures located in the ear?
membranous labyrinth
- filled with endolymph
- located in bony labyrinth
What part of the ear provides info about linear acceleration?
- utricle
- saccule
What part of the ear provides info for angular/rotational acceleration?
semicircular canals
What is the purpose of hair cells?
receptors for equilibrium
What do hair cells have?
each have 20-50 hairlike extensions (stereocilia)
- 1 is a kinocilium
How is the 8th nerve (vestibulocochlear nerve) stimulated?
stereocilia are bent toward kinocilium
- hair cell depolarizes
- releases neurotransmitter and stimulates 8th nerve
What happens when stereocilia are bent away from kinocilium?
hair cell is hyperpolarized
- frequency of action potential in hair cell carries information about movement
What are the characteristics of utricle and saccule?
- have macula with hair cells embedded with gelatinous otolithic membrane
- contains calcium carbonate crystals (otoliths) that resist change in movement
What is utricle sensitive to? What direction does the hair move?
horizontal acceleration
- hair pushed backward during forward acceleration
What is the saccule sensitive to? Which direction does the hair move?
vertical acceleration
- hairs pushed upward when person descends
What are the characteristics of the semicircular canals?
- each have semicircular duct
- the base has crista ampullaris (sensory hair cells reside)
Where do hair cell processes occur?
cupula of crista ampullaris
What are waves characterized by?
frequency: hertz (cycles/sec)
intensity: loudness (decibels)
What does the middle ear have? Where is it?
has ossicles
- between tympanic membrane and cochlea
What wavelengths count as visible light?
400-700nm
What does the iris do?
controls size of pupil
How does the pupil constrict?
contraction of circular muscles
- under parasympathetic control
How does the pupil dilate?
contraction of radial muscles
What is accommodation?
ability of eyes to keep image focuses on retina as distance between eyes and object varies
What does accommodation result from?
contraction of ciliary muscle
What happens to eyes at distances more than 20 feet?
ciliary relaxation places tension on suspensory ligament
- pulls lens taut
- least convex
What happens to eyes when distance decreases?
ciliary muscles contract, reducing tension on suspensory ligament
- lens are more convex
What is visual acuity?
sharpness of vision
What does visual acuity depend on?
resolving power
- ability to resolve 2 closely spaced dots
What is myopia?
nearsightedness
- image focused in front of retina
- eyeball is too long
What is hyperopia?
farsightedness
- image is focused behind retina
- eyeball too short
What is astigmatism?
cornea or lens is not symmetrical
- light is bent unevenly
- uneven focus
What is the retina?
multilayered epithelium with neurons, pigmented epithelium and photoreceptors (rods and cones)
Where do rods and cones face? Where do they send sensory info to?
face away from pupils
- send sensory info to bipolar cells
Where do bipolar cells send electrical activity to?
ganglion cells
Where do ganglion cells project signals to?
project axons through optic nerve to brain
What are horizontal cells and amacrine cells?
interneurons involved in visual processing in retina
What is the main characteristic of rods and cones?
inner segments
outer segments: stacks of photopigment discs
- new discs are added at the base and removed at the tip
What do retinal pigment epithelium do?
phagocytizes old discs from tips
- absorbs excess light
- delivers nutrients from blood to the photoreceptors
- suppresses potential immune attack on retina
- stabilizes ion levels for photoreceptors
How are rods activated?
when light produces chemical change in rhodopsin
- dissociates into retinal and opsin (bleaching reaction)
- causes changes in permeability, resulting in action potential in ganglion cells
Which retinal cells produce action potentials?
ganglion and amacrine cells
Which retinal cells produce graded potential changes?
rods, cones, bipolar, horizontal cells
What happens to photoreceptors in the dark?
release inhibitory neurotransmitter that hyperpolarizes bipolar cells
What happens to photoreceptors in the light?
inhibits photoreceptors from releasing inhibitory neurotransmitters
- stimulates bipolar cells
What ion channels do rods and cones have? How does it change in dark and light?
have many Na+ channels that open in dark
- depolarizing influx is dark current
- light hyperpolarizes by closed Na+ channels
What keeps Na+ channels open?
cGMP
- light converts cGMP to GMP and Na+ channels close
