Bio 225 - Exam 2 - Sensory Systems 2.0

What is the labeled line theory? (I)

Each neuron goes to one sensor that goes to one brain region

True or false? overlapping receptive fields improve ability to localize stimulus (I)

true

How is sensory discrimination improved? (I)

Distributing sensitivity amongst the receptor population

Define adaptation in a context of tonic receptors (I)

Decrease response to stimulus as duration increases

True or false? Adaption continues until the stimulus is “tuned out” (I)

true

How do odorant receptor neurons work? (II)

Expressing G-protein coupled receptors (metabotropic)

What are some details about ORNs? (II)

Aerosol based, sensory receptor (not epithelial), uses specialized G protein (gOLF)

Each afferent ORN expresses ____ odorant GPCR (II)

one

How is olfactory information passed? (II)

The combination of the different odorant GPCR is encoded as a scent, passed to brain

Gustatory receptor cells use ____ to detect __ and __ tastes (II)

GCPRs, sweet, bitter

What ion does salty taste convey? (II)

Na+

What ion does sour taste convey? (II)

H+

How does the gustatory cell convey information (II)

Voltage gated calcium channels trigger the release of neurotransmitters

True or false? Gustatory systems are constant between vertebrates and invertebrates. (II)

False

What are the variations on mechanoreceptors? (II)

Touch/pressure, proprioception, equilibrium/balance, hearing, baroreception

What do mechanoreceptors do? (II)

Couple mechanical stimuli to ion channels

What do tonic receptors do? (II)

Keeps firing APs until stimulus is gone (does not fade)

What do tonic receptors do? (II)

Stops firing APs once the stimulus has remained for a while

Are touch receptors tonic of phasic? (II)

Both. Corpuscles are phasic, Merkels disks are tonic

What do stereocilia deflections do? (II)

Modulate K+ conductance and transmitter release in hair cells

What does the middle ear do? (II)

transforms sound waves into basilar membrane vibrations

The hair cells here amplify and transduce basilar membrane movement

cochlea

True or false? Both inner and outer hair cells detect basilar membrane movement (II)

True

Higher frequency sounds are detected ____ ____ the oval window then lower frequency sounds (II)

closer to

What is a primary difference between rhabdomeric photoreceptors and ciliary photoreceptors? A similarity? (III)

Ciliary work through hyperpolarization, rhabodomeric (depolarization) do not. They both produce graded potentials.

What are the photoreceptive opsins? (III)

Seven membrane spanning GPCRs

What do opsins covalently bond to? (III)

Vitamin A derived pigments/chromophores

What do photons do to pigments? (III)

Cause isomerization of pigments/chromophores from cis to trans

What does isomerization of pigments (Rhodopsin) do? (III)

Induces conformational change causing G protein signaling

What do rhabdomeric photoreceptors employ? (III)

R-Opsins which signal through Gq

What do ciliary photoreceptors express? (III)

C-Opsins which signal through Gi

Summary of light-induced events

Opsins covalently bonded to vit. A derived chromophores —> Chromophores are usually in a cis-conformation —> Photon sensing causes isomerization to trans-conformation —> Isomerization leads to changes in the opsin / Dissociation of chromophore from opsin (called bleaching) / Conformational change in opsin —> G-protein signaling causes changes in membrane potential

What are four eye types discussed in lecture? (III)

Flat sheet, cup shaped, vesicular, convex

What does the iris do? (III)

lets more or less light in

Muscle fibers there change the pupil diameter in response to light

Pupil gets ____ in dim light and ___ in bright light (III)

wider, narrower

The cornea and lens are _____ lenses (III)

converging, convex

This organ does most of the focusing (III)

Cornea (is fixed)

This organ does fine tuning focusing on the retina (not the primary focusing organ) (III)

Lens

Label L down R down

Lens, Iris, Pupil, Cornea, Aqueous humor, Ciliary muscle

Vitreous humor, retina, choroid, fovea, optic nerve, optic disk, sclera

Define accommodation (III)

The ability of the eye to focus light from different distances

Look at this and say “if a man cooks once he is not a chef”

if a man cooks once he is not a chef

What are the two types of photoreceptor cells found in mammals? (III)

Rods and cones

Give some facts about rod cells. (III)

Ciliary photoreceptors, rod shaped outer segment, sensitive to very dim light (sense intensity - grey-scale)

Give some facts about cone cells (III)

Ciliary photoreceptors, cone shaped outer segment, sensitive to brighter light (sense color)

True or false? one rod synapses to each bipolar cell. (III)

False - many rods synapse on a single bipolar cell

Cones in the ___ ____ connect to a single ganglion cell via a single bipolar cell (III)

Fovea centralis

What is the basis for color discrimination? (III)

The absorbance spectra for rods and cones

Activated horizontal cells _____ neighboring ____ cells (III)

inhibit; bipolar

True or false? lateral inhibition suppresses gaglion cells (III)

False

The neural circuitry of retinal processing

1) light hyperpolarizes photoreceptor, reducing transmitter release (dec.s inhibition)

2) a dec. in inhibitory signaling depolarizes the bipolar cell

3) depolarization inc.s excitation of ganglion cell

Sensory systems do what (broad)

detect stimuli and send information to an integrating center

convert info abt stimulus into action potentials

What detects sensory stimuli

neurons (receptor protein in neuron) or accessory cells (receptor protein in epithelial censory cell) (in areas/tissues that need to be replaced a lot such as skin)

Sensory receptors what do they do

convert incoming stimuli into changes in membrane potential

sensory receptors can be classified by their…

stimulus modality

Sensory receptor types

chemoreceptors - detect the presence of chemicals in the environment

mechanoreceptors - detect pressure and movement, including proprioception

photoreceptors - detect light

thermoreceptors - detect temperature

electroreceptors - detect electric fields (fish)

magnetoreceptors - detect magnetic fields (birds)

sensory receptors encode 4 important features

stimulus modality, location, intensity, and duration

labeled line theory

separate and dedicated sensory pathways encode different stimulus modalities (ex: taste, smell, and touch)

A _____ _____ neuron is associated with one type of ______ (label line theory)

particular afferent; receptor

Each afferent neuron follows a particular ____ for ______

pathway; integration

Polymodal receptors

are sensitive to multiple sensory modalities

Polymodal nocireceptors tranduce _____, ____, and _____ cues into ____ that are sensed as _____

thermal; mechanical; chemical; signals; pain

_____ of action potentials likely encodes ______ information from some polymodal receptors

pattern; modality

Types of receptive fields

large receptive fields and small receptive fields

Overlapping receptive fields do what

improve ability to localize stimulus

Lateral inhibition function

improves acuity (defining exactly where touch is)

Action potential frequency encodes

stimulus strength

Receptor potential

a graded potential w/in the receptor

Sensory receptors encode a _____ range of stimulus ______

limited; intensities

Dynamic range

at what point does a receptor start sensing something and at what point does it reach saturation

Sensory discrimination improves by

distributing sensitivity amongst the receptor population

graph shows good sensitivity and large dynamic range

_______ _____ ___ __________ allows for a compromise b/w dynamic range and discriminaiton

logarithmic encoding of intensity

Tonic receptors

can encode stimulus duration

Phasic receptors

encode changes in stimulus

can do so in several ways

Types of chemoreceptors

exteroceptors:

interoceptors:

Exteroceptors

external to body (could be in the mouth/nasal passages)

• olfaction

• gustation

• nocioception

• ?pheromones?

Interoceptors

internal to body

• blood pH

• Chemosensors in stomach

• BP sensors

Odorant receptors neurons - receptor type and mechanism

express G-protein coupled receptors

Each afferent ORN expresses a

single odorant receptor

Combinatorial code for odors

odorant molecules binds G-protein receptor (can bind multiple different receptor types) —> tiggers combination of ORNs —> transmitted to brain for processing (diff. combinations = different smells)

Afferent ORNs w/ same GPCR connect to

the same region of the olfactory bulb (glomerulus) - the brain reads these combinations as distinct patterns of activation in the olfactory bulbs - this is the combinatorial code for odors

5 tastes

sweet, bitter, salty, sour, umami

Gustatory receptors use

GPCRs to detect sweet and bitter tastes

Sweet Sensory Pathway

Bitter Sensory Pathway

Sour Sensory Pathway

Salty Sensory Pathway

Variations on mechanoreception

touch/pressure

proprioception

equilibrium/balance

hearing

baroreception (BP sensing)

What kind of receptors are widely disperesed in the skin

touch receptors

combination of tonic (Merkel’s disks - for light and fine touch) and phasic (Ruffini corpuscle - sense deep touch - have large receptive fields that don’t overlap as much) receptors which allows for detection of both transient and sustained stimuli

Proprioceptors monitor

the position of the body in space - knowing where you are in space

vertigo: not knowing where you are in space

Muscle spindle fiber

senses stretch - causes contraction - incresaes contractile force

ex: stretching before box jump by bouncing/loading

lack of causes muscle discordination

Golgi tendon organ

senses overstretching of muscle - cause muscle relaxation

protection mechanism

Invertebrate ______ employ _____ for equilibrium

statocysts; mechanoreceptors

ciliated sensory neurons: the mechanoreceptors

helps signal which direction the lobster is moving in/oriented

The ____ cell is the _______ responsible for hearing and ______ in vertebrates

hair; mechanoreceptor; balance

Hair cells general

are bathed in endolymph

maintain high external K+ relative to internal K+

hair cell is and main components

is an epithelial cell

kinocilium and stererocilia

tip links

mechanically-gated K+ (cation) channels (TRP) at stereocilia tips

voltage-gated Ca2+ channels at body of epithelial cells

Hair cells maintain ______ ____ on to _____ ____, even in the absence of ______

transmitter release; afferent neuron; delfection

____ deflections modulate K+ conductance and _______ _____ in hair cells

sterocilia; transmitter release

movement to left - cilia move right: depolarization —> higher frequency of APs

movement to right - cilia move left: hyperpolarization —> lower frequency of APs

Where are the mechanreceptors necessary for hearing and balance located

inner ear - vestibular apparatus which includes utricle, saccule, and semicircular canals

Hair cells in _____ and _____ detect movements of _______ _____

utricle; saccule; otolithic membranes

x+y movement (front/back and up/down)

Macula of utricle

recognizes veritcal movement