BIOL216 EXAM 2 TOPIC 7

what are the special senses?

1. hearing and balance

2. olfaction

3. gustation

4. vision

what are sensory receptors formed of?

• terminals of afferent axons

• specialized cells that synapse with afferent neurons (can be sensory receptors)

What is the function of sensory receptors?

to get info about the external and internal environment

Respond to stimuli (such as light, heat, chemicals, mechanical stress) by changing their conductance to ions (such as Na+, K+, Ca+) —> responds to change in membrane potential

sensory transduction

conversion of a stimulus to a change in membrane potential

what are the main 2 types of sensory receptors?

• formed by terminals of afferent neurons

• consists of separate cells

how do sensory receptors formed by the terminals of afferent neurons work?

stimulus causes a change in membrane potential that generates AP in the axon of the neuron

ex) temperature and pain receptors

how do sensory receptors consist of separate cells work?

stimulus causes a change in membrane potential that releases a NT from the cell

NT triggers an AP in the axon of a nearby afferent neuron

ex) mechanoreceptor, photoreceptor, chemoreceptor

mechanoreceptor

detect changes in body position, pressure, acceleration (i.e. auditory receptors of the ear)

photoreceptors

detect light and are located in the eye

chemoreceptors

detect specific molecules or conditions such as acidity (i.e. taste buds)

thermoreceptors

Consist of free nerve endings

At the body surface

In the body interior (in limited numbers)

Detect changes in body temperature

nocioreceptors

Detect stimuli that can damage body tissues

Located on body surface and interior

Information from receptors is integrated in the brain resulting in the sensation of pain

meissner corpsucle

low frequency vibration, skin slip

grip control

light touch, surface vibrations

merkel receptor

skin deformation at high spatial resolution

points, edges, texture, and curvature

pacinian corpuscle

skin deformation (nm), vibration from objects held in the hand

tool use

deep pressure and vibration

ruffini corpuscle

skin stretch, movement direction

detection of hand shape and finger position

deep pressure

free nerve endings

light touch

where are stretch receptors found?

muscles and tendons

tendons = golgi tendon organs —> nerve fiber with collagen strands that connect the muscle to the tendon (detects muscle tensions)

what is the function of stretch receptors?

detect position and movement in limbs by detecting how fast and how much a muscle is stretched

when muslce generates forces, the sensory terminals can be compressed, opening stretch-sensitive cation channels on the afferent axon

axon is depolarized and fires APs that are propagated to the spinal cord

vestibular apparatus

3 semicircular canals

2 fluid filled chambers: utricle and saccule

perceives the position and motion of the head using mechanoreceptors

what do the semicircular canals detect?

perpendicular orientation and rotational motion

endolymph

scale media

rich in K+

perilymph

scala media + tympani

rich in Na+

found in between the membrane and bone of the semicircular canal

ampulla

region at the base of semicircullar canals with sensory hair cells

detects rotational movement of the head/body: movement of the endolymph

How does endolymph help detect motion?

displaces the cupula and bends sensory hair cells

mechanoreceptors

generates AP in afferent neurons that synapse with the hair cells

how do we stay balanced?

vestibular system of the inner ear

each hair has one direction of maximum NT release

stereocilia are bent in this direction, receptor cell depolarizes and increases the AP frequency in the afferent neuron activated by it

movement in the opposite direction dec the relative rate

utricle and saccule

oriented 30 degrees to each other

contain sensory hair cells with stereocilia

what information do the utricle and saccule give?

1. head position (up/down)

2. change in the rate of linear motion of the body

otoconia

calcium carbonate crystals found in the hair cells membrane

similar to cupula

what is the pathway to maintain balance?

•When the head tilts or body moves non-linearly, the otolithic membrane moves —> bends hair cells —> neurotransmitter release —> action potential —> brain perceives movement

what is the neuronal pathway for balance?

1. sensory axons from the vestibular ganglion pass through the vestibular nerve to the vestibular nucleus, which also recieves input from several other sources, such as proprioception from the legs

2. vestibular neurons send axons to the cerebellum, which influences postural muscles

3. vestibular neurons also send axons to motor nuclei, whcih control extrinsic eye muscles

4. vestibular neruons also send axons to the posterior ventral nuclues of the thalamus

5. thalamic neurons project to the vestibular area of the cortex

sound waves

variations of pressure air

created by the vibration of an object which causes air surrounding it to vibrate

function of wave amplitude

volume/loudness

frequency of wave

pitch

eardrum

tympanic membranem

malleus

hammer

inucs

anvil

stapes

stirrup

eustachian tube

leads to throat

when we swallow, tube opens, air flows in/out of the ear to equalize pressure

what is the pathway for hearing?

vibration transmitted from teh eardrum to though the fluid in the inner ear → makes basilar membrane vibrate —> bends hair cells against tectoral membrane —> AP in afferent neruons that lead to auditory regions of the brain

cochlea

spiraled, hollow, conical chamber of bone

scala vestibuli

lies superior to the cochlear duct; abuts the oval window (is on outer side of cochlea) (perilymph: rich in Na+)

blood plasma across a hemtoperilymphatic barrier

scala media

which is the membranous cochlear duct containing the organ of Corti (endolymph: rich in K+)

scala tympani

lies inferior to the scala media; terminates at the round window (is on outer side of cochlea) (perilymph: rich in Na+)

CSF

endocochlear potential

sum of two potentials

active secretion of K+ by the stria vascularis

negative potential from passive diffusion of K+ ions from the hair cells

net positive voltage of 80-100 mV

basilar membrane

forms part of the floor of the cochlear ducts

anchors sensory hair cells in the organ of corti

vibrates in response to the vibrations transmitted through the inner ear

narrow and stuff near the oval window, wider at the outer end of the cochlear duct

organ of corti

region that contains sensory hair cells that detect the sound vibrations transmitted to the inner ear

distributed along the partition separating fluid chambers in coiled tapered tube of the cochlea (in cochlear duct)

what is the pathway to the brain for hearing?

basilar membrane —> stimulate hair cells —> synapse to afferent neurons —> auditory nerve —> auditory center in the termporal lobe of the brain

how are hair cells tuned?

sound frequencues are location in the cochlea to teh degree of stiffness in the basilar membrane

high pitched sounds vibrate where?

high frequency vibrations

vibrates basilar membrane in narrow, stiff beginnign end

low pitched sounds vibrate where?

wider and less stiff farther end

travel down the tube, less stiff membrane is moved more easily by them where the reduced stiffness allows

how are hair cells arranged to detect sound vibrations?

rows of inner hair cells (responsible for hearing) and outer hair cells (regulate tension on basilar membrane)

•As stereocilia bend, they open K⁺ gates (mechanically gated ion channel)

tip link (gating spring)

•attaches tip of each stereocilium in a hair bundle to the side of the next longer stereocilium.

how does sound go through the ear?

what is the pathway to the brain? (hearing)

1. cochlear nucleus

2. superior olive

3. lateral lemniscus

4. inferior collicuus

5. medial geniculate complex of the thalamus

cornea

Transparent, admits & refracts light; covers the iris, pupil and anterior chamber

sclera

white outer layer of the eyeball, protective layer

choroid

vascular layer of the eye, between the sclera and the retina

lens

focuses image on the retina

iris

regulates pupil diameter

works in conjunction with the pupil to control how much light enters the eye

constrictor pupillae

circular muscles

when they contract pupil diameter decreases (miosis)

dilator pupillae

radial muscles

when they contract, pupil diameter increases (mydriasis)

retina

Layer of neural cells that lines the back of the eye

Photoreceptor cells that are sensitive to light

macula

pigmented area in the retina

contains fovea, involved in high acuity vision

fovea

region of the macula in the retina

has a high density of cone cells, needed for sharp vision

anterior chamber

lies between the cornea (the front of the eye) and the iris (colored part of the eye). Filled with aqueous humor

posterior chamber

located behind the iris and in front of the lens. Filled with aqueous humor

vitreous chamber

located behind the lens. Filled with vitreous humor

aqueous humor

A thin, watery fluid in both the anterior and posterior chambers of the eye

Maintains intraocular pressure

Supplies nutrients to avascular parts of the eye

Removes wastes

vitreous humor

A thick, viscous fluid (gel like substance)

Helps maintain the shape of the eye and absorb shock

Occupies space behind the lens and in front of the retina at the back of the eye

ciliary body

Part of the eye that includes the ciliary muscle

Controls the shape of the lens

Controls ciliary epithelium, which produces the aqueous humor

what is the basic process of visual processing?

To see, the eye must first form a precise image on the retina.

Light energy striking the retina must be converted to action potentials transmitted to the brain by the optic nerve.

Several cells, especially photoreceptor cells called rods and cones are needed for the eye to process light.

cornea

Refraction—the bending of light rays

Light passing through center = no bend

Light striking off-center = bend toward center

Focus is fixed

lens

•Made of crystallin proteins

•Focuses and directs light towards retina

alters shape through ocular accommodation

ocular accommodation

Lens flattens = lower refractive power and improves depth of focus

Increased curvature of lens = Increased optical power

rods

Work well in dim conditions (night vision)

No color detection

95% of photoreceptors in the eye

Located mostly in peripheral retina

rhodopsin

photoreceptive molecule in rods, GPCR

retinal+opsin = photopigment

cones

Mostly in the fovea and macula lutea; fewer over rest of retina

Each with iodopsins

Contain the protein-pigment complexes photopsin I, II, and III

Respond to blue, red and green light

Gives rise to the perception of a particular color in the brain

why would you want better peripheral vision at night?

detecting predators or movement in low light

what happens to rods in the dark?

Rod cells are depolarized

Release glutamate

what happens to rods in the light?

Rod cells become hyperpolarized

Glutamate release is greatly diminished

When glutamate is not released (or reduced) from the rod cell, the bipolar cell is no longer inhibited

Can now stimulate ganglion cells produce APs

Send signal to brain

what does overlapping visual fields allow?

Improved ability to judge distances

Objects to be seen in three dimensions

Increases depth perception (trade-off for peripheral vision)

why did primates adopt binocular vision?

Foraging: Advantage for finding food

Social signaling: Interpreting others behavior and finding available mates

Other constraints: Avoiding predators

trichromacy

well developed color vision

horizontal cells

Receive information from the photoreceptors

Transmit it to surrounding bipolar neurons

Responsible for allowing eyes to adjust to see well under both bright and dim light conditions

Involved with lateral inhibition

amacrine cells

Receive their inputs from the bipolar cells

Activate the ganglion neurons in their vicinity

Dopamine-secreting neurons located in the retina

Active during daylight hours, becoming silent at night

Retinal dopamine enhances the activity of cone cells in the retina and suppressed rod cells

The result is an increase in sensitivity to color and contrast during bright light conditions, at the cost of reduced sensitivity when the light is dim

what are the two types of bipolar cells?

on center and off center

receptive field

smaller receptive field - sharper images

Receptive field center provides a direct input from the photoreceptors to the bipolar cells

Receptive field off center provides an indirect input from the photoreceptors to the bipolar cells via horizontal cells

what kind of potentials do bipolar cells experience?

graded potetnials

what is the on center pathway? (dark)

Glutamate released from the photoreceptor stimulates metabotropic glutamate receptors on the on-center bipolar cells

K+ channels are opened = an efflux of K+

The on-center bipolar cell is hyperpolarized, results in a decrease in the release of their transmitter

In turn, results in a decrease in the firing of the corresponding on-center ganglion cells

what is the off center pathway? (dark)

Glutamate released from the photoreceptor terminals stimulates ionotropic glutamate receptors on the off-center bipolar cells

Na+ channels are opened, Na+ flows into the cell

The off-center bipolar cell is depolarized, release transmitter (probably glutamate) is increased

Results in an increase in the firing of the corresponding off-center ganglion cells

what is the on center pathway? (light)

When the photoreceptor cell in the receptive field center receives a light stimulus, it hyperpolarizes and the glutamate release from its terminals is decreased

Causes depolarization of the on-center bipolar cell and an increase in its transmitter

Resulting in an increase in the firing of the corresponding on-center ganglion cells

what is the off center pathway (light)

a light stimulus, it hyperpolarizes and the glutamate release from its terminals is decreased

Causes hyperpolarization of the off-center bipolar cell and there is a decrease in its transmitter release

Resulting in a decrease in the firing of the corresponding off-center ganglion cells

vision neuronal processing location determination

Comparing input:

From two eyes gives: left/right location, and distance (or depth perception)

When eyes move up and down gives: up/down location

Map-like projection from retina to cortex relays the left/right, up/down location, and distance (depth perception) information

contralateral processing

Half the fibers from each optic nerve cross to the opposite side of the brain

Information from the left visual field (from both eyes) goes to the right hemisphere

Information from the right visual field (from both eyes) goes to the left hemisphere

Provides combined input from both eyes to each hemisphere of the brain

Each hemisphere of the brain sees the visual field on the side of the body it has motor control over

relaxed: distance vision

Ciliary muscle relaxes and zonular fibers under tension

Lens is flattened = lower refractive power

Improves depth of focus

accommodated (contraction): near vision

Contraction of ciliary muscle and zonular fibers under reduced tension

Lens becomes more convex due to its elasticity

Increased curvature = Increased optical power

optic tract

Axons end at the lateral geniculate nucleus (LGN) of the thalamus

lateral geniculate nucleus

Acts as an amplification station for visual signals

Neurons here form the optic radiation (white matter fiber of the cerebrum)

Projects to primary visual cortex of occipital lobe

primary visual cortex

Each hemisphere has its own visual cortex within the occipital lobe

Where conscious visual sensation occurs

Consists of five regions (V1 - V5)

Process object location, motion, color, shape, boundaries

Processed information from the visual cortex is sent to other regions of the brain to be analyzed and utilized

The occipital lobe identifies writing, then works with the temporal lobe to recognize the written shapes and symbols

Store visual memories (recognize printed words)