4.3 - NS: afferent - special senses

special senses

what part of the electromagnetic spectrum can our eyes detect?

visible light

Our eye receptors can detect wavelengths between ___ and _____ nm

between 400 and 750 nm

what determines colour?

diff wavelengths

general job of they eye structures:

refract lightwaves and focus them on the retina where the sensory receptors are.

phototransduction:

• what does it do, where does it occur?

• turn light (photons) into a neural signal

• occurs at the retina

2 types of photoreceptors

rods and cones

rods

• sensitivity level

• what do they help see? (what kind of light)

• very sensitive

• respond to low light - see in the dark

cones

• sensitivity level

• what do they help see? (what kind of light)

• less sensitive

• bright light - help see colour

photoreceptors have two parts:

• name and their purpose/components

• outer segment - composed of discs

  • discs respond to light

• inner segment - contain mitochondria and org.

photoreceptors contain ______ that ____ ____

they contain photopigments that absorb light

rhodopsin - what is it

photopigment found in rods. they absorb light

photopigments contain what molecules?

contain proteins called opsins which are bound to a chromophore molecule

chromophore is …

light sensitive.

overall: explain photoreceptors.

photoreceptors have inner and outer segments. the outer segments are composed of discs that have mechanisms that respond to light.

they have photopigments that absorb light.

• in rods, that pp is rhodopsin.

• PPs contain proteins called opsins which are bound to chromophore molecule.

  • chromophore is light sensitive

compare Photoreceptors when depolarized to regular cells.

most cells get depolarized when stimulated. But photoreceptor cells get hyperpolarized when stimulated.

at rest and when there is a stimulus:

• photoreceptors are … (and number)

at rest = depolarized (-35mV)

when stimulus = hyperpolarized (-70mV)

what happens when photoreceptor is at rest? and when there is a stimulus?

(what happens to the ion channels and whatever)

when at rest, there is open cation channel (constant + ion flow), and it closes in response to light stimulus.

clarification: what happens when photoreceptors are stimulated by light?

the cation channel closes.

when at rest, cation channels open.

photoreceptors can generate what? and what can they not generate?

photoreceptors can generate graded potentials, not APs.

photoreceptor cells → ______ cells → _______ cells

photoreceptors —> bipolar cells —> ganglion cells

which cell in the eye generates APs?

• (which ones do not generate APs?)

• (which generate graded potentials?)

• ganglion cells generate APs.

• photoreceptors and bipolar cells do not.

  • photoreceptors generate graded potentials.

map the path of the action potential production starting with light going into the retina…

• light goes in to the retina, photoreceptors …

light goes in eye, to retina, photoreceptors generate graded potentials, that connect with bipolar cells , which connect with ganglion cells, which generate APs.

what do the axons of the ganglion cells form?

their axons form the optic nerve to carry info to CNS

defects in colour vision result from

mutations in cone pigments, making it hard to differentiate shades.

what is sound?

airwaves coming into the ear

Map the path of sound:

• start with sound funnels into EAC

• sound funneled into external auditory canal

• tympanic membrane

  • sound hits here and it vibrates

• middle ear bones

  • amplify vibrations.

  • connect eardrum to oval window

• cochlea

  • vibrations enter cochlea fluid:

• Organ of Corti:

  • Hair cells on the organ of Corti detect fluid movement

  • converted to electrical signal for nerve to send to CNS

organ of Corti:

• where is it?

• receptors name and type? and detail

• function

organ of Corti is in the cochlea.

mechanoreceptors in here are the hair cells.

• they have stereocilia on top

as pressure waves move thru, these cells are stimulated. turn waves to signal to CNS

what happens when the hair cells get pushed in the long direction and the other direction?

when pushed, ion channels, opens, calcium enters, depolarized, and NT released to neuron to carry signal to brain.

other direction = repolarize. ion channels close.

vestibular system

• where is it located?

• what does it do?

• in inner ear, next to cochlea

• it determines the position of the head, which determines balance

Parts of the VS:

1. Semicircular canals 

2. Utricle 

3. Saccule

semicircular canals detect…

angular acceleration during rotation of head along 3 axes

Utricle and Saccule provide info about…

linear acceleration of head.

• changes in position relative to gravity (straight line)

describe how semicircular canals detect rotation

• Stereocilia surrounded by a jelly mass (aka cupula), which is in ampulla. 

as you turn ur head, fluid lags, and when it catches up, you get used to the movement. then same when it stops.

• fluid moves relative to bone. (moves differently)

How does the utricle and saccule detect linear movement. 

• Steroecilia on hair cells are covered with gel layer with crystals on top. (otoliths) 

  • Otoliths are calcium carbonate crystals. 

• Otoliths make the gel heavier, so it pushes on hair cells when you change direction

• gravity

vestibular info is used to: (3)

1. Control eye movements 

2. Maintain upright posture and balance (bc it determines head position) 

3. Provide awareness of body position, acceleration, spatial info. 

what’s the pathway of info from vestibular nerve fibers?

• start with thru brainstem …

info goes thru brainstem, then thru thalamus, then to vestibular centers in parietal lobe of the c.cortex.

chemical senses include: (2)

taste and smell

what detects chemicals to detect taste and smell

chemoeceptors

what are the sensory organs for taste? and where

sensory organs are the taste buds in mouth and throat

what are the 5 taste receptors (the tastes)

1. sweet - fr sugar

2. sour - from acid

3. salty - from sodium

4. bitter - some base

5. umami - glutamate protein

sour and salty : signaling pathway

direct changes to ion channel flow

sweet, bitter, umami : signaling pathway

uses G protein-coupled receptors

(indirect)

pathway for olfactory: how do odorants lead to smell signal

• Odorant go up the nasal cavity  to the olfactory epithelium

• They bind to oderant receptors and activate G-proteins 

• Cation channels open and cell depolarizes → AP → signal to brain