Mechanoreception

3 main sensory systems that use mechanoreception

1. touch/pressure

2. proprioception

3. hearing

all mechanoreception systems use

mechanically gated ion channels

touch receptors

• channel proteins in integument have external fibers

• when stretched, fibers pull open gates to ion channels

• cations enter channel, leading to receptor potential and maybe increased action potential

pacinian corpuscle

detects pressure in skin, rapidly adapts

Merkel cells

close to skin surface, numerous dendrites with large surface area, very sensitive

proprioception

• detection of motion and position

• “stretch” receptors provide feedback about positioning of muscles. when they are absent, movements are uncoordinated

proprioception 2 main roles

1. limbs in space (stretch receptors)

2. vestibular apparatus: equilibrium, head in space (hair cells)

TRP-N1

mechanically gated channel found in afferent neurons responsible for proprioception in model organisms

vestibular apparatus

• provides proprioception information about equilibrium, head position, eye movement, posture

• located in vertebrate inner ear

• utilizes hair cells

hair cells

transduce movement using externally gated mechanical channels

stereocilia

in hair cells, graded heights, connected by tiplinks

tiplinks

• cell adhesion molecules that connect stereocilia

• when a force causes them to bend, tip links stretch and open the channels → depolarization!

semicircular canals

detect spinning/rotation

ampulla

hair cells protrude off this structure at the base of ear canal

cupula

encases ampulla

bending, spinning causes

fluid within semicircular canals to move, leading to bending of cupula and hair cells

why do you remain dizzy/disoriented after spinning?

takes time for fluid to stop spinning, inertia

hearing

the perception of sound into waves of energy that travel through air

components that allow for sound localization

size, structure, and placement of external ear components allows for sound localization

tympanic membrane

• ear drum, where initial sound reception occurs

• internal for mammals, external for amphibians

• vibrate in response to sound waves, leading to movement in a chain of 3 bones, transmitting frequency of movement to oval window of ear

vibration of oval window reproduces

wave-like movements in the fluid of inner ear

why doesn’t sound hit the oval window directly?

waves are not strong enough → need to amplify sound

pressure = force/ unit area → amplified sounds

organ of corti

• hearing organ, located in the cochlea, surrounded by fluid

• contains hair cells arranged in 4 parallel rows → 1 row of inner hair cells, 3 rows of outer hair cells

• each has ab 100 stereocilia embedded in the tectorial membrane

inner hair cells

• transform mechanical forces into electrical impulses of hearing

• stereocilia are bent back/forth by movement of basilar membranes

• contact with tectorial membranes leads to tiplinks stretching and channels opening

• communicate via chemical synapse with afferent nerve fibers that make up auditory (cochlear) nerve

outer hair cells

• change length in response to membrane potential changes (electromotility)

• amplify of movement of basilar membrane

• enhances stimulation of inner hair cells

• protein prestin

pitch discrimination

different frequencies vibrate different regions on the cochlea, high pitch at narrow end near oval window

loud discrimination

larger amplitudes of vibration strike more forcefully

aging

hair cells do not grow back!