Physiology 2130 Unit 3: Sensory System

how does the body detect external changes rapidly?

• many sensory systems → help keep homeostasis

  • detect external stimuli to keep internal enviro

1. Somatosensory (touch) system

2. Visual system

3. Auditory system

4. Vestibular system

5. Olfactory (smell) system

6. Gustatory (taste) system

sensory receptor

• specialized cell or structure

• detects internal + external stimuli → converts it into electrical signals the NS can interpret

how does stimuli become AP?

• transduction of enviro info → how info from external envrio become info brain uses w/ APs

• sensory receptors 1st take info from external stimuli & convert to APs

what are sensory receptors stimulated by?

• external stimuli detected by sensory receptor 4 conscious perception

• need adequate stimulus

1. Mechanical stimuli

2. Chemical stimuli

3. Electromagnetic stimuli

4. Other stimuli

mechanical stimuli

• stretch sensory receptors in skin → open ion channels, depolarization of sensory neuron making AP

• EX → touch, pressure, vibration, proprioception, sound

chemical stimuli

• stimuli bind w receptor, depolarize cell & cause AP

• EX → taste, odours, pain

electromagnetic stimuli

• light E absorbed by photoreceptors of eye (rod & cone in retina) → AP

• EX → light

other stimuli

• detected by hairs in vestibular system → convert it into AP

• EX → gravity, motion, acceleration, heat

adequate stimulus

• need specfic envrio stimulus that sensory receptor most sensitive

• GOAL → optimize sensory detection

somatosensory system

• detects & processes sensations of → touch, vibration, T, pain

  • each need many sensory receptors in skin 4 adequate stimulus

• most sensations found from skin

cutaneous receptor

receptors in skin

1. free nerve endings

2. tactile (meissner) corpuscles

3. lammilar (Pacinian) corpuscles

4. bulbous (ruffini) corpuscles

5. hair follicles

free nerve endings

• type of cutaneous receptor

• LOCATION→ thru out (skin, mucous membranes, muscles, internal organs)

• FUNCTION → diff sensory stimuli & protect (sense harmful conditions)

  • pain (nociception)

  • temperature (thermoreception)

  • touch (mechanoreception) types

• SENSITIVTY → wide range stimuli b/c unspecified, diff lvls based on location & f(x)

tactile (meissner) corpuscles

• type of cutaneous receptor

• LOCATION → glabrous skin (hairless)

  • fingertip, palm, feet soles, lip, tongue tip

• FUNCTION → touch 4 detailed info, light & low frequency vibration (30-50 hz)

  • adaptive receptors → then DEC response if constant stimuli

• SENSITIVTY → VVV & esp texture/fine touch

  • good 4 fine motor, specfic manipulation & recog. small object

lammilar (Pacinian) corpuscles

• type of cutaneous receptor

• LOCATION → DEEP dermis & hypodermis (subcutaneous tissue)

• FUNCTION → deep pressure & high frequency vibrations (250-350 hz)

  • adaptive receptors → then DEC response if constant stimuli

• SENSITIVTY →

  • VV mechanical changes → deep pressure, stretch, INC frequency

  • DEC light touch & low frequency vibrations

bulbous (ruffini) corpuscles

• type of cutaneous receptor

• LOCATION →

  • dermis & subcutaneous tissue

  • joint capsule, tendon, ligament

• FUNCTION →

  • info abt sustained pressure, skin stretch → pov object manipulate & grip

  • know shape & move of objects

  • proprioception MAINLY → body position & moves

  • DEC adaptive receptors → respond as long as stimuli exist

• SENSITIVTY → cont. pressure, stretch skin

  • DEC light, touch, rapid stimuli change

hair follicles

• type of cutaneous receptor

• LOCATION → all over except palm & soles

• FUNCTION →

  • make hair w proliferate keratocytes in hair bulb

  • anchor points 4 hair shaft

  • form sense of touch & aware of hair moves

• SENSITIVTY → X sensory cell

  • moves of hair follicle stimulate hair follicle receptors/hair root plexuses

hair root plexuses

AKA hair follicle receptors

• associated nerve endings near hair follicles

• USE → sense movement of hair follicle

  • impt to detect insects & object contact skin/hair

• adapt to cont. stimuli & keep sensitivity to changes in hair position over time

When are sensory receptor stimulated?

• Ion channels open

• Membrane permeability changes

• A receptor-generated potential forms

• If threshold is reached, action potentials are produced

when sensors sense something, where does info go?

• senses make receptor generated potential

  1. receptor pressed = skin receptor cells respond to stimuli, release neurotransmitters

     • movement detected in receptive field

  2. neurotransmitters stimulate dendrites of sensory neuron & make receptor generated potential

  3. receptor generated potential move down neurons & make AP @ axon terminals

  4. axon terminals send info to another neuron take info to brain

receptor generated potential

• changes in the membrane potential of sensory receptor cells in response to a stimulus

  • graded potentials that generate APs +send sensory info to CNS

• X APs

• X neurons

• POTENTIAL DEPOLARIZING

• release neurotransmitters

how are receptor generated potential similar to EPSP & IPSP

1. depolarize main but can hyper polarize

2. INC cell membrane permeability to Na/K

3. local & X propagate DOWN neuron → spread like EPSP

4. DEC over time & space

5. proportionate to stimuli (X all or nothing)

neural coding

• how NS covert frequency info of neural activity 4 brain to understand

  • interpret changes of stimuli in waves & respond proportional to stimuli

• MOSTLY → sensory cell release neurotransmitters proportional to stimuli

• RESULT → make DEC/INC AP based on object weight

  • INC object weight = INC AP = brain sense INC AP frequency

What are the 2 paths a sensory signal takes to reach the brain?

Spinothalamic tract

Dorsal column-medial lemniscus pathway

Spinothalamic tract

• USE →

  • (1) pain

  • (2) T

  • (3) crude touch

• free nerve endings signal this path

—

1. 1st order nerve (sensory nerve) detects info

2. send info ASAP & contralaterally to signals to 2nd order nerves

3. info sent to thalamus → signal 3rd order nerve

4. info stimulates sensory cortex & sent to correct places in brain

Dorsal column-medial lemniscus pathway

• USE →

  • (1) fine detail

  • (2) vibration

  • (3) proprioception

• tactile lammilar, bulbous corpuses signal this path

• USE → detailed sensory discrimination & sense body position

—

1. 1st order nerve (sensory nerve) detects info

2. send info to second order nerve and synapse contralaterally (longer time taken)

3. info sent to thalamus → signal 3rd order nerve

4. info stimulates sensory cortex & sent to correct places in brain

precentral gyrus

• used 4 motor control

• get info from frontal lobe

central sulcus

• btwn precentral gyrus & postcentral gyrus

• central ditch/divot

• anterior = motor control

• posterior central = somatosensory cortex

what describes the somatotopic organization of the postcentral gyrus?

• postcentral gyrus has primary somatosensory cortex

• somatotopic organization into a sensory homunculus

  • diff regions to specific cortical region

  • adjacent body part adjacent on cortical area

  • feet + leg = media

  • face + tongue = lateral

somatosensory cortex

• in parietal lobe + within postcentral gyrus

• USES →

  1. interpret sensory data from receptors onto homunculus

     • pain, touch, T

  2. perceive tactile sensation

  3. proprioception → sense body position

  4. localize stimuli 4 proper response & interact w enviro

  5. where all info from sensory receptors sent & interpreted on homunculus map

How does the somatosensory cortex relate to the motor cortex?

• somatosensory cortex lies directly posterior to motor cortex

• sensory feedback from cortex helps guide & refine movement

• both cortices organized somatotopically with corresponding body maps

Importance of the relationship between somatosensory cortex and motor cortex

• sense body position

• coordinate voluntary movement

• adjust motor output based on sensory input

visual system

• USE →

  • (1) detect light → convert to APs

  • (2) send info to primary visual area to process

  • (3) process & aware of visual world

What structures make up the visual system?

1. EYE

   • has photoreceptors that detect light & convert to electrical signals

2. VISUAL PATHWAY

   • carry APs from retina → brain

3. PRIMARY VISUAL CORTEX

   • on occipital lobe & process incoming visual info

what are the structures of the eye?

1. cornea

2. iris

3. lens

4. retina

5. fovea

6. optic nerve

Cornea

USE →

• main light focusing structure

• bends/focuses incoming light rays to make clear image on retina

• protect eye

ANATOMY →

• transparent

• dome shaped

• cover iris, pupil, anterior of eye

• avascular (X blood vessels) & get nourishment from tears

Iris

USES →

• regulates amt of light entering eye → control pupil size w/ muscles

  • EX → bright = constrict, dim = dilate

• helps eye look & colour → based on pigments it has

ANATOMY →

• colored part of eye surround pupil

Lens

USES →

• focuses light onto retina by ACCOMODATION

• send info to retina & fovea

ANATOMY →

• transparent + flexible

• behind iris & pupil

accommodation of lens

• contract & relax muscles in lens 4 visual acuity & distances

Retina

USES →

• photoreceptors (rods + cones) + other cells → convert light into electrical signals → transmit to brain w optic nerve

• vision &→ help see detailed image & colour

ANATOMY →

• thin light sensitive tissue layer

• back of eye

Fovea

USES →

• highest lvl visual acuity

• dense w cone photoreceptors (X rods) → good 4 detailed, colour vision in BRIGHT LIGHT

• sharp central vision → read & drive

ANATOMY →

• small central pit in retina

Optic nerve

USES →

• send visual info to brain

• get info from fovea & retina

ANATOMY →

• nerve run from optic disc → brain

• retinal ganglion cell axons + supportive cells

What cell types in the retina and how does their organization contribute to their function?

• organized cells in layers to process visual info progressively

1. Rod cells

2. Cone cells

3. Bipolar cells

4. Ganglion cells

5. Amacrine cells

6. Pigment layer

photoreceptor & photopigment

• receptor = respond to light

• pigment = chem sensitive to light

How do rods and cones function?

• in retina

• X axon → X neuron, X APs make itself

• receptor cells → release neurotransmitters & make graded receptor potentials to pass along info

  • can add or subtract signals → modulate by amacrine & bipolar cells to send ganglion cells proper info

FULL DARK→

• ROD & CONE depolarize = release NTM inhibit bipolar cell = X make graded receptor potentials = X info sent to visual cortex w ganglion cells = X see much

  • depolarize → Na in & K out of cell lead to APs & inhibit NTMs

DIM LIGHT→

• ROD hyperpolarize = X release NTM inhibit bipolar cell = make graded receptor potentials = info sent to visual cortex w ganglion cells = see B/W + objects w/o fine detail & colour

  • hyperpolarize → Na channel close bc light hit photopigments & change shape (Na permeability DEC & channel close) BUT K channel still open

    • THUS → cell hyperpolarize b/c Na DEC in & K INC out

• CONE depolarize little = release NTM inhibit bipolar cells = X see much (X colour, X info sent to visual cortex)

BRIGHT LIGHT →

• CONE hyperpolarize more = X release NTM inhibit bipolar cells = make graded receptor potentials = info sent to visual cortex w ganglion cells = see colour & fine details

Rod cells

USE →

• low light, night vision, peripheral vision

• XXXX detail

• dark = rod cells depolarizes & release neurotransmitter inhibit bipolar cells

ANATOMY →

• mainly in retina (out & around fovea)

• VV sensitive to light

FAIL → detail, colour (1 photopigment only)

Cone cells

USE →

• bright light, high detail, colour

• dark = cone cells depolarizes & release neurotransmitter inhibit bipolar cells

ANATOMY →

• 3 photopigments of wavelength sensitivity

  • S → short like BLUE

  • M → medium like GREEN

  • L → long like RED

• mainly in fovea area (#1 [ ] in this area)

Bipolar cells

• integrate visual signals BEFORE send forward

• each cell gets info from diff rods + cones → collect visual info & INC sensitivity to light & colour

• depolarized by cone & rod cell’s neurotransmitters in the dark

Ganglion cells

• LAST output neurons of retina → get processed visual info from bipolar & amacrine cells

• send info w axon (form optic nerve) → brain

Amacrine cells

• modify signals btwn bipolar & ganglion cells → synapse both & affect visual signal before get to ganglion

Pigment layer

• cell layer in retinal support photoreceptors → absorb excess light

• RESULT → DEC scattering & INC photoreceptor health

how does the the eye process info?

1. light pass thru CORNEA of eye

2. IRIS regulates light passed in eye

3. LENS focus light on retina (back of eye)

4. RETINA uses photoreceptors to convert light as electrical signals → see image

   • uses graded potentials to transfer APs along visual path to primary visual area

5. signals transmit to brain w OPTIC NERVE

6. vision focused on FOVEA

Visual information flows ?

Photoreceptors → Bipolar cells → Ganglion cells → Brain

how does the retina convert light into electrical signals?

• use graded potentials

which cells make graded potentials

• bulbous + rod

• both release NTMs cause graded potentials down line

  • sum OR subtract potentials to be proportional to stimuli

How is light transduced to action potentials?

Ganglion cell axons form the optic nerve and send APs to the visual cortex.

types of eye movements

focus on object = ensure image focused on fovea b/c most cone cells present here

1. Saccades

2. Smooth pursuit

3. Vestibular ocular reflex (VOR)

4. Vergences

Saccades

• rapid jerky eye movements

• quick move eye to object

• EX → reading or gazing around a room while keeping head still

Smooth pursuit

• smooth movement of eyes to follow path & keep moving object focused on fovea

• EX → the butterfly moving from one flower to the next with just your eyes if you are able

vestibular ocular reflex (VOR)

• eye movement when focus attention on object + shake up/down or back/froth

• EX → shake your head, yes or no

Vergences

• movements made when object approach/move away → eyes converge or diverge

• EX → staring at a pencil and moving it away or towards your face

what are the structures of the ear?

1. OUTER EAR

   1. auricle

   2. external auditory canal (ear canal)

   3. tympanic membrane (ear drum)

2. MIDDLE EAR

   1. eustachian/auditory tube

   2. auditory ossicles

      1. incus

      2. malleus

      3. stapes

3. INNER EAR

   1. oval window

   2. round window

   3. semi-circular canals

   4. cochlea

auricle

• collect & amplify sound by capture sound wave & direct → ear canal

• localize sound → tell sound direction & distance

external auditory canal

• AKA ear canal

• (1) sound transmission

  • carry sound waves from external envrio to eardrum

  • S shape curve → amplify & enhance frequences & help hearing process

• (2) protect eardrum & middle ear

  • canal curve → protect eardrum from foreign objects

  • cermen (earwax) → trap dust, debris, antimicrobe & stop infection

cermen

AKA earwax

• made from glands on cartilaginous part of canal

tympanic membrane (eardrum)

• thin cone membrane

• (1) sound transmission

  • convert sound waves in air → mechanical vibrations

  • sound wave strike eardrum = eardrum vibrate = vibration sent to malleus (on inner eardrum)

• (2) protection

  • barrier separate external ear & protect middle ear

  • keep sterile envrio of middle ear

Eustachian/auditory tube

• part of middle ear

• narrow canal → connect middle ear to nasopharynx (upper part of throat behind nose)

• USE →

  • equalize air pressure on eardrum sides

  • drain fluid from middle ear

auditory ossicles

• part of middle ear

• connect to oval window via stapes

• 3 tiny bones

  • incus → anvil

  • malleus → hammer

  • stapes → stirrup

• USE → transmit sound vibration from eardrum to inner ear

  • sound waves strike tympanic membrane → membrane vibrate → malleus move → movement send to incus → sent to stapes → inner ear

oval window

• part of inner ear

• USE →

  • control movement of fluid in cochlea

  • activate receptors for hearing

  • stapes vibrate on oval window → standing waves in cochlea → detected by specialized hairs on nerve cells → cells carry APs to auditory centre of brain

round window

• part of inner ear

• USE → pressure-relief valve from cochlea

  • after sound travel thru cochlea → stops waves spread thru round window = X vibrate in cochlea

semicircular canals

• part of inner ear

• 3 look shapes

• USE → keep balance + spatial orientation

  • each canal used for specfic movement plane → horizontal, anterior/superior, posterior (X/Y/Z)

cochlea

• part of inner ear

• spiral shape → 3 divisions

  • 1. scala vestibili

  • 2. cochlear duct

  • 3. scala tympani

• fluid filled → transform sound vibration to neural signals & send to brain (AP made & send via cochlear nerve)

divisions of the cochlea

1. upper → scala vestibili (vestibular duct)

2. middle → cochlear duct

3. lower → scala tympani

4. tectorial membrane

5. basilar membrane

6. organ of corti

• scala tympani & vestibli filled w perilymph

• cochlea duct filled w endolymph

perilymph

ionic sol’n → INC [Na], DEC [K]

like extracellular fluid

fills scala tympani & vestibli

endolymph

sol’n → INC [K], DEC [Na]

like intracellular fluid

basilar membrane

• separate cochlear duct & tympanic duct

• has organ of corti

organ of corti

• has special hair cels turn sound waves → AP

• hairs embedded in tectorial membrane

  • sound waves = basilar membrane vibrates → fixed hair cells in tectorial membrane bend

what is sound?

• series of pressure WAVES emitted, travel thru air, collected in ear

• wave features

  • amplitude → V & loudness of sound

  • frequency → distant of waves & sound pitch

• pressure wave moves thru air & hit ear → transmit to tympanic membrane → membrane vibrates = ossicles vibrate → oval window vibrates, make standing wave in cochlea → vibrates basilar membrane

how does the ear detect different frequencies and how is sound heard?

WAVE IN AIR

1. sound waves rep alternating areas of high & low volumes

   • pressure waves from stimuli measured for specfic wavelength

2. sound waves funneled through outer ear

   1. auricle → ear canal → tympanic membrane

1. tympanic membrane vibrates to respond to sound waves

   • transfer pressure wave to middle ear to ossicles

2. vibrations amplified across ossicles

   • pass thru malleus, incus, stapes

   • 3 bones connect tympanic membrane to oval window (inner ear)

     • (1) malleus → attach tympanic membrane, move based on vibration of eardrum → sent to incus & stapes

     • (2) stapes → connect oval window & move to create pressure waves in perilymph fluid of cochlea

WAVE IN FLUID

4. vibrations against oval window create standing wave in endolymph OR vestibuli

   1. oval windows vibrate

   2. cochlea fluid vibrates → pressure wave travelling thru perilymph OG & displace endolymph fluid

   3. create standing waves when waves resonate @ specfic frequence of sound wave → standing wave in fluid bending of cochler duct me

   4. standing wave in basilar membrane → go to cochlear duct

5. pressure bend cochlear duct membrane @ resonance

   • basilar membrane airs vibrate at specfic point → connect to specfic sound frequency

6. sound frequency is determined

sound resonates throughout whole cochlea & return back out round window → stop vibration & resonance forever

resonance

bending of cochlear duct membrane @ max vibration of a frequency

how are standing waves in the cochlea formed?

USE OF WAVES →

• part of process to make cochlea’s fluid filled structure convert mechanical E → neural signals

PROCESS →

• standing wave = when incoming pressure wave & its reflection in cochlear duct interfere

  • RESULT → regions of max & min displacement occur as the frequency of sound tries to match natural frequency of a region on basilar membrane

    • basilar membrane has variations for stiffness & width = resonance occur at diff frequences

how are different frequencies detected by the ear?

• tonotopic organization → based on location in cochlea

  • CAUSE → diff thickness & flexibility of material

max vibrations found at →

• BASE of basilar membrane = DEC frequency heard

  • thicker narrow & DEC flexible membrane

• APEX of basilar membrane= INC frequency heard

  • thinner wider & INC flexible membrane

stereocilia

• hair cells embedded on tectorial membrane

• tectorial X move BUT basilar membrane moves

how does the cochlea create APs?

1. fluid waves move through cochlea → moves oval window & create standing wave in cochlear fluid

2. basilar membrane vibrates & hair cells bend

   1. basilar membrane fluid movement = bend hair cell’s stereocilia as response to vibrations

   2. hair cells = organ of corti

3. mechanically gated ion channels open

   1. K⁺ enters hair cells & depolarize

4. neurotransmitter release

   1. depolarized hair cells release neurotransmitter onto auditory neurons

5. auditory nerve fibers generate APs

   1. AP travel to auditory cortex

6. cochlear nerve used to take info to brain

What transforms sound vibrations into neural signals that are sent to the brain?

the cochlea

What would happen if the basilar membrane was damaged at the apex?

hard time detecting low pitch sounds

what is damaged if a person is having trouble hearing quieter sound?

• affect structures needed to make vibrations in cochlea to detect sound

  • malleus + incus → amplify sound by causing stapes to vibrate in the oval window

  • tympanic membrane → vibrate ossicles as sound pressure waves hit it

T/F. The tympanic membrane, or eardrum, vibrates when sound pressure waves strike it, and these vibrations are passed through the ossicles

T

vestibular system

USE → balance + spatial orientation

• coordinate w other sensory systems to share info → semicircular canal + otolith organ inputs + visual & proprioceptive system

• semicircular canals sed in VOR → stabilize vision w eye movements counteract head moves

FOUND → inner ear

PROCESS → detect head move, change in position & sends sensory info to brain to keep balance, posture, eye movement

structures of vestibular system

vestibular apparatus →

1. 3 semicircular canals/ducts

   1. anterior

   2. lateral

   3. posterior

   4. all looped tubulars in inner ear

2. ampullae

3. utricle

4. saccule

semicircular canals

USE → balance + spatial orientation

ANATOMY →

• inner ear

• 3 looped canal tublar structures

  1. anterior (superior) → vertical

     • ROLE → front/back moves

  2. posterior → vertically BUT perpendicular to anterior

     • ROLE → head tilts to shoulders

  3. lateral (horizontal) → horizontal

     • ROLE → detect horizontal head moves

ampullae

• sensors detect where body is in space w/ sensory hair cells

• @ end of each semicircular duct

• filled w/ endolymph & pushes cupula → hair cells in cupula move as endolymph moves → hair cells release NTMs (constant) → fire APs along sensory nerve toward head

how does the body detect angular & rotational moves?

• use semicircular canals’ AMPULLAE

• based on move, cause change in hair cells of cupula inside ampullae → change release of NTMs that affect AP firing frequency

EX → stand still

• baseline amt of NTMs released

• NTMS stimulate sensory nerve fibers & cause APs

• AP frequency (based on amt of NTMs released) interpreted by brain

EX → dancing

• inertia of endolymph lag after canal wall moves

• lag push against cupola & stimulate hair cells

• hair cells bent & based on direction, release INC/DEC NTMs → change AP frequency along sensory nerve

• info sent to brain w vestibular nerve & brain interprets it as movement of heads

utricle

USE → balance + spatial orientation (horizontal)

ANATOMY →

• inner ear

• filled w endolymph

• bigger + horizontal position

• has hair cells in gelatinous layer w/ otoliths

saccule

USE → balance + spatial orientation (linear + vertical)

ANATOMY →

• inner ear & closer to cochlea

• filled w endolymph

• smaller + vertical position

• has hair cells in gelatinous layer w/ otoliths

compare contrast utricle & saccule

(+) →

• both have hair cells w/ otoliths

• detect linear acceleration & head position change

• send info to brain w vestibular nerve

• work for balance + spatial orientation

(-) →

• U → horizontal

• S → vertical

how does the body detect up and down moves?

• UTRICLE + SACCULE

• MACULA → tissue & structure

• based on head move, otolith crystals move → affect hair cell direction & change NTM release & ATP pxdtn on neuron (still release NTMs during rest)

STRUCTURE →

• vestibular division of vestibular cochlear nerve nerves in tissue → connect to hair cells in gelatinous membrane (like cupula) that release NTMs

• membrane connected to otolith & has Ca carbonate crystals

EX → look ahead & upright

• all structures upright, hair cells release NTMs → cause frequency of APs in nerve → brain detect head stable & align

EX → head tilt forward

• gravity move otolith crystals forward, pulling on hair cells → change amt NTMs released → affect amt APs along neuron → brain interpret & know head move forward

• head move forward so lag of hair cells & they bend back as they slowly move forward

how does a hair cell of the vestibular apparatus tell how much neurotransmitters are released?

• based on bending of hair cells

USE →

• stereocilia + kinocilia vertical = AP steady

• stereocilia bend → kinocilia = INC AP frequency

• stereocilia bend ← kinocilia = DEC AP frequency

ANATOMY →

• stereocilia = shorter hair

• kinocilia = 1 long hair

• stereocilia + kinocilia connect to cell body at base in nucleus

• nucleus connected to sensory nerve

what is the clinical significance of the vestibular system?

semicircular canal pxb = vertigo, dizziness, balance issue

EX → benign paroxysmal positional vertigo (BPPV)

• dislodged otoliths from utricle enter a semicircular canal

• RESULT → disrupt function & cause vertigo

• SOLVE → series of head positions help restore position of otolith crystals, & DEC symptoms