Sensory Receptors 8 th ed 50.1 to 50.4 7 th ed 49.1 to 49.4

Sensory Receptors8th ed 50.1 to 50.4

7th ed 49.1 to 49.4

Physiological basis for all animal activity: processing sensory information and generating motor output in response to that information

This is a continuous cycle

Sensory information can be from external or internal environment.

Sensory pathway:

Sensory reception Transduction Transmission Perception Amplification and adaptation

Sensory pathway:


Sensory reception

1st step of sensory pathway Sensory receptors: Specialized neurons or

epithelial cells; Single cells or a collection of cells in organs

Very sensitive

Sensory pathway:


Sensory transduction: Conversion of physical, chemical and other

stimuli to change in membrane potential

Receptor potential: change in membrane potential itself

Sensory pathway:


Transmission:

Sensory information is transmitted through the nervous system as nerve impulses or action potential to the Central Nervous System (CNS).

Some axons can extend directly into the CNS and some form synapses with dendrites of other neurons

Sensory neurons spontaneously generate action potential without stimulus at a low rate

Magnitude of receptor potential controls the rate at which action potentials are generated (larger receptor potential results in more frequent action potentials)

MuscleWeakmuscle stretch

Receptor potential

Action potentials

Mem

bra

ne

po

ten

tial

(m

V)

Time (sec)0 1 2 3 4 5 6 7

–70

–70

–50

0

Stretchreceptor

Dendrites

Axon

Strongmuscle stretch

Time (sec)0 1 2 3 4 5 6 7

–70

–70

–50

0

Sensory pathway:


Perception:

Action potential reach the brain via sensory neurons, generating perception of a stimulus

All action potentials have the same property, what makes the perceptions different are the part of the brain they link to.

Sensory pathway:


Amplification and adaptation:

Strengthening of stimulus energy during transduction (involves second messengers)

Continued adaptation: decrease in responsiveness upon prolonged stimulation

Types of sensory receptors:

Mechanoreceptors Chemoreceptors Electromagnetic receptors Thermoreceptors Pain receptors

Mechanoreceptors:

sense physical deformation caused by pressure, touch, stretch, motion, sound

Stretch receptors are mechanoreceptors are dendrites that spiral around small skeletal muscle fibers

MuscleWeakmuscle stretch

Receptor potential

Action potentials

Mem

bra

ne

po

ten

tial

(m

V)

Time (sec)0 1 2 3 4 5 6 7

–70

–70

–50

0

Stretchreceptor

Dendrites

Axon

Crayfish stretch receptors have dendrites embedded in abdominal muscles. When the abdomen bends,

muscles and dendrites stretch, producing a receptor potential in the stretch receptor. The receptor potential triggers action potentials

in the axon of the stretch receptor. A stronger stretch produces a larger receptor potential and higher frequency of action potentials.

Strongmuscle stretch

Time (sec)0 1 2 3 4 5 6 7

–70

–70

–50

0

Lighttouch

HairStrongpressure

Hypodermis

Nerve Connectivetissue

Dermis

Epidermis

Touch receptors (light and deep touch) are embedded in connective tissue

Chemoreceptors:

General receptors: respond to total solute concentrations

Specific receptors: respond to concentrations of specific molecules

LE 49-4

Electromagnetic receptors:

Detect various forms of electromagnetic energy like visible light, electricity, magnetism

Snakes can have very sensitive infrared receptors – detect body heat of prey

Animals can use earth’s magnetic field lines to orient themselves during migration (magnetite in body) – orientation mechanism

This rattlesnake and other pit vipers have a pair of infrared receptors, one between each eye and nostril. The organs are sensitive enough to detect the infrared radiation emitted by a warm mouse a meter away.

Eye

Infraredreceptor

Some migrating animals, such as these beluga whales, apparently sense Earth’s magnetic field and use the information, along with other cues, for orientation.

Cold HairHeat


Thermoreceptors:

Detect heat and cold Located in skin and

anterior hypothalamus Mammals have many

thermoreceptors each for a specific temperature range

Capsaicin triggers the same thermoreceptors as high temperature

Menthol triggers the same receptors as cold (<28oC)

Pain Hair


Pain receptors (nociceptors):

Stimulated by things that are harmful – high temperature, high pressure, noxious chemicals, inflammations

Defensive function

Sensing gravity and sound in invertebrates:

Hair of different stiffness and length vibrate at different frequencies and pick up sound waves and vibrations

Statolith

Sensorynerve fibers

Ciliatedreceptor cells

Cilia

Statocyts: organ with

ciliated receptor cells surrounding a chamber containing statoliths in invertebrates – sense gravity

Tympanic membrane stretched over their “ear” help sense vibrations

1 mm

Tympanicmembrane

Sensing gravity and sound in humans:

Human ear: sensory organ for hearing and equilibrium

Our organ for hearing “hair cells” are mechanoreceptors because they respond to vibrations

Moving air pressure is converted to fluid pressure

Ear structure:

Outer ear: pinna, auditory canal, tympanic membrane (separates outer and middle ear)

Middle ear: three small bones malleus (hammer), incus (anvil) and stapes (stirrup) transmit vibrations from tympanic membrane to the oval window.

Eustachian tube connects middle ear to the pharynx and equalizes pressure

Inner ear: consists of fluid filled chambers including semicircular canals (equilibrium) and cochlea (hearing)

Moving air travels through the air canal and causes the tympanic membrane to vibrate

Three bones of the middle ear transmit the vibrations to the oval window, a membrane on the cochlear surface

That causes pressure waves in the fluid inside the cochlea

The cochlea: Upper vestibular canal and inner tympanic

canal filled with perilymph; middle cochlear duct filled with endolymph

Organ of Corti: Floor of the cochlear duct is the

basilar membrane Organ of corti is located on the

basilar membrane, with hair cells which has hair projecting into the cochlear duct.

Many of the hairs are attached to the overhanging tectorial membrane.

Sound waves cause the basilar membrane to vibrate. This results in displacement and bending of the hair cells within the bundle.

This activates the mechanoreceptors, changes the hair cell membrane potential (sensory transduction) which generates action potential in the sensory neuron.

Ovalwindow

Cochlea

Tympaniccanal

Basilarmembrane

Vestibularcanal

Perilymph

Stapes Axons ofsensoryneurons

Apex

Base

Roundwindow

Equilibrium:

In the vestibule behind the oval window are urticle, saccule and three semicircular canals

Three semicircular canals arranged in three spatial planes detect angular movements of the head

The hair cells form a cluster. They have a gelatinous capula.

Fluid in the semicircular canals pushes against the capula deflecting the hairs, stimulates the neurons

Semicircular canals

Flowof endolymph

Vestibular nerve

Nerve fibersVestibule

Utricle

Saccule

Ampulla

Flowof endolymph

Cupula

Body movement

Hairs

Haircell

Utricle (oriented horizontally), saccule (oriented vertically) tell the brian which way is up and the position of the body and acceleration

Sheet of hair cells project into a gelatinous capula embedded with otoliths (ear stones). Movement of the head causes otoliths to in different directions against the hair protruding from the hair cells. This movement is detected by the sensory neurons

Dizziness: false sensation of angular motion

http://www.dizziness-and-balance.com/disorders/bppv/otoliths.html

Hearing and equilibrium in fish:

Vibrations in the water – conducted by skeleton to inner ear canals, move otoliths which stimulate hair cells

Swim bladder: air filled, responds to sound

Lateral line sense organ

Lateral line sense organ:

Water flows through the system

Bends hair cells; generates receptor potential

Nerve carries action potential to the brain

Helps them sense water currents, moving objects, low frequency sounds

Lateral line

Lateral line canal

Epidermis NeuromastOpening oflateral line canal

Scale

Lateral nerveSegmental muscles of body wall

Cupula

Supportingcell

Nerve fiber

Sensoryhairs

Hair cell

Nerve tobrain

Screeningpigment

Ocellus

Visual pigment

Photoreceptor

Light

Light shining frombehind is blockedby the screening pigment

Light shining fromthe front is detected

VisionPhotoreceptors Planarians: Ocelli or eye

spots in the head region Light stimulates

photoreceptors Brain compares rate of

action potential coming form the two ocelli

Brain directs the body to turn until sensation form both ocelli are equal and minimal

Animal can move to shade, under a rock away from predators

Compound eyes:

Very good at detecting movement Very good at detecting flickering light (6 times

faster than human eye) Some bees can see in the ultraviolet range of

light

Several thousand omatidia (facets) in every eye Cornea and crystalline cone form the lens which

focuses light on the rhabdom Light stimulates the photoreceptors to generate

receptor potential which generates action potential

2 m

m

Ommatidium

Rhabdom

PhotoreceptorAxons

Cornea

Crystallinecone

Lens

Vertebrate eye Single lens system (very different from

invertebrate single eyes)

Central artery andvein of the retina

Optic disk(blind spot)

Opticnerve

ChoroidSclera Eyeball or globe consists of

Sclera: tough white outer connective tissue

Cornea: clear part of sclera in the front of the eye – lets light into the eye, acts as a fixed lens

Choroid: pigmented inner layer: forms iris (doughnut shaped) – can change size to regulate the amount of light coming in

Iris

Cornea

Pupil

Aqueoushumor

Vitreous humor

Fovea (centerof visual field)

Retina Retina: innermost layer with neurons and photoreceptors

Aqueous humor: fluid that fills the anterior cavity (blockage of ducts increases pressure and causes glaucoma)

Vitreous humor: jellylike, fills the posterior chamber

Ciliary body

Suspensoryligament

Lens

Lens: clear disk of protein

Retina

Choroid

Suspensoryligaments

Front view of lensand ciliary muscle

Ciliarymuscle

Lens (rounder)

Lens (flatter)

Near vision (accommodation)

Distance vision

Humans and other mammals

spherical ( ciliary muscles contract, sensory ligaments relax – near objects)

flatter (ciliary muscles relax, edge of choroid moves away from lens, suspensory ligaments contract and pull the lens – distant objects)

Fishes, squids and octopuses focus by moving lens forward and backward

Photoreceptors Rods: sensitive to light, do not distinguish

colors Cones: detect color, not very sensitive to

light Nocturnal animals have a higher proportion of

rods

Rods and cones have stacks of disks

rhodopsin (retinal - vitamin A derivative + opsin) in the membrane

get activated and cause sensory transduction

Outersegment

Disks

Rod

Insideof disk

Cell body

Synapticterminal

Rhodopsin

Cytosol

Retinal

Opsin

Leftvisualfield

Rightvisualfield

Lefteye

Righteye

Primaryvisual cortex

Lateralgeniculatenucleus

Optic nerve

Optic chiasm

Information from the each eye is carried by the optic nerve (each with about a million axons)

Optic nerves meet cross at the optic chiasm

Information from right visual field of both eyes goes to the left side of the brain

Information from the left visual field of both eyes goes to the right side of the brain

Synapse with interneurons which take the information to the primary visual cortex

Perception of gustation (taste) and olfaction (smell)

Insects In insects taste sensation is located within sensory

hairs called sensilla (on feet and mouthparts) Olfactory odorants are detected by olfactory hairs

Sensillum

Mammals In mammals specialized epithelial cells form taste

buds Tastants detect five perceptions of taste: sweet,

sour, salty, bitter and savory (MSG) Chemoreceptors generate receptor potential by

triggering a chain of reactions involving different proteins for different tastes in the receptor cells

Tongue

Taste pore Sugarmolecule

Tastebud

Sensoryneuron

Sensoryreceptorcells

Sensory neurons lining the nasal cavity and extending into the mucus layer get stimulated by odorants. The stimulus is transmitted directly to the olfactory bulb of the brain

Nasal cavity

Brain

Odorant

Odorantreceptors

Odorant

Plasmamembrane

Mucus

Olfactory bulb

Action potentials

Bone

Epithelial cell

Cilia

Chemoreceptor

Documents

Sensory Receptors 8 th ed 50.1 to 50.4 7 th ed 49.1 to 49.4