chapter 29 sensory reception © 2012 pearson education, inc

Chapter 29

SENSORY RECEPTION

© 2012 Pearson Education, Inc.

Sensory Receptors

Sensory receptors = specialized cells or neurons that detect

– conditions of the external and internal world

Sensory receptors convert stimulus to action potential

– This is called sensory transduction

Message of stimulus carried to CNS

– Interpretation of stimulus depends on area of CNS stimulated


Fig. 27.2

• Sensory transduction begins with a receptor protein that opens or closes ion channels in response to stimulus

• Changes in ion flow change membrane potential of sensory cell

• Receptor potential = membrane potential of sensory cell

Notice how each stimulus binds a receptor protein to open or close ion channel.

Figure 29.UN04

Sensoryreceptors

electromagneticreceptors

pain andthermoreceptors

(b)(a)

are grouped into several types

involvedin

involvedin

many typesfound in

sensitiveto

(c)human skintaste andsmell

touch, hearing,balance

many are

(d)

most common are

(e)

Mechano-receptors

Chemo-receptors

light

Rods andconesHair cells

Sensory Receptor May be Found on Plasma Membrane of a Separate Sensory Cell or on a Sensory Neuron


Sensory receptor on Separate Sensory Cell

– Vision (rods and cones)

– Taste (taste buds)

– Hearing (hair cells)

– Balance (hair cells)

Sensory receptor on specialized sensory nerve ending

– Pain

– Heat

– Touch

– smell

– If receptor found on separate cell - stimulus triggers release of neurotransmitters from sensory cell

Changes in receptor potential lead to formation of action potentials in sensory neurons


“Hairs” of areceptor cell

Neurotransmitterat a synapse

Sensoryneuron

Actionpotentials

Actionpotentials

Figure 29.2ASugarmolecule

Sensoryreceptorcells

Tastepore

Tastebud

Sensoryneuron

Sugar molecule(stimulus)

Membraneof a sensoryreceptor cell

Sweetreceptor

Signaltransductionpathway

Ionchannels

Ion

Sensoryreceptorcell

Receptorpotential

Neurotransmitter

Sensory neuron

Action potentialto the brain

5

4

3

2

1

6

No sugar Sugar present

Rates of action potentials

mV

Example of sensory reception – Sense of Taste

Notice how binding of sugars to receptor on taste bud leads to action potential in sensory neuron

Let’s look at the details….

Figure 29.2A_1

Sugarmolecule


Tastepore

Tastebud

Sensoryneuron

1

1. sugar molecules enter the taste bud

Sugar molecule(stimulus)

Membraneof a sensoryreceptor cell

Sweetreceptor

Signaltransductionpathway

Ionchannels

Ion

Sensoryreceptorcell

2

3

4

2. sugar molecules bind to sweet receptors

3. the binding triggers some ion channels (usually Na channels) in the membrane to close and others to open

4. Change in ion flow changes membrane potential (receptor potential) of sensory cell

Receptorpotential

Neurotransmitter

Sensory neuron

Action potentialto the brain

No sugar Sugar present

Rates of action potentials

mV

Ion channels

Ion

Sensoryreceptorcell

4

5

6

5. Change in receptor potential triggers release of neurotransmitter

6. AP triggered in sensory neuron

LE 49-14

Tongue

Taste pore Sugarmolecule

Tastebud

Sensoryneuron


G proteinAdenylyl cyclase

Sugar

Sugar receptor

Proteinkinase A

SENSORYRECEPTORCELL

Synapticvesicle

K+

Ca2+

Sensory neuron

Neurotransmitter

ATP

cAMP

Note:Release of neurotransmitter from taste bud due to opening of Ca2+ channels!!

Different stimuli trigger different receptors and sensory cells; which trigger different sensory neurons and travel to different parts of brain

How is stimulus interpreted?

“Sugar” interneuron

Sugarreceptorcell

Tastebud

Brain

Sensoryneurons

Saltreceptorcell

“Salt” interneuron

Tastebud

No sugar No salt

Increasing sweetness Increasing saltiness

The stronger the stimulus,

– the more neurotransmitter released by the receptor cell and

– the more frequently the sensory neuron transmits action potentials to the brain.

Repeated stimuli may lead to sensory adaptation, the tendency of some sensory receptors to become less sensitive when they are stimulated repeatedly.

How is INTENSITY of stimulus detected?


“Hairs” of areceptor cell

Fluidmovement

Neurotransmitterat a synapse

Sensoryneuron

Actionpotentials

Actionpotentials

Receptor cell at rest Fluid moving in one direction Fluid moving in the other direction

Moreneurotransmittermolecules

Fewerneurotransmittermolecules

Fluidmovement

321

The stronger the stimulus,

– the more neurotransmitter released by the receptor cell and

– the more frequently the sensory neuron transmits action potentials to the brain.

Repeated stimuli may lead to sensory adaptation, the tendency of some sensory receptors to become less sensitive when they are stimulated repeatedly.

HEARING AND BALANCE

Both hearing and balance use hair cells as sensory cells

Hair cells = type of mechanoreceptor


LE 49-8

Outer earMiddle

ear Inner ear

Pinna Auditorycanal

Tympanicmembrane

Eustachiantube

Middleear

Stapes

Incus

Malleus

Skull bones

Semicircular canals

Auditory nerve,to brain

Tympanicmembrane

Ovalwindow Round

window

Cochlea

Eustachian tube

Auditory nerve

Tympaniccanal

Cochlea duct

Organ of Corti

Vestibularcanal

Bone

To auditorynerve

Axons ofsensory neurons

Basilarmembrane

Hair cells

Tectorialmembrane

You do not need to all theparts of the ear

Outer ear Middle ear

Eardrum Bones

Inner ear

Organ ofCorti (insidethe cochlea)

Pressure waves transmitted to the fluid of the cochlea

– bend hair cells in the organ of Corti against the basilar membrane and

– trigger nerve signals to the brain.

Louder sounds generate more action potentials.

Various pitches stimulate different regions of the organ of Corti.

LE 49-9

Ovalwindow

Cochlea

Tympaniccanal

Basilarmembrane

Vestibularcanal

Perilymph

Stapes Axons ofsensoryneurons

Apex

Base

Roundwindow

LE 49-10

Cochlea(uncoiled) Basilar

membrane Apex(wide andflexible)

Frequencyproducingmaximum vibrationBase

(narrow and stiff)

16 kHz(high pitch)

8 kHz4 kHz

2 kHz1 kHz

500 Hz (low pitch)

Healthy ear (cilia intact)

Ear damaged by loud music (cilia destroyed)

29.5 The inner ear houses our organs of balance

The three semicircular canals detect changes in the head’s rotation or angular movement.


Figure 29.5Semicircularcanals

Nerve

Cochlea

Saccule

Utricle

Flow of fluid

Cupula

Flowof fluid

Cupula

Hairs

Haircell

Nerve fibers

Direction of body movement

VISION


All animal light detectors are based on cells called photoreceptors that contain pigment molecules that absorb light.

Figure 29.7A

Don’t you wish you had eyes like this?

Figure 29.7B

Or this?

29.10 The human retina contains two types of photoreceptors: rods and cones

The human retina contains two types of photoreceptors.

1. Rods

– contain the visual pigment rhodopsin, which can absorb dim light, and

– can detect shades of gray in dim light.

2. Cones

– contain the visual pigment photopsin, which absorbs bright colored light, and

– allow us to see color in bright light.


Cones provide for color vision. 3 types of cones absorb red, blue, and green light

Can you tell what number is hiding in here?

If not – you might have trouble with your cones

29.10 The human retina contains two types of photoreceptors: rods and cones

When rhodopsin and photopsin absorb light,

– they change chemically, and

– the change alters the permeability of the cell’s membrane to ions

– The resulting receptor potential triggers a change in the release of neurotransmitter


Figure 29.10B

Retina

Opticnerve

Retina

Neurons Photoreceptors

Rod Cone

Opticnervefibers

To the brain

The rods and cones are located at the back of the eye

LE 49-20

Outersegment

Disks

Rod

Insideof disk

Cell body

Synapticterminal

Rhodopsin

Cytosol

Retinal

Opsin trans isomer

Light Enzymes

cis isomer

When light hits a rod or cone, the pigments change conformation, triggering our sense of vision

TASTE AND SMELL


Figure 29.12

29.11 Taste and odor receptors detect chemicals present in solution or air

Taste and smell depend on chemoreceptors that detect specific chemicals in the environment.

Chemoreceptors

– in taste buds detect molecules in solution and

– lining the nasal cavity detect airborne molecules.

Taste and smell interact. Much of what we taste is really smell.

Taste buds are specialized cells that detect chemicals in our food, while chemoreceptors for smell are located directly in sensory neurons.


Taste receptors

– are located in taste buds on the tongue and

– produce five taste sensations:

1. sweet,

2. salty,

3. sour,

4. bitter, and

5. umami (the savory flavor of meats and cheeses).

29.11 Taste and odor receptors detect chemicals present in solution or air


Figure 29.11

Brain

Nasal cavity

Odoroussubstance

MucusCilia

Sensoryneuron(chemo-receptor)

Epithelialcell

Bone

Olfactorybulb

Action potentials

Chemoreceptors for smell are located on cilia of nerve endings. These sensory nerves are directly connected to olfactory bulb

chapter 29 sensory reception © 2012 pearson education, inc

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