MO Figure

Sensory Receptors

and the CNS

Perennou Nuridsany/Science Source.

Sensory pathwaysInvolve four steps

• Sensory reception: sensory receptors

detect a stimulus

• Sensory transduction: in response to

the stimulus, ion channels open or close,

which changes the membrane potential

• Transmission: an action potential is

carried to the CNS

• Perception: awareness of the stimulus

occurs in the brain.

Figure 1

Sensory reception

Figure 1a

Figure 1b

Figure 2

Amplification is the

process through which a

signal is strengthened;

often involves signal

transduction pathways.

Amplification

Figure 2a

Figure 2b

Sensory perceptionIntegration: several weak stimuli are added into one

large perceived stimulus. Occurs at several steps:

• During signal transduction, separate stimuli are

added together to generate an action potential.

• During transmission, several rapid action potentials

are integrated into one.

• In the CNS, signals from multiple sensory cells are

integrated into one signal.

Sensory adaptation

Sensitivity of sensory receptors changes

in response to constant stimulation

• Enables an animal to adjust to

changing environmental conditions.

• Enables an animal to ignore constant

stimuli that might otherwise be

distracting.

Types of sensory receptor

• Mechanoreceptors

• Chemoreceptors

• Electromagnetic receptors

• Thermoreceptors

• Nociceptors (pain receptors)

Mechanoreceptors

• Respond to mechanical stimulation, such

as pressure and sound.

• Responsible for senses of touch and

hearing

• Ion channels open or close in response to

deformation or movement.

Figure 3

Skin mechanoreceptors

Sensory

receptors in the

skin and

surrounding hair

follicles respond

to pressure.

Figure 4

Lateral line system

Used to sense movement

of water.

Figure 4a

Figure 4b

Chemoreceptors

Bind chemicals, responsible for senses of taste

and smell.

Olfaction: sense of smell, involves detection of

airborne chemicals called odorants.

Gustation: sense of taste, involves detection of

dissolved chemicals called tastants.

Aquatic animals do not have distinct senses of

taste and smell.

Figure 5

Pheromones

for navigation

Lampreys detect

pheromones secreted

by the larvae of their

species to navigate to

breeding sites.

(a) Jacana/Science Source. (b)

Gary Meszaros/Science Source.

Electromechanical receptors• Detect electromagnetic energy such as light,

electricity, and magnetism

• Photoreceptors detect light and are responsible for

vision.

Visual organs:

Eyespots (planaria): sense light and dark

Compound eyes (insects): detect motion.

Single-lens eyes (vertebrates and some invertebrates):

focus image.

Figure 6

Photoreception

Planaria move away from light sources using

photosensitive eyespots.

Figure 7

Electromagnetic reception

Monarch butterflies

use magnetite to orient

themselves with

respect to Earth’s

magnetic field and

navigate during winter

migrations.

Courtesy of Gene Nieminen/USFWS.

Sense changes in temperature

Thermoreceptors

(pain receptors)

• Detect injurious stimuli such as extreme

heat, pressure, and dangerous chemicals.

• In humans, many nociceptors are naked

dendrites of other types of receptors;

thermoreceptors, mechanoreceptors, and

chemoreceptors can act as nociceptors.

Nociceptors

MO Figure

Auditory and

Balance System

Courtesy of B. Peterson/USFWS.

Figure 1

The Auditory System

Figure 2

The Cochlea

Primary site of auditory sense reception. Contains

the fluid-filled vestibular and tympanic canals.

Vibration of the basilar membrane causes cilia on

hair cells to bend. Signals are transmitted to the

brain through the auditory nerve.

Figure 2a

Figure 2b

Figure 2c

Figure 3

Hair

cellsBend back and forth in

response to fluid

movements from sound

waves. The bending

movements are translated

into neural signals that are

transmitted to the brain.

© 2004 Nature Publishing Group Modified from Frolenkov, G. I., et al., Genetic insights

into the morphogenesis of inner ear hair cells. Nature Reviews Genetics 5, 489–498

(2004) doi:10.1038/nrg1377. Used with permission.

Figure 4

Mechanism

of hearing

Figure 4a

Figure 4b

Figure 4c

Figure 5

Mechanism of hearing

The basilar

membrane

gets thinner

and more

flexible

toward the

center of the

cochlea.

Figure 5a

Mechanism of hearing

Figure 5b

Mechanism of hearingThe basilar membrane gets thinner and more

flexible toward the center of the cochlea.

Figure 6

The balance systems

Figure 6a

Figure 6b

Figure 6c

Semicircular canals

Clearly visible in normal newborns (left) and

missing in CHARGE affected newborns (right).

Figure 7

© 2007 Nature Publishing Group Sanlaville D. & Verloes, A. CHARGE syndrome: an update. European Journal of

Human Genetics 15, 389–399 (2007) doi:10.1038/sj.ejhg.5201778. Used with permission.

MO Figure

Vision

Courtesy of Gary M. Stolz/USFWS.

Figure 1

Eyespots

Planaria have primitive eyespots with

photosensitive tissue.

Eric V. Grave/Science Source.

Figure 2

Compound eyes

Contain many ommatidia, each with its own

lens. Highly sensitive to motion.

Thomas Shahan/Science Source.

Figure 3

Eye and retina anatomy

Figure 3a

Figure 3b

Figure 4

Both have lenses that refract light.

Both can focus an image.

Both have an iris that adjusts light

levels.

Microscope vs. eyes

Figure 4a

Figure 4b

Figure 5

Myopia, hyperopia,

and astigmatism

Abnormal curvature of the lens or cornea results

in light focusing incorrectly on the retina.

Figure 5a

Figure 5b

Figure 5c

Figure 6

Retinal

neuronsSeveral types of neurons in

the retina communicate with

each other to refine, sharpen,

and process visual stimuli.

These include bipolar cells

(green), rod photoreceptors

(red/purple), cones, amacrine

cells, ganglion cells, and

others.© 2010 Nature Publishing Group Markus, A. Speedy rod

signaling. Nature Neuroscience 13, 410 (2010)

doi:10.1038/nn0410-410. Used with permission.

Figure 7

Visual processing

Although images are inverted at the retina, the visual cortex of the

brain reorients the images properly.

MO Figure

Taste and Smell

Picture Partners/Science Source.

Figure 1

Chemoreceptors

Insects have olfactory receptors that are typically

found on their antennae. Gustatory receptors can

be found on mouthparts and legs.

Robert Noonan/Science Source.

Figure 2

Taste buds

Associated

with papillae of

the tongue.

Contain cells

that detect

sweet, salty,

bitter, sour, and

umami (savory)

tastes.

Figure 2a

Figure 2b

Figure 2c

Figure 3

Figure 4

Olfaction

Skunks use odorants for defense.

Greg Dimijian/Science Source.

Figure 5

Binding of odorants

to chemoreceptor

neurons triggers

action potentials that

are transmitted to

the olfactory bulb

and brain.

The

olfactory

pathway

Figure 5a

Figure 5b