Sensory Perception

Chapter 34 Part 1

Impacts, Issues

A Whale of a Dilemma

Whales communicate and sense the world

around them using sound – a problem when

ships and defense-systems testing flood the

seas with noise

34.1 Overview of Sensory Pathways

Sensory receptors determine what stimuli an

animal can detect and respond to

Different kinds of sensory receptors produce

action potentials in response to different types of

stimuli

Sensory Receptor Diversity

Mechanoreceptors: mechanical energy

• Body position or acceleration

• Touch or stretching

• Pressure waves (hearing)

Pain receptors (nociceptors): tissue damage

• Some reflexes

Osmoreceptors: change in solute concentration

Sensory Receptor Diversity

Thermoreceptors: specific temperature or

temperature change

Chemoreceptors: specific solutes dissolved in

fluid (also function in smell)

Photoreceptors: light energy

• Including UV receptors in insects

Sensory Receptors

Mechanoreceptors in bat hearing,

thermoreceptors in snakes

Photoreceptors and UV Light

From Sensing to Sensation

In animals with a brain, input from sensory

neurons can give rise to sensation

The brain determines stimulus location and

strength by which axons respond, how many

respond, and frequency of action potentials

In sensory adaptation, sensory neurons cease

firing under continued stimulation

Sensory Information in Action

34.1 Key Concepts

How Sensory Pathways Work

Sensory receptors detect specific stimuli

Different animals have receptors for different

stimuli

Information from sensory receptors becomes

encoded in the number and frequency of action

potentials sent to the brain along particular

nerve pathways

34.2 Somatic and Visceral Sensations

Somatic sensations are signals from receptors in

the skin, joints, and skeletal muscles

• They travel along sensory neuron axons, to the

spinal cord, to the somatosensory cortex

Visceral sensations are signals from sensory

neurons in walls of internal organs

• Relayed to the spinal cord and the brain

The Somatosensory Cortex

Somatosensory cortex

• Part of the cerebral cortex

• Like the motor cortex, neurons are mapped to a

plan of the body

Example: Skin receptors

• Free nerve endings around roots of hairs,

Meissner’s corpuscles (touch), Pacinian capsules

(pressure), Ruffini endings, bulb of Krause

Body Regions in

the Somatosensory Cortex

Sensory Receptors in Human Skin

Fig. 34-6, p. 581

hair shaft inside follicle epidermis

dermis

free nerve

endings

Pacinian

corpuscle

Ruffini

endings

bulb of

Krause

Meissner’s

corpuscle

Animation: Sensory receptors in the

human skin

Pain

Pain

• Perception of a somatic or visceral tissue injury

• Injured cells release chemicals that stimulate pain

receptors, affected by neuromodulators

Referred pain

• Because pain signals usually originate with

somatic sources, the brain sometimes

misinterprets visceral pain as coming from the

skin or joints

Referred Pain

Fig. 34-7, p. 581

lungs,

diaphragm

heart

stomach

liver, gallbladder

pancreas

small intestine

ovaries

appendix

urinary bladder

kidney

ureter

colon

Animation: Referred pain

34.2 Key Concepts

Somatic and Visceral Senses

Somatic sensations such as touch are easily

localized and stem from receptors in the skin,

muscles, or near joints

Visceral sensations, such as a feeling of fullness

in your stomach, are less easily pinpointed; they

arise from receptors in the walls of internal

organs

34.3 Sampling the Chemical World

Both smell and taste begin when chemoreceptors

are stimulated by the binding of specific dissolved

molecules

Sense of Smell

Olfaction (sense of smell)

• Olfactory receptors detect water-soluble or

volatile chemicals, send signals to olfactory bulbs

• Olfactory nerves send signals to cerebral cortex

Pheromone

• A type of signaling molecule secreted by an

individual that affects others of the same species

• Detected by a vomeronasal organ

Sense of Smell

Fig. 34-8, p. 582

olfactory tract

from receptors

to the brain

olfactory

bulb

bony

plate

ciliated

endings of

olfactory

receptor

that project

into mucus

inside nose

Sense of Taste

Taste receptors detect chemicals dissolved in

fluid, and have different structures and locations

in different animals

Humans have taste buds (in epithelial papillae

on the tongue) that detect five main sensations:

sweet, sour, salty, bitter, and umami

Sense of Taste

34.3 Key Concepts

Chemical Senses

The senses of smell and taste require

chemoreceptors, which bind molecules of

specific substances dissolved in the fluid bathing

them

34.4 Sense of Balance

Organs inside your inner ear are essential to

maintaining posture and a sense of balance

Somatic sensory receptors also contribute to

balance

Organs of Equilibrium

Organs of equilibrium

• Parts of sensory systems that monitor the body’s

positions and motions

Vestibular apparatus

• Contains organs of equilibrium in vertebrates

• Semicircular canals, sacs, saccule and utricle

Hair cells

• Mechanoreceptors with modified cilia

Organs of Equilibrium in the Inner Ear

Fig. 34-10, p. 583

semicircular canals

vestibular

nerveA Vestibular apparatus

inside a human inner

ear. The organs of

equilibrium in its fluid-

filled sacs and canals

contribute to a sense of

balance.

saccule

utricleB Components of

one of the organs

inside a semicircular

canal. Shifts in the

position of the head

bend hair cells and

alter their frequency

of action potentials.

gelatinous membrane

in a semicircular canal

hair cells with their cilia

embedded in membranesensory neurons

Animation: Dynamic equilibrium

34.5 Sense of Hearing

Hearing

• Perception of sound (mechanical energy)

Sound waves

• Human ears collect, amplify, and sort out sound

waves (pressure waves traveling through air)

• Wave amplitude determines loudness

• Wave frequency determines pitch

Wave Properties

Fig. 34-11, p. 584

one cycle

Am

pli

tud

e

Frequency per

unit time

Soft

Loud

Same frequency,

different amplitude

Low

note

High

note

Same amplitude,

different frequency

Animation: Properties of sound

The Vertebrate Ear

Outer ear gathers sound

Middle ear amplifies and transmits air waves

• Vibrations are transmitted from eardrum

(tympanic membrane), to hammer, anvil and

stirrup bones, to oval window

Inner ear (vestibular apparatus and cochlea)

• Cochlea contains organs of Corti with hairs cells

that generate action potentials

How Humans Hear

Fig. 34-12a, p. 584

Fig. 34-12a, p. 584

INNER EAR

vestibular

apparatus,

cochlea

OUTER EAR

pinna, auditory

canal

MIDDLE EAR

eardrum, ear

bones A The outer ear’s flap and

canal collect sound waves.

Fig. 34-12b, p. 584

Fig. 34-12b, p. 584

oval window

(behind stirrup)MIDDLE EAR BONES:

stirrup

anvilauditory nerve

hammer

auditory

canalround

windowEARDRUM COCHLEA

B The eardrum and middle ear bones amplify sound.

Fig. 34-12 (c-e), p. 585

Fig. 34-12c, p. 585

Fig. 34-12c, p. 585

the cochlea, “uncoiled” for claritywaves

of air

pressureoval window vestibular duct

waves

of fluid

pressure

eardrum cochlear duct tympanic duct

round window

C Pressure waves are transferred to

fluid inside the ducts of the cochlea

(shown here uncoiled).

Fig. 34-12d, p. 585

Fig. 34-12d, p. 585

vestibular duct

cochlear duct

organ of Corti

sensory

neurons (to

the auditory

nerve)

tympanic duct

D Pressure waves are detected by the organ of Corti in the cochlear duct.

Fig. 34-12e, p. 585

Fig. 34-12e, p. 585

hair cells of organ of Corti

tectorial membranebasilar membrane

E Movement of the basilar membrane (the floor of the cochlear

duct) bends hair cells against the organ of Corti’s tectorial

membrane. This bending causes hair cells to fire. The action

potentials travel along the auditory nerve to the brain.

Animation: Ear structure and function

Animation: Action potentials

Animation: Olfactory pathway

Animation: Somatosensory cortex

Animation: Taste receptors