CHAPTER 49 :SENSORY AND MOTOR

MECHANISMS

By:

Nicole Huffman

Period 7

KEY TERMS

Sensations: action potentials that reach the brain via sensory neurons.

Perception: constructions formed in the brain and do not exist outside it

such as colors, smells, sounds, and tastes.

Sensory Reception: the detection of a stimulus by sensory cells.

Sensory Receptors: are specialized neurons or epithelial cells that exist

singly or in groups with other cell types in sensory organs.

Exteroreceptors: sensory receptors that detect stimuli coming from outside

the body.

Interoreceptors: detect stimuli coming form within the body, such as blood

pressure and body position.

KEY TERMS CONTINUED…

Sensory Transduction: the conversion of stimulus energy into a change

in the membrane potential of a sensory receptor.

Receptor Potential: the change in membrane potential itself.

Amplification: the strengthening of stimulus energy by cells in sensory

pathways.

Sensory Adaptation: a decrease in responsiveness during continued

stimulation.

Mechanoreceptors: sense physical deformation caused by stimuli such

as pressure, touch, stretch, motion, and sound – all forms of mechanical

energy.

KEY TERMS CONTINUED…

Muscle spindles: dendrites of sensory neurons that spiral around the

middle of small skeletal muscle fibers each containing 2 to 12 of these

fibers surrounded by connective tissue, parallel to other muscle fibers.

Chemoreceptors: include both general receptors that transmit

information about the total solute concentration of a solution and specific

receptors that respond to individual kinds of molecules.

Electromagnetic Receptors: detect various forms of electromagnetic

energy, such as visible light, electricity, and magnetism.

Photoreceptors: electromagnetic receptors that detect the radiation

known as visible light.

KEY TERMS CONTINUED…

Thermoreceptors: respond to heat or cold, help regulate body

temperature by signaling both surface and body core temperature.

Pain Receptors/Nociceptors: a class of naked dendrites in the

epidermis.

Lateral Line System: mechanoreceptors that detect low-frequency

waves by a mechanism similar to the function of the inner ear.

Compound eyes: consists of several thousand light detectors called

ommatidia.

Sclera: a touch, white outer layer of connective tissue.

KEY TERMS CONTINUED…

Choroid: a thin, pigmented inner layer

Conjunctiva: A delicate layer of epithelial cells forms a

mucous membrane that covers the outer surface of the

sclera and helps keep the eye moist.

Cornea: At the front of the eye and lets light into the eye

and acts as a fixed lens.

Iris: The anterior choroid that gives the eye its color.

Pupil: the hold in the center of the iris.

KEY TERMS CONTINUED…

Retina: the innermost layer of the eyeball and contains

the photoreceptors.

Ciliary Body: produces the clear watery aqueous humor

that fills the anterior cavity.

Vitreous Humor: fills the posterior cavity and constitutes

most of the volume of the eye.

Fovea: the center of the visual field.

Retinal: a light-absorbing molecule.

KEY TERMS CONTINUED…

Opsin: a membrane protein.

Rhodopsin: a visual pigment in rods.

Photopsins: the three visual pigments of cones.

Ganglion cells: synapse with bipolar cells and transmit

action potentials to the brain via axons in the optic nerve.

Horizontal cells and Amacrine cells: help integrate

the information before it is sent to the brain.

KEY TERMS CONTINUED…

Lateral Inhibition: sharpens edges and enhances

contrast in an image.

Hydrostatic Skeleton: a skeleton consisting of fluid

held under pressure in a closed body compartment.

Skeletal Muscle: muscle attached to the bones and

is responsible for their movement.

Accommmodation: the focusing of light in the retina.

SENSORY RECEPTORS

Figure 49.2a

(a) 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.

Muscle

Dendrites

Stretchreceptor

Axon

Mem

bran

epo

tent

ial (

mV

)

–50

–70

0

–70

0 1 2 3 4 5 6 7

Time (sec)

Action potentials

Receptor potential

Weakmuscle stretch

–50

–70

0

–70

0 1 2 3 4 5 6 7

Time (sec)

Strongmuscle stretch

(b) Vertebrate hair cells have specialized cilia or microvilli (“hairs”) that bend when sur-rounding fluid moves. Each hair cell releases an excitatory neurotransmitter at a synapse

with a sensory neuron, which conducts action potentials to the CNS. Bending in one direction depolarizes the hair cell, causing it to release more neurotransmitter and increasing frequency

–50

–70

0

–70

0 1 2 3 4 5 6 7

Time (sec)

Action potentials

No fluidmovement

–50

–70

0

–70

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

Receptor potential

Fluid moving inone direction

–50

–70

0

–70

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

Fluid moving in other direction

Mem

bran

epo

tent

ial (

mV

)

Mem

bran

epo

tent

ial (

mV

)

Mem

bran

epo

tent

ial (

mV

)

“Hairs” ofhair cell

Neuro-trans-mitter at synapse

Axon

Lessneuro-trans-mitter

Moreneuro-trans-mitter

Figure 49.2b

Electromagnetic Receptors

• Electromagnetic receptors detect various forms of electromagnetic energy– Such as visible light, electricity, and

magnetism

DIVERSE PHOTORECEPTORS

Eye cups

Compound Eyes

Single-lens eyes (used by vertebrates)

HUMAN RETINA

Rods are sensitive to light but do not distinguish

colors

Cones distinguish colors but are not sensitive

Rod Cells are light sensitive but do not distinguish

colors

Cone Cells are not as light sensitive as rods but

provide color vision and are mostly concentrated on

the fovea

The absorption of light by rhodopsin initiates a

signal-transduction pathway

CONES

Have 3 subclasses and more complex than the

rhodopsin mechanism.

Each has its own type of photopsin.

RETINA, CEREBRAL CORTEX AND PROCESSING VISUAL INFO

Visual processing begins with rods and cones

synapsing with bipolar cells which then synapse with

ganglion cells.

Visual processing in the retina also involves

horizontal cells and amacrine cells.

Lateral pathways involving horizontal or amacrine cells

can inhibit adjacent pathways:

Photoreceptors horizontal cells other photoreceptors

Photoreceptors bipolar cells amacrine cells ganglion

cells

The resulting lateral inhibition (More distance

photoreceptors and bipolar cells are inhibited sharpens

edges and enhances contrast in the image)

The optic nerves of the

two eyes meet at the

optic chiasm.

Ganglion cell axons

make up the optic tract.

Most synapse in the

lateral geniculate nuclei

of the thalamus

The neurons then

convey information to

the primary visual cortex

of the optic lobe

Vibrations create pressure waves in the fluid in the

cochlea that travel through the vestibular canal and

strike the round window

Cochlea

Stapes

Oval window

Apex

Axons ofsensoryneurons

Roundwindow Basilar

membrane

Tympaniccanal

Base

Vestibularcanal Perilymph

Cochlea(uncoiled) Basilar

membrane

Apex(wide and flexible)

Base(narrow and stiff)

500 Hz(low pitch)1 kHz

2 kHz4 kHz

8 kHz16 kHz(high pitch)

Frequency producing maximum vibration

EAR AND BALANCE

Behind the oval window is a vestibule that contains

the utricle and saccule

The utricle opens into three semicircular canals

Utricle and saccule respond to changes in head

position relative to gravity and movement in one

direction.

Hair cells are projected into a gelatinous material

containing otoliths.

Semicircular canals respond to rotational

movements of the head

Most fish and

amphibians have a

lateral line system along

both sides of their body

Provides a fish with

information concerning

its movement through

water or the direction

and velocity of water

flowing over its body.

INVERTEBRATES WITH GRAVITY SENSORS AND

SOUND THAT ARE SOUND-SENSITIVE

Statocysts are mechanoreceptors that function in

an invertebrates sense of equilibrium

INSECTS

Sound sensitivity in insects depends on body hairs

that vibrate in response to sound waves.

Many insects have a tympanic membrane stretched

over a hollow chamber

TRANSDUCTION IN TASTE RECEPTORSTaste pore Sugar molecule

Sensoryreceptorcells

Sensoryneuron

Taste bud

Tongue

G protein Adenylyl cyclase

—Ca2+

ATP

cAMP

Proteinkinase A

Sugar

Sugarreceptor

SENSORYRECEPTORCELL Synaptic

vesicle

K+

Neurotransmitter

Sensory neuron

MAMMALS’ OLFACTORY RECEPTORS LINE THE UPPER

PORTION OF THE NASAL CAVITY

The binding of odor molecules to olfactory receptors

initiate signal transduction pathways involving a G-protein-

signaling pathway and, often, adenylyl cyclase and cyclic

AMP.

THE KEY TO FLIGHT IS THE AERODYNAMIC STRUCTURE OF

WINGS

PERISTALTIC MOTION PUSHES AGAINST HYDROSTATIC

SKELETON

When myosin

binds to actin it

forms an ATPase

which releases

the energy from

ATP for

contraction

Graded muscle

contraction can be

controlled by regulating

the number of motor

units involved in the

contraction

Recruitment of motor neurons increases the

number of muscle cells involved in a contraction.

Some muscles, such as those involved in posture

are always at least partially contracted.

FAST AND SLOW MUSCLE FIBERS

Fast muscle fibers are adapted for rapid powerful

contractions and fatigue relatively quickly

Slow muscle fibers are adapted for sustained

contraction

Relative to fast fibers, slow fibers have:• Less SR → Ca2+ remains in the cytosol longer• More mitochondria, a better blood supply, and

myoglobin

OTHER MUSCLE TYPES

Vertebrates have cardiac and smooth muscles

Invertebrate muscle cells are similar to vertebrate

skeletal and smooth muscle cells

Cardiac muscle: is similar to skeletal muscle• Intercalated discs facilitate the coordinated

contraction of cardiac muscle cells.• Can generate their own action potentials of long

duration.

MUSCLE TYPES CONTINUED…

Smooth muscle: lacks the striations seen in both

skeletal and cardiac muscle.• Contracts with less tension, but over a greater range

of lengths, than skeletal muscle.• No T tubules and no SR

• Ca2+ enters the cytosol from via the plasma membrane

• Slow contractions, with more control over contraction strength than with skeletal muscle.

• Found lining the walls of hollow organs.

Skeletal, voluntary or striated muscles are multinucleated, innervated by somatic nervous system

Skeletal, voluntary or striated muscles are multinucleated, innervated by somatic nervous system

Smooth or Viceral muscles are long and spindle shaped, innervated by two nerve fibers from autonomic nervous system, one from the sympathetic and one from the parasympathetic nervous system

Smooth or Viceral muscles are long and spindle shaped, innervated by two nerve fibers from autonomic nervous system, one from the sympathetic and one from the parasympathetic nervous system Cardiac muscle is

branched with intercalated discs

Cardiac muscle is branched with intercalated discs