Sensory and Motor Mechanisms

Samaneh Bolourchi, Jennifer Tszeng &

Athena Zeng

Introduction: Sensory Pathways Sensory receptors transduce stimulus energy & transmit

signals to CNS (central nervous system) Reception: detection via exteroreceptors or interoreceptors Transduction: stimulus energy converted into ∆ in membrane

potential of sensory receptor (receptor potential) Amplification: stimulus energy strengthens in cells in pathways Adaptation: decrease in responsiveness

Transmission: action potentials transmitted to the CNS Perception: constructions formed in brain (ie color, smell, sounds)

Introduction: Types of Receptors Sensory receptors are specialized neurons or

epithelial cells that exist singly or in groups with other cell types in sensory organs, such as eyes or ears.

Mechanoreceptors sense physical deformation cause by forms of mechanical energy such as pressure, touch, etc.

Chemoreceptors respond to chemical stimuli. Electromagnetic receptors respond to various

forms of electromagnetic energy such as visible light, electricity, and magnetism.

Thermoreceptors respond to heat or cold and help regulate body temperature by signaling surface and body core temperature.

Pain receptors, or nociceptors, are a class of naked dendrites in the epidermis.

Mechanoreceptors Detect mechanical energy typically consist of ion channels linked to

external cell structures (ie hairs) & internal structures (ie cytoskeleton)

Bending/stretching plasma membrane changes permeability to sodium & potassium ions

Type of mechanoreceptor varies greatly between organisms Crustaceans - vertebrate stretch receptors Mammals - dendrites of sensory neurons

Introduction: Sound & Balance Ear receives vibrations of moving air and

converts into what the mind perceives as sound

Also detects body movement, position & balance

Structures vary between organisms Terrestrial vertebrates: inner ear is main organ of hearing

& equilibrium Fish/Amphibians: lack certain parts but also contain

homologous structures Invertebrates - statocysts

Sound in Humans: Structure of Human Ear

Outer ear Pinna Tympanic

membrane Middle ear

Malleus, incus, stapes

Oval window Eustachian tube

Inner ear Fluid-filled

chambers ie semicircular canals & cochlea

Sensory Reception: Hair Cells

Rod-shaped hairs in corti Vibration of basilar membrane bends hairs against surrounding fluid

& tectorial membrane Bundle direction affects reception Activates mechanoreceptors

Balance in Humans: Utricle & Saccule

Sound & Balance: Variation in Organisms Terrestrial vertebrates: ear has = main organ of hearing &

equilibrium Fish/Amphibians - similar to mammalian ears; lack several

structures Frogs/toads - single middle bone (stapes) Frogs: small side pocket in saccule - basis for evolution of

mammalian cochlea Birds - cochlea; single middle bone (stapes)

Sound & Balance: Fish/Amphibians lateral line system have ears outside of body; no eardrum or

cochlea; air-filled swim bladder also vibrates in response to sound

Sound & Balance in Invertebrates

Thermoreceptors

Detect heat Located in skin and anterior hypothalamus Mammals contain a range of thermoreceptor

types for particular temperature ranges Receptor proteins open a calcium channel upon

binding certain products At least five different types of thermoreceptors

belong to the transient receptor potential (TRP) family of channel proteins

Pain Receptors

Nociceptors detect noxious conditions Essential - stimulus prompts defensive

reaction Animals also produce chemicals to

enhance pain perception

Touch

Receptors usually on skin Humans contain naked dendrites to detect

noxious thermal, mechanical & chemical stimuli Epidermis, dermis, hypodermis * structure of connective tissue & location of

receptors dramatically affect the type of mechanical energy that best stimulates them

Heat

Light touch Pain

Cold

Hair

Nerve Connective tissue Hair movement Strong pressure

Dermis

Epidermis

Human Integumentary System

Chemoreceptors

The most sensitive chemoreceptors

are on sensory hairs of

the male silkworm which

detect sex pheromones.

0.1

mm

Gustation

In mammals, taste receptors are located in taste buds, most of which are on the surface of the tongue

Each taste receptor responds to a wide array of chemicals, but is most responsive to a particular type of substance.

It is the pattern of taste receptor response that determines perceived flavor.

Transduction in taste receptors occurs by several mechanisms.

Taste pore Sugar molecule

Sensoryreceptorcells

Sensoryneuron

Taste bud

Tongue

G protein Adenylyl cyclase

—Ca2+

ATP

cAMP

Proteinkinase A

Sugar

Sugarreceptor

SENSORYRECEPTORCELL

Synapticvesicle

K+

Neurotransmitter

Sensory neuron

4 The decrease in the membrane’s permeability to K+

depolarizes the membrane.

5 Depolarization opens voltage-gated calcium ion (Ca2+) channels, and Ca2+ diffuses into the receptor cell.

6 The increased Ca2+ concentration causes synaptic vesicles to release neurotransmitter.

3 Activated protein kinase A closes K+ channels in the membrane.

2 Binding initiates a signal transduction pathway involving cyclic AMP and protein kinase A.

1 A sugar molecule binds to a receptor protein on the sensory receptor cell.

Taste pore Sugar molecule

Sensoryreceptorcells

Sensoryneuron

Taste bud

Tongue

G protein Adenylyl cyclase

—Ca2+

ATP

cAMP

Proteinkinase A

Sugar

Sugarreceptor

SENSORYRECEPTORCELL

Synapticvesicle

K+

Neurotransmitter

Sensory neuron

Taste pore Sugar molecule

Sensoryreceptorcells

Sensoryneuron

Taste bud

Tongue

G protein Adenylyl cyclase

—Ca2+

ATP

cAMP

Proteinkinase A

Sugar

Sugarreceptor

SENSORYRECEPTORCELL

Synapticvesicle

K+

Neurotransmitter

Sensory neuron

4 The decrease in the membrane’s permeability to K+

depolarizes the membrane.4 The decrease in the membrane’s permeability to K+

depolarizes the membrane.4 The decrease in the membrane’s permeability to K+

depolarizes the membrane.

5 Depolarization opens voltage-gated calcium ion (Ca2+) channels, and Ca2+ diffuses into the receptor cell.

5 Depolarization opens voltage-gated calcium ion (Ca2+) channels, and Ca2+ diffuses into the receptor cell.

5 Depolarization opens voltage-gated calcium ion (Ca2+) channels, and Ca2+ diffuses into the receptor cell.

6 The increased Ca2+ concentration causes synaptic vesicles to release neurotransmitter.

6 The increased Ca2+ concentration causes synaptic vesicles to release neurotransmitter.

6 The increased Ca2+ concentration causes synaptic vesicles to release neurotransmitter.

3 Activated protein kinase A closes K+ channels in the membrane.

3 Activated protein kinase A closes K+ channels in the membrane.

3 Activated protein kinase A closes K+ channels in the membrane.

2 Binding initiates a signal transduction pathway involving cyclic AMP and protein kinase A.

2 Binding initiates a signal transduction pathway involving cyclic AMP and protein kinase A.

2 Binding initiates a signal transduction pathway involving cyclic AMP and protein kinase A.

1 A sugar molecule binds to a receptor protein on the sensory receptor cell.

1 A sugar molecule binds to a receptor protein on the sensory receptor cell.

1 A sugar molecule binds to a receptor protein on the sensory receptor cell.

Olfaction

In mammals, olfactory receptors line the upper portion of the nasal cavity.

The receptive ends of the cells contain cilia that extend into the layer of mucus coating the nasal cavity.

Each olfactory receptor cell expresses only one or a few odorant receptor genes.

Brain

Nasal cavity

Odorant

Odorantreceptors

Plasmamembrane

Odorant

Cilia

Chemoreceptor

Epithelial cell

Bone

Olfactory bulb

Action potentials

MucusFigure 49.15

Brain

Nasal cavity

Odorant

Odorantreceptors

Plasmamembrane

Odorant

Cilia

Chemoreceptor

Epithelial cell

Bone

Olfactory bulb

Action potentials

MucusFigure 49.15

Electromagnetic Receptors Respond to various forms of electromagnetic

energy such as visible light, electricity, and magnetism.

Photoreceptors detect energy in form of light

Examples:

• Snakes—body heat of prey.

• Fish—electric currents—prey.

• Animals—earths magnetic field. (birds)

Types of Eyes

the simplest is the eye cup of planarians

In invertebrates, there are compound eyes and single-lens eyes: Compound: in crustaceans , insects,

etc. (have several thousand facets called ommatidia)

Single-lens: jellies, spiders, etc (single lens that focuses light)

In vertebrates Evolved independently and differ from

the single-lens eyes of invertebrates

Eye Structure

Sensory Transduction The human retina contains two types of photoreceptors

Rods are sensitive to light but do not distinguish colors Cones distinguish colors but are not as sensitive

Each rod or cone in the vertebrate retina contains visual pigments consisting of light-absorbing molecules called retinal bonded to membrane proteins called opsin Rhodopsin (retinal + opsin) is the visual pigment of

rods. Absorption of light by retinal triggers a signal

transduction pathway!

Signal Transduction cont.EXTRACELLULARFLUID

Membranepotential (mV)

0

– 40

– 70

Dark Light

– Hyper- polarization

Time

Na+

Na+

cGMP

CYTOSOL

GMP

Plasmamembrane

INSIDE OF DISK

PDEActive rhodopsin

Light

Inactive rhodopsin Transducin Disk membrane

2 Active rhodopsin in turn activates a G protein called transducin.

3 Transducinactivates theenzyme phos-phodiesterae(PDE).

4 Activated PDE detaches cyclic guanosine monophosphate (cGMP) from Na+ channels in

the plasma membrane by hydrolyzing cGMP to GMP.

5 The Na+ channels close when cGMP detaches. The membrane’s permeability to Na+ decreases, and the rod hyperpolarizes.

1 Light isomerizes retinal, which activates rhodopsin.

Signal Transduction (cont.) Three other types of neurons contribute to information

processing in the retina Ganglion cells, horizontal cells, and amacrine cells

Signals from rods and cones travel from bipolar cells to ganglion cells, which then transmit info to brain by optic nerve (axon of ganglion)

Horizontal cells and amacrine cells function in neural pathways that integrate visual info before sent to brain.

Lateral inhibition causes a greater contrast b/n light and dark (as the horizontal cells inhibit more distant photoreceptors) and this enhances the image, and sharpens its edges.

Synaptic activity of rod cells in light and dark Dark Responses

Rhodopsin inactive

Na+ channels open

Rod depolarized

Glutamatereleased

Bipolar cell eitherdepolarized orhyperpolarized,depending onglutamate receptors

Light Responses

Rhodopsin active

Na+ channels closed

Rod hyperpolarized

No glutamatereleased

Bipolar cell eitherhyperpolarized ordepolarized, depending on glutamate receptors

Evolution of Visual Perception All photoreceptors contain similar pigment

molecules that absorb light (despite diversity) Genetic underpinnings of all photoreceptors

evolved in the earliest bilateral animals.

Vertebrate Skeletal Muscle

Myofibrils consist of: Thin filaments: two strands of actin

and two strands of a regulatory protein Thick filaments: staggered arrays

of myosin molecules Striated Muscle: regular arrangement

of filaments create light/dark band pattern Sarcomere: basic contractile unit

between Z- lines

Muscle

Bundle ofmuscle fibers

Single muscle fiber(cell)

Plasma membrane

Myofibril

Lightband Dark band

Z line

Sarcomere

TEM 0.5 mI band A band I band

M line

Thickfilaments(myosin)

Thinfilaments(actin)

H zoneSarcomere

Z lineZ line

Nuclei

Muscle

Bundle ofmuscle fibers

Single muscle fiber(cell)

Plasma membrane

Myofibril

Lightband Dark band

Z line

Sarcomere

TEM 0.5 mI band A band I band

M line

Thickfilaments(myosin)

Thinfilaments(actin)

H zoneSarcomere

Z lineZ line

Nuclei

Thick filament

Thin filaments

Thin filament

ATPATP

ADPADP

ADP

P i P i

P i

Cross-bridge

Myosin head (low-energy configuration)

Myosin head (high-energy configuration)

+

Myosin head (low-energy configuration)

Thin filament movestoward center of sarcomere.

Thick filament

ActinCross-bridge binding site

Thick filamentThick filament

Thin filamentsThin filaments

Thin filamentThin filament

ATPATP

ADPADP

ADP

P i P i

P i

Cross-bridge

Myosin head (low-energy configuration)

Myosin head (high-energy configuration)

+

Myosin head (low-energy configuration)Myosin head (low-energy configuration)

Thin filament movestoward center of sarcomere.

Thick filamentThick filament

ActinActinCross-bridge binding siteCross-bridge binding site

ACh

Synapticterminalof motorneuron

Synaptic cleft T TUBULEPLASMA MEMBRANE

SR

ADP

CYTOSOL

Ca2

Ca2

P2

Cytosolic Ca2+ is removed by active transport into SR after action potential ends.

6

Acetylcholine (ACh) released by synaptic terminal diffuses across synapticcleft and binds to receptor proteins on muscle fiber’s plasma membrane,triggering an action potential in muscle fiber.

1

Action potential is propa-gated along plasmamembrane and downT tubules.

2

Action potentialtriggers Ca2+

release from sarco-plasmic reticulum(SR).

3

Myosin cross-bridges alternately attachto actin and detach, pulling actinfilaments toward center of sarcomere;ATP powers sliding of filaments.

5

Calcium ions bind to troponin;troponin changes shape,removing blocking actionof tropomyosin; myosin-bindingsites exposed.

4

Tropomyosin blockage of myosin-binding sites is restored; contractionends, and muscle fiber relaxes.

7

ACh

Synapticterminalof motorneuron

Synaptic cleft T TUBULEPLASMA MEMBRANE

SR

ADP

CYTOSOL

Ca2

Ca2

P2

ACh

Synapticterminalof motorneuron

Synaptic cleft T TUBULEPLASMA MEMBRANE

SR

ADP

CYTOSOL

Ca2

Ca2

P2

Cytosolic Ca2+ is removed by active transport into SR after action potential ends.

6 Cytosolic Ca2+ is removed by active transport into SR after action potential ends.

6 Cytosolic Ca2+ is removed by active transport into SR after action potential ends.

6

Acetylcholine (ACh) released by synaptic terminal diffuses across synapticcleft and binds to receptor proteins on muscle fiber’s plasma membrane,triggering an action potential in muscle fiber.

1 Acetylcholine (ACh) released by synaptic terminal diffuses across synapticcleft and binds to receptor proteins on muscle fiber’s plasma membrane,triggering an action potential in muscle fiber.

Acetylcholine (ACh) released by synaptic terminal diffuses across synapticcleft and binds to receptor proteins on muscle fiber’s plasma membrane,triggering an action potential in muscle fiber.

1

Action potential is propa-gated along plasmamembrane and downT tubules.

2 Action potential is propa-gated along plasmamembrane and downT tubules.

Action potential is propa-gated along plasmamembrane and downT tubules.

2

Action potentialtriggers Ca2+

release from sarco-plasmic reticulum(SR).

3 Action potentialtriggers Ca2+

release from sarco-plasmic reticulum(SR).

3 Action potentialtriggers Ca2+

release from sarco-plasmic reticulum(SR).

3

Myosin cross-bridges alternately attachto actin and detach, pulling actinfilaments toward center of sarcomere;ATP powers sliding of filaments.

5 Myosin cross-bridges alternately attachto actin and detach, pulling actinfilaments toward center of sarcomere;ATP powers sliding of filaments.

5 Myosin cross-bridges alternately attachto actin and detach, pulling actinfilaments toward center of sarcomere;ATP powers sliding of filaments.

5

Calcium ions bind to troponin;troponin changes shape,removing blocking actionof tropomyosin; myosin-bindingsites exposed.

4 Calcium ions bind to troponin;troponin changes shape,removing blocking actionof tropomyosin; myosin-bindingsites exposed.

44

Tropomyosin blockage of myosin-binding sites is restored; contractionends, and muscle fiber relaxes.

7 Tropomyosin blockage of myosin-binding sites is restored; contractionends, and muscle fiber relaxes.

7 Tropomyosin blockage of myosin-binding sites is restored; contractionends, and muscle fiber relaxes.

7

Types of Muscle

Cardiac muscle is similar to skeletal muscle

with striations.

• Smooth muscle

• lacks striations• lines walls of

blood vessels and digestive system organs.

• Skeletal Muscle

• Voluntary movements

• Attatched to bones

Skeletal Systems Support, protection, and

movement Hydrostatic Skeleton – consists of fluid

held under pressure in a closed body compartment. Form and movement are controlled by changing the shape of this compartment. Examples: Flatworms, Nematodes,

Annelids, Jellyfish Exoskeleton – encasement deposited

on the surface of an animal. -> chitinous or made from calcium salts, etc. Examples: Insects, Crustaceans,

Mollusks Endoskeleton – Interior skeleton

within muscles and skin. Act as levers when the muscles contract to allow the organism to move. Examples: Mammals, Birds,

Reptiles, Fish, Sponges

Locomotion Requires energy to

overcome friction & gravity Swim: friction is major

issue; gravity is minor Land: requires self-

support & movement against gravity

Flight: requires wings developed enough to lift & overcome gravity

Diseases: Color Blindness Color-Blindness: due to alterations

in the genes for one or more photopsin proteins.

There are different types:

No color vision deficiencies.

with protanopia.

with deuteranopia. with tritanopia.

Diseases (Cont.)

\ALS, amyotrophic lateral sclerosis, or Lou Gehrig’s Myasthenia gravis

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