Chapter 49
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Chapter 49. Sensory and Motor Mechanisms. Types of Sensory Receptors. Mechanoreceptors Chemoreceptors Electromagnetic receptors Thermoreceptors Pain receptors. Hair. Cold. Gentle touch. Pain. Heat. Epidermis.

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Chapter 49

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Chapter 49

Chapter 49

Sensory and Motor Mechanisms


Types of sensory receptors

Types of Sensory Receptors

  • Mechanoreceptors

  • Chemoreceptors

  • Electromagnetic receptors

  • Thermoreceptors

  • Pain receptors


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Hair

Cold

Gentletouch

Pain

Heat

Epidermis

Mechanoreceptors- sense physical deformation caused by stimuli such as pressure, stretch, motion, and sound

Dermis

Hypodermis

Hairmovement

Connectivetissue

Strongpressure

Nerve


Chemoreceptors

Chemoreceptors

  • Generalchemoreceptorstransmit information about the total solute concentration of a solution

  • Specific chemoreceptors respond to individual kinds of molecules


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Electromagnetic Receptors- detect electromagnetic energy such as light, electricity, and magnetism

Eye

Infraredreceptor

(a) Rattlesnake

(b) Beluga whales


Thermoreceptors pain receptors

Thermoreceptors, Pain Receptors

  • Thermoreceptors- respond to heat or cold

  • Pain Receptors- respond to excess heat, pressure, or chemicals released from damaged or inflamed tissues


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Middleear

Outer ear

Inner ear

Stapes

Skullbone

Semicircularcanals

Incus

Malleus

Auditory nerveto brain

Cochlea

Ovalwindow

Eustachiantube

Pinna

Auditorycanal

Roundwindow

Tympanicmembrane


Hearing

Hearing

  • Vibrating objects create percussion waves in the air that cause the tympanic membrane to vibrate

  • Hearing is the perception of sound in the brain from the vibration of air waves

  • The three bones of the middle ear transmit the vibrations of moving air to the oval window on the cochlea


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  • These vibrations create pressure waves in the fluid in the cochlea that travel through the vestibular canal

  • Pressure waves in the canal cause the basilar membrane to vibrate, bending its hair cells

  • This bending of hair cells depolarizes the membranes of mechanoreceptors and sends action potentials to the brain via the auditory nerve


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Axons ofsensory neurons

Apex

Ovalwindow

Vestibularcanal

Stapes

Vibration

Basilar membrane

Tympaniccanal

Base

Fluid(perilymph)

Roundwindow


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500 Hz(low pitch)

1 kHz

Flexible end ofbasilar membrane

Apex

2 kHz

Basilar membrane

4 kHz

8 kHz

Base(stiff)

16 kHz(high pitch)


Taste

Taste

Sugar molecule

G protein

Sweetreceptor

Tongue

Phospholipase C

SENSORYRECEPTORCELL

Sugarmolecule

Receptor cells for taste are modified epithelial cells organized into taste buds

Five taste perceptions: sweet, sour, salty, bitter, and umami (elicited by glutamate)

Taste pore

PIP2

Sensoryreceptorcells

Tastebud

IP3(secondmessenger)

Sodiumchannel

Sensoryneuron

IP3-gatedcalciumchannel

Nucleus

ER

Ca2+(secondmessenger)

Na+


Smell

Smell

  • Olfactory receptor cells are neurons that line the upper portion of the nasal cavity

  • Binding of odorant molecules to receptors triggers a signal transduction pathway, sending action potentials to the brain


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Brain

Action potentials

Olfactorybulb

Odorants

Nasal cavity

Bone

Epithelialcell

Odorantreceptors

Chemo-receptor

Plasmamembrane

Cilia

Odorants

Mucus


Vision

Vision

  • Iris: regulates the size of the pupil

  • Retina: contains photoreceptors

  • Lens: focuses light on the retina

  • Optic disk: a blind spot in the retina where the optic nerve attaches to the eye


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  • Light is focused by changing the shape of the lens

  • The retina contains two types of photoreceptors: rods and cones

    • Rods are light-sensitive but don’t distinguish colors

    • Cones distinguish colors but are not as sensitive to light


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Sclera

Choroid

Retina

Ciliary body

Suspensoryligament

Fovea (centerof visual field)

Cornea

Iris

Opticnerve

Pupil

Aqueoushumor

Lens

Central artery andvein of the retina

Vitreous humor

Optic disk(blind spot)

Animation: Near and Distance Vision


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Rightvisualfield

Opticchiasm

Righteye

Lefteye

Leftvisualfield

Optic nerve

Primaryvisual cortex

Lateralgeniculatenucleus


Skeletal muscle

Skeletal Muscle

  • Characterized by a hierarchy of smaller and smaller units

  • A skeletal muscle consists of a bundle of long fibers, each a single cell, running parallel to the length of the muscle


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  • Each muscle fiber is itself a bundle of smaller myofibrils arranged longitudinally

  • The myofibrils are composed to two kinds of myofilaments:

    • Thin filaments consist of two strands of actin and one of regulatory protein

    • Thick filaments are staggered arrays of myosin molecules


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  • Striated muscle- the regular arrangement of myofilaments creates a pattern of light and dark bands

  • Sarcomere- the functional unit of a muscle, separated by Z lines


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Muscle

Bundle ofmuscle fibers

Nuclei

Single muscle fiber(cell)

Plasma membrane

Myofibril

Z lines

Sarcomere


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TEM

0.5 µm

M line

Thickfilaments(myosin)

Thinfilaments(actin)

Z line

Z line

Sarcomere


The sliding filament model of muscle contraction

The Sliding-Filament Model of Muscle Contraction

  • Filaments slide past each other longitudinally, producing more overlap between thin and thick filaments


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Sarcomere

0.5 µm

M

Z

Z

Relaxedmuscle

Contractingmuscle

Fully contractedmuscle

ContractedSarcomere


Types of skeletal muscle fibers

Types of Skeletal Muscle Fibers

  • Skeletal muscle fibers can be classified

    • As oxidative or glycolytic fibers, by the source of ATP

    • As fast-twitch or slow-twitch fibers, by the speed of muscle contraction


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Oxidative fibers- rely on aerobic respiration to generate ATP

  • Many mitochondria, a rich blood supply, and much myoglobin

  • Myoglobinis a protein that binds oxygen more tightly than hemoglobin does

    Glycolytic fibers- use glycolysis as their primary source of ATP

  • Less myoglobin than oxidative fibers, and tire more easily

    In poultry and fish, light meat is composed of glycolytic fibers, while dark meat is composed of oxidative fibers


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Slow-twitch fibers- contract more slowly, but sustain longer contractions

  • All slow twitch fibers are oxidative

    Fast-twitch fibers- contract more rapidly, but sustain shorter contractions

  • Fast-twitch fibers can be either glycolytic or oxidative

    Most skeletal muscles contain both slow-twitch and fast-twitch muscles in varying ratios


Skeletal systems transform muscle contraction into locomotion

Skeletal systems transform muscle contraction into locomotion

  • Skeletal muscles are attached in antagonistic pairs, with each member of the pair working against the other


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Human

Grasshopper

Extensormusclerelaxes

Bicepscontracts

Tibiaflexes

Flexormusclecontracts

Forearmflexes

Tricepsrelaxes

Bicepsrelaxes

Extensormusclecontracts

Tibiaextends

Forearmextends

Flexormusclerelaxes

Tricepscontracts


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