Download Sensory and Motor Mechanisms

Sensory and Motor
Mechanisms
Chapter 49
Sensing and Acting



Bats use sonar to detect
their prey
Moths can detect the
bat’s sonar and attempt
to flee
Both of these organisms
have complex sensory
systems that facilitate
their survival
Types of Sensory Receptors

Based on the energy they transduce,
sensory receptors fall into five
categories




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Mechanoreceptors
Chemoreceptors
Electromagnetic receptors
Thermoreceptors
Pain receptors
Mechanoreceptors

Mechanoreceptors
sense physical
deformation


Caused by stimuli such
as pressure, stretch,
motion, and sound
The mammalian sense of
touch

Relies on
mechanoreceptors that
are the dendrites of
sensory neurons
Figure 49.4 Mechanoreception by a hair cell
Chemoreceptors



General receptors that transmit
information about the total solute
concentration of a solution
Specific receptors that respond to
individual kinds of molecules
EX: Taste, Smell
Figure 49.5 Chemoreceptors in an insect: Female silk moth
Bombyx mori releasing pheromones;
SEM of male Bombyx mori antenna
Figure 49.x1 Chemoreceptors: Snake tongue
Electromagnetic Receptors

Electromagnetic receptors detect
various forms of electromagnetic
energy


Such as visible light, electricity, and
magnetism
Some snakes have very sensitive
infrared receptors

That detect body heat of prey against a
colder background
Figure 49.6 Specialized electromagnetic receptors:
Rattle snake with infrared recpters, beluga whale pod

Many mammals appear to use the
Earth’s magnetic field lines
 To
orient themselves as they migrate
Figure 49.6bx Beluga
whale pod
Thermoreceptors

Thermoreceptors, which respond to
heat or cold

Help regulate body temperature by
signaling both surface and body core
temperature
Pain Receptors

In humans, pain receptors, also called
nociceptors
Are a class of naked dendrites in the
epidermis
 Respond to excess heat, pressure, or
specific classes of chemicals released
from damaged or inflamed tissues

The mechanoreceptors  hearing and
equilibrium detect settling particles or
moving fluid
Hearing and the perception of body
equilibrium are related in most animals
 Three regions of the human ear

 The
outer ear
 The middle ear
 The inner ear
Ear Structure
The outer ear
external pinna
and the auditory
canal
 Collects sound
and directs it to
the tympanic
membrane
(eardrum)

Middle Ear
Three small bones
malleus (hammer), the
incus (anvil) and
stapes (stirrup)
collect vibrations
 The eustacian tube
equalizes air
pressure between the
outer and middle ear

The Cochlea

Snail shaped structure organ of corti
Cochlea
Stapes
Axons of
sensory
neurons
Oval
window
Vestibular
canal
Perilymph
Base
Round
window
Tympanic
Basilar
canal
membrane
Apex
Hearing

Vibrating objects create percussion waves in the
air


The three bones of the middle ear


That cause the tympanic membrane to vibrate
Transmit the vibrations to the oval window on the
cochlea
These vibrations create pressure waves in the
fluid in the cochlea

That travel through the vestibular canal and
ultimately strike the round window

The pressure waves in the vestibular canal


Cause the basilar membrane to vibrate up and
down causing its hair cells to bend
The bending of the hair cells depolarizes
their membranes

Sending action potentials that travel via the
auditory nerve to the brain
Figure 49.18 How the cochlea distinguishes pitch
Figure 49.19 Organs of balance in the inner ear
Senses of Taste and Smell
Are closely related in most animals
 The perceptions of gustation (taste)
and olfaction (smell)

 Are
both dependent on chemoreceptors
that detect specific chemicals in the
environment
Taste in Humans
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The receptor cells for taste in humans
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Are modified epithelial cells organized into
taste buds
Five taste perceptions involve several
signal transduction mechanisms

Sweet, sour, salty, bitter, and umami
(elicited by glutamate)
Figure 49.2 Sensory transduction by a taste receptor
Smell in Humans
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
Olfactory receptor cellsAre neurons
that line the upper portion of the nasal
cavity
When odorant molecules bind to
specific receptors

A signal transduction pathway is
triggered, sending action potentials to the
brain
Olfaction in Humans
Vision in the Animal Kingdom

Two major types of image-forming eyes have
evolved in invertebrates
 The

compound eye and the single-lens eye
Compound eyes are found in insects and
crustaceans
 And
consist of up to several thousand light
detectors called ommatidia

Single-lens eyes
 Are
found in some jellies, polychaetes, spiders, and
many molluscs
 Work on a camera-like principle
Simplest Eye

The eye cup of planarians provides information
about light intensity and direction but does not
form images
Figure 49.8 Compound eyes
(a)
Vertebrate Eyes
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
Camera-like they evolved independently and
differ from the single-lens eyes of
invertebrates
The main parts of the vertebrate eye are
 The
sclera, which includes the cornea
 The choroid, a pigmented layer
 The conjunctiva, that covers the outer surface of
the sclera
 The iris, which regulates the pupil
 The retina, which contains photoreceptors
 The lens, which focuses light on the retina
Structure of the Human Eye
Focusing of the Mammalian Eye
Photoreceptors

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
Figure 49.13 From light reception to receptor potential: A
rod cell’s signal-transduction pathway
The effect of light on
synapses between rod
cells and bipolar cells
Figure 49.15 The vertebrate retina
Neural pathways for
vision
The Human Skeleton
Functions in support, protection, &
movement
 Animal movements result from muscles
working against some type of skeleton
 The mammalian skeleton is built from
more than 200 bones

 Some
fused together and others connected
at joints by ligaments that allow freedom of
movement
The Human Skeleton
Muscles contraction Move Skeletal Parts
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
The action of a
muscle always to
contract
Skeletal muscles are
attached to the
skeleton in
antagonistic pairs
 With
each member of
the pair working
against each other
Vertebrate Skeletal Muscle
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Is characterized by a hierarchy of smaller
and smaller units
A skeletal muscle consists of a bundle of long
fibers

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A muscle fiber


Running parallel to the length of the muscle
Is itself a bundle of smaller myofibrils arranged
longitudinally
Skeletal muscle is also called striated muscle

Because the regular arrangement of the
myofilaments creates a pattern of light and dark
bands

The myofibrils are composed to two kinds of
myofilaments
Thin filaments, consisting of two strands of actin
and one strand of regulatory protein
 Thick filaments, staggered arrays of myosin
molecules
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Each repeating unit is a sarcomere

Bordered by Z lines

Are the I band, A band, and H zone
The areas that contain the myofilments
Skeletal Muscle
The sliding-filament model of muscle
contraction
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The filaments slide past each other
longitudinally, producing more overlap
between the thin and thick filaments
As a result of this sliding
 The

I band and the H zone shrink
The sliding of filaments is based on
 The
interaction between the actin and myosin
molecules of the thick and thin filaments

The “head” of a myosin molecule binds to an
actin filament
 Forming
a cross-bridge and pulling the thin
filament toward the center of the sarcomere
The sliding-filament
model of muscle
contraction
One hypothesis for how myosin-actin interactions generate
the force for muscle contraction
Hypothetical mechanism for the control of muscle contraction
Review of skeletal muscle contraction
Types of Skeletons

The three main functions of a skeleton
are
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Support, protection, and movement
The three main types of skeletons are

Hydrostatic skeletons, exoskeletons, and
endoskeletons
Hydrostatic Skeletons
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A hydrostatic skeleton


This is the main type of skeleton


Consists of fluid held under pressure in a closed
body compartment
In most cnidarians, flatworms, nematodes, and
annelids
Annelids use their hydrostatic skeleton for
peristalsis

A type of movement on land produced by rhythmic
waves of muscle contractions
Exoskeletons
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An exoskeleton is a hard encasement
Deposited on the surface of an animal
 Are found in most molluscs and arthropods
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Endoskeletons
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An endoskeleton consists of hard
supporting elements


Such as bones, buried within the soft tissue
of an animal
Endoskeletons

Are found in sponges, echinoderms, and
chordates