Sensory and Motor MechanismsChapter 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 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

Figure 49.6bx Beluga whale pod

Many mammals appear to use the Earth’s magnetic field linesTo orient themselves as they migrate

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 earThe outer earThe middle earThe 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

Oval window

Apex

Axons ofsensoryneurons

Roundwindow Basilar

membrane

Tympaniccanal

Base

Vestibularcanal Perilymph

Hearing Vibrating objects create percussion waves in

the air That cause the tympanic membrane to vibrate

The three bones of the middle ear 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

The receptor cells for taste in humans 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

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 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 bonesSome fused together and others

connected at joints by ligaments that allow freedom of movement

The Human Skeleton

Muscles contraction Move Skeletal Parts 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 Is characterized by a hierarchy of smaller

and smaller units A skeletal muscle consists of a bundle of

long fibers Running parallel to the length of the muscle

A muscle fiber 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 Each repeating unit is a sarcomere

Bordered by Z lines The areas that contain the myofilments

Are the I band, A band, and H zone

Skeletal Muscle

The sliding-filament model of muscle contraction 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 Support, protection, and movement

The three main types of skeletons are Hydrostatic skeletons, exoskeletons,

and endoskeletons

Hydrostatic Skeletons

A hydrostatic skeleton Consists of fluid held under pressure in a closed

body compartment This is the main type of skeleton

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

An exoskeleton is a hard encasement Deposited on the surface of an animal Are found in most molluscs and

arthropods

Endoskeletons

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