Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sensing and acting Bats use sonar to detect their prey Moths, a common prey for

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Sensing and acting

• Bats use sonar to detect their prey

• Moths, a common prey for bats can detect the bat’s sonar and attempt to flee


• Both bats and moths have complex sensory systems that facilitate their survival

• The structures that make up these systems have been transformed by evolution into diverse mechanisms that sense various stimuli and generate the appropriate physical movement


• Concept: Sensory receptors transduce stimulus energy and transmit signals to the central nervous system

• Sensations are action potentials that reach the brain via sensory neurons

• Once the brain is aware of sensations it interprets them, giving the perception of stimuli.


• Sensations and perceptions begin with sensory reception, the detection of stimuli by sensory receptors

• Exteroreceptors

– Detect stimuli coming from the outside of the body

• Interoreceptors

– Detect internal stimuli


Functions Performed by Sensory Receptors

• All stimuli represent forms of energy

• Sensation involves converting this energy into a change in the membrane potential of sensory receptors


• Sensory receptors perform four functions in this process

• Sensory transduction is the conversion of stimulus energy into a change in the membrane potential of a sensory receptor. This change in the membrane potential is known as a receptor potential

• Amplification is the strengthening of stimulus energy by cells in sensory pathways

• Transmission: after energy in a stimulus has been transduced into a receptor potential some sensory cells generate action potentials, which are transmitted to the CNS

• Integration is the evaluation and coordination of stimuli to produce a response. It occurs at all levels of the nervous system.


Hair cell found in vertebrates

of action potentials in the sensory neuron. Bending in the other direction has the opposite effects. Thus, hair cells respond to the direction of motion as well as to its strength and speed.s

(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


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


Mechanoreceptors

• The mammalian sense of touch relies on mechanoreceptors that are the dendrites of sensory neurons

Figure 49.3

HeatLight touch Pain

Cold

Hair

Nerve Connective tissueHair movementStrong pressure

Dermis

Epidermis


Chemoreceptors

• Chemoreceptors include

– General receptors that transmit information about the total solute concentration of a solution

– Specific receptors that respond to individual kinds of molecules


• Two of the most sensitive and specific chemoreceptors known are present in the antennae of the male silkworm moth. The males use their antennae to detect two components in pheromones released by females.

Figure 49.4 0.1

mm


Electromagnetic Receptors

• Electromagnetic receptors detect various forms of electromagnetic energy such as visible light, heat, electricity, and magnetism


• Some snakes have very sensitive infrared receptors that detect body heat of prey against a colder background

(a) This rattlesnake and other pit vipers have a pair of infrared receptors, one between each eye and nostril. The organs are sensitive enough to detect the infrared radiation emitted by a warm mouse a meter away. The snake moves its head from side to side until the radiation is detected equally by the two receptors, indicating that the mouse is straight ahead.


• Many mammals and birds appear to use the Earth’s magnetic field lines to orient themselves as they migrate

Figure 49.5b(b) Some migrating animals, such as these beluga whales, apparently

sense Earth’s magnetic field and use the information, along with other cues, for orientation.


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

• They respond to excess heat, pressure, or specific classes of chemicals released from damaged or inflamed tissues


Hearing, balance and the ear.

• The mechanoreceptors involved with hearing and equilibrium detect settling particles or moving fluid

• Hearing and the perception of body equilibrium are related in most animals


Hearing and Equilibrium in Mammals

• In most terrestrial vertebrates the sensory organs for hearing and equilibrium are closely associated in the ear.

• The ear is divided into three areas:

– The outer ear which contains the auditory canal.

– The middle ear which includes the tympanic membrane and the three ear bones that transmit vibrations to the inner ear

– The inner ear which contains the cochlea where vibrations are converted to nerve impulses and sent to the brain as well as the organs of balance: utricle, saccule and semicircular canals.


Structure of the human ear

Figure 49.8

Pinna

Auditory canal

Eustachian tube

Tympanicmembrane

Stapes

Incus

Malleus

Skullbones

Semicircularcanals for balance

Auditory nerve,to brain

Cochlea

Tympanicmembrane

Ovalwindow

Eustachian tube

Roundwindow

Vestibular canal

Tympanic canal

Auditory nerve

BoneCochlear duct

Hair cells Tectorialmembrane

Basilarmembrane

To auditorynerve

Axons of sensory neurons

1 Overview of ear structure 2 The middle ear and inner ear

4 The organ of Corti 3 The cochleaOrgan of Corti

Outer earMiddle

ear Inner ear


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


Hearing

• These vibrations create pressure waves in the fluid in the cochlea that travel through the vestibular canal and ultimately strike the round window

Figure 49.9

Cochlea

Stapes

Oval window

Apex

Axons ofsensoryneurons

Roundwindow Basilar

membrane

Tympaniccanal

Base

Vestibularcanal Perilymph


Hearing

• The pressure waves in the vestibular canal cause the basilar membrane in the organ of Corti within the cochlea 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 where they are interpreted as sounds.


Hearing

• The cochlea can distinguish pitch because the basilar membrane is not uniform along its length. Each region of the basilar membrane vibrates most vigorously at a particular frequency and leads to excitation of a specific auditory area of the cerebral cortex.

Cochlea(uncoiled)

Basilarmembrane

Apex(wide and flexible)

Base(narrow and stiff)

500 Hz(low pitch)1 kHz

2 kHz

4 kHz

8 kHz

16 kHz(high pitch)

Frequency producing maximum vibration

Figure 49.10


Equilibrium

• Several of the organs of the inner ear detect body position and balance

• The utricle and saccule tell the brain which way is up.

• Semicircular canals in the inner ear detect angular movements of the head and function in balance and equilibrium


The semicircular canals, arranged in three spatial planes, detect angular movements of the head.

Body movement

Nervefibers

Each canal has at its base a swelling called an ampulla, containing a cluster of hair cells.

When the head changes its rate of rotation, inertia prevents endolymph in the semicircular canals from moving with the head, so the endolymph presses against the cupula, bending the hairs.

The utricle and saccule tell the brain which way is up and inform it of the body’s position or linear acceleration.

The hairs of the hair cells project into a gelatinous cap called the cupula.

Bending of the hairs increases the frequency of action potentials in sensory neurons in direct proportion to the amount of rotational acceleration.

Vestibule

Utricle

Saccule

Vestibular nerve

Flowof endolymph

Flowof endolymph

CupulaHairs

Haircell


Odor detection in humans

• Olfactory receptor cells

– Are neurons that line the upper portion of the nasal cavity


Odor detection in humans

• When odorant molecules bind to specific receptors a signal transduction pathway is triggered, sending action potentials to the brain

Brain

Nasal cavity

Odorant

Odorantreceptors

Plasmamembrane

Odorant

Cilia

Chemoreceptor

Epithelial cell

Bone

Olfactory bulb

Action potentials

MucusFigure 49.15


Vision

• Many types of light detectors have evolved in the animal kingdom ranging from simple eye cups of planarians (flatworms) to the compound eyes of insects and crustaceans to the camera-like eyes of vertebrates and cephalopods (octopuses and relatives).


Structure of the Vertebrate Eye

• The main parts of the vertebrate eye are

– The sclera, a layer of tough connective tissue, which includes the transparent cornea which allows light into the eye and acts as a fixed lens.

– The choroid, a pigmented layer inside the sclera.

– The conjunctiva, that covers the outer surface of the sclera (except the cornea) and keeps it moist.


Structure of the Vertebrate Eye

– The iris, which regulates the size of the pupil the hole in the middle of the iris that lets light in.

– The retina, which contains photoreceptors that detect light and convert it to nervous impulses.

– The lens, which focuses light on the retina


The structure of the vertebrate eye

Figure 49.18

Ciliary body

Iris

Suspensoryligament

Cornea

Pupil

Aqueoushumor

Lens

Vitreous humor

Optic disk(blind spot)

Central artery andvein of the retina

Opticnerve

Fovea (centerof visual field)

Retina

ChoroidSclera


Humans and other mammals focus light by changing the shape of the lens

Figure 49.19a–b

Lens (flatter)

Lens (rounder)

Ciliarymuscle

Suspensoryligaments

Choroid

Retina

Front view of lensand ciliary muscleCiliary muscles contract, pulling

border of choroid toward lens

Suspensory ligaments relax

Lens becomes thicker and rounder, focusing on near objects

(a) Near vision (accommodation)

(b) Distance vision

Ciliary muscles relax, and border of choroid moves away from lens

Suspensory ligaments pull against lens

Lens becomes flatter, focusing on distant objects


• 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 to light.


Sensory Transduction in the Eye

• Each rod or cone in the vertebrate retina contains visual pigments that consist of a light-absorbing pigment called retinal bonded to a protein called opsin.

• Opsins vary in structure from one type of photoreceptor to another

• Rods contain the visual pigment rhodopsin, which changes shape when it absorbs light.

• Cones contain one or other of three different photopsins and are either red, green or blue cones.


• Rods are used under low light conditions and cones in bright light for color vision.

• Absorption spectra of the different types of cones overlap and the differential stimulation of the three types of cones allows the brain to produce the perception of color.

• For example, if both red and green cones are stimulated we may see orange or yellow depending on which cones are more strongly stimulated.


Processing Visual Information

• The processing of visual information begins in the retina itself

• When a cone or rod is struck it absorbs light and its retinal changes shape.

• This change in shape triggers a signal transduction pathway that generates an action potential and nerve impulses that travel to the brain.


Figure 49.21

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.


• Signals from rods and cones travel from bipolar cells to ganglion cells

• The axons of ganglion cells are part of the optic nerve that transmit information to the brain

Leftvisualfield

Rightvisualfield

Lefteye

Righteye

Optic nerve

Optic chiasm

LateralgeniculatenucleusPrimaryvisual cortex


• Several integrating centers in the cerebral cortex are active in creating visual perceptions.

• You should be aware that the “reality” you perceive is a a simulation generated by your brain that builds a mental model of the world.


Animal Skeletons

• Animal skeletons function in support, protection, and movement

• The various types of animal movements all result from muscles working against some type of skeleton


Functions of the skeleton

• The three main functions of a skeleton are

– Support,

– Protection,

– and Movement


• The mammalian skeleton is an endoskeleton of bones buried within the soft tissue. It is built from more than 200 bones

• Some bones are fused together and others are connected at joints by ligaments that allow freedom of movement


Human skeleton

1 Ball-and-socket joints, where the humerus contactsthe shoulder girdle and where the femur contacts thepelvic girdle, enable us to rotate our arms andlegs and move them in several planes.

2 Hinge joints, such as between the humerus andthe head of the ulna, restrict movement to a singleplane.

3 Pivot joints allow us to rotate our forearm at theelbow and to move our head from side to side.

key

Axial skeletonAppendicularskeleton

Skull

Shouldergirdle

Clavicle

Scapula

Sternum

RibHumerus

Vertebra

RadiusUlnaPelvicgirdleCarpals

Phalanges

Metacarpals

FemurPatella

Tibia

Fibula

TarsalsMetatarsalsPhalanges

1

Examplesof joints

2

3

Head ofhumerus

Scapula

Humerus

Ulna

UlnaRadius


• Muscles move skeletal parts by contracting

• The action of a muscle is always to contract.

• Skeletal muscles are attached to the skeleton in antagonistic pairs with each member of the pair working against each other e.g. triceps and biceps in the upper arm.


Figure 49.27

Human Grasshopper

Bicepscontracts

Tricepsrelaxes

Forearmflexes

Bicepsrelaxes

Tricepscontracts

Forearmextends

Extensormusclerelaxes

Flexormusclecontracts

Tibiaflexes

Extensormusclecontracts

Flexormusclerelaxes

Tibiaextends


• 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.

• Myofibrils are composed of myofilaments.


Figure 49.28

Muscle

Bundle ofmuscle fibers

Single muscle fiber(cell)

Plasma membraneMyofibril

Lightband Dark band

Z line

Sarcomere

TEM 0.5 mI band A band I band

M lineThickfilaments(myosin)Thinfilaments(actin)

H zoneSarcomere

Z lineZ line

Nuclei


• The myofibrils are composed of 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

• Skeletal muscle is also called striated muscle because the regular arrangement of the myofilaments creates a pattern of light and dark bands


• Each repeating unit is a sarcomere bordered by Z lines. The Z lines are aligned vertically and are attached to the thin filaments (made of actin).

• The thin filaments project into the sarcomere.

• The thick filaments are aligned in the center of the sarcomere and align with and partially overlap with the thin filaments.


• At rest the thick and thin fibers only partially overlap and this produces a pattern of bands in the sarcomere that are identified by letters.

• The A-band is the area in the middle of the sarcomere where the thick filaments are located and appears dark.

• The I-band is the area at either end of the sarcomere where only thin filaments are found. This appears light.

• The H-zone in the middle is where only thick filaments occur. It appears less dark than the rest of the A-band.


Figure 49.28

Muscle

Bundle ofmuscle fibers

Single muscle fiber(cell)

Plasma membraneMyofibril

Lightband Dark band

Z line

Sarcomere

TEM 0.5 mI band A band I band

M lineThickfilaments(myosin)Thinfilaments(actin)

H zoneSarcomere

Z lineZ line

Nuclei


The Sliding-Filament Model of Muscle Contraction

• According to 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.


Figure 49.29a–c

(a) Relaxed muscle fiber. In a relaxed muscle fiber, the I bandsand H zone are relatively wide.

(b) Contracting muscle fiber. During contraction, the thick andthin filaments slide past each other, reducing the width of theI bands and H zone and shortening the sarcomere.

(c) Fully contracted muscle fiber. In a fully contracted musclefiber, the sarcomere is shorter still. The thin filaments overlap,eliminating the H zone. The I bands disappear as the ends ofthe thick filaments contact the Z lines.

0.5 m

Z HA

Sarcomere

I band


• 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


Myosin-actin interactions underlying muscle fiber contraction

Thick filament

Thin filaments

Thin filament

ATP

ATP

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 moves toward center of sarcomere.

Thick filament

Actin

Cross-bridge binding site

1 Starting here, the myosin head is bound to ATP and is in its low-energy confinguration.

2 The myosin head hydrolyzes ATP to ADP and inorganic phosphate ( I ) and is in its high-energy configuration.

P

1 The myosin head binds toactin, forming a cross-bridge.

3

4Releasing ADP and ( i), myosinrelaxes to its low-energy configuration, sliding the thin filament.

P

5 Binding of a new mole-cule of ATP releases the myosin head from actin,and a new cycle begins.


The Role of Calcium and Regulatory Proteins

• A skeletal muscle fiber contracts

– Only when stimulated by a motor neuron


• When a muscle is at rest the myosin-binding sites on the thin filament are blocked by the regulatory protein tropomyosin

Figure 49.31a

ActinTropomyosin Ca2+-binding sites

Troponin complex

(a) Myosin-binding sites blocked


• For a muscle fiber to contract the myosin-binding sites must be uncovered

• This occurs when calcium ions (Ca2+) bind to another set of regulatory proteins, the troponin complex

Figure 49.31b

Ca2+

Myosin-binding site

(b) Myosin-binding sites exposed


• The stimulus leading to the contraction of a skeletal muscle fiber is an action potential in a motor neuron that makes a synapse with the muscle fiber

Figure 49.32

Motorneuron axon

Mitochondrion

Synapticterminal

T tubule

Sarcoplasmicreticulum

MyofibrilPlasma membraneof muscle fiber

Sarcomere

Ca2+ releasedfrom sarcoplasmicreticulum


• The synaptic terminal of the motor neuron releases the neurotransmitter acetylcholine, depolarizing the muscle and causing it to produce an action potential


Neural Control of Muscle Tension

• Contraction of a whole muscle is graded

– Which means that we can voluntarily alter the extent and strength of its contraction.

• There are two basic mechanisms by which the nervous system produces graded contractions of whole muscles

– By varying the number of fibers that contract

– By varying the rate at which muscle fibers are stimulated


• In a vertebrate skeletal muscle each branched muscle fiber is innervated by only one motor neuron

• Each motor neuron may synapse with multiple muscle fibers

Figure 49.34

Spinal cord

Nerve

Motor neuroncell body

Motorunit 1

Motorunit 2

Motor neuronaxon

Muscle

Tendon

Synaptic terminals

Muscle fibers


• A motor unit consists of a single motor neuron and all the muscle fibers it controls

• Recruitment of multiple motor neurons results in stronger contractions


• A twitch results from a single action potential in a motor neuron

• More rapidly delivered action potentials produce a graded contraction by summation

Figure 49.35

Actionpotential

Pair ofaction

potentials

Series of action potentials at

high frequency

Time

Te

nsi

on

Singletwitch

Summation of two twitches

Tetanus


• Tetanus is a state of smooth and sustained contraction produced when motor neurons deliver a volley of action potentials.


Cardiac muscle

• Cardiac muscle, found only in the heart

– Consists of striated cells that are electrically connected together. As a result an action potential in one part of the heart spreads to all cardiac cells and the heat contracts.

– Cardiac muscle can generate action potentials without neural input because the heart has its own pacemaker cells that cause rhythmic depolarizarions.


Smooth muscle

• In smooth muscle, found mainly in the walls of hollow organs (e.g. the digestive tract) the contractions are relatively slow and may be initiated by the muscles themselves

• In addition, contractions may be caused by stimulation from neurons in the autonomic nervous system

Documents

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sensing and acting Bats use sonar to detect their prey Moths, a common prey for