2.10 Animal Support-MNR

8/18/2019 2.10 Animal Support-MNR

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Support


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Animal skeletons function in support, protection,

and movement

•The various types of animal movements – All result from muscles working against some type

of skeleton

• The three main functions of a skeleton are

– Support, protection, and movement

• The three main types of skeletons are

– Hydrostatic skeletons, exoskeletons, and

endoskeletons


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Hydrostatic Skeletons

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

ody compartment

• This is the main type of skeleton – !n most cnidarians, flatworms, nematodes, and

annelids


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• Annelids use their hydrostatic skeleton for

peristalsis

– A type of movement on land produced yrhythmic waves of muscle contractions

Figure 49.25a–c

(a) "ody segments at the head and #ust in front

of the rear are short and thick $longitudinalmuscles contracted% circular muscles

relaxed& and anchored to the ground y

ristles' The other segments are thin and

elongated $circular muscles contracted%longitudinal muscles relaxed'&

(b) The head has moved forward ecausecircular muscles in the head segments have

contracted' Segments ehind the head and

at the rear are now thick and anchored, thus

preventing the worm from slipping ackward'

(c) The head segments are thick again and

anchored in their new positions' The rear

segments have released their hold on theground and have een pulled forward'

(ongitudinal

muscle relaxed

$extended&

Circular muscle

contracted

Circular

muscle

relaxed

(ongitudinal

muscle

contracted

Head"ristles


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Exoskeleton• An exoskeleton is a hard encasement

– )eposited on the surface of an animal• *xoskeletons

– Are found in most molluscs and arthropods

Endoskeleton• An endoskeleton consists of hard supporting

elements

– Such as ones, uried within the soft tissue of an

animal

• *ndoskeletons

– Are found in sponges, echinoderms, and chordates


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• The human skeleton

Figure 49.26

1 Ball-and-socket oints! where the humerus contacts

the shoulder girdle and where the femur contacts the

pelvic girdle, enale us to rotate our arms and

legs and move them in several planes'

2 "inge oints! such as etween the humerus and

the head of the ulna, restrict movement to a singleplane'

# $i%ot oints allow us to rotate our forearm at the

elow and to move our head from side to side'

ke&

Axial skeleton

Appendicular

skeleton

Skull

Shoulder

girdle

Clavicle

Scapula

Sternum

+i

Humerus

ertera

+adius-lna.elvic

girdle

Carpals

.halanges

/etacarpals

0emur

.atella

Tiia

0iula

Tarsals/etatarsals.halanges

1

Exa'les

o oints

2

#

Head of

humerus

Scapula

Humerus

-lna

-lna+adius


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.hysical Support on (and

• !n addition to the skeleton – /uscles and tendons help support large land

verterates

•Concept1 /uscles move skeletal parts ycontracting

• The action of a muscle

– *s al+a&s to contract

• Skeletal muscles are attached to the skeletonin antagonistic pairs – 2ith each memer of the pair working against each

other


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Figure 49.2,

"u'an rassoer

"iceps

contracts

Triceps

relaxes0orearm

flexes

"iceps

relaxes

Triceps

contracts

0orearm

extends

*xtensor

muscle

relaxes

0lexor

muscle

contracts

Tiiaflexes

*xtensor

muscle

contracts

0lexor

muscle

relaxes

Tiia

extends


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erterate Skeletal /uscle• erterate skeletal muscle

– !s characteri3ed y a hierarchy of smaller andsmaller units

Figure 49.2/

/uscle

"undle of

muscle fiers

Single muscle fier

$cell&

.lasma memrane

/yofiril

(ight

and )ark and

4 line

Sarcomere

T*/ 5'6 µm

I and A and I and

/ line

Thick

filaments

$myosin&

Thin

filaments

$actin&

H 3one

Sarcomere4 line4 line

7uclei


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• A skeletal muscle consists of a undle of long fiers – +unning parallel to the length of the muscle

• A muscle fier

– !s itself a undle of smaller myofirils arranged longitudinally• The myofirils 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

• Skeletal muscle is also called striated muscle – "ecause the regular arrangement of the myofilaments

creates a pattern of light and dark ands – *ach repeating unit is a sarcomere

– "ordered y 4 lines

– The areas that contain the myofilments

– Are the ! and, A and, and H 3one


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The Sliding-Filament Model of

Muscle Contraction• According to the sliding8filament model of muscle

contraction

– The filaments slide past each other longitudinally, producing

more overlap etween the thin and thick filaments

• The sliding of filaments is ased on

– The interaction etween the actin and myosin molecules of

the thick and thin filaments

• The 9head: of a myosin molecule inds to an actinfilament

– 0orming a cross8ridge and pulling the thin filament toward

the center of the sarcomere


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• As a result of this sliding

– The ! and and the H 3one shrink

Figure 49.29a–c

(a) 0elaxed 'uscle iber. !n a relaxed muscle fier, the I andsand H 3one are relatively wide'

(b) ontracting 'uscle iber. )uring contraction, the thick and

thin filaments slide past each other, reducing the width of the

I ands and H 3one and shortening the sarcomere'

(c) Full& contracted 'uscle iber. !n a fully contracted muscle

fier, the sarcomere is shorter still' The thin filaments overlap,

eliminating the H 3one' The I ands disappear as the ends of

the thick filaments contact the 4 lines'

5'6 µm

4 H A

Sarcomere


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• /yosin8actin interactions underlying

muscle fier contraction

Figure 49.#

Thick filament

Thin filaments

Thin filament

AT.

AT.

A). A).

A).

.i . i

.i

Cross8ridge

/yosin head $low8

energy configuration&

/yosin head $high8

energy configuration&

;

/yosin head $low8energy configuration&

Thin filament moves

toward center of sarcomere'

Thick

filament Actin

Cross8ridge

inding site

< Starting here, the myosin head is

ound to AT. and is in its low8

energy confinguration'

= The myosin head hydroly3es AT. to A). and inorganic

phosphate $ ! & and is in its

high8energy configuration'

.

< The myosin head inds to

actin, forming a cross8

ridge'

>

? +eleasing A). and $ i&, myosin

relaxes to its low8energy configuration,

sliding the thin filament'

.

6 "inding of a new mole8

cule of AT. releases the

myosin head from actin,

and a new cycle egins'


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The Role of Calcium and Regulatory

Proteins• A skeletal muscle fier contracts

– @nly when stimulated y a motor neuron

• 2hen a muscle is at rest

– The myosin8inding sites on the thin filament are

locked y the regulatory protein tropomyosin

Actin

Tropomyosin Ca=;8inding sites

Troponin complex

(a) 3&osin-binding sites blocked


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• 0or a muscle fier to contract

– The myosin8inding sites must e uncovered• This occurs when calcium ions $Ca=;&

– "ind to another set of regulatory proteins, the

troponin complex

Figure 49.#1b

Ca=;

/yosin8

inding site

(b) 3&osin-binding sites exosed


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• The stimulus leading to the contraction of

a skeletal muscle fier

– !s an action potential in a motor neuron thatmakes a synapse with the muscle fier

Figure 49.#2

/otor

neuron axon/itochondrion

Synaptic

terminal

T tuule

Sarcoplasmic

reticulum

/yofiril

.lasma memrane

of muscle fier

Sarcomere

Ca=; released

from sarcoplasmic

reticulum


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• The synaptic terminal of the motor neuron

– +eleases the neurotransmitter acetylcholine,

depolari3ing the muscle and causing it to

produce an action potential


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• Action potentials travel to the interior of the

muscle fier – Along infoldings of the plasma memrane calledtransverse $T& tuules

• The action potential along the T tuules

– Causes the sarcoplasmic reticulum to releaseCa=;

• The Ca=; inds to the troponin8tropomyosin

complex on the thin filaments – *xposing the myosin8inding sites and allowingthe cross8ridge cycle to proceed


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ACh

Synaptic

terminal

of motor neuron

Synaptic cleft T T-"-(*.(AS/A /*/"+A7*

S+

A).

CT@S@(

Ca=+

Ca=+

.=

Cytosolic Ca=; is

removed y active

transport intoS+ after action

potential ends'

6

• +eview of contraction in a skeletal muscle fier

Figure 49.##

Acetylcholine $ACh& released y synaptic terminal diffuses across synaptic

cleft and inds to receptor proteins on muscle fierBs plasma memrane,

triggering an action potential in muscle fier'

1

Action potential is propa8

gated along plasma

memrane and down

T tuules'

2

Action potentialtriggers Ca=;

release from sarco8

plasmic reticulum$S+&'

#

/yosin cross8ridges alternately attach

to actin and detach, pulling actin

filaments toward center of sarcomere%

AT. powers sliding of filaments'

5

Calcium ions ind to troponin%

troponin changes shape,removing locking action

of tropomyosin% myosin8inding

sites exposed'

4

Tropomyosin lockage of myosin8inding sites is restored% contraction

ends, and muscle fier relaxes'

,


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Neural Control of Muscle

Tension• Contraction of a whole muscle is graded

– 2hich means that we can voluntarily alter the extent andstrength of its contraction

• There are two asic mechanisms y which the nervoussystem produces graded contractions of whole muscles – "y varying the numer of fiers that contract

– "y varying the rate at which muscle fiers are stimulated

A t it


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• A motor unit – Consists of a single motor neuron and all the muscle fiers it controls

• +ecruitment of multiple motor neurons – +esults in stronger contractions

• A twitch

– +esults from a single action potential in a motor neuron• /ore rapidly delivered action potentials

– .roduce a graded contraction y summation

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

Action

potential .air of

action

potentials

Series of action

potentials at

high freuency

Time

T e n s i o n

Singletwitch

Summation of

two twitches

Tetanus


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@ther Types of /uscle

• Cardiac muscle, found only in the heart

– Consists of striated cells that are electrically connected

y intercalated discs

– Can generate action potentials without neural input• !n smooth muscle, found mainly in the walls of

hollow organs

– The contractions are relatively slow and may e

initiated y the muscles themselves

• !n addition, contractions may e caused y

– Stimulation from neurons in the autonomic nervous

system

2.10 Animal Support-MNR

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