The Human Muscular System.pdf

7/29/2019 The Human Muscular System.pdf

1/28

2009 The McGraw-Hill Companies, Inc. All rights reserved

THE MUSCULAR SYSTEM


2/28


26-2

FUNCTIONS movement of the body

maintenance of posture

respiration

production of body heat

communication

constriction of organs and vessels

contraction of the heart


3/28


26-3

Types of Muscle Tissue Skeletal (responsible for locomotion, facial

expression, posture, respiratory movements,

etc.) Smooth (found in walls of hollow organs and

tubes)

Cardiac (found only in the heart)


4/28


26-4


5/28


26-5

Characteristics of Skeletal Muscle ~40% of the body

striatedmuscles (transverse bands/striations)

Contractility

Excitability

Extensibility Elasticity


6/28


26-6

Characteristics of Skeletal Muscle contractility: to shorten with force

excitability: respond to stimulus

extensibility: capability to stretch

recoil/elasticity: recoil to their original resting

length after they have been stretched


7/28 2009 The McGraw-Hill Companies, Inc. All rights reserved

26-7

Skeletal Muscle Structure



26-8

Muscle Fiber Structure

sarcolemma

sarcoplasmicreticulum

transverse tubules

sarcoplasm

myofibrils

actin myofilaments

myosin myofilaments



26-9

Actin and Myosin Filaments

actin

troponin (containsbinding site for calcium

ions)

tropomyosin (covers theattachment site for

myofilaments)



26-10

Actin and Myosin Filaments

myosin heads bind to attachment in actin

myofilaments

bend and straighten

during contraction they can break down ATP

to release energy



26-11

Outer Structure of Sarcomeres

Z disk(forming attachment

site for actin filaments;

gives the banded

appearance)

I band (actin filaments;

spans each Z disk and endsat myosin)

A band (extends length of

myosin filaments)



26-12

Nerve Supply

skeletal muscles do not

contract unless stimulated by

motor neurons (nerve cellsthat generate the action

potentials)

neuromuscular

junction/synapse (cell to cell

junction between nerve and a

muscle fiber)

26 13



26-13

Nerve Supply

neuromuscular

junction

presynaptic terminal

(contains synapticvesicles)

synaptic cleft (space

between presynaptic

terminal and musclefiber)

postsynaptic

membrane

26 14



26-14

26 15



26-15

Muscle Contraction

sliding filament model (sliding of actin

myofilaments past myosin myofilaments)

actin and myosin do not shorten duringcontraction

I bands shorten

A bands do not change in length relaxationsarcomeres lengthen by

opposing force or gravity

26 16



26-16

Excitability of Muscle Fibers

Resting membrane potential

concentration of K+ inside the cell is higher thanoutside

concentration of Na+ outside is higher than inside

the cell

cell membrane is more permeable to K+ than to

Na+

26 17



26-17

Ion Channels and Action Potential

26 18



26-18


26 19



26-19


26-20



26-20

26-21



26-21

CROSS-BRIDGE MOVEMENT

26-22


22/28


26 22

26-23


23/28


26 23

26-24


24/28


26 24

26-25


25/28


26 25

26-26


26/28


26-27


27/28


Cross-Bridge Movement

Exposure of attachment sites. During contraction of a muscle, Ca+ binds to troponin

molecules, causing tropomyosin molecules to move, which exposes myosin attachment sites

on actin myofilaments.

Cross-bridge formation. The myosin heads bind to the exposed attachment sited on the

actin myofilaments to form cross-bridges, and phosphates are released from the myosinheads.

Power stroke. Energy stored in the myosin heads is used to move myosin heads, causing

actin myofilament to slide past the myosin myofilament, and the ADP molecules are

released from the myosin heads.

ATP binds to myosin heads. ATP molecules bind to the myosin heads

Cross-bridge release. As ATP is broken down to ADP and phosphates, the myosin headsrelease from the actin attachment sites.

Recovery stroke. The heads of the myosin molecules return to their resting position, and

energy is stored in the heads of the myosin molecules. If Ca+ are still attached to troponin,

cross-bridge formation and movement are repeated. This cycle occurs many times during a

muscle contraction. Not all cross-bridges form and release simultaneously.

26-28


28/28

The Human Muscular System.pdf

Documents

Transcript of The Human Muscular System.pdf