1 Muscular System Poudre High School Human Anatomy/Physiology Mr. Bradley.

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Muscular System

Poudre High School

Human Anatomy/Physiology

Mr. Bradley

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I. The Muscular SystemI. The Muscular System

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Muscles are responsible for all types of body movement

1. Muscle cells are elongated (muscle cell = muscle fiber)

2. Contraction of muscles is due to the movement of microfilaments

3. All muscles share some terminologya. Prefix myo refers to muscleb. Prefix mys refers to musclec. Prefix sarco refers to flesh

A. Characteristics of MusclesA. Characteristics of Muscles

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http://academic.wsc.edu/faculty/jatodd1/351/muscle_gross_anatomy.JPG

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4. Made up of tissue with the ability to

a. Excitability – ability to receive and respond to stimuli

b. Contractility – ability to shorten and thicken

c. Extensibility – ability to stretch d. Elasticity – ability to return to the original

shape

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1. Skeletal Muscle

a. striated

b. voluntary

c. Multi-nucleated – fibers in bundles

d. 1-40 mm long, 10-100 microns thick

e. 42% of male body weight, 36% in females

General Characteristics:a. sarcoplasm – cytoplasm of muscle fibers

b. sarcolemma – plasma membrane covering the muscle fibers

c. location – any muscle attached to bones as well as in the tongue, the pharynx, and certain muscles of the eye

d. functions – locomotion, posture, transport of blood and lymph, and heat production (85% of the body’s heat)

B. Three basic types of muscle:

Description:

http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19917.jpg

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http://www.meddean.luc.edu/lumen/MedEd/Histo/HistoImages/hl3A-45.jpg

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2. Cardiac Muscle

a. Involuntary

b. Similar to skeletal muscles (striated)

c. Branched fibers

Characteristics:

a. Purkinje fiber (conduction myofiber)

- Stimulate actual contraction of the ventricles

b. Innervation – autonomic nervous system

c. Location – heart

d. Functions to move blood through the heart and through the vessels

Description

http://www.ucl.ac.uk/~sjjgsca/MuscleCardiacCells.gif

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3. Smooth Muscle

a. Involuntary – maintenance of the body’s internal environmentb. Nonstriatedc. Spindle shaped d. 15-500 microns long

Characteristicsa. contractions are slowb. Location – in the walls of internal organs such as digestive organs, trachea, gall bladder, blood vessels, urinary and genital ducts, and the iris of the eyec. Functions – propulsion,expulsion, regulation of openings, and regulation the diameter of tubes / blood vessels

Description:

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C. Skeletal Muscle Tissue1. Connective tissue components

a. Fascia – sheet or broad band of fibrous connective tissue outside of epimysium

superficial – under the skin deep – holds the muscles together

thus forming functional groups

b. Epimysium – fibrous connective tissue surrounding (covering) an entire muscle

c. Perimysium – covers (surrounds) a bundle of fibers called fascicles

d. Endomysium – surrounds each muscle fiber

e. Aponeurosis –the tendon that extends as a broad, flat layer around the skull or as a part of the abs – figure 7-14

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2. Must also have:

Action Potential – the electric current stimulation necessary for contraction

Nerve impulse – causes the stimulation

Muscle action potential – the result

b. Blood supply to bring nutrients and oxygen, as well as to carry wastes

Generally there is one artery along with 1 or 2 veins to accompany each nerve

a. Nerve supply

http://biology.clc.uc.edu/fankhauser/Labs/Anatomy_&_Physiology/A&P202/Nerve_Histology/motor_end_plate_400x_PC231459_labeled.JPG

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3. Structure – Skeletal Muscle Fibers a. Sarcolemma – coveringsb. Sarcoplasm – “stuff” inside – many nuclei,

and mitochondriac. Sarcoplasmic reticulum – network of tubules

similar to E.R.d. Transverse tubules – Perpendicular to the

S.R. –open to exterior of the muscle fibere. Myoglobin – reddish pigment similar to

hemoglobin that carries 02

http://www.etsu.edu/cpah/hsci/forsman/Histology%20of%20musclefor%20web_files/image009.jpg

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http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter42/animations.html#

Sarcomere shortening

http://lessons.harveyproject.org/development/muscle/swstfast.html

Functional Unit of Sarcomere

http://www.blackwellpublishing.com/matthews/myosin.html

Neuromuscular endplate

http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/muscles/muscles.html

Muscle Contraction

http://msjensen.cehd.umn.edu/1135/Links/Animations/Flash/0010-swf_action_potenti.swf

If this link doesn’t connect, cut and paste the address

Troponin/Tropomyosin

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Fibers - continuedf. Myofibrils – Cylindrical structures that run longitudinally through the fibers and contain: thin myofilaments – Made mostly of actin (protein)

and small amounts of tropomyosin and troponin thick myofilaments – made mostly of myosin

(protein) Shaped like a golf club Heads are called cross-bridges

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D. Microscopic Anatomy of Skeletal MuscleD. Microscopic Anatomy of Skeletal Muscle


1. Basic organization of the sarcomere

a. Thick filaments = myosin filaments

Composed of the protein myosin

Has ATPase enzymes

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Microscopic Anatomy of Skeletal MuscleMicroscopic Anatomy of Skeletal Muscle


b. Thin filaments = actin filaments

Composed of the protein actin

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2. Myofibril

a. Bundles of myofilaments

b. Myofibrils are aligned to give distrinct bands

I band = light band

A band = dark band

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More - fibers c. Sarcomeres – Basic compartments of

myofilaments – functional unit “A” bands – dark area composed of overlapping

actin and myosin “H” bands (zone) – narrow area in the center of

the A band that contains only myosin “I” bands – contains only actin “Z” bands – (discs) – dense material between

sarcomeres where the myofilaments attach

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3. Sarcomere

a. Contractile unit of a muscle fiber

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b. Myosin filaments have heads (extensions, or cross bridges)

c. Myosin and actin overlap somewhat

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d. At rest, there is a bare zone that lacks actin filaments

e. Sarcoplasmic reticulum (SR) – for storage of calcium

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E. Muscle Contraction

1. Sliding filament mechanism –

a. The myofilaments slide inward towards the center of the sarcomere so the sarcomere shortens but the myofilaments DO NOT!

b. Sufficient Ca2+ and adequate energy are required (ATP)

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2. The Sliding Filament Theory of 2. The Sliding Filament Theory of Muscle ContractionMuscle Contraction


a. Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filament

b. Myosin heads then bind to the next site of the thin filament

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The Sliding Filament Theory of Muscle The Sliding Filament Theory of Muscle ContractionContraction


c. This continued action causes a sliding of the myosin along the actin

d. The result is that the muscle is shortened (contracted)

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter42/animations.html#

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3. Neuromuscular Junction (Motor-end plate)

a. Consists of a motor neuron and the muscle fibers it stimulates

Precise movements require 10:1 or less fiber to MEP ratio Gross movements may have as many as 2000:1 ratio

Synaptic vesicles – Sacs at the end of the axon of a neuron

Synaptic cleft – The space between the axon and the sarcolemma of the the muscle fiber

Acetylcholine(ACh) – A neurotransmitter that is released as a result of Ca2+ from the interstitial fluid

Changes the permeability (especially to Na+) Carries the impulse to receptors on sarcolemma

Cholinesterase(AChE) – found in the synaptic cleft Deactivates ACh within 1/500 of a second by breaking it

into acetate and choline thus preventing continuous stimulation

26http://psyche.knu.ac.kr/notebook/images/ch5fi05.jpg

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Neuromuscular Junction – cont.

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4. Physiology of contractiona. The relaxed muscle is low in Ca2+ because the S.R. has

calcium active pumps to remove it from the sarcoplasm.

b. When the action potential travels along the sarcolemma Ca2+ channels open in the S.R. and a flood of Ca2+ move into the sarcoplasm around the thick and thin myofilaments

c. Ca2+ combine with troponin changing it’s shape thus the troponin –tropomyosin complex move away from the bonding sites on actin (exposed)

d. ATP attaches to the myosin crossbridges

e. A portion of each myosin head acts as ATPase (enzyme) which splits ATP into ADP+P

f. The myosin head becomes energized

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Physiology of contraction – cont.

g. This causes the myosin heads to bind to the binding sites on the the troponin- tropomyosin complex

h. Now the heads pivot causing the “power stroke” of muscle contraction.

i. As the thin filaments draw past the thick filaments they release ADP

j. ATP reforms and returns to the myosin crossbridges and the myosin detaches from the actin . ( about ½ of the crossbrides are bound and ½ are preparing to bind at any one time)

* * As long as ATP is available and the Ca2+ is high the contraction will repeat.

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5. Energy for muscle contraction ATP is the immediate energy source but the muscle only

contains enough for 5-6 seconds of sustained activity.

a. Creatine Phosphate – high energy molecule found in muscles that can break down into creatine, phosphate, and energy to form enough ATP to last for 15 more seconds.

b. Now we must access glucose for energy - respiration Glucose is stored as glycogen in the muscle

Glycogen is broken into 2 pyruvic acids(glycolysis) anaerobically (no O2 needed) – this requires 2 ATP but it produces 4 ATP – 30-40 seconds of energy -

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Energy for muscle contraction Pyruvic acid enters the

mitochondria to be catabolized into C02 and water – Aerobic (02 required)

This is called the Krebs cycle or the citric acid cycle

This will occur 100,000 times/second as long as there is pyruvic acid and O2 available

Each cycle will produce 36 – 38 ATP

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F. Relaxation 2 changes permit the muscle to relax

1. ACh is broken by AChE which prevents the action potential by stopping Ca2+ release

2. Calcium active transport pumps remove the Ca2+ from the sarcoplasm rapidly

At death Ca2+ leaks and causes rigor mortis – no ATP to release the actin from the myosin

1 Muscular System Poudre High School Human Anatomy/Physiology Mr. Bradley.

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Transcript of 1 Muscular System Poudre High School Human Anatomy/Physiology Mr. Bradley.