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Lecture

Physiology of Muscles.doc


Department
Anatomy and Physiology
Course Code
ANP 1105
Professor
Jacqueline Carnegie

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Physiology of Muscles
-there are 3 types of muscles: skeletal, cardiac, and smooth muscle
-skeletal and smooth muscle cells are elongated and are called muscle fibres
-the prefixes, myo, mys, and sarco (flesh) all refer to muscle (i.e.: sarcolemma refers to
plasma membrane of muscle cells and sarcoplasm refer to cytoplasm of muscle cells)
Skeletal Muscle Tissue
-attach and cover bony skeleton
-striated
-voluntary muscle
-responsible for overall body mobility; contract rapidly and tires easily
Cardiac Muscle Tissue
-occurs only in the heart at the heart walls
-striated
-involuntary
Smooth Muscle Tissue
-found in walls of hollow visceral organs
-forces fluids and other substances through internal body channels
-nonstriated
-involuntary
-slow, sustained contractions
Characteristics of Muscle Tissue
1) Excitability
-responsiveness and irritability
-the ability to receive and respond to stimulus (i.e.: NT released by a nerve cell or local
change in pH)
-generation of electrical impulse that passes along plasma membrane of muscle cell and
causes cell to contract
2) Contractility
-ability to shorten forcibly when adequately stimulated
3) Extensibility
-ability to be stretched and extended
-muscle cells can shorten when contracting and can stretch as well
4) Elasticity
-ability of muscle cell to recoil and resume its resting length after being stretched
Muscle Functions
1) Generating Movement

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-all movements in the body are a result of muscle contraction
-locomotion, manipulation, blood flow and pressure, respiration, digestion, etc.
2) Maintaining Posture and Body Position
-muscles function making one adjustment after another to counter act the downward pull of
gravity
3) Stabilizing Joints
-as muscles pull on bones to cause movements, they stabilize the joints of the skeleton
4) Generating Heat
-muscles generate heat as they contract and heat is important to maintain body temperature
-skeletal muscle accounts for at least 40% of body mass
-skeletal muscles protect fragile internal organs by enclosing them
Skeletal Muscle
-each muscle is served by ne nerve, an artery, and one or more veins
-skeletal muscle is supplied with a nerve ending that controls its activity; it has a rich blood
supply
Connective Tissue in Skeletal Muscle
1) Epimysium
-an overcoat of dense irregular CT that surrounds the whole muscle
2) Perimysium and Fascicles
-muscle fibres are grouped into fascicles that resemble bundles of sticks
-perimysium surrounds each fascicle
3) Endomysium
-CT that surrounds each individual muscle fibre; consists of find areolar CT
Anatomy of Skeletal Muscle Fibre
-each skeletal muscle fibre is a long cylindrical cell with multiple oval nuclei beneath its
sarcolemma (plasma membrane)
-sarcoplasm is similar to cytoplasm of other cells but it contains large amounts of
glycosomes (stored glycogen that proves glucose during muscle cell activity) and
myoglobin (red pigment that stores oxygen)
Myofibrils
-each muscle fibre contains many rodlike myofibrils and are very densely packed
-they contain the contractile elements of skeletal muscle cells, the sarcomeres, which
contain even smaller rodlike structures called the myofilaments
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striations- a repeating series of dark and light bands that are evident along the length of
each myofibril
-the dark A bands and light I bands are aligned with one another, giving the striated
appearance
-each dark A band has a lighter region in its midsection called the H zone (H for helle,
meaning bright)
-each H zone is bisected vertically by a dark M line (M for middle)
-the sarcomere (literally, muscle segment) is the functional unit of skeletal muscles
-the sarcomere is the region of myofibril between 2 successive Z discs; it contains an A
band surrounded by an I band at each end
-this arrangement is made up of myofilaments which is made up of actin and myosin
myosin- thick filaments; they are red and extend the entire length of the A band
actin- the more lateral, thin filaments that extend across the I band and partway into the A
band
z disc- coin shaped and composed largely of alpha-actinin (anchors the thin filaments)
-the H zone of the A band appears less dense because the thin filaments do not extend into
this region
-the M line in the centre of the H zone is slightly darker because of the presence of protein
strands that hold adjacent thick filaments together
Structure of Myofilaments
-muscle contraction depends on the myosin-and-actin-containing myofilaments
-each myosin molecule consists of 2 heavy and 4 light polypeptide chains
-each myosin has a rodlike tail attached by a flexible hinge to 2 globular heads
-during contraction, they link the thick and thin filaments together, forming cross bridges
-each thick filament consists of 300 myosin molecules, where there tails from the central
part of the thick filament and their heads face outward at each end
-thin filaments are composed of actin and contain globular actin or G actin which bear the
active sites to which myosin heads attach during contraction
-in thin filaments, G actin subunits are polymerized into long actin filaments called fibrous
actin or F actin
tropomyosin- rod-shaped protein that spirals about the actin core and help stiffen and
stabilize it
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