The Muscular SystemThe Muscular System

Skeletal Muscle Tissue and Skeletal Muscle Tissue and Muscle OrganizationMuscle Organization

Chapter 9Chapter 9

Alireza Ashraf, M.D.Professor of Physical Medicine & Rehabilitation

Shiraz Medical school

The Muscular SystemThe Muscular System

Skeketal Muscle, Cardiac Muscle, Smooth MuscleSkeketal Muscle, Cardiac Muscle, Smooth Muscle

Share 4 basic properties:Share 4 basic properties:

1) Excitability – respond to stimulation by either 1) Excitability – respond to stimulation by either the nervous system or to circulating hormonesthe nervous system or to circulating hormones

2) Contractility – ability to shorten actively and 2) Contractility – ability to shorten actively and exert a pull or tension harnessed by CTexert a pull or tension harnessed by CT

3) Extensibility – ability to contract over a range 3) Extensibility – ability to contract over a range of resting lengthsof resting lengths

4) Elasticity – ability of a muscle to rebound 4) Elasticity – ability of a muscle to rebound toward its original length after a contractiontoward its original length after a contraction

Skeletal Muscle FunctionsSkeletal Muscle Functions

Contractile organs directly or indirectly attached Contractile organs directly or indirectly attached to bonesto bones

Functions include:Functions include:1) Produce skeletal movement: muscle 1) Produce skeletal movement: muscle contractions pull on tendons and move the contractions pull on tendons and move the bonesbones- effects range from simple motions to highly - effects range from simple motions to highly coordinated movements of swimming, skiing, or typingcoordinated movements of swimming, skiing, or typing

2) Maintain posture and body positions: 2) Maintain posture and body positions: contraction of secific muscles contraction of secific muscles – – involves the contraction of muscles that stabilize involves the contraction of muscles that stabilize joints, without constant muscular contraction, we could joints, without constant muscular contraction, we could not sit upright without collapsing or stand without not sit upright without collapsing or stand without toppling overtoppling over

Skeletal Muscle FunctionsSkeletal Muscle Functions3) Support soft tissues: the abdominal wall and 3) Support soft tissues: the abdominal wall and the floor of the pelvic cavity consist of layers of the floor of the pelvic cavity consist of layers of skeletal muscle skeletal muscle - support the weight of visceral organs and protect - support the weight of visceral organs and protect internal tissuesinternal tissues

4) Regulate entering and exiting of material: 4) Regulate entering and exiting of material: openings or orifices, of the digestive and urinary openings or orifices, of the digestive and urinary tracts are encircled by skeletal muscles tracts are encircled by skeletal muscles

- - provide voluntary control over swallowing, defecation, provide voluntary control over swallowing, defecation, and urinationand urination

5) Maintain body temperature: muscle 5) Maintain body temperature: muscle contractions require energy some is converted to contractions require energy some is converted to heatheat- heat lost by contracting muscles maintains our body - heat lost by contracting muscles maintains our body temptemp

Anatomy of Skeletal Anatomy of Skeletal MusclesMuscles

Epimysium (mys = muscle) - outer layer of dense Epimysium (mys = muscle) - outer layer of dense irregular CT connected to the deep fascia:irregular CT connected to the deep fascia: - surrounds the entire skeletal muscle and separates the - surrounds the entire skeletal muscle and separates the muscle from surrounding tissuesmuscle from surrounding tissues

Perimysium - CT fibers that surrounds each fascicle:Perimysium - CT fibers that surrounds each fascicle:- divides the muscle into a series of internal compartments - divides the muscle into a series of internal compartments each containing a bundle of muscle fibers called fascicleseach containing a bundle of muscle fibers called fascicles- collagen and elastic fibers, BVs and nerve supply- collagen and elastic fibers, BVs and nerve supply

Endomysium – surrounds each skeletal muscle fiberEndomysium – surrounds each skeletal muscle fiber- binds each muscle fiber to its neighbor and supports the - binds each muscle fiber to its neighbor and supports the capillaries that supply each individual fibercapillaries that supply each individual fiber- consists of a network of reticular fibers with scattered - consists of a network of reticular fibers with scattered myosatellite cells that function in repair of damaged musclemyosatellite cells that function in repair of damaged muscle

Fig 9.1Fig 9.1 Structural Organization of Skeletal MuscleStructural Organization of Skeletal Muscle

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Tendons and AponeurosesTendons and Aponeuroses

CT fibers of the all 3 are interwoven, those CT fibers of the all 3 are interwoven, those of the perimysium blend into the epimysiumof the perimysium blend into the epimysium

At each end of the muscle, collagen fibers At each end of the muscle, collagen fibers often converge often converge - form a fibrous tendon that attaches muscle to - form a fibrous tendon that attaches muscle to bone, skin, or another musclebone, skin, or another muscle- tendons resemble thick cords or cables those that - tendons resemble thick cords or cables those that form flattened sheets are called aponeurosesform flattened sheets are called aponeuroses

Tendon fibers are interwoven into the Tendon fibers are interwoven into the periosteum and matrix of associated boneperiosteum and matrix of associated bone- provides an extremely strong bond to withstand - provides an extremely strong bond to withstand muscle contractionsmuscle contractions

Nerves and Blood VesselsNerves and Blood Vessels

3 CT layers contain the nerves and BVs that 3 CT layers contain the nerves and BVs that supply the muscle fiberssupply the muscle fibers

Called voluntary muscles because their Called voluntary muscles because their contractions can be controlledcontractions can be controlled- provided by the nerves of the nervous system- provided by the nerves of the nervous system

Nerves, bundles of axons, penetrate the Nerves, bundles of axons, penetrate the epimysiumepimysium- branch through the perimysium and enter the - branch through the perimysium and enter the endomysium to innervate individual fibersendomysium to innervate individual fibers

Neuromuscular synapse or myoneural junction Neuromuscular synapse or myoneural junction – – site of chemical communication between a synaptic site of chemical communication between a synaptic terminal of the neuron and a skeletal muscle fiberterminal of the neuron and a skeletal muscle fiber

Skeletal Muscle InnervationSkeletal Muscle Innervation

Each muscle fiber is stimulated by a nerve fiber usually Each muscle fiber is stimulated by a nerve fiber usually located midway along its length located midway along its length - the synaptic terminal of the neuron is bound to the motor - the synaptic terminal of the neuron is bound to the motor end plate (specialized area of the muscle cell membrane) end plate (specialized area of the muscle cell membrane) - entensive vascular supply delivers oxygen and nutrients - entensive vascular supply delivers oxygen and nutrients

Fig 9.2

Microanatomy of Skeletal Muscle Microanatomy of Skeletal Muscle FibersFibers

Sarcolemma (sarkos = flesh + lemma = husk)Sarcolemma (sarkos = flesh + lemma = husk) - cell membrane of a skeletal muscle fiber surrounds the - cell membrane of a skeletal muscle fiber surrounds the cytoplasm, or sarcoplasmcytoplasm, or sarcoplasm

Skeletal muscle fibers differ from the ‘typical’ cell:Skeletal muscle fibers differ from the ‘typical’ cell:- very large, a fiber from a leg muscle can have a 100 um - very large, a fiber from a leg muscle can have a 100 um diameter and a length equal to that of the entire musclediameter and a length equal to that of the entire muscle

- are multinucleate, during development groups of - are multinucleate, during development groups of embryonic cells or myoblasts fuse together to form fibersembryonic cells or myoblasts fuse together to form fibers

- deep indentations called transverse tubules or T tubules - deep indentations called transverse tubules or T tubules in the sarcolemmal surface form a network of narrow in the sarcolemmal surface form a network of narrow tubules that extend into the sarcolemma to help stimulate tubules that extend into the sarcolemma to help stimulate and coordinate muscle contractionsand coordinate muscle contractions

Fig 9.3Fig 9.3 The Formation and Structure of a Skeletal Muscle FiberThe Formation and Structure of a Skeletal Muscle Fiber

Fig 9.4

Sarcomere StructureSarcomere Structure

Development of a skeletal muscle fiber

Muscle FascicleMuscle Fascicle

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Levels of Levels of Functional Functional Organization in a Organization in a Skeletal Muscle Skeletal Muscle FiberFiber

Muscle Fiber

Myofibril

Sacromere

Fig 9.6Fig 9.6 Thin and Thick FilamentsThin and Thick Filaments

During a contraction, the A During a contraction, the A band stays the same width, band stays the same width, but the Z lines move closer but the Z lines move closer together and the I band and together and the I band and H band are reduced in widthH band are reduced in width

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Changes in the Changes in the Appearance of a Appearance of a Sarcomere during Sarcomere during Contraction of a Skeletal Contraction of a Skeletal Muscle FiberMuscle Fiber

Fig 9.8Fig 9.8 The Effect of Sarcomere Length on TensionThe Effect of Sarcomere Length on Tension