Ch.11: Physiology of the Muscular System

Ch.11: Physiology of the Muscular

System

Ch.11: Physiology of the Muscular

System Part 4Part 4

Smooth MuscleSmooth MuscleSmooth MuscleSmooth Muscle

Composed of spindle-shaped fibers with a Composed of spindle-shaped fibers with a diameter of 2-10 diameter of 2-10 μμm and lengths of several m and lengths of several hundred hundred μμmm

Lack the coarse connective tissue sheaths of Lack the coarse connective tissue sheaths of skeletal muscle, but have fine endomysiumskeletal muscle, but have fine endomysium

Organized into two layers (longitudinal and Organized into two layers (longitudinal and circular) of closely apposed fiberscircular) of closely apposed fibers


Found in walls of hollow organs (except Found in walls of hollow organs (except the heart)the heart)

Have essentially the same contractile Have essentially the same contractile mechanisms as skeletal musclemechanisms as skeletal muscle

PeristalsisPeristalsisPeristalsisPeristalsis

When the longitudinal layer contracts, the When the longitudinal layer contracts, the organ dilates and contracts organ dilates and contracts

When the circular layer contracts, the When the circular layer contracts, the organ elongatesorgan elongates

Peristalsis – alternating contractions and Peristalsis – alternating contractions and relaxations of smooth muscles that mix relaxations of smooth muscles that mix and squeeze substances through the and squeeze substances through the lumen of hollow organslumen of hollow organs

Innervation of Innervation of Smooth MuscleSmooth MuscleInnervation of Innervation of

Smooth MuscleSmooth Muscle

Smooth muscle lacks neuromuscular Smooth muscle lacks neuromuscular junctionsjunctions

Innervating nerves have bulbous swellings Innervating nerves have bulbous swellings called varicositiescalled varicosities

Varicosities release neurotransmitters into Varicosities release neurotransmitters into wide synaptic clefts called diffuse wide synaptic clefts called diffuse junctionsjunctions

Innervation of Innervation of Smooth MuscleSmooth MuscleInnervation of Innervation of

Smooth MuscleSmooth Muscle

Microscopic Microscopic Anatomy of Smooth Anatomy of Smooth

MuscleMuscle


MuscleMuscleSR is less developed than in SR is less developed than in skeletal muscle and lacks a skeletal muscle and lacks a specific patternspecific pattern

T tubules are absentT tubules are absent

Plasma membranes have Plasma membranes have pouchlike infoldings called pouchlike infoldings called caveolicaveoli


MuscleMuscle


MuscleMuscleCa2+ is sequestered in the extracellular Ca2+ is sequestered in the extracellular space near the caveoli, allowing rapid space near the caveoli, allowing rapid influx when channels are openedinflux when channels are opened

There are no visible striations and no There are no visible striations and no sarcomeressarcomeres

Thin and thick filaments are presentThin and thick filaments are present

Proportion and Organization of Proportion and Organization of Myofilaments in Smooth Myofilaments in Smooth

MuscleMuscle


MuscleMuscle

Ratio of thick to thin filaments is much lower Ratio of thick to thin filaments is much lower than in skeletal musclethan in skeletal muscle

Thick filaments have heads along their entire Thick filaments have heads along their entire lengthlength

There is no troponin complexThere is no troponin complex


MuscleMuscle


MuscleMuscle

Thick and thin filaments are arranged Thick and thin filaments are arranged diagonally, causing smooth muscle to diagonally, causing smooth muscle to contract in a corkscrew mannercontract in a corkscrew manner

Noncontractile intermediate filament Noncontractile intermediate filament bundles attach to dense bodies (analogous bundles attach to dense bodies (analogous to Z discs) at regular intervalsto Z discs) at regular intervals

Contraction of Contraction of Smooth MuscleSmooth MuscleContraction of Contraction of Smooth MuscleSmooth Muscle

Whole sheets of smooth muscle exhibit Whole sheets of smooth muscle exhibit slow, synchronized contractionslow, synchronized contraction

They contract in unison, reflecting their They contract in unison, reflecting their electrical coupling with gap junctionselectrical coupling with gap junctions

Action potentials are transmitted from cell Action potentials are transmitted from cell to cellto cell

Contraction of Contraction of Smooth MuscleSmooth MuscleContraction of Contraction of Smooth MuscleSmooth Muscle

Some smooth muscle cells: Some smooth muscle cells:

Act as pacemakers and set the Act as pacemakers and set the contractile pace for whole sheets of contractile pace for whole sheets of musclemuscle

Are self-excitatory and depolarize Are self-excitatory and depolarize without external stimuliwithout external stimuli

Contraction Contraction MechanismMechanismContraction Contraction MechanismMechanism

Actin and myosin interact according to Actin and myosin interact according to the sliding filament mechanismthe sliding filament mechanism

The final trigger for contractions is a rise The final trigger for contractions is a rise in intracellular Cain intracellular Ca2+2+

CaCa2+2+ is released from the SR and from the is released from the SR and from the extracellular spaceextracellular space

CaCa2+2+ interacts with calmodulin and interacts with calmodulin and myosin light chain kinase to activate myosin light chain kinase to activate myosinmyosin

Smooth muscle relaxes when intracellular Smooth muscle relaxes when intracellular CaCa2+2+ levels drop levels drop

Special Features of Special Features of Smooth Muscle Smooth Muscle

ContractionContraction

Special Features of Special Features of Smooth Muscle Smooth Muscle

ContractionContractionUnique characteristics of smooth muscle Unique characteristics of smooth muscle include:include:

Smooth muscle toneSmooth muscle tone

Slow, prolonged contractile activitySlow, prolonged contractile activity

Low energy requirementsLow energy requirements

Response to stretchResponse to stretch

Response to StretchResponse to StretchResponse to StretchResponse to Stretch

Smooth muscle exhibits a phenomenon called Smooth muscle exhibits a phenomenon called stress-relaxation response in which: stress-relaxation response in which:

Smooth muscle responds to stretch only Smooth muscle responds to stretch only briefly, and then adapts to its new lengthbriefly, and then adapts to its new length

The new length, however, retains its ability The new length, however, retains its ability to contractto contract

This enables organs such as the stomach This enables organs such as the stomach and bladder to temporarily store contentsand bladder to temporarily store contents

HyperplasiaHyperplasiaHyperplasiaHyperplasia

Certain smooth muscles can divide and Certain smooth muscles can divide and increase their numbers by undergoing increase their numbers by undergoing hyperplasiahyperplasia

This is shown by estrogen’s effect on the This is shown by estrogen’s effect on the uterusuterus

At puberty, estrogen stimulates the synthesis At puberty, estrogen stimulates the synthesis of more smooth muscle, causing the uterus to of more smooth muscle, causing the uterus to grow to adult sizegrow to adult size

During pregnancy, estrogen stimulates uterine During pregnancy, estrogen stimulates uterine growth to accommodate the increasing size of growth to accommodate the increasing size of the growing fetusthe growing fetus

Types of Smooth Types of Smooth Muscle: Single UnitMuscle: Single Unit

Types of Smooth Types of Smooth Muscle: Single UnitMuscle: Single Unit

The cells of single-unit smooth muscle, commonly The cells of single-unit smooth muscle, commonly called visceral muscle:called visceral muscle:

Contract rhythmically as a unitContract rhythmically as a unit

Are electrically coupled to one another via gap Are electrically coupled to one another via gap junctionsjunctions

Often exhibit spontaneous action potentialsOften exhibit spontaneous action potentials

Are arranged in opposing sheets and exhibit Are arranged in opposing sheets and exhibit stress-relaxation responsestress-relaxation response

Types of Smooth Types of Smooth Muscle: MultiunitMuscle: MultiunitTypes of Smooth Types of Smooth Muscle: MultiunitMuscle: Multiunit

Multiunit smooth muscles are found:Multiunit smooth muscles are found:

In large airways to the lungsIn large airways to the lungs

In large arteriesIn large arteries

In arrector pili musclesIn arrector pili muscles

Attached to hair folliclesAttached to hair follicles

In the internal eye musclesIn the internal eye muscles

Types of Smooth Types of Smooth Muscle: MultiunitMuscle: MultiunitTypes of Smooth Types of Smooth Muscle: MultiunitMuscle: Multiunit

Their characteristics include:Their characteristics include:

Rare gap junctionsRare gap junctions

Infrequent spontaneous depolarizationsInfrequent spontaneous depolarizations

Structurally independent muscle fibers Structurally independent muscle fibers

A rich nerve supply, which, with a number A rich nerve supply, which, with a number of muscle fibers, forms motor unitsof muscle fibers, forms motor units

Graded contractions in response to neural Graded contractions in response to neural stimulistimuli

Muscular DystrophyMuscular DystrophyMuscular DystrophyMuscular Dystrophy

Muscular dystrophy – group of inherited Muscular dystrophy – group of inherited muscle-destroying diseases where muscles muscle-destroying diseases where muscles enlarge due to fat and connective tissue enlarge due to fat and connective tissue deposits, but muscle fibers atrophydeposits, but muscle fibers atrophy


Duchenne muscular dystrophy (DMD)Duchenne muscular dystrophy (DMD)

Inherited, sex-linked disease carried by Inherited, sex-linked disease carried by females and expressed in males (1/3500)females and expressed in males (1/3500)

Diagnosed between the ages of 2-10Diagnosed between the ages of 2-10

Victims become clumsy and fall Victims become clumsy and fall frequently as their muscles failfrequently as their muscles fail


Progresses from the extremities Progresses from the extremities upward, and victims die of respiratory upward, and victims die of respiratory failure in their 20sfailure in their 20s

Caused by a lack of the cytoplasmic Caused by a lack of the cytoplasmic protein dystrophinprotein dystrophin

There is no cure, but myoblast transfer There is no cure, but myoblast transfer therapy shows promisetherapy shows promise

Developmental Developmental AspectsAspects


Muscle tissue develops from Muscle tissue develops from embryonic mesoderm called embryonic mesoderm called myoblastsmyoblasts

Multinucleated skeletal muscles Multinucleated skeletal muscles form by fusion of myoblastsform by fusion of myoblasts

The growth factor The growth factor agrinagrin stimulates stimulates the clustering of ACh receptors at the clustering of ACh receptors at newly forming motor end platesnewly forming motor end plates



As muscles are brought under the As muscles are brought under the control of the somatic nervous control of the somatic nervous system, the numbers of fast and system, the numbers of fast and slow fibers are also determinedslow fibers are also determined

Cardiac and smooth muscle Cardiac and smooth muscle myoblasts do not fuse but develop myoblasts do not fuse but develop gap junctions at an early gap junctions at an early embryonic stageembryonic stage

Developmental Developmental Aspects: Aspects:

RegenerationRegeneration

Developmental Developmental Aspects: Aspects:

RegenerationRegenerationCardiac and skeletal muscle become Cardiac and skeletal muscle become amitotic, but can lengthen and thickenamitotic, but can lengthen and thicken

Myoblastlike satellite cells show very Myoblastlike satellite cells show very limited regenerative abilitylimited regenerative ability

Cardiac cells lack satellite cellsCardiac cells lack satellite cells

Smooth muscle has good regenerative Smooth muscle has good regenerative abilityability

Developmental Developmental Aspects: After BirthAspects: After Birth

Developmental Developmental Aspects: After BirthAspects: After Birth

Muscular development reflects Muscular development reflects neuromuscular coordinationneuromuscular coordination

Development occurs head-to-toe, and Development occurs head-to-toe, and proximal-to-distalproximal-to-distal

Peak natural neural control of muscles is Peak natural neural control of muscles is achieved by midadolescenceachieved by midadolescence

Athletics and training can improve Athletics and training can improve neuromuscular controlneuromuscular control

Developmental Developmental Aspects: Male and Aspects: Male and

FemaleFemale


FemaleFemale

There is a biological basis for greater There is a biological basis for greater strength in men than in womenstrength in men than in women

Women’s skeletal muscle makes up 36% of Women’s skeletal muscle makes up 36% of their body masstheir body mass

Men’s skeletal muscle makes up 42% of Men’s skeletal muscle makes up 42% of their body masstheir body mass


FemaleFemale


FemaleFemale

These differences are due primarily to the These differences are due primarily to the male sex hormone testosteronemale sex hormone testosterone

With more muscle mass, men are With more muscle mass, men are generally stronger than womengenerally stronger than women

Body strength per unit muscle mass, Body strength per unit muscle mass, however, is the same in both sexeshowever, is the same in both sexes

Developmental Developmental Aspects: Age RelatedAspects: Age Related


With age, connective tissue increases and With age, connective tissue increases and muscle fibers decreasemuscle fibers decrease

Muscles become stringier and more Muscles become stringier and more sinewysinewy

By age 80, 50% of muscle mass is lost By age 80, 50% of muscle mass is lost (sarcopenia)(sarcopenia)



Regular exercise reverses sarcopeniaRegular exercise reverses sarcopenia

Aging of the cardiovascular system affects Aging of the cardiovascular system affects every organ in the bodyevery organ in the body

Atherosclerosis may block distal arteries, Atherosclerosis may block distal arteries, leading to intermittent claudication and leading to intermittent claudication and causing severe pain in leg musclescausing severe pain in leg muscles

HomeworkHomework

Due Monday 3/11

P. 370

Review questions 8-10

Critical thinking questions 9-10

Muscle Contraction song/video project

Due Friday 3/15

Ch.11: Physiology of the Muscular System

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Transcript of Ch.11: Physiology of the Muscular System