Lecture 4: Muscles & Tissue Flashcards by Emily Cross

Define muscle contraction

Response to stimuli

Not a muscle shortening because in eccentric contractions the muscle is lengthening

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Contraction where the length of muscle does not change

Isometric

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Define ‘isotonic’ contraction

Length of the muscle changes
Shortens or lengthens
Concentric or eccentric

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What are the 6 characteristics that muscles can be named from?

Shape, origin-insertion, function, size, fiber arrangement, location

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What are the four ways fibers can be arranged?

Straight - fibers run parallel
Fusiform - thick center, tapers at ends, fibers run parallel
Unipennate - feather like, one side only (pennate = feather)
Bipennate - feather with both sides
Multipennate - multiple feathers

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Compare strength between a fusiform fiber arrangement and a pennate arrangement. Explain

Pennate = feather like - increase in surface area

Each cross section allows for a greater force to be created across small areas

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How far can muscles contract compared to their resting state?

Half their size

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Define agonist

Muscle doing the desired action, two types
Prime mover - muscle whose function is to cause that mvt or muscle that makes the strongest contribution towards the mvt
Assistant mover - muscle that causes the same mvt but it’s force is only of secondary importance

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Define antagonist

Muscle that opposes the agonist, typically on the opposite side of the body
Example: biceps and triceps in a bicep curl

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A muscle that eliminates unwanted action by the agonist

Synergist

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Muscle that stabilizes base of attachment of agonist

Fixator - when acting as a stabilizer it is usually an isometric contraction (meaning?)

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Define unijoint muscles

Muscle that crosses only one joint

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Define multijoint muscle

Muscle that crosses multiple joints

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Mulit-joint muscles are subject to what phenomenon?

Muscle Insufficiency

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The inability of a multijoint muscle to contract maximally over all joints crossed, at one time

Muscle insufficiency

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What are the two types of muscle insufficiency?

Active insufficiency —- agonist

Passive insufficiency —- antagonist

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The diminished ability of a muscle to produce or maintain active tension

Active insufficiency

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Characteristics of active insufficiency

The muscle is so elongated that there are no overlaps between microfilaments

When all cross bridges have been formed, the muscle is excessively shortened

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Passive Insuficiency

Occurs when the antagonist muscle is at a insufficient length to allow the full force that a full ROM would produce

Mainly associated with multijoint muscles

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Synergist muscle is also know as what?

Neutralizer

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A pure neutralizer will cause….?

The opposite motion of the prime mover, without actually assisting with the mvt

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What type of muscles do not allow full ROM in all joints it crosses at one time?

Multi-joint muscles

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Give examples of a pure synergist vs. a helping synergist

Pure synergist - causes opposite motion w/o assisting in mvt
Ex. Triceps during elbow flexion, so the biceps can supinate forearm
Helping synergist - only opposes one component of mvt
Ex. Pronator teres helps in elbow flexion by biceps, it nullifies the supination component

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Muscles that pass anterior to the axis of a joint

Flexors

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Muscles that pass posterior to the axis of a joint

Extensors

Muscles that pass lateral to a joint

Abductors

Muscle tissue appearances

Striated or smooth

Muscle nuclei can be.....?

Multi-nucleated (syncytium) = more than 1 nucleus Mono-nucleated

Voluntary vs. involuntary muscle function. Give examples

Voluntary = conscious control of muscle contraction Ex. Most skeletal muscles - biceps Involuntary = have no control over Ex. Arrector pili muscles, heart

Name the types of muscle tissue

Skeletal/striated Smooth Cardiac (4th special kind - branchiomeric muscle)

Skeletal muscle characteristics

Striated and voluntary Attached directly or indirectly to the skeletal system Peripheral nuclei - not in center of cell Multi-nucleated Conducts action potential

Where does the striated appearance of skeletal muscle come from?

When subunits are viewed under microscope they have a banded appearance

Smooth muscle characteristics

Referred to as visceral or involuntary Not striated Most commonly associated with viscera - especially gut tubes and hollow structures

Groups of spindle-shape, mononucleated cells, with a centrally located nuclei

Smooth/visceral/involuntary muscle

What are the most common places smooth muscle is found?

Viscera - gut tube and other hollow structures

What type of muscle tissue is only found in one organ?

Cardiac muscle tissue

Cardia muscle tissue shares characteristics with.....

Striated and smooth muscle tissues

Cardiac muscle characteristics

Striated Involuntary Intercalated discs - special intercellular junctions

Consists of chains of individual cells that are mononucleated and striated

Cardiac muscle tissue

Muscle tissue associated with pharyngeal arches

Branchiomeric muscle tissue

Characteristics of branchiomeric muscle tissue

A transition between smooth and striated muscle tissues Innervated by cranial nerves

Define origin

Usually the proximal attachment of muscle

Define insertion

Usually the distal attachment of a muscle

Which attachment zone is more moveable?

Distal = more moveable (insertion) Proximal = fixed with regard to mvt (origin)

Tendons

Attach muscle to bone Dense collection of collagenous CT Poorly vascularized

Aponeuroses

Flat/fan-shaped tendons that turns into multiple tendons Ex. Palm of hand

List the hierarchical structure of skeletal muscle from outmost in

Muscle - fascicle - myofiber - myofibril - myofilament - sarcomere - myosin or actin filaments

Myofilament

Are either thick (myosin) or thin (actin) filaments Are organized into chains of sarcomeres

Myofibril

Chain of sarcomeres

Myofiber

Bundle of myofibrils Also referred to as the muscle cell Each fiber is formed from fused myoblasts

Fascicle

Bundle of myofibers

Muscle

Composed of multiple fascicles | Contains blood vessels too

Surrounds each muscle fiber (also called?)

Endomysium surrounds each myofiber and lies outside the sarcolemma

Sarcolemma

Name of the cell membrane for a muscle cell

Membrane surrounding each fascicle within a muscle

Perimysium

Membrane surrounding an entire muscle and continuous with tendons? What does it attach to?

Epimysium | Attached to the periosteum of bone

CT provides.....what for nerves and vessels?

CT provides a physical support and framework for nerves and vessels

Types of myofilaments

Actin & myosin Also called thin & thick filaments

A thin filamentous protein polymer

Actin

Each actin filament is made up of.....

2 helically wound polymers of G-actin

What molecules are associated with Actin?

Tropomyosin | Troponin

Bundles of long molecules that form a tail + ATPase head. How is that tail attached?

Myosin Tail attached via a swivel mechanism

Myosin ATPase heads attach to ......

Binding sites on actin filaments

Sliding filament theory of contraction

Attach-swivel release cycles Allow myosin and actin to slide along one another in opposite directions which = a contraction

Myosin and actin organization into myofibrils

Organized in cylindrical units, aligned end to end to form the myofibril Filaments are like a round stone, and each one is stacked on top of another to create a long rod which = a myofibril

Name the 3 main components of sarcomere structure

Z-lines I-bands A-bands

Z-lines

Composed of z-actin Separate the sarcomeres in a fibril Z=between

Sarcomere

Each cylindrical unit that when all put together forms a myofibril Thus myofibril = chain of sarcomeres

I-bands

Composed entirely of actin | Make up ends of each sarcomere = located on either side of z-line

A-bands

Composed of actin and myosin | Located in middle of sarcomere

After birth the number of myofibers....

Cannot be increased

After birth the number of myofibrils.....? Relate to myofiber

Can be increased Thus the mass of a myofiber can be increased === muscle increase

What replaces lost muscle tissue

Scar tissue = fibrous CT

Equivalent to the endoplasmic reticulum of regular cells

Sarcoplasmic reticulum

T-tubule gross structure

Tubular extensions that reach from the sarcolemma into the sarcoplasm (cytoplasm)

T-tubule function

Conduct action potential from sarcolemma surface to cell interior

Cisternae

Sac like extensions from sarcoplasmic reticulum, that release Ca ions in responses to action potential

What structure releases calcium ions in a sarcomere? What causes their release? What is the significance of Ca ions?

Cisternae release ions - extensions of sarcoplasmic reticulum Released in response to action potential conducted by t-tubule Ca ions trigger sliding of myosin and actin filaments = resulting in a muscle contraction

Sliding filament theory - mechanism? Occurs inside of?

During a contraction, the I & H bands shorten, A band does not Within a sarcomere/myofibril ATPase heads of myosin attach to actin via troponin and swivel mechanism

F-actin

Thin filamentous protein polymer

G-actin

Globular - free monomer