Chapter 12 Physiology

Under Microscope: Skeletal Muscle

Striated

Under Microscope: Smooth Muscle

Smooth

Under Microscope: Cardiac Muscle

Striated

Fiber Arrangement: Skeletal Muscle

No Sarcomeres

Fiber Arrangement: Smooth Muscle

No Sarcomeres

Fiber Arrangement: Cardiac Muscle

Sarcomeres

Location: Skeletal Muscle

Attached to bones; a few sphincters close off hollow organs

Location: Smooth Muscle

Forms the walls of hollow organs and tubes; some sphincters

Location: Cardiac Muscle

Heart Muscle

Tissue Morphology: Skeletal Muscle

Multinucleate; large, cylindrical fibers

Tissue Morphology: Smooth Muscle

Uninucleate; small spindle-shaped fibers

Tissue Morphology: Cardiac Muscle

Uninucleate; shorter branching fibers

Internal Structure: Skeletal Muscle

T-tubule and Sarcoplasmic Reticulum

Internal Structure: Smooth Muscle

No T-tubulues; sarcoplasmic reticulum

Internal Structure: Cardiac Muscle

T-tubule and Sarcoplasmic Reticulum

Fiber Proteins: Skeletal Muscle

Actin, Mysosin; troponin and tropomyosin

Fiber Proteins: Smooth Muscle

Actin, Myosin; Tropomyosin

Fiber Proteins: Cardiac Muscle

Actin, Myosin; Troponin and Tropomyosin

What does Skeletal Muscle do and how?

* Control Body Movement through

Voluntary control: responds to somatic motor neurons

What does cardiac muscle do?

Moves blood through the circulatory system

How does Cardiac Muscle perform its function?

Involuntary control: responds to autonomic innervation, spontaneous contraction, modulated by endocrine system

What is smooth muscle?

Primary muscle of the internal organs and tubes

What does Smooth Muscle do?

Influence the movement of material into, out of and within the body

How does Smooth Muscle perform its functions

Involuntary control: respond to autonomic innervation, spontaneous contraction, modulated by endocrine system

Origin

cloest to the trunk or to more stationary bone

Insertion

more distal or attachment to movable bone

Flexor

brings bones together

Extensor

Moves bones away

Flexor-extensor pairs form what?

antagonistic muscle groups

Skeletal muscles are composed of what?

A collection of muscle cells or muscle fibers

Muscle cells are called what?

Muscle Fibers

What is the morphology of muscle fibers?

* Long cylindrical
* Fused cells with many nuclei

What are satellite cells?

Stem cells that differentiate into muscle for growth or repair WHEN NEEDED

What are fascicles?

bundles of muscle fibers

What are muscle fibers bundled into?

Fascicles surrounded by connective tissue sheath

What surrounds the entire muscle and why?

* Connective Tissue
* Holds muscle to bone with tendon

What is connective tissue continuous with?

Connective tissue sheath

Sarcolemma

muscle cell membrane of a muscle fiber

Sarcoplasm

The cytoplasm of a muscle fiber

Myofibril

Bundles of contractile & elastic proteins responsible for muscle contraction

* the main intracellular structures in striated muscles

Sarcoplasmic Reticulum

A form of modified endoplasmic reticulum that wraps around each myofibril like a piece of lace

What is Myosin?

A motor protein with the ability to create movement

What is a Sarcomere?

contractile unit of a muscle fiber

What is myosin composed of?

Heavy Chains: Motor domain; Myosin ATPase

Light Chains: Regulatory Functions

Myosin forms

thick filaments

the microfilament actin creates

thin filaments

Thin Filament

An actin-containing filament of the myofibril

Actin

A globular protien (G-protien) that polymerizes to form thin filaments

Thick Filament

An aggregation of myosin in muscle

What are two regulatory proteinns?

Tropomyosin and Troponin

What is tropomyosin?

It is a long, fibrous protein that winds around the actin polymer, blocking all the myosin-binding sites.

What is troponin?

a regulatory protein that moves tropomyosin aside & exposes myosin binding sites when Ca+ is released during muscle contraction

What are two accessory proteins?

Titin and Nebulin

What is titin?

elastic protein, keeps thick and thin filaments aligned

What is Nebulin, and what is its function?

This is an anchoring protein for actin,. it coextends with actin and appears to play a regulatory role in mediating actin and myosin interactions.

What is Nebulin?

inelastic giant protein that aligns filaments of the sarcomere

* helps titin

What are crossbridges?

Connection formed when the myosin head attaches to the binding sites on the actin myofilament.

What two states do crossbridges have?

Low force (relaxed muscles) and High force (Contracting Muscles)

Muscle Tension

the force created by contracting a muscle

Load

A weight or force that opposes contraction of a muscle

Contraction

the creation of tension in a muscle

Relaxation

release of tension created by a contraction

What are Z disks?

sarcomere protein that serves as attachment site for thin filaments

What are I bands?

region of the sarcomere occupied only by thin filaments

What are A bands?

Band of striated muscle sarcomere whose length equals that of the thick filaments

What is the H zone?

Region of the sarcomere with only thick filaments

What is the M line?

Represents proteins that form the attachment site for thick filaments

What major steps lead up the skeletal muscle contraction?

1. Events at the neuromuscular junction
2. Excitation-Contraction (E-C) Coupling
3. Contraction-Relaxation Cycle

What are the events at the neuromuscular junction?

Convert acetylcholine signal from a somatic motor neuron into an electrical signal in the muscle fiber

What is Excitation-Contraction (EC) Coupling?

The process in which muscle action potentials are translated into calcium signals

What is a Contraction Relaxation Cycle?

sliding filament theory

* can also be called a muscle twitch

What is the sliding filament theory of contraction?

Overlapping actin and myosin filaments of fixed length slide past one another in an energy-requiring process, resulting in muscle contraction

What is the power stroke?

the movement of myosin head while attached to actin myofilament

* basis for muscle contraction

What happens during the power stroke?

When myosin crossbridges swivel and push the actin filaments toward the center of the sarcomere

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* A calcium signal initiates

What happens at the end of power stroke?

each myosin head releases actin, then swivels back and binds to a new actin molecule, ready to start another contractile cycle.

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during contraction, the heads do NOT all release at the same time or the fibers would slide back to their starting position

during contraction, the heads do NOT all release at the same time or the fibers would slide back to their starting position

What else does Myosin do?

converts the chemical bond energy of ATP into the mechanical energy of crossbridge motion

What chemical signal initiates contraction?

Calcium (Ca2+)

What are the contraction steps?

1. Calcium release from terminal cisternae
2. Calcium binds troponin
3. Troponin pulls tropomyosin from myosin-binding sites on actin
4. Myosin binds tightly to and moves actin
5. Repeated as long as binding sites are uncovered and ATP is available

What else does troponin do?

Controls position of tropomyosin

What else does tropomyosin do?

* Prevents myosin and actin from interacting
* partially covers myosin binding site on actin

What is the Rigor State?

Occurs when no ATP or ADP are bound to myosin

What is Rigor Mortis?

Muscles "freezes" if no ATP is available to release myosin

What is phosphocreatine?

A muscle molecule that stores energy in high-energy phosphate bonds

What happens when phosphocreatine is brokendown?

A short burst of energy is produced

What is the most rapid and efficient store of energy?

Carbhohydrates (glucose)

What are characteristics of Anaerobic glycolysis?

* Quick
* No oxygen required
* Small amount of energy released (2 ATP per glucose)

What are characteristics of Aerobic respiration?

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* Slow
* Oxygen Required
* Large amount of energy released (30 ATP per glucose)

What are the end products of anaerobic glycolysis?

Lactate and acid

What is an Isotonic Contraction?

A contraction that creates force and moves a load

Concentric action

shortening action

Eccentric action

lengthening action

What is an Isometric Contractions?

A contraction that creates force without movement

What is series elastic elements?

Elastic fibers in the muscle that stretch during isometric contraction

What is a lever?

A rigid bar that pivots around a point called a fulcrum

What do bones form?

levers

What do flexible joints form?

Fulcrums

What is a muscle cramp?

a sustained, painful, involuntary muscle contraction

What is overuse?

Fatigue or soreness

What does disuse of muscles lead to?

Atrophy