Exercise Physiology - Muscular System

Move the bony levers of the skeletal system, enabling movement of the body

• (SCS)
• Skeletal muscles;
• cardiac muscles
• smooth muscles

Assist in regulation of blood flow to various parts of the body

Skeletal muscles

Skeletal muscle cells/fibers that are considered "excitable"

• (EPE)
• Epimysium
• Perimsysium
• Endomysium

• Outer layer of connective tissue that surrounds the entire muscle and separates muscle from surrounding tissue and organs;
• Converges at the end of the muscle to form the tendon that attaches to the bone

Central layer of connective tissue w/in muscle that divides muscle into fascicles (singular = fasiculus)

Group of as many as 150 myofibers lying in parallel and bundled together

Inner layer of connective tissue w/in muscle that surrounds myofiber

• Controls each skeletal myofiber;
• Central Nervous System

A motor neuron and all the myofibers that it innervates.

All myofibers of a motor unit contract simulatneously and at maximal force

All the same type (either Type II, Type IIa, or IIb)

• By controlling the number of motor units that are activated;
• By varying the firing rate of neural impulses delivered by the motor neuron to its myofibers
• For maximal force output, all of the muscles motor units have been recruited and each one is firing at it's highest possible rate

Junction where communication between a motor neuron and a skeletal muscle fiber occurs

• Located at the end of an axon of the motor neuron;
• Contains the neurotransmitter acetylcholine (ACh)

Separates the synaptic knob from sarcolemma of the skeletal muscle fibers.

More than one, and up to 200-300/mm of fiber length

• The plasma membrane of the myofiber
• Contains chemically-gated sodium channels allow electrical stimulation of myofibers via action potentials

• Mitochondrial content;
• Provides ATP via oxidative pathway

Cytoplasm of the myofiber

Extensions of the sarcolemma that form a network of tubules

• Richly developed in the myofiber to store calcium in special sacs called terminal cisterna;
• Needed to stimulate muscle contraction

myofilaments

• Contractile proteins actin and myosin;
• Orgainzed in repeading functional units called sarcomeres;

• Account for 60% of protein content of myofiber;
• Form crossbridge to slide past one another during muscle contraction, shortening the sarcomeres

Larger contractile protein sometimes called "thick filament"

Smaller contractile protein sometimes called "thin filament"

• Covers the actin bridging site during resting condition;
• Attached to troponin

Regulate bridging of actin and myosin for muscle contraction and relaxation

Based on the isoform of myosin expressed by the cell

• Type I - slow twitch fibers w/ high oxidative capacity - exercise w/ low intensity and longer duration
• Type IIB - fast twitch fibers w/ low oxidative potential - exercise w/ high intensity and short duration
• Type IIA - intermediate fibers, both in twitch and oxidative capacity - exercise w/ high intensity and short duration

Regulatory and contractile filaments

Function of both the number of myofibers within that muscle that are twitching and the rate at which the twitches occur

• Cause conversion of type IIB fibers to type IIA;
• Doesn't cause conversion between type I and Type II myofibers

• Significant increase in myofiber size, particularty type II;
• Hypertrophy

• Explains how protein filaments interact to produce a twich of the myofiber
• 1) Nervous system excites myofiber's sarcolemma and T-Tubules
• 2) Calcium stored within sarcoplasmic reticulum releases into cell's cytosol
• 3) Calcium binds to troponin, causing associated tropomysin to change shape
• 4) Active sites of actin filament are exposed
• 5) Cross-bridge heads on myosin molecule bind to exposed active sites of actin
• 6) Adenosine triphosphatase (ATPase) cleaves ATP, resulting in "power stroke" that pulls actin towrad the center of the myosin molecule
• 7) Results in fiber shortening and force generation
• 8) When ATP binds to cross-bridge head, link between myosin and actin is broken, allowing process to repeat

Responsible for delivering cytosolic calcium back into sarcoplamic reticulum, returning myofiber to state of relaxation

• - Begins at at proximal attachment (origin)
• - Ends at distal attachment (insertion)
• - Contracts to produce a specific action

A prime mover, responsible for producing a particular movement

A primer mover that opposes the agonist

Assists the prime mover but is not the primary muscle responsible for the action

Body composition and exercise testing

• (SPBT)
• Sternocleidomastoid -- radial pulse;
• Pectoralis major;
• Biceps brachii;
• Triceps brachii

• (GQG)
• Gluteus maximus;
• Quadriceps femoris;
• Gastrocnemius

• Inguinal crease;
• Natural diagonal crease in the skin formed where the musculature of the thing meets the pelvic girdle