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Kinesiology 2230A/B Study Guide - Final Guide: Pulmonary Circulation, Cardiac Muscle, Myoglobin

Course Code
Kinesiology 2230A/B
Glen Belfry
Study Guide

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Muscle Function During Exercise
Types of Muscles
Smooth muscle: involuntary, not under conscious control blood vessels, organ walls
Cardiac muscle: not under conscious control, controls itself
Skeletal muscle: voluntary, under conscious control SO, FOG, FG
Basic Structure
Filaments muscle fibrils muscle fibres fasiculus muscle
Layers of the muscle:
o Epimysium: outer connective tissue covering
o Fasiculus: wraps around bundles of fibres
o Perimysium: sheath surrounding each fasiculus
o Endomysium: tissue which covers each muscle fibre
These tissues come together as a tendon that attaches to bone. This transmits the
force to the bone, allowing the muscle to generate significant forces without tearing
Scaffolding proteins help the muscle keep their shape
Muscular dystrophy: dystrophin isn’t attached to actin, so actin disintegrates and
muscle is unable to shorten
Muscle bellies often divide into compartments, so the longest human muscle fibres are around 12cm,
which is about 500000 sarcomeres
Basic structure:
o Plasmalemma: plasma membrane surrounding one fibre
o Sarcolemma: plasmalemma and basement membrane
o At the end of each muscle fibre, the plasmalemma fuses to the bone via the tendon
o Plasmalemma assists in APs and acid-base balance
Satellite cells: between plasmalemma and basement membrane, responsible for growth and
development of skeletal muscle
Sarcoplasm: gelatin-like substance which fills the spaces between the myofibrils (cytoplasm of the
muscle fibres) contains proteins, minerals, glycogen, fats, myoglobin
o Contains transverse tubules (T-tubules), extensions of the plasmalemma that pass laterally
through the muscle fibres. They are interconnected as they pass among myofibrils, so they
pass along nerve impulses rapidly
o Sarcoplasmic reticulum (SR): membranous channel, loops around the myofibrils, storage site
for calcium
Sarcomere: basic functional unit of a myofibril, and basic contractile unit
o Joined at Z-lines to make myofibrils
o Thin filaments = actin
o Thick filaments = myosin
Thick filament: 2/3 of the muscle is myosin (1 filament = 200 myosin molecules)
o 2 protein strands twisted together

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o One end of each strand is folded into a globular head called the myosin head
o Titin stabilizes the myosin filaments (Z-disk to M-line)
Thin filament: 3 protein molecules
o Tropomyosin twists around actin, holds troponin
o Troponin covers the myosin-binding sites on the actin
o Actin: anchored by nebulin, is the backbone
o One end inserts into a Z-disk, other to the centre of the sarcomere
Muscle Fibre Contraction
Initiation of Muscle Contraction overview:
o Nerve is depolarized
o AP moves along nerve
o AP crosses neuromuscular junction
o AP enters muscle, causes calcium release
An action potential is a rapid and sustained depolarization of the nerve membrane. AP must reach
threshold first before it is propagated along the nerve
o Resting membrane potential: K permeability is > than Na permeability, there is a small
negative charge in the cell
o Action of the Na/K pump increases Na permeability, and depolarization occurs. AP happens,
followed by a repolarization where K leaves the cell (it will be pumped back later)
Once initiated, the AP will go to the dendrites of the alpha-motor neuron. These axon terminals are
located close to the plasmalemma
o ACh is secreted by the axon terminals, which binds to receptors on the plasmalemma
o If enough Ach binds, the AP will be transmitted along the muscle fibre depolarization
occurs, Na gates open
o AP also travels over the T-tubules, which causes the SR to release its stored calcium into the
o Calcium causes troponin to bind, therefore lifting off of the myosin-binding sites
Note: APs are faster in myelinated fibres than unmyelinated. Myelin sheaths are 80% lipid, 20%
protein, so are insulatory Saltatory Conduction: on myelinated axons, APs don’t propagate as
waves, but recur at successive nodes (Nodes of Ranvier)
o The impulse jumps from one node to the next in 120ms
o Temporal Summation: several impulses from one neuron over time to create a nerve impulse
o Spatial summation: impulses from several neurons at the same time
Transmission of Nerve Impulse:
o Occurs at the neuromuscular junction
o Transverse Tubule System is perpendicular to myofibrils, partial function is spreading the
action potential through the fibre. Depolarization from outer areas to deep areas
o Sarcoplasmic Reticulum: extensive network of tubular channels, parallel to myofibrils. Each
tubule ends in a vesicle containing calcium. Once depolarized, it releases calcium, activating
the actin filaments
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