KINE 1020 Study Guide - Final Guide: Anaerobic Glycolysis, Motor Neuron Disease, Upper Motor Neuron
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Published on 21 Apr 2014
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Chapter 17-Muscular Structure and Function
3 Main types of muscles
Cardiac muscle
•The muscle within the heart
•Striated-aligned structures
•Electrically coupled cells –if one is activated, the next one is also activated
•Involuntary-controlled by the Autonomic Nervous System
Smooth muscle
•No striated muscle
•Responsible for blood vessel tone (vasoconstriction or vasodilation)
•Involuntary
•Muscle surrounds the blood vessels and controls blood vessel size
•Lines intestines, stomach
Skeletal muscle
•Striated – aligned structures
•Not electrically coupled and voluntary
•Helps in locomotion, with posture, and heat production in cold stress
•600 skeletal muscles
Skeletal Muscle Structure
−Muscle – composed of a number of fasciculi
−Fascicle – bundle of muscle cells
−Muscle cell – elongated structure unlike other cells
−Myofibril – contractile unit, also the cause of striation in muscles, responsible for force and speed is generated by
muscle
Sarcomere
•Located within myofibrils
•Responsible for the action produced by a muscle
•The different regions are categorized by the amount of protein found in the various regions of the sarcomere
•A band: more protein thus appears darker in the muscles, composed of actin
•I band: fewer proteins thus appears lighter
•H band: composed of myosin
Muscle Proteins
Actin
•Composed of globular proteins that binds together to form microfilaments
•Two F-actin(filamentous) wind together into a double helix, together with troponin and tropomyosin to form the
thin filament
•Actin is a structural protein that acts like scaffolding
Tropomyosin
•Long, double-stranded protein that weaves around the F-actin in a double helical arrangement
•During rest: the tropomyosin blocks the active sites on actin so myosin cannot bind
Troponin
•A globular protein made up of 3 sub-units(Troponin C, I & T)
•Troponin-T binds the troponin to the tropomyosin
•During contraction: the calcium will bind to troponin-C and cause it to change shape and removes the
tropomyosin exposing the active binding sites on actin
•Troponin-I inhibits this process during resting state
Myosin
•Has 2 globular head regions and a rod-like tail region
•Myosin form the thick filament with the tail regions coming together in a thick rod like structure with the heads
extending outwards
•Each head has two reactive sites: one for binding to actin and the other to bind to ATP
Intermediate proteins
Titan
−One of the largest proteins located from Z-line to M-line
−1 titan protein extends half the length of a sarcomere thus providing a scaffolding structure for the sarcomere
−This allows for the force transmission at the Z-line and contributes to the passive stiffness of muscle
Desmin
−Acts as a scaffolding anchoring the Z-line to the Z-line of the next later sarcomere.
−Titan provides support lengthwise and desmin is more like the cord that binds all the sarcomere chains
(myofibrils) together via Z-lines
C-protein
−Located in the middle of the A-band
−Binds myosin tail region
−Maintains thick filaments of myosin
Sarcoplasmic Reticulum
•Site of storage for calcium
•T-tubule interacts with the exterior of the cell, to regulate calcium levels in the cell
•Nerve impulse (action potential) sends signal entering through T-tubule thus releasing calcium
•After the movement (during rest) calcium is taken up again into the reticulum
Muscle Contractions
http://www.youtube.com/watch?v=BMT4PtXRCVA
Muscle Fibre Contractile Activity
1. Nerve stimulation is followed by action potential called the latent period (takes 1-2 msec). During this time there
is no muscle contraction or force production
2. The contraction begins. There is a gradual increase in the force/tension until the force reaches the climax.
Referred to as contraction time (lasts 40-120 msec)
3. After the climax the muscle force/tension returns to rest called relaxation time(lasts 50-200 msec)
Motor Unit Recruitment
•Composed of a motor nerve that innervates a particular # of muscle cells or muscle fibres
•When activated, all muscle fibres in a motor unit are activated
•The more motor units activated, the stronger the contraction
Motor Unit Type: Fast Fatiguing vs. Fatigue Resistant
Type I Slow Twitch
−Slow contracting
−Fatigue resistant
−Maintains posture
−Produce less force but can sustain the force production for a very long time
Type IIa Fast Twitch: Fatigue Resistant
−Fast contracting
−Moderate resistance to fatigue
−Produce more force than slow twitch but cannot sustain the force production for as long before fatiguing
−Used for non-exertive movement (walking)
Type IIx Fast Twitch: Fast Fatiguing
−Fastest contracting
−Produce much more force than Type IIa but are more easily fatigued than Type IIa
−Used for powerful movements with quick bursts of energy (sprinting, jumping)
Frequency Summation
•Staircase effect: summation of first stimulus and second stimulus (2 action potential)
Fibre length