Study Guides (238,613)
Canada (115,253)
Kinesiology (540)

Kinesiology 2230 Final Exam

7 Pages
Unlock Document

Western University
Kinesiology 2230A/B
Glen Belfry

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 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 sarcoplasm 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  Sliding Filament Theory: At rest, myosin is in its bent position, ready to bind to actin. When myosin cross-bridges are activated, a conformational change occurs causing the myosin head to tilt, and drag the thin filament  Mg activates the myosin head o Tilting of the head is called the “power stroke” o Pulling shortens the sarcomere and generates force o When contraction is not occurring, the myosin head remains in contact with the actin, but the site is blocked by tropomyosin o Repeated attachment to actin sites further along continues until the ends of the myosin reaches the Z-disks, or until calcium is pumped back into the SR o Myosin binds, ATP ADP, swivels, releases, attaches again further down  Myosin has a binding site for ATP o ATPase splits to ADP + pi, releasing energy, which is then used to tilt the myosin head (release it from the actin)  Muscle contraction continues as long as calcium is in the SR. After contraction, calcium is pumped back into the SR via an active calcium-pumping system. Energy is required for this too, so energy is therefore needed for both contraction and relaxation  Summary: 1. Binding of myosin to its actin site  crossbridge at 45 degree angle 2. ATP binds to myosin, myosin dissociates from actin 3. ATPase acts on ATP, hydrolyzing to ADP +pi 4. This energy allows myosin to swing over and bind to a new actin (crossbridge at 90 angle) 5. Release of pi, powerstroke, myosin head rotates and pulls actin past it 6. Myosin head releases ADP, still bound to actin  Rigor mortis: there is no supply of ATP left, which means that myosin is left bound to actin (nothing to release it) Muscle Fibre Types  ST fibres: 110ms, type I, FT fibres: 50ms, type II  Type IIa are the most frequently recruited, ST are sometimes used more  The muscle is 50% type I, 25% type IIa, and 25% type IIb  ATPase: type IIa and type I differ in their speed of contraction, primarily from different forms of myosin ATPase they contain  the type I ATPase is slower at splitting ATP  The staining technique to see type I vs. type II fibres looks at the ATPase activity in the fibres to differentiate fibre types  Sarcoplasmic reticulum: o Type II have a more developed sarcoplasmic reticulum than type I, so type II can better deliver calcium into the muscle, making it a faster contraction speed (5-6x faster than type I)  Motor units: a single alpha-motor neuron, and the muscle fibres it innervates o The alpha-motor neuron appears to determine whether the fibre is type I or type II o Type I alpha-motor neuron is small, innervates <300 fibres o Type II has a large cell body, innervates >300 fibres  If you have a majority of one type of fibre in your arm, it will likely be the same case for your leg  Type I fibres: high aerobic endurance, so recruited more during low-intensity events  Type II fibres: poor aerobic endurance, more of an anaerobic capacity. Considerably more force generated than type I o Fatigue easily, for shorter, high-intensity endurance for type IIa o Type IIb: highly explosive events, like 100m dash  Fibre type is for the most part genetically determined: we inherit which alpha-motor neurons innervate, and after inn
More Less

Related notes for Kinesiology 2230A/B

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.