DISCLAIMER: This post is notes based on a textbook and is not meant to be a replacement for a proper education
Chapter 8- Muscular System
Muscle
One of 4 basic tissues of the body characteristics:
- excitability
- contractibility
- extensibility
- elasticity
- Provide motion
- maintain posture
- generate heat
Types of Muscle
Cardiac Muscle- only found in the HEART
Smooth muscle- found all over the body & carries out unconsious internal movements
Skeletal muscle- moves bones of the skeleton & voluntary
Skeletal muscle (again)
- Voluntary Striated
Skeletal Muscle Attachments
- Tendons: Attach to bones by fibrous tissue bands
- Aponeuroses: Attach to bones or muscle by broad sheets of fibrous tissue (ex. linea alba)
- Origin: More stable site, doesn't move much when muscle contracts
- Insertion: Site that undergoes the most movement when a muscle contracts
Agonist- Prime mover, directly produces a desired movement
Antagonist- directly opposes the action of an agonist
Synergist- contracts at the same time as agonist to assist its action
Fixator- stabilizes joint to allow other movements
Skeletal muscle cell= muscle fiber
- very long, large & thin
- multinucleated
- Myofibrils form interior of muscle fiber
- network of sarcoplasmic reticulum
- system of transverse tubules (T tubules)
Sarcomere- Two primary protein filaments, responsible for contraction
Thick dark myosin (sounds like MElanin)
Thick light actin
Filaments are made of various visible bands
- A band
- H band
- I band
- Z line
Neuromuscular Junction- site where ends of motor nerve fibers connect to muscle fibers
- Synaptic vesicles at the end of nerve fibers have neurotransmitter acetylcholine
One nerve fiber and all the muscle fibers in innervates
- few muscle fibers per motor unit
- small, delicate movement of muscles
Holds components of muscle together
- endomysium
- fascicle
- epimysium
- Continuous w/ tendons of aponeuroses, muscle contraction and relaxation
- Nerve impulses comes down motor nerve fiber
- impulse reaches end bulb of nerve fiber
- acetylcholine released into synaptic space & binds to receptors on sarcolemma surface
- Impulse reaches sarcoplasmic reticulum
- Ca++ (calcium ions) are RELEASED into sarcoplasm
- Ca++ diffuses into myofibrils & starts contraction
- Energy is supplied by ATP
- Ca++ is pulled OUT of myofibrils
- energy supplied by ATP
- contraction STOPS
- muscle returns to original length
Muscle fibers in a relaxed state
- Actin & myosin filaments slightly overlap
- cross-bridges ratches back and forth
- actin filaments pulled towards center of myosin filaments
- sarcomere SHORTENED
Characteristics of Muscle contraction
All of nothing principal=when stimulated, individual muscle fiber contracts completely or not all
- nervous system controls number of muscle fibers stimulated
-Single muscle fiber contraction
- latent phase
- contracting phase
- relaxation phase
Max contraction efficiency
- When nerve impulses arrive 0.1 seconds apart
- the result is a series of complete muscle fiber twitches
- average out activity actually of all muscle fibers
- contractions in sync with each other
- ATP provides energy to allow sliding of actin & myosin filaments
- Creatine Phosphate (c.p) converts ADP back to ATP
- Catabolism of glucose & oxygen help to produce ATP & cp
- glucose is stored in muscle as glycogen
- oxygen is stored as myoglobin
ATP regeneration
- Direct Phosphorylation of ADP by creatine phosphate
- Anerobic and Aerobic respiration
- Only enough ATP for sustained 4-6 second contraction is available at 1 time
- Regeneration of ATP is rapid, but there are consequences to continued requirements
Creatine Phosphate (cp)= high energy molecule stored in muscles
- CP gives up its energy to ADP to make creatine & ATP through an enzyme called creatine kinase
- There are ~15 seconds of vigorous muscle contractions stored later when the muscles aren't active by taking Creatine+ATP--->CP+ADP
- As ATP & CP are being used, ATP is being produced by breakdown of glucose
- Glucose is found in the blood & is also stored as glycogen in the muscle
- This process is called anaerobic glycolysis as glucose is broken down w/no production of oxygen but instead lactic acid is produced
- Each molecule of glycogen is broken down into two molecules of pyruvic acid and two molecules of ATP
- Normally pyruvic acid would go along aerobic pathways to make more ATP
- Very efficient in the short term BUT only produces 2 molecules of ATP but is 2 1/2 times FASTER than aerobic pathways
- Glycolysis can produce ~30-40 seconds of fuel for muscle contractions in the anerobic pathway
- DISADVANTAGES are a large amount of glucose produces only a small amount of ATP & lactic acid will contribute to muscle soreness.
- Lactic Acid diffuses out of most muscles in ~30 minute through the bloodstream
- It's then used by the liver, heart & kidneys for energy
- Liver can convert the lactic acid back into pyruvic acid or glucose for muscle use
- During rest & light exercise, most of the ATP can be produced through aerobic means
- Pyruvic acid goes through the Krebs cycle oxidative phosphorylation & electron transport chain & the glucose is completely broken down into carbon dioxide, water and lots of ATP
- Each molecule of glucose can result in 36 molecules of ATP
- Disadvantages are that it's a slow process, requires oxygen & there's only a small amount of glucose & oxygen stores in myoglobin
- Any carbon dioxide diffuses into the blood to be exhaled into the lungs
- The state of physiological inability to contract despite stimuli
- NOT one of the issue is a lack of ATP...muscle fatigue occurs before ATP is used up
- Ionic imbalances & problems w/ the excitation contraction coupling system including lack of available calcium for release and then no contraction
- Increased inorganic phosphate may interfere w/ calcium ions release
- Maybe increased magnesium
- Lactic acid is NOT actually the cause just causes discomfort
EPOC= Excessive Post exercise Oxygen Consumption
- Oxygen MUST be replenished
- Lactic acid must be removed and converted to pyruvic acid
- Glycogen MUST be replaced
- ATP and CP must be remade
- Liver must convert lactic acid into glucose or glycogen
- During anaerobic exercise the EPOC is the additional oxygen that the body must take in to complete the restoration
- High levels of lactic acid in the blood lead to increased carbon dioxide in the blood which then stimulated deeper breathing in the respiratory centers causing deep breathing
- Muscle activity generated heat
Mechanisms to eliminate excess heat:
- Panting
- Sweating
- Radiation from the body surfaces (i.e skin)
- Shivering
*Striated Involuntary muscle
- found only in the heart
- Small cells with single nucleus
- LONGER than wide, with multiple branches
- intercalated disks fasten cells together
- Cells w/no external stimulation
- Groups of cells contract at the rate of the most rapid cell in the group
- Contractions are rapid and wavelike
Sinoatrial (SA) node
- Located in the wall of RIGHT ATRIUM
- generates impulse to start each heartbeat
- impulse follows controlled path through the heart
- structures in heart transmit, delay and redirect
Nerve supply to cardiac muscle
*NOT NEEDED TO INITIATE CONTRACTIONS*
Heart Innervated from two systems
- Sympathetic System
- Parasympathetic System
Smooth Muscle
2 Main forms:
- Visceral Smooth muscle
- large sheets of cells in walls of some hollow organs
- Multiunit smooth muscle
- small discrete groups of cells
- NOT under conscious control
- cells small and spindle shaped
- single nucleus in center
- smooth, homogenous appearance
- cell balls up as it contracts
- dense bodies at each end corresponds to Z lines of skeletal muscle
Visceral Smooth Muscle
- Found in walls of many soft internal organs
- Stomach, intestines, uterus, urinary bladder
- Contracts without external stimulation
- reacts to stretching
- Sympathetic system DECREASES activity
- Parasympathetic system INCREASES activity
- Individual smooth muscle cells or small groups of cells
- found where small delicate contractions are needed
- contraction requires impulses from autonomic nervous system
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