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Muscular System - Richard Nguyen P.6 - Coggle Diagram
Muscular System - Richard Nguyen P.6
Muscle Actions and Interactions
Prime Mover (Agonist)
Major responsibility for producing specific movement
Antagonist
Opposes or reverses particular movement
Prime mover and antagonist are located on opposite sides of joint across which they act
Synergist helps prime movers
Adds extra force to same movement
Reduces undesirable or unnecessary movement
Fixators: type of synergist that immobilizes bone or muscle’s origin rather than enhancing movement of prime movers
Gives prime mover stable base on which to act
Naming Skeletal Muscles
Muscle location: bone or body region with which muscle associated
Muscle shape: distinctive shapes
Muscle size
Direction of muscle fibers or fascicles
Number of origins
Location of attachments: named according to point of origin and insertion (origin named first)
Muscle action: named for action they produce
Several criteria can be combined
3 Types of Muscle Tissue
Skeletal
Attached to bones or (some facial muscles) to skin
Single, very long, cylindrical, multicleanate cells with obvious striations.
Cardiac
Walls of the heart
Branching chains of cells; uni- or binucleate; striations
Smooth
Unitary muscle in walls of hollow visceral organs (other than the heart); multi unit muscle in intrinsic eye muscles, airways, large arteries
Single, spindled shaped, uniucleate; no striations
Characteristics of Muscle Tissue
Excitability (responsiveness): ability to receive and respond to stimuli
Contractility: ability to shorten forcibly when stimulated
Extensibilty: ability to be stretched
Elasticity: ability to recoil to resting length
Muscle Functions:
Produce movements: responsible for all locomotion and manipulation
Maintain posture and body position
Stabilize Joints
Generate heat as they could
Skeletal Muscle Anatomy
Nerve and Blood Supply
Each muscle receives a nerve, artery, and veins
Contracting muscle fibers require huge amounts of oxygen and nutrients
Connective Tissue Sheaths
Each skeletal muscle, as well as each muscle fiber, is covered in connective tissue
Support cells and reinforce whole muscle
Sheaths from external to internal
Epimysium: dense irregular connective tissue surrounding entire muscle; may blend with fascia
Perimysium: fibrous connective tissue surrounding fasciclces
endomysium: fine areolar connective tissue surrounding each muscle fiber
Attachments
Muscles span joints and attach to bones
Muscles attach to bone in at least two places:
Insertion: attachment to movable bones
Origin: attachment to immovable or less movable bone
Modified Organelles
Myofibrils
Striations
stripes formed from repeating series of dark and light bands along length of each myofibril
A Bands: Dark Regions
I Bands: Lighter Regions
Sacromeres
Smallest contractile unit (functional unit) of muscle fiber
Contains A band with half of an I band at each end
Myofilaments
Orderly arrangement of actin and myosin myofilaments within sacromere
Actin Myofilament: thin filaments
Myosin Myofilaments
Molecular composition of myofilaments
Thick Filaments
composed of protein myosin that contains two heavy and four light polupetide chains
Thin Filaments
Composed of fibrous protein actin
Tropomyosin and troponin
regulatory proteins bound to actin
Sarcoplasmic Reticulum and T Tubules
Sarcoplasmic Reticulum
network of smooth endoplasmic reticulum tubules surrounding each myofibril
T Tubule
Tube formed by protrusion of sarcolemma deep into cell interior
Triad Relationships
T Tubule contains integral membrane proteins that protrude into intermembrane space (space between tubule and muscle fiber sarcolemma)
Sliding Filament Model of Contraction
Contraction: The activation of cross bridges to generate force
Sliding filament model of contraction states that during contraaction, thin filaments exceeds forces opposing shortening
When nervous system stimulates muscle fiber, myosin heads are allowed to bind to actin, forming cross bridges, which cause sliding (contraction) process to begin
Events at the Neuromuscular Junction
Calcium entry causes realease of ACh neurotransmitter into synaptic cleft
ACh diffuses across to ACh receptors (𝑁𝑎+chemical gates) on sarcolemma
Voltage-gated calcium channels open, calcium enters motor neuron
ACh binding to receptors, opens gates, allowing 𝑁𝑎+to enter resulting in end plate potential
AP arrives at axon terminal
Acetylcholinesterase degrades ACh
Generation of an Action Potential Across the Sarcolemma
Depolarization
generation and propagation of an actionpotential(AP)
Large influx of 𝑁𝑎+through channels into cell triggers AP that is unstoppable and will lead to muscle fiber contraction
If end plate potential causes enough change in membrane voltage to reach critical level called threshold, voltage-gated𝑁𝑎+channels in membrane will open
Repolarization
restoration of resting conditions
𝐾+efflux out of cell rapidly brings cell back to initial resting membrane voltage
𝑁𝑎+voltage-gated channels close, and voltage-gated 𝐾+channels open
Generation of End Plate Potential
ACh released from motor neuron binds to ACh receptors on sarcolemma
Causes chemicallygatedion channels (ligands) on sarcolemma to open
𝑁𝑎+diffuses into muscle fiber
Because 𝑁𝑎+diffuses in, interior of sarcolemma becomes less negative (more positive)
Muscle Fiber Contraction: Cross Bridge Cycling
Working (power) stroke: myosin head pivots and pulls thin filament toward M line
Cross bridge detachment: ATP attaches to myosin head, causing cross bridge to detach
Cross bridge formation: high-energy myosin head attaches to actin thin filament active site
Cocking of myosin head: energy from hydrolysis of ATP “cocks”myosin head into high-energy state
Clinical - Homeostatic Imbalance
Rigor mortis
3–4 hours after death, muscles begin to stiffen
Intracellular calcium levels increase because ATP is no longer being synthesized, so calcium cannot be pumped back into SR
ATP is also needed for cross bridge detachment
Muscles stay contracted until muscle proteins break down, causing myosin to release
The Motor Unit
Motorunitconsists of the motor neuron and all muscle fibers (four to several hundred) it supplies
Muscle fibers from a motor unit are spread throughout the whole muscle, so stimulation of a single motor unit causes only weak contraction of entire muscle
Muscle Twitch
Muscletwitch: simplest contraction resulting from a muscle fiber’s response to a single action potential from motor neuron
Muscle fiber contracts quickly, then relaxes
Muscle Tone
Constant, slightly contracted state of all muscles
Due to spinal reflexes
Groups of motor units are alternately activated in response to input from stretch receptors in muscles
Isotonic and Isometric Contractions
Isotoniccontractions: muscle changes in length and moves load
Isometric contractions
Load is greater than the maximum tension muscle can generate, so muscle neither shortens nor lengthens
Muscle Fatigue
Fatigue is the physiological inability to contract despite continued stimulation
Possible causes include:
Ionic imbalances can cause fatigue
Decreased ATP and increased magnesium
Decreased glycogen
Lack of ATP is rarely a reason for fatigue, except in severely stressed muscles
Factors of Muscle Contraction
Number of muscle fibers stimulated(recruitment): the more motor units recruited, the greater the force.
Relative size of fibers: the bulkier the muscle, the more tension it can develop
Frequencyofstimulation: the higher the frequency, the greater the force
Degreeofmusclestretch: muscle fibers with sarcomeres that are 80–120% their normal resting length generate more force
Aerobic(Endurance) Exercise
Aerobic(endurance) exercise, such as jogging, swimming, biking leads to increased:
Muscle capillaries
Number of mitochondria
Myoglobin synthesis
Resistance Exercise
Resistance exercise(typically anaerobic), such as weight lifting or isometric exercises, leads to
Muscle hypertrophy
Due primarily to increase in fiber size
Increased mitochondria, myofilaments, glycogen stores, and connective tissue
Increased muscle strength and size
Skeletal Muscles
Deltoid
Biceps brachii
Triceps brachii
Gluteus maximus
Sartorius
Quadriceps group
Hamstrings group
Tibialis anterior
Gastrocnemius
Pectoralis
Rectus abdominus
External oblique
Trapezius (upper back)
Latissimus dorsi (lower back)