Muscle System Flashcards
3 types of muscle
Skeletal, cardiac, and smooth
Skeletal muscle
Striated. Voluntary somatic muscle. Gross skeletal muscles for movement (isotonic contraction). Large, long, unbranched cylindrical fibers w/transverse striations (stripes), arranged in parallel bundles
Cardiac muscle
Striated. Involuntary visceral muscle, walls of the heart, great vessels like the aorta
Smooth muscle
Un-striated or un-striped. Involuntary visceral muscle, walls of the most vessels, hollow organs, sphincter activity
Satellite cells
For injury repair and are a source of myoblasts
Skeletal muscle form and function
- Can be attached to bones, ligaments, cartilage, fascia, and organs
- Most have a fleshy red contractile head or belly
- Most have a fibrous white non-contractile organized collage tendon
- Some skeletal muscles are attached to organs like the eyeball, skin, and mucous membranes (tongue)
- Organs of movement, stabilization, body form, and heat
- Some skeletal muscles have their tendons form or attach into broad flat structures like aponeurosis
- Named by basis of their shape, function, position, length, and attachment point
- Muscle fibers can be replaced after an injury by myoblasts from satellite cells
Flat skeletal muscles
Have parallel fibers often with an aponeurosis. Sartorius muscle (longest muscle) is a narrow flat muscle with parallel fibers
Penate muscles
- Feather-like belly fiber arrangement, uni, bi, and multi-pennant
- Extensor digitorum longus (unipennate)
- Rectus femoris (bipennate)
- Deltoid (multitenant)
Fusiform muscles
Spindle shaped with a round thick belly or bellies and tapered ends (biceps brachii)
Convergent muscles
Muscles that originate from broad areas of attachment to a narrow area of insertion into bone (pectoral is major)
Quadrate muscles
Skeletal muscles that have four equal sides (rectus abdominals between tendonous intersections)
Circular muscles
Circular or sphincteral muscles surround a body opening or orifice (orbicularis oculi)
Multiheaded/multibellied muscles
Muscles that have more than one head (belly) of attachment
Contraction of muscles
- Skeletal muscles function by contracting (pulling NEVER pushing)
- During contraction one muscle end remains fixed while the other end is pulled towards it
- The proximal end (origin) stays fixed while the distal end (insertion) is the point of movement or action
- Some muscles can act in both directions under different circumstances, such as weight bearing (closed chain) and non-weight bearing (open chain)
Types of contractions
Reflexive, tonic, and phasic
Reflexive contraction
Skeletal muscles are voluntary, but some contraction is autonomic
Tonic contraction
When relaxed, muscles of a conscious person are slightly contracted, this slight contraction is called muscle tone, no movement but gives muscles their firmness, supports posture, readiness for contraction when called upon
Phasic contractions
Two phases:
1. Isometric - muscle length remains the same during contraction (no motion)
2. Isotonic - muscle changes its length and produces motion at insertion
Concentric isotonic contractions
Causes the muscle to shorten
Eccentric isotonic contraction
Muscle is lengthening while contracting
What is the structural unit of a muscle?
Striated muscle fiber
What is the functional unit of a muscle?
Motor unit
Muscle contraction physiology
- A nerve impulse reaches the end of a motor neuron and triggers release of the neurotransmitter acetylcholine (ACh)
- ACh diffuses rapidly across the gap of the neurotransmitter junction and binds to ACh receptors on the motor endplate of the muscle fiber
- Stimulation of ACh receptors initiates an impulse that travels across the sarcolemma through the tubules, to the sacs of the sarcoplasmic reticulum (SR)
- Ca++ is released from the SR into the sarcoplasm, where it binds to troponin molecules in the thin filaments
- Tropomyosin molecules in the thin myofilaments shift and expose actins active sites
- Energized myosin cross bridges of thick myofilaments bind to actin and use their energy to pull thin myofilaments toward the center of each sarcomere
- The cycle repeats itself many times a second, as long as adenosine triphosphate (ATP) is available
Hiltons law
“Rule of thumb”, nerves supplying a joint also supply the muscles moving the joint, and skin covering their distal attachments
Functions of muscles
Prime mover, fixation, synergist, antagonist
Prime mover
“Agonist”. Main muscle responsible for producing a specific movement (isotonic concentric contraction)
Fixator
A muscle that steadies proximal part of limb through isometric contraction while movement occurs to distal limb part
Synergist
Compliments the action of the prime mover directly, or as a fixator of intervening joint the prime mover is acting on
Antagonist
A muscle that opposes the action of another muscle. A primary antagonist directly opposes a primary mover. Antagonists eccentrically contract to ensure a smooth movement of limb
Energetics
A branch of science dealing with the. Properties of energy and how it is redistributed in physical, chemical, and biological processes
3 metabolic pathways
Phosphagen, glycolytic, oxidative
Phosphagen pathway
Activated during the first 10-20 seconds of high intensity exercise and it fueled by ATP-CP (anaerobic)
Glycolytic pathway
The primary system for exercise lasting 15 seconds - 3 minutes. Stored glucose used in muscle to form ATP. This pathway creates a lactic acid build up, causing fatigue. (Aerobically or anaerobically)
Oxidative pathway
Requires oxygen (aerobic), increased respiration rate meets oxygen demand. System is slow but most efficient pathway. Uses fat as primary energy substrate for moderate intensity activity
