Muscular system Flashcards
Three basic muscle types are found in the body
Skeletal muscle
Cardiac muscle
Smooth muscle
Each muscle is a discrete organ, composed of:
Each muscle is a discrete organ, composed of: muscle fibers blood vessels nerve fibers connective tissue
Endomysium
Endomysium - encloses a single muscle fiber
Perimysium
wraps around a fascicle (bundle) of muscle fibers
Epimysium
Epimysium - surrounds entire muscle
Sites of muscle attachment
Bones (with or without tendons)
Cartilage
Aponeuroses - connective tissue sheet-like covering
Skeletal muscle functions
Produce skeletal movement
Maintain body posture and body position
Stabilize joints
Generate heat
Support soft tissue and surrounding visceral organs and internal tissues
Move blood and fluids through body, plus aiding with respiration
Guard entrances and exits – swallowing, digestive, urinary
Provide nutrient reserves - starvation
Muscle cell (myocyte) =
Muscle cell (myocyte) = muscle fiber
Cell membrane =
Cell membrane = sarcolemma
Cytoplasm =
Cytoplasm = sarcoplasm
Endoplasmic reticulum (ER) =
Endoplasmic reticulum (ER) = sarcoplasmic reticulum (SR)
Contain hundreds of nuclei
Filled with cylindrical structures called myofibrils
Contain actin and myosin
muscle fibers
complex organelle composed of bundles of myofilaments
Myofibril or Fibril
Specialized smooth endoplasmic reticulum
Stores and releases calcium
Surrounds the myofibril
Sarcoplasmic reticulum (SR)
How do actin and myosin act to contract the muscle and make it move?
Actin and myosin slide past each other causing the fibre to shorten
The fibre lengthens when the actin and myosin go back to their original places
Actin & myosin give the muscle it’s striated look under the microscope
When a nerve impulse reaches the axon terminal of the motor neuron,
1.Calcium channels open, and calcium ions enter the axon terminal
2.Calcium ion entry causes some synaptic vesicles to release acetylcholine (ACh)
3. ACh diffuses across the synaptic cleft and attaches to receptors on the sarcolemma of the muscle cell
I4.f enough ACh is released, the sarcolemma becomes temporarily more permeable to sodium (Na)
5.Depolarization opens more sodium channels that allow sodium ions to enter the cell
Once started, the action potential cannot be stopped, and contraction occurs
6. Enough depolarization allows for Ca2+ to be released from the sarcoplasmic reticulum (SR)
Surrounds the myofibrils and allows for actin and myosin to link
7. K+ efflux causes repolarization and reuptake of Ca2+ back into the SR
8. Acetylcholinesterase (AChE) breaks down acetylcholine into acetic acid and choline
AChE ends muscle contraction
If neuromuscular junction sites are altered
If neuromuscular junction sites are altered
can’t bind with ACh - muscle weakness will occur
Ex: Myasthenia Gravis
Muscle fibers contain a reddish brown pigment called ________
Fibers that are red have high amounts of _______, while those that are white have low amounts
_______ allows for high amounts of oxygen to be available to muscle fibers
Myoglobin
Properties of muscle fibers
Excitability (also called responsiveness or irritability) - ability to receive and respond to a stimulus
Contractility - ability to shorten when an adequate stimulus is received
Extensibility - ability of muscle cells to be stretched
Elasticity - ability to recoil and resume resting length after stretching
Skeletal muscles must be stimulated by a ________ _______ to contract
Skeletal muscles must be stimulated by a motor neuron (nerve cell) to contract
one motor neuron and all the skeletal muscle cells stimulated by that neuron
Motor unit
Single, brief contraction
Not a normal muscle function
Twitch
One contraction is immediately followed by another
Because stimulations are more frequent, the muscle does not completely return to a resting state
The effects are “summed” (added
Summing of contractions
Some relaxation occurs between contractions, but nerve stimuli arrive at an even faster rate than during summing of contractions
Unless the muscle contraction is smooth and sustained, it is said to be in ______ _______
Unfused (incomplete) tetanus
No evidence of relaxation before the following contractions
Frequency of stimulations does not allow for relaxation between contractions
The result is a smooth and sustained muscle contraction
Fused (complete) tetanus
If muscle activity is strenuous and prolonged, muscle fatigue occurs because:
If muscle activity is strenuous and prolonged, muscle fatigue occurs because:
Ionic imbalances occur
Lactic acid accumulates in the muscle
Energy (ATP) supply decreases
The common reason for muscle fatigue is
The common reason for muscle fatigue is O2 debt
Isotonic contractions
Isotonic contractions
Muscle shortens and the muscle contraction causes movement
Example is bending knee, rotating arms, smiling
Isometric contractions
Isometric contractions
Tension in the muscles increases – generate force without movement
The muscle does not shorten
Aerobic exercise – uses high amounts of O2
Aerobic exercise – uses high amounts of O2 Increases heart rate Increases blood supply to muscles Increases body metabolism increases digestion and elimination Improves coordination Increased bone density Improved blood flow to whole body Efficient gas exchange at lungs
atrophy
response when muscles are not used as much and they decrease in size
fixator
designed to stabilize a joint during movement. fixators groups in ankle prevent them from wobbling when standing
antagonist
muscles that oppose the action of another muscle
synergist
synergist also known as “helper muscles”, that assist the primer mover. can produce same movement or stabilize joints across where prime mover acts, preventing undesirable movements
_____ of the muscle attaches to the more movable bone
Insertion
_____ of the muscle attaches to the stationary (unmovable) bone
origin