Muscular System Flashcards
Describe the four characteristics of muscle tissue, and the major structural and functional differences among the three types of muscle tissue.
3 types of muscle tissue
- cardiac muscle
- Found in the heart, pushes blood around body
- Has striations
- Involuntary action
- regenerations can occur as stem cells in blood to move into the heart
- smooth muscle
- In walls of internal structures
- non-striated
- involuntary action
- regeneration is better than muscle tissue but still poor compared to other tissues.
- skeletal muscle tissue
- attached to bone and moves parts of the skeleton
- has striations
- moves voluntarily
- has a limited capacity for regeneration
4 Properties of Muscle Tissue
- Electrical Excitability
- responds to actions potentials, electrical impulses
- Contractibility
- ability to generate force when stimulated by an action potential
- Extensibility
- ability to stretch without damaging the tissue
- Elasticity
- ability to return to its original shape and length after contracting
What is the name for the scientific study of muscles?
Myology
Describe the five key functions of muscle.
Through a sustained alternation of contraction and relaxation, muscle performs the following five key functions:
- Produces body movements
- Stabilizes body positions
- Regulates organ volume
- Moves substances within the body
- Generates heat
Describe the relationship of the fascia, nerves, tendons, and blood vessels to skeletal muscle.
- Each skeletal muscle is a separate organ composed of cells called muscle fibres.
Fascia:
- Superficial fascia (or subcutaneous layer) separates muscle from skin,
- functions to provide a pathway for nerves and blood vessels, stores fat, insulates and protects muscles from trauma.
- Deep fascia, which lines the body wall and limbs and holds muscles with similar functions together
- allows for the free movement of muscles; carries nerves, blood vessels, and lymph vessels; and fills the spaces between muscles.
There are 3 layers of connective tissue coverings that extend from the deep fascia as follows:
- Epimysium—covers the entire muscle
- Perimysium—covers the fascicles
- Endomysium—covers individual muscle fibres
Tendons and aponeuroses attach muscle to bone or muscle to other muscles. Are composed of the extension of the epimysium, perimysium and endomysium.
Nerves:
- Nerves (containing motor neurons) convey impulses for muscular contraction.
Blood Vessels:
- Blood provides nutrients and oxygen for contraction.
- an artery and 1 or 2 blood vessels accommodate each nerve
- capillaries are found within the endomysium
Describe the microscopic anatomy of a skeletal muscle fibre.
Skeletal muscle fibres arise from myoblasts. A few myoblasts persist in mature skeletal muscle as satellite cells.
Sarcolemma
- Covers muscles fibres (cells) of the Skeletal muscle
- which is a plasma membrane of the cell.
T tubules (transverse tubules)
- tunnel towards the center of the muscle cell from the sarcolemma
- quickly spread the muscle action potential to all parts of the muscle fibre.
Sarcoplasm
- is the muscle cells’ cytoplasm
- a large amount of glycogen for energy production
- myoglobin for oxygen storage.
- many mitocrondria throughout the cell
- multiple nuclei located in the periphery of the cell
Myofibrils
- found extending along the entire length inside the muscle cells
- Each fibre consist of thin and thick filaments (myofilaments).
Sarcoplasmic reticulum
- surrounds each myofibril.
- It is similar to smooth endoplasmic reticulum in non-muscle cells
- Stores calcium ions in the relaxed muscle which is used for muscle contractions
Sarcomeres
- the basic functional units of a myofibril
- made up of thick filaments and Thin Filaments
- There are 4 distinct areaas of the filament; A bands, I bands, H zones and Z discs
- A Band has overlapping Thick fillaments with Thin Filaments
- I bands have only thin filaments attached to the Z disc
- Z discs seperate the sarcomeres running perpendicular to the filaments
- Striations of the muscles are patterns of distinct dark (A band) and light (I band) areas.
Identify the contractile elements—myofibrils—of skeletal muscle.
- Sarcomeres that make up the myofibrils consist of Contractile proteins that generate force during contraction. There are 2 protein filaments that are responsible.
Thick Filaments
- Myosin is the main component of thick filaments
- Myosin forms a twisted golf club shape
- contains myosin heads that project outwards
- parallel tails are twisted around one another form the body of the protein
- functions as a motor protein.
- Motor proteins push or pull their cargo to achieve movement by converting energy from ATP into the mechanical energy of motion or force.
Thin Filaments
- Actin is the main component of thin filaments
- actin binds together to form a helix shape
- has myosin-binding sites where myosin “heads” attach to produce the sliding together of the filaments.
- Actin is anchored by Z discs
- 2 other proteins in thin filaments control the binding of actin and myosin.
- Tropomyosin - covers the myosin-binding sites of actin
- Troponin holds the tropomyosin in place
- In relaxed muscle, tropomyosin, which is held in place by troponin, blocks the myosin-binding sites on actin to prevent myosin from binding to actin.
- During contraction, myosin heads pull on the actin and shorten the muscle cell. This process is the sliding-filament mechanism.
Describe the neuromuscular junction and motor unit.
Muscle action potentials arise at the neuromuscular junction (NMJ), which is the synapse between a somatic motor neuron and a skeletal muscle fibre.
A motor unit is a nerve and the muscle fibres it stimulates.
A synapse is a region of communication between two neurons or a neuron and a target cell. The two neurons or a neuron and a target cell are separated by a gap or a synaptic cleft.
Neurotransmitters bridge that gap.
The neurotransmitter at an NMJ is acetylcholine (ACh).
A nerve action potential elicits a muscle action potential through the release of acetylcholine, the activation of ACh receptors, the production of a muscle action potential, and the termination of ACh activity.
Outline the steps involved in the sliding filament mechanism of muscle contraction.
During muscle contraction, myosin cross-bridges pull on thin filaments, causing them to slide inward toward the H zone; Z discs come toward each other, and the sarcomere shortens, but the thick and thin filaments do not change in length. The sliding of filaments and the shortening of sarcomeres cause the shortening of the whole muscle fibre and ultimately the entire muscle. This process is called the sliding filament mechanism.
The Full Series of Events
- a neuron action potential moves through the axon terminal. Which stimulates acetylcholine release
- Acetylcholine binds to receptors at the motor endplate triggering the muscle action potential
- Acetylcholinesterase destroys acetylcholine to avoid another muscle action potential unless another is sent from the axon terminal.
- the action potentials travel through the T tubules which signals the release of Ca2+ ions from the sarcoplasmic reticulum.
- Ca2+ binds to the troponin on the thin filaments exposing the myosin-binding sites on actin.
- contraction: myosin heads attach to myosin creating cross bridges and undergo power strokes and release the thin filaments pulling it closer to the center of the sarcomere
- Sarcoplasmic reticulum channels close and Ca2+ release pumps use ATP to restore the low levels of Ca2+ in the sarcoplasm
- Tropomyosin slides back over the myosin-binding sites on action.
- muscle relaxes.
Define muscle tone, and note how it normally works in body posture maintenance
A sustained partial contraction of portions of a relaxed skeletal muscle results in a firmness known as muscle tone.
At any given moment, a few muscle fibres within a muscle are contracted, while most are relaxed. This small amount of contraction is essential for maintaining posture.
Describe energy use in muscle cells, and list the three sources for adenosine triphosphate (ATP) production in muscle cells.
Three sources for ATP production in muscle cells are as follows:
Creatine phosphate can power maximal muscle contraction for about 15 seconds, and is used for maximal short bursts of energy.
Creatine phosphate is unique to muscle fibres.
Anaerobic cellular respiration (glycolysis) can provide enough energy for about 30–40 seconds.
Aerobic cellular respiration (reactions requiring oxygen) completes the oxidation of glucose via cellular respiration, and provides energy for prolonged activity.
Muscle tissue has two sources of oxygen: diffusion from the blood and release by myoglobin inside muscle fibres.
The inability of a muscle to maintain its strength of contraction or tension is called muscle fatigue, which occurs when a muscle cannot produce enough ATP to meet its needs.
Define a twitch, and discuss its component parts.
A twitch contraction is a brief contraction of all the muscle fibres in a motor unit in response to a single action potential.
A twitch contraction includes three periods: latent, contraction, and relaxation
Define wave summation, and differentiate it from unfused and fused tetanus.
Wave summation is the increased strength of a contraction, which is the result of the application of a second stimulus before the muscle has completely relaxed after a previous stimulus.
A sustained muscle contraction that permits partial relaxation between stimuli is called incomplete (unfused) tetanus.
A sustained contraction that lacks even partial relaxation between stimuli is called complete (fused) tetanus.
Describe the structural and functional characteristics that allow skeletal muscle to be classified into three main types.
All skeletal muscle fibres are not identical in structure or function.
Colour varies according to the content of myoglobin.
Fibre diameter varies, as do the cell’s allocations of mitochondria, blood capillaries, and sarcoplasmic reticulum.
Contraction velocity and resistance to fatigue also differ between fibres.
On the basis of structure and function, skeletal muscle fibres are classified as follows:
- Slow oxidative
- Fast oxidative-glycolytic
- Fast glycolytic fibres
Define isotonic and isometric contraction.
Isotonic contraction
An isotonic contraction is a contraction that occurs when the tension in the muscle remains the same but the muscle shortens. An example of an isotonic contraction is when you lift a textbook from a table.
Isometric contraction
An isometric contraction is a contraction that occurs when tension is applied to a muscle but it does not shorten. An example of an isometric contraction is when you carry a box of books.
Describe the structure and function of cardiac muscle.
Cardiac muscle tissue is found only in the heart wall.
Structure:
- has striations
- involuntary actions
- fibres are connected buy intercalated discs
- contain gap junctions and desmosomes
Function:
- Cardiac muscle contractions last longer than the skeletal muscle twitch due to the prolonged delivery of calcium ions from the sarcoplasmic reticulum and the extracellular fluid.
- Cardiac muscle fibres contract when stimulated by their own autorhythmic fibres.
- This continuous rhythmic activity is a major physiological difference between cardiac and skeletal muscle tissue.
