Muscular system Flashcards
What are the four characteristics of muscle tissue?
Excitability, contractibility, extensibility, elasticity
Describe excitability in muscle tissue
Muscle tissue have the capacity to respoind to the stimulation of nervous impulses or hormones
Describe contractibility in muscle tissue
Muscle tissue has the capacity to contract or shorten with force
Descrive extensibility in muscle tissue
Muscle tissue can stretch beyond resting length
Describe elasticity in muscle tissue
Muscle tissue returns to resting length after being stretched
Describe skeletal muscles (structure and function)
Skeletal muscle is primarily attached to the bones, it is striated and volontary
Describe cardiac muscle (structure and function)
Forms the walls of the heart, it is striated and involuntary
Describe smooth muscle (structure and function)
Located in the viscera, it is non striated (smooth) and involuntary
What are the five key functions of muscle ?
- Produces body movements
- Stabilizes body positions
- Regulates organ volume
- Moves substances within the body
- Generates heat
What are muscle cells called?
Muscle fibers
What are the functions of superficial fascia and where is it located?
Superficial fascia is localed between the muscles and the skin, it provides a pathway for nerves and blood vessels, stores fat, insulates and protects muscles
What are the functions of deep fascia and where is it located?
It lines the body wallls and limbs and holds muscles with similar functions together. It allows for the free movement of muscles, carries nerves, blood vessels, lymph vessels, and fills the space between muscles.
What are the three connective tissues involved in the muscles?
Epimysium, perimysium and endomysium
What is epimysium and what is its use?
The CT that wraps the entire muscle, it allows the muscle to contract and move while maintaining structural integrity
What is perimysium and what is its use?
The CT that covers fascicules. It allows the nervous system to trigger specific movement of a muscle by activating a subset of fibers
What is endomysium and what is its use?
It covers individual muscle fibers and contains extracellular fluid and nutrients to support the muscle
What are tendons and aponeuroses?
They attach muscle to bone or to other muscle. Aponeuroses are large flat tendons.
What is the role of nerves and blood in muscle function?
Nerves convey impulses for muscle contraction and bloos provides nutrients and oxygen for contraction
What type of cells do skeletal muscle fibers arise from ?
Myoblasts
What is the name of the cell membrane for muscle fibers?
Sarcolemma
What are T-tubules?
They are transverse tubules that go into the sarcolemma to quickly spread the muscle action potential to all parts of the muscle fibers
What is the sarcoplasm?
The muscle fiber cytoplasm
What are the two molecules most present in the sarcoplasm?
glycogen for energy production and myoglobin for oxygen storage
What are myofibrils?
A muscle cell organelle
What are myofibrils composed of?
Myofilaments
What are myofilaments composed of ?
actin and myosin
What is the name of the subunit in myofilaments?
sarcomeres
Describe a sarcomere
Basic unit of a myofibril. Show distinct bands of dark (A, with actin and myosin overlappping) in the middle. Light (I) bands, with only actin, with junction points called z-lines. The H zone has only myosin. The thick filaments in the middle is made of myosin, and the thin ones on both extremities are made of actin.
What is the equivalent of the endoplasmic reticulum in muscle fibers and what is its use?
The sarcoplasmic reticulum, located just below the sarcolemma. It stores calcium ions that it releases when an action potential depolarizes the sarcolemma
Name the two regulatory proteins in myofibrils
tropomyosin and troponin.
What is the role of tropomyosin and troponin?
Tropomyosin is wrapped around actin and hides the binding sites to myosin. Troponin holds tropomyosin in place.
What is the name of the motor protein in myofibrils?
Myosin
Where do actions potenial arise in muscles?
At the neuromuscular junction.
What is the neuromuscular junction ?
The synapse between a somatic motor neuron and a skeletal muscle fiber
What is a motor unit?
A nerve and the muscle fibers it stimulates
What is a synapse?
A region of communication between two neurons, or a neuron and a target cell. They are separated by a gap, or a synaptic cleft.
What bridges the synaptic cleft?
The neurotransmitters
What is the neurotransmitter in a neuromuscular junction?
Acetylcholine
Describe how a neuron transmists an action potential to a muscle cell
A nerve action potential elicits a muscle action through the release of acetylcholine. The activation of ACh receptors depolarizes the sarcolemma and goes to the t-tubules.
Describe the sliding filament model of muscle contraction
- Action potential releases calcium ions from the sarcoplasmic reticulum.
- The calcium ions combine with troponin, which pulls on tropomyosin, which exposes the myosin-binding sites on the actin filaments
- Myosin heads form a cross bridge with actin, which pulls the actin filaments (bring the z lines closer together) in a power stroke. ADP and P are released at that step
- The accumulation of all sarcomeres shortening causes the muscle as a whole to contract
- ATP reattaches to the myosin head, which uncouples the myosin to the actin
- The hydrolysis of the ATP returns the myosin head to the resting cocked position.
What is the relationship between the calcium ion concentration and the contraction of muscles ?
The contraction stops when there is no calcium ions available
What is muscle tension?
Force generated by the contraction of a muscle
What is muscle tone ?
Sustained partial contraction of portions of relaxed skeletal muscle results in a firmness known as muscle tone
What is an isotonic contraction? Give an example
A contraction that shortens the muscle and that presents movement. Lifting a book from a table
What is an isometric contraction? Give an example
A contraction that does not present movement and does not involve muscle contraction. Carrying a box.
What is a concentric contraction?
a contraction that involves shortening a muscle to move a load
What is an eccentric contraction?
When muscle tension diminishes and muscle lengthens
What are the three sources of ATP production in muscle cells?
Creatine phosphate, anaerobic cellular respiration, and aerobic cellular respiration
Describe creatine phosphate ATP production
Creatine phosphate stores energy in the phosphate bonds. At rest, the ATP transfers its energy to creatine to make it creatine phosphate, which transfers it back through enzymatic reaction to the muscle cells. Its very fast, but can only power short 15 sec bursts of energy.
Describe anaerobic cellular respiration
It is the process of glycolysis (break down of glucose into ATP). The glucose can come from the blood sugar or the metabolized glycogen in the muscle cell. It is inefficient and moderately fast, it can produce 30-40 s energy
Describe aerobic cellular respiration
It is the breakdown of glucose and other nutrients in the mytochondria. It is a very efficient, but slow process that requires oxygen in constant supply. It provides energy for prolonges activity.
What are the sources of oxygen in muscles?
Diffusion from the blood and release by myoglobin inside muscle fibers.
What is muscle fatigue ?
The inability to maintain strength of contraction due to finite storage of ATP.
What is a twitch?
A brief contraction of all muscle fibers in a motor unit in response to an action potential
What are the three periods of a twitch?
Latent, contraction, and relaxation
What happens during the latent period of a twitch?
The action potential is being propagated along the sarcolemma
What is wave summation in the context of muscle twitches?
When an additional action potential occurs before the end of a first twitch, the tension waves will sum. It’s the excitation-contraction coupling effect of successive motor neurons signalings.
What is fused and unfused tetanus?
When the stimulus frequency is so high that there is no relaxation period between stimuli and the contractions become continuous, it is fused. If some relaxation remains, it is unfused.
Describe the classification of skeletal muscle fibers
Slow oxidative, fast oxidative-glycolytic, fast glycolytic
What is the difference between SO, FO and FG fibers?
SO use aerobic respiration and perform slow contractions, FO use mostly aerobic respiration and perform fast contraction, but they fatigue faster than SO. FG produce faster contractions, use anaerobic respiration, and fatigue very fast.
Describe the arrangement of cardiac muscle fibers
It is similar to skeletal muscle fibers (sarcomeres), but they connect to adjacent fibers using intercalated discs that contain desmosomes and gap junctions.
What are pacemaker cells?
Specialized cells in the heart that stimulate the heart by depolarizing themselves (autorythmicity)
What are desmosomes and gap junctions for in the heart?
Desmosomes make sure the heart cells resist to the contraction stress, and gap junction allow a flow of cations for depolarization to reach all cells
What are two differences between cardiac muscle fibers and skeletal muscle fibers?
The cardiac muscle contractions last longer because the prolonged delivery of calcium ions from the sarcoplasmic reticulum. The autorythmic property of cardiac cells.
Describe smooth muscle cells structure
Non striated because they do not possess sarcomeres. They have dense bodies that are like z-lines which anchor the thin filaments.
Do smooth muscle cells possess myosin, actin, tropomyosin and troponin?
They possess myosin, actin, but not tropomyosin and tropponin
What is the equivalent of neuromuscular junctions in smooth muscles?
Variscosities
What are the two types of smooth muscle?
Visceral and multiunit
What is visceral smooth muscle and where is it found?
It is found in walls of hollow viscera and small blood vessels. The fibers are joined by gap junctions, which allows them to contract as a single unit
What is multiunit smooth muscle and where is it found?
Found in large blood vessels, large arways, arector pilli muscles and iris of the eye. Fibers are not electrically coupled by gap junctions, but innerved individually.
Which contractions are longer between smooth muscle and skeletal muscle?
Smooth
What is the process of contraction in smooth muscles?
A regulatory protein called calmodulin binds to calcium ions in the cytosol, which activates the myosin kinase, which facilitates the myosin-actin binding and allows contraction to occur at a relatively low rate.
What is smooth muscle tone?
A state of continued partial contraction due to the prolonged presence of calcium ions
What is stretch relaxation response in smooth muscles?
The fact that the fibers can stretch considerably without developing tension
What is insertion, and what is origin of a muscle?
Insertion is the movable end of a muscle attached to the bone that’s pulled. The origin is the end of the muscle attached to the fixed bone.
What is an agonist ?
The principal muscle involved in a movement
What is a synergist muscle?
A muscle that supports a movement
What is a fixator muscle?
A muscle that helps stabilize a movement
What is an antagonist muscle?
A muscle with opposite action of the agonist muscle
What are the possible classifications of fascicle arangement in muscles?
Parallel (fusiform or non fusiform), circular, convergent, pennate (unipennate, bipennate or multipennate)
What are the characteristics muscles can be named after? give an example for each
Relationship to bone (frontalis), shape (orbicularis), size (maximus, medius, minimus), length (brevis, longus), position (lateralis, medialis), direction of fascicles (rectus, oblique), number of origins (biceps, triceps), attachements (sternocleidomastoid), action (flexor, extensor)
What is unipennate, bipennate and multipennate?
Unipennate is when the fascicles are on one side of the tendon, bipennate on both sides, and multipennate around the tendon
