CHAPTER NINE: MUSCLE AND MUSCLE TISSUE Flashcards
COMPARE THE 3 TYPES OF MUSCLES
→ skeletal: is striated and is poorly nucleated. Facilitates voluntary movement and generates heat, is found on bones.
→ cardiac: found in the heart and is highly nucleated and branched. Contains intercalated disks to facilitate action potentials for constant and rapid heartbeats. Is involuntary.
→ smooth: is involuntary and is found in most internal organs.
LIST THE FOUR FUNCTIONS OF MUSCLE
→ generate heat: skeletal muscles will twitch and rapidly move to generate heat
→ movement: done through muscle contractions
→ stabilize joints: muscles strengthen and stabilize joints
→ maintains body posture and position: muscles will make small minor and constant movements to maintain body position and posture.
DESCRIBE GROSS ANATOMY OF MUSCLE
→ epimysium: cover the entirety of the outer muscle
→ perimysium: surround the fascicles of muscles
→ endomysium: cover the individual muscle fiber
→ blood vessels: vascularized muscles and provide nutrients and oxygen
→ nerves: control muscle contraction
LEVELS OF ORGANIZATION IN SKELETAL MUSCLE
→ muscle organ: the muscle as a whole
→ fascicle: contains bundles of muscle fibers
→ muscle fiber: contains elongated multinucleated striated cells.
→ myofibrils: contains sarcomeres arranged end to end
→ sarcomere: smallest functional unit of muscle
→ myofilaments: myosin and actin filaments
MICROSCOPIC ANATOMY OF SKELETAL MUSCLE
→ Z lines: are located on the ends of each sarcomere, are the defining ends of each sarcomere.
→ I band: there are 2 I bands on each side of the sarcomere, this portion is lighter and only contains actin
→ A band: is located in the middle of the sarcomere, contains overlapping myosin and actin.
→ H zone: is the dark area in the central area of the sarcomere, containing only myosin.
→ M line: is the very middle line of the sarcomere
→ t tubules: are extensions of the sarcolemma and extend throughout the sarcomere
→ sarcolemma: is the plasma membrane
→ sarcoplasmic reticulum: calcium storage unit in the muscle
→ actin and myosin: contractile proteins
EVENTS THAT OCCUR AT NEUROMUSCULAR JUNCTION
The action potential will arrive at the axon terminal of the presynaptic neuron, this triggers the voltage gated calcium channels to release calcium into the axon terminal. This triggers exocytosis of acetylcholine which will travel across the synaptic cleft onto toe ligand gated receptors at the motor end plate. The acetylcholine triggers an excitatory response, causing the sodium and potassium channels to open up. Potassium leaves at a slower rate than sodium entering, causing a graded potential of depolarization. These small depolarizations will spread across the sarcolemma, eventually triggering a large depolarization.
EVENTS THAT OCCUR DURING EC-COUPLING AND RELAXATION
The events at the neuromuscular junction set the stage for EC-Coupling. As the graded potentials travel through the sarcolemma it will trigger a larger depolarization. This depolarization travels down the T-tubules and sarcolemma, causing the proteins on them to change shape. This allows for the release of calcium from the sarcoplasmic reticulum into the cytosol. The calcium will bind onto troponin and then cause the cross bridge cycle, this is EC coupling. Relaxation is the reverse of all these steps.
THE CROSS BRIDGE CYCLE
The events during EC coupling set the stage for EC coupling. The calcium will bind onto troponin, removing the tropomyosin block from the myosin binding site. The myosin in its excited state will latch onto the myosin binding site of the actin, releasing ADP and P in the process. This causes myosin to go into its low energy state and pull on the actin towards the M-line, causing contraction. ATP will then bind onto myosin, breaking the bonds between myosin and actin and causing them to break apart from one another. This cycle will continue until calcium is no longer released.
DIFFERENT TYPES OF GRADED RESPONSES
→ twitch: involves muscle contraction when the next contraction is done after the refractory period is over frequency and strength remains constant.
→ temporal summation: occurs when contractions don’t wait for the refractory period to be over, strength increases with each contraction.
→ unfused (incomplete) tetanus: frequency increased and so does strength, strength is almost hitting maximum level. There is little relaxation between contractions
→ fused (complete) tetanus: is one long constant contraction at constant high strength, is often caused by electrolyte imbalance. There is no relaxation between contractions
THREE WAYS ATP CAN BE REGENERATED
→ direct phosphorylation of creatine phosphate: creatine phosphate donates a phosphate to ADP through creatine kinase.
→ anaerobic pathway: glycolysis and lactic acid: use of glycogen storage to have glucose undergo glycolysis, which results in the production of lactic acid. 2 atp produced for each glucose is a fast process.
→ aerobic respiration: is a very slow process and involves the usage of oxygen, however it makes a lot of ATP, around 32, but the process takes hours.
FACTORS THAT INFLUENCE FORCE, VELOCITY, AND DURATION OF SKELETAL MUSCLE CONTRACTION
→ Force: degree of muscle stretch, motor unit recruitment, size of the muscle, and frequency.
→ velocity and duration: load placed on the muscle, the type of ATp regeneration and whether or not there are oxidative slow or glycolytic fast fibers present.
DIFFERENCE BETWEEN FAST, SLOW AND OXIDATIVE AND GLYCOLYTIC FIBERS
→ fast glycolytic: has low endurance, does not require oxygen and relies on glycogen supply, is short liver because glycogen supply runs out quickly. Contract quickly. Appears white.
→ fast oxidative: relies on oxygen, has a rich supply of myoglobin, capillaries, etc. contract quickly.
→ slow oxidative: relies on oxygen, high endurance and is resistant to fatigue, has a rich supply of myoglobin, capillaries, mitochondria, etc. have a thin diameter, and have little power.
COMPARE GROSS ANATOMY OF SKELETAL AND SMOOTH MUSCLES
→skeletal: has a neuromuscular junction, wider, elaborate sarcoplasmic reticulum, striations, and T-tubules, adaptable and can generate heat.
→ smooth: does not have a neuromuscular junction, has bulbous axon terminals called varicosities, no T-tubules and have a less elaborate sarcoplasmic reticulum, no striations, spindle shaped cells, etc.
COMPARE AND CONTRAST CONTRACTILE MECHANISMS OF SKELETAL AND SMOOTH MUSCLES
→ similarities: both rely on calcium release as the final trigger for contraction, both use atp, and both use the sliding filament model.
→ differences: smooth muscle uses calmodulin. It also doesn’t have a troponin complex on the actin filament. Relaxation is more complicated and there is more beyond dropping of calcium levels to cause relaxation, skeletal muscles only need calcium levels to drop. Calcium also comes from the extracellular space and the SR for smooth muscle, whereas skeletal mainly gets it from the SR. smooth muscle takes longer to contract (30 times longer) but it can stay contracted because it uses such little energy (<1%) to stay contracted, skeletal muscle contracts and relaxes very quickly but uses a lot of energy.
COMPARE UNITARY AND MULTI UNIT SMOOTH MUSCLE IN TERMS OF LOCATION, STRUCTURE AND FUNCTION
Unitary: Structure: nerve fibers connected by gap junctions, meaning they all contract together as a unit. It is also arranged in opposing sheets.
Multi-Unit: Structure: muscle fibers that are structurally independent, rich in nerve fibers, no gap junctions.
contract seperatley from one another
