Module 2b - Muscles Flashcards
What are the three muscle types and their functions?
Smooth (Muscles mainly line internal organs and are not under voluntary control), Cardiac (only located in the heart, generates force to pump blood around the body and is not under voluntary control), Skeletal (Applies force to bones to generate movement and is under voluntary control).
What is the anatomical composition of Skeletal muscle?
Arranged into increasingly small but still parallel bundles. Individual muscles cells are called fibres, Rich in blood vessels and nerves and are striated in appearance.
What are sarcomeres?
The contractile units of skeletal muscle
What are sarcomeres made up of?
Thick (one myosin filament) and thin filaments (two actin filaments) that contract and pull on each other
Aside from actin and myosin what are other contractile proteins found in sarcomeres?
alpha-actinin, Titin and Nebulin
What are muscle excitation problems?
muscles should contract near simultaneously along the whole length
What is the structure and function of the Neuromuscular junction?
motor Neuron attached to a muscle binds Acetylcholine to receptors generating the release of calcium causing a muscle contraction.
What are key structural features of the Neuromuscular Junction?
Active Zone, Sarcolemma, Myelin, Axon, terminal, Schwann cells, receptors, Junctional Folds. vesicles and Synaptic cleft.
What are the key components of a muscle cell?
Sarcolemma (Cell membrane), Myofibril (Muscles fibres), Myofilaments (Components of the Myofibril), Mitochondrial, Sarcoplasmic reticulum (stores calcium) and the T-zone (AP travels).
What is the process of excitation coupling?
AP from nerve arrives at the NMJ generating an AP in the muscle fibre. Muscle AP spread over the sarcolemma and invade the T-tubular system. Depolarization within the T-tubular system triggers release of Ca from SR. Ca release in the cytoplasm and binds to Troponin on the sarcomere. This changes Troponin’s shape releasing the Troponin-Tropomyosin protein which exposes and actin binding site. Myosin binds to actin and the filaments slide = contraction.
What causes relaxation after excitation coupling?
Ca is pumped out of the intracellular space and back into the SR via SERCA, Ca unbinds from contractile apparatus = Relaxation
What happens in the first step of crossbridge cycling?
at rest Ca levels are low in the muscle fibre cytoplasm, Myosin heads are in the cocked position. Arrival of Ca initiates contractile cycle.
What happens in the second step of crossbridge cycling?
AP triggers release of Ca from SR. Ca concentration in the cytoplasm rises quickly, Ca binds to troponin. Troponin changes shape causing tropomyosin to roll. Myosin binding site on actin is exposed. Interaction between actin and myosin is now possible
What happens in the third step of crossbridge cycling?
Myosin binds to actin forming cross bridges. After this the bound ADP and Pi are released from myosin head. This changes the myosin head shape and it flexes while bound to actin. This is called a power stroke. The ends of the sarcomere are pulled together.
What happens in the fourth step of crossbridge cycling?
After ADP and Pi are released the ATP binding site on myosin is exposed. If ATP is available it will bind to myosin. This causes the myosin head to release the actin fibres
What happens in the fifth step of crossbridge cycling?
The Myosin ATPase hydrolyses ADP and Pi and the myosin head is recocked. This process occurs many times in a contraction
What is summation and Tetanus?
Summation is when multiple muscles twitches occur at the same time meaning they are summed together causing a larger contraction and Tetanus occurs when a muscle is so stimulated it cannot relax between contractions.
What are the two muscle fibre types?
Slow (Slow response but don’t tire easily) and fast fibres (Fast response but tire quickly).
What are the three key differences between muscle fibre types?
Type of Myosin expressed, Oxidative vs Glycolytic energy production, Type of SERCA pump expressed
What are Type 1:Oxidative fibres
Contain slow form of Myosin, many mitochondria, high levels of oxidative enzymes and rich blood supply, slow form of SERCA
What are type 2B:Glycolytic fibres
Fast form of Myosin ATPase, few mitochondria, low levels of oxidative enzymes, fewer capillaries, Fast Form of SERCA
Type 2A: Intermediate Fibres
Fast form of Myosin ATPase, mix of oxidative and glycolytic enzymes. Intermediate speed/fatigue
What are the effects of strength training?
More actin and myosin=increased fibre diameter, More cross bridges = more force
What are the effects of endurance training?
Increased oxidative capacity=increased ability for sustained activity
