Muscles (nervous system) Flashcards
Describe how the recruitment of different motor units can help in smoothing the initiation of voluntary movements.
A motor unit is made up of one motor neuron and many muscle fibres. Multiple motor units control one muscle contraction, and they can be recruited gradually and take turns contracting and relaxing to keep a steady, smooth muscular contraction. Smoothing can also be helped by recruiting larger motor units with larger cells, and gradually recruiting more motor units and closer together to keep a muscle continuously contracting (frequency coding).
Describe the 5 main steps of the cross-bridge cycle.
1.The influx of calcium, triggering the activation of the binding sites, and ATP is required to bind to myosin.
2. Once ATP is connected to the myosin head, it causes the release of the myosin head from actin, hydrolysis occurs separating ATP into ADP and Pi.
3. The myosin head, with ADP and Pi attached bends and attaches to the next actin site.
4. This causes the myosin head to pull actin towards the M-line of the sarcomere, where ADP is released, followed by Pi due to the force of the pull on actin.
5. The myosin head stays attached to the current actin site, and another ATP molecule is required to complete the cycle and move the myosin head to another actin site.
Describe the gross anatomy of a skeletal muscle.
Attaching to a tendon which is attached to a bone, is the epimysium, a strong connective tissue sheath wrapping around the muscle. Within the muscle, there are many perimysium wrapping around a fascicle. Within a fascicle, there are many muscle fibres wrapped in endomysium, an areola stretchy connective tissue. All muscle cells have multiple nuclei.
Describe the microscopic anatomy of a skeletal muscle.
All muscle fibres have multiple nuclei. Within one muscle fibre, there is the sarcolemma, which is the muscle cell membrane, the sarcoplasm, which is muscle fibre specific cytoplasm where calcium ions are stored, and the sarcoplasmic reticulum, where calcium ions are taken and released to trigger muscular contraction.
Describe the molecular structure of the sarcomere.
The two main components of the sarcomere is actin (thin protein filaments) and myosin (protein thick filaments) that slide along each other. There are Z-lines/disks on either side of the sarcomere where actin and titin (shock absorber) attach. The M-line sits in the middle of the sarcomere and myosin filaments, where the H zone is. There is an A band which covers the length of myosin and these all contribute to the sliding filament theory.
Describe the role of the sarcoplasmic reticulum in muscle contraction.
The sarcoplasmic reticulum forms a triad with t-tubules and terminal cisternae, to pump calcium ions out of the muscle cell with the use of ATP to stimulate muscle contraction, after receiving an action potential at the NMJ.
Describe and explain sliding filament theory.
The sliding filament theory suggests that through the cross-bridge cycle, myosin pulls actin so that the two filaments slide along each other. A muscle contraction occurs when the thin filaments slide past the thick filaments, and the sarcomere shortens.
Describe the histological characteristics of the three main types of muscle: skeletal, cardiac and smooth.
Skeletal - supports and moves the skeleton, striated and voluntary, stripy looking due to the organised placement of fibres and sarcomeres.
Cardiac - makes up muscular walls of the heart, striated and involuntary, similar structure to skeletal muscle because of the sarcomere alignment.
Smooth - found in walls of blood vessels and tubular organs, non-striated and involuntary, not stripy because no repeating sarcomeres and contractile proteins (myosin and actin) are randomly arranged.
Describe the role of myosin, actin, tropomyosin, and titin in muscle contraction.
Myosin - is a protein that produces thick, contractile filaments within muscle cells.
Actin - is a protein that produces small, contractile filaments within muscle cells.
BOTH SLIDE ALONG EACH OTHER TO SHORTEN SARCOMERE TO ALLOW MUSCULAR CONTRACTION.
Tropomyosin - binds along actin filaments and regulates actin-myosin interaction in muscles.
Titin - upon muscle activation, titin binds calcium at specific sites, thereby increasing its stiffness
Describe the events of excitation-contraction coupling.
- Action potential travels across sarcolemma.
- Action potential travels down T-tubules.
- Sarcoplasmic reticulum releases calcium via ryanodine sensitive channels.
- Calcium ions bind to troponin.
- Tropomyosin exposes active myosin binding sites on actin.
- Myosin binds to actin.
- ATP binds to myosin – providing energy
LEADS TO CROSS-BRIDGE CYCLE BUT NOT THE SAME THING.
Describe and explain the function of the neuromuscular junction.
The neuromuscular junction (NMJ) is a synaptic connection between the terminal end of a motor neuron and a muscle (skeletal/ smooth/ cardiac). It is the site for the transmission of action potential from neuron to the muscle.
Describe the role of adenosine triphosphate in the functioning of skeletal muscle.
Adenosine triphosphate (ATP) is the sole fuel for muscle contraction. It is a critical requirement for muscle contraction because it breaks the myosin-actin cross-bridge, freeing the myosin for the next contraction. Without ATP, muscles would remain in their contracted state, rather than their relaxed state.
Outline some factors contributing to ageing effects in skeletal muscle.
Ageing of skeletal muscle is also known as sarcopenia, which has been defined as an age related, involuntary loss of skeletal muscle mass and strength. Factors contributing to this are the reduction of myosin production, mitochondrial malfunction (leading to axon degradation), motor axon and muscle fibre atrophy.
Define the term motor unit and describe its relevance to motor control of skeletal muscle.
A motor unit is defined as a single efferent neuron and all of the muscle fibres it controls. There are several different sized motor units for each skeletal muscle, and how intense a muscular contraction is will determine how many and what strength of motor units are required to make the contraction to make it as smooth as possible, especially for contractions that are longer and require a strain.
Describe the concept of frequency coding in skeletal muscle control.
Varying the discharge rate of motor units that have been recruited for a muscular contraction to stop it from being twitchy, and to let it be smooth and at the same level of contraction for a period of time.
