Tutor profile: James H.
Subject: Biomedical Science
What is meant by an 'all-or-none response' in a neuron?
In neurons, there can be several inputs telling the neuron to fire or not to fire a signal down its axon and to transmit signals. However, for the neuron to send a signal down its axon for release of neurotransmitters, a specific threshold has to be met. All of this threshold saying "go" has to be reached or none of the signal will get sent down the neuron's axon. Once the threshold is met though, the 'go' signal gets propagated or passed down the neuron's axon at the same level all the way along to the end until the axon terminal, where the neurotransmitters get released.
What's the importance of the side chains of amino acids?
Side chains of amino acids will decide how that amino acid behaves, how it can be modified, and can even affect the shape and behaviour of the protein that it's a part of. For example, chains of non-polar amino acids would make hydrophobic regions of proteins, so those parts of the protein would likely avoid water. Charges on amino acids will affect how proteins interact as well. Big, 'bulky' side chains on amino acids like tryptophan and tyrosine make these amino acids better for protein structures like beta-sheets. Also, common protein modifications - like the addition of a phosphate group in a signalling pathway - can only be done on specific amino acids (e.g. serine and tyrosine in this case).
How does skeletal muscle repair itself?
Skeletal muscle has the beneficial ability to grow and to repair itself many times throughout an individual's lifetime. This is because muscle stem cells or 'satellite' cells reside in muscle and are available to contribute to repair. When muscle is injured, satellite cells will proliferate (divide and multiply). Some of these cells will go back to being dormant, but many will differentiate into more muscle-specific cells. They will first become myoblasts, which can proliferate some more before differentiating into myocytes. Myocytes are single-celled but won't proliferate. Instead, they start fusing to each other and to existing muscle fibres, to create new and/or larger muscle fibres. That's why we see skeletal muscle fibres are multi-nucleated: several cells fused together to form those large cells.
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