Lecture 18 - Muscles

pg 1 slide 3 note about connective tissue: provide mechanical protection from trauma take force from interior and transfer out

A single motor-neuron and all the skeletal muscle fibres, it innervates is known as a motor unit. The fibres of a single motor unit are generally dispersed throughout the muscle and are not adjacent –> cannot individually control muscle fibres, need to control a group – learn diagram pg2 slide 1 (and pic on phone)

• NMJ is the meeting point of a branched end of a motor neuron and the muscle fibre • when an electrical signal arrives at the end of a motor neuron, a special chemical known as ACETYLCHLORINE [neurotransmitter] is released into the gap which exists between the end of the neuron and the muscle fibre • ACETYLCHLORINE makes contact with the fibre surface and initiates the generation of an electrical signal within muscle fibre thereby literally “transferring” the signal from neuron to muscle • the electrical signal in muscle then causes the muscle fibre to contract • there is only ONE NMJ for each muscle fibre

slide 3 pg 3, slide 1 pg 4

• Recruitment of more motor units - activating a single motor unit would lead to contraction of all the muscle fibres it innervates - so, if multiple motor units are activated (or recruited), more and more muscles fibres would contract thereby generating more forces • Signal frequency —- ADD FROM SHAANS PIC

Achieved by progressively subjecting a muscle or functional muscle group to increased resistance. NB: hyperplasia = increased muscle mass due to muscle cell splitting. Known to occur in some animals, limited evidence for this in human

it is a chemical produced and released by skeletal muscles into blood which inhibits muscle growth. The timely turning on/off of myostatin expression is crucial in the controlling of normal muscle development. Increase myostatin in the body will mean decrease muscle mass as it limits muscle mass growth. Myostatin is primarily produced in skeletal muscle cells, and circulates in the blood and lymph and acts on muscle tissue

Non-invasively – asking person to do MRI [measure what happens in muscle BUT do not have a sample] Invasive – Muscle biopsy (have actual fibres BUT can be painful)

• Increased number of capillaries to increase blood flow and thus oxygen supply. • Increased concentration of enzymes to aid in metabolism (glycolytic capacity ↑, oxidative capacity ↑). • Increase in size and number of mitochondria – “the energy producing organelle of cells”. • Increased storage of energy producing substrates i.e. glycogen and fat

• Sensory neurons conduct electro-chemical signals from throughout the body to the central nervous system • Neurons located in our eyes, ears, nose, tongue, and skin (touch, pressure, temperature, pain receptors) are all sensory neurons because they sense different types of stimulation (light, vibrations, chemicals) and relay it to the brain

During the early phases of training (0-2 weeks), changes in neural factors are primarily responsible (90%) for the increases in strength. • After this period, changes in muscle factors become relatively more important, so that by 6 weeks muscle factors are primarily responsible for changes in strength

Loss of physiological and performance training adaptations when training is terminated. • The time-course of physiological adaptations to detraining appears to be faster compared to training adaptations. • Characteristics of detraining. - Loss of hypertrophy - Loss of metabolic adaptations

• neurons are specialised cells which conduct electro-chemical signals throughout the body • motor neurons conduct signals from the Central nervous system to skeletal muscles. These signals are called motor signals and drive skeletal muscle contractions

Oxidative capacity - the ability to produce energy in the form of atp by using oxygen Gylcolytic capacity - the ability to produce energy in the form of atp without the use of oxygen Type I are better adapted to carry out oxidative respiration while Type IIb ones are more suited glycolytic. Fibre IIa is an intermediate form