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Muscle control Muscles and how they work: a review The more you read/see something explained in a different way, the more sense it makes. Here are some more You Tube finds, which explain how muscles work. • First, an overview: • http://www.youtube.com/watch?v=hzXVe4RS8-A • Next, the detail of the sliding filament theory: • http://www.youtube.com/watch?v=ELyoJZom5N0 • Finally, a good explanation of how muscle spindle and Golgi tendon organs work. We will refer to these when we look at REFLEXES next week. • http://www.youtube.com/watch?v=7T4NI_2qDEM Acetylcholine • A key neurotransmitter in the PNS and also found in the CNS • Drugs to treat a number of the conditions which we are interested in as SLT have their action on Ach • If they reduce the action of Ach they are called anticholinergics (PD, CPOD) • If they prevent the breakdown of Ach they are called cholinesterase inhibitors (MG, AD) • Each muscle fibre is innervated by one neuron… • But one neuron can innervate a large number of muscle fibres • The greater the number of motor neurons that are activated, the greater the number of muscle fibres that will contract • Each muscle fibre contracts in an all-or-nothing fashion (just like nerve fibres fire in an all-or-nothing fashion) to their fullest extent • Factors that affect the force of contraction include the number of muscle fibres contracting (ie the number of motor units, and the size of these units) Facial muscles, tongue, muscles of mastication and larynx • Have a low ratio of nerve fibre: muscle fibres • Enables high degree of precision in movement • Contrast this with larger limb muscles, or muscles to control posture • Larynx 1:6-12 v Hip 1:2000 • ie one neuron innervates 6 to 12 muscle fibres in the larynx,; in the eye muscles, this ratio can be as low as 1:5; for some of the larger, postural muscles, the ratio is much higher • In addition, the type of muscle fibre determines the speed and sustainability of muscle contractions • Video of the vocal cords in action: • https://www.youtube.com/watch?v=v9Wdf-RwLcs Types of skeletal muscle fibre • Muscle fibres vary in colour…depending on the amount of myoglobin they contain • Myoglobin= a red-coloured protein, binds oxygen, found in muscles (like haemoglobin, found in red blood cells) a. Slow-twitch, fatigue resistant fibres: found in the postural muscles of neck, back and legs b. Fast-twitch, fatigue resistant fibres: found in leg muscles c. Fast-twitch, B fibres: fatigable. White as opposed to a & b which are red in colour. Produce strong, rapid contractions; for eg, in the muscles of the shoulders and arms MUSCLES have a mixture of all 3 fibres; proportion depends on the particular function of the muscle, and its use Exercise can induce change in muscle fibres • Think of a marathon runner v a weighlifter • What type of fibres predominate in the key muscles in these athletes?