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4.1 - Neuromuscular Function - Slideshow (1).pptx

  1. 1. Unit 4 – Movement Analysis 4.1 – Neuromuscular Function
  2. 2. Neuromuscular Function - Background Information  The Central Nervous System (CNS) is where most of the sensing and control takes place. The CNS is made up of the Brain and the Spinal Cord.  Sensory neurons (Afferent Neurons) carry signals to the CNS from receptors that sense various factors such as body temperature, blood pressure, blood oxygen and carbon dioxide levels (and more).  Motorneurons (Efferent Neurons) are nerves which carry information from the CNS to the muscles and which tell muscles to contract or relax.  When a muscle is required to contract, an electrical impulse is emitted from the central nervous system. The electrical impulse, or action potential, begins at the brain and is transmitted via the spinal cord and by nerve cells called motor neurons.
  3. 3. 4.1.1 – Label a diagram of a motor unit 
  4. 4. 4.1.2 – Explain the role of neurotransmitters in stimulating skeletal muscle contraction.  Neurotransmitters are chemicals that are used for communication between a neuron at the synapse and another cell.  Acetylcholine is the primary neurotransmitter for the motor neurons that innervate skeletal muscle and for most parasympathetic neurons. It is generally an excitatory neurotransmitter, but it can have inhibitory effects at some parasympathetic nerve endings, such as the heart.  Cholinesterase is an enzyme that catalyzes (breaks down) the hydrolysis of the neurotransmitter acetylcholine into choline and acetic acid, a reaction necessary to allow a neuron to return to its resting state after activation.
  5. 5. 4.1.3 – Explain how skeletal muscle contracts by the sliding filament theory.
  6. 6. 4.1.3 – Explain how skeletal muscle contracts by the sliding filament theory.  Pre-curser to Sliding Filament Theory: 1. A nerve impulse (Action Potential) arrives at the neuro muscular junction (motor-end plate). 2. causing cells to release acetylcholine into the synapse where they bind with acetylcholine receptors. 3. This then sends action potential along the sarcolemma and down the T – tubules. 4. The action potential then travels over the sarcoplasmic reticulum.
  7. 7. 4.1.3 – Explain how skeletal muscle contracts by the sliding filament theory.  Sliding Filament Theory: 1. Now the action potential is chemically on the sarcoplasmic reticulum it causes the release of Calcium Ions (Ca+). 2. The calcium ions now in the sarcomere search out and bind to the troponin. This changes the shape of troponin. 3. With this change of troponin shape the bands of tropomyosin now move to expose the myosin binding sites (on the actin bands). 4. The ATP molecule binds to the myosin head and reaches out to the myosin binding sites on the actin. 5. When the myosin reaches out to the actin, it forms a cross bridge.
  8. 8. 4.1.3 – Explain how skeletal muscle contracts by the sliding filament theory.  Sliding Filament Theory: 6. It is the breakdown of ATP (adenosine triphosphate) at this cross bridge which allows the myosin heads to pull the actin filaments inward, shortening. 7. This action and breakdown of ATP to ADP is called the “power stroke”. 8. After this the cross bridge is broken and myosin detaches from the actin. 9. This process will repeat its self and is often know as the “ratchet mechanism”. 10. The process will also continue for as long as the Ca+ stores and ATP lasts, or until the impulse stops. 11. When the impulse stops Ca+ is pumped back to the sarcoplasmic reticulum and actin returns to its resting position, causing muscle to lengthen and relax.
  9. 9. 4.1.3 – Explain how skeletal muscle contracts by the sliding filament theory.
  10. 10. 4.1.3 – Explain how skeletal muscle contracts by the sliding filament theory.
  11. 11. 4.1.4 – Explain how slow and fast twitch fibre types differ in structure and function  Slow Twitch Muscle Fibres (Type 1)  Slow-twitch, or type I, fibres (sometimes referred to as "Red") have more mitochondria, store oxygen in myoglobin, rely on aerobic metabolism, have a greater capillary to volume ratio and are associated with endurance exercise/activity; these produce ATP more slowly.  Marathon runners tend to have more type I fibres, generally through a combination of genetics and training.  Colour – Red  Myoglobin Content – High  Glycolytic Capacity – low  Mitochondria – High  Capillarization - High  ATP – Low  Contractions Speed – Low  Fatigue resistant – High
  12. 12. 4.1.4 – Explain how slow and fast twitch fibre types differ in structure and function Fast Twitch (Type 2A)  Colour – Pink  Myoglobin Content – Medium  Glycolytic Capacity – High  Mitochondria – Medium  Capillarization - Medium  ATP – High  Contractions Speed – Moderate  Fatigue resistant – Medium / Low Fast Twitch (Type 2B)  Colour – White  Myoglobin Content – Low  Glycolytic Capacity – High  Mitochondria – Low  Capillarization - Low  ATP – High  Contractions Speed – High  Fatigue resistant – Low

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