Musculoskeletal Module - Semester Three Lecture Notes PDF

Semester Three Musculoskeletal Module Session 2 – Lecture 2 Professor Lecture link … https://youtu.be/4TrpAbYiJdE Dr. Ihsan M Ajeena 26 slides Consultant of Clinical Neurophy...

Semester Three Musculoskeletal Module Session 2 – Lecture 2 Professor Lecture link … https://youtu.be/4TrpAbYiJdE Dr. Ihsan M Ajeena 26 slides Consultant of Clinical Neurophysiology Objectives By the end of this lecture, you should be able to: 1. Identify skeletal muscle types, action and structure 2. Apply these facts on muscle function 3. Outline the requirements for their action 4. Demonstrate the types of muscle contraction 5. Discuss their force, tone, fatigue and contracture 6. Identify energy sources and its expenditure 7. Realize types of muscle fibers and their benefit 8. Distinguish some related clinical problems Shapes of skeletal muscles  Structure of skeletal muscle Muscle Fasciculi M. Fibers Myofibrils myofilaments These are the contractile unit of the muscle  Coordinated movement For each movement at a given joint … Flexion at the elbow joint Prime Mover (agonist): main muscle (s) responsible for a particular movement Antagonist: opposes prime mover Synergist: (i) assists prime mover (ii) stabilizes action of prime mover (fixator), e.g. fixes non- moving joint when primer mover acting over two joints  Compartments For most long bones there are anterior compartments (on the front side) and posterior compartments (on the back side) that works antagonistic to each other. Ex. In elbow flexion, the anterior compartment will be the agonist (primer mover) while the posterior compartment will be the antagonist. In knee flexion, the posterior compartment will be the primer mover while the anterior compartment will be the antagonist, and so on… Requirements of muscle function This is called LEVER FUNCTION The function of each skeletal muscle requires: … a joint (with a fixed point – F) It will result in … so the muscle can contract (exert an effort – E) MOVEMENT … to overcome resistance (R) This activity will generate HEAT  Steps for motor movement Sensory neurons Signals from the muscle go back to the CNS through these nerves (sensory feedback) …… Motor neurons Signals from the brain reaches skeletal muscles through these nerves either directly or through the spinal cord (descending signals) …… Motor unit is composed of single motor neuron and all the muscle fibers it enervate There are so many motor units, - small and large. - fast and slow.  Neuromuscular junction a synapse in which a nerve meets skeletal muscle Composed of: Nerve terminal, Synaptic cleft, Muscle How muscle contraction occur ? 1- nerve signal (AP in a nerve). 2- transmitter release. 3- AP at the muscle. 4- Ca++ release into the sarcoplasm. 5- Start the contraction. Ca++ ion is the trigger For muscle contraction Muscle contraction occur by the cross bridge mechanism (Swiveling, walk along, power stroke) This will end with decreasing the length of the sarcomere and, subsequently, the muscle  Excitation contraction coupling 1- Ca++ bind with Troponin C. 2- Troponin I will be inhibited. 3- Troponin T will move tropomyosin. 4- Actin active binding sites uncovered 5- Myosin will bind to these sites. 6- Swiveling will take place Think about the energy & Where do we spend it …  Type of muscle contraction The work (joint movements) depends on the length & tone of the muscle Length changed No length change work done No work done The usual daily movements are something in between …  Gradation of motor activity… If we want to lift a heavy weight … We need to do one or two of the following actions Force summation Recruitment (increase frequency) (size principle) Start with Start with slow stimulating frequency of small motor signals then units then the increase it large motor gradually until units then the you got the larger … until action wanted you got the action wanted How muscle relaxation occur ? It started when Ca++ is actively pumped into the sarcoplasmic reticulum It is energy consuming process … What happen to the muscle at rest ? Muscle tone is the continuous and passive partial contraction of the muscles Present in muscles at rest, due to: (1) motor neuron activity (2) muscle elasticity Control of muscle tone occur by: (1) motor control centers in the brain (efferent) (2) Signals from the muscle themselves (afferent) (sensory feedback) Muscle energy (fuel): ATP stored in the muscle Last for few seconds Muscle energy (fuel): Phosphorylation of ADP by Creatine Phosphate Last for about 15 seconds Cr. Phos. ADP Creatine ATP Muscle energy (fuel): Aerobic respiration (Oxidative phosphorylation) Glucose Prolonged muscular events - O2 Pyrovic acid Fatty acid + + O2 Amino acid Aerobic resp. 36 ATP Muscle energy (fuel): Anaerobic glycolysis and lactic acid formation Glucose / Glycogen Last for 20 – 40 seconds 2 ATP - O2 Pyrovic acid - O2 Lactic acid How do we get rid of lactic acid? Where do muscle spend this fuel? 1. Physical activity (contraction and relaxation) 2. Regeneration of ATP molecules 3. Removal of lactic acid (Oxygen debt?) 4. Heat production What happen when there is … prolonged muscle contraction ? Muscle contracture A state of continuous muscle contraction Occurs when the energy (ATP) is depleted Resulted in failure of detachment of the actin filaments from myosin heads Examples: Writers cramps … Compartment syndrome … Rigor mortis …  Muscle fatigue when you can’t continue performing motor activities as you want … Depletion of muscle glycogen Fatigue of NMJ Blood interruption (intermittent claudication) Types of muscle fibers Some muscles are specialized for some motor activities? Because our skeletal muscles have different types of muscle fibers (the structure of the skeletal muscles): Type I (Slow, Oxidative-SO)(back muscles): red, small fibers that are rich in mitochondria. These are capable of prolonged powerful muscular contraction. Type II a: (Fast, Oxidative, Glycolytic-FOG)(fast resistant to fatigue-FR). Type II b (Fast, Glycolytic-FG)(fast to fatigue-FF)(finger muscles): lighter color (white fibers), rich in sarcoplasmic reticulum with less mitochondria and less blood vessels and are responsible for rapid, precise and short duration type of contraction. Think about diseases that may affect the muscle tone and contractility In Rest Hypotonia Hypertonia In Contraction Decrease power Increase power Good luck …