Muscle Physiology Twitch Contraction of muscle in response
- Slides: 46
Muscle Physiology
Twitch • Contraction of muscle in response to stimuli – Action potential in one or more muscle fibers • Phases – Lag/latent • Interval between stimulus application to the motor neuron to actual contraction – Contraction – Relaxation
• Relationship between strength of stimulation and contraction – All or none law of contraction • Threshold must be reached – Generation of action potential • Stimuli stronger than threshold level – Identical contraction to the stimuli @ threshold level – No difference in level of action potential being generated
Motor unit
• Role of motor unit – Respond as a single unit to stimulation – Generation of action potential by muscle fibers by neural action potential
• Muscle response to a neural action potential – Graded • Different strength of contraction • Number of motor units being stimulated by an action potential
Concepts of summation • Muscle – Many motor units – Innervation • Combination of axons that branch from a neuron • Force of contraction – Number of motor units being stimulated • Multifiber/multiple motor unit summation
• Relationship between level of stimulation and contraction – Subthreshold • No action potential generated = no contraction – Threshold – Submaximal stimuli • Progressively increasing stimulation – Increased number of motor units being stimulated – Maximal stimuli • All motor units stimulated – Supramaximal stimuli • No additional effects
• Increased level of stimuli – Increased number of motor units being stimulated • Motor units being “recruited” • Number of muscle fibers in a motor unit – Different in different muscle – Depends on types of motion/contraction being generated • Delicate movement =fewer fibers per motor unit
• Frequency of stimulation and contraction – Relationship between action potential and muscle contraction • Action potential completed before muscle completes its contraction phase • No relaxation of muscle required before stimulation of subsequent contraction by subsequent action potentials • Increased frequency of stimulation, increased frequency of contraction
• Tetanus – Incomplete • Partial relaxation of muscle between contraction – Complete • Rapid generation of action potential • No muscle relaxation – Increased force of contraction in response to increased action potential frequency • Frequency/multiple wave summation
• Frequency of action potential – Increased frequency • Additional amount of Ca ions – No/partial removal – Additional release in response to AP • Results – Increased force of contraction
• Elasticity of connective tissue and sacroplasm • Treppe – Staircase effects of increased frequency of stimulation • Second contraction generates greater force than the first in response to the same level of stimulation • Eventually reach the maximum level
• Importance of treppe – Proper warm-up before exercise • Increased muscle efficiency – Increased blood flow – Increased muscle metabolism
Types of muscle contraction • Isometric – No change in length of muscle – Change in force generated by muscle during contraction – Postural muscle • Maintenance of posture without altering the length of muscle
• Isotonic contraction – No change in tension generated – Change in length of the muscle • Movement of upper limbs and fingers • Concentric contraction – Tension of muscle great enough to overcome the load/resistance – Changes in length – Many movements
• Eccentric contraction – Increased length of muscle in response to the resistance/load – Tension being maintained against the load
• Muscle tone – Constant tension • Generated by non-synchronous contraction of a small percent of motor units – Maintenance of the posture
Fatigue • Decreased capacity – Work – Efficiency of performance • Psychological – Muscles can function – Mental perception • Muscular – Loss of ATP • Synaptic – Loss of acetylchorine
• Physiological contracture – Inability to contract or relax – Loss of ATP • No release of cross-bridges • Rigor mortis – Rigidity of muscle after death • No removal of Ca from sacroplasm due to loss of ATP • No release of cross-bridge
Energy source • ATP (1 -2 second full contraction) • Creatine phosphate/phosphocreatine (8 -10 seconds full contraction) • Anaerobic metabolism (2 -3 min) – Glycolysis – Production of lactic acid – Less efficient • Aerobic metabolism (80 -90 % total ATP) – Requires oxygen – Slow process
• Source of ATP – Glucose • Glycogen in the muscle – Fatty acids • More energetic than glucose
Oxygen requirement • Deficit – Initiation of exercise – Lack of oxygen compared to the demand – Delayed generation of ATP via aerobic metabolism • Recovery – Generation of ATP via aerobic metabolism – Restoration of homeostasis • Body temperature • Ion concentrations • Metabolite/hormone levels
Muscle fiber types and contraction • Slow twitch muscle/type I – Slower contraction – Smaller fiber diameter – Extensive vasculature – Higher mitochondria and myoglobulin concentrations • Dark appearance – Slow ATPase on myosin heads – More fatigue resistant
• Fast twitching muscle/type II – Faster response to nervous stimulation – Fast ATPase on myosin heads – Less vascurature – Less myoglobulin and mitochondria • Lighter color – Higher glycogen content – More susceptible to fatigue
Muscle growth • Exercise – Increased size and capacity • Both muscle types – Increased anaerobic metabolism (weight lifting) • Enlargement of fast-twitch muscle – Increased aerobic metabolism (running) • Enlargement of slow-twitch muscle – No conversion of muscle type
• Increased force of contraction – Increased recruitment (neuromascular coordination) • Enlargement of muscle – Increase accumulation of myofilaments – Increased mitochondria and blood supply • Increased metabolism (endurance) – Results • Hypertrophy (majority of muscle growth) • Hyperplasia (rare)
• Atrophy – Decreased muscle size and function due to lack of use – Irreversible – Prevention • Exercises (contraction and extension) – Prevention of contracture formation in people with spinal cord damage
Heat production • ATP metabolism during muscle contraction – Release of heat • Normal body temperature – Rate of heat production • Related to rate of contraction – Shivering • Uncoordinated contraction of skeletal muscle • Generation of heat in response to cold air temperature – Reduced body core temperature
Smooth muscle • More variable functions • Shaped differently – Spindle shaped cells – No cell fusion • Single cell per fiber – Arrangement of actin and myosin • Bundle – Action to myosin ratio • > 2: 1
• Less developed SR – Caveolae – Ca ions from the extracellular fluid for contraction
Types • Unitary smooth muscles – More common – Sheet • Digestive tracts • Reproductive tracts • Urinary tracts – Cells connected via gap junction • Transfer of action potentials between cells – Often autorythmic
• Multiunit – Sheet – Contracts only when stimulated • Neural • Hormonal
Smooth muscle contraction • No tropomyosin-troponin complex associated with actin • Ca ion binds to calmodulin – Activates myosin kinase • Adds phosphate ion to myosin head for cross-bridge formation and cycling • Relaxation – Removal of phosphate group by myosin phosphatase
• Latching – Sustained tension during contraction due to slow release of myosin heads from actin • Removal of phosphate ions while cross-bridges are formed • Role of Ca ions – Same as the skeletal muscle • Extracellular source • Movement between sacroplasm and the ECF regulates contraction and relaxation
• Electrical potential – Higher resting potential – Slow wave • Slow depolarization – Spike potential • Action potential – Some muscles have action potential with plateau • Prolonged depolarization
• Action potential in smooth muscles – Not all-or-nothing potential • Series of slow waves resulting in prolonged contraction and slow relaxation • Pacemakers – Generation of action potential
Unique functional properties of smooth muscles • Autorythmicity • Contraction in response to stretching – Action potential generated by physical stimulation • Smooth muscle tones – Relatively constant tension • Constant tension amplitude
Regulation of contraction • Various factors – Change in membrane permeability • Na and Ca ions – Neural • Neurotransmitters from autonomic nerve fibers – Acetylchorine and norepinephrine – Hormones
• Response to neurotransmitters – Presence of specific receptor – Reciprocal relationship • If one is stimulatory, then the other is inhibitory • One depolarizes the membrane but the other hyperpolarizes the membrane
- Pic of smooth muscle
- Physiology of skeletal muscle
- Epimysium tendon
- Fast twitch and slow twitch muscles
- Twitch height of contraction
- 3 phases of muscle contraction
- Treppe
- Muscle twitch
- Staircase phenomenon
- Publisher
- Muscle movement
- Phases of muscle contraction
- Muscle contraction animation mcgraw hill
- Ciliary muscle contraction
- Biochemistry of muscle contraction
- Properties of cardiac muscles
- Hierarchy of muscle organization
- Explain sliding filament theory
- Muscle contraction
- Muscular contraction
- Incomplete tetanus muscle contraction
- Sarcoplasmic reticulum
- Muscle contraction
- Frank starling law
- Latent phase muscle contraction
- Phases of muscle contraction
- Muscle tissue ppt
- Tetanus vs summation
- 3 phases of muscle contraction
- Whole muscle contraction
- Isotonic contraction
- Phases of muscle contraction
- Muscle contraction
- Muscle refractory period
- Muscle physiology
- Nerve muscle physiology
- Acetylcholine binding site
- Primary immune response and secondary immune response
- Natural and forced response
- First order system transfer function
- Porann
- Twitch labels
- Twitch threshold
- Corina bautista
- Single twitch
- Tone twitch
- Twitch runers