Myoglobin Myoglobin is a common protein, which has the ability to store oxygen in muscle cells. The myoglobin has a high level of red pigment, so the more myoglobin the meat has, the redder it will be. The terms “red meat” and “white meat” are actually an indicator for the level of myoglobin.
Myoglobin This protein is also the main reason that the red meat turns darker while you’re cooking it. During the heating process, iron atoms of the myoglobin lose electrons and they move up to a higher oxidation level. Thus, the meat turns from pinkish-red to brown.
Compare the Muscle Fiber to Pull and Peel Twizzlers How amazing is that?
Sarcoplasmic Reticulum Sarcoplasmic reticulum – specialized smooth endoplasmic reticulum Function: Stores ionic calcium & releases it on demand
Sarcoplasmic Reticulum Surrounds myofibrils At junction of A band and I band, sarcolemma forms hollow T-tubule to conduct stimulus deep into every sarcomere
How muscle knows WHEN to contract Mechanism of contraction on a cellular level
Motor Unit One motor neuron and ALL the muscle cells that it stimulates Spread throughout muscle
Explanation - then see next slide! Stimulation of one motor unit results in weak contraction of ENTIRE muscle –Since a motor unit is spread throughout the muscle & not clustered together, it stimulation will activate cells scattered throughout the entire muscle –This causes a weak contraction of the entire muscle –Muscles requiring fine control have small motor units that only activate a few cells at a time.
Transmission – know the steps Sarcolemma becomes temporarily permeable to sodium (Na + ) Na+ ions rush into muscle cell which reverses electrical conditions Action potential is caused which moves along sarcolemma and down T tubules deep into muscle fiber Once initiated – action potential is unstoppable (all or none principle) resulting in full contraction of that particular muscle fiber (cell) Excitation-Contraction Coupling
Safeguard When nerve stimulation stops: –Ach is destroyed by acetylcholinesterase (AChE) to prevent continued contraction –Substances such as certain organophosphates found in pesticides and fertilizers destroy AChE causing convulsions
End of stimulation K+ ions leaves cell rapidly to restore electrical balance Then Na-K pump restores ions to original positions for relaxation of muscle fiber
Sliding Filament Theory HOW a muscle contracts
Sliding Filament Theory The thin filaments slide past the thick filaments so the overlap increases This shortens the muscle fiber and thus the entire muscle
What causes the filaments to slide? Cross bridge attachment: in presence of Ca ions, high energy myosin cross bridge binds to actin binding site Power Stroke: energy from ATP is used to bend cross bridge and pull actin toward center of sarcomere 1% shortening for each power stroke
Neuromuscular junction animation animation Focus Questions: What is the name of the stimulus that travels down the axon to the muscle fiber? An action potential Does the terminal (end) of the axon enter the muscle fiber? No. There is a gap between the two. Does acetylcholine enter the muscle fiber? No. What chemical does enter the muscle fiber, resulting in an action potential through the muscle fiber? Sodium
Sliding Filament theory Boat = Myosin (thick filament) Oar = Myosin side arm Water = Actin (thin filament) Life ring = Calcium
Resting 1.ATP is bound to myosin side arm. 2.ATP cleaves into ADP + P (high energy)
Step 1 Action potential 1.A nerve action potential releases acetylcholine into the synaptic cleft opening the Na+ channels. 2.Action potential spreads across sarcolemma releasing Ca into sarcoplasma
Step 2 Myosin-actin binding 1.Ca binds to troponin. 2.A shape change in troponin moves tropomyocin out of the way of actin binding site. 3.Actin and myosin bind using energy from cleaved ATP.
Step 3 Power Stroke 1.Side arm pivots so myosin and actin slide by each other shortening the sarcomere. 2.ADP and P released (low energy)
Step 4 ATP Binding Actin-myosin release 1.A different ATP molecule binds to active site. 2.Actin released
Step 5 ATP cleavage 1.Return to high energy state 2.Cycle will repeat if Ca still available.
Think it over The boat (myosin) does not move far in one cycle, can a muscle contraction occur with one cycle? No If a muscle is contracted what happens if a new molecule of ATP is not available? Muscle stays contracted- cramps Why does rigor mortis occur? (Hint: What chemical is no longer available to the body?) ATP is not available to control Ca release so contractions are continuous 6-8 hours after death. Body relaxes hours as enzymes break down contractile structures. Myofilament Contraction
Sliding Filament Theory Focus questions: What happens to the length of the sarcomere during a contraction? The sarcomere shortens.
Sliding Filament Animation animation 2 Focus Questions: What chemical exposes the binding site for actin and myosin? Ca What is the source of energy for a contraction? ATP What is the name of the step in which the actin filament is actively contracted? Powerstroke What chemical must be present in order for the actin and myosin filaments to separate? ATP
Muscle contraction at the macroscopic level 1.Place your fingers along the angle of your jaw just in front of your ear. Grit your teeth and fell what happens to the hardness of the masseter muscle. During muscle contraction the muscle becomes ________________________.
2.With your thumb and little finger of one hand, span the opposite arm’s bicep’s from the elbow to as close to the shoulder as possible. Bend the arm and observe the change in the length of the muscle. During muscle contraction the muscle ___________________ in length.
3.Wrap a string around your extended upper arm and determine the circumference. Clench your fist tightly and flex your arm to contract the muscle. During muscle contraction the diameter of the muscle _____________________.
Developmental Aspects Progresses superior to inferior direction –Baby can lift head before walking Progresses proximal to distal –Baby can move arm before grasping object –This is due to the way that neural pathways are built in your brain.
Men vs. women Women’s skeletal muscles make up 36 % of body weight Men’s is 42 % due to effects of testosterone Muscle strength per unit mass is equal
Building Muscle Mass Type of joint involved in motions Direction of muscle fibers (contained in fascicle) Anatomy of the muscle Angles of body parts In order to work a muscle effectively & to minimize risk of injury, the above factors must be considered. Number of reps and amount of weight depends on purpose of exercise (building vs. toning).
Aerobic vs. Anaerobic 3 main factors affect your respiration type: –Your nutrition –Your respiratory efficiency –Your cardiovascular fitness IMPORTANT NOTE TO UNDERSTAND: –The type of respiration that is happening depends on what is going on in a particular muscle at a particular time. You will have some muscles doing aerobic and others doing anaerobic AT THE SAME TIME!
Aerobic Respiration Is the most efficient type of respiration – producing the most ATP per glucose molecule –Glucose + oxygen produce ATP + carbon dioxide + water It is slower and requires continuous delivery of oxygen & nutrients to the muscle
Aerobic Respiration Duration of energy produced can be hours This type of energy production is used for activities that require endurance rather than power –Jogging, marathon running, walking, etc
Anaerobic Respiration Muscle uses up oxygen faster than circulatory and respiratory systems can deliver it Glucose gets converted to lactic acid in that muscle Lactic acid will get converted to pyruvic acid and enter aerobic mechanism when oxygen becomes available
Anaerobic Respiration Circulatory and respiratory system cannot deliver oxygen as fast as muscles are using it up. This leads to lactic acid buildup - when oxygen is again available – lactic acid is converted to pyruvic acid and oxidized
Anaerobic Respiration For muscle to be restored to resting state: Oxygen stores must be replenished Lactic acid converted to pyruvic acid Glycogen stores replaced ATP & creatine phosphate reserves replenished Liver must reconvert the pyruvic acid produced to glucose or glycogen ALL of these processes require oxygen
Oxygen Debt The amount of oxygen that must be taken into the body to provide for these restorative processes The difference between amount of oxygen needed for totally aerobic respiration during muscle activity AND the amount that is actually used. All nonaerobic sources of ATP used during muscle activity contribute to this debt
Oxygen Debt Repaid by rapid, deep breathing (hyperventilation) triggered by change in pH from lactic acid) after exertion is ended Breathing pure oxygen does not help recovery time – oxygen has to have time to get to the muscles that require it. There are limitations due to your circulatory and respiratory systems.
Efficiency of Oxygen Use Athlete: ~10 % greater rate and efficiency of oxygen use than normal person Marathon runner: ~45 % greater Working your muscles, heart, lungs, etc out on a regular basis increases your efficiency –Things like smoking, poor nutrition, too much sugar, etc. decreases your efficiency
Muscle Strain Commonly called a “pulled muscle” Is excessive stretching & possible tearing of muscle due to overuse/abuse Injured muscle becomes painful & inflamed (myositis) Treatment: adjacent joints are usually immobilized
Muscle Strain Factors contributing –Degree of stretch (more flexible at a joint the less likely you are to strain a muscle than someone who’s “tight” –Speed of stretch
Contusions A bruise or bleeding within a muscle Caused by impact to muscle When already injured muscle is repeatedly struck, a more serious condition, myositis ossificans, can develop
Myositis Ossificans Involves formation of a calcium mass with the muscle over a period of 3-4 weeks After 6-7 weeks the mass usually begins to dissolve and is reabsorbed by the body. In rare cases, a bony lesion can remain in the m
Muscle Cramps Moderate to severe muscle spasms that cause pain Possible causes –Electrolyte imbalance –Ca, Mg or K deficiency –dehydration
DOMS (Delayed Onset Muscle Soreness) Follows participation in a long or strenuous activity Soreness begins hours after activity Involves multiple microscopic tears in muscle tissue & causes inflammation, pain, swelling & stiffness
Muscle Disorders Torticollis – a twisting of the neck which causes rotation and tilting of the head to one side – caused by injury to one of the sternocleidomastoid muscles Pulled groin muscles – Strain or stretching of adductor muscles (magnus, longus, brevis) Foot drop – paralysis of anterior muscles in lower leg – caused by injury to the peroneal nerve
Muscle disorders Shin splints – inflammation of the anterior muscle group of the lower leg (& the periosteum they pull on)– caused by trauma or strain – usually felt on the medial &/or anterior borders of the tibia
Muscle Disorders Charley horse – officially a trauma induced tearing of muscles followed by bleeding into the tissues (NOT just a cramp)
Halux valgus – permanent displacement of the great toe – caused by wearing pointy toed shoes
Duchenne Muscular Dystrophy Page 194 Genetic – affects primarily males – X linked trait Dystrophin protein not produced correctly – leads to muscle fiber degeneration & atrophy Progresses from extremities upward Generally do not live beyond young adulthood
Myasthenia gravis Probably autoimmune Shortage of neurotransmitter receptors in muscle Muscles not stimulated properly & grow progressively weaker Death occurs when respiratory muscles fail to function
Myasthenia Gravis Drooping of eyebrow & eyelid called Ptosis