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Flashcards in Case 9 Deck (67):

How do skeletal muscles develop?

The fusion of 100+ small mesodermal cells (myoblasts), this is why each skeletal muscle fiber has 100+ nuclei.


How do skeletal muscles grow?

Through hypertrophy, muscle fibers lose their ability to divide after fusion.


What is a sarcolemma?

Plasma membrane of a muscle cell


What are the two layers of sarcolemma?

True cell membrane called the plasma membrane and an outer thin layer of polysaccharide, containing collagen fibers, at each end this layer fuses with a tendon fibre.


What are transverse (T) tubules?

Invaginations of the sarcolemma which tunnel in from the surface toward the centre of each muscle fibre. They are open to the outside of the fibre and so contain interstitial fluid.


What is sarcoplasm?

Cytoplasm of a muscle fiber, it contains large quantities of potassium, magnesium, phosphate and multiple protein enzymes.


What are the sarcoplasmic reticulum?

Fluid-filled system of membranous sacs that encircle each myofibril. Composed of two parts: 1)large dilated chambers called terminal cisternae that touch the T tubules 2)longitundinal tubulesthat surround the actual surface of the myofibril.


Whats a triad?

Transverse tubule and two terminal cisterns on either side.


What ion is in abundance in the sarcoplasmic reticulum?



What are myofibrils composed of?

1500 adjacent myosin (thick) filaments and 3000 actin (thin) filaments.


What are the basic functional unit of a myofibril?

The filaments of a myofibril do not extend the entire length, they are arranged in compartments called sarcomeres, which are the basic functional units.


What are myosin molecules composed of?

6 polypeptide chains, 2 heavy and 4 light. The two heavy wrap around each other, the tail points towards the center of the sarcomere, parallel to neighboring molecules. The heads of the heavy chains fold bilaterally and 2 light chains are attached to each head. Part of the body hangs to the side, providing and arm, the head and arm together are called cross-bridges, which have two hinges, thus cross-bridges extend in all directions.


How many myosin molecules make up a filament?



What are the tree portine components of actin filaments?

Actin, tropomyosin and troponin.


What is actin made up of?

Double-stranded F-actin protein molecule wound in a helix.


What are the F-actin molecules of actin made up of?

Polymerised G-actin molecules each of which is attached to a molecule of ADP (the active sites), which interact with the cross-bridges of myosin fibers in muscle contraction.


What are regualtory proteins?

Tropomyosin and troponin, they help switch contraction on and off.


Where is tropomyosin located?

Wrapped spirally around the sides of F-actin helix, in resting state they lie on top of the active sites.


What is troponin?

Attached intermittently along the tropomyosin moleculescomplex of three subunits that are thought to attach the topomyosin and the actin.


What are the three subunits in the troponin complex?

Troponin I - storng affinity for actin, Troponin T - strong affinity for tropomyosin, Troponin C - strong affinity for calcium ions, initiates contraction process.


What are structural proteins?

Keep thick and thin filaments in proper alignement, give the myofibril elasticity and extensibility, link the myofibrils to the sarcolemma and extracellular matrix.


What are the types of twitch fibers?

Type 1 - slow twitch, type 2a - intermediate of fast oxidative-glycolytic fibres. Type 2b - fast glycolytic fibers.


How do slow fibers compare to fast fibers?

Half the diameter and take 3 times aslong to reach peak tension after stimulation.Continue contracting long after fast fibers would fatigue.


What do slow twitch fibers contain large volumes of?

Mitochondria and myoglobulin, a globular protein similar to haemoglobin that reversibly binds to oxygen allowing a substantial reserve of oxygen. Slow twitch fib ers also have a great oxygen supply from capillaries.


What are fast glycolytic fibres?

Make up most skeletal fibres in the body, reach peak tension in 0.01s, large diameter, densly packed with myofibrils, large glycogen reserves, few mitochondria, fatigue rapidly as they use massive amounts of ATp during contraction.


What are fast oxidative-glycolytic fibers?

Hybrid of slow and fast fibers, contain little myoglobin with an intermediate capillary and mitochondrial supply.They utilise glucose and fats and maufacture and use ATP.


Can training change fibre type?

Resistance training can change 2b into 2a fibers.


What three layers surround skeletal muscle?

Epimysium - surrounds entire muscle, Perimysium - surrounds 10-100 muscle fibres seperating them into bundles called fasicles, Endomysium - seperates individual fibers. All three extend to form tendons.


What is the general mechanism for muscle contraction after ACh binds its receptor?

1) ACh-gated channels open and large quantities of Na+ ions diffuse in initiating an AP at the membrane.
2) AP travels along the muscle fibre.
3)Depolarises the muscle membrane, and much of the AP electricity flows to the center of the muscle fibre where it causes the sacroplasmic reticulum to release large quantities of CA2+.
4)Ca2+ initiate attractive forces between actin and myosin filaments, causing the to slide alongside each other, which is the contractile process.
5)After a fraction of a second the CA2+ is pumpedf back into the sarcomplasmic reticulum by a calcium ion membrance pump, where they are stored until a new AP.


What depolarises a T-tubule and what does this depolarisation cause?

Depolarised by an action potential, which activates a non-gated voltage sensor called dihydropyridine (DHPRs).


What happens when DHPRs are activated?

Undergo a conformational change, which controls the opening of ryanodine receptors (RyR) which are calcium ion channels. These open along the membrane in the SR cisternae and the longitudinal tubules.


What do the calcium ions bind to?

Troponin C.


What is the name of the pump that pumps calcium ions back to the SR?

Sacro/endoplasmic reticulum calcium ATPase (SERCA)


What happens after the calcium ions have cause the troponin to uncover the active sites?

The cross-bridges are attracted to the active sites.


What happens when the head of the cross-bridges bind to the active sites?

Changes in intramolecular forces cause head to tilt towards arm which drags the actin filament around with it (this head tilt is called a power stroke). The head then automatically breaks away and returns to its original position. It combines with a new active site and undergoes a new power stroke, in this way moving the actin fiber along step by step.


How is ATP utilised in this action?

Before contraction an ATP binds to the head and is cleaved leaving ADP and a phosphate ion attached to the head. The head binds to the active site and undergoes a power stroke with the energy from this. During the power stroke ADP and Phosphate are released and a new ATP binds (this is what causes the detachment of the head from actin. The new ATR is then cleaved.


What can the force of contraction depend on in muscles?

How contracted or stretched the muscle was before it was stimulated?


What is the definition of a twitch?

At threshold or higher, a stimulus causes a quick cycle of contraction and relaxation called a twitch.


What is the latent period?

A delay of about 2 ms between onset of stimulus and onset of twitch.


What is summation?

If a skeletal muscle is stimlated and a second stimulus is applied before relaxation is complete the contractions are fused.


what is Tetanus?

If stimulation is repeated at a sufficiently high rate, the muscle will not relax between each stimulus but will remain in a contracted state.


What is the other name for shin splints?

Medial tibila stress syndrome


What are shin splints?

General term used to describe excersie-induced pain in the front lower legs, caused by repeated trauma to the connective muscle tissue surrounding the tibia.


What is the most common cause of shin splints?



What is over-pronation?

Occurs when ankle moves downward and medially to create a more stable point of contact with the ground. The ankle rolls inwards so more of the arch has contact with the ground. This abnormal movement causes the muscles to fatigue quicker.


What is the treatment for shin splints?

Rest until symptoms resolve.


What are the symptoms of a tibila stress fracture?

Pain in shin bones that gradually gets worse, tender to touch, pain at night when resting.


What factors increase the risk of a tibila stress fracture?

Increased training routine, poor or altered movements of leg, weak or fatigue muscles, menstrual problems, poor diet, reduced bone density.


Treatment for TSF?

Rest, painkillers, ice, adapt exercise to low impact.


What is the other name for runners knee?

Patellofemoral (PFP) syndrome.


What is pain the result of in PFP?

Abnormal forces or prolonged repetitive compressive or shearing forces between the patella and the femoral. These can be due to overuse, alignment issues, foot problems (flat foot), repeated minor knee injuries.


Treatment of PFP?

Physiotherapy and foot orthoses.


Why are ACL injuries more common in women?

Smaller size and different shaped intercondylar notch, greater ligamnet laxity.


What causes an ALC injury?

Sudden stop or change of direction maneuvers.


What are the different grades of ALC injuries?

Grade I - fibers are stretched but not torn, little swelling or tenderness. Grade II - Fibers partially torn or incomplete tear with haemorrhage, little tenderness, some swelling, some loos of function. Grade III - Fibers completely torn, ligamnet is in two parts, tenderness, little or lot of swelling, ligamnet cannot control knee movements.


What is a Lachmans test?

Flexing the knee to 90 degrees.


What are osteophytes?

Bone spurs, bony projection that form along joint margins due to increase in a damaged joint surface area. They limit joint movement and cause pain. NSAIDs and surgery for treatment.


What is amennorrhoea?

Ansence of a menstrual period which can be caused by low energy availibility.


What are the four phases of the stance phase of gait?

Heel strike, loading response, midstance and heel off.


What percentage of gait is swing and stance phase respectively?

40% and 60%.


What is an apraxic gait?

Small stepping, broad-based gait, patient seems to have forgotten how to walk. Caused by a problem with cortical integration - frontal lobe damage.


What is a waddling gait?

Patient bend hips forward and walks with a waddle. Caused by muscle/hip disease.


Crossing over gait/scissoring gait?

Caused by bilateral spaciticy, patient may walk stiffly on toe and have problems turning.



Small paces, slow, shuffling gait, stooped posture, reduced arm swing usually unilateral. basal ganglia dysfunction.



Flexed upper limb, extended lower limb on affected side, circumduction of affected leg. Caused by unilateral upper motor neurone lesion.


Cerebellar ataxia?

Broad-based gait, patient may swing from side to side, possibly fall, patient appears drunk.


High stepping/foot drop?

Occur in a patient with peripheral neuropathy. patien lifts knee high and slaps foot down on walking.