Bone & Biomechanics 5 Flashcards
Where is the neuromuscular junction positioned?
In the middle third of the muscle fibre
What is the reason for the position of the neuromuscular junction?
So that the wave of depolarisation(action potential) spreads over the sarcolemma and propagates the whole fibre
What is excitation-contraction coupling?
The term used to describe the steps from plasma membrane excitation to calcium release to muscle excitation
Where does the action potential travel?
After it has reached the neuromuscular junction it causes depolarisation and travels along the sarcolemma and down the transverse tubule
What happens once the action potential is inside the transverse tubule?
The change in membrane potential because of depolarisation is sensed by the voltage sensor
What does the voltage sensor do once it senses the action potential?
It makes contact with the ryanodine receptor found on the sarcoplasmic reticulum terminal cisternae and this triggers the release of calcium ions from the channel in the SR
Where is the calcium released?
Into the sarcoplasm
What does the calcium do?
It binds to the contractile apparatus which then initiates the sliding to produce tension and force for contraction
What happens to the calcium after it has initiated sliding?
It unbinds from the contractile apparatus and is pumped back into the SR by SERCA which uses ATP energy. This then causes the muscles to relax
When does cross bridge cycling occur?
When the calcium ion binds to the myofilaments
What is a cross bridge?
When a myosin head is bound to an actin filament
What is the natural state of the myofibrils?
There is a myosin head attached to actin and the calcium ion levels are very low
What does ATP do in the cross bridge cycle?
Causes the dissociation of the myosin head from actin
What does ATP hydrolysis do?
Causes a shape change so that the myosin head is cocked and moved from where it initially was
What are the products of ATP hydrolysis?
ADP and phosphate which remain bound to the myosin head
What happens when the myosin head is cocked?
It is put in line with a new binding site on the actin filament
What happens after the myosin head is cocked?
It binds to the new actin site and the power stroke occurs (head flexes) generating the force to pull the thin filament towards the centre of the sarcomere and initiate contraction of the myofilaments
What is the final step of the cross bridge cycle?
Another ATP molecule binds to the myosin head and causes dissociation from the actin and the process to repeat
What affects muscle tension?
The rate at which muscle is stimulated (action potential is delivered) and the number of muscle fibres recruited (used to generate force)
What is a twitch?
A twitch occurs when a single action potential results in a pulse of calcium ions being released into the sarcoplasm and a short period of tension development (contraction)
What is a twitch summation?
This occurs when a muscles fibre is restimulated before I is completely relaxed so the second twitch adds to the first
What is a tetanus?
This occurs when many action potentials are fired in a rapid sequence and there is a sustained release of calcium from the SR, a sustained period of actin-myosin interaction and a sustained period of contraction
What is meant by the length- tension relationship?
Each muscle has an optimal length where it will be strongest and when longer or shorter than that length it will be weaker
What happens when the muscle fibre is optimal length?
It causes optimal overlap for myosin heads to make contact with the actin filament
What happens when the muscle fibres are stretched?
It causes very little overlap so it is difficult for actin-myosin interaction to occur
What happens when the muscle fibres are slack?
It causes too much overlap and doesn’t allow for much cross bridging to occur
What does the amount of force developed match?
The situation requiring the force
What regulates the number of muscle fibres activated?
The amount of neurons which are active at the same time
What is recruitment?
When more motor units are activated to make up more force
How many factors does muscle form depend on?
3
What factors does muscle form depend on?
Length of muscle fibres, number of muscle fibres and arrangement of muscle fibres
How much can fibres shorten?
Up to 50% of their length
What does long muscle fibres give?
A large range of motion
What contracts?
Muscle fibres and not the tendons
What is another measure of the number of muscle fibres?
Cross-sectional area
What is directly proportional to CSA?
The amount of tension and therefore force produced
What does a greater number of fibres mean?
Greater CSA and so greater tension
What are the two possible arrangements of muscle fibres?
Parallel and pennate
What is parallel structure?
Muscle fibres run vertically between the muscle tendons
What is pennate structure?
Muscle fibres are arranged oblique to the muscle tendons
What is the benefit of parallel arrangement?
Gives a good range of motion as muscle fibres are long
What is the disadvantage of parallel arrangement?
Less CSA so therefore less strength
What is the benefit of pennate structure?
More fibres fit into the space so there is increased CSA and strength
What is the disadvantage of pennate structure?
Reduced shortening and therefore range of motion because muscle fibres only shorten to 50% of the length of the shortest fibre
What are bones when it comes to anatomical levers?
Levers
What are joints when it comes to anatomical levers?
Pivot/Fulcrum
What is the muscle contraction when it comes to anatomical levers?
Pull/applied force
What is the load when it comes to anatomical levers?
Internal or External
What gives the different types of levers?
Where the fulcrum, load and force are positioned
What is the positioning of class 1 levers?
Load, fulcrum, applied force
What is the positioning of class 2 levers?
fulcrum, load, applied force
What is the positioning of class 3 levers?
fulcrum, applied force, load
What is an example of a class 1 lever?
Head sitting on neck
What is an example of a class 2 lever?
Ankle
What is an example of a class 3 lever?
Elbow
How many types of muscle action are there?
3
What are the three types of muscle action?
Cocentric, eccentric and isometric
What occurs in concentric muscle action?
Muscle is active and tension is developed, change in joint position (angle), muscle shortens
What occurs in eccentric muscle action?
Muscle is active and tension is developed, change in joint position (angle), muscle lengthens
What occurs in isometric muscle action?
Muscle is active and tension is developed, no change in joint position, no change in length of muscle
How many roles are there for muscles?
4
What are the possible roles of muscles?
Agonist, antagonist, stabiliser and neutraliser
What is the role of the agonist?
Act concentrically and shorten
What is the role of the antagonist?
Act eccentrically and lengthen
What is a stabiliser?
When a muscle is active and holding a joint still
What muscle action do stabilisers exhibit?
Isometric
What is the function of a neutraliser?
To eliminate unwanted movement caused by another muscle
What muscle action do neutralisers exhibit?
It depends on the movement occurring
Anterior positioned muscles cause…
Flexion
Posterior positioned muscles cause…
Extension
Medial positioned muscles cause…
Adduction
Lateral positioned muscles cause…
Abduction
What is the exception to the concentric actions of muscles rule?
The knee as it flexes posteriorly, anterior positioned muscles cause extension and posterior positioned muscles cause flexion
List the 16 muscles needed?
Biceps brachii, triceps brachii, deltoid, iliopsoas (psoas major and iliacus), gluteus maximus, quadriceps femoris (rectus femoris, vasts lateralis, vasts intermedius, vasts medialis), Hamstrings (biceps femoris, semi-membranosus, smi-tendinosus), tibialis anterior, triceps surae (gastrocnemius and soleus)
How many heads does the biceps brachii have and where do they attach?
2 heads which attach to the scapula
Where does the bottom of the biceps brachii attach?
Radial tuberosity
What movement(s) are caused by the biceps brachii?
Shoulder flexion, elbow flexion, radioulnar supination
How many heads does the triceps brachii have and where do they attach?
3 heads- long heads attach to scapula and lateral and medial heads attach to the humerus
What movement(s) are caused by the triceps brachii?
Shoulder extension and elbow extension
What is the shape of the deltoid?
Triangle
What does the deltoid attach to?
Clavicle, scapula and humerus
What movement(s) are caused by the deltoid?
Shoulder flexion by the anterior fibres, shoulder abduction by the lateral fibres and shoulder extension by the posterior fibres
What is the structure of the iliopsoas?
psoas major attaches to the vertebrae and joins at the iliacus
Where does the iliopsoas sit?
Anteriorly to hip and femur
What movement(s) is caused by the iliopsoas?
Hip flexion
What does the gluteus maximus attach to?
Hip, sacrum, coccyx and femur
What movement(s) is caused by the gluteus maximus?
Hip extension
How many heads does the quadriceps femoris have?
Four heads and four muscles
What is the position of the rectus femoris?
It sits superficially and runs straight along the femur, also attaching to the hip
Where do the quadriceps femoris muscles attach?
To the patella and the patella ligament attaches to the tibial tuberosity so the quadriceps are attached to the knee
What movement(s) are caused by the quadriceps femoris?
Knee extension, and the rectus femoris also flexes the hip because it is the only part touching the hip joint
How many heads does the hamstring have?
2
How many sections of the hamstrings are there?
3
What movement(s) are caused by the hamstrings?
Flexion of the knee and rotation when flexed
What is the position of the tibias anterior?
It doesn’t cross the knee, runs anterior to the ankle and to the medial portion of the foot
What movement(s) is caused by the tibias anterior?
Ankle dorsiflexion and foot inversion
How many heads does the triceps surae have?
3
What is the structure of the triceps surae?
Superficial gastrocnemius has 2 heads which attach to the femur while the deep soleus has one which attaches to the tibia/fibula
Where do the gastrocnemius and soleus meet?
The Achilles (calcanea tendon)
What movement(s) is caused by the triceps surae?
Ankle plantar flexion
