11.2 - movement Flashcards
essential idea
The roles of the musculoskeletal system are movement, support and protection.
what is the function of bones
The rigid nature of bone both supports and protects organs within the body. It also gives a structure for muscles to pull, by their contraction, to create movement.
Describe grasshoppers
Grasshoppers (Acrididae) are insects, and insects have a skeleton on the outside of the body called an exoskeleton. The muscles are inside the hard shell.
The back leg is much longer than the others to aid jumping. Long legs increase the distance over which the jumper can push on the ground.
The two main muscles inside are the extensor tibiae muscle which contracts to extends the leg, and the flexor tibiae muscle which contracts to flex the leg.
These muscles pull on tendons which are attached to the tibia on either side of the joint pivot.
Skeletal muscles, such as the extensor and flexor that occur in pairs are often antagonistic: when one contracts the other relaxes to produce controlled movement in opposite directions.
description of elbow
components of elbow (structure and function)
- the elbow is a hinge joint
- it has a limited range of movement
Biceps
Bends the arm (flexor)
Triceps
Straightens the arm (extensor)
Humerus
Anchors the muscle (muscle origin)
Radius / Ulna
Acts as forearm levers (muscle insertion) – radius for the biceps, ulna for the triceps
Cartilage
Smooth surface to allow easy movement, absorbs shock and distributes load
Synovial fluid
Provides lubrication, reduces friction in the joint.
Joint capsule
Seals the joint, contains the synovial fluid.
Tendons
non-elastic tissue connecting muscle to bone
Ligaments
non-elastic tissue connecting bone to bone
Description of knee
- the knee is a pivotal hinge joint
- It’s main range of movement is like a hinge joint yet it allows some pivotal movement as well.
- Its is one of the most complex joints in the human body
- cartilage and synovial fluid protect and lubricate the knee joint, reducing impact harm
- strong ligaments hold the knee in place
Description of the hip
- the hip is an example of a ball and socket joint
- it allows movement in all axes and planes
- ball and sock joints allow the greatest range of movement
- shoulder is a ball and socket joint
Different aspects of muscle cells
- Muscle fibre cells are held together by the plasma membrane referred to as the sarcolemma.
- A single skeletal muscle cell is multinucleated, with nuclei positioned along the edges
- Many mitochondria are present due to the high demand for ATP
- Muscle cells contain sarcoplasmic
reticulum, a specialised type of
endoplasmic reticulum*, that
stores calcium ions and
pumps them out into the sarcoplasm when the muscle fiber is stimulated.
-Myofibrils are the basic rod-like contractile units with a muscle cells.
What is a sarcomere
A sarcomere is a repeating unit of striated muscle cell
Sarcomere: description of bands
- where we see dark bands - the acting and myosin are overlapping
- light bands show just actin or myosin fibers with no overlapping
n 1. Z-line – end of one sarcomere
n 2. A Bands – dark in color and extend the entire length of the myosin
n 3. H bands – middle of A band – contains only myosin
n 4. M-Line – Contains supporting protein and holds myosin together and found in center of the H band
n 5. I Bands – Light in color and only contain actin
Muscle Contraction/Sliding Filament Theory
- Motor neuron carries an action potential (AP) until it reaches the neuromuscular junction
- A neurotransmitter – Ach – is released between the gap between the axon terminal and the sarcolemma of the muscle fiber
- Ach – binds to the receptors on the sarcolemma
- Sarcolemma ion channels open up and Na+ ions move through the membrane (depolarizes the cell)
- This generates a muscle AP
- The AP moves along the membrane through the t-tubules
- After AP – Ach is broken down by an enzyme called acetyl cholinesterase so that only one nerve impulse cause one muscle AP
- The muscle AP moving through the t-tubules causes Ca+ to be released from the sarcoplasmic reticulum. Ca+ ions flood into the sarcoplasm
- Ca+ ions bind to the troponin and cause a conformational change. Troponin released
tropomyosin and exposes the myosin binding site on the actin myofilament - Myosin head – ATPase – this splits ATP and releases energy
- Myosin head binds to the myosin binding site on the actin
- This forms a cross-bridge and ADP is released and the myosin head bends due to lack of energy (power stroke). The bending is towards the center of the sarcomere and the actin is moved inwards.
- ATP binds to myosin and myosin detaches from the actin attachment sites
- If there are no more AP, Ca+ levels decrease in the sarcoplasm. Troponin-Tropomyosin complex moves back to its original position (blocking the myosin binding sites)
- Muscle relaxes
Describe skeletal muscle contractions
- when an action potential reaches a striated muscle cell, the sarcoplasmic reticulum release clacium ions into the myofribrils. ca opens up binding sites on actin
- myosin heads are bound to actin binding sites (making a cross bridge) and are stimulated ot move. This causes the actin to slide over myosin, towards the center of the sarcoere.
- atp releases the myosin head and re-sets it. It forms a new cross bridge with a different actin binding site and continues contraction.
- this happens up to 5 times per second and ends when no more ca is released
Nature of science: Developments in scientific research follow improvements in apparatus - fluorescent calcium ions have been used to study the cyclic interactions in muscle contraction.
Ashley and Ridgway (1968) were the first to study the role that Calcium ions (Ca2+) plays in the coupling of nerve impulses and muscle contraction.
Their work was made possibly by the use of aequorin, a Ca2+ binding bioluminescent protein.
Upon Ca2+-binding aequorin emits light. The timing of light emission peaks between the arrival of an electrical impulse at the muscle fibre and the contraction of the muscle fibre.
This is consistent with theory of release of Ca2+ from the sarcoplasmic reticulum
The light emissions are detected and recorded using specially adapted microscopes and cameras.
A number of researchers have used fluorescent dyes to visualise and measure the movement of myosin and actin.
aequorin and the fluorescent dyes used in research only emit for a few short nano-seconds making them ideal to measure the rapid movements found in muscle cells.
