Musculoskeletal System- PART 3
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Physical Ed
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11th - 12th Grade
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Practice Problem
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Medium
Haylee Penny
Used 17+ times
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25 Slides • 23 Questions
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Musculoskeletal System- PART 3
The Structure of the Muscle and Muscle Actions
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Microscopic Structure of the Muscle
* Muscles attach to bone via tendons.
* The muscle belly consists of thousands of muscles fibres called fascicles, which run side by side& are encased in perimysium.
* Each group of fascicles is encased in endomysium. All of these are then encased in epimysium.
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Microscopic Structure of the Muscle
Each muscle fibre is made up of myofibrils
Myofibrils are similar in appearance to an telephone cable with many wires within it.
These 'wires' are myofilaments known as Actin and Myosin
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Multiple Choice
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Microscopic Structure of the Muscle
Myofibrils are made up of many units arranged end to end along the length of the muscle and are known as sarcomeres.
Within each sarcomere, the actin and myosin filaments form cross-bridges which cause a the filaments to overlap. This is known as the Sliding Filament Theory.
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Multiple Choice
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Microscopic Structure of the Muscle
Each muscle fibre is surrounded by the cell membrane- Sarcolemma which encases a gel-like substance called Sarcoplasm.
The Sarcoplasm contains Mitochondria, Myoglobin, energy fuels, and enzymes.
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Microscopic Structure of the Muscle
The Sarcoplasmic Reticulum surrounds each muscle fible and is responsible for releasing Calcium and regulating the contraction and relaxation of the muscle.
It responds to activity of motor neurons.
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Multiple Choice
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Open Ended
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Neuromuscular System
* The brain is responsible for initiating all actions and the spinal cord carries all of its messages.
* Messages are sent as electrical impulses via motor neurons, which stimulate muscle contraction.
* Motor neurons are nerve cells that transmit impulses to the muscles to contract.
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Neuromuscular System
Image 'a' on the right shows the motor neuron (yellow part) attaching to the myofibril.
Nerves connect (indirectly) to muscle as synapses on the individual myofibrils known as neuromuscular junctions.
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Open Ended
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All or nothing principle
When the electrical impulse reaches a certain threshold, all of the fibres of that motor unit will contract at the same time and as forcefully as possible.
However, until this threshold is reached, none of the fibres will contract.
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Muscle Fibre Recruitment (Size Principal)
Recruitment is the term used to describe the number of active motor units activated by the brain.
Motor units themselves vary in the number of fibres they stimulate and in the type of fibres they stimulate within each muscle.
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Muscle Fibre Recruitment (Size Principal)
* Smaller motor units can generate force in smaller increments to control fine movements, while larger motor units can generate greater force.
* Large motor units are recruited more gradually due to larger motor neurons requiring more stimulation to fire.
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Muscle Fibre Recruitment (Size Principal)
The body recruits fibres according to the activity demand= preferential recruitment
The intensity of the task will determine which muscle fibre type is preferentially recruited for the task:
Fast-twitch fibres- quickest to respond, recruited first
Slow-twitch fibres- recruited first if intensity is low.
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Open Ended
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Fibre Types
Muscles are made up of two types of muscles:
1. Slow-twitch (Type I fibres)- red fibres which are best suited to aerobic endurance work.
2. Fast-twitch (Type II Fibres)- white fibres that are best suited to short- duration, high-intensity anaerobic work.
* The proportion of slow and fast-twitch fibres varies from muscle to muscle and person to person.
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Fibre Types
Slow-twitch fibres:
- contract slowly, but able to perform for extended periods of time
Fast-twitch fibres:
- produce larger forces, but fatigue more quickly than slow twitch.
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Fibre Types
* Slow twitch fibres can not be converted to fast-twitch fibres or visa versa.
* However, fast-twitch fibres can take on slow-twitch fibre characteristics after aerobic training.
* Fast-twitch fibres can be classified as :
Type 2A- partially aerobic
Type 2B- purely anaerobic
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Multiple Choice
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Open Ended
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Types of Muscle Contractions
There are 3 categories of muscle actions:
- Isometric
- Isokinetic
- Isoinertial
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Isometric Contractions
* Involves muscle contraction against a force with no significant movement occurring.
* Tension is produced, but no joint movement or action takes place.
* The main disadvantage= elevated systolic blood pressure because muscles contract around blood vessels and restrict blood flow.
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Open Ended
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Isokinetic actions
Speed of movement is held constant regardless of the force being applied.
Specialised hydrolic equipment regulate the resistance produced.
Any force applied results in an equal and opposite reaction force from the machine, which ensures the muscle works maximally through the entire range of motion.
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Multiple Choice
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Isoinertial Contractions
During these contractions, the muscle changes length to move a limb through its range of motion.
These exercises strengthen the target muscle as well as the synergists and attachments.
There are 2 types of isoinertial contractions: concentric and eccentric
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Isoinertial Contractions
Concentric contractions occur when the muscle shortens during an effort. Eg. the upward phase of a bicep curl.
Eccentric contractions occur when the muscle lengthens while tension occurs. This occurs in all; gravity-resisting movements. Eg. the downward phase of a bicep curl.
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Musculoskeletal System- PART 3
The Structure of the Muscle and Muscle Actions
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