Download When a motor unit contracts it will contract completely or not at all

MUSCLE CONTRACTION
Part 2
LEARNING GOALS
• I will understand the neurological portion of muscle contraction.
• I will be able to identify the types of muscle contraction.
NERVOUS SYSTEM
• Motor nerves
extend from spinal
cord to muscle
fibers
MOTOR UNIT
• A single nerve that activates a group
of fibers is called a motor unit.
• Large muscles may have hundreds of fibers in each unit (quads)
• Small muscles may have as little as 10 fibers in each unit (muscles of the eye)
• The smaller the motor unit the more precise the movement.
PRE CONTRACTION
1) Electrical signal called an Action Potential travels down motor neuron.
2) Synaptic vesicles release Acetylcholine (Ach)
3) Ach crosses synapse (gap) and binds to receptors on muscle fibre
4) Another action potential induces Sarcoplasmic Reticulum to release Ca …
ALL OR NONE PRINCIPLE
• An impulse from the CNS needs to be of a certain magnitude to cause fibers to
contract.
• A smaller impulse does not result in a smaller contraction.
• Once the needed magnitude is reached, the muscle contracts.
• This is called the all-or-none principle.
When a motor unit contracts it will
contract completely or not at all.
• In other words, if a motor unit consists of 10 muscle fibres (or 800 muscle fibres)
and they are “turned on,” either all fibres will contract or none will contract.
INTRAMUSCULAR COORDINATION
• Increased strength requires more motor units being activated.
• Trained athletes are able to recruit more motor units than untrained
individuals (Olympic weight-lifters – 85%, untrained individuals – 60%).
• Trained athletes can further increase strength only by increasing muscle
diameter.
INTERMUSCULAR COORDINATION
• Recruiting motor units from different muscles allows for improved
performance.
• A high performance athlete has trained all agonists and antagonists to work
together for a fluid skill movement.
MUSCLE CONTRACTION
• results in tension developed within the muscle which either overcomes a
resistance, equals a resistance or is overcome by resistance.
• dynamic or static
CONCENTRIC CONTRACTION
• occurs when tension overcomes the resistance.
• The origin and insertion
move closer together.
• Muscle shortens
e.g.: Biceps contract
concentrically during
flexion of the elbow
ECCENTRIC CONTRACTION
• occurs when the tension is overcome by the resistance.
• The origin and the insertion of the muscle
move apart.
• Muscle lengthens
• Biceps contract eccentrically during the
controlled lowering of the pail.
Any controlled lowering where gravity would
otherwise accelerate the movement involves
eccentric contraction.
ISOMETRIC (STATIC) CONTRACTION
• results when tension is developed in the muscle but no movement is produced
by the contraction.
• Internal and external force equal.
• No change in muscle length during contraction.
• No work is done but high amount of tension is produced and muscle fatigue
occurs quickly.
• Examples: Gymnastics, wrestling, skiing, archery...
HOMEWORK QS
1. List these structures from largest to smallest: perimysium, endomysium,
epimysium
2. List these structures from largest to smallest: muscle fibre, muscle belly, fibre
bundle
3. How are sarcomeres different from myofibrils?
4. Explain what is happening inside a sarcomere that accounts for why it
becomes shorter during contraction.
5. Where is Ca stored? What is its function in the SFT?
6. Where does Ca bind? Where does ATP bind?
7. What happens to the ATP molecule in order to provide energy to the myosin
head?
8. What is that energy used to do?
9. What has to happen in order for ADP to be released from the myosin head?
10. Why is your rectus femoris “strongest” when your leg is in partial extension?
11. What structures make up your CNS?
12. What structure carries the electrical impulse from your CNS to your
muscles?
13. Explain why your obicularis oculi (eye muscle) has much smaller motor units
that your rectus abdominis.
14. How does your brain allow you to lift both light objects and heavy objects?
LEARNING GOALS
• I will understand the neurological portion of muscle contraction.
• I will be able to identify the types of muscle contraction.