1. Muscle Contraction
Part 2

2. Learning goals
I will understand the neurological portion of muscle contraction.
I will be able to identify the types of muscle contraction.

3. Motor nerves extend from spinal cord to muscle fibers
Are you Nervous yet?
Motor nerves extend from spinal cord to muscle fibers

4. Motor unit
A single nerve that activates a group of fibers is called a motor unit.

5. It’s a Numbers game
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.

6. Let’s diagram it
Back to the beginning …

7. 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 …

8. What’s gona work?
Team Work!

9. When a motor unit contracts it will
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
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

10. Intramuscular coordination
increased strength requires more motor units being activated.
1. trained athletes are able to recruit more motor units than untrained individuals (Olympic weight-lifters – 85%, untrained individuals – 60%).
2. trained athletes can further increase strength only by increasing muscle diameter.

11. 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.

12. Reciprocal innervation
ensures that protagonist and antagonist are not working against each other
nervous system relaxes the antagonist while contracting the protagonist

13. Muscle contraction
dynamic or static

14. concentric contraction
occurs when tension overcomes the resistance.
origin and insertion move closer together
muscle shortens
e.g.: Biceps contract concentrically during flexion of the elbow

15. Eccentric contraction
occurs when the tension is overcome by the resistance
origin and 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.

16. 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...

17. Learning goals
I will understand the neurological portion of muscle contraction.
I will be able to identify the types of muscle contraction.

18. Homework Qs
List these structures from largest to smallest: perimysium, endomysium, epimysium
List these structures from largest to smallest: muscle fibre, muscle belly, fibre bundle
How are sarcomeres different from myofibrils?
Explain what is happening inside a sarcomere that accounts for why it becomes shorter during contraction.

19. Where is Ca stored? What is its function in the SFT?
Where does Ca bind? Where does ATP bind?
What happens to the ATP molecule in order to provide energy to the myosin head?
What is that energy used to do?
What has to happen in order for ADP to be released from the myosin head?

20. Why is your rectus femoris “strongest” when your leg is in partial extension?
What structures make up your CNS?
What structure carries the electrical impulse from your CNS to your muscles?
Explain why your obicularis oculi (eye muscle) has much smaller motor units that your rectus abdominis.
How does your brain allow you to lift both light objects and heavy objects?