1. Neuromuscular System
The complex linkages between the muscular system and the nervous system
Nerves transmit impulses in “waves” that ensure smooth movements
A single nervous impulse and the resulting contraction is call a muscle twitch
One neuron or nerve may be responsible for stimulating a number of
muscle fibres

2. Neuromuscular System
The electrical impulse begins at the spinal cord (CNS) travels along the nerve axon to the contact point between the nerve and muscle (neuromuscular junction)

3. Neuromuscular System
At the junction, the neurotransmitter acetylcholine is released, which is detected by receptors on the surface of the muscle fibre, initiating a muscle contraction

4. Neuromuscular System
The signal is transmitted into the muscle fibre through the transverse tubulae system, which is a network of interconnecting tubes that surround a myofibril and act as a link between the outside of the muscle fibre and the actin & myosin filaments
The tubulae then initiates a rapid release of calcium ions, leading to muscle contraction

5. Neuromuscular System
The calcium ions are released in to the sarcoplasm by the terminal cisternae, which form part of the sarcoplasmic reticulum (a network of membranes surrounding the myofibrils)
The calcium ions interact with the troponin molecules, causing the tropomyosin to allow the myosin heads to bind with the actin

6. Neuromuscular Junction Clip

7. Sliding Filament Theory
A contraction is caused by an overlapping of the actin and myosin filaments,
which causes the sarcomere to contract

8. Sliding Filament Theory
Myosin crossbridges attach, rotate, detach and reattach in rapid succession, resulting in the overlapping of the filaments, shortening of the sarcomere and muscle contraction

9. Sliding Filament Theory
The trigger mechanism is the release of calcium ions, by the
terminal cisternae, when the nerve impulse is transmitted
through the muscle fibre.
The energy source behind the release of calcium and
detachment of myosin from actin is adenosine triphosphate
(ATP).
As the work of the muscles increases, more and more ATP is
used up and must be replaced through food metabolism
Sliding Filament Theory Clip

11. The Sarcomere Arrangement of myofibrils in a sarcomere:
A contractile unit, or compartment of myofibrils
A sarcomere goes from one Z-band to the next Z-band
Sarcomeres contain two types of tiny filaments called myofibrils
(actin and myosin)
Arrangement of myofibrils in a sarcomere:
Z disk – attaches actin
A band – portion containing both actin and myosin
I band – portion containing actin myofilament only
H zone – portion containing only myosin

13. Muscular Contraction The All-or-None Principle
Whether or not a motor unit activates upon the arrival of an
impulse depends upon the so called all-or-none principle
An impulse of a certain magnitude (or strength) is required to
cause the innervated fibres to contract
Every motor unit has a specific threshold that must be
reached for such activation to occur
Sliding Filament Theory Clip

14. Types of Muscle Fibres Slow Twitch (Type I ) More mitochondria
Most people have an even mix of fast and slow twitch fibers in their bodies, which is genetically determined
Slow Twitch (Type I )
More mitochondria
More capillaries
More of a red colour (due to increased blood supply)
Activated more slowly by motor neurons
Slower contraction speed, but contraction can be maintained for a longer period.

15. Types of Muscle Fibres Fast Twitch (Type II) Higher glycogen stores
More of a white colour (less blood)
Activated more quickly by their motor neurons
Contracts more quickly, but fatigues much more easily