The Muscular System II PSK 4U NGDHS S. Kelly The Neuromuscular - - PowerPoint PPT Presentation

The Muscular System II

PSK 4U NGDHS – S. Kelly

The Neuromuscular System

• Simply put: the system in which our brain tells
• ur muscles what to do
• Incorporates brain, spinal cord, nerves,

muscles

• Both the nervous system and the

neuromuscular system can be improved and refined with training

• Training involves (among other things)

consistent use and practice

The Neuromuscular Junction

• Contact point between nerves and muscles in

these simplified steps:

• 1. Electrical impulse travels along the nerve

pathway

• 2. At the junction, neurotransmitter chemical

acetylcholine (ACh) is released

• 3. ACh detected by receptors on muscle fiber and

contraction occurs

• 4. Next slide: events 1-7 are labeled in order of
• ccurrence (steps 1-3 above are a

simplification…)

Neuromuscular Junction

Motor Units

• Twitch: wave transmission of nervous impulse

(ensures smooth movement) and the associated contraction

• Motor Unit: motor neuron + axon + all muscle

fibers it stimulates

• Small vs. large motor units: basically few

muscle fibers and/or fine motor movement vs. many muscle fibers and/or gross motor movements

All Or None Law

• When a motor unit is stimulated by a nervous

impulse, it will do so to its fullest potential

• Stimulus must exceed threshold potential for

muscle contraction and when it does:

• Either ALL of the fibers in a motor unit will

contract or NONE will contract

Excitation-Contraction Coupling

• Conversion of chemical energy to mechanical

energy

• Transverse tubulae system: network of

connected rings surrounding each myofibril, links myosin/actin to outside of muscle

• Change in electrical properties of tubulae

causes release of Ca ions

The Role of Calcium

• Trigger mechanism for excitation-contraction

coupling

• Ca released into sarcoplasm
• Without Ca, actin and myosin do not interact

with each other

• Calcium interacts with troponin and

tropomyosin to allow myosin and actin to interact and coupling then occurs, muscle contracts

Sliding Filament Theory

• Theory from mid-1950s, still widely accepted
• Actin and myosin filaments overlap and

sarcomere shortens

• “Crossbridges” from myosin (thick) to actin (thin)

attach, rotate, detatch, reattach in rapid succession

• Re-uptake of calcium causes muscle relaxation,

process requires ATP as fuel

• ATP also required to detach myosin and actin

from one another

Sliding Filament Theory

Some Additional Resources

What’s Next?

• Lesson: Neuromuscular Adaptation to Training
• Anatomy quiz Thursday