Transcript How Do Muscles Work?

How Do Muscles
Work?
Chapter 7: Lesson 3
Initiation of Contraction
1. A nerve impulse reaches the
neuromuscular junction
Arrival of an action potential
at the synaptic terminal
Step Two
2. The Motor Neuron releases
acetylcholine (neurotransmitter) into
synapse
Step Three
3. Acetylcholine opens channels in the
plasma membrane (sarcolemma) of
the muscle fiber allowing Na+ ions into
the cell and activate an action
potential.
Step Four
4. The action potential sweeps across
the membrane and through the ttubules
Action potential
Axon
Arriving action potential
Synaptic terminal
Sarcolemma
Vesicles
ACh
AChE molecules
Synaptic
cleft
Sarcolemma of
motor end plate
Release of acetylcholine
Release of acetylcholine
Vesicles in the synaptic terminal fuse with
the neuronal membrane and dump their
contents into the synaptic cleft.
ACh
receptor
site
Muscle
fiber
ACh binding
the
AChatbinding
at the
motor andmotor
plate and plate
The binding of ACh to the receptors
increases the membrane permeability to
sodium ions. Sodium ions then rush into the
cell.
Appearance of an action
potential in the sarcolemma
An action potential spreads across the
surface of the sarcolemma. While this
occurs, AChE removes the ACh.
Step Five
5. When the t-tubules depolarize they
trigger the adjacent sarcoplasmic
reticulum to release Ca+ ions which
spill into the cytoplasm (sarcoplasm).
Step Six
6.
The calcium ions cause the movement of troponin
and tropomyosin on their thin (actin) filaments,
which then enables the myosin molecule heads to
"grab and swivel" their way along the thin filament.
•When muscle contracts the actin filaments slide into the A band, overlapping with myosin
When Muscle
Contracts Protein
Filaments Slide
Together