The Neuromuscular
Junction
Chapter 10
Anatomy and Physiology
Mr. Knowles
Liberty Senior High School
Neuromuscular Junction
(NMJ)
Communication b/w the nervous
system & skeletal muscle fiber.
Soma
Soma
Neuromuscular Junction
(NMJ)
As an axon enters a muscle, it
branches into a number of
synaptic terminals, each of which
forms a NMJ with a single muscle
Fiber.
Synaptic Terminal
• Contains Molecules of
Acetylcholine (ACh).
• ACh is a neurotransmitter,
chemical released by neurons
to change the membrane
properties of other cells.
Synaptic Cleft
• A narrow space that
separates the synaptic
terminal of the neuron from
the sarcolemma surface.
• Contains Acetylcholinesterase
(AChE) which breaks down
Ach.
Motor End Plate
• The surface of the
sarcolemma that contains
membrane receptors that
bind ACh.
When a neuron
stimulates a muscle fiber,
Heeeeere’s
what happens . . .
The arrival of an
action potential
• Sudden change in the
transmembrane potential
along the axon.
• This stimulates the release
of ACh at the synaptic
terminal.
The release of ACh
• Vesicles that contain ACh,
in the synaptic terminal,
fuse with the membrane
of the neuron & are
released by exocytosis
into the synaptic cleft.
ACh binding at the
motor end plate
• ACh molecules diffuse across
the synaptic cleft & bind to ACh
receptors on the motor end
plate’s surface.
• When ACh binding occurs,
sodium ions (Na+) now can rush
into the sarcoplasm.
Appearance of an action
potential in the sarcolemma
• The Na+ results in an action potential
in the sarcolemma.
• The action potential sweeps across
the entire membrane surface &
travels down each of the T tubules
which triggers the release of Ca2+ at
the terminal cisternae.
• While this is occurring, AChE
removes the ACh.
Return to the initial state
• Even before the action potential
has spread across the entire
membrane, the ACh has been
broken down by AChE.
• This sequence of events can now
be repeated, should another AP
arrive at the synaptic terminal
Normal
Show me the action!
Potential, that is!
What happens at the
neuromuscular junction
when exposed to
botulinum toxin?
Effects of a
Nerve Agent
Atropine
Antidote
What is myasthenia
gravis?