Transcript How does the muscle get the message?

How does the muscle
get the message?
Nerve Impulse!
 Motor
Neuron –
 Nerves
 Motor
that send messages to muscles
Unit–
 One
(1) motor neuron (branched out) and
all the muscle fibers it controls
Motor Unit
How many muscle fibers are stimulated by this ONE neuron?
Fine or Gross?

Fine motor control –
 Few
muscle fibers controlled by one motor neuron.
 Move
few fibers with each stimulus = fine control
 Fingers

Gross motor control –
 Many

muscle fibers controlled by one motor neuron.
Move lots of fibers with each stimulus – gross
control
 Legs
Where does the message go?
 Neuromusclular
junction:
 Site
where a motor neuron and muscle
come together.
 They Do Not Touch
 The
space between =
– Synaptic cleft (“cliff”)
Who Has What?
 Motor
Neuron:
 Neurotransmitters
= chemicals that carry
the message.
 Acetylcholine – signal that produces
movement.
 Acetylcholine esterase (erases the message)
stops the movement.
 Muscle
Fiber:
 Motor
End Plate = specialized part of the
sarcolemma with chemical receptors.
How Does It All Work Together?
Muscle Contraction
 Nerve
impulse – stimulates the
release of Acetylcholine into the
synaptic cleft
 Sarcolemma – depolarizes (swaps
charged ions) transmits action
potential along T-tubules
 Calcium released from Sarcoplasmic
reticulum
 Myosin
cross bridges attach to actin
 Actin fibers are pulled together
– Shortening the sarcomere
 Acytylcholine
Esterase released –
– Stops impulse (message)
 Calcium
transported back into SR
(ATP is required).
 Myosin detaches from Actin (ATP
required)
 Actin slides back to relaxed state.
Animation: Action Potentials and
Muscle Contraction
All or Nothing!
 Once
a threshold stimulus is sent All
the fibers stimulated will contract
fully.
 Heavy
Load
 Lots
of fibers stimulated (lots of motor
units)
 Light
Load
 Few
fibers stimulated (few motor units)