Do Now:
1. What is the difference between
actin and myosin?
2. Explain how a muscle feels when
it contracts. Then draw a picture of what you believe a muscle looks like
before and after contraction.
How A Muscle
Contracts:
A True Story…
Today’s
Objective: SWBAT explain the process of a muscle cell contraction including
sliding filament theory.
4 Steps of a Muscle Contraction
1.Nerve
Impulse Crosses the Neuromuscular Junction
●
2.Acetylcholine
Attaches to the Sarcolemma
●
3.Action
Potential Causes Muscle Contraction
●
4.Muscle
Returns to Normal
5.Nerve Impulse Crosses the Neuromuscular Junction
All skeletal muscle contractions begin with the nervous system.
A nerve impulse (or message) is sent from the nervous system to
the muscle via a neuron (nerve cell).
1.Nerve Impulse Crosses the Neuromuscular Junction
The
nerve impulse reaches the end of the neuron called the axon terminal.
The axon
terminal forms a junction with the sarcolemma of a muscle cell called the Neuromuscular Junction
The axon terminal & the
sarcolemma NEVER TOUCH!
The gap between them is a synapse called the synaptic cleft.
Neuromuscular Junction = Axon Terminal, Synapse, and
Sarcolemma.
The axon terminals release a neurotransmitter across the
synaptic cleft.
A neurotransmitter is a chemical that carries the message of the impulse.
The neurotransmitter that stimulates skeletal muscle
contraction is Acetylcholine
(ACh)
Turn To Your Partner
Partner A – Describe the following new vocabulary terms: AXON
TERMINAL, NEUROMUSCULAR JUNCTION, SYNAPTIC CLEFT, NEUROTRANSMITTER.
Partner B – Describe the first step in muscle contraction.
STEP
2:
Acetylcholine Attaches to the Sarcolemma
2. Acetylcholine Attaches to the Sarcolemma
Acetylcholine
crosses the synaptic cleft & attaches to receptors on the sarcolemma.
Acetylcholine
makes the sarcolemma more permeable to
sodium ions.
Sodium
ions rush into the cell.
The increase of sodium ions in the
cell causes the cell’s charge to change from a negative
(-) charge to a positive (+) charge.
This
change causes a surge of electrical current called an Action Potential.
TURN TO YOUR PARTNER
Partner A – Discuss what is acetylcholine and what does it
cause within the muscle cell?
Partner B – Discuss what happens to the sodium ions around the
cell and why is that important for muscle contraction?
Step 3:.
Action Potential Causes Muscle Contraction
3. Action Potential Causes Muscle Contraction
ACh causes the sarcoplasmic reticulum to release Calcium
ions into the sarcoplasm.
The calcium ions bind to the
regulatory proteins on the thin filaments which allows the myosin to attach to
the actin.
Myosin
attaches to actin and pulls the actin closer to the center of the sarcomere.
ATP is
used by the myosin to pull the actin closer.
Turn To Your Partner
Partner A – Discuss what the role of calcium ions is in the
muscle cell contraction and why they are important?
Partner B – Discuss how the myosin and actin work together to
create a contraction.
Sliding Filament Theory
Process by which myosin heads pull actin towards the center of
the sarcomere
All-Or-None Principle
If a stimulus is strong enough to cause a contraction, the
whole muscle fiber will respond or not all.
TURN TO YOUR PARTNER
Partner A – Explain the All-OR-None Principle
Partner B – Explain the Sliding Filament Theory (SFT)
Step 4:
Muscle Returns to Normal
4. Muscle returns to normal
While the action potential occurs:
acetylcholine is broken down
Calcium
ions are reabsorbed
The
electrical charge in the cell returns to negative
Tell Your Partner
Alternate starting with Partner B the three things that happen
to return the muscle cell back to its normal non-contracted state.
Animation Review
FOLDABLE SUMMARY SHEET
Independent Practice
Questions in your notes
Cartoon of Muscle Contraction- Use Textbook pgs. 160-163 as
reference
Using at least 8 frames you will create a cartoon that depicts
the process of a muscle contraction.
Within your cartoon you need to explain the following:
The 4 Steps of the Muscle Contraction
Neuromuscular Junction
Acetylcholine and its effects
Action Potential and its effects
Sliding Filament Theory
You will also need to use the following vocabulary at least
once each in your cartoon:
Axon Terminal, Neurotransmitter, Sodium Ions, Calcium
Ions, Regulatory Proteins, Permeable
Number each Frame in the top left corner
Exit Ticket
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