Download Unit 08 Notes

Muscular System
Muscle Contractions
• Neuromuscular Interactions:
Neuromuscular Junction: The site where the motor
neuron and muscle fiber meet is the neuromuscular
junction
The muscle fiber membrane (sarcolemma) forms a
_______
Motor ____
End _______
Plate in which the sarcolemma is tightly
folded and where nuclei and mitochondria are abundant.
Acetylcholine – neurotransmitter released
from the _____
Axon of the neuron.
Acetylcholinesterase – What is it’s function?
Breaks down acetylcholine; stops muscle contraction
Where is it found?
Motor End Plate
Motor neuron and the muscle
Motor Unit: A _______
Fiber it controls make up a motor unit; when
_____
stimulated to do so, the muscle fibers of the motor
unit contract all at once.
• Skeletal Muscle Contraction:
Muscle Contraction involves several components that
result in the shortening of sarcomeres, and the pulling
of the muscle against it’s attachment.
• http://www.sumanasinc.com/webcontent/animati
ons/content/muscle.html
• http://highered.mheducation.com/sites/00724958
55/student_view0/chapter10/animation__sarcome
re_contraction.html
• http://wps.prenhall.com/wps/media/objects/2688
/2752944/Web_Tutorials/25_A01.swf
Myosin consists of two twisted strands with
• The protein _______
globular cross- bridges projected outward along the
strands.
Cross Bridge
Actin is a globular protein with myosin binding sites.
• _______
What two proteins are associated with it?
Tropomyosin
Troponin
4
1
2
7
6
3
5
• According to the sliding filament theory of muscle
contraction, if allowed to, myosin cross bridge attaches
to the binding site on the actin filament and bends,
pulling on the actin filament; it then releases and
attaches to the next binding site on the actin, pulling
again.
• What prevents this from happening continuously?
Aceytlycholinesterase
• Energy from the conversion of ATP to ADP is provided to
the cross-bridges from the enzyme ATPase, causing
them to be in a cocked position.
• Stimulus for Contraction
The motor neuron must release the neurotransmitter
Aceytlycholine
____________________
from its synaptic
Vesicles
Synaptic
_________________
into the _____________
cleft in
order to initiate a muscle contraction.
Daily Warm Up
1.
C Sarcoplasmic Reticulum
___
a. Enzyme that breaks down acetylcholine
2.
G Sarcolemma
___
b. Part of the myosin filament that attaches to actin
3.
F T Tubule
___
c. Net like structure that surrounds each myofibril
and stores Calcium ions (Ca2+)
4.
H
___Troponin
d. Neurotransmitter that triggers a muscle
contraction
1.
I
___Tropomyosin
e. Cytoplasm of a muscle fiber
2.
B Cross Bridge
___
f. Tubes are found around the myofibril and signal
the sarcoplasmic reticulum to release calcium
3.
J Calcium Ion
___
g. Cell membrane of a muscle fiber
4.
E
___Sarcoplasm
h. Protein found on actin that interacts with calcium
ions
5.
D
___Acetylcholine
i. Ribbon like protein on Actin that covers up binding
sites
6.
A
___Acetylcholinesterase
j. Ion that causes troponin and tropomyosin to shift
and expose the myosin binding sites
• Stimulus for Contraction
Protein receptors in the motor end plate detect the
neurotransmitters, and a muscle impulse spreads over
Transverse
the surface of the sarcolemma and into the __________
tubules, where it reaches the Sarcoplasmic
___________ reticulum
• Stimulus for Contraction
Upon receipt of the muscle impulse, the sarcoplasmic
Calcium (Ca 2+to
) the
reticulum releases its stored ___________
sarcoplasm of the muscle fiber.
The high concentration of calcium in the sarcoplasm
Tropomyosin molecules,
interacts with the Troponin
________ and ___________
which move aside, exposing the myosin binding sites on
the actin filaments.
https://www.youtube.com/watch?v=gJ309LfHQ3M
• Stimulus for Contraction
Cross bridges now bind and pull on theActin
Myosin ______________
_____
filaments, causing the sarcomere to shorten.
After the nervous impulse has been received, the enzyme
Acetylcholinesterase
__________________ rapidly decomposes the
acetylecholine.
Then, calcium is returned to the sarcoplasmic reticulum,
and the linkages between myosin and actin are broken.
Contraction cycle
1. Start with a cocked myosin head
1. (ADP and P are attached)
2. Myosin head binds to the actin when troponin
and tropomyosin move to expose the binding
sites
1. (ADP and P are attached)
3. Myosin head goes through the powerstroke
and moves the actin filament
1. (ADP and P detach)
4. Myosin head is stuck until ATP releases it from
the actin filament
1. (ATP attaches; Myosin head releases)
5. Myosin head goes back into cocked position)
1. (ATP breaks down into ADP and P. ADP and P is still
attached to the myosin head)
1. Muscle contractions begin at the neuromuscular junction.
2. The axon of a motor neuron is attached to the motor end
plate of a muscle fiber’s sarcolemma.
3. To create a muscle contraction, acetylcholine is released
from the motor neuron axon. Acetylcholine will trigger a
muscle impulse.
4. The muscle impulse will travel across the sarcolemma and
through the muscle fiber via the T tubules.
5. The muscle impulse travelling through the T tubules will
cause the sarcoplasmic reticulum to release Calcium Ions
into the sarcoplasm.
6. The calcium ions released will attach to troponin and
cause the ribbon like tropomyosin to shift. This exposes
the myosin binding sites necessary for muscle
contraction.
7. Once the myosin binding sites are exposed,
myosin cross bridges will attach to the actin and
perform a power stroke which will move the actin
filaments closer together.
8. The myosin cross bridge is stuck to the actin
filament until an ATP molecule attaches.
9. Breaking ATP into ADP and P will cock the myosin
head. Preparing it for another Power Stroke
10. In order to stop a muscle contraction,
acetylcholinesterase will break down the
acetylcholine.
Reading Review
• Read from your textbook pages 172 – 178.
• On a separate piece of paper, answer the check
your recall questions in complete sentences.
• 175 (1-4)
• 175 (1-4)
• 178 (1-4)
Muscle Contraction Paragraph
• Using the following vocabulary words, write a
paragraph explaining how muscles contract.
• Neuromuscular Junction, Motor End Plate, Synaptic
bulb, synaptic cleft, synaptic vesicles, Acetylcholine,
Sarcolemma, Sarcoplasm, Myofibril, T Tubule,
Sarcoplasmic Reticulum, Calcium Ions, Actin
Filaments, Myosin Filaments, Cross Bridges,
Troponin, Tropomyosin, Power stroke, ATP, ADP/P,
Acetylcholinesterase.
Review Video
• https://www.youtube.com/watch?v=4201SrN0WlY
Daily Warm Up
• List the steps of muscle contraction from 1 to 6. 1 being first and 6 being last.
1. ___ Myosin cross bridges attach to the binding sites, go through a power stroke and
move the actin filaments closer together.
2. ___ Calcium ions attach to the troponin causing the tropomyosin to move and expose
the myosin cross bridge binding sites
3. ___ Acetylcholine is released from the axon of the motor neuron into the synaptic
cleft of the sarcolemma triggering a muscle impulse.
4. ___ When the muscle contraction is over, Acetylcholinesterase breaks down
acetylcholine.
5. ___ The muscle impulse travels across the sarcolemma and down through the T
tubules stimulating the sarcoplasmic reticulum to release Calcium Ions (Ca2+) into the
sarcoplasm.
6. ___ Attachment of ATP to the myosin cross bridge releases them from the binding
sites. The breakage of the ATP cocks the myosin cross bridge preparing it for its next
powerstroke.
Energy Sources for Contraction
ATP: Energy for contraction comes from molecules of
ATP.
This chemical is in limited supply and so
must often be
regenerated.
Creatine Phosphate: As ATP decomposes, the energy from
creatine phosphate can be transferred to ADP molecules,
converting them back to ATP.
Cellular Respiration: The early phase of cellular respiration yields
few molecules of ATP, so muscle has a high requirement for
oxygen, which enables the complete breakdown of glucose in the
mitochondria.
Cross bridges stores oxygen in muscle tissue.
The pigment ______________
What happens to respiration during exercise?
Respiration increases
https://www.youtube.com/watch?v=BR3dDO1Sz0E
Oxygen Debt:
Oxygen deficiency may develop during strenuous exercise, and
Lactic acid accumulates as an ened product of anaerobic
___________
respiration. This acid diffuses out of muscle cells and is carried in
the bloodstream to the liver.
Oxygen debt refers to the amount of oxygen that liver cells
require to convert the accumulated lactic acid into glucose, plus
the amount that muscle cells need to resynthesize ATP and
creatine phosphate to their original concentrations.
Repaying oxygen debt may take several hours.
When a muscle loses its ability to contract during
Muscle
strenuous exercise, it is referred to as ________
fatigue
_________.
This usually arises from the accumulation of
pH
lactic acid in the muscle causing a lowered ____
cramp occurs due to a lack of ATP required to
A muscle ________
return calcium ions back to the sarcoplasmic reticulum so
muscle fibers can relax.
• HEAT: Why does muscle contraction cause so much
heat?
Muscles make up a large proportion of the body and
therefore give off a lot of heat
Muscle Responses:
A muscle fiber remains unresponsive to
stimulation unless the stimulus is of a certain strength,
Threshold
Stimulus
called the _________________
______________.
When a muscle fiber contracts, it contracts to its full
extent, it cannot contract partially. This is called the
All
or ______
none response.
___ __
Muscle Twitch: A single short contraction involving
only a few motor units is referred to as a twitch.
Is this considered a very useful contraction?
No
A muscle fiber receiving a series of stimuli of increasing
frequency reaches a point when it is unable to relax
completely and the force of individual twitches
summation
combine by the process of ____________.
If the sustained contraction lacks any relaxation, it is
tetanus
called a _______________
contraction.
An increase in the number of activated motor units
within a muscle at higher intensities of stimulation is
recruitment
called _______________.
How is this done? Increases the stimulus
A series of twitches
Summation
Tetanic contraction
tone is achieved by a continuous state of
Muscle _______
sustained contraction of motor units within a muscle.
Why would this be useful?
Maintain Posture
Reading assignment
• Use 184 – 187 to complete your notes
• Read: 8.5, 8.6, and 8.7