Today's lab uses human subjects. The classic animal lab is the "frog
nerve-muscle" preparation, one of the labs at University
of Missouri - Columbia. Electrodes
in the gastrocnemius muscle (right) stimulate the muscle directly while
a cuff on the sciatic nerve (left) stimulate the muscle via the nerve. One
tendon is fixed down while the other is tethered
to the force transducer. The force transducer can be calibrated by using
a weight. In another lab, smooth muscle from rabbit gut was studied. A chamber,
an air tube, and a transducer are used for the gut
preparation. The demonstration involved manipulations like atropine to block
were monitored on a computer.
Slide 2 (See Figure 12-1 and Table 12-3 in your text).
1.) Muscle Generates force and motion.
2.) There are three types of muscle:
A.) Skeletal Muscle is striated and arranged in sarcomeres.
-It is under voluntary control (Ca++ and troponin).
-Skeletal muscle is attached to bone and serves to function with a few sphincters
(the external sphincter on the bladder, which controlled by somatic motor
-Skeletal muscle cells are multinucleated and have large, cylindrical fibers.
B.) Cardiac Muscle is striated and arranged in sarcomeres.
-It is under involuntary control (Ca++ and troponin).
-Cardiac muscle is the tissue of the heart.
-Cardiac muscle cells are uninucleated and have short, branching fibers
(Example: Purkinje fibers that rapidly conduct electrical signals at the
base of the heart).
C.) Smooth Muscle is non-striated and arranged in long bundles.
-It is under involuntary control (Ca++ and Calmodulin.Remember from Cell??)
-Smooth muscle comprises the walls of hollow organs; present in some sphincters
(the internal sphincter on the bladder, which is actually a continuation
of the bladder wall. Also, it is normally contracted).
-Smooth muscle cells are uninucleated and are arranged in small, spindle-like
Slide 3 (See Figure 12-2)
Skeletal muscle can be arranged into flexors and extensors.
-Flexors pull the center of two bones closer together, like the biceps brachii
muscle bringing the humerus and ulna closer together.
-Extensors push the center of two bones farther apart, like the triceps
brachii muscle pushing the humerus and ulna farther apart.
Slide 4 (See Figure 12-3 a)
This figure shows the macro-organization of skeletal muscle.
-Skeletal muscle (seen here attached to a tendon) is comprised of muscle
-Muscle fasicles are comprised of muscle fibers.
-Muscle fibers are comprised of myofibrils.
Slide 5 (See Figure 12-3 b)
This figure shows the micro-organization of the muscle fiber.
-The sarcolemma is the cellular membrane for muscle fiber.
-The sarcoplasm is the cytoplasm of the muscle fiber.
Again, myofibrils comprise the basis of each muscle fiber.
-The sarcoplasmic reticulum wraps around each myofibril. Terminal
cisternae are located at each end of the sarcoplasmic reticulum.
The sarcoplasmic reticulum release calcium ions, while the terminal
cisternae concentrate the calcium ions. The t-tubules (transverse
tubules) are a continuation of the fiber membrane (see the holes in
Slide 6 (See Figure 12-3 c)
This figure shows the composition of a myofibril.
-H Zone=myosin only.
-M Line=the attachment site for the thick filaments.
-A Band=entire length of thick filament (notice that this includes
-I Band=actin only.
-Z Disk=attachment site for thin filaments (has protein).
Therefore, one sarcomere is found between two Z Disks.
Titin and Nebulin help stabilize the filament structure and
return the sarcomere to it's resting state.
Troponin and Tropomyosin regulate sarcomere function.
H Zone and I Band shorten, while the A Band remains constant.
Slide 7 (See Figure 12-5)
This figure shows the two and three dimensional arrangement of a sarcomere.
Again, I Band has thin filaments.
H Zone has thick filaments only.
M Line has thick filaments and attachment proteins.
A Band has thick and thin filaments.
Slide 8 (See Figure 12-9)
This figure explains the events of a contractile cycle.
1.) The Rigor State is the state where no nucleotide (ADP or ATP)
is bound to the myosin head. The myosin heads are tightly bound to G-actin.
[The rigor state is actually the state of "rigor mortis", which
is when the body has no ATP available to complete the contractile cycle.
A body with rigor mortis is therefore very stiff.]
2.) ATP binds to the myosin head and myosin detaches from G-actin
(change in the binding affinity.
3.) ATP is hydrolyzed to ADP and Pi (inorganic phosphate).
4.) Myosin weakly attaches to G-actin because energy is released
from the hydrolysis of ATP. ADP and inorganic phosphate are still bound
to myosin, which provides the potential energy to drive a power stroke.
5.) Pi releases from myosin and actin is pushed towards the center
of the sarcomere. This is Cross-bridge tilting because the myosin
and actin binding angle shifts from 90 degrees to 45 degrees.
6.) ADP is released and myosin is again tightly bound in the rigor
Slide 9 (See Figure 12-10)
This figure shows how contraction is actually regulated.
-Tropomyosin is a long protein that wraps around the actin filament. Tropomyosin
blocks the binding site on actin so that the myosin heads cannot complete
a contractile cycle.
-Troponin is bound to tropomyosin and regulates its position.
-Actually, when tropomyosin is turned "off", the myosin heads
are still weakly bound to actin. The weak binding is not enough to complete
the power stroke.
-When Cytosolic Calcium increases from Excitation-Contraction Coupling,
it binds to troponin. Troponin moves tropomyosin and muscle contraction
can take place.
(1) An action potential in the spinal motor neuron goes to the neuromuscular
junctions of all the muscle fibers (cells) in the motor unit (all the
striated muscle cells innervated by one spinal motor neuron.
(2) Vesicles of acetylcholine
are released and bind to nicotinic acetylcholine receptors (channels) on
the end plate.
Excitation Contraction Coupling (Figure 12-11)
1. Initiated by Acetylcholine from the somatic motor neuron onto the motor
2. This opens Na and K channels in the end plate and creates a positive
charge on the muscle fiber due to more Na being pumped in that K out because
the electrochemical driving force is greater for Na than for K
3. This creates an "end-plate" potential which then initiates
a muscle action potential
4. The action potential goes down the t-tubules on the surface of the muscle
fiber by the opening of voltage gated Na channels
5. Eventually the action potential causes the dihydropyrididne (DHP) receptor
to open a mechanically linked Ca release channels on the sarcoplasmic reticulum.
The release channels are called ryanodine receptors.
6. The stored Ca then moves into the cytoplasm (which is down its chemical
Free cystolic Ca levels are typically very low, but after an action potential
they typically increase about 100 times their initial amount.
7. Because the cystolic Ca is so high, Ca can bind to troponin which allows
tropomyosin to moves to its "on" position and contraction occurs
the way that was just described.. using the power strokes to lift the myosin
heads off of the actin filament and reach towards the z disk to contract
8. Relaxation begins when the sacroplasmic reticulum pumps Ca back into
the system using a Ca ATPase. When the cystolic Ca levels decrease Ca loses
its binding affinity for troponin and tropomyosin slides back into place
and the fiber relaxes.
Twitch (Figure 12-12)
1. The timing of electrical and mechanical events is seen here.
2. It is easy to see that the somatic motor neuron (although it operates
in the same way by moving an action potential by sodium voltage gated channels)
actually moves much faster than the muscle action potential. Also you can
see that the nerve cell action potential creates a single muscle action
potential which leads to one muscle contraction which is called a twitch.
3. This short delay here is called the latent period (time between muscle
action potential and muscle contraction)
4. The speed of muscle twitches depends on the particular fiber
Muscle Fiber Types (Table 12-2)
1. Muscle fibers are divided groups based upon their speed of contraction,
and their resistance to fatigue.
2. There are 3 types of fibers a) Slow Twitch Oxidative (Red Muscle) b)
Fast Twitch Oxidative (Red Muscle) c) Fast Twitch Glycolytic (White Muscle).
3. The term fast twitch means that they develop tension 2 to 3 times faster
than slow twitch muscles. However fast twitch muscle contractions do not
last as long as slow twitch. Actually slow twitch muscles may last up to
10 times as long.
4. Fast twitch muscles fatigue quicker than slow twitch muscles due to the
fact that fast twitch muscles rely on ATP and anaerobic glycolosis, which
leads to a back up of lactic acid. Lactic acid contributes to acidosis thus
leading to fatigue.
Slow twitch rely on oxidative phosphorylation for production of ATP. They
also have more mitochondria and more blood vessels to bring in oxygen.
5. Slow twitch have the red color because of the fact that there are more
blood vessels and more myoglobin (which gives the red color) also they are
of a smaller diameter so it takes less distance for blood to get to the
mitochondria. Fast twitch muscles are white because there is less blood
flow and less myoglobin and they have a larger diameter.
6. Fast Twitch oxidative Red Muscle-smaller that gylcolytic, contain some
myoglobin, and use a combo of oxidative and glycolytic metabolism to make
ATP. Fast twitch oxidative are more fatigue resistant than fast twitch glycolytic.
In previous years, in this lab, we stimulated the forearm of subjects with
small electrical pulses. Phan and Nicole got this
series from Matt M in response to increasing stimulation at low frequency
Here is the result
from that from Joel and his lab partners for tetanus using the force transducer
1. 'A' shows that muscle relaxes completely between twitches in single twitch
stimulation when muscles have time to relax
2. B shows that if two stimuli happen close to one another, then the muscle
contraction is additive. Unlike in the nerve system, where if an action
potential is going, there is a refactory period where the nerve will not
3. C shows that eventually muscles get to a point where the stimuli no longer
add up. That is called maximum tension. C demonstrates unfused, or imcomplete
tetnus because the muscle is given a brief relaxation.
4. D is called compete tetanus and shows that the stimulation rate is so
fast that the muscle cannot relax. As you can see eventually the muscle
fatigues even though the stimuli are still coming.
Today's Lab = Knee Jerk Reaction Figure 13.7
1. Knee Jerk Reflex- Stimulus is the hammer hitting the pattelar tendon.
The tap stretches the muscle fibers on the front of the thigh. Stretching
sends an action potential through to the spinal cord. (Afferent path). There
are then two different Efferent paths away from the integrating center in
the spinal cord. One goes through a somatic motor neuron to the quadriceps
and tells the quadriceps to contract. The other goes to the Hamstring and
tells the hamstring to relax. The response of the first efferent path is
that the quadriceps swing the lower leg forward, and the response to the
second efferent path is that the hamstring allows the quadriceps to swing
the foot forward by relaxing.
Motor units (Fig. 12-18)
1.There could be more than one type and numerous motor neurons attaching
to one muscle fiber. This allows the muscle to do a variety of muscle contractions
and strengths of contractions.
2. This slide demonstrates the way a muscle contracts. First, it starts
in the integrating center (spinal cord brain) and then an efferent stimulus
is sent to your muscles via these motor neurons and lastly your muscle contracts
by excitation coupling.
TODAY'S MUSCLE LAB
(1) You should become versatile with the use of the electrophysiological
(2) You will achieve the above in the context of learning muscle physiology.
(1) This will be our first, after the tutorial, use of the LabScribe for
recording electrical signals
(2) We will generate strong responses with the hand dynamometer feeding
(3) We will record reflexes, and the plethysmograph will show us the stimulus
Quiz and midterm questions from 2005 - 2006 relating to this lecture,
interactive physiology and lab.
List the three types of muscle found in the body.
What are bundles of skeletal muscle called?
A.) blocks the binding sites on myosin, preventing actin cross-bridge
attachment at high Ca++ levels.
B.) blocks the binding sites on actin, preventing myosin cross-bridge
attachment at low Ca++ levels.
C.) blocks the binding sites on actin, preventing myosin
cross-bridge attachment at high Ca++ levels.
D.) blocks the binding sites on myosin, preventing actin cross-bridge
attachment at low Ca++ levels.
E.) assists the binding of actin to myosin at low Ca++ levels.
The M lines serve as the attachment site for __________, while the Z disks
serve as the attachment sites for ___________.
Name the state when no nucleotide is bound to the myosin head.
The Rigor State
Skeletal muscles are commonly defined as flexors and extensors. The biceps
would be a __________, while the triceps would be a __________.
What is the regulatory protein that helps to determine the position of tropomyosin?
What determines the speed of relaxation of a muscle fiber?
The rate that the Ca++ ATPase pumps Ca++ into the sarcoplasmic reticulum
How large is the increase in Ca2+ into the cytosol after it is released
from the sarcoplasmic reticulum.
Name four differences between fast twitch glycolytic muscle and slow twitch
See 12.2 in your book
What is happening during the "latent" period?
The Ca++ is being released into the cytosol
What is the stimulation of additional motor units for increased speed and
What is the difference in desired function between large motor units and
small motor units?
Fine motor skills versus gross movement
Skeletal muscles are commonly arranged into flexors and extensors. The quadriceps
would be a _flexor_, and the hamstring would be a_extensor_.
__Tropomyosin__ blocks the binding site on actin so that the myosin
heads cannot complete a contractile cycle.
Calcium has to bind to troponin/tropomyosin before muscle contraction
Name the state during the contractile cycle when no nucleotide is bound
to the myosin head.
The Rigor State
When inorganic phosphate is released from myosin,
a.) Cross bridge tilting occurs because the myosin-actin binding angle shifts
from 90 degrees to 45 degrees.
b.) Myosin is pushed towards the center of the sarcomere.
c.) Actin is pushed towards the center of the sarcomere.
d.) Two of the above.
Matching--- There may be more than one correct answer.
1.) H Zone ___ B,G A.) Actin Only
2.) M Line ___ D B.) Myosin Only
3.) A Band ___ E,F, H C.) Attachment site for thin filaments
4.) I Band ___ A,G D.) Attachment site for thick filaments
5.) Z Disk ___ C E.) The entire length of thick filaments
F.) Actin and Myosin
G.) These bands shorten
H.) This band is constant
Muscle fibers are comprised of _myofibrils_.
The cellular membrane of a muscle fiber is the__sarcolemma__, while
the cytoplasm of a muscle fiber is the__sarcoplasm__.
Name one of the two filament proteins that stabilize the filament structure
and help return the sarcomere back to its resting state.
Titin or Nebulin
For most people, although the force transducer worked for the muscle lab,
the hand dynanometer did not. Why not?
we could not stimulate merve and get a full grip, so we measured twitches
Depletion of what chemical after death causes rigor mortis?
What initiates EC coupling in muscle cells?
Acetylcholine from the somatic motor neuron onto the motor endplate
_End plate potential__________ initiates muscle action potential.
Which action potential moves faster, muscle or neural?
What color are fast twitch muscles?
What type of metabolism do fast-twitch muscles utilize?
Put the three different muscle types into the correct order from easiest
fatigued to most fatigue resistant.
Fast twitch (glycoltyic) Fast Twitch Oxidative Slow Twitch
What does lactic acid contribute to?
What happens when two muscle contractions happen close to each other? How
is this different from what happens in the nervous system?
The sum together (summation). Summation does not occur in the nervous system
because of the mandatory refractory period.
What determines the twitch speed of muscles?
Describe the difference between complete tetanus and incomplete tetanus?
Complete tetanus there is no relaxation between twitches. In incomplete
tetanus there is some relaxation inbetween contractions.
In the knee jerk reaction, we are hitting the __patellar_____________ tendon.
In the knee jerk reaction, what are the efferent paths and what is the afferent
Afferent- stretch of tendon sensory neuron to spinal cord
Efferent - 1. Somatic motor neuron to quadriceps muscle to contract
- 2. Interneuron inhibiting somatic motor neuron to hamstring to relax
What is recruitment?
Stimulation of additional motor units for increased speed and contraction
Similar to the situation for breakdown of polysaccharides and proteins,
what type of reaction takes off a phosphate from ATP to convert it to ADP.
Not counting the neuromuscular junction, how many synapses are present in
the knee jerk reflex?
The Z disc is a connection point for which protein?
Which protein does Ca2+ bind to, thus exposing the binding site on actin?
In the myofibril, what is the contractile unit that extends from Z disc
to Z disc?
Will a flexor bring the centers of the connected bones together or push
bring them together
Why did we measure the weights of books and place them on the grip ball?
to calibrate the computer
When an inorganic phosphate is released from the myosin binding site, what
Of the 3 muscle fiber types, which would a person use to exert all of their
energy in doing
one very heavy bench press at the gym?
fast twitch glycolytic
What is the name of the protein that gives muscles their dark red color?
myoglobin (also hemoglobin and cytochrome)
In the lab, how long did it say that synaptic transmission takes?
When a muscle goes into tetany, what is happening electrically?
actin potentials are coming one after another so soon that twitches summate
Name the receptor in the sarcoplasmic reticulum that is mechanically linked
What is the stimulus that activates the DHP receptor?
During contraction, will actin slide toward or away from the center of the
toward the center
A motor neuron and all of the muscle cells that are stimulated by that motor
referred to as a(n) ____________________.
When muscle relaxation begins, what type of protein/enzyme pumps Ca2+ back
Acknowledgements - Thanks to Chris Hawkins and Katie Richards, 2005 TAs,
for part of this lecture.
This page was last updated 1/25/08
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