Advanced anatomy Lab 1 practical

Which of the following does not affect the twitch duration in fast and slow twitch fibers? Number of mitochondria Speed of ATP utilization Speed of Ca2+ release Speed of Ca2+ reuptake

Number of mitochondria

motor endplate diease

NMJ botulism myasthenia gravis (an auto-immune disease resulting most commonly from antibodies to ACh receptors.Muscles controlling eye and eyelid movement, facial expression, chewing, talking, and swallowing are especially susceptible. The majority of patients also have thymus abnormalities.)

Intramuscular EMG

Needle electrodes are inserted through the skin into the muscle - records individual muscle action potentials measured using an extracellular electrode (needle).

Unlike the discrete waveform from an ECG, the EMG waveform is irregular. Why is this?

The EMG record muscles that are not contracting at the same time while the ECG is recording the muscle that contracts all at the same time.

Elasticity

The ability to bounce back after being stretched

Look at the latency for ulnar nerve stimulation at the wrist and at the elbow. How do these latencies differ? Why do you suppose this is?

The distance from the elbow to the muscle is greater than the wrist to the muscle. This will affect the latency. The latency is the time it takes for the nerve impulse to travel from the stimulated area to the muscle.

Above is an EMG trace. What does an EMG record? The mechanical contraction of skeletal muscle fibers. The electrical potential of the motor nerves supplying skeletal muscle fibers. The electrical potential generated by skeletal muscle fiber activity.

The electrical potential generated by skeletal muscle fiber activity.

_ is the response of recruitment of motor units. It involves one complete cycle of contraction and relaxation. _ occurs following the recruitment of all available motor units.

Twitch, Maximum twitch

In skeletal muscle, what is a minimum unit of contraction caused by a single action potential called? Summation Tension Tetanus Twitch

Twitch

Summation

Twitch force can be increased by increasing the number of motor units firing simultaneously. This additive effect of muscle stimulation is called_

If the rate at which energy is demanded is low, then energy production is _ , utilizing oxygen.

"aerobic"

Skeletal muscle is sometimes called _ because it is the only type of muscle under conscious control.

"voluntary muscle"

Impaired skeletal muscle function may be a result of disorder in the central nervous system

(e.g, strokes, Parkinson's disease, multiple sclerosis).

transducer

records signals - Transducers are sensors that convert biological signals into electrical analog signals. Biological signals that require amplification, filtering, and isolation are pre-processed by signal conditioners such as the Bio Amp or Spirometer Pod

process of progressively activating motor units is called _

recruitment.

The functional units of skeletal muscle cells are called _ and they are found in myofibrils.

sarcomeres

When a muscle contracts, the sarcomeres _ as actin and myosin molecules slide past each other. This is the sliding filament theory of contraction.

shorten

Did you know? With progressively increasing simulation, motor units are recruited based on _. That is, smaller motor units are recruited first. This was first described by Elwood Henneman following his studies on cats.

size.

The _ the motor unit, the finer the control of movement in that muscle. (fingers and eyes)

smaller

a smooth contraction many times stronger than a single twitch: a _ The muscle is now said to be in a state of _

tetanic contraction, tetanus

Starting with release of ACh from the NMJ, arrange the events below in the order in which they would occur.

-release of ACH from neuromuscular junction -binding of ACH to nicotinic receptors on motor endplate -opening of cation selective channels in motor endplate -endplate depolarization -depolarization of muscle cell membrane -raised intracellular CA2+ concentration -muscle contraction

Based on your results and calculations for nerve conduction velocity, how long would it take for a nerve impulse to travel from the spinal cord to the big toe? Assume that the distance traveled is 1 meter. 1 / 2

0.03 or 30ms

When _ fails to keep pace with _ usage, muscles contract less and less effectively. Ultimately, muscle fatigue sets in and muscle activity ceases, even though the muscle may still be receiving stimuli.

ATP production, ATP

What is the approximate conduction velocity of motor nerves? 2 m/s 10 m/s 50 m/s

50 m/s (40-60)

Which statements are true of summation? A second nerve stimulus occurs before the muscle has had time to relax (i.e., before cell Ca2+ concentration has been restored to resting values). A second stimulus is delivered while the nerve axon is depolarized. A second stimulus occurs while the muscle cell membrane is depolarized. More motor units are recruited.

A second nerve stimulus occurs before the muscle has had time to relax (i.e., before cell Ca2+ concentration has been restored to resting values).

Which of the following best describes a motor unit? All the nerve fibers and muscle fibers in a single muscle bundle. A single motor neuron and all the muscle fibers that it innervates. One muscle fiber and its single nerve fiber. The neuron that provides the CNS with information on the state of contraction of the muscle.

A single motor neuron and all the muscle fibers that it innervates.

_ muscles are sometimes called "prime movers" as they are the primary muscle responsible for generating movement through their contraction.

Agonist

Which tiny electrical signals can you record with the Bio Amp? ECG EEG EMG All of the above

All of the above

What signal does the pulse transducer "transduce" into an electrical signal? The changes in force generated by the contraction and relaxation of the heart. The changes in pressure from pulsatile blood flow in the arteries. The sounds of the heart valves closing. All of the above.

All of the above.

Which of the following factors have been suggested as contributing to muscle fatigue? Loss of "central drive". Reduction in calcium release in excitation-contraction coupling. Reduction in muscle blood flow owing to compression of blood vessels. All of the above.

All of the above.

In the absence of oxygen, glycolosis ("sugar splitting") breaks down glucose two and a half times faster than during aerobic respiration.

Anaerobic glycolysis

_ muscles control (or oppose) specific movement, and return the muscle to its initial position.

Antagonist

"What happens when the interval between two electrical stimuli to a nerve supplying a muscle is progressively decreased?"

As the intervals were reduced the twitches got closer together. Each curve, which represents a response to the stimuli, got closer until they finally became one. This represents summation which is when the muscle is unable to completely relax before the next stimulus occurs.

A milder version of the disease, _, arises from deletions in the dystrophin gene that permit synthesis of a shorter but semifunctional protein.

Becker's muscular dystrophy

During sustained skeletal muscle contraction, can you think of three places in which true fatigue might occur?

Blood vessels Metabolic change Reduction of Ca

The removal of which ion causes the muscle to relax after contraction? Ca2+ K+ Na+

Ca2+

The gene codes for dystrophin, a protein that connects the cell cytoskeleton to the extracellular matrix. Defects in dystrophin result in an excess of _ entering muscle cells leading to damage to mitochondria, which leads to cell death.

Ca2+ions

A child has recently been diagnosed with Duchenne muscular dystrophy, an X-linked, recessive condition. The parents are receiving genetic counseling prior to planning another pregnancy. Which of the following statements includes the most accurate information? Duchenne muscular dystrophy is an X-linked recessive disorder, so both daughters and sons have a 50% chance of developing the disease. Duchenne muscular dystrophy is an X-linked recessive disorder, so daughters have a 50% chance of being carriers and sons a 50% chance of developing the disease. Each child has a 1 in 4 (25%) chance of developing Duchenne muscular dystropy. Sons only have a 1 in 4 (25%) chance of developing Duchenne muscular dystropy.

Duchenne muscular dystrophy is an X-linked recessive disorder, so daughters have a 50% chance of being carriers and sons a 50% chance of developing the disease.

Now you have observed a muscle twitch, can you explain what you are seeing in the EMG and Force channels? As the nerves were stimulated, the muscle contracted and resulted in a twitch response recorded on the graphs. In the _ channel, you can see the compound muscle's _ . In the _ channel, you can see the muscle _ that is generated by the arrival of the CAMP, a derivative of ATP.

EMG, action potential, Force, twitch

Which statement about what happens when a motor nerve is stimulated, is false? As the stimulus strength is increased, more of the nerve fibers are stimulated until finally all are stimulated. As the stimulus strength is increased, the contractile force of the muscle increases up to a maximum force. Either all or none of its constituent nerve fibers are stimulated.

Either all or none of its constituent nerve fibers are stimulated.

What does EMG record? Contractions of the innervated muscle fibers. Electrical activity of the innervated muscle fibers. Electrical activity of the motor nerves supplying the muscle fibers.

Electrical activity of the innervated muscle fibers.

Surface EMG

Electrodes are placed on the skin's surface.

What happens to ACh in the synaptic cleft?

In the synaptic cleft, acetylcholinesterase breaks down (hydrolyzes) ACh into acetate and choline, which terminates the local membrane depolarization. Choline is then taken up by the nerve terminal to be recycled in the synthesis of more ACh.

How can muscle fibers show a range of responses to different levels of stimulation? A new contraction can occur only after the resting condition is reached. Each muscle fiber contraction is all or none. Individual twitches in the same fiber can summate. Following stimulation, the fiber stays contracted.

Individual twitches in the same fiber can summate.

Which statement is true of a single motor neuron? It innervates one motor unit. It may innervate a number of motor units.

It innervates one motor unit.

Which of the following statements regarding acetylcholine at the neuromuscular junction is true? It causes opening of ion channels on the pre-synaptic membrane. It is broken down by acetylcholinesterase. It is released from muscle cells. It is taken up by endocytosis into muscle cells.

It is broken down by acetylcholinesterase.

Which statement is true regarding muscle twitch? Following maximal nerve stimulation, it represents the greatest force that the stimulated muscle can produce. It is only seen following peripheral nerve stimulation. It is the normal type of contraction in a functioning skeletal muscle.

It is only seen following peripheral nerve stimulation.

Which describes the phenomenon of "coactivation"? It is the relaxation of the antagonist muscle during the contraction of the agonist muscle. It is the simultaneous contraction of other agonist muscles. It is the weaker contraction of the antagonist muscle during the contraction of the agonist muscle.

It is the weaker contraction of the antagonist muscle during the contraction of the agonist muscle.

In skeletal muscle, ATP is not generated through: Aerobic metabolism Anaerobic metabolism Breakdown of phosphocreatine Lactic acid metabolism

Lactic acid metabolism

The image to the right depicts a motor neuron along with all of the muscle fibers it innervates. What is this called? Motor axon Motor unit Neuromuscular junction

Motor unit

What occurs during an isometric contraction? Muscle shortens. Muscle length is unchanged. Muscle lengthens. Muscle may either lengthen or shorten.

Muscle length is unchanged.

What occurs during an isotonic contraction? Muscle length is unchanged. Muscle may either lengthen or shorten.

Muscle may either lengthen or shorten.

is associated with various combinations of motor, sensory, and autonomic dysfunction.

Peripheral neuropathy

The botulinum toxin: Is given in large doses in the cosmetics industry. Is relatively non-toxic. Produces muscle paralysis by inhibiting the release of acetylcholine from muscle endplates.

Produces muscle paralysis by inhibiting the release of acetylcholine from muscle endplates.

What causes the ratched action of skeletal muscle contractions? Attachment of ATP on the myosin head. Release of Pi from the myosin head. The formation of a cross-bridge between the actin and myosin.

Release of Pi from the myosin head.

How do you relieve tired and achy muscles after intense exercise? Drink highly caffeinated beverages to regain your energy. Keep pushing through the pain. Rest the muscles to allow blood flow to carry away the lactic acid, which needs to be broken down in the liver.

Rest the muscles to allow blood flow to carry away the lactic acid, which needs to be broken down in the liver.

How many muscle fibers may a single motor neuron innervate? Only one muscle fiber Several muscle fibers

Several muscle fibers

When the volunteer contracts his biceps, what activity would you expect to record in the electrodes over his triceps muscle? (coactivation) As much as in the biceps None Some

Some

How is acetylcholine removed from the synaptic cleft? Acetylcholine is broken down by acetylcholinesterase in the plasma. Acetylcholine simply diffuses away from the synaptic cleft. The enzyme acetylcholinesterase hydrolyzes the acetylcholine within the synaptic cleft. There is a reuptake pump for acetylcholine on the presynaptic membrane.

The enzyme acetylcholinesterase hydrolyzes the acetylcholine within the synaptic cleft.

threshold stimulus

The minimal strength required to cause a contraction

In a person with a motor endplate disease: Muscle fasciculations (spontaneous twitches) are common. There are no sensory changes. Weakness normally first develops in the limb muscles.

There are no sensory changes.

Why would there be a lag between the raw data signal and the channel calculation signal that you see on screen?

There is a lag because the system needs time to process the number of beats.

Which statement regarding evoked EMG is true? The amplitude of the measured EMG is independent of the number of motor units recruited. There is synchronous excitation of the muscle fibers innervated by the stimulated nerve.

There is synchronous excitation of the muscle fibers innervated by the stimulated nerve.

A short period of rapid electrical stimuli is used to observe muscle fibers contracting continuously (tetanus). Chemical agents can cause tetanus by interfering with the motor neurons. These agents include a toxin produced by the soil bacterium Clostridium tetani. One of the symptoms of these agents is called "spastic paralysis". Explain in your own words why these agents would have a negative effect on you and your muscles.

These agents would have a negative effect on our muscles because if the muscles involved in breathing (such as the diaphragm) were affected, that would simply lead to death. They can also tighten the muscles, slowing down reactions and movement, and cause muscles withdrawals.

Latency

Time it takes for a bit to travel from its sender to its receiver.

Which statement about muscle contractions is false? An action potential in the muscle cell activates contraction by releasing Ca2+ within the muscle. A single action potential at the neuromuscular junction is sufficient to cause a muscle to twitch. Summation of twitches leads to a graded increase in the tension that can be generated by a single muscle fiber. The tension generated by a muscle can be varied by controlling how many of its motor units are active. When maximum muscle tension is achieved, no ATP is required to maintain that level of tension.

When maximum muscle tension is achieved, no ATP is required to maintain that level of tension.

RMS

You will have noticed that in the raw EMG signal, values fluctuate about and below zero. The mathematical "trick" to deal with this is to square all the values, for the square of a negative value gives you a positive one. Then you can add all of the squared values, take their mean and then the square root of that mean to give you an indication of the strength of the contraction at any time - hence the description of this manipulation, the root mean square (RMS).

Duchenne's muscular dystrophy

a recessive X-linked condition that usually develops in young boys before the age of 5. As well as the effects on skeletal muscle, cardiac muscle can also be affected.

electrical stimulation of the median nerve at the wrist results in contraction of the _ muscle on the palmar surface of the hand.

abductor pollicis brevis

Excitability

ability to respond to stimuli

Contractibility

ability to shorten/contract

extensibility

ability to stretch/extend

Autonomic dysfunction

abnormal blood pressure abnormal heart rate sexual dysfunctions (not symptoms = muscle spasms, sweating, balance)

myopathy

affects the muscle itself Duchenne muscular dystrophy

neurological disorder

affects the nerves damage to myelin sheath ALS

during a bicep curl, the bicep acts as the _ muscle while the tricep acts as the _

agonist, antagonist

skeletal muscle

are essential for locomotion. They also work to maintain posture, stabilize our joints, and produce heat for maintenance of internal body temperature. Hence, conditions which affect the muscular system affect many aspects of our daily functioning.

For effective stimulation to occur, the two pads of the stimulating bar electrode should be aligned along the _ length. If the stimulus status light changes in color from green to _ , you will need to put more electrode paste on the pads.

arm's, yellow

Motor units fire _. This means that, when very few motor units are firing, there may be times, with exceedingly weak contractions, when only a single motor unit is firing at any one time. So it is possible that the activity of a single motor unit can be seen in an EMG.

asynchronously. (helps prevent fatigue)

The role of the _ in muscle activity explains why, in extreme situations, some people can show "super-human" strength for brief periods.

central drive

How would neuromuscular transmission be affected in the presence of an acetylcholinesterase inhibitor?

it would be prolonged

Clinically, the breakdown of muscle may be indicated through raised levels of

creatine kinase.

muscular dystrophy. (false)

detected during adulthood (true) muscle weakness is caused by a damaged protein symptoms become more pronounced over time there is no cure calves may be enlarged no sensory changes

The hand _ and PowerLab used to measure the decline in maximal force during a sustained contraction.

dynamometer

We can assess the health of muscles using _. _ is a recording of the electrical activity of skeletal muscle at rest and during contraction. The strength and pattern of _ recordings can be used to diagnose a variety of muscle conditions.

electromyography (EMG), EMG, EMG

External stimulation with muscle recording is called

evoked EMG. The stimulated muscle fibers all contract at the same time.

Anaerobic respiration produces _ (from pyruvate) in the muscles, causing fatigue.

lactate- and H+ ions

Neurons carry electrical signals that__ the muscles. This triggers the release of a neurotransmitter which results in _ of the muscle, leading to _. The neuron, along with the muscle fibers it innervates, constitutes a _.

innervate, depolarization, contraction, motor unit

Botulism

is a paralytic illness caused by the botulinum toxin, a neurotoxic protein produced by Clostridium botulinum. The toxin acts directly on the NMJ to inhibit acetylcholine release, resulting in muscle paralysis. Botulism is a "descending" paralysis, so the first muscles to be affected are those controlling eye and eyelid movement, facial expression, chewing, talking, and swallowing. This is followed by muscles in the torso (including lungs) and arms and finally, the legs. Botulinum is the most toxic protein known

Tetanus

is a state of sustained maximal muscle contraction.

Lambert-Eaton Myasthenic Syndrome (LEMS)

is an auto-immune disease causing muscle weakness, resulting from antibodies that affect voltage-sensitive calcium channels of motor end plates, inhibiting acetylcholine release. While ___ may be found as a solitary disease, 50% of cases are cancer-associated. In contrast to myasthenia gravis, symptoms of LEMS tend to be worse in the morning and improve with exercise and nerve stimulation.

myoglobin

is an oxygen binding protein in muscle tissues which is red in color. (Slow twitch fibers are darker in color due to the presence of more myoglobin. slow twitch fibers are more oxygen dependent).

A _________ contraction is when your joints do not move and your muscle fibers are kept at a constant length. concentric eccentric isometric isotonic

isometric

factors in muscle fatigue

lactic acid accumulation failure of neuromuscular propagation loss of central drive reduction in Ca2+ release in excitation contraction coupling Metabolic changes in the muscle cell reduction of muscle blood flow (non factors are increased blood flow and prolonged muscle cell degeneration)

Receptors that bind the neurotransmitter at the post-synaptic cell membrane are

ligand gated

With _ stimulatory currents, no motor nerves are depolarized and no contractions are seen. As the stimulus strength is _ , some motor neurons are brought above their threshold potential, and an action potential is fired. This results in all the muscle fibers in that motor unit contracting, causing a _

low, increased, twitch.

More rarely, diseases may affect the _, the peripheral nerves (neurological disorder), the neuromuscular junction (motor endplate disease), or the muscles themselves (myopathy).

lower motor neurons

Some muscle fibers (slow twitch) are more resistant to fatigue than others (fast twitch). Several factors may contribute to this. For example, muscles may have more _ and hence a greater capacity for oxidative metabolism, or they may have greater stores of phosphocreatine.

mitochondria, phosphocreatine

Each individual muscle fiber is innervated by a branch of a

motor axon

isotonic

movement doing bicep curls running up a hill peddling a bike swimming

skeletal muscle structure order

muscle (organ) muscle facile muscle fiber myofibril

myasthenia gravis (true)

muscle fatigue developed during muscle activity 20% of patients have antibodies to a protein in... thymus abnormalities are common (false) increased number of ACH increased activity of ACH Inhibited ACH release

ecentric

muscle lengthens

concentric

muscle shortens

What is the functional unit of a skeletal muscle fiber is called? Actomyosin Fascicle Myofibril Sarcomere

myofibril

Diseases affecting muscle itself are called _. Among these are muscular dystrophies, which are characterized by progressive muscle weakness as a result of the death of muscle cells.

myopathies

isometric

no movement pushing against a wall doing plank exercises balancing on toes holding a bench press in the same position

It is useful to _ the raw EMG signal during voluntary contractions, as the intensity of the contraction is then shown more clearly.

process

The release of Pi causes the myosin head to bend and pull on the actin filament, in a _ This is called the working stroke.

ratchet effect.

What is the term given to summation of frequent muscle twitches to give maximum contraction? Facilitation Motor unit summation Tetanus Twitch

tetanus

calculate nerve conduction velocity from

the difference in latency between responses evoked at the wrist and the elbow.

The action potential causes the release of calcium ions from ________________ in the muscle cell. the cytosol the motor end plate the sarcoplasmic reticulum the T tubule

the sarcoplasmic reticulum

In the relaxed state, actin and myosin are prevented from interacting by the presence of _

tropomyosin

Some of this Ca2+ binds to_ , a protein associated with tropomyosin. The resulting shape change in the troponin and the consequent shift in tropomyosin exposes _ for myosin on the actin filaments.

troponin, binding sites

muscle shortening

twitch contraction

coactivation

when the motor units in both the agonist and the antagonist are active at the same time... contraction of an agonist muscle leads to minor activity in the antagonist muscle. ... has been suggested that it helps to stabilize the joint during isotonic contractions.

slow twitch type I

• Used for endurance activities standing walking long distance running

fast twitch type II

• Used for short bursts of strength or speed typing on keyboard playing piano weight lifting throwing a ball sprinting