Term
| Composition of skeletal muscle |
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Definition
- Muscle comprises the largest group of tissues in the body, accounting for approximately half the body’s weight. - - Skeletal Muscle is made up of muscle fibers (individual muscle cells)
- Muscle fibers contain many myofibrils, that are further broken down into myosin (thick filaments) and actin (think filaments). |
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Term
| What happens during muscle contraction? |
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Definition
Myosin (thick) binds to actin (thin), and slides it, pulling the Z-lines closer together, and reducing the width of the H-bands and I-bands.
Note that filament lengths have not changed. |
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Term
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Definition
| branch to innervate many individual muscle fibers |
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Term
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Definition
- consists of the motor neuron and all the muscle fibers it innervates
- Muscles are made up of different size motor units, which help control the force of the muscle contraction.
- small motor units allow for fine muscle control (eyes), and large ones for gross muscle control (legs). |
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Term
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Definition
Physiologically, motor units are activated from smallest to largest. However, dDirect stimulation causes the recruitment of motor neurons from largest to smallest, due to larger diameter neurons having a lower threshold to direct electrical stimulation (have a lower resistance
R=rL/A) |
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Term
| Excitation-Contraction Coupling |
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Definition
- Neuromuscular Junction: Area where the motor neuron synapses with the muscle fiber
- Depolarization causes the release of Acetylcholine (ACh) into the synaptic cleft
- ACh binds to nicotinic ACh Receptors (nAChR) causing them to open
- nAChR are ligand gated cation channels (Do Not confuse with muscarinic ACh receptors) |
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Term
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Definition
- A twitch (small muscle contraction) can be caused by a single action potential or by direct stimulation
- At low stimulus frequencies tension will appear as separate unfused twitches
- As stimulus frequency increases individual twitches began to merge and sum together (Temporal Summation)
- At a certain frequency the tension developed will reach a maximum (Tetanic Contraction) |
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Term
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Definition
| - Ca is released from the sarcoplasm after an action potential is sent. |
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Term
| what are the roles of Ca, tropinin, and trypomyosin? |
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Definition
| - tropomyosin is a thread like protien that is normally bound to troponin in a resting state covering the myosin binding sites. once Ca enteres from the sacroplasm after stimulation, troponin bind to Ca allowing actin to bind to myosin |
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Term
| How is each muscle fiber innervated? |
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Definition
| Each muscle fiber is innervated by the depolarization of a single motor neuron! |
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Term
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Definition
| A motor unit is composed of a motor neuron and the skeletal muscle fibers that are innervated by the axon.Together a collection of motor units coordinate the contraction of individual muscle cells. |
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Term
| A motor unit is composed of a motor neuron and the skeletal muscle fibers that are innervated by the axon.Together a collection of motor units coordinate the contraction of individual muscle cells. |
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Definition
| The sciatic nerve was electrically stimulated in order to elicit the biological signal. |
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Term
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Definition
| Threshold is the value of stimulus intensity that elicits the smallest increase in the response parameter above its baseline value. |
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Term
| what is the difference between THRESHOLD in a muscle versus that in a neuron? |
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Definition
The difference between threshold in a muscle versus that in a neuron is that if a neuron hits threshold an action potential will occur -- an all or nothing response!
"All-or-nothing" refers to fixed amplitude in the presence of varying stimulus strengths
In contrast, threshold in a muscle can occur without having the whole muscle respond because the muscle recruits motor units as needed. Smaller motor units are recruited first because they have smaller thresholds while larger ones are later recruited if needed. |
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Term
| What is the relationship between the muscle THRESHOLD and the biological signal that was recorded? |
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Definition
Any stimulus value below the electrical threshold will result in muscle tension equal to the baseline tension, i.e., not a signal.
Once the electrical stimulus passes threshold, the muscle will respond with a transient increase in force (is recorded by the transducer as a "spike" on the computer screen)
The spike quickly diminishes toward baseline unless another above-threshold stimulus is received within |
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Term
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Definition
| small contraction caused by one action potential or direct stimulation; small, local, involuntary muscle contraction and relaxation visible under the skin |
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Term
| does a muscle twitch differ from the type of muscle contraction we use everyday? |
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Definition
yes
1. Everyday skeletal muscle contraction is voluntary and not spontaneous (whereas muscle twitching is involuntary and spontaneous).
2. Types of voluntary skeletal muscle contraction: (depends on what you are doing)
- Isometric (same length, different tension): Example= holding a heavy object.
- Isotonic (same tension, different length): Example= kicking a ball
- Isokinetic (constant limb movement, varying resistance): Example= riding a stationary bike |
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Term
| with regards to skeletal muscle, define recruitment. |
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Definition
Motor unit Recruitment
Motor unit: a motor neuron and the all of the muscle fibers it innervates
An activated motor neuron stimulates the muscle fibers to contract.
↑ motor neurons = ↑muscle fibers stimulated = ↑contractile activity
Small motor units are recruited first and progress to recruitment of larger motor units. |
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Term
| what is the importance of motor unit recruitment? |
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Definition
higher the recruitment → the stronger the muscle contraction
Muscles activated in order of size
Hennemen’s Size Principle:
smallest recruited first → largest
motor units are recruited according to force, where small units recruited to use fatigue resistant muscle fibers before the less fatigue-resistant muscle fibers |
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Term
In lab, Did tension increase when you set the stimulator to voltages greater
than the maximum voltage (explain why or why not)? |
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Definition
As shown in the data, when we increased the voltage on the stimulator, the
force of contraction/tension increased until we reached our Vmax, where the
tension reached a maximum force and remained constant. The force of contraction
remained at 166 grams when we continually increased the voltage on the stimulator. |
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Term
| Why does tension remain constant? |
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Definition
• Force is directly related to how many cross bridges are formed
• At Vmax, all of the cross bridges in the gastrocnemius muscle are formed to generate the maximum force of 166 grams
• Although the increase in voltage beyond Vmax would increase the release of Ca+, this does not increase the number of cross bridges formed
• At Vmax, Ca+ removes all the tropomyosin molecules from the binding sites to allow all the cross bridges to form
• Therefore, when we increase the voltage, the excess Ca+ will not remove more tropomyosin molecules/generate more cross bridges
– the maximum tension is already produced with Vmax |
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Term
| what is temporal summation? |
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Definition
| In temporal summation, individual twitches merge and sum together. The merging of twitches is caused by an increase of stimulus frequency, which doesn’t give enough time for the muscle to completely relax before another twitch. This ultimately leads to a stronger muscle contraction where the twitches add on top of each other. |
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Term
| Stimulus Intensity vs. Stimulus Frequency |
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Definition
• As you increase the stimulus intensity you see an increase in force because more motor units are recruited.
• Normal stimulus frequency will create waves, which are muscle contractions (twitches). An Increase in stimulus frequency will result in temporal summation. If we continue to increase stimulus frequency, you will eventually see tetanus |
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Term
| What is the role of acetylcholine in muscle contraction? |
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Definition
Acectylcholine is released by the motorneuron, into the neuromuscular junction. It is then free to cross the junction and bind to nicotinic acetylcholine receptors on the motor end-plate located on the muscle.
This instigates an action potential which can travel across the muscle fiber membrane and down a t-tubule, across the myofibrils, which leads to Ca2+ ions being released from the sarcoplasmic reticulum. The calcium ions then go on to play a vital role in the formation of cross bridges necessary for muscle contraction. |
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Term
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Definition
Curare is a naturally occurring alkaloid obtained from the bark of South American plant Chondodendron Tomentosum.
It is a skeletal muscle relaxant that acts as a competitive inhibitor for nicotinic acetylcholine receptors.
It is a non-depolarizing neuromuscular agent (it outcompetes acetylcholine and binds to its receptors preventing depolarization - and thus, muscle contraction - from occurring). |
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Term
| what is the effect of curare? |
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Definition
muscle contractions decreased at a relatively constant rate after curare was injected until they almost reached a flatline several minutes later.
This decrease occurred as the curare binded to the receptors acting as an antagonist and preventing acetylcholine from binding - thus inhibiting muscle contractions. |
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Term
| Suppose that, in the presence of curare, the twitches reappear when the motor neuron were continuously stimulated. Explain what might be happening. |
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Definition
The frog is (was >.>) a living system with an internal system built to defend itself, such as kidneys capable of filtering blood. As time goes on, the body would begin to remove the curare from its system, while acetylcholine would consistently be released and built up due to continued stimulation.
The unchanging concentration of curare (because no additional curare would be added), and the increase in concentration of acetylcholine (through the repetitive stimulation), would cause twitches to reappear eventually as the curare begins to be overwhelmed by the acetylcholine. |
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