Physiology of Muscle Contraction Flashcards by michael perna

Sarcomeres end to end make up…

Myofibril

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Many myofibrils make up the…

Muscle fiber

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A single motor neuron and all of the muscle fibers it supplies

Motor Unit

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A single nerve cell

A bundle of neurons

Neuron

Nerve

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Smallest recordable contraction, a response to a single threshold stimulus large enough to create Action Potential

Muscle Twitch

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First phase of muscle twitch between the stimulus and initiation of muscle twitch response

Time when excitation is recurring, action potential release of Ca and up to initial binding of myosin head to actin. No tension is generated yet

Latency

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Phase where power stokes occur, onset of shortening to peak of tension development

Contraction

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Phase where Ca is taken back into terminal cysternae, ATP comes and and causes cross bridges to let go

Relaxation

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Does twitch duration vary with muscle fiber type?

Yes

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Which muscle have a slower twitch? Which ones have a faster?

Posturals have slower twitches

Rapid response muscles have faster twitches

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Way to increase tension past the muscle twitch

Graded Muscle Response

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This graded muscle response that increases the rate of stimulus delivery

Temporal Summation

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What occurs when there is no relaxation from temporal summation, analagous to a charlie horse

Tetany

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Type of temporal summation that is good for daily activity

Wave Summation

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Graded muscle response where sequentially more units are recruited as stimulus intensity increases. Results in smooth steady increase in force.

Multiple Motor Unit Summation

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Are smaller or larger units recruited first?

Smaller (less fiber associated with single nerve cell)

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Graded muscle response of the warm up effect, with repeated stimuli, muscle warms up and enzymes (myosin ATPase, etc) become more efficient and stronger contraction ensues

Treppe

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How does treppe differ from temporal summation?

Treppe has COMPLETE relaxtion between stimuli

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This is the force that is generated by cross bridge formation

Force on object

Weight on object

Contraction

Tension

Load

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Type of contraction same tension but changing length of muscle

Isotonic contraction

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Type of isotonic contraction that shortens the muscle, only type explained by Huxley’s theory (sarcomere shortening)

Concentric

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Type of isotonic contraction where the muscle lengthens

Ex: lift heavy weight and place it down on the table. Not explained by Huxley’s theory

Eccentric

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Contraction where the muscle stays same length but force changes.

Ex: Getting up out of chair and push against wall

Isometric

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Type of contraction that is mechanically induced, performed at same speed with a controlled angular velocity of joint. Doesn’t happen in daily life.

Typically on exercise machines

Isokinetic

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What to type of contractions are performed in daily life?

Isotonic and Isometric contraction

Larger muscle means larger force

(DUH)

The 4 non-contractile elements of muscle cells that are elastic

Connective tissue covering Tendons Organelles Sarcolemme

2 proteins that are non contractile in muscle

Titin and Nebulin

Tension in a muscle that is directed at overcoming non contractile element elasticity

Internal

In a twitch, most of stimulus is used as...

Internal tension

This type of tension is done first

Internal Tension

Too much overlap gives how much contraction? Not much room to pull.

75%`of resting length

Resting length, sufficient overlap so that when stimulus arrives in sarcoplasm, a good overlap so that crossbridges can form

100%`

too little overlap, impossible for crossbridges to form because myosin heads cannot reach the actin. Happens if muscle is

Overstretched

Force that can be generated is related to two things about the contraction. What are they

Velocity and Duration of the Contraction?

Greater load = more or less muscle shortening = shorter or longer contraction

Less shortening | Shorter Contraction

Greater load is slower or faster contraction?

Slower contraction (too heavy can't lift at all, v=0)

Most all human muscle is of mixed

Fiber type

Some cells/fibers that have slow myosin ATPase (takes a while to cleave ATP into ADP and inorganic phostphate during activation phase), have lots of myoglobin, many capillaries and mitochondria, O2 dependent, low glycogen stores

Slow Oxidative Fiber Types

Slow oxidative fiber type is commonly used in what type of exercise

Endurance

Fast ATPase, less myoglobin, not O2 dependent with high glycogen storage

Fast glycolytic

Fast glycolytic is commonly used for what type of exercise?

Sprint exercise

Fast ATPase, moderate glycogen stores, little endurance, some dependence on oxygen (in the middle of the other two)

Fast Oxidative Glycolytic

Does the amount of fibers types an individual have depend upon genetics?

Yes.

Similar to skeletal muscle because it is excitable, stretches, contracts, and moves things. Different in shape and size of cell, lack of striations, and location. Typically located within walls of different organs

Smooth Muscle

The organization of smooth muscle consists of ____ of muscle cells

Sheets

2 layers of smooth muscle

Longitudinal and Circular

What is the functional outcome of smooth muscle?

Can squeeze and push material through a tube

Innervation of skeletal muscle is different, every single smooth muscle cell has its own _____ _______ This directs every muscle when and how to contract

Terminal Bouton

Because the smooth muscle is organized in sheets, it is generally supplied by the

Autonomic Nervous System

Is the neuromuscular junction of smooth muscle as tightly organized as skeletal muscle?

What is the neuromuscular junction in smooth muscle called? What about terminal boutons?

Diffuse Junction Bulbous Varicosities

What joins smooth muscle cells together to allow communication between the cells? (Unlike skeletal muscle)

Gap Junctions

What is the thin layer of connective tissue that surrounds each muscle cell?

Endomysium

This structure in the smooth muscle is less well developed than skeletal muscle and touches the plasma membrane.

Sarcoplasmic Reticulum

Structure that smooth muscle has within plasma membrane that stores Calcium. It is also stored in sarcoplasmic reticulum

Caveoli

Are there T-Tubules in smooth muscle cells? Why?

No. The sarcoplasmic reticulum touches plasma membrane. No need

What is the ratio of thick to thin filaments in smooth muscle? Much greater than skeletal muscle

1:16

Thick filaments in smooth muscle are made of Thin filaments are made of

Myosin Actin and Tropomyosin NO troponin

Are the thick and thin filaments arranged in bands like skeletal muscle cell?

No. Hence "smooth"

Where is neurotransmitter (NT) released from in smooth muscle?

Bulbous varicosity

This structure receives the NT stimulus directly

Sarcoplasmic Reticulum (SR)

SR stimulus allows what to enter the cytoplasm from the SR and caveoli, allowing contraction to occur.

Calcium

For APs that are so far from bulbous varicosity that the AP doesn't go through, where does it receive AP from?

Gap Junctions

Therefore, smooth muscle contracts as a

Unit (or sheet)

Smooth muscle contraction is initiated by this which comes from SR and caveoli after AP goes into bulbous varicosity

Ca going into cytoplasm

Because there is no troponin/tropomyosin complex, Ca binds to what intracellular protein?

Calmodulin

What does calmodulin activate, which typically phosphorilate something?

Kinase Proteins

What does kinase transfer phosphate to using ATP?

Myosin Head

What happens when ATP is phosphorilated, in other words, given energy to perform a contraction?

Cross bridges form bt myosin head and thin filaments

Type of smooth muscle where cells contract as a unit. It is rhythmical. Gap junctions allow current flow directly. This is typically found in organs

Single Unit (Unitary)

Muscle Fibers that are independent of one another. Rare gap junctions and rare spontaneous action potentials. Respond to hormones and have ANS innervation. Muscle that regulate pupil size, arrector pili, large airways to lungs and larger arteries

Multi Unit

What neurotransmitters are important in regulating smooth muscle?

Acetylcholine and norepinephrine

The receptors that receive NT are either... Results in increased or decreased contraction. Ex: sitting verse running when digesting

Inhibitory or excitatory

Smooth muscle, when stretched, results in more vigorous or less vigorous contraction?

More vigorous (opposite of skeletal muscle)

Hormones and local factors, like NTs, can be either.... Depends on receptor too

Inhibitory or excitatory

Unique feature of smooth muscle that stretch stimulates contraction

Length Tension

Increase in # of muscle (can grow or increase) Ex: Uterus in pregnancy

Hyperplasia

Smooth muscle cells can secrete elastin and collagen of connective tissue

Secretion