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Flashcards in Muscle Physiology Deck (44):

What are Effectors?

Glands and organs and locomotory structures that produce a response to sensory input by the CNS.


What are three types of animal skeletons for body support, locomotion, and protection?



What is the Hydrostatic Skeleton?

Worms, annelids, segmented bodies with muscle layers.
Involved in muscle contraction, it creates pressure on coelomic fluid. There is no hard skeleton in the body. When the muscles in one particular segment contractions, it creates pressure in the body fluid - the fluid changes the shape in the next segment, allowing locomotion.


What is the Exoskeleton?

External, made up of chitin and calcium carbonate.
Most of the muscles are attached to the exoskeleton. It has moveable joints that are attached through points of the exoskeleton and muscles.
Examples: lobsters, crabs.


What is the Endoskeleton?

Internal, hard, and mineralized support structures (bones). Primarily made up of calcium.


What controls vertebrate movement?

Interactions between muscles and bones.


What is Muscle?

Highly specialized tissue with the ability to contract in response to stimuli; a muscle is one individual cell [a grouping of contractile cells, termed muscle fibres, bound together by connective tissue]. Bundles of elongated, cylindrical muscle fibres - multinucleate from cell division.


What is Muscle Contraction based on?

Interaction between supporting filaments (actin) and a motor protein (myosin); almost all cells have actin and myosin. In muscle cells, they occur in a specific type of arrangement.


What is Cardiac Muscle?

Striated muscle. Heart muscle involuntary, ANS.


What is Smooth Muscle?

Digestive system, arteries, and veins; involuntary (ANS), un-striated muscle.


What is Skeletal Muscle?

Striated muscle, voluntary movements (somatic nervous system); 30-40% of vertebrate mass is from skeletal muscle.


What is the Physiology of Vertebrate Skeletal Muscle?

Shortening of muscle generates a force and movement; force is generated by mechanical energy generated from the sliding of two filaments in the muscle.


What is the Sliding Filament Theory?

The electrical energy stimulates the chemical energy in the form of ATP to generate force, force is generated by the sliding of 2 filaments.
Explains muscle contraction.


What are Muscle Fibres?

Muscle fibres are 10-100 micronM in diameter, and run the entire length of the muscle.
A muscle fibre contains many myofibrils; a muscle fibre contains a single muscle cell.


What are Tendons?

Connective tissue that link bones to skeletal muscle. Fibres are bound together into bundles of connective tissue termed fascicles; bundles are then grouped together to form muscle.


What does 1 myofibril contain?

Many sacromeres.


What is a sacromere?

A unit of contraction containing myofilaments.


What is the thick myofilament?

Myosin, A band, dark band.


What is the thin myofilament?

Actin, I band, light band.


What is the H zone?

Myosin only, bisected by the M line that anchors the myosin to a specific arrangement.


What is the Z disk?

Anchors actin, mark the sacromere ends. Located in I band.


What is Contraction caused by?

The actin sliding over the myosin; the H zone and I band shorten, Z-lines move toward each other. Muscles can contract to half their resting length.


What is the ratio of action to myosin?

1 A:6 M


What is the structure of the myofilament structure?

Mostly myosin and actin, but also has tropomyosin and troponin. The tropomyosin blocks connection between the myosin and the actin at rest.


What is the Myosin Structure?

Consists of two identical, golf-club like subunits with their tails intertwined and with globular heads. Each contain a actin binding site and a myosin ATPase site.
A thick filament is made up of myosin molecules laying lengthwise, parallel, to one another. Half are oriented in each direction.
The globular heads form the cross bridges.


What is the Actin Structure?

Helical arrangement of actin monomers.


What is Tropomyosin (TM)?

Wraps around actin.


What is Troponin (TN)?

Bound to Tropomyosin, contains calcium ion binding sites. Calcium is released by cells by stimulus by an electrical signal/action potentials; changes the conformation of TM to expose actin binding site on myosin.


Where does the Energy for Muscle Contraction come from?

ATPase; catalyze decomposition of ATP into ADP and Pi. Released energy which the enzyme harnesses to drive other reactions.


What happens during the period of Muscle Relaxation?

ATP binds to myosin, causing cross bridges to detach from actin.
ATP bound to the myosin head is hydrolysed, and the ADP+Phosphate+energy released are stored in the myosin.


What is the Cross Bridge?

The binding of myosin to actin creates a crossbridge between the two molecules, resulting in a change in the conformation of the myosin head (45 degrees).
Triggers the release of the phosphate and ADP.


The Power Stroke?

This release snaps the head of the myosin back towards the tail, producing the power stroke that pulls the thin filament over the thick filament. Several power strokes have to occur in order for the muscle to contract.


How does a Muscle Contract?

Neuromuscle Synapse - Motor Neuron axon synapses onto muscle cell membrane [sacrolemma], the synapse site is called the Motor End Plate or Neuromusclular Junction. Synapses located over Junctional folds, increasing the surface area for neurotransmitter transactions. The Motor Neuron releases ACh, the receptors are nicotinic receptors, this opens sodium channels; binding to nAChR (nicotinic ACh receptor) causes influx of Na+ (muscle fibre depolarizes).


What is Excitation-Contraction Coupling?

Sodium ion influx created an Endplate Potential (EPP) that spreads over the surface of the cell membrane until it reaches a volume potential and a muscle action potential forms. The MAP spreads the length of the fibre, and inside via Traverse tubule system - creating a path for the MAP to penetrate into the fibre, filed with extracellular fluid. The MAP spreads to the T-tubules and triggers the opening of voltage-gated calcium ion channel on the Sacroplasmic Reticulum; this has a high concentration of calcium ions at rest.
Calcium ions flow out of the SR, binding to TN, transforming TM, causing muscle contraction. When MAP passes, calcium ion channel close. Calcium ion ATPase recalls calcium back into the SR, and the cytoplasmic calcium concentration decreases rapidly.
Calcium ions dissociates from TN.


What is Neuromuscular Innervation?

Muscle fibre is innervated by the axon of Motor Neurons - excitatory.
In vertebrates, each fibre is innervated by only 1 motor neuron, but the neuron can innervated many fibres.
Motor Neuron + fibres = Motor Unit; recruitment controls muscle tension.
Invertebrates (anthropods) = fibres can be innervated multiple times, causing excitatory and inhibitory functions that are governed by the sum.


What is a Muscle Twitch?

Contraction converts electrical energy to mechanical energy, transient change in muscle tension = twitch; the tension that is generated by a muscle fibre by one, single, AP.


What is a Single Twitch?

If a muscle fibre is restimulated after it has completely relaxed, the second twitch is the same magnitude as the first.


What are Summed Twitches?

If a muscle fibre is restimulated before it has completely relaxed, the second twitch is added to the first twitch; summation.


What is Tenatnus?

If a muscle fibre is stimulated so rapidly that it does not have an opportunity to relax at all between stimuli, a peak level of continuous contraction occurs.


Calcium ion concentration in the cytoplasm can:

Regulate muscle tension by regulating how many cross bridges can be formed.


What are the three important roles of ATP in muscle contraction/relaxation?

1. Hydrolysis of ATP provides the energy that leads to the Power Stroke
2. When myosin is attached to the thin filament, it can no longer detach itself unless a new ATP becomes available
3. Role of ATP in the Calcium Pump to allow the muscle to relax


What are Oxidative Fibres?

Muscle fibres that do not fatigue easily, and are used for prolonged activity.
Contain a large number of mitochondria; high capacity for oxidative phosphorylation; require lots of energy.
Surrounded by many small blood vessels; myoglobin.


What are Glycolytic Fibres?

Muscle fibres that fatigue rapidly, used for rapid, intense actions.
Few mitochondria, but high concentration of glycolytic enzymes and large stores of glycogen. Limited oxygen use (glycolysis), few blood vessels, little myoglobin. White/pale.


What does Exercise do?

Produces an increase in the size of muscle fibres and increases their capacity for ATP production. The number of cells remains the same.