Muscle Physiology

Question 1

What are Effectors?

Answer 1

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

Question 2

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

Answer 2

Hydrostatic
Exoskeleton
Endoskeleton

Question 3

What is the Hydrostatic Skeleton?

Answer 3

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.

Question 4

What is the Exoskeleton?

Answer 4

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.

Question 5

What is the Endoskeleton?

Answer 5

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

Question 6

What controls vertebrate movement?

Answer 6

Interactions between muscles and bones.

Question 7

What is Muscle?

Answer 7

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.

Question 8

What is Muscle Contraction based on?

Answer 8

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.

Question 9

What is Cardiac Muscle?

Answer 9

Striated muscle. Heart muscle involuntary, ANS.

Question 10

What is Smooth Muscle?

Answer 10

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

Question 11

What is Skeletal Muscle?

Answer 11

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

Question 12

What is the Physiology of Vertebrate Skeletal Muscle?

Answer 12

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

Question 13

What is the Sliding Filament Theory?

Answer 13

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.

Question 14

What are Muscle Fibres?

Answer 14

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.

Question 15

What are Tendons?

Answer 15

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.

Question 16

What does 1 myofibril contain?

Answer 16

Many sacromeres.

Question 17

What is a sacromere?

Answer 17

A unit of contraction containing myofilaments.

Question 18

What is the thick myofilament?

Answer 18

Myosin, A band, dark band.

Question 19

What is the thin myofilament?

Answer 19

Actin, I band, light band.

Question 20

What is the H zone?

Answer 20

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

Question 21

What is the Z disk?

Answer 21

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

Question 22

What is Contraction caused by?

Answer 22

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.

Question 23

What is the ratio of action to myosin?

Answer 23

1 A:6 M

Question 24

What is the structure of the myofilament structure?

Answer 24

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

Question 25

What is the Myosin Structure?

Answer 25

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.

Question 26

What is the Actin Structure?

Answer 26

Helical arrangement of actin monomers.

Question 27

What is Tropomyosin (TM)?

Answer 27

Wraps around actin.

Question 28

What is Troponin (TN)?

Answer 28

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.

Question 29

Where does the Energy for Muscle Contraction come from?

Answer 29

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

Question 30

What happens during the period of Muscle Relaxation?

Answer 30

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.

Question 31

What is the Cross Bridge?

Answer 31

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.

Question 32

The Power Stroke?

Answer 32

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.

Question 33

How does a Muscle Contract?

Answer 33

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).

Question 34

What is Excitation-Contraction Coupling?

Answer 34

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.

Question 35

What is Neuromuscular Innervation?

Answer 35

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.

Question 36

What is a Muscle Twitch?

Answer 36

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.

Question 37

What is a Single Twitch?

Answer 37

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

Question 38

What are Summed Twitches?

Answer 38

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

Question 39

What is Tenatnus?

Answer 39

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.

Question 40

Calcium ion concentration in the cytoplasm can:

Answer 40

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

Question 41

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

Answer 41

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

Question 42

What are Oxidative Fibres?

Answer 42

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.

Question 43

What are Glycolytic Fibres?

Answer 43

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.

Question 44

What does Exercise do?

Answer 44

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