A&P I Chapter 10 Muscle Tissue

Actin filaments

"Thin filaments." Actin myofilaments contain both contractile and regulatory proteins. Actin is a contractile protein that has a globular structure. Contains a binding site for myosin.The Regulatory proteins involved with the actin myofilament is the troponin/tropomyosin complex.

3 parts to every NMJ

1.) Axon Terminal- Synaptic vesicles are contained within the terminal which contain neurotransmitters. Neurotransmitters are chemicals that will bind to receptors on the sarcolemma and trigger changes resulting in an action potential in the sarcolemma. The neurotransmitters used at all NMJs is Acetylcholine (Ach) 2.) Synaptic Cleft- The synaptic cleft is the narrow space between the axon terminal and the sarcolemma. 3.) Motor End Plate- The sarcolemma at the Motor End Plate contains many receptors for Acetylcholine. The receptors for Ach are actually ligand-gated channels and ACh is ligand.

There are several different types of stimuli that can elict a smooth muscle contraction

1.) Mechanical (stretch) 2.) Hormornal 3.) Nerve Stimulation 4.) Spontaneous Independent Contraction

Refractory Period

A Refractory Period is a period of time after stimulation when a cell (in this case muscle fiber) can't be stimulated again.

Disuse

A Sedentary lifestyle involving disuse of muscles results in Atrophy. Atrophy is a decrease in the diameter of the muscle fibers as well as a decrease in the ability of oxidative catabolism by the muscle.

The Motor Unit

A motor unit is a motor neuron and all of the muscle fibers it innervates (joins). Each motor neuron is branched and can thus innervate more than 1 muscle fiber. Muscles that exhibit fine motor control will have a small number of muscle fibers per motor unit. Muscles that exhibit control will have a larger number of muscle fibers per motor unit.

Sarcomere

A sarcomere is the individual contractile unit of skeletal muscle. A single sarcomere runs from one Z-disc to the next Z-disc.

ATP stores

ATP is stored as ATP in the muscle

Type 1

Also known as: Slow Oxidative "Slow twitch" "Red Muscle" Relies heavily on oxidative metabolism. Has a high number of mitochondria. Has a high amount of myoglobin. Able to produce all of the ATP it needs aerobically. Optimal for Distance Runners or those in endurance type sports.

Action Potentials

An action potential is a quick depolarization followed by a rapid repolarization of a section of the cell membrane. Action potentials are generated by the opening and closing of protein channels in the cell membrane which allows the movement of sodium and potassium ions. The protein channels are referred to as "gated channels" because there are "gates" that are normally closed and open in response to a stimulus. The movement of the Na and K ions causes rapid changes in the membrane potential. Ligand-Gated Channels, aka Chemically gated channels. These gates open in response to the presence of certain chemicals called "Ligands."

Terminal Cisterene

An enlarged portion of the SR which are "end sacs" containing calcium.

Decreased availability of oxygen to muscle fibers

As the need for ATP by the muscle increases, more oxygen is used to make ATP.

Cardiac Muscle

Cardiac muscles are autorhythmic meaning they can contract on their own without input from the nervous system.

Creatine Phosphate

CrP contains a high-energy Phosphate bond similar to ATP. 10 seconds of maximal activity. Useful for high intensity, short duration activities suh as sprinting & weight lifting.

Depletion of key metabolites

Creatine phosphate, glycogen, and blood glucose are all metabolites which serve as fuel.

Myofibril

Each muscle fiber contains numerous myofibrils which are composed of thousands of bundles of protein bundles known as myofilaments.

Elasticity

Elasticity is ability to return to normal size and shape after being stretched.

Endurance Training

Endurance training is defined as training with a large increase in the frequency of motor unit activation and a moderate increase in force production- more repetition with lighter weight. Activities that are endurance training are cycling, jogging, cross-country skiing, distance swimming, etc.

Extensibility

Extensibility refers to the ability of a muscle and muscle cell to be stretched.

Type IIB

Fast Glycolytic "Fast Twitch" White Muscle Relies heavily on anaerobic metabolism has a low number of mitochondria Optimal for sprinters and weight lifters. Everyone's muscle are made up of differing amounts of all three types of fibers.

Type IIA

Fast Oxidative glycolytic (IIA) The "best of both worlds" Optimal for long sprints or completing long distances at a rapid pace

Energy Sources for Skeletal Muscle

For skeletal muscle to be able to use energy, it must be in the form of ATP. ATP is necessary for both muscle contraction and muscle relaxation.

Tropmyosin

Functions to block the myosin binding sites on the actin molecules. Troponin complex- 3 parts to the troponin complex: 1.)T-binds the complex to the Tropomyosin molecule. 2.)I- binds the complex to the actin strands. 3.) C- Binds calcium and enables muscle contraction to be regulated by the presence or absence of calcium.

Short term energy/Glycolytic Energy Sources

Glycolyctic sources are anaerobic pathways, (pathways do not require oxygen). A drawback is that they produce latic acid which causes acute muscle fatigue and burning. Glycolysis is able to provide energy for about 40 seconds of maximal sustained activity.

Immediate Sources of Energy

Immediate sources are available instantaneously to provide energy for muscle contraction.

Depolarization stage of an Action Potential

In response to a stimulus, voltage gated sodium channels open allowing sodium to enter the cell making the membrane potential less polarized and thus less negative. Hence the term "depolarization."

Myosin Myofilaments

Known as the "thick filaments." Contractile protein Myosin. A myosin molecule resembles 2 golf club drivers with the shafts twisted around each other. "Head" of each myosin molecule contains 2 items: 1.) A binding site for actin. 2.) A molecule for ATP.

Accumulation of Certain Chemicals

Lactic Acid

Sarcoplasmic Reticulum

Modified smooth endoplasmic reticulum. SR functions in the storage, release, and reuptake of calcium ions.

Multi-unit Smooth Muscle

Multi-Unit smooth muscle consists of muscle cells whose plasma membranes are not joined by gap junctions. This allows each cell to contract independently of the others which allows for precise control of contractions.

Excitability

Muscle Cells are responsive and can be stimulated by chemical signals, nerves, and stretch.

Muscle Twitch and Tetanus

Muscle Twitch- It is the result of a single muscle fiber responding to a single action potential.

Skeletal Muscle Relaxation

Muscle relaxation has 2 components: ACh release stops, & the re-sequestration of calcium into the SR. 1.) The enzyme Acetylcholinesterase (AChE) degrades ACh remaning in the snyaptic cleft which results in the ligand gated sodium channels in the motor end plate to close.

Muscular Fatigue

Muscular fatigue is defined as the inability to maintain a given level of intensity of a particular exercise. Muscular fatigue results from a combination of different factors.

Long term energy/Oxidative Energy Sources

Oxidative energy sources use aerobic pathways, or those that use oxygen. Myoglobin is an oxygen building protein similar to hemoglobin. Myoglobin thus is able to serve as a storage reservoir of oxygen in the muscle. Fat stores are virtually unlimited so ATP production is virtually unlimited. After several minutes nearly %100 of the ATP is produced by oxidative metabolism.

Oxygen Debt

Oxygen Debt is the extra amount of oxygen above a normal baseline amount that is used AFTER exercise stops. This extra amount of oxygen is required to return the body to homeostasis.

Changes caused by physical training

Physical training refers to the repetitive use of skeletal muscles that leads to changes in the structure and biochemistry of the muscle fibers. Myoplasticity is the method in which a muscle will alter its structure to follow its function.

Propagation of action potentials

Propagation is the process of an Action Potential spreading across a membrane.

Repolarization Stage of an Action Potential

Repolarization is caused by a simultaneous closing of voltage gated Na channels and an opening of voltage gated potassium channels.

Resistance Training

Resistance Training, aka "strength training" involves increased frequency of motor unit activation and a large increase in force production- fewer reps with heavier weights. Examples of activities that involve resistance training are free weights or a resistance exercise machine.

Environmental Conditions

Severe environmental conditions such as extreme heat will lead to more rapid fatigue.

Single-Unit Smooth Muscle

Single-Unit smooth muscle is also known as Visceral Smooth Muscle. Single Unit Smooth Muscle consists of many thousands of muscle cells whose cell membranes are linked electrically via gap junctions which enables all of the cells to contract as a single unit.

Skeletal muscle fibers as Electrically Excitable Cells

Skeletal muscle contracts in response to impulses from the nervous system. Nerve impulses cause a change in the electrical property (membrane potential) of the sarcolemma.

The Neuromscular Junction=NMJ

Skeletal muscle fibers are innervated meaning they are connected to a neuron. The "connection" is refereed t as a synapse. The NMJ is the name given to the synapse between a motor neuron meets a muscle fiber. Each muscle fiber contains one NMJ (is innervated by only 1 motor neuron). The function of the NMJ is to transmit the nerve impulse (action potential) to the sarcolemma.

Structure of Smooth Muscle

Smooth muscle contains the same contractile proteins as skeletal muscle; however their arrangement is quite different. Smooth muscle doesn't contain striations, and their myofilaments are longer, there are no motor end plates, there are no T-tubules, and the SR is much less extensive. Smooth muscle also doesn't contain the troponin complex.

Smooth Muscle

Smooth muscle is present anywhere in the body that there is muscle that you do not have voluntary control over, except in the heat.

Cause of the Membrane Potential

Sodium is more concentrated on the outside of the cell. Potassium is more concentrated on the inside of the cell. The Na/K pump transports 3 positively charged NA+ions from the inside to the outside of the cell while it transports 2 positively charged K + ions inside to the outside of the cell. This results in an accumulation of positive ions on the outside of the cell.

Contractility

The ability of a cell to contract which involves the ability of proteins within the muscle cells to draw together. Contractility is a property unique to muscle cells

Excitation- Concentration Coupling

The action potential is propagated across the sarcolemma and down the T-tubules. The depolarization of the T-tubules causes the calcium channels in the Terminal Cisternae of the Sarcoplasmic Reticulum to ope and calcium enters the cytosol of the muscle fiber.

Contraction phase

The energized (cocked) myosin heads bind to the actin molecules forming a crossbridge. ADP and phosphate detach from the myosin head and it flexes pulling the actin toward the center of the sarcomere. This is known as a "powerstroke." Another ATP molecule binds to the myosin head which breaks the crossbridge and allows it to reattach and make another "powerstroke."

Sarcolemma

The term that is used to refer to the cell membrane of a muscle cell.

Sarcoplasm

The term that is used to refer to the cytoplasm of a muscle cell.

Skeletal Muscle Contraction

There are 3 phases to a muscle contraction: excitation, excitation-contraction coupling, and the contraction phase.

Membrane Potentials in Cells

There is an unequal distribution of positive and negative charges across the cell membrane. The separation of charges is an electrical gradient which represents potential energy, or more specifically, "electrical potential." "Membrane potential"- refers to the electrical potential across the plasma membrane. "Resting membrane potential" (RMP)- the membrane potential while a cell is resting (not being stimulated)

Voltage- Gated Channels

These gates open and close in response to changes in the membrane potential.

Rapid, repeated stimulation

This is due to an accumulation of calcium in the cytoplasm. Tetanus is a term used to refer to a muscle that remains contracted and doesn't fully contract, or doesn't contract at all during stimulation.

Excitation phase

Vesicles release the neurotransmitter Acetylcholine into the synaptic cleft. ACh released into the synapse is degraded almost instantaneously by the enzyme Acetylcholinesterase (AChE) which is locted in the synaptic cleft. The neuron must continuously fire and release ACh. ACh diffuses across and binds to receptors (ligand gated channels) on the motor end plate.

Function of a motor unit

When a motor unit is stimulated the ENTIRE motor unit responds---i.e. ALL of the muscle fibers in the motor unit will contract. When a motor unit is stimulated the motor unit will contract with as much force as possible.

Conductivity

When a muscle cell is excited, the resulting electrical changes do not stay in one place but rather are rapidly conducted along the entire cell membrane.

Sliding filament theory of muscle contraction

When a muscle contracts, it shortens; however the contractile proteins making up the muscle remain the same size. According to the Sliding Filament Theory, the actin myofilaments slide past the Myosin myofilaments causing each individual sarcomere and thus the entire muscle to shorten.