MUSCULAR SYSTEM CHAPTER 8. Muscles l 3 types: l Skeletal –We will concentrate mostly on this one....

MUSCULAR SYSTEMMUSCULAR SYSTEM

CHAPTER 8

MusclesMuscles

3 types: Skeletal

– We will concentrate mostly on this one. Smooth Cardiac All three are composed of more than just muscle

tissue.– Example: Skeletal muscles are composed of skeletal

muscle tissue, nervous tissue, blood, and connective tissue.

Structure of Skeletal MusclesStructure of Skeletal Muscles Why has it been hard to see some of the

muscles within the cats? They are covered with connective tissue.

– There is loose connective tissue and the other type.

FASCIA - connective tissue that covers muscles.

Has two purposes:– separates individual muscles from adjacent

muscles – hold muscles in position.

How does it hold muscles in position? 2 ways

Structure of Skeletal MusclesStructure of Skeletal Muscles

TENDONS - connective tissue that connects muscles to the bone.– It is an area beyond the end of the muscle

where the fascia gets very dense and compact.

APONEUROSES - associated with sheet-like muscles, connects muscle to muscle.

Structure of Skeletal MusclesStructure of Skeletal Muscles Muscles have multiple layers

– Cylinders within cylinders Levels of muscles, big to small: Muscle fascicle muscle fiber myofibril

filaments (page 178) Each level of a muscle is enclosed in a layer of

connective tissue Epimysium – covers entire muscle Perimysium – separates muscle into fascicles Endomysium – separates fascicles into muscle

fibers

Skeletal Muscle FibersSkeletal Muscle Fibers

What is the purpose of all the levels? Help with contraction, all of them can work

together Skeletal muscle fiber – individual cell that

contracts in response to stimulation. Each one is a thin, elongated cylinder with

rounded ends These have different names for the cell

membrane and cytoplasm– Cell membrane = sarcolemma– Cytoplasm = sarcoplasm


The sarcoplasm contains numerous threadlike myofibrils that lie parallel to one another.

Myofibrils are involved in muscle contraction.

Myofibrils contain two kinds of protein filaments.


Myosin Filaments - The “thick” filaments that are composed of protein.

Actin Filaments – The “thin” filaments that are composed of protein

What effect do these have on the appereance of muscle tissue?

The arrangement of these filaments is the reason for the striations that we see with skeletal muscles.


Striation pattern parts: I band (light bands) – where only actin

filaments are. Where they meet is known as the Z line.

A bands (dark bands) – where the thick myosin filaments are overlapping with thin actin filaments. – Usually thicker bands– H zone is in the middle

From Z line to Z line is one sarcomere.

Structure of Skeletal MuscleStructure of Skeletal Muscle

Sarcoplasmic reticulum - network channels that run parallel to each myofibril

Transverse tubules – tubes that extend inward and pass through the fiber.

What would these be used for? Activate muscle contraction when the fiber

is stimulated.

Muscle activationMuscle activation

How are muscles activated to contract? The neuromuscular junction Each skeletal muscle fiber is connected

to an extension of a motor neuron. The nerve fiber and the muscle meet at

the neuromuscular junction.

Neuromuscular JunctionNeuromuscular Junction

There is a tiny gap between the neuron and the muscle called the synaptic cleft.

How does the nerve actually stimulate the muscle with a gap there?

The neuron contains many tiny vesicles (synaptic vesicles) that store chemicals called neurotransmitters.

Neuromuscular JunctionNeuromuscular Junction

When the nerve receives and impulse, the neuron releases the neurotransmitter into the synaptic cleft.

What will this cause? Binds with a channel protein, allowing

Ca+ to pass through, it is then able to enter the muscle fiber

This action stimulates the muscle fiber to contract.

Motor UnitsMotor Units

Does each nerve only control one muscle fiber?

NO, we have motor units. A motor unit consists of a motor neuron and

all of the muscle fibers it controls. The number of muscle fibers in a motor unit

varies considerably. Why would that be? The fewer muscle fibers in the motor units,

the finer the movement.

Skeletal Muscle ContractionSkeletal Muscle Contraction

Myosin has protein strands with globular parts called cross-bridges projecting outward along their length.– Think about your arm while flexing your

bicep Actin molecules, arranged together in a

double twisted strand, form an actin filament.

Tropomyosin & troponin are the two proteins associated with actin filaments.


The sliding filament theory is the most widely accepted theory on how muscle contraction works.

It says that the head of a myosin cross-bridge can attach to an actin binding site and bend slightly– What will this cause?

The actin to move (or slide) with it The head can then release, straighten itself, and

combine with another binding site farther down the actin filament. – Example, arms with a meter stick

This can happen several times causing the muscle fiber to shorten dramatically


All of this binding and changing of shape will take energy, where will it come from?

ATP The enzyme ATPase causes the breakdown

of ATP to supply energy for these actions. Acetylcholine (ACh) is a neurotransmitter

that is synthesized in the cytoplasm of the motor neuron and is stored in vesicles.

Muscular ResponsesMuscular Responses

How does a muscle respond to activation? The stimulus increases until it reaches the

threshold stimulus Threshold stimulus is the minimum strength

of stimulus required to cause a contraction. Once stimulated the muscle will respond

completely. There is no partial contraction. This is called an All-or-None Response.

Steps to muscle contractionSteps to muscle contraction

1. Nerve impulse arrives at the neuromuscular junction

2. Acetylcholine diffuses across the gap at the neuromuscular junction

3. T Tubules carry acetlycholine to sarcoplasmic reticulum, which causes cell membrane to permeable to Ca2+

4. Ca2+ binds to troponin

Steps to muscle contractionSteps to muscle contraction

5. Conformation shift - troponin pulls tropomyosin off active binding sites

6. One ATP per myosin Head releases and activates myosin

7. Actin and myosin filaments form linkages8. Myosin cross-bridges pull actin filaments

inward9. Muscle fiber shortens and contracts

Isotonic and IsometricIsotonic and Isometric

Isotonic contractions Contractions that shorten the muscle. Isometric contractions Tension in the muscle but no change in

length.

Muscle RelaxingMuscle Relaxing

What happens when a muscle needs to relax?

When a muscle relaxes, the Ach is rapidly decomposed by action of an enzyme called acetylcholinesterase. (Ach-ase)– What was Ach used for in the first place?

This enzyme is present at the neuromuscular junction in the membranes of the motor end plate.

Muscle RelaxingMuscle Relaxing The Ach-ase stops a single nerve impulse from

continuously stimulating the muscle fiber. As this ceases, the calcium pump quickly

moves calcium ions back into the sarcoplasmic reticulum.

What does this do? The linkages will break

– the troponin and tropomyosin return to the normal conformation, blocking the binding sites.

The muscle fiber relaxes.

Muscle FatigueMuscle Fatigue

Muscle fatigue most often occurs from an accumulation of lactic acid. – What is this caused by?

Anaerobic respiration An interruption of the blood supply or

the lack of ACh can also cause fatigue. Muscle fatigue can cause the muscle to

cramp.

Muscle CrampsMuscle Cramps

Cramps occur when the muscle contracts spasmodically, but does not relax completely.

The condition is due to a lack of ATP needed to move calcium or other ions, can also be caused by a lack of those ions

Why would there be a lack of ATP? Anaerobic respiration does not produce much

ATP. Exercise stimulates new capillaries to grow

within the muscles and it also causes an increase in the number of mitochondria.

Fast and Slow MusclesFast and Slow Muscles

There are two types of muscles relating to the speed of contraction.– Fast and Slow

The speed of contraction is related to the specialized function of a muscle.– Example: Eye muscles that blink are ten

times faster than the muscles involved in posture.

Fast and Slow MusclesFast and Slow Muscles Slow-contracting (slow twitch) muscles Often called red muscles

– Why?

Most of their fibers contain red, oxygen-storing myoglobin.

Well supplied with blood. Have a high respiratory capacity. They generate

enough ATP to keep up with the activities. (which means they have a lot of what?)


Fast-contracting (fast twitch) muscles Also called white muscles.

– Why? They contain less myoglobin and have

a poorer blood supply than red muscles. White muscles contains fewer

mitochondria which reduces the respiratory capacity.


What makes white fibers able to contract quicker?

White Fibers have more extensive sarcoplasmic reticulum.– Why does this help?

Most skeletal muscles contain both types of fibers.

Research has discovered an intermediate fiber.

AssignmentAssignment

Due Friday Pg. 210

– Review Ex. #2,8,12,15,– Critical thinking #3

DIDN’T USEDIDN’T USE

ANY SLIDES AFTER THIS POINT, I DID NOT USE, BUT KEPT IN CASE I WANTED TO.


In the presence of calcium ions, the myosin cross-bridges react with actin filaments and form linkages with them.

This reaction between the myosin and actin filaments provides the force that shortens myofibrils during muscle contraction.


Actin accounts for about 1/4 of the total protein in skeletal muscle.

Actin molecules, arranged together in a double twisted strand, form an actin filament.

Tropomyosin & troponin are two proteins associated with actin filaments.


The tropomyosin-troponin complex blocks the binding sites on the actin molecules when the muscle is at rest.

If a high concentration of calcium ions is present, the calcium ions bind to the troponin, and this modifies the position of the tropomyosin.


The tropomyosin molecules move, exposing the binding sites on the actin filaments, and the linkages form between the actin and myosin filaments.


The sliding filament theory of muscle contraction suggests that the head of a myosin cross-bridge can attach to an actin binding site and bend slightly, pulling the actin filament with it.

Then the head can release, straighten itself, and combine with another binding site farther down the actin filament.


The enzyme ATPase causes the breakdown of ATP to supply energy for these actions.

Stimulus for ContractionStimulus for Contraction

Acetylcholine (ACh) is a neurotransmitter that is synthesized in the cytoplasm of the motor neuron and is stored in vesicles.

A nerve impulse reaches the end of the axon, some of these vesicles release ACh into the gap between the nerve and the motor end plate.


The ACh diffuses rapidly across the gap, combines with certain protein molecules in the sarcolemma, and thus stimulates the muscle fiber membrane.

This stimulus causes a muscle impulse that passes in all directions over the surface of the sarcolemma.


It also travels through the sarcoplasmic reticulum and the transverse tubules.

The sarcoplasmic reticulum contains a high concentration of calcium ions compared to the sarcoplasm.


In response to a muscle impulse, the membranes of the cisternae become more permeable to these ions and the calcium ions diffuse into the sarcoplasm of the muscle fiber.


When a relatively high concentration of calcium ions is present in the sarcoplasm, linkages form between the actin and myosin filaments, and a muscle contracts.

Energy Sources of Energy Sources of ContractionContraction

The energy for muscle contractions comes from ATP.

The muscle has enough ATP to contract briefly. Therefore, when a fiber is active, ATP must be regenerated.

Creatine phosphate supplies the energy to change ADP back to energy rich ATP

Oxygen Supply and Cellular Oxygen Supply and Cellular RespirationRespiration

Oxygen is transported by the red blood cells. It is loosely bound to molecules of hemoglobin.

The hemoglobin releases the oxygen in areas of the body that are low in oxygen content

Oxygen Supply and Cellular Oxygen Supply and Cellular RespirationRespiration

Myoglobin, in the muscle cells, can store oxygen temporarily.

This reduces a muscle’s need for a continuous blood supply during a contraction.

Oxygen DebtOxygen Debt

During strenuous exercise, the available oxygen supply may be used up. The body then relies on anaerobic respiration creating an oxygen debt.

Anaerobic respiration builds up lactic acid. The liver converts lactic acid back to glucose, but it takes several hours to complete the conversion.

Heat ProductionHeat Production

Since muscle tissue represents a large proportion of the total body mass, it is a major source of heat.

About 25% of the energy released in cellular respiration is available for use in metabolic processes.

Heat ProductionHeat Production

Active muscles release large amounts of heat.

Blood transports this heat to other tissues to help maintain body temperature.

Smooth MuscleSmooth Muscle

Smooth muscle characteristics: Shorter than the fibers of skeletal

muscle. Single, central nucleus. Cells are elongated with tapering ends. Filaments are more randomly arranged

than skeletal muscle.


The two types of smooth muscle are multiunit and visceral.

Multiunit muscles are less organized and occur as separate fibers.

Multiunit are found in the irises of the eyes and walls of blood vessels.

They contract through motor nerve impulse or hormone action.


Visceral smooth muscle is composed of sheets of spindle shaped cells held together by gap junctions.

Visceral smooth muscles are found in walls of hollow organs (ex. Stomach, intestines)

There usually will be two muscle layers, a longitudinal and a circular layer.


When one fiber is stimulated, the impulse will also excite adjacent cells causing a rhythmic contraction.

Peristalsis - wavelike contraction that occurs in tubular organs.

Smooth Muscle ContractionSmooth Muscle Contraction

Smooth muscle contraction is similar to skeletal muscle contraction.

Smooth muscle lacks troponin. Instead it uses a protein called calmodulin to bind calcium ions.

Calcium diffuses into the cell from the extracellular fluid.


Smooth muscle reacts to the neurotransmitter ACh and norepinephrine.

Some hormones cause smooth muscle contraction. (Ex. Childbirth)

Stretching smooth muscle can cause contractions. (Ex. Digesting food in the stomach)


Smooth muscle is slower to contract and slower to relax.

Smooth muscle can contract for a longer time with the same amount of ATP.

Smooth muscles stretch without changing tautness while a hollow organ fills.

Cardiac MuscleCardiac Muscle

Found only in the heart. Striated cells joined end to end forming

interconnecting branched three-dimensional network.

Each cell contains a single nucleus. Well developed sarcoplasmic reticulum

and transverse tubules.


Sarcoplasmic reticulum stores less calcium but the enlarged transverse tubules store extra calcium.

The extra calcium allows cardiac muscle to maintain a contraction longer than skeletal muscles.


Intercalated disks separate opposing ends of cardiac cells.

The disks help hold adjacent cells together and transmit the force of contraction from cell to cell.


When one portion of the cardiac network is stimulated, the impulse passes throughout the network causing the whole structure to contract as a unit.

Muscle ActionMuscle Action

The main muscle is the prime mover. Muscles that contract along with the

prime mover are called synergists. Muscles opposing the prime mover are

called antagonists.

MUSCULAR SYSTEM CHAPTER 8. Muscles l 3 types: l Skeletal –We will concentrate mostly on this one....

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