A&P Chapters 10-11 Muscular System Flashcards Preview

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What are the functions of Muscles?

Movement: Generates force to move bones and move body contents ie. food through the digestive tract or expelling substances from the body.

Stability: Muscle tone resists gravity and helps stabilize some joints. Provides for posture.

Communication: Speaking, writing, facial expressions, ect...

Control of Body Openings: Sphincter muscles control openings of the eyes, mouth, digestive system, anus.

Heat Production: Muscles generate alot of heat when contracting (85% of total body heat). Maintains body temp which is important for enzyme function.


What do SPHINCTER muscles do?

Control openings in the body regulating the flow of contents in and out of the body as well as controling the opening of the eyes and mouth.


Muscle are _______ with all the primary _______.

Organs, Tissues


Why do muscles have connective tissues?

To keep the muscle fibers organized and aligned for contraction in the same direction.

Connective tissues allow for muscles to attache to bones and other structures.


What are the connective tissues of a muscle?

Endomysium, Perimysium, Epimysium, and Fascia.


Describe the Endomysium

The loose areolar connective tissue that surrounds each muscle fiber.

The innermost connective tissue layer made of loose Areolar tissue.

Empty space in the Areolar tissue allows the space needed for blood vessels and nerves to access each muscle fiber.


What is a Fascicle?

A grouping of ~10 muscle fibers in a bundle surrounded by Perimysium.

Fascicles can be seen as the "grains" on a piece of steak.


Describe the Perimysium

It is the thicker connective tissue that surrounds each FASCICLE.


Describe the Epimysium

Thicker connective tissue that surrounds the ENTIRE MUSCLE. This keeps all the fascicles of a muscle bundled together.


Describe Fascia, What are the two types?

The connective tissue that surrounds and separates muscles from other tissues.

Deep and Superficial


Describe Deep Fascia

Deep fascia separates one muscle from another.


Describe Superficial Fascia

Superficial Fascia separates muscles from overlying skin.

Superficial Fascia blends into and is hard to differentiate from Epimysium.

Superficial Fascia is the "gauze" layer.


What are the 3 attachments of Muscles to Bone?

Direct, Indirect and Aponeurosis


Describe a Direct Attachment of Muscle to Bone

The Epimysium surrounding the muscle fuses DIRECTLY with the periostium of the bone.

Intercostal and some facial muscles fuse attach this way.


Describe an Indirect attachment of a Muscle to Bone

Epimysium and Deep Fascia transition into a tendon which then inserts into the periosteum of a bone.

This is the most common attachment.

Creates a physical gap between muscle and bone.


Describe the Aponeurosis attachment of Muscle to Bone

The broad, thin, wide sheet like tendon that fuses muscle to bone found in muscles such as the Abdominal muscles.


Define ORIGIN as it relates to muscle attachment.

The origin is the stationary attachment point of a muscle to a bone. The bone that originates the muscle does NOT move.

Ex: The brachialis m. originates on the anterior surface of the humerous. The humerous doesn't move when the brachialis contracts.


Define INSERTION as it relates to muscle attachment.

The insertion is the MOVEABLE attachment point of a muscle to a bone. This bone moves when a muscle contracts.

Ex: The brachialis inserts on the proximal portion of the ulna. The ulna moves when the brachialis is contracted.


Define Agonist

The muscle in a group of muscles acting together to produce a movement that produces the MOST force during the movement.


Define Synergist

The muscle in a group of muscle acting together that AIDES the agonist in producing a given movement.

The synergist muscle typically has a different insertion. This helps to ensure a stable joint and prevents damage to a muscle or joint.


Define Antagonist

The muscle in a group of muscles acting together that OPPOSES the agonist, the antagonist creates movement in a joint that is in the opposite direction of the agonist.


Define Fixator

The muscle in a group of muscles acting together that PREVENTS MOVEMENT of a bone.

Ex: Rhomboids prevent movement of the scapula when the biceps brachii contracts.


What are Instrinsic muscles?

Muscles that have an origin and insertion in the SAME region. Ie. Tongue/Back Muscles, ect...


What are Extrinsic muscles?

Muscles that have an origin and insertion in DIFFERENT regions.

Ex: The Flexor digitorum superficialis originates on the humerous and proximal radius but inserts on the phalanges.


What is an example of a Skeletal Muscle that can also be considered Involuntary?

The Diaphragm


What does it mean when we say that muscle fibers are Terminally differentiated cells?

They don't divide and carry out mitosis.


What creates the striations of skeletal muscle fibers?

Overlapping bands of Actin and Myosin


What do muscle fibers start as when your young? What happens as you grow older?

They start as MYOBLASTS with a SINGLE nucleus.

As you grow older the myoblasts fuse together becoming muscle fibers with several nuclei as we know them.


What do undifferentiated myoblasts exist in adults as?

Satellite Cells which are a form of a Stem Cell.

We only have a small number of these cells and they are not very mitotically active.


What is the Plasma Membrane of a Muscle Fiber called?

The Sarcolemma


What is the Cytoplasm of a Muscle Fiber called?



What is the Endoplasmic Reticulum of a Muscle Fiber called?

The Sarcoplasmic Reticulum


Why is the Sarcoplasmic Reticulum so important to muscle function?

Because it acts as the internal storage site of Ca2+ Ions needed for muscle contraction.


Why do skeletal muscle fibers have more Mitochondria than most cells in the body?

Because they need to generate large amounts of ATP.


What are Myofilaments? What kinds are there?

Myofilaments are the protein filaments that cause the cell to contract. They are bundled together to form Myofibrils.

There are Thick, Thin and Elastic Filaments


What are Myofibrils?

They are the bundles of Myofilaments that allow a cell to contract.

Larger muscle fibers (cells) will contain more Myofibrils.


What are Muscle Fibers made of?

Myofibrils, which are made of myofilaments.

Muscle fibers also contain the nuclei, mitochondria and sacroplasmic reticulum of a muscle cell as well as the other components of the cell.


What are Transverse Tubules?

Small tubes that are created by the infolding of the Sarcolemma.

T-Tubules carry the electrical signals to the interior of a cell and triggers the release of Ca2+ ions needed for muscle contraction from the Sarcoplasmic Reticulum and the Terminal Cisternae.


What is a Triad?

The Transverse Tubule and BOTH Terminal Cisternae on either side of the Transverse Tubule.


Where are most of the Ca2+ ions stored prior to muscle contraction?

In the Terminal Cisternae and the Sarcoplasmic Reticulum.


What makes the Thick Myofilaments?

Myosin protein molecules twisted together with the "golf club head"

The Myosin filaments are then arranged end to end in a spiral fasion with the heads facing out to create the THICK myofilament.


What can the "Golf Club" Head on a Myosin protein molecule HYDROLYZE?



What are Thin Myofilaments made of?

Actin, Tropomyosin and Troponin


Describe the Thin Myofilaments

They are composed of long winding strands of Actin. Actin has an ACTIVE SITE that has the potential to bind to the "golf club" head of a Myosin protein.

The ACTIVE SITES are blocked during relaxation by Tropomyosin and Troponin.

When Ca2+ Binds to the Troponin the Tropomyosin moves exposing the ACTIVE SITE allowing it to bind to the MYOSIN HEADS.


Describe the Elastic Myofilaments

They are the Smallest of the filaments made of the protein TITIN.

These are the stretchy filaments that anchor the thick filaments in place.


Which proteins are considered the Contractile Proteins?

Myosin and Actin. They are responsible for the actual shortening of the muscle fiber causing a contraction.


Which proteins are considered the Regulatory Proteins?

Tropomyosin and Troponin, there job is to regulate when and if a muscle cell will contract.


What does DYSTROPHIN do?

It is the HUGE linking protein that anchors the Actin filaments to the Endomysium.


Why are linking proteins important?

Because without them the myofilaments would contract but they wouldn't cause the cell to shorten, the myofilaments must be anchored to the Sarcolemma and to the outer connective tissue via linking proteins like Dystrophin.


Explain what happens with people who have Muscular Dystrophy

The Dystrophin protein is mutated and non-functional so the myofilaments contract but they are not properly connected to the rest of the cell and so the muscle fiber does not contract resulting in loss of skeletal muscle function.


Describe a Sarcomere

Everything between the Z-Discs.

The A-Band (Dark MYOSIN Myofilaments)

The H-Band (the Space in the center that dissapears during contraction)

The I-Band (Light Actin/Elastic Filaments)


What are the Thin and Elastic Filaments attached to?

The Z-Disc


The Z-Disc is attached to what three things?

The Thin Filaments, Elastic Filaments AND the SARCOLEMMA.

This helps translate the contraction of myofibrils to the contraction of the muscle fiber.


What is the FUNCTIONAL UNIT OF CONTRACTION in a myofibril?

The Sarcomere


What do the Elastic Filaments attach to?

The Z-Disc and the Thick Myosin Myofilament.


Describe the I-Band

The LIGHT band of the sarcomere that contains Elastic and Actin Myofilaments. The Z Disc divides the I-Band.


Describe the A-Band

The DARK band of the sarcomere that contains overlapping thin, thick and elastic myofilaments. The H-Band is in the middle of the A-Band.


Describe the H-Band

The region in the middle of the A-Band where only Thick Myosin Myofilaments exist since the thin Actin and Elastic myofilaments do not extend that far.


What are the Elastic Myofilaments made of?



What myofilaments do Dystrophin attach to?

The Thin myofilaments made of Actin, Tropomyosin and Troponin


What is needed to make the myofibril, the muscle fiber and eventually the muscle to contract? Where does it come from?

A stimulus, it can come from a Nerve Impulse in the body or an Electrical Stimulation in the lab.


What are the specialized neurons that trigger muscle contraction?

Motor Neurons


What does the an Axon of a Motor Neuron do when it approaches a muscle?

It branches out into hundreds of smaller fibers.

This allows ONE nerve to stimulate MANY different muscle fibers.


What prevents muscle fibers from being sent mixed signals?

The fact that only ONE muscle fiber can be stimulated by only ONE nerve fiber.


What is a MOTOR UNIT?

All of the muscle fibers that a single motor neuron controls.

Large muscle may have hundreds of Motor Units.


What dictates the OVERALL STRENGTH of a muscle contraction?

The number of Motor Units stimulated.


What allows a muscle fiber to contract evenly and uniformly during a WEAK contraction?

The fact that muscle fibers of a motor unit are spread out over a large area rather than being centered in one area.



The process of adding more motor units during a strong contraction.


What allows for fine control of SMALL movements?

The ability to vary the # of motor units.


What is required for repeated sustained muscle contractions?

Having MANY motor units. When some motor units fatigue others will take over (shift work).


Nerves are made of MANY _______.



A weak nerve impulse results in...

Fewer and smaller motor units being stimulated causing a WEAK contraction and FINE movement.


A strong nerve impulse results in...

More, larger motor units being stimulated causing a STRONG contraction and LARGE movements.


Neurons "talk" to muscle fibers via the __________?

Nueromuscular Junction


What is a SYNAPSE?

The interaction between a Motor Neuron and a Muscle Fiber.



The very small gap between the Synaptic Bulb and the Sarcolemma of a Muscle Fiber.


What are the 3 cells involved in signaling a muscle fiber?

The Motor Neuron, The Muscle Fiber and the Schwann Cell.


What is a Schwann Cell?

A type of Glial Cell that aides the axon of a motor neuron to signal a cell.


What NEUROTRANSMITTER is involved in signaling a muscle fiber?

Acetylecholine, ACh

It acts like a chemical messenger that carries the signal from the neuron to the muscle cell.


Where are the vesicles filled with ACh located?

The Synaptic Bulb


What is the MOTOR END PLATE?

The portion of the Sarcolemma that contains the ACh RECEPTORS.


Describe the result of a nerve impulse at the synaptic bulb.

Gated ion channels in the synaptic bulb open allowing Ca2+ ions into the Synaptic bulb.

This triggers the exocytosis of vesicles filled with ACh.

ACh travels across the Synaptic Cleft and binds on the receptor sites of the Motor End Plate.

After ACh binds to the receptors it is rapidly degraded by Acetylcholinesterase.


What is the enzyme that degrades Acetylcholine?



Why is it important for ACh to be rapidly degraded once it binds to receptor sites on the motor end plate?

If ACh isn't broken down it will continue to stimulate the muscle cell. The degrading of ACh allows the muscle fiber to relax.


What does it mean to say that Motor Neurons and Muscle Fibers are ELECTRICALLY EXCITABLE?

The voltage across the cell membrane changes when it is stimulated.


In a resting state where is the negative charge located? What about the postive?

The INSIDE is Negative, the Outside is POSITIVE.


What are the main negatively charged things in a cell?

Negativly charged Ions, Proteins, and DNA.


What does it mean for a cell to be POLARIZED?

When there is a charge difference across the cell membrane.


Where are the Na+ ions when a cell is resting? What about the K+ ions?

Most are Outside, Most are Inside


What maintains the Polarized cell? Think Na+ outside and K+ inside.

The Na+/K+ ATPase pump.


What happens to Polarization when a stimulus is introduced?

The cell becomes Depolarized.

Na+ ion channels open and Na+ rushes in down it's concentration gradient (Facilitated Diffusion).

For a BRIEF period the inside of the cell becomes positively charged.


What happens when a cell becomes Depolarized?

The Na+ ion channels close and K+ channels open this allows the cell to regain the Negative charge inside and the positive charge outside leading to REPOLARIZATION.



Return of membrane charge to negative inside and positive outside.


What is the change from negative to positive and back to negative inside a cell reffered to as?

An Action Potential


What does it mean to say that an action potential is a LOCAL occurance at a specific region of the cell membrane?

It means that only a small portion of the cell membrane is depolarized at a given time.


What does it mean that Action potentials are self propagating?

Depolarization of one region triggers the depolarization of the region next to it.


Depolarization is IMMEDIATELY followed by what? Why is this important?

Repolarization, this is nessecary to allow a nerve or muscle cell to be restimulated.


What is the neuromuscular junction? What are the major parts and actors in the junction? What happens?

It is the junction where a nerve tells a muscle when and how to contract.

Major parts include the Motor Nerve Fiber, A Schwann cell, the Synaptic Bulb, the Synaptic Cleft, and the ACh receptor sites on the Motor End Plate.

Ca+ introduced to the Synaptic Bulb triggers exocytosis of vesicles containing ACh. The ACh binds to receptor sites and opens channels allowing the depolarization of the cell leading to voltage gated channels to be opened propogating the depolarization of the cell membrane.


The ACh receptor sites play two roles what are they?

They bind ACh which changes the channels conformation.

The change in conformation allows the channels to OPEN allowing Na+ ions to rush across the cell membrance to depolarize the portion of the cell membrane. At the same time the SLOWER diffusion of K+ ions out of the cell causes REPOLARIZATION.


What are Ligand-Gated Ion channels?

Channels that change confirmation and open in response to a ligand (ACh) binding to them.


What is the first part of the muscle fiber to become depolarized?

The Motor End Plate


What happens when the LOCAL fluctuation of membrane voltage occurs at the Motor End Plate?

It leads to the activation of VOLTAGE GATED ion channels which propagates over the rest of the cell membrane.


Where will you find the VAST majority of Ligan gated ion channels on a Muscle fiber?

The Motor End Plate


What are Voltage gated ion channels?

Ion channels that require a change in membrane voltage to open and cause depolarization.

They sense changes in membrane voltage and when a nearby depolarization occurs it triggers them to open and let Na+ ions enter the cell. This is reponsible for proagating the action potential across the surface of a muscle fiber.


What is Excitation/Contraction coupling?

The poscess by which we translate the action potential on the sarcolemma to the contraction of myofilaments inside the muscle cell.


Describe what happens after an action potential leaves the motor end plate.

It travels along the sarcolemma by the use of voltage gated ion channels that were triggered when the action potential began with the Ligand gated ion channels.

The action potential spreads over the entire surface of the muscle cell and down the T-Tubules.

The action potentials travelling down the T-Tubules triggers the opening of Voltage gated Ca2+ ion channels in the Sarcoplasmic Reticulum allowing Ca2+ ions to exit the SR and enter the sarcoplasm where the myofilaments are located.


What happens when Ca2+ ions are released into the Sarcoplasm from the Sarcoplasmic Reticulum?

The Ca2+ ions bind to the Troponin on the thin myofilaments causing Troponin to change conformation moving the Tropomyosin and exposing the ACTIVE SITES of the Actin molecules.


What is contraction?

The process by which the muscle fiber generates Tension (force) and is capable of contraction.


What is the Sliding Filament Theory?

The theory that states, during contraction, myofilaments (thick and thin) slide past each other thereby generating tension and pulling the Z-Discs closer to each other and thus shortening the Sarcomere.


Which band dissapears during full contraction?

The H-Band


Describe the 1st step of Contraction

The Myosin Head binds to one molecule of ATP.

The enzyme Myosin ATPase hyrolyzes ATP releasing energy.


The energy produces is used to activate the Myosin head, it reaches out to bind to the active sites of Actin.


Describe the 2nd step of Contraction

The myosin heads BIND to the exposed active sites of Actin creating a CROSS BRIDGE

After binding to Actin the Myosin head releases ADP+P causing it to return to it's original conformation. This pulls on the THIN filament bringing the Z-Disc closer.

The Biding of a new ATP molecule causes the Myosin Head to release the Actin Molecule.


What is a Cross Bridge?

The link between a Myosin Head and the exposed active sites of Actin.


Each time a myosin head rachets it uses what? How many times per second can a single myosin head rachet?

ATP, 5x Per Second

1000's of myosin heads all racheting at the same time uses a VERY LARGE amount of ATP.


Describe the Relaxation phase

The motor neuron stops releasing ACh, the remaining ACh bound to receptors are degraded by Acetylcholinesterase.

This prevents action potentials from being generated at the motor end plate.

The Ca2+ Ions in the Sarcoplasm are pumped back into the SR and Ca2+ ions diffuse away from Troponin causing Tropomyosin to cover the active sites of Actin and prevent Myosin from binding.

Without Myosin biding the Thin filaments slide BACK over the Thick filaments and the Sarcomere lengthens returning to resting length.


What happens to the Ca2+ ions in the Sarcoplasm during relaxation?

They are PUMPED back into the Sarcoplasmic Reticulum using Active Transport requiring ATP.


Where in the process of Muscle Contraction is Ca2+ required?

At the Synaptic Bulb to release the vesicles containing ACh.

In the Sarcoplasm so the Ca2+ ions can bind to the Troponin causing Tropomyosin to expose the Actin Active Sites allowing Crossbridge Formation.


Where in the process of Muscle Contraction is ATP required?

Maintenance of cell polarization: In the Na+/K+ ATPase pump requiring ATP to maintain the Na+ gradient thereby keeping the interior of the cell negatively charged.

Muscle Fiber Contraction: At the Myosin head to provide the energy for the racheting.

Muscle Fiber Relaxation: In the Active Transport of Ca2+ ions back into the Sarcoplasmic Reticulum for relaxation.


Where in the process of Muscle Contraction is ACh required?

At the motor end plate to translate the action potential across the synaptic cleft and to the Sarcolemma of the muscle cell. This allows the voltage change to occur on the cell membrane and causes the nearby voltage gated ion channels to propagate the action potential across the cell membrane and down the T-Tubules.