Muscle Contraction Flashcards
Types of tissue
Epithelial
Connective
Nervous
Muscular
Types of muscle tissue
Skeletal, cardiac, smooth.
Muscle cells
Thanks to their unique protein arrangement they can contract
Skeletal muscle tissue
Long, multinucleate, stritated. Can be up to 30 cm in length
Smooth muscle
Sickle shaped
No striations
Muscle of involuntary nervous system.
Can constrict airways and blood vessels. Can move food down via peristalsis.
Involuntary
Single nucleus
What causes striations?
Sarcomeres: highly organized protein structures
Cardiac muscle
Striated
Only one nucleus
Have highly organized actin myosin sarcomeres
Branched
Sometimes a capillary between branching
Have intercalated discs.
Lots of sarcomeres
Huge number of mitochondria. Can make up 35-40% of cell
Dark lines are intercalated discs
Intercalated discs
Looks like egg cartons together
Has lots of gap Junctions and desmosomes
Beats in syncytium.
Creates cytoplasm to cytoplasm connections between all cardiac muscle cells. Anchoring junctions prevents shear stress
Ability to repair of muscle tissues
Skeletal muscle: a little bit
Smooth muscle: best ability to repair itself
Cardiac muscle : not at all. Amitotic. Causes higher risk of ischemia(stop blood flow) and hypoxia (lack of oxygen).
Cardiomyocyte
Cardiac muscle cell death.
That section of heart dies that lost its oxygen supply. Gets filled with connective tissue. Limits heart capacity
Muscle fiber is
Muscle cell
Fuse together early on
Can be up to 30 cm in length.filled with cables called myofibrils
Myofibrils
Made up of myofilaments (smallest units) like myosin and actin.
Have lots of mitochondria. Needed for muscle movement.
Smallest structure in a muscle cell is
Myofilaments. Bundle together to make myofibrils
Endomysium
Layer or connective tissue that covers muscle fiber.
Satellite cells in muscles
Help muscles grow.
Grow by enhancing or creating more of the myofibrils of the muscle fiber itself.
Muscle fascicle
Group of muscle cells together. Column of muscle cells.
Perimysium
Around fascicles peri-around
Groups of fascicles together
Belly of muscle itself
Surrounded by epimysium
Deep fascia
Wraps in and around groups of muscles and organs above epimysium
Possible length of smooth muscle
200 micrometers in length
Sarcolemma
Plasma membrane around q skeletal muscle cell
Sarcolemma=cell membrane
Myosin
Thick filament
Actin
Thin filament
-in
Protein suffix
Sarcomere
Distance between 2 z discs
From halfway between light band to halfway between light band
Including dark band between
Hundreds and thousands in a single muscle cell. All contract at once to make cell shorter
Basic functional protein unit of contraction in skeletal muscle cells and cardiac muscle cells. In smooth muscle, arrangement is different
Sarcomere
Z discs made of
Titin. One of the biggest proteins made in the human body.
Function of Z discs
Anchoring points
Myosin
ATP-ase, carries out the motion.
Grab onto actin and change shape pulling against the actin. Shrinks ends of sarcomeres
I band
Light band
A band
Dark. Mostly myosin with some overlapping actin.
M line
Line down middle of connecting myosin strands
As the ends of sarcomere contract
I have myosin, I have actin
When sarcomere contracts, the actin gets pulled along the myosin. Neither protein gets shorter, the myosin just rachets the actin past it. As myosin begins to overlap actin during muscle contraction, the I bands get really small and disappear.
Sarcoplasmic reticulum
Same as endoplasmic reticulum. Important for the synthesis of proteins
In muscle fibers and around the myofibrils where we find the sarcoplasmic reticulum, it does the normal endoplasmic reticulum stuff, but it becomes an important storage location for calcium.
Important because calcium is part of signaling pathway that leads to muscle contractions taking place. Think about it storing calcium
T-tubules
Nearby to sarcoplasmic reticulum. connect the sarcolemma to the inside of the cell. Wrap around in a net-like pattern around myofibrils
Why?
Bring outside of the cell in deep and around myofibrils. When depolarization happens, that depolarization travels very quickly. Rapid transmission of action potentials and help regulate calcium concentration
Recap of action potentials:
When signal arrives(depolarization). Motor neuron plugs into muscle fiber and at the end of synaptic knobs ACh is going to be released and travel across the synaptic cleft to bind to ligand gated receptors on the sarcolemma called motor end plate. Sodium rushes in and starts the depolarization of the next muscle cell
Structures that help myosin pull actin
Has two heads, looks like double headed golf club.
Heads have binding sites for actin. Myosin is gonna bind to ATP and change shape. When it changes shape, that gives us one tug on actin. To move great distance have to. Shrink sarcomeres a lot
When is muscle contraction happening
As long as calcium is present, it’s been released from sarcoplasmic reticulum, those myosin heads are going to pull. Think tug of war or climbing a rope end over end. Pulling over and over. Each myosin molecules out of the billions of myosin molecules is going to be pulling against that actin.
- Reach forward
- Pull against it
- Let it go
Why don’t myofilaments shrink?
They slide past eachother like fingers pushing between fingers. Sliding movement caused by ATPase or myosin
Actin subunits
Similar to a ping pong ball. One one side has a little “Velcro” that acts as binding site for myosin.
When not in use, binding sites are: covered up.
Bond between Actin and myosin
Super strong bond.
One of strongest in human body
How are actin subunits covered up?
Tropomyosin helps cover up actin subunits: when there’s no calcium signal present in sarcoplasm (cytoplasm of muscle cell) it covers up binding sites on actin from myosin
“switch” protein troponin
Troponin: has binding site for tropomyosin, Binding site for actin, binding site for calcium
Light switch that tells muscle to contract
Importance of Calcium in muscle contraction
No calcium present and bound to troponin, therefore tropomyosin covers actin binding sites. The myosin, even if ATP is present has nothing to grab onto. Myosin has nothing to do.
Motor unit
Motor neuron + all of the muscle fibers it innervates in any given muscle
Nervous system innervation of muscles
- Peripheral motor neuron leaves through ventral root and sends out signal. Motor neuron from somatic motor system. Myelinated
- Motor neuron innervates a group of muscle fibers
Motor units
Allow same set of muscles to use different amounts of force to pick up different items
Made of: motor neuron+ all the muscle fibers that it innervates.
Come in different kinds
Different kinds of motor units
Small, fast,
medium,
huge, slower acting
Recruit motor units from smallest to largest as more force is needed
Neuromuscular junction
Where a motor unit meets a muscle.
It’s where the synaptic knob is going to hover over a special part of the sarcolemma called the motor end plate
Why does motor end plate wind back and forth?
To increase surface area so we can have more ligand gated sodium channels.
What happens after depolarization of a muscle fiber?
- Have to get signal in and around all myofibrils.
At this point ach has been released. (Neurotransmitter of neuromuscular junctions) In voluntary or skeletal system.
Na is going to rush into the cell
Openings in sarcolemma
Connect to t-tubules
Transverse tubules
T-tubules
Transverse tubules because they connect and surround myofibrils in the transverse plane along the long cylindrical muscle fiber cell. Cause depolarization to occur in and around all of the myofibrils
What happens as signal reaches down into myofibrils?
When it gets next to terminal cisterna of sarcoplasmic reticulum
In skeletal muscle these are a swollen area of sarcoplasmic reticulum that specializes in calcium storage
When signal gets down and around t-tubules, it’s going to cause
Calcium to be released from sarcoplasmic reticulum into sarcoplasm or the cytoplasm of the muscle cell
- Calcium is out of sarcoplasm and can bind to troponin.
What’s going to happen when calcium binds to troponin? Long helical tropomyosin strands unwind exposing the myosin binding sites on actin subunits - Within fraction of millisecond, myosin heads are going to stick to the actin.
- Contraction process starts
Starting from the outside, describe the process of muscle fiber contraction
- Depolarization signal reaches the axon terminals whose synaptic knobs are
- Depolarization causes calcium to rush into the synaptic knob, causing vesicles with acetylcholine to be released by exocytosis into the synaptic cleft. Ach diffuses across synaptic cleft.
- Ach binds to ligand gated sodium channels on motor end plate
- Na starts to rush into cell, that action potential travels along the t-tubules
- AP gets down to cisterna. Releases calcium into sarcoplasm.
- Calcium binds to troponin. Troponin causes tropomyosin to unwind, exposing myosin binding sites
7.. cycling by pulling on actin and letting it go. Happens billions of time with all the myosins molecules
8.sarcomeres shrink, contracting the muscle cell
- Muscle shortens and produces tension
Cisterna
Collection area, swollen region of sarcoplasmic reticulum filled with calcium
How to undo muscle contraction
Everything happens in reverse
Store Ca in sarcoplasmic reticulum, break down ACh
- Pump calcium back into sarcoplasmic reticulum which requires energy (ATP).
- Once calcium is missing from troponin, tropomyosin goes back to it’s normal shape and covers up all of the myosin binding sites
3.ach that’s left is denatured with help of acetylcholinesterase. Some can be pumped back into synaptic knob and remade into acetylcholine. Some of it will diffuse away. Have to get rid of it to stop Na from rushing in. NaK pumps help reestablish concentration gradients.
Undo everything we just did
Products of acetylcholinesterase
Acetic acid & choline
Cross bridge cycling
1.when myosin head first connects we have ADP and inorganic phosphate connected to the head.(Myosin has already used ATP, byproducts are left)
- ADP and inorganic phosphate are released from myosin head. Shape of myosin head has changed. (Power stroke) Getting ready to pull, think cocking
When proteins bind something, they usually change shape - As it’s getting ready to pull(power stroke occurs) when we lets those go, it pulls. Use ATP to break that strong bond between myosin head and the myosin binding site on actin subunit. Once that happens, we break away when ATP dissociates into ADP and inorganic Phosphate
- Myosin head straightens out again
Generates the force necessary to move skeleton
Contraction of skeletal muscle
Contraction is triggered by
Series of molecular events known as the cross-bridge cycle
Sarcomere shortens when
Myosin heads in thick myofilaments form cross bridges with actin molecules in thin myofilaments
When is the formation of a cross bridge initiated?
When calcium ions are released from sarcoplasmic reticulum to bind to troponin . Binding causes troponin to change shape
Myosin head must be ____ before cross bridge cycle can begin
Activated. Occurs when ATP binds to myosin head and is hydrolyzed into ADP and inorganic phosphate. The energy liberated from the hydrolysis of ATP activated the myosin head, forcing it into cocked position.
Four steps of cross bridge cycle
- Cross bridge formation: activated myosin head binds to actin, forming a cross bridge and inorganic phosphate is released..the bond between myosin and actin becomes stronger.
- Power stroke: ADP is released and the activated myosin head pivots sliding the thin myofilament towards the center of the sarcomere.
3.cross-bridge detachment: when another ATP binds to the myosin head, the link between the myosin head and the actin weakens and the myosin head detaches
4.reactivation of the myosin head
ATP is hydrolyzed to ADP and inorganic phosphate. The energy released during hydrolysis reactivates the myosin head. ATP is hydrolyzed to ADP and inorganic phosphate. The energy released during hydrolysis reactivates the myosin head, returning it to the cocked position.As long as the binding sites on actin remain exposed, the cross-bridge cycle will repeat. As the cycle repeats, thin myofilaments are pulled toward each other and the sarcomere shortens, causing the whole muscle to contract
When does cross bridge cycling end?
When calcium ions are actively transported back into the sarcoplasmic reticulum. Troponin returns to its original shape, allowing tropomyosin to glide over and cover the myosin binding site on actin.
Pathophysiological example of something that can go wrong with muscle
Myasthenia gravis- autoimmune disorder that attacks ligand gated sodium channels that bind ACh. Starts in face, causing partial paralysis of facial muscles.
Usually stops at face.
Can sometimes lead to early mortality.
How to fix: immune suppressants
Some drugs affect acetylcholinesterase in synaptic cleft, ach stays longer to find ligand gated sodium channels in receiving muscle cell
How do we power muscle contraction
Cellular respiration
Some muscle cells do mostly glycolysis. Generate a little bit of ATP for a short burst of energy
Steps of cellular respiration
- Glycolysis: occurs in cytosol, makes a little ATP and some NADH that can be passed on to next two steps.
- Citric acid cycle : in mitochondria, require oxygen as terminal electron acceptor
3.oxidative phosphorylation: in mitochondria, require oxygen as terminal electron acceptor.
After 2&3 lots of ATP is generated
Myoglobin
Makes muscles red.
Helps bind oxygen and keep it in muscle cells
Steps for powering muscle contractions
- Use free ATP: available ATP in muscle, lasts 2-3 seconds
2.phosphagen system: creatine phosphate bumps into ADP to make ATP. 4-5 second s
3.glycolysis: 30s taking glucose in the cytosol and break it down to pyruvate to make a little bit of ATP
4.oxidative phosphorylation: most energy
Take pyruvate at end of glycolysis and releases some CO2 and convert it into acetocoenzyme A, enters citric acid cycle and use high powered electrons and use them in electron transport chain to make lots of ATP
Fast twitch and slow twitch muscles
Fast glycolytic, slow oxidative.
Endurance training increases slow oxidative fibers (red has myoglobin, helps make ATP)
Sprinting training develops what kind of fibers?
White glycolytic fibers
Fast twitch fibers
Few mitochondria
Low myoglobin
Does lots of glycolysis to make a little ATP
Slow oxidative fibers
Slow twitch fibers,
Red fibers,
Lots of myoglobin,
Lots of mitochondria,
Active over long haul,
Produce lots of ATP using citric acid cycle and electron transport chain
Types of muscle contractions
Concentric
Eccentric
Isometric
Concentric and centric are types of
Isotonic contractions
Isotonic contractions
Under load, the muscle is actually going to shrink or lengthen under the load. The muscle itself changes length
Isometric contractions
Muscle is under load,
Does not change length
Holding a weight in place
Concentric contraction
Muscle contracts, lifting weight
Eccentric contraction
Muscle elongates
Putting weight down
Ideal length of a sarcomere
As muscle becomes completely contracted, tension or contractile force is reduced.
At maximum tension: standard distance between Actin and myosin.
When muscles are stretched too far no cross bridges form. Occurs when you pick up really heavy iron weight with either arm. Muscles are stretched out as far as they go.
Muscle twitch
- Single stimulus
Single muscle twitch
2.latent period:ach released, sodium goes into muscle cell. Depolarization goes down around t-tubules. Calcium is released and binds to troponin. Tropomyosin has to unbind. Have to do cross bridge cycle.takes around 5 milliseconds
Contraction period
Cross bridge cycle. Happens again and again
Myosin heads grab actin and let go. Takes another 20 or so milliseconds to reach maximum contraction period
Extended relaxation period
Pump all calcium back out
Get rid of ACH through ach, or through diffusion through synaptic cleft. Pump sodium back into extra cellular fluid 1/10 of a second
Wave summation
Signal repeatedly to increase tension. Do summation event . Never lets muscle completely relax. Muscle twitch is not allowed to end completely
Tetanus
Only achievable through lab or pathology.
Maximum contraction over an extended period of time
Atrophied muscle
Caused by macrophages with lysosomes. Body streamlines energy use.
Number of myofibrils is significantly lower.
Smooth muscle locations
Blood vessels, airways, digestive system, urinary system, reproductive system
Gap Junctions
Connect cytoplasm of one of those cardiac muscle cells to another. Allow muscle cells to work together in syncytium (bunch of cells acting as one big cell)
Have lots of fascia,. adherens junctions and desmosomes
Difference between skeletal and cardiac muscle
Sarcomeres are well developed
Sarcoplasmic reticulum is well developed, do have t-tubules.,
Cardiac muscle cells do not have cisterna(swollen long regions along t-tubules, not as advanced as storage of calcium) of sarcoplasmic reticulum.
In cardiac muscle extracellular calcium
May represent up to 40% of calcium needed to lead sarcomere contractions
Leading cause of early mortality
Cardiovascular disease
Ischemia
Lack of blood flow to an area, hypoxia, leads to cell death because can’t produce ATP. Cells are amitotic, don’t divide often. Tissue is going to die
Dense connective tissue
Used to fill gaps, can fill gaps in the heart. Heart never functions the same.
Function of spiral pattern of heart tissue
Twist or wrenching motion. Twists and contracts.
Endocardium
Inner lining of heart. Continuous blood vessels connected to the heart
Serous membranes around heart
Pericardium: around heart
Visceral pericardium: on surface of heart. (Epicardium)
Pericardial cavity
Filled with serous fluid
Parietal pericardium and fibrous pericardium
Located on outside
Serous pericardium function
Serous pericardium allows the heartbeat to beat and move and reduce friction around thoracic cavity and mediastinum
Single unit (visceral smooth muscle)
Digestive system, urinary system, respiratory system, blood vessels, reproductive system
Functioning like sheets of muscle contracting
Most common
Has varicosities
Instead of motor neuron terminating into smooth muscle, varicosity would wrap around smooth muscle.
Multi unit smooth muscle tissue
Individual cells are going to be contracting.
Found in eye
Varicosities
Vesicles with neurotransmitters. Allows for smooth, slow, pulsing contractions of sheets
Set of smooth muscle is made of
Circular inner layer, makes tube
Longitudinal outer muscle
Instead of sarcomere units, smooth muscle cells have
Active myosin bundles and dense bodies more like net.
When contracted, net shrinks up. Different than in skeletal and cardiac muscle
Deep to circular layer of stomach, we have an
Oblique layer of smooth muscle. Let’s stomach carry out wrenching motion.
Only found in stomach
Peristalsis
Push food down through peristalsis
Segmentation
Mixing action.
Makes food into single, homogenous mix.
Intestines can carry out peristalsis and segmentation.
Submucosal plexus
Plexus of autonomic nerves
Meissner’s plexus
In submucosa
Myenteric plexus
In between layers of the muscle circular to the inside, longitudinal and the outside.
What creates complicated intestinal movements
Myenteric plexus and submucosal plexus working together
Artery
Lots of smooth muscle around edge.
Can help raise blood pressure
Ruffled endothelium
Ruffled layer or simple, squamous epithelium inside of artery.
Peripheral nerves
Surrounded by perineurium
Smooth muscle can be found in
Arteries,
Ureters(has longitudinal muscle inside, circular muscle outside)
Bronchioles
Sarcolemma
Plasma membrane of a muscle fiber
Myofibrils
Rod-like bundle of contractile filaments (myofilaments) found in muscle fibers (cells).
Myofilaments
Filament that constitutes myofibrils. Of two types. Actin and myosin
Explain cross bridge cycle in your own words
- The myosin heads have ADP+P from a previous contraction.
- Calcium exposes the myosin binding sites on actin when Ca2+ binds to troponin, causing tropomyosin to lift, exposing the myosin binding sites.
- The myosin heads bind to the myosin binding sites, causing P to detach from the myosin head.
- The myofilaments glide past each other,powered by chemical energy in the heads.
ADP detaches
- Gliding motion stops when ATP binds to myosin heads, breaking the Actin-myosin bond.
- ATP turns into ADP and P, with the energy released stored in the myosin heads
- Presence of Ca 2+ ions reactivates the cycle
