Muscles Flashcards
Tissue types, compositions, theory of movement
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Attributes of muscles
Contract - generate movement in and of the body
Extensible - they can be stretched
Elastic - passively resists stretching, no E needed
Excitable - can have an electrical signal run through them
Contractile - uses E to generate forceful contractions
Action Potential
An electrical signal that travels along a cell.
Neurons → muscle cell
Tissue Types
Skeletal - strucute + stability
Cardiac - heart only
Smooth - organs, GI tract, etc.
Skeletal muscle attributes
Attached to bones
Moves body parts
Voluntary movement controlled by the motor cortex
Fibers are multinucleated , large, cylindrical in shape + striated
Somatic Motor Neurons
Neurons that leave the CNS to stimulate skeletal muscle contraction
Cardiac Muscle Attributes
Only in the heart
Cells are branching
Have intercalated discs
Striated
Autorythmic
Involuntary
Intercalated Discs
Protein structures in cardiac muscle that separate cells and allow AP to spread between cells
Smooth Muscle Attributes
Not striated
Involuntary
Sometimes autorythmic
Cells are spindle shaped
No epimysium
Have endomysium around cells
Some can be controlled by the hypothalamus
Doesn’t need a change in the membrane potential to contract
Striated vs Smooth
Muscle
Striated: Organized bands of proteins that generate movement (sarcomeres)
Smooth: Have similar proteins to generate movement that don’t line up.
Sarcomeres
Protein complexes composed of myosin, actin, z-discs, titin, and m-lines to generate contractions in muscle cells.
Myosin
The motor protein that generates contractions in striated muscle.
Has a head and long tail (not going to see it alone)
Myosin Thick Fillament
Big thick fiber with many myosin molecules wrapped together with the heads sticking out of the sides to face opposite directions.
The heads are responsible for pulling towards the midline.
Actin Thin Filaments
Several actin molecules surround each myosin thick filament.
The heads of myosin filaments grab onto the actin + pull.
Z-Disc
Protein complexes on either side of a sarcomere.
Actin filaments are attached to the disk,
when myosin pulls on actin → z-discs are pulled closer together.
M-line
Located in the middle of the sarcomeres to hold myosin thick filaments in place + is attaches to the plasma membrane.
Sliding Filament Theory
How sarcomeres contract:
Myosin and actin filaments slide past each other, heads on opposite ends of myosin pull actin in the opposite direction
Myosin heads pull actin toward the M-line, Actin is attached to z-discs, myosin thick filament heads with actin pull z-discs toward each other, z-discs are attached to the plasma membrane so the entire cell contracts.
10,000 sarcomeres contracting = muscle contraction
Steps of Sarcomere Contraction
- Myosin head forms a cross-bridge with actin
- Power stroke - Releases ATP
- Myosin head binds ATP + releases actin
- ATP → ADP + Pi gets energy out
Uses energy to cock head (think of cocking a gun) - Cycle repeats
+ Next time a myosin head grabs the actin further down
+ All the heads on one myosin pull on actin together
+ Some heads are holding actin at any time
Myosin uses ATP for energy
Myoson head is pulling on the actin filament
Crossbridge
The attachment between myosin head + actin.
Power stroke
When a myosin head swings back and pulls actin with it.
A-Band
DArk band = myosin thick filaments all lined up
Striation band
I-Band
LIght band = space between adjacent myosin thick filaments
Striation band
Z-disc is in the middle of the I-Band
What happens to striation bands during contractions?
A-Band: doesn’t change size - do get closer together
I-Bands: get shorter - as sarcomeres contract, myosins pull closer so there’s less space between them
Muscle Fiber
Components
- Sarcomere
- Myofibril
- Saracoplasm
- Sarcoplasmic Reticulum
- Sarcolemma
- T-tubules
- Satelite cells
Myofibril
A bundle of sarcomeres lined up one after another.
Sarcoplasm
Cytoplasm of skeletal muscle fibers
Sarcoplasmic Reticulum
Specialized smooth ER in skeletal muscle cells that surround myofibrils & are full of Ca++.
Sarcolemma
Skeletal muscle’s plasma membrane.
T-Tubules
Tubes that act as extensions of sarcolemma by making contact with the sarcoplasmic reticulum. Visible tubes going down into cell skeletal muscle cells.
Where does a muscle action potential travel in a muscle fiber?
Travels along sarcolemma + down T-tubules.
Satellite cells
Little cells that sit around muscle fibers, located next to the sarcolemma.
When muscle cell grows or is damaged, the satellite cells merge with muscle cells + become part of the cells, making muscle bigger (why skeletal muscle tissue is multinucleated)
Skeletal Muscle Organ
Components
A muscle
Many muscle fibers bundled into fascicles with other connective tissues.
* Dense irregular tissue membranes
* Blood vessels
* Motor neurons
* White blood cells
* Sensory neurons
Fascicle
Multiple muscle fibers bound together.
Many bound together create an organ.
Endomesium
Connective tissue that surrounds muscle fibers.
gives muscle some elasticity
Perimysium
Connective tissue that surrounds fascicles.
gives muscle some elasticity
Epimysium
Connective tissue that surrounds the entire muscle organ + is continuous with tendon.
gives muscle some elasticity
Muscle sensory neurons
Covered in class + what they detect
Generally detect:
Touch
Pain
Temperature
Chemicals
Muscle spindles detect how much a muscle is stretched.
Golgi tendon organs detect force on muscle
Muscle Contraction
Overview
ATP in neuron → neuron releases ACH → ion channels open in muscle cell = Muscle Action Potential → sarcoplasmic reticulum releases Ca++ into the sarcoplasm → Ca++ binds troponin → troponin moves tropomyosin, so myosin can bind acting → myosin grabs actin + pulls
Excitation contraction coupling
Definition
muscle cell has an action potential that leads to a contraction
Somatic Motor Neurons
Purpose in skeletal muscle
- start in the spinal cord or brain (CNS)
- Axons (long extensions) travel out of the CNS and touch the muscle cells
- When they signal skeletal muscle cell → muscle contracts
Neuromuscular Junction
Where the tip of an axon of a somatic motor neuron touches a muscle cell.
ACH is released by the neuron at the neuromuscular junction, this chemical is responsible for making muscles contract.
Acetylcholine
(ACH) - chemical released by the neuron at the neuromuscular junction.
Makes muscles contract.
Action Potential
Electrical signal that travels along the axon of motor neurons
From opening + closing ion channel
What happens when an action potential reaches a neuromusclular junction?
The neuron releases ACH.
When receptors + ion channels bind ACH → they open → Na+ + Ca++ flood into the cell, cell becomes more positive.
Muscle Action Potential
(MAP)
Occurs when the cell becomes positive from Na+ & Ca++ channels opening → make more Na+ channels open further away from the neuromuscular junction.
* MAP spreads out along sarcolemma and down t-tubules = a wave of positive charge spreads through the cell + down t-tubules
Tropomyosin
A protein that wraps around actin filaments and prevents myosin from forming crossbridges (myosin can’t contract).
Troponin
Protein that binds tropomyosin
* When Ca++ is present - troponin binds Ca++
* Moves tropomyosin
* Now myosin can bind actin
Muscle Relaxation
process
No MAP → sarcoplasmic reticulum ion channels close + Ca++ is pumped back into the sarcoplasmic reticulum (Active transport) → with no Ca++, troponin moves tropomyosin back into place so that it blocks myosin → myosin can’t bind actin - no more contraction, cell relaxes
Motor Unit
1 motor neuron + all the muscle fibers it controls
* Each muscle fiber is controlled by 1 motor unit
* Each motor unit controls several muscle fibers
* Each muscle organ has many motor units
Recruitment
Occurs when a motor unit is activated + its muscle fibers contract.
+ electrical stimulation → + strength of contraction; because it recruits more motor units
+ motor units → + contraction
Twitch
A contraction from a single stimulation with 3 parts.
1. Latent period
2. Contraction
3. Relaxation
Twitch
Latent Period
Time between stimulation + when contraction happens
Contraction
Myosin pulls on actin, muscle shortens
Twitch
Relaxation
Ca++ is pumped back into sarcoplasmic reticulum + muscle goes back to resting length.
Temporal Summation
2 contractions close to each other = get a stronger contraction; one starts before the other ends + add up together.
Tetanus
Many stimulations in a row + contraction gets bigger + bigger
Fused Tetanus
Contractions close enough together that get some increase in strength.
Can reach maximum strength for muscle fiber- When it reaches max, it can’t get stronger
Unfused Tetanus
Stimulations have some time between them making the contraction look bumpy aka Steppes.
Length Tension Relationship:
Too Long
Not all myosin heads overlap with actin filaments, and myosin can’t generate as much force.
Intermediate length is ideal for maximum strength
Length Tension Relationship:
Too Short
Actin filaments bump into each other at the M-line - can’t generate as much force
Intermediate length is ideal for maximum strength
Tension
Force generated by muscle.
Dependant on how far a muscle is stretched.
Isotonic Contraction
Same force, contraction strong enough to shorten the muscle
* Muscle gets shorter but the tension remains the same
Isometric Contraction
Same length, contraction where the muscle doesn’t get any shorter
* Muscle stays the same but the force increases
* Can’t lift it
Phosphocreatine
What is it? What’s its role in muscle energetics?
A short source of energy for muscles.
When a muscle doesn’t need energy, takes P out of ATP → puts it on creatine to make phosphocreatine
When it needs energy, takes P off of phosphocreatine and puts it on ATP
Aerobic respiration
What is it? What does it do?
Cellular respiration by the mitochondria for generating ATP from energy in glucose and sometimes free fatty acids floating in the blood using O2.
When muscles don’t need energy - it’s stored as glycogen
When it needs energy- glucose is broken off of glycogen + uses glucose for energy
Myoglobin
Protein similar to hemoglobin that makes muscles red and brings O2 from the plasma membrane to the mitochondria.
Anaerobic Respiration
Not oxygen respiration.
Burning glucose through glycolysis.
Glycolysis
The first stage of cellular respiration happening in the cytoplasm.
Glucose → 2 Pyruvate + energy
Faster and less efficient than cellular/ Aerobic respiration.
What do we do with the leftover pyruvate?
- Converts to lactic acid
- Lactic acid is transported to the liver
- Turned back into glucose using energy
How do muscles use energy sources?
- Creatine phosphate
- Anaerobic respiration = glycolysis
- Aerobic respiration of glucose
- Aerobic respiration of fatty acids for long-sustained contraction
When muscle rests:
Restores reserves of phosphocreatine, glycogen (to make glucose), and fatty acids.
How do muscles reach fatigue?
- Run out of ATP for contraction
Muscle will stop contracting before completely running out or else the cell would die - Ion imbalances
Ca++ coming out of sarcoplasmic reticulum
K+ in plasma membrane from muscle action potential - CNS can shut muscles down so it doesn’t get overused
Not from lactic acid build-up
Muscle Fiber Types
- Slow oxidative - Slow twitch
- Fast oxidative
- Fast glycolitic - Fast twitch
Characteristics of slow oxidative muscle fibers:
Slow twitch fibers:
* Use mostly Aerobic respiration
* Slower + weaker contractions
* Take a long time to fatigue
* Used for long contractions (posture)
* Fine motor movements (hands)
Characteristics of fast glycolytic muscle fibers:
Fast twitch fibers:
* Use mostly glycolysis + anaerobic respiration
* Faster + stronger contractions
* Fatigue quickly
* For bursts of action (jumping)
Characteristics of fast oxidative fibers:
- Use an intermediate balance of glycolysis + aerobic cellular respiration
- Intermediate in all ways
- Sustained actions (running, walking)
Slow oxitative
vs
Fast glycolytic
Slow -vs- Fast
Mitochondria: Lots – Fewer
Size: Small (skinny) – Large (wide)
For O2 diffusion
Blood vessels: Lots – Few
Color: Darker (+blood) – Lighter
Motor unit types and differences
Slow Units -vs- Fast Units
Unit size: Small — Large
Fiber type: Slow oxidative — Fast glycolytic
Neuron size: Small — Large
How many controlled: Few — Many
Type of movement: Fine — Big course
Where is smooth muscle found?
Lining: Digestive, respiratory, unrinary, and reproductive tracts + blood vessels
Inside the eye
Within skin (arrector pili)
What are the layers of smooth muscle in hallow organs?
- Circular layer:
Deeper - closer to the lumen
Goes in circles around the lumen
Contraction narrows the lumen
Blood vessels are present - Longitudinal layer - outside circular
Runs along the length of the organ
Contraction makes organ shorter
Characteristics of smooth muscle contration
Longer to contract or relax than skeletal or cardiac
Fatigues very slowly, maybe never
Changes in length are greater than skeletal or cardiac
Myosin + actin aren’t organized into sarcomeres (angles) so they use dense bodies
Contractions pinch + twist cells
Dense Bodies
Protein complexes that attach plasma membrane to actin filament in smooth muscle to act like a z-disc in contraction.
When myosin pulls on actin → dense bodies are pulled closer together
Smooth muscle
contraction process
- Ca++ flows into cytoplasm
Can come from sarcoplasmic reticulum - like skeletal muscle
Can also come from extra cellular fluid (Ca++ channels in the plasma membrane) - Ca++ activates calmodulin, not troponin (like in skeletal muscle)
- Calmodulin activates Myosin Light Chain Kinase (MLCK)
- MLCK adds a phosphate to myosin for activation
- Myosin grabs Actin + pulls
- Relaxation
Calmodulin
Protein in smooth muscle that’s activated by Ca++ and acts like troponin in striated muscle.
Smooth muscle
relaxation process
- Ca++ levels drop
- Calmodulin is deactivated
- Calmodulin no longer activates MLCK
- Myosin Light Chain Phosphatase (MLCP)
Removes phosphate from myosin - Myosin no longer contracts
- Cell relaxes
Variosities
Bulges along axons of motor neurons that release neurotransmitters to effect smooth muscle contractions.
Allows neurons to release neurotransmitters over large areas
Skeletal muscle motor neurons only release from the end of axons
Single-Unit smooth muscle
Cells connected by a gap junction, ions can spread from cell to cell, membrane , all cells contract at once.
Pharmacomechanical coupling
Chemicals make smooth muscle contact without changing the membrane potential. Ca++ channels - open when bind chemical
