Muscles Flashcards
What are the characteristics of muscle tissue?
Excitability
Contractility
Extensibility
Elasticity
What is excitability?
The ability to receive and respond to stimulus
What is contractility?
The ability to produce tension/force when stimulated
“Shortening”
What is extensibility?
The ability to be stretched, “lengthen”
What is elasticity?
The ability to recoil to resting length
What are the functions of muscle tissue?
Movement of bones or fluids
Maintaining of posture and body position
Stabilizing joints
Heat generation (esp. true for skeletal)
What is the difference between skeletal muscles and cardiac and smooth muscles as far as nerve impulses?
Skeletal muscles are voluntary
Cardiac/Smooth muscles are involuntary
True or False: Skeletal muscles regenerate after being “torn” during exercise.
False. We are born with a set number and that’s how many we have
What is unique about the structure of cardiac muscles?
They are branched and connect to each other in chains
What is the epimysium?
The top, dense layer of connective tissue covering everything
What are fascicles?
Groups of muscle tissue fibers connected together
What is the perimysium?
The connective tissue holding fascicles together
What is sarcolemma?
The special name for the plasma membrane of muscle cells
What is a myofibril?
A stack of fibrous muscle cells (sarcomeres) within the sarcolemma.
This organelle is unique to skeletal muscles
What is a sarcomere?
The smallest prt of a myofibril
An A-Band (stacks of overlapping actin and myosin*)between two protein “caps” called Z-Discs.
The middle space between two z-discs is just myosin, this is called the M-line
Which protein is a thin filament and which is a thick filament?
Actin: Thin
Myosin: Thick
The thin membrane coating each myofibril is called what?
Sarcoplasmic Reticulum
What is a Triad?
1 T-tubule aka Transverse tubule of sarcolemma around 2 terminal cisternae storing Ca2+
What are the “contractile proteins”
Actin and myosin
What is the difference between troposin and tropmyosin?**
Tropomyosin covers actin and myosin heads bind to it
Troponin covers tropomyosin. When it binds to Ca2+ it changes its shape, revealing the active sites
Where does activation happen and what is that?
In the motor end plate
A stimulation (AP) travels down a neuron to a neuromuscular junction.
ACh is released into the sarcolemma via exocytosis
What is a neuromuscular junction?
A muscle synapse: the place where a muscle neuron’s synaptic bulb meets the motor end plate
Where does excitation take place, what is it?
In the muscle membrane (sarcolemma)
The membrane is depolarized, ACh binds to receptors on motor end plates and opens ligand-gated channels, allowing Na+ in and K+ out
This depolarization opens voltage-gates Na+ channels, which causes an AP that changes the shape of T-tubules
The sarcolemma receives an influx of Ca2+, which binds to troponin and exposes the active sites on actin
Note: This is always a nicotinic receptor, EPSP
What happens during Excitation-Contraction?
ATP provides energy for mysofilaments to slide together. Myosin heads bind to actin and shorten the sarcomere.
A second ATP causes the mysosin head to unlatch
What is the latent period?
The time between excitation and depolarization
What is the Cross-Bridge Cycle?
Energized myosin heads attach to actin, this is called the “working stroke” or “power stroke”
The myosin head is cocked back by a second ATP molecule
Note: This will happen as long as ATP and Ca2+ are present
What is meant by muscle relaxation?
Ca2+ is pumped back into the SR, tropomyosin rolls back over and covers the binding sites of actin
What is rigor mortis?
When a person dies the stored Ca2+ in their terminal cisternae flood the sarcolemma and the ATP still left in their system causes all the myosin to keep cocking forward and contracting until it runs out
What is the difference between isometric and isotonic contractions?
Isometric - Tension is constant but muscle length stays the same
Isotonic - Muscle length changes the same but tension remains the same
What is tension
The force exerted on the load of an object, created by contraction
True or False: contraction means the muscle shortens
False. In concentric contractions the muscle shortens, in eccentric contractions the muscle grows in length
What is a motor unit?
A single motor neuron and the muscle fibers it supplies
What parts of the body have more motor end units?
Fingers, lips, etc.
Areas where fine, precise motor control is more important
What parts of the body have large motor units?
Thighs, back, anywhere that is weight-bearing
What is the definition if a muscle twitch?
The response if a muscle to a single, brief threshold stimulus.
It is the simplest contraction observable in a lab
What are the three phases of a muscle twitch?
Latent Period - E-C Coupling
Period of Contraction - Cross-Brudge formation, increasing tension
Period of Relaxation - Ca2+ re entering SR, tension declines to 0
What are the factors that affect tension?
Type
Load
Recruitment
True or false: If a muscle fiber is re-stimulated after it has relaxed it will have the same magnitude as the initial twitch but if second twitch occurs before relaxation the magnitude will stack
True
What do we cal maximum, sustained contraction?
Tetanus
What involuntary factors will cause a muscle to relax?
Running out of ATP or Ca2+
What is threshold stimulus?
The first observable muscle contraction
What controls contraction force?
Recruitment. More and larger fibers are recruited as stimulus intensity (load) increases. This is known as the size principle
What is the optimum sarcomere operating length?
80-120% of resting length
What is the effect of steroids on skeletal muscles?
Increased protein synthesis
What is the effect of HGH on skeletal muscles?
An increased number of fibers in myofilaments
What is hypertrophy?
An increase in the size of a muscle fiber
What is treppe?
aka “The Staircase Effect”, an increased contraction in a response to multiple stimuli of the same intensity due to increased Ca2+ release and heat. A little relaxation occurs, then a stacked magnitude, creating a staircase effect
What is muscle tone?
There is a small alternating current passing through muscles at all times due to spinal reflexes responding to stretch receptors. Keeps muscles ready to respond.
How are different muscle fiber types classified?
Speed and Metabolic Pathway:
Slow oxidative (red, endurance)
Fast oxidative (pink)
Fast glycolytic (white, power strokes)
True or False: The smaller the load the faster the contraction
True
What is the only energy source for contractive activities?
ATP
What are the ways ATP is generated for contraction?
Stores are depleted in 4-6 seconds
Regenerated via:
10 sec in
Direct phosphorylation of ADP by creatine phosphate
40-40 sec in
Anaerobic pathway (glycolysis)
theb
Aerobic Respiration
What is muscle fatigue and what causes it?
The inability to contract
Caused by:
-ionic imbalances (K+, Ca2+, K+, P) interferes with E-C coupling
-Prolonged exercise damaging SR
-A complete and total lack of ATP (rare)
What is a muscle fiber’s membrane called?
Sarcolemma
What is the sarcolemma called when it is deep in a muscle fiber?
A t-tubule
What are the Calcium-filled sacs on the side of t-tubules called?
Terminal cisternae
What organelle contains the thick and thin filaments?
Myofibrils
Which filament is thick?
Myosin
Which filament is thin?
Actin
Where are the cell bodies of motor neurons for the head and neck located and how do they exit the skull?
The brianstem, cranial nervea
Where are the cell bodies of motor neurons for most muscles and how do they exit the spine?
The ventral horn, via spinal nerves
For skeletal muscles to contract action potentials have to happen where?
In both a motor neuron and a muscle fiber
What is the name flor action potential of a sarcolemma? For a motor nerve?
Sarcolemma: Excitation
Motor Nerve: Activation
What is the name of the invaginated region of the muscle membrane at the NMJ?
Motor End Plate
What NT excites nicotinic receptors in skeletal muscles?
ACh
True or False: When the Sacrolemma is at rest Na+ voltage-gates channels are open.
False. They are closed
An action potential causes a shape change to what protein, allowing Ca2+ to flow into the sarcolemma?
A voltage-gated calcium channel on the terminal cisternae of the sarcolemma
What do Ca2+ ions bind to in muscle fibers? What does this cause?
Troponin, which causes a shape change in neighboring tropomyosin, revealing the bind site on the actin
What causes myosin to “cock” position?
ATP hydrolyzes
What happens if the myosin/actin binding site is not covered?
Cross-bridges continue to form, the muscle will continue to contract
What is the degree of stretch range at which max tension can be developed in a skeletal muscle?
Optimal length (80-120%)
What does optimal stretch length indicate?
The amount of overlap between thick and thin filaments
How is ACh removed from the NMJ?
It diffuses away from the membrane or is destroyed by Acetylcholinase
What would happen if a person was poisoned with organophosphates?
No ACh breakdown could occur, so it would continue to build-up in muscles and the muscles would fasciculate without voluntary input due to continuous contractions
How do drugs increase the time ACh is present at the NMJ?
They inhibit acetylcholinesterase allowing ACh build-up by preventing it from being broken down
What is the definition if muscle tone?
A small alternating contraction due to spinal reflexes that keeps muscles contracted somewhat at all times so they are ready for a response
What are the three phases of a muscle twitch?
Period of Contraction (sarcomeres shorten)
Period of Relaxation (Sarcomeres return to rest)
Latent Period (sarcomeres remain at resting length)
What are the three factors affecting tension in a muscle?
Stimulus strength
Stimulus frequency
Sarcomere length/muscle size
What is twitch summation?
An increase in frequency of stimulation on a muscle fiber will cause an increase in tension for each twitch
What process is most efficient at making ATP?
Aerobic restoration
What are the three pathways of aerobic restoration?
Glycolosis, Krebs cycle, electron transport chain
If oxygen is not available what is pyurvic acid converted to?
Lactic acid
What’s Oxygen Deficit?
The state of depleted resources after exercise
What three things must be replenished during Oxygen Deficit?
O2, Glycogen, creatine phosphate reserves
What do white muscle fibers have that makes up for their lack of capillaries and myoglobin?
Many myofibrils (which makes them larger in diameter)
What type of activities are white muscle fibers best suited for?
Resistance (Anaerobic) Exercise
Short, Powerful strokes
What is the other name for white muscle fibers?
Fast Glycolitc
Why are white muscle fibers bad for endurance?
They fatigue quickly
What is the other name for red muscle fibers?
Slow oxidative
What types if activities are red muscle fibers best suited for?
Endurance activities
What exactly is “slow” or “fast” about different muscle fibers?
Speed of oxidation and velocity of contraction
What type of muscle fiber is best for distance runners?
Red
What is a motor unit?
A motor nerve and all of the muscle fibers it innervates
Where do small motor units tend to be found?
In areas of fine motor movement (the eyes, the fingers)
What is the advantage if having only a few muscle cells per unit?
It allows for Precise control
Where do large motor units tend to be found?
Weight-bearing muscles (the legs and back)
What is the advantage of having large motor units in a muslce?
They fatigue leas quickly
What is recruitment?
The stimulation if additional motor units of a muscle, which strengthens the contraction
Temporal summation occurs due to the increased presence of what particle?
Ca2+ ions in the sarcoplasm
What is mechanism?
The process by which muscles contract and relax
When carrying something upstairs what kind of contraction is happening in your arms?
Isometric
True or False: both the A-band and I-band decrease in width as the muscle cell contracts
False. Only the I-Band decreases in width
True or False: Motor Unit (MU) recruitment usually begins with glycolytic fibers
False. Recruitment usually begins with slow oxidative, white fibers are recruited third (last)
Why do fast twitch fivers contract faster than slow twitch?
Their myosin hydrolyzes ATP faster
True or False: When T-Tubules depolarize Ca2+ pumps are activated to pump ions out terminal cisternae into the sarcoplasm
False: They are channels, not pumps
True or False: Motor unit and motor neuron are terms that can be used interchangeably
False. A motor unit includes a motor nerve AND a motor neuron
Is force generated during the latent period?
No
True or False: The number of motor units activated is proportional to the amount of tension produced by a skeletal muscle
True
Muscles in the back that maintain an erect posture for long periods are mostly what kind of fiber?
Slow Oxidative (red)
A muscle performing weak-to-medium output for a very long duration would be using what kind of metabolic pathways?
Aerobic
What can skeletal muscles use to regenerate ATP?
Creatine phosphate
What is the coupler ion of excitation and contraction in skeletal muscles?
Ca2+
If you press your hands together you are creating what kind of contraction?
Isometric
What kind of muscle is able to be stretched to twice its resting length and still produce a contraction force
Smooth
What kind of receptors to skeletal muscles always have?
Nicotinic, which are always excitatory, use ACh
What kind of loads result in isometric contractions?
Overload
What is an EMG measuring?
Electrical activity generated by action potentials innervating a muscle
True or False: As load increases more and larger units are recruited and the amount of electric activity picked up by an EMG increases.
True
What is the difference between an isometric and an isotonic contraction?
In an isotonic contraction the tension on the muscle remains the same but the length changes.
In an isometric the length if the muscle stays the same but the tension changes
What is the difference between an agonist and an antagonist?
An agonist is the contraction responsible for a muscle action, an antagonist performs the opposite action
What is the difference between a concentric and eccentric contraction?
A concentric contraction is a contraction where the muscle shortens, an eccentric contraction is one where the muscle lengthens
What is the difference in electrical output between concentric and eccentric contraction?
Concentric: Two peaks, when muscle is engaged and at the peak of its contraction
Eccentric: Overall activity is sustained
Why does the EMG show activity when the muscle is relaxes?
Tonus, the electrical activity that is always pulsing through the body
When holding an object does the number of motor units used remain the same?
Yes
As one reaches physiological fatigue force exerted by muscles drops. Why?
ATP use exceeds ATP generation and lactic acid build-up creates a low pH environment, which interferes with ATPase’s ability to break down ATP into ADP and phosphate, to be reused
What is fatigue?
When a muscle exerts half its maximum force
Where is Ca2+ stored in smooth muscle?
The extracellular space. When intracellular Ca2+ drops the smooth muscle relaxes
Do smooth muscles grow?
Yes, they divide and increase in number via hyperplasia
How is smooth muscle innervated?
Contractions via intrinsic contraction, ANS modulates contractions.
What is unique about smooth muscle neuromuscular junctions?
They don’t have them :P
They have gap junctions
What are varicosities?
Bulbous swellings that release NTs
What is unique about smooth muscle contraction?
It can stretch and still contract, it is rhythmic
How does neural control of muscles develop as we grow?
Head to toe, proximal to distal
