Skeletal Muscle Flashcards
sarcomere
individual contractile units of skeletal muscle
thin filament
actin which gets pulled during contraction
thick filament
myosin which pulls the muscle fibre to initiate contraction
Neuromuscular Junction
the junction where the nerve is meeting the muscle between the actual presynaptic terminal and muscle fibers
- not an actual synapse
what is the other name for NMJ?
motor end plate
Myelin sheath
coats the nerves as it helps with the conductance of electrical signals
schwann cells
a type of glial cells which sorrounds a neuron (forms a myelin sheath), and is mostly responsible in the metabolic processes
Junctional folds
increases the surface membrane of the sarcolemma and for the of acetylcholine (the area is densely pack with acetylcholine and ach receptors)
agonist
a drug or substance (nicotine) that will stimulate more functions
antagonist
a substance that is able to block functions of another substance
Myasthenia Gravis
a chronic immune diseases, a neuromuscular diseases which cause weakness in the skeletal muscle
Occupancy
how much acetylcholine has been released and is bound to the receptor itself
Sarcoplasmic Reticulum
- encloses all the individual myofibrils which also contains connections to itself
- Calcium storage
Why does the sarcomere have striped pattern?
it contains intercalated thin and thick filaments which are contractile proteins
What does the body mass mostly contained?
skeletal muscles
Sarcolemma
an outer membrane which encapsulates the myofibril
When does a triad occurs?
occurs when we have the terminal cristernae of an Sr and a T-tubule
- triad is important for regulation of excitation-contraction coupling
What is the function of a serca pump?
it uses ATP to move calcium from the cytoplasmic space up to the SR itself
myosin complex
part of thick filament (long arms and flexible heads)
actin helix
thin filament (made up of globular proteins)
Tropomyosin
wraps around the actin filament which acts as a stabiliser
What is rigor mortis?
the stiffening of the body muscles due to the chemical changes in the myofibrils (this occurs due to the lack of ATP)
Fast fibres
- are big in diameter and have a large cross sectional area
- they produce lots of energy and stores them (energy ready for used) because they are slow at producing energy
slow fibres
are smaller in diameter and cross sectional area
- they produce energy faster as their function is to support, therefore flow is steady and slow and that is why they have lots of capillaries beds for bloods supply and to produce more energy
Motor unit
motor neuron and the recruitment of a muscle fibres
Active zone
docking sites of vesicles
What effects does having action potential in the motor neuron
Action potential in the motor neuron leads to depolarization of muscle fibers via Acetylcholine (Ach)
- depolarization is caused by having a negative membrane potential going into a positive membrane potential due to sodium channels opening
Synthesise Acetylcholine
- Acetyl coA + choline gets synthesise through an enzyme called acetyltransferase (ChAT)
- we can then break this down to have acetylcholine as an input
- Ach, we then use acetylcholinesterase (AchE) to break it down into acetic acid + choline
What is the function of the NMJ?
this is the area where we get a transferal of action potential or electrical signal from an actual nerve to translating it into an action potential into the muscle itself
- this action potential tells the muscle it is time to contract
Importance of the NMJ structure?
- important for linking the signal from the nerve and the brain to the muscle
- the structure of NMJ allows the muscle to be under involuntary control
Features of a muscle fibres
- contain lots of mitochondria which is located between myofibrils
- nuclei are dotted in regular interval throughout the outer membrane (sarcolemma of the cell
-multinucleated
Why are slow fibres more efficient than fast fibres?
slow muscle fibres uses oxygen to generate more adenosine triphosphate for continuous muscle contraction over a long period of time
- they fire AP more slowly which means than they can go longer before experiencing fatigue
Type I: slow oxidative fibres
slower form of serca
- slower increase of tension produced
- slow muscle twitch fibres
- smaller and pinker fibres
- slow contractors
- slow at utilizing ATP
Type II: Glycolytic Fibres
faster form of serca
- rapid increase to tension produce and very rapid relaxation phase which is due to having a fast form of myosin
- fast twitch fibres
- fast contractions
- fast relaxation (super fatigable)
Feature of Nicotinic acetylcholine receptor
- has five subunit and four transmembrane domain
- have pore gated: gate normally closed (at rest)
Transmembrane domain
- organised in a way that we have a subunit with a central pore
- purpose of the central pore is to to use as transporter though passive diffusion
Nicotinic AchR
- chemically gated (opens when two Ach binds)
- Non-slective; permeable to both Na+ and K+
- opening results in depolarisation due to entry of sodium ions
Concentration Gradient
Outside cell:
-High Na+
-Low K+
Inside cell:
- High K+
-Low K+
Local depolarisation
- having sodium ions in a negative space
muscarinic acetylcholine receptor
- not located in neuromuscular juncton, mostlyfound in smooth muscle
- not chemically gated
Nicotine recptors
-nicotine comes into the system via smoking or vaping, thesewill then affect more of the central located nicotinic receptors not the one in the neuromuscular junction
- more effect in the CNS than the PNS
Agonist
stimulate more function of the drugs
Antagonist
able to block the function of how drugs or chemical works
Effects of reduce number of Ach receptors?
Reducing the number of Ach recptors and we damage them, this results in impaired response of acetylcholine so there is a reduce in the neuromuscular junction function. This means that it is not getting enough nerve signal to muscle and will cause weakness
e.g. Myasthenia Gravis
Fasciculi
individual bundle of muscle fibres in skeletal muscle
skeletal muscle features
- heavily multinucleated cells (formed from the fusion of embryonic myoblast)
- large diameter in fast twitch fibre compare to the slow twitch fibre
Type IIA: Intermediate fibres
- fast form of myosin ATPase
- mix of oxidative and glycolytic enzymes
- intermediate speed / fatigue
Slow oxidative fibres
useful for endurance events
fast-oxidative fibres and fast-glycolytic fibres
useful for power and sprint events
Recruitment
The process of activating more fibres to make force
- the number of fibres activated is regulated by how many neurons are activated at one time
- small number of active neurons tends to produce low force from the muscle
Size principle of motor units
small units are recruited first, so more tonically active (results in fine graded control of small forces e.g. fingertips)
- bigger units are autimatically recruited as required force increases
Isometric
length of the muscle remains constant during contraction
- no external force is being generated by the muscle
concentric
muscle shortening during contraction
- shortening against fixed load, speed dependent on M.ATPase activity and load
eccentric
muscle lengthens during contraction
- most likely to cause muscle injury
voltage sensor (EC-Coupling)
senses any changes across the membrane potential of the actual sarcolemma itself of the skeletal muscle fibre
Ryanodine receptor
a calcium release channel that sits on the terminal cisternae
- contain lots of calcium
Voltage sensor is not a g-coupled protein
It does not have a secondary messenger system
- but can mechanically activate the ryanodine receptor (calcium release channel) on the terminal cisternae of the sarcoplasmic reticulum
Difference between EEG and EMG?
- Electroencephalogram (EEG) is a non-invasive brain imaging technique that uses scalp electrodes to measure the voltage fluctuations induced by the mass electrical activity of neurons
whereas,
- Electromyography (EMG) technique is usually used to record the electrical activity produced by skeletal muscles
