Muscles and Nerves Flashcards
What are the 3 phases of muscle contraction?
1) Latent Period (between action potential and contraction)
2) Contraction phase (Tension is increasing and cytosolic Ca2+ increasing)
3) Relaxation Period (Tension is decreasing and cytosolic Ca2+ decreasing)
What are the 5 types of muscle?
1) Pennant
2) Fusiform
3) Convergent
4) Parallel
5) Circular
Name the 4 glial cells in CNS and brief function:
1) Astrocytes: Exchange between the blood and the nerve cells
2) Oligodendocytes: Myelination, can myelinate more than one axon at once
3) Microglia: Macrophages
4) Ependyma cells: Dilated cells that secrete cerebro spinal fluid, lining cells
Name the 3 types of neurones:
1) Multipolar : dendritic tree (motor neurones)
2) Uni polar (pseudounipolar): Axon splits into 2, no clear dendrites (Sensory neurones)
3) Bi polar, 2 axons, in sensory structures
What factors affect speed of nerve conductance velocity (NCV)?
1) Extent of Myelination
2) Relative diameter of muscle fibre
What factors affect speed of nerve conductance?
1) Extent of Myelination
2) Relative diameter of muscle fibre
What factors affect strength of muscle contraction?
1) Length of sarcomere (optimum overlap of myosin and actin filaments)
2) Number of/size of motor units stimulated
3) Number of action potentials
Sarcomere H zone?
Only myosin filaments (shortens on contraction)
Sarcomere A band?
Complete length of myosin filaments (stays same on contraction)
Sarcomere I band?
Only actin filaments (shortens on contraction)
Sarcomere Z line? What attaches this to myosin filmanets?
Z line attaches actin filaments together, Giant protein titan (connectin) attaches the Z line to myosin filaments
Sarcomere M line?
Middle of H zone, M lines get closer together on contraction
What are the glial cells in the PNS?
1) Schwann cells: Myelination, can only myelinate one portion of an axon at once
2) Satellite cells: surround cell bodies in ganglia, similar to astrocytes
What are the glial cells in the PNS?
1) Schwann cells: Myelination, can only myelinate one portion of an axon at once
2) Satellite cells: surround cell bodies in ganglia, similar to astrocytes
How are unmyelinated axons supported?
Supported by neighbouring Schwann cells
What are the gaps in myelinated axons called?
Nodes of Ranvier
What are the 2 types of ganglia in the body?
Sensory ganglia (cell bodies of sensory neurones) Autonomic ganglia (cell bodies of efferent neurones: where sympathetic nerves can synapse)
What are ganglia?
Nodular masses of neuronal cell bodies and supporting neuroglia (satellite cells)
What is a bundle of nerve fibres (ie. axons) called?
Fascicle
What is endoneurium, perineurium and epineurium?
Endoneurium: covers indicidual nerve axons
Perineurium: covers a fascicle
Epineurium: covers the whole nerve (made up of lots of fascicles)
Where are the ganglia of parasympathetic fibres (and thus where do they synapse)?
Near or in target tissues
Where are the ganglia of sympathetic fibres (and thus where do they synapse)?
Sympathetic chain
What are the pre ganglionic and post ganglionic neurotransmitters for sympathetic and parasympathetic fibres?
Both preganglionic and parasympathetic post ganglionic = ACh
Post ganglionic sympathetic = NA
What are the types of sensory receptors as defined by location?
Exteroceptors, Interoceptors and Proprioceptors
What are the types of sensory receptors as defined by stimulus detected?
Mechanoreceptors, Thermoreceptors, Photoreceptors, Chemoreceptors and Nociceptors (pain)
Name 5 types of sensory receptor endings:
1) Muscle spindles
2) Pacinian Corpuscle
3) Free, unencapsulated endings
4) Ruffini organs
5) Meissener’s or Krause’s bulbs
What are myofibrils made up of and what can they be divided into?
Made up of filaments and can be divided into sarcomeres
What is myosin formed by and what is its rough structure?
Made up of many filaments wrapped together each with a head and a tail
What is actin formed from?
Globular actin, troponin complex which moves tropomyosin
What is the mechanism of muscle contraction?
1) Action potential arrives at neuromuscular junction, ACh is released which binds to receptors and opens Na+ channels leading to an action potential in the sarcolemma
2) Action potential travels along T tubules
3) Ca 2+ is released from SR
4) Ca2+ binds to TnC region of troponin and cause a comformational change which exposes myosin binding sites on actin
5) Mysosin head with ADP+Pi bound attaches, Pi is released initiating power stoke
6) ADP then released after power stroke
7) New ATP binds causing myosin head to be detached, As the ATP splits into ADP and Pi the myosin head is energised
What 3 things do muscles contract in the presence of?
ATP, Ca2+ and Mg2+
2 main types of contractions and there sub types?
Isometric (no change in length): have concentric (muscle gets shorter) and eccentric (muscle gets longer)
Isotonic: no change to muscle length
3 types of muscle fibres and there characteristics?
1) Slow twitch (Type 1) (red, lots of myoglobin, lots of mitochondria, contracts slowly producing low amounts of power, for aerobic activity)
2) Fast twitch A (Type 2a) (red, myoglobin, mitochondria, contract relatively quickly producing moderate amount of power, for long term anaerobic)
3) Fast twitch B (Type 2b) (White, low myoglobin, low mitochondria, contract quickly producing high amounts of power, for anaerobic)
What are the 3 different types of muscle tissue?
1) Skeletal
2) Cardiac
3) Smooth
What is sarcolemma and sarcoplasm?
Sarcolemma contain many myofibrils surrounded by sarcoplasm
What are endomysium, perimysium and epimysium?
Endmysium surrounds sarcolemma, perimysium surrounds fasciculus (made up of sarcolemma) and epimysium surrounds muscle belly (made up of many fasciculus)
What is an electromyography test?
Test to measure the effect of electrical activity on a muscle, test ap and see how muscle twitches, 2 types:
1) INVASIVE - needle in muscle
2) LESS INVASIVE - electopads on the surface corresponding to the muscle
What are the 2 types of synapses?
1) Chemical synapses (neurotransmitter released)
2) Electrical synapses (gap junctions, cytosolic continuity, movement is unidirectional in vertebrates)
What is the refractory period and what does it ensure?
Absolute refractory period, no action potential can be propagated during this interval
Relative refractory period, only a large stimulus can generate an action potential (as the cell is hyperpolarised so takes the influx of more Na+ to reach the threshold potential)
It ensures that conductance of nerve impulses is uni directional
What type of conductance occurs in myelinated axons?
Saltatary conduction
What is the resting potential of normal neurone?
-65mV
What is the threshold potential of a normal neurone?
-40mV
What is the ‘all or nothing principal’?
Unless the cell reaches the threshold potential no impulse will be fired
How does increasing strength of stimulus affect the action potential?
Doesn’t affect the magnitude of the action potential but increases the frequency of action potentials being fired
What 4 things maintain the resting potential of a neurone?
1) Negatively charged intracellular proteins
2) Sodium/potassium ATPase
3) Electrical and chemical K+ gradients
4) Electrical and chemical Na+ gradients
How does the action of Sodium/Potassium ATPase help to maintain resting potential?
It pumps out 3 sodium for 2 potassium in
How does the electrochemical gradient of potassium help to maintain the resting membrane potential? And what is the potassium resting potential?
Potassium wants to move out of the cell along the chemical gradient but into the cell along the electrical gradient, if the resting potential was simply dependent on these 2 gradients when they were in equilibrium the potassium resting potential would be -75mV.
How does the electrochemical gradient of sodium affect the resting membrane potential?
Sodium wants to move into the cell both along its electrical and chemical gradient, therefore the presence of sodium raises the resting membrane potential by 10mV to -65mV. As the membrane is much more permeable to potassium than sodium (more potassium transporters, sodium only has this small affect).
What channels are open during phase 1 of an action potential?
Sodium channels are open, sodium flows into the cell and the membrane potential rises towards threshold potential
What channels are open during phase 2 (Depolarisation) of an action potential?
As membrane potential has reached threshold potential, voltage gated sodium channels are open so sodium flows into cell (positive feedback) and the membrane depolarises
What channels are open during phase 3 (Repolarisation) of an action potential?
Voltage gated sodium channels close and potassium channels open, potassium flows out of cell repolarising membrane
What channels are open during phase 4 (Hyperpolarisation) of an action potential?
Sodium channels still closed and potassium channels still open so membrane becomes hyper polarised
What 4 ways can neurotransmitter be removed from the synapse?
1) Taken up by pre synaptic (or post synaptic) terminals
2) Broken down by enzymes in the synaptic cleft and then the products reabsorbed into the pre synaptic terminal
3) Taken up by glial cells surrounding and transported back into pre synaptic terminal
4) Taken up by glial cells, broken down by enzymes within glial cells and products transported back into pre synaptic terminal
What role does calcium have in transmission across a chemical synapse?
Voltage gates calcium channels located near the active zone of a pre synaptic terminal, action potential at the pre synaptic terminal causes opening of voltage gated calcium channels, influx of calcium causes synaptic vesicles to fuse with pre synaptic membrane and release neurotransmitter into the synaptic cleft which binds to receptors on the post synaptic membrane
What are the 2 types of receptors on the post synaptic membrane of a chemical synapse?
1) Ionotropic - ion channel, binding of neurotransmitter can result in channel opening and influx of negative ions (to inhibit an excitory response in post synaptic neurone) or positive ions (to stimulate an excitory response in post synaptic neurone)
2) Metatrobic receptors, coupled with G proteins
What is an electromyography test?
Test to measure the effect of electrical activity on a muscle, test ap and see how muscle twitches, 2 types:
1) INVASIVE - needle in muscle
2) LESS INVASIVE - electropads on the surface corresponding to the muscle
What is the ‘all or nothing principal’?
Unless the stimulus is sufficient to reach the threshold potential no action potential will occur
What 4 things maintain the resting potential of a neurone?
1) Negatively charged intracellular proteins (cannot cross membrane to leave cell)
2) Sodium/potassium ATPase
3) Sodium ions
4) Potassium ions
How does the action of Sodium/Potassium ATPase help to maintain resting potential?
It pumps out 3 sodium for 2 potassium in, thus the inside gets more negative. Its present in the membranes of all animal cells
How does the electrochemical gradient of potassium help to maintain the resting membrane potential? And what is the equilibrium potential for K+?
Potassium leaks out of the cell along the chemical gradient through leak channels, but into the cell along the electrical gradient, if the resting potential was simply dependent on these 2 gradients when movement in and out was in equilibrium, the equilibrium potential for K+ would be -75mV.
How does the electrochemical gradient of sodium affect the resting membrane potential?
Some sodium moves into the cell both along its electrical and chemical gradient, therefore the presence of sodium raises the resting membrane potential by 10mV to -65mV. The membrane is only slightly permeable to Na+ (its much more permeable to K+, due to more K+ leak channels) so the effect of this movement on resting potential is only small
What channels are open during phase 3 (Repolarisation) of an action potential?
Voltage gated sodium channels close when Na+ equilibrium is reached) and potassium channels open, potassium flows out of cell repolarising membrane
What channels are open during phase 4 (Hyperpolarisation) of an action potential?
Sodium channels still closed and potassium channels still open so membrane becomes hyper polarised
What channels are open during phase 0 of action potential?
This is resting potential so both gated sodium and potassium channels are closed
What are the 2 major kinds of proprioceptors in muscle?
1) Muscle spindles
2) Golgi tendon organs
What are muscle spindles and how do they work?
Specialised muscle fibres enclosed in connective tissue capsule located in the muscle. Stimulated when the muscle is passively stretched (as they stretch too) and send a message to CNS which initiates a reflex that makes the muscle contract. This prevents the muscle from being over stretched and tearing.
What are Golgi tendon organs and how do they work?
Small bundles of collagen fibres enclosed in a layered capsule within the tendon, responds to tension (so stimulated when muscle contracts and stretches). Action potentials triggered when muscle contracts or stretches and sends a message to the CNS which triggers a reflex which makes the Golgi tendon organ either stretch or contract with the muscle. Acts as a tension detector to protect the muscle against excessive load.
What are the 2 types of synapses?
1) Chemical synapses (neurotransmitter released)
2) Electrical synapses (gap junctions, cytosolic continuity, movement of current ions is unidirectional in vertebrates)
What 4 ways can neurotransmitter be removed from the synapse?
1) Taken up by transporters on pre synaptic (or post synaptic) terminals
2) Broken down by cell surface enzymes and then the products reabsorbed into the pre synaptic terminal via transporters
3) Taken up by transporters into glial cell processes surrounding the pre synaptic zone and transported back into pre synaptic terminal
4) Taken up by glial cells, broken down or converted by enzymes within glial cells and products transported back into pre synaptic terminal
What are the 2 types of receptors on the post synaptic membrane of a chemical synapse?
1) Ionotropic - ion channel, binding of neurotransmitter can result in channel opening and influx of negative ions (to inhibit an excitory response in post synaptic neurone) or positive ions (to stimulate an excitory response in post synaptic neurone)
2) Metabotropic receptors, coupled with G proteins
What is the knee jerk reflex pathway and what sensory receptor is involved?
Monosynaptic stretch reflex. When patellar ligament is stretched the muscle spindle of the quadriceps is stretched and initiates reflex.
4 main types of neurotransmitters?
1) ACh
2) Amines (including dopamine, NA, Adr, Histamine and serotonin)
3) Amino acids
4) Peptides
What is a motor unit?
A motor unit is all of the muscle fibres supplied by one motor nerve, all muscle fibres in one motor unit contract simultaneously when the motor nerve fires
How is the post synaptic membrane of a neuro muscular junction adapted?
Folded so it has a larger area for receptors of neurotransmitter
What kind of receptors are found on post synaptic membranes at neuromuscular junctions?
Nicotinic ACh receptors
What is the structure of a Nicotinic ACh receptor?
Made up of 5 sub units, each of which is made up of 4 transmembrane segments. It has 2 alpha sub units which are what the 2 molecules of ACh bind do
Describe the neurotransmitter and receptor interaction at a neuromuscular junction?
Nicotinic ACh receptor forms a pore, the binding of 2 molecules of ACh to the 2 alpha sub units of the receptor cause a conformational changes which opens the channel and leads to influx of sodium
What is the role of calcium at a presynaptic terminal in a neuromuscular junction?
Action potential at pre synaptic terminal causes opening of voltage gated calcium channels, calcium influx causes fusion of pre synaptic vesicles with pre seynpatic membrane and ACh released
What is docking of synaptic vesicles?
Synaptic vesicles containing neurotransmitter are docked in the active zone of a pre synaptic terminal ready to fuse with pre synaptic membrane
The presynaptic membrane doesn’t make contact with the muscle fibre at a neuromuscular junction, what structure provides support within the cleft?
Basal lamina
Which ions is the nicotinic ACh receptor specific for?
Sodium and potassium
What is an EPSP
Excitatory post synaptic potential
What is an MEPP?
Small excitatory post synaptic potential produced by a single quantum of ACh (1 quantum = contents of 1 vesicle)
What is an EPP?
End plate potential, produced from the summation of MEPP’s and reaches the threshold potential in muscle fibre
What is the 1:1 principal in transmission at neuromuscular junctions?
Every pre synaptic potential results in a post synaptic potential
What is docking of synaptic vesicles?
Synaptic vesicles containing neurotransmitter are docked in the active zone of a pre synaptic terminal ready to fuse with pre synaptic membrane, V snare protein on vesicle binds to t snare protein on membrane at active zone
What happens to ACh at a neuromuscular junction when its released from its receptor?
Broken down by acetyl cholinesterase to acetate and choline. Choline is taken back up into nerve terminal and acetate is excreted as a waste product
What reactions are incolved in the synthesis of ACh?
Acetate + Coenzyme A = Acetylcoenzyme A
Acetylcoenzyme A + Choline = Acetyl Choline
The second reaction is catalysed by acetyl-transferase enzyme found in cytoplasm so this is where synthesis occurs
How is ACh packaged into vesicles?
Pumped in by exchange with H+
In neuromuscular junctions how are reserve vesicle tethered near active zone?
Achored by synapsin to actn filaments
Neuromuscular blocking drugs: what is TUBOCURARINE?
Used in surgery, competitive nAChR antagonist
Neuromuscular blocking drugs: what is SUCCINYLCHOLINE?
Used in surgery, binds to nAChR and doesn’t get released for a while, end plate potential eventually disappears but succinylcholine stays attached
What are cholinesterase inhibitors used for?
Treatment of myasthenia gravis
What is SARIN?
Cholinesterase inhibitor used as a weapon in war
What is SARIN?
Cholinesterase inhibitor used as a weapon in war
What is Lambert-Eaton syndrome?
Autoimmine disease which inhibits Ca2+ channel and thus the release of ACh, symptoms include muscle weakness and fatigue
How is Lambert-Eaton syndrome diagnosed?
Using electromyography - have a reduced compound muscle action potential (CMAP). Repetitive stimulation increases CMAP
What is the treatment of Lambert-Eaton syndrome?
If underlying malignancy (small cell lung cancer) that is treated, Immunosuppressants such as corticosteroids, amifampridine (blocks K+ channels, action potential duration increased, more ACh released)
Is cardiac muscle striated?
Yes
What is the rough structure of cardiac muscle?
Striated, single nucleus, involuntary, branched
What is the rough structure of skeletal muscle?
Striated, multinucleated, non branching, voluntary, attached to skeleton
What is the rough structure of smooth muscle?
Non striated, single nucleus, involuntary, tapered, forms walls of organs
What is functional syncytium and where does it occur?
When cardiac muscle cells all contract simultaneously behaving as a single unit due to gap junctions between cells
What are the 2 types of cardiac muscle cells?
1) Contractile cells
2) Autorhythmic cells
Also cardiac muscle is autorhythmic what 2 things can modulate contraction of heart muscle?
1) Autonomic nervous system
2) Endocrine system (hormones)
What is calcium induced calcium release?
Occurs in cardiac muscle, extracellular calcium moving through plasma membranes and T tubule into sarcoplasm causes calcium release from SR
What is Wolf Parkinson White syndrome?
When there is an abnormal accessory conduction pathway from the atria to the ventricles (known as the bindle of kent) which stimulate the ventricles to contract prematurely, resulting in atrioventricular reciprocal tachychardia where electrical impulses travel in the normal direction in one manner but back up to the atria via this bundle of kent
Why is characteristic of the refractory period in cardiac muscle?
The refractory period is as long as the muscle twitch so can’t get stimulation until the end of the muscle twitch so cant get summation and cant therefore get fused tetanus, muscle doesn’t get fatigued as don’t reach fused tetanus
What is phase 0 of the cardiac action potential?
Depolarisation, Na+ channels flow in through fast channels
What is phase 0 of the cardiac action potential?
Depolarisation, Na+ channels flow inward through fast channels
What is phase 1 of the cardiac action potential?
Partial repolarisation, Na+ channels closed
What is phase 2 of the cardiac action potential?
Plateau due to slow inward flow of Ca2+, Ca2+ channels open and fast K+ channels close
What is phase 3 of the cardiac action potential?
Repolarisation, Ca2+ channels close, slow K+ channels open, efflux of K+ channels Na+/K+ATPase re establish distribution of ions
What is phase 4 of the cardiac action potential?
Interval between action potentials when ventricular muscles are at there stable resting potential
What are the four main classes of antiarrythmic agents and what do they treat?
Class 1 = Sodium channel blockers (treatment ventricular ectopics)
Class 2 = Beta blockers (block B1 adrenergic receptors and therefore sympathetic activity on the heart). (treatment of ventricular tachychardia and AF)
Class 3 = Potassium channel blockers (therefore prolonging depolarisation)
Class 4 =Calcium channel blockers, decrease conduction through AV node (upstroke Ca2+ dependent) and shorten phase 2 and reduce contractility.
What are L type calcium channels and where are they located?
Located in the membrane of T tubules, when action potential arrives in the T tubules, these channels open and Ca2+ influx causes further Ca2+ release from nearby SR (each L type channel appears to control only 1 SR release channel)
How is calcium removed from within cardiac muscle cytosol after contraction?
Some taken back up into SR, some excreted from cell by exchange with K+
What is digoxin and how does it work?
It increases contractility of heart by inhibiting the K+Ca2+ antiporter which is used to remove Ca2+ from the cells after contraction and thus cytosolic Ca2+ remains high
Describe the depolarization of the SA node
Resting membrane potential not stable due to slow influx of Ca2+, threshold is reached, voltage gated Ca2+ channels open and rapid depolarisation occurs, Ca2+ channels then close and K+ channels open, K+ efflux until reach potential of 60mV
What is the threshold potential in cardiac muscle?
-40mV
How does the autonomic nervous system affect pacemaker function?
NA, (from sympathetic nerves) increases rate of action potentials at SA node
ACh (from parasympathetic nerves) causes cells to become hyperpolarised so takes longer to reach threshold potential
What is Frank-Starling law of heart?
Increased pre-load will lead to increased contraction of the heart up to a point, then it leads to decreased force of contraction. This is due to reaching optimum overlap of actin-myosin filaments
Why is smooth muscle not striated?
Actin and myosin filaments are not well organised
Do smooth muscle cells contain T tubules or sarcomplasmic reticulum?
Contain no T tubule and SR is poorly developed
What is the mechanism of contraction in smooth muscle?
Increased cytosolic Ca2+ stimulates contraction, Ca2+ binds to calmodulin which then interacts with the enzyme myosin kinase which phosphorylates myosin so it can bind to actin, when Ca2+ concentration falls, Ca2+Calmodulin complex dissociates and myosin kinase is inactivated, cross bridges are dephosphorylated by myosin phosphatase
Why is smooth muscle able to maintain its force over long periods of time?
1) Myosin has a slow ATP ase rate so once attached it takes a long time for each crossbridge to detach from actin filament
2) Rate if Ca2+ removal from smooth muscle is slow prolonging the duration of contraction
What are the characteristics of multi unit smooth muscle
No gap junctions, cells innervate individually, not spontaneously active, innervation is autonomic, contractions are slow and sustained
What are the characteristics of single unit smooth muscle?
Most common, gap junctions, activity may arise spontaneously due to the presence of pacemaker cells, nervous regulation via autonomic system
What is dilated cardiomyopathy?
Heart enlarged and weakened, (left heart failure) can result in pulmonary oedema, pitting oedema in ankles
What is hypertrophic cardiomyopathy?
Heart muscle becomes hypertrophied, making it harder for heart muscle to pump blood, can happen in normal individuals or athletes
