Nerves & Muscles Flashcards
sWhat is the nervous system?
A network of nerve cells (neurons) and fibres that transmit nerve impulses between parts of the body
What structures make up the CNS?
Brain & Spinal Cord
What structures make up the PNS?
Nerves not in the brain or spinal cord
What is the autonomic nervous system?
Part of the nervous system responsible for involuntary movements made up of both the PNS and CNS
Do dendrites send afferent or efferent signals?
Afferent
Do Axons send afferent or efferent signals?
Efferent
What makes up the phospholipid bilayer?
Hydrophilic Phosphate Heads and Hydrophobic Lipid Bodies/Tails
What is needed for ions (charged) to pass through the phospholipid bilayer?
Channels or transporters
Are there more potassium (K+) cells inside than outside of the cell? and by how many?
30x more inside
Are there more Na+, Cl- and Ca2+ ions inside or outside the cell?
Outside
What maintains the cell membrane charge/potential?
The outflow of K+ ions via potassium channels
At rest, what are ions are cell membranes most permeable to?
Potassium (K+)
Does the sodium-potassium pump maintain or establish a cells membrane potential?
Establishes
What is depolarisation?
The polarity of the cell becoming more positive
What is hyperpolarisation?
The polarity inside the cell becoming more negative
What is the ‘potassium diffusion potential’?
K+ diffusing the concentration gradient across the neuronal cell membrane via K+ leaky channels that causes the cell to become more negative compared to outside the cell.
Is the ‘potassium diffusion potential’ passive or active?
Passive - it goes with the concentration gradient
At what voltage do nerve cells reach equilibrium?
At -74mV where K+ outflow is equal to inflow
Is the sodium-potassium pump passive or active?
Active - it’s ATP activated
How many sodium and potassium ions are pumped out/in in the sodium-potassium pump?
3 x Na+ ions OUT
2 x K+ ions IN
What is the ‘resting negative membrane potential’?
The diffusion of ions on either side of the cell membrane, membrane permeability to different ions and the action of the sodium-potassium pump
What is the process that occurs during an action potential?
1) The membrane potential hits -55mV due to stimulus
2) Voltage-gated sodium channels open and sodium (Na+) flows out the cell via the concentration gradient (passive) which depolarises the cell.
3) At around +40mV the voltage-gated sodium channels close and voltage-gated potassium channels open causing K+ ions to rapidly go down the concentration gradient = repolarisation
4) However, K+ are slow to close leading to hyperpolarisation (going beyond the -74mV resting state).
5) RMP is restored once both the Na+ and K+ have closed which is restored mainly by the K+ outflow from leaky channels
What is the ‘absolute refractory period’?
When there are no further action potentials available as voltage-gated sodium channels have already started an AP
What is the ‘relative refractory period’?
Once voltage-gated Na+ close but K+ open for hyperpolarisation a stronger stimulus is needed to reach the threshold (-55mV) for another AP to occur
What is the process of faster conduction along myelinated nerve fibres called?
Saltatory conduction
What lies between each myelinated section of an axon?
Nodes of Ranvier
Myelin is produced by which neuroglia in the PNS and CNS?
PNS - Schwann Cells
CNS - Oligodendrocytes
Action potentials travel in both directions, what dictates the direction of the impulse?
Chemical synapses
How do chemical synapses occur?
1) AP arrives at the pre-synaptic neuron
2) Calcium voltage-gates open
3) Calcium diffuses into the pre-synaptic neuron
4) The synaptic vesicle moves with the neurotransmitters across the cell membrane
5) The vesicle fuses with the membrane an allow the ACh to diffuse across the synpatic cleft to the post-synaptic neuron (Noradrenaline at the post-synaptic)
What neurotransmitter occurs pre and post-ganglionic in the:
1) Skeletal Muscles?
2) Parasympathetic System?
3) Sympathetic System?
1) Skeletal Muscle - ACh only. Voluntary movements.
2) Parasym. (rest & digest) - ACH both pre-and-post ganglionic receptors
3) Sympathetic (fight or flight) - ACh at pre-ganglionic and Epinephrine and Norepinephrine for post-ganglionic
Neurotransmitter molecules can attach to neurotransmitter receptors. What are the two types of receptors?
Ionotropic (open/close ion channels, fast, all or nothing and trigger APs)
or
Metabotropic (slower on/off, amplify or dampen signals, trigger post-synaptic events including APs)
What are the three types of muscle?
Skeletal, Smooth and Cardiac
What are the features of skeletal muscle?
Striated, multinucleated, tubular fibres and under voluntary control
What are the features of smooth muscle?
Non-striated, uninucleated, involuntary control and responsible for veins etc.
What are the features of cardiac muscle?
Striated, uninucleated, branched and under involuntary control
What is the skeletal muscle micro-anatomy?
Muscle cell (myocyte) are muscle fibres –> a bundle of multinucleated myofibrils make up a contractile unit called a sarcomere and can either be thin (actin) or thick (myosin) –> a bundle of myocytes have surrounding connection tissues called endomysium and make up a fascicle –> Perimysium sheath fascicles –> epimysium sheath perimysium
What part of skeletal muscles want to move together by attaching and moving past one another in the sliding filament mechanism?
Myofibrils
What does myosin want to bind to during the sliding filament mechanism?
Myosin wants to bind to Actin
What is blocking the way during the sliding filament mechanism?
Troponin-Tropmyosin complex
What can expose the actin binding site during the sliding filament mechanism?
Calcium
What is the process for muscle contraction?
1) AP arrives in the terminal axon causing an influx of Ca2+
2) Increased Ca2+ stimulates the release of ACh into the synaptic cleft which depolarises the cell.
(Botox prevent ACh from going into the cell)
3) Once depolarises, the muscle holds calcium in troponin.
4) ACh bind to ligand-gated ion channels (nicotinic ACh receptors) that generates an AP along the muscle fibre
5) T-tubles conduct APs to sarcoplasmic reticulum which releases Ca2+ into sarcoplasm.
6) This calcium binds to the troponin which exposes the binding site for myosin
7) ATP binds to myosin which hydrolyses to ADP and Phosphate
8) Myosin head binds to Actin and bends which releases ADP and Phosphate
9) A new molecule of ATP will then bind to the myosin head which would detach from actin myofibril
How does muscle relaxation occur?
Sarcoplasm pumps Ca2+ out into the sarcoplasmic reticulum and then troponin-tropmyosin slides back into position by blocking the actin binding site.
At the neuromuscular junction AChE (acetylcholinesterase) breaks down ACh to allow for transmission.
What type of poisoning inhibits AChE?
Organophosphate Poisoning
What are muscle cells called?
Myocyte
A bundle of what make up a contractile unit?
Myofibrils
What’s the name of a contractile unit?
Sarcomere
What is thin or thick sarcomere called?
Thin = Actin
Thick = Myosin
What is the surrounding connection tissues around a bundle of myocytes called?
Endomysium
What makes up a fascicle?
Endomysium
What sheaths fascicles?
Perimysium
What sheaths perimysium?
Epimysium
What is pumped out of the sarcoplasmic reticulum for troponin-tropmyosin for muscle relaxtion?
Calcium
In muscle contraction how does the cell become depolarised?
Ca2+ stimulates the release of ACh into the synaptic cleft
What does botox prevent?
ACh from going into the cell
In muscle contraction, what does ACh bind to?
Ligand-gated ion channels
During muscle contraction, what are action potentials conducts by?
T-tubles
In muscle contraction, what does myosin bind to?
Actin
What does ATP bind to? What does it hydrolyses to?
Myosin and to ADP and Phosphate
Once myosin binds to actin it bends to release what?
ADP and Phosphate
What causes the myosin head from detaching from actin myofibrils?
A new molecule of ATP
