Action potentials and membranes Flashcards
What is influx?
The movement of ions into the cell
What is efflux?
The movement of ions out of the cell
What drives the passive movement of ions across the cell membrane?
The electrochemical gradient, which combines concentration and electrical gradients
Which side of the cell membrane contains a higher concentration of Na+?
The outside of the cell
which side of the cell membrane contains a higher concentration of K+?
The inside of the cell
What are some examples of common membrane lipids?
Phosphatidylserine
Phosphatidylinositol
Phosphatidylcholine
Sphingomyelin
Galactocerebroside
What are the 2 broad classes of membrane proteins?
Peripheral proteins
Integral proteins
What are peripherally associated membrane proteins?
Proteins that are not embedded in the cell membrane but are usually associated with the cytoplasmic or extracellular surfaces of the membrane
What is the role of membrane bound carbonic anhydrase?
It plays a role in the reabsorption of bicarbonate in the kidneys
What is the collective name for the layer of glycoproteins and glycolipids on the cells surface?
The glycocalyx
What is cystinuria?
A genetic disorders which prevents the reabsorption of cysteine (Amino acid) into the blood, so it crystallises and build up in the kidneys
What is meant by an isotonic solution?
A solution that has an equal water potential to the cells in it
What is meant by a hypotonic solution?
A solution that has a greater water potential to the cells in it - movement of water into the cells
What is meant by a hypertonic solution?
A solution that has a lower water potential to the cells in it - movement of water out of the cells
What is the modified Fick’s equation for calculating the net rate of diffusion?
Q = ∆C x A x P
Q = Net rate of diffusion
∆C = Concentration gradient
A = Surface area of membrane
P = Membrane permeability
What is the Goldman-Hodgkin-Katz equation for calculating membrane potential?
. ( Pk [K]out x Pna [Na]out)
.Em = 61 x Log10 (————————————)
. (Pk [K]in x Pna [Na]in )
How is permeability linked to equilibrium potential?
The greater the permeability for a given ion, the greater the tendency for that ion to drive the membrane potential towards the ion’s own equilibrium potential
What is the simplified Nernst equation for calculating the equilibrium potential of a monovalent ion at 37ºC?
. [ion]outside
Ion = 61 x Log10 (——————–)
[ion]inside
What is the relative membrane permeability for Na+?
1
What is the relative membrane permeability for K+ for a skeletal muscle cell?
100
How is an electrical gradient set up in a cell?
Excess charges on one side of the cell are attracted to the membrane edge
What are the 2 types of refractory period?
Absolute refractory period - no stimulus can cause AP
Relative refractory period - Greater than usual stimulus can cause AP
What is the name of the start of the axon?
The axon hillock
What are the two types of conduction?
Contiguous conduction
Saltatory conduction
What is the name given to the spaces between the schwann cells or oligodendrocytes?
Nodes of Ranvier
What are some examples of demyelinating disorders?
Multiple sclerosis (CNS)
Guillian-Barré syndrome (PNS)
What are the 3 divisions of the peripheral nervous system?
Somatic efferent
Somatic afferent
Autonomic
What are the 3 divisions of the autonomic nervous system?
Sympathetic
Parasympathetic
Enteric
What are the 3 main sections of the motor autonomic nervous system?
Preganglionic neurone
Autonomic ganglion
Postganglionic neurone
What type of neurotransmitters are found in the preganglionic neurone of the autonomic nervous system?
Acetylcholine
What types of neurotransmitters can be found in the postganglionic neurone of the parasympathetic division?
Acetylcholine - rapid
Nitric oxide - Intermediate
Vasoactive Intestinal Peptide (VIP) - slow
What types of neurotransmitters are found in the postganglionic neurone of the sympathetic division?
Adenosine TriPhosphate (ATP) - rapid
Noradrenaline - intermediate
Neuropeptide Y - slow
What effect does parasympathetic stimulation have on heart rate and contraction force?
Decreased heart rate and force by stimulation of M2 muscarinic acetylcholine receptors
What effect does parasympathetic stimulation have on the bronchi
Bronchi contraction and mucus production by stimulation of M3 muscarinic acetylcholine receptors
What effects does parasympathetic stimulation have on the intestine?
Increased intestinal motility (Movement) and secretions by stimulation of the M3 muscarinic acetylcholine receptors
What effects does parasympathetic stimulation have on the sphincters of the GI tract?
Relaxation of sphincters by stimulation of the Nitric oxide and M3 muscarinic acetylcholine receptors
What effects does parasympathetic stimulation have on vasculature?
Mostly no effect
What effects does parasympathetic stimulation have on the bladder?
Constriction of the bladder wall by stimulation of M3 muscarinic acetylcholine receptors
Which receptors are stimulated by the parasympathetic division, leading to penile erection?
Nitric oxide and M3 muscarinic acetylcholine receptors
What effect does sympathetic stimulation have on heart rate and force of cardiac contraction?
Increased heart rate and force of contraction caused by stimulation of ß1 adrenoceptors
What effect does sympathetic stimulation have on bronchi?
Relaxation of bronchi and reduced mucus production due to stimulation of ß2 adrenoceptors
What effect does sympathetic stimulation have on intestinal motility and sphincters of the GI tract?
Reduced intestinal motility and constrction of sphincters by stimulation of α1, α2 and ß2 adrenoceptors
What effect does sympathetic stimulation have on vasculature?
Constriction in most locations due to α1 adrenoceptor stimulation
Relaxation of skeletal muscle due to ß2 adrenoceptor stimulation
What effect does sympathetic stimulation have on the adrenal glands?
Release of adrenaline from adrenal medulla by stimulation of nicotinic acetylcholine receptors
What is the detrusor muscle?
A muscle found in the bladder wall that contracts during urination
What effect does sympathetic stimulation have on the bladder?
Relaxation of the detrusor muscle of the bladder due to ß1 and ß2 adrenoceptor stimulation, and constriction of the internal urethral sphincter due to α1 stimulation
Which receptors are stimulated by the sympathetic division, leading to ejaculation?
α1 receptors
Which enzyme breaks down acetylcholine?
Acetylcholinesterase
What occurs during synaptic transmission at a cholinergic synapse?
Precursor molecules are chemically altered to form the neurotransmitter
These are enveloped in vesicles
Ca2+ influx caused by action potential, moves vesicle to membrane along microtubules
Exocytosis of neurotransmitters
Binding of neurotransmitters to Nicotinic or muscarinic acetylcholine receptors causing effect
What type of molecule is A234 (Novichok Nerve agent)?
Acetylcholinesterase inhibitor
What occurs in myasthenia gravis?
Antibodies target the acetylcholine receptors, causing a reduced muscle tone and so muscle weakness
What are the 2 precursor molecules of acetylcholine?
Acetyl-Coenzyme A
Choline
What enzyme converts acetyl-coenzyme A and choline into acetylcholine?
Choline Acetyltransferase
What type of receptor are nicotinic acetylcholine receptors?
Ligand-Gated Ion Channels
What type of receptor are muscarinic acetylcholine receptors?
G-Protein Coupled Receptors
How many glycoprotein subunits form a cation conducting channel?
5
What are the different types of glycoprotein subunits, forming the cation conducting channels?
α1-10
ß1-4
γ
𝛿
ε
How does varenicline act upon α4ß7 receptors in the CNS?
It acts as a partial agonist on α4ß7 receptors in the forebrain
How does varenicline act upon α7 receptors in the CNS?
It acts as a full agonist on α7 receptors in the forebrain
What is the medical name given to pupil contraction?
Mydriasis
What is the medical name given to focussing of the eye for far vision?
Cycloplegia
What is the medical name given to dry mouth?
Xerostomia
What is the medical name given to the absence of sweating?
Anhidrosis
What are some of the effects caused by stimulation of the M1 muscarinic acetylcholine receptor?
Gq causes stimulation of phospholipase C increases stomach acid secretion
What are some of the effects caused by stimulation of the M2 muscarinic acetylcholine receptor?
Gi causes inhibition of adenylyl cyclase, causing opening of K+ channels and decreasing heart rate
What are some of the effects caused by stimulation of the M3 muscarinic acetylcholine receptor?
Gq causes stimulation of phospholipase C, leading to increased salivation and broncho-constriction
