Neurophysiology Lecture notes
Lecture 1: Intro to neurons
Ion channels: gated, ion selectivity and differen characteristics
- AP pattern determines message - Know the ratio of ions in the neuron
Ion transporters
Actively move ions against conc. gradient (create larger gradient), E depedent - Na+/K+ pump : move K and Na against conc gradient
o 2 subunits ( alpha and beta ) alpha has Na+/K+ binding site, ATP binding site
o Quabain (stop function, poison)
- Ca+ pump: move Ca+ against conc gradient with ATP Ion exchangers
Use ion gradient to drive movement
- Energy from Na+ to transport Ca+,K+,Cl-,H+,GABA - Energy from K+ to transport cl-
Neural cells
- At rest selectively permeable to K+ ( leak channels) membrane potential ≈ K+ equilibrium potential Ion selectivity of Voltage gated K+ channel
4 Subunits combine to form a pore to let ions through
Hydrated K ion line up in filter K leaves and another comes in
How does it differentiate with “ion selectivity filter”?
- The amino acids minics the oxygen (red) around K (green) as though it is in its relaxed state/E efficient form
- K and water molecules always at the same distance in external environment aa will be at same position
Gating – stimulus to open channel
- Voltage, Ligand (neurotransmitter) and mechanical (deform) - Gating hinge (red) to shift open and change structure
(E) Excitatory
(F) Intracellular messengers
(C,D,E) one pore from 4 subunits (homo or heteromer)
(D) Inward rectifier- passes current (+ve/ K+) easily into the cell - tend to work when the cell is hyperpolarised
- rectifier Permeability of ions change with voltage What’s the characteristic of an K+ channel (leak)that can set the RMP?
Difference in movement of the K+ in the different ion channels - Closes when its back to rest (underpins AP)
o K+ Conductance is 0 at RMP Thus doesn’t set RMP
- opens and closes immediately, conductance 0 at rest, doesn’t set RMP
- Ca activated) Condutance 0 at rest o Doesn’t set RMP
- Inward rectifier –open by hyperpolarisation, conductance 1 at rest determine RMP
2 conditions for ion channels for RMP - Open at rest
- Selective of K+
o THUS “inward rectifier” and “K2P” channels – not voltage gated ion channels RMP important for function of neuron
- Resistance is the inverse of conductance - Condutance= 1 fully open
Anaesthetics
- Differentiates different neurons by changing the responsiveness of different groups of cells Chloroform
LORR- loss of righting reflex (getting up from falling over) chloroform works by altering the channels TREK-2, Inward recitfier and K2P thus contribute to RMP
Mouse without the channels need more chloroform to knock out
Lecture 2
NEURONS
Ways to classify neurons: function, neurotransmitter, projection, shape, system - morphologically highly specialised
- Recognise the structure of these two cells o Left :Purkinje cell highly branched o Right: Pyramidal cell of cerebral cortex
- Highly synthetic protein producing cell ion channels, receptors and cytoskeleton - Cytology shows a large pale nucleus and Nissl bodies (ribosomes, rough E) Dendrites
- Increase SA for synthetic input,lack major organelles Axon
- Up to 1m long
- Carry AP from cell body (hillock) or tip of axon (sensory neuron)
Volume of distribution High proportion in axons/dendrites damages usually at axon Structurals protiens
- Cytoskeleton - Actin
o Dynamic allows for shape changes and movement o Spines(excitatory input) and growth cones
- Intermediate filaments
o Permanent protein filament in all processes - Microtubules
o Dynamic rapid assembly/disassembly o Protein tubulin
o Basis of axonalplasmic transport o MAP- microtubule associated proteins Axon transport
- Fast transport: membrane bound components (40cm/day) o microtubule dependent +use kinesin
- Slow transport: Soluble material(4mm/day) - Retrograde axonal transport
Damaged organelles taken back to cell body recycle
Samples of local environment
Virus/bacteria (exploit system)
Axon terminal Target cell: neuron or effector cell (muscle or secretory) Synapse
- Synaptic vesicles
- Presynaptic density- elements to dock and exocytose the vesicle - Postsynaptic density- receptors to respond to neurotransmitter - Mainly supplied by axonal support
- Neurotransmitter release Ca+ dependent - Post synaptic effect is limited by:
o Destruction of transmitter by enzymes
o Re-uptake of transmitter by target, axon and glial cell
Neuronal energy budget
o Dominated by synaptic transmission - Brain metabolic demand
o Brain uses 20% of oxygen and 25% of glucose
o Sensitive to low blood flow (oxygen and glucose) little E reserves
o Brain sensitive to glucose but nerves only use lactate and pyruvate ( that can’t cross BBB) - Activity dependent vasodilation(CNS)
o Synaptic activity increase blood flow increase glucose and oxygen
Shown in MRI and PET GLIAL CELLS
Astrocytes
- Neuron survival structural and metabolic support
- Lots of processes associated with blood vessels (astrocyte end-feet), dendrites, synapses - Don’t overlap with other astrocytes connected by gap junctions
- ROLE:
o Blood vessel dilationSynaptic activity signal increase blood flow o Neuronal E supply metabolise glucose for lactate/pyruvate into ECF
glycolytic pathway suppressed in neurons o Synaptic plasticity
o Neurotransmitter recycling o K+ and water homeostasis
o Protection from oxidative stress and injury recovery Oligodendrocytes
- Insulation/ myelination in CNS - Many axons per oligodendrocyte
o AP velocity proportional to axon diameter
o Wrap around and lays down myelin on cell membrane o Nodes of Ranvier
Microglia
- Defence cells from bone marrow resemble macrophage
- Activation: inflammation, injury (up regulate cytokines and growth factors) - Lacking develop disease
PNS
- Schwann cells- support and protect axons in PNS/myelination o One axon per schwann cell
- Satellite cells – support nerve cell bodies in PNS ganglia BLOOD BRAIN BARRIER
- BBB at capillaries , prevent free diffusion
o CSF low in K+, Ca and protein (diff to rest of body)
Lipophilic substance diffuse easily (heroin and nicotine) - Usually other substances use active transport
Lecture 3: ionotropic receptors 1 (excitation)
Yellow part : passive change in input (glutamate acting on cell) - Synaptic inputs (graded potential)
- 2 main classes of receptor
o Ionotropic(for fast neuronal regulation)
Collection of subunits o Metabotropic
Alpha subunit –activate 2nd messenger, change conformation
Beta and gamma – physically bind to receptor for change - Receptors or TM spanning proteins have highly specific ligand binding domains
that interact to form a pore Types of neurotransmitters
Small molecule neurotransmitters - Acetylcholine
- Amino acids on and off transmitters
o Glutatmate- principle fast excitatory neurotransmitter in mammalian CNS o Aspartate
o GABA- main inhibitatory neurotransmitter o Glycine- inhibitory
- Purine o ATP
- Biogenic amines – based on amino acids
o Catecholamines fine tuning/modulatory transmitters
Dopamine, NA, A tyrosine derived o Indoleamine
Serotonin o Imidazoleamine
Histamine
- Peptide neurotransmitters fine tuning/modulatory transmitters
Rarely for fast neurotransmission Types of receptors for glutamate
- Glutamate ionotropic receptors are non-selective cation channels - 3 families: AMPA, kainate and NMDA
- AMPA, NMDA, Kainate all bind to glutamate name based on another ligand that can also bind to receptor - One subunit = I gene need at least 4 subunits to make a channel with pore in the middle
- Variations 4 GLU R1 or one of each more than one binding site for glutamate change binding ratio receptor ligand different variations and affinities
- Fast rapid exitation
- NTA: amino terminal domain
o If removed, wont be desensitised constant glutamate exposure o Normal cell- will respond to prolonged explosure ???
o Doesn’t affect ability to bind
- Ligand binding domain interact with M1,M3,M4 - Non-selective for Na+ and K+
o Excitatory more drive for Na+ in than K+ out (already at electrochemical equilibrium) THUS DEPOLARISE
NMDA
- Modulatory, important for plasticity - LIKE AMPA BUT
o Mg2+ is present to block the gate
Gate open to Glutamate but Mg 2+ will still block
Mg2+ removed by depolarisation Mg2+ will move out as cell is less +ve inside
o Permeable to Ca, Na and K
Drive for Ca and Na but less for K
Increase intracellular Ca (secondary messenger) o Binding site for glycine
Allosteric modulator here usually inhibitory transmitter
- 2 events to active : Depolarisation and Glutamate binding o activated more slowly wait for depolarisation
Kainate
- Also provide fast rapid excitation and modulation Glutamate cycle in the neuron
How does the cell differentiate between glutamate (excitatory) and GABA (inhibitory)[ only extra carboxyl group]?
Must fit perfectly within in the binding domain of the receptor
R485: sits perfectly to interact with glutatmate K730: important to keep in exact alignment
Glutamine – inactive, floats around in cell and ECF Glutaminase- convert glutamine to glutamate
Glutamate – from food[protein] high levels in blood after a meal BBB excludes from brain (protect from excess activity)
VGLUT-Vesicular glutamate transporter (VGLUT-2 common in brain) must be able to take up glutamate quickly
EATT- excitatory amino acid transporters (fast)
- Reuptake of Glutamate back into the neuron for recycling and repackaging
- Taken up into Glial cell to break down and release glutamine back into ECF
- Thus able to have high frequency of APs Nicotinic acetylcholine receptor
- Ionotropic receptor(ligand-gated )
- 5 subunits and 2 of which are alpha subunits ( pentamers of 4 TM spanning channels) - Toxins from animals will bind to and inactivate this receptor paralyse you
o A-bungarotoxin- paralyse PNS but can’t cross BB and thus CNS works fine - Ach acticity removed by breaking down Ach with AchE rather than being taken up
