Neurophysiology: Neurons and Circuits Flashcards
Describe the difference between ionotropic and metabotropic receptors
- ionotropic: ligand-gated channels, fast response, direct ion flow
- metabotropic: GCPR, slower response, modulate ion channels indirectly
different classes of neurotransmitters
small-molecule neurotransmitters
amines
peptides
small-molecule neurotransmitters
small-molecular neurotransmitters (acts on ionotropic receptors, rapid responses, rapidly cleared from synaptic cleft)
amines
(released upon depolarisation and Ca2+ influx, can act on both ionotropic and metabotropic receptors, cleared by reuptake or enzymatic degradation)
peptides
(requires sustained stimulation to be released, typically acts on metabotropic receptors, thus slower and more prolonged responses, slow inactivation i.e. slower removal from synaptic cleft)
Explain graded changes in membrane potential from synaptic inputs
- synaptic inputs modulate the RMP
- can result in depolarisation (excitation) or hyperpolarisation (inhibition)
- information conveyed through chemical or electrical messages
Describe the difference between the different families of glutamate receptors
- AMPA, kainate and NMDA receptors
- subunits determine receptor chacterstics
- different subunit combinarions create various receptors
- AMPA receptors are non-selective cation channels mainly allowing Na+ influx
- NMDA contain an Mg2+ ion which blocks ions from flowing through channel so requires depolarisation before can function properly
Describe the steps in glutamate fast excitatory neurotransmission
- glutamate binds to ionotropic receptors AMPA and NMDA
- AMPA receptor activation leads to rapid Na+ influx and therefore depolarisation
- NMDA receptors allow Ca2+ entry after Mg2+ removal (triggered by teh depolarisation)
AMPA and NMDA receptors often work together for efficient transmission
Describe the different mechanisms for inactivating neurotransmitters
- recycling: glutamate removed, recycled and repackaged
- vesicular glutamate transporters (VGLUT) package glutamate into vesicles
- excitatory amino acid transporters (EATT) rapidly remove glutamate from the synaptic cleft
Describe the difference between electrical and chemical synapses
- chemical synapses: neurotransmitters released, bind to post-synaptic receptors
- electrical synapses: gap junctions physically connect neurons, allowign direct ionic passage
Describe the composition of gap junctions and the movement of ions through gap junctions
- gap junctions are composed of connexons with connexins
- connexons form a pore allowing bidirectional movement of ions
- communication of small molecules like calcium and ATP can occur through gap junctions
Discuss the Goldman and Nernst equations
- Goldman equation: calculates resting membrane potential, considering multiple ions and their permeabilities
- Nernst equation: calculates the equilibrium potential for a single ion based on its concentration
Describe how a potential is established across the neuronal membrane
- neurons exist in a state with a potential difference across their membrane
- changes in membrane potential occur due to excitatory or inhibitory inputs
- action potentials, triggered by reaching the threshold, allow long-distance communication
Identify the major constituent ions in intracellular and extracellular solution
- intracellular: High K+, low Na+, low Cl-, low Ca2+
- extracellular: low K+, high Na+, high Cl-, high Ca2+
Describe the electrical gradient, the chemical gradient and the electrochemical gradient
- electrical gradient: movement of charged particles along potential differences
- chemical gradient: movement along concentration differences
- electrochemical gradient: combined influence of electrical and chemical gradients
Define and explain why the plasma membrane is “semi-permeable”
- the neuronal plasma membrane allows some ions to pass through by restricts others
- ion channels play a crucial role in this selectivity
Explain how ions can move across the semi-permeable neuronal plasma membrane
- ions move along electrical and concentration gradients
- cell membrane is semi-permeable, allowing selective ion movement
- ion channels facilitate the passage of ions
Explain ion transporter, ion exchangers, ion pumps
- ion transporters (pumps) uses ATP to move ions agaisnt their concentration gradient
- ion exchangers utilise ion concentration gradients to move other ions without ATP
- the Na+/K+ pump, an ATPase pump, maintains ion concentration gradients
Describe how ion channels are gated and selective
- ion channels can be voltage-gated, ligand-gated or mechanically gated
- selectivity means specific ion channels allow specific ions to pass through
- channels open and close in response to various stimuli
Explain what is meant by the “equilibrium potential” of an ion
- equilibrium is reached when electrical and chemical gradients balanc
- no net movement of an ion at equilibrium
- membrane potential at equilibrium is the equilibrium potential
functional phenotype
- describes what a neuron does e.g. excites skeletal muscle cells for motor function
- identified through electrophysiology or observing its effect on post-synaptic cells
name the different types of glial cells and briefly describe their role in the nervous system
- oligodendrocytes (CNS) and Schwann cells (PNS) form myeline sheaths
- microglia act as local immune cells
- astrocytes support CNS, contribute to the blood-brain barrier and regulate ion balance
- ependymal cells create barriers and produce neural stem cells
- radial glia guid neuronal migration during development
chemical phenotype
- involves neurotransmitters produced/used (e.g. acetylcholine in motor neurons)
- identified through direct labelling, mRNA analysis, or genetic markers
combined phenotype example
cholinergic motor neuron is both functionally excitatory and uses acetylcholine