Neuro Flashcards
What are the function of dendrites?
Post-synaptic signal conduction and integration - collects synaptic input from many different neurons
What are the function of the axonal hillock(/soma)?
Generation of AP
What is the function of the axon?
Propagation of AP
What are temporal and spatial summation?
Temporal: converts a rapid series of weak pulses from a single source into one large signal
Spatial: converts several of weak signals from different locations into a single large one
What is the length constant?
Quantifies the decrease in signal. The bigger the length constant the bigger the chance of an AP (needs to be the length of the dendrite to generate an AP)
But not all dendrites are <1 length constant, so what can they do?
Dendrites are capable of effectively increase the length constant and amplify the signal via voltage-gated ion channels (Cav). Dendrites debranch –> cell diameter becomes larger –> allows for activity along cable –> length constant becomes longer
What causes the unique low threshold in the axon hillock?
High density of Nav (app. 2000 channels/µm2)
Why is the signal unidirectional?
Due to the refractory period (channels inactivate before they close, ergo they can’t be activated for a while)
True or false: most info within a neural system is encoded in the temporal pattern of APs
True
What are rate coding vs temporal coding?
Rate: info is contained in the fire rating - number of spikes, not timing
Temporal: info is contained in the timing of spikes, such as first spike latency and inter-spike periods
How is the axonal conduction of APs tuned for speed?
Myelin: oligodendrocytes in CNS, Schwann cells in PNS
What does an increased diameter lead to?
A decrease in intracellular resistance (Ri)
What is the time constant?
Quantifies the rate at which charge spreads. T = RmCm
Rm = resting membrane resistance
Cm = membrane capacitance
What are and what are the function of the internodes in myelin sheats?
Myelinated regions
Function: Works as an insolater - AP “jumps” from node to node (saltatory conduction)
What are and what are the function of the nodes of Ranvier in myelin sheats?
Regions not covered by myelin, with a high density of ion channels
Function: act as mini axonal hillocks
How does the myelin effect the Rm and Cm?
High Rm, low Cm –> higher rates of AP propagation
What can multiple sclerosis lead to?
Demyelation –> disrupts the CNS ability to effectively conduct electrical signals –> increase the Cm, decrease the Rm
Results in a wide range of syndroms
What are the different types of synapses?
Axosecretory: directly into bloodstream
Axoaxomatic
Axodendritic
Axoextracellular: secretes into extracellular fluid
Axosomatic
Axosynaptic
What are the two types of synapses?
Electrical and chemical
How do electrical and chemical synapses differ?
Electrical: smaller distance (3.5 nm), gap junction, carries info as ion currents, no delay, didirectional, no plasticity
Chemical: longer distance (20-50 nm), presynaptic vesicle, chemical transmitter, at least 0.3 ms delay (usually 1-5 ms), unidirectional, plasticity
Where are chemical- and electric synapses found?
Chemical: everywhere
Electrical: heart and secretory cells
What are the two types of vesicles in chemical synapses (presynaptic)?
Clear secretory: enzyme synthesized transmitters, concentrated at active zones
Dense core: neuropeptides, dispersed at the presynaptic terminal
Describe some properties of the post synaptic side.
Dense neurotransmitter receptor concentration, downstream molecular signaling proteins, often specialized dendritic architecture (spines)
What are some NTs derived from amino acids?
GABA, glycine
What are some NTs derived from mono amines?
Acetylcholine, serotonine, histamine
What are some NTs derived from catecholamines?
Dopamine, adrenaline, noradrenaline, DOPA, tyrosine
What are some NTs derived from peptides?
Oxytocin, comatostatin, arginine vasopressin, substance P
How can NTs be synthesized?
Enzyme or ribosome
What are the properties of enzyme synthesized NTs?
Made throughout the neuron, selectively packed into vesicles, often recovered after release, activates both ionotropic and metabotropic receptors
What are the properties of ribosome synthesized NTs?
Synthesized on rough ER –> packed in golgi = long transport, not recovered, activates only metabolic receptors
What are the two types of receptors NTs bind to?
Ionotropic: single receptors, but protein complexes, opens upon binding, very fast response, different effects of changing membrane permeability
Metobatropic: GPCRs, slower response (up to days), produce modulatory responses, that typically change neuronal excitability
The same NT can have different effects based on the receptor it binds to. Use ACh as an example.
When ACh binds to nicotinic ACh receptor (ionotropic):
Excitatory stimuli, cation channels activation. Found in: neuromuscular junction
Muscarinic M2/4 (metabotropic):
Inhibatory, K+ channels activation. Found in: cardiac muscles
M1/3/5: hyperexcitable, inhibits K+ channels. Found in: sympathetic neurons
Describe the properties of excitatory synapses.
Often on dendrites, most use glutamate, most use ionotropic Rs, generate EPSP by a non-selective cation channel, EPSP is usually very small: 0.01 - a few mV –> need for summation
Decribe the properties of inhibitory synapses.
Often on cell bodies, most use GABA or glycine, ionotropic, generate IPSP by activation of Cl- selective channels bringing Vm–> E_Cl, IPSPs oposes EPSPs. GABA is the source of action of alcohol and other anaesthetics
What are the two main classes of ionotropic glutamate receptors?
NMDA (slow phase, voltage gated, high Ca2+ permeability, Mg2+ block) and AMPA (fast phase, ligand gated cation channel)
Why must synaptic inhibition be tightly regulated?
Too much –> coma
Too littel –> seizure
Decribe the properties of modulatory synapses.
Can be found throughout neurons, use neuropeptides and monoamines, use metabotropic Rs
What are the difference between spatially focused and widely divergent neurons?
Spatially focused: only a few synapses close to each other - fast, specific, spatially organized
Widely divergent: a lot of synapses - mood, sleep, awareness
Describe the general effect of NA and adrenalin on the brain, and when it is active.
Active during: new, unexpected, non-painful sensory stimuli in the environment
Role: general arousal of the brain during interesting events
Regulation of attention, arousal, sleep/awake, behavioural flexibility, anxiety, pain and emotion
“mobilizing the brain”, directing resources away from maintenance toward active movement
Describe the general effect of serotonine on the brain, and when it is active.
Active during: wakefulness
Role: regulation of mood, memory processing, sleep and cognition
Specifically in control of sleep/wake cycles
Modulation of certain emotional behaviours
What are some diseases linked to altered serotonin signaling in the CNS?
Depression and anxiety (reduced levels)
Obsessive-compulsive disorder (depletion of serotonin)
Falling in love has recently been shown to result in depleted serotonin levels –> might explain the obsessive component of this phase
What is the function of the neuronal microenvironment?
To protect the brain from itself and the rest of the body. Consists of fluids, barriers and cells
What is the CSF?
The cerebrospinal fluid, secreted from the choroid plexus cells (epithelial cells lining the ventricles)
Communicates and stabalizes fluid around the neurons
What is the fluid composition of CSF that varries most from BECF?
Low [K+] app. 2.9 mM, low [amino acids] app. 0.7 mM, low [proteins] app. 0.03 g/dL
Where do we find CSF?
In the ventricles, subarachnoidal space, and spinal cord
The brain floats in CSF
What is CSF reabsorped by, and what is reabsorped?
Arachnoid granulation and villi
Descripe what is secreted/absorped by choroid plexus.
Secreted: NaCl and NaHCO3, and osmotically driven H2O
Absorped: K+ and metabolites of serotonin and dopamine
What is the BECF?
Brain ECF
Similar to CSF and plasma, but not identical
Where is BECF found?
Around neurons, glia cells and capillaries in the brain
What is the role of BEFC?
Plays a role in cell-cell communication
Describe the properties of BEFC.
Tortuous (snoede) and limiting diffusion
Decreases with cell swelling
Route for O2, CO2, catabolized transmitters, and spilled over amino acids
Large changes in extracellular ion concentrations, e.g., K+
Communicates with CSF
What can cause cell and brain swelling (edema, when fluid is drawn from capillaries)?
Traumatic brain injury, ischemic stroke, intracerebral haemorrhage, brain infection, tumor, low Na+
What is the function of the BBB?
Tight control of transfer of nutrients and ions
Stabalizes CSF and BECF
Describe the anatomy of the BBB.
From inside-out: Capillary, endothelial cell, pericyte, basement membrane, astrocyte
Describe the transfer properties of the BBB.
Can pass: uncharged and lipid-soluble molecules (gases, ethanol, caffeine)
May pass (needs protein to pass): glucose
What can altered BBB permeability cause?
Multiple sclerosis, stroke, brain tumors, metastatic tumor cells, CNS infections
What are the circumventricular organs?
Very small contact areas without BBB
Produce prehormones, important for regulation of body fluids, located where the brain needs to secrete something (e.g., melatonin, oxytocin) or sense something
What are the most prominent cells in the CNS?
Glial cells - comprise half of the volume of the brain and outnumber neurons 10:1
What are the main glial cell types in the CNS?
Astrocytes, oligodendrocytes, and microglial cells
What are the general properties of glial cells?
Non-excitable, can proliferate
What are the functions of oligodendrocytes?
Sustain myelin, involved in pH regulation and iron metabolism
True or false? Oligodendrocytes are targeted by immune cells in MS.
True
What are the function of astrocytes?
Supply fuel to neurons in form of lactic acid, permeable to K+, synthesize and take up neurotransmitters
How are astrocytes coupled?
Via gap junctions (connexins, not permeable to Ca2+)
Describe the K+ homeostasis of astrocytes.
Na-K-ATPases, inwardly rectifying K+ channels, Na-K-Cl-transporters facilitate K+ uptake by astrocytes
Describe how astrocytes are involved in the glutamate cycle.
Takes up glutamate (via EAAT1/2) –> converts it to glutamine (via glutamine synthetase) –> secretes glutamine (via SNAT3/5) –> glutamine taken up by neurons (via SNAT1/2) –> resynthesized as glutamate (by glutaminase)
Describe the communication properties of astrocyte.
They are Ca2+ excitable (does not communicate via APs). They release gliotransmitters (e.g., ATP, glutamate, prostglandins). Release trophic factors, cytokines, and factors affecting blood flow. Express specialized receptors e.g., purinergic.
Describe how ATP is involved in astrocyte communication.
Extracellular ATP stimulates intracellular release of Ca2+. ACs communicates in Ca2+ waves stimulate by extracellular ATP
What are the function of microglial cells?
They are the immunoreactive cells of the brain aka. macrophages of the CNS
What are the microglial cells associated with in the PNS?
Pain transmission
