Neurophysiology Flashcards
Name the 4 main types of glia.
Oligodendrocytes
Astrocytes
Microglia
Ependymal cells
What are the differences between glia and neurones?
- Newly generated in adult brain (most neurones do not do this, but neurones are regenerated in the hippocampus)
- Do not have an excitable membrane so no action potentials
- Do not form synapses. Doesn’t mean they cannot release neurotransmitters.
What is the role of oligodendrocytes?
Oligodendrocytes provide insulation to myelinated axons and have a similar role to Schwann cells in the PNS. Oligodendrocytes in the CNS typically myelinate 3-50 axons.
What is the role of microglia?
Microglia are the principal components of the immune system of the CNS and have a similar role to macrophages.
What is the role of ependymal cells?
Ependymal cells make CSF in the choroid plexus and keep it circulating through ventricular system with cilia beating.
What are the roles of astrocytes?
- Extend processes to “fence in” neurones and oligodendrocytes, dendrites, synapses and nodes of Ranvier.
- Help maintain integrity of the blood brain barrier.
- Role in CNS homeostasis, such as spatial buffering of K+.
- “Listen and talk to synapses”.
- Take up and processing of neurotransmitters that spill over from synapses.
- Role in regulating energy supply to neurons and even release gliotransmitters such as ATP and adenosine Radial glia migration of neurones and axonal pathfinding during development.
How are neurones highly specialised?
- Dendrites are generally specialised for input.
- Information input at synapses on dendrites – convergence.
- Axons are generally specialised for output.
- Information output at presynaptic terminals (branches axons – divergence)
- Neurones integrate and distribute information.
Describe the relationship between diameter and myelination.
Increasing fibre diameter increases the amount of myelination and increases speed of action potential propagation.
Describe the properties of electrical synapses.
- Fast transmission
- Bi-directional
- Synchronisation of neural networks
- Synchronisation of astrocyte networks
What are the properties of chemical synapses?
- Slower transmission
- Essentially uni-directional
- Amplification
- Flexibility
- Plasticity
Explain how ionotropic receptors are multimeric.
Different subunit compositions give different responses of ionotropic channels to drugs.
What is temporal summation?
If repetitive stimulation of the same input occur is sufficiently high frequency, their epsps will summate to produce a larger depolarisation, which may reach threshold.
What is spatial summation?
Sub-threshold epsps and ipsps from synapses at different inputs propagate passively to the axon hillock where they summate. Inputs from distal regions of the dendritic tree will have weaker effects than inputs on the cell soma.
Describe presynaptic inhibition.
- Release of neurotransmitter can be inhibited by autoreceptor mediated inhibitory feedback.
- Presynaptic/axo-axonic inhibition reduces transmitter release from a presynaptic terminal and can selectively inhibit certain inputs to a neuron without affecting the synaptic integration of other inputs.
- Pre-synaptic receptors can regulate synaptic transmitter release.
What are neural circuits?
The anatomical specificity of connections between neurones determines how sensory information is processed to produce an appropriate motor response.
Neurones are connected into circuits to process information and produce appropriate responses.
What is long term potentiation?
High frequency (100Hz for 1 second) presynaptic stimulation of certain glutamatergic synapses results in long-lasting enhancement of transmission, as seen in the greater magnitude and slope of the epsp. Change needed for memory and learning.
Describe the action of NMDA receptors being both ligand and voltage gated.
- At normal resting potentials Mg2+ ions bind in the open channel, blocking ion flow.
- When the membrane is partially depolarized the Mg2+ is repelled.
- The channel is now permeable to Na+, K+ and Ca2+.
- Increased postsynaptic Ca2+ triggers a series of changes resulting in LTP.
- Ca2+-influx via the NMDA receptor is also thought to be important in excitotoxic neuronal death during stroke. If Ca2+ concentration is too high, causes lytic cell death.
What is the link of NMDA to stroke?
NMDA receptors can detect coincident pre and posy synaptic activity. The overactivity of NMDA receptors can lead to neuronal death in stroke.
What is the purpose of synaptic plasticity?
Synaptic plasticity enables experience to change behavioural responses.
What is the pavlovian conditioning of the eyeblink reflex?
Puff of air to eye > neurone in somatosensory system > synapse to motor neurone > blink reflex
What is selective attention?
Not all sensory information can be acted upon at the same time. Therefore, the spotlight of attention is moved around, allowing detailed processing of only limited amount of sensory information at any one time. Shifts in attention are driven by internal motivation or external stimuli.
What is habituation?
One of the ways the brain can cope with sensory information. The responses to constant or predictable sensory stimuli decrease. Occurs to maintained and unimportant stimuli.
What is arousal?
The state of wakefulness, vigilance and responsiveness to novel stimuli. The level of arousal, attention and behavioural responsiveness is controlled by central neuromodulatory systems.
Unexpected or novel stimuli grab the attentional mechanisms and increase the level of arousal.
What are the noradrenergic projections of the ARAS system?
Originate in only about 10,000 neurones in the human in a structure called the locus coeruleus, located in the pons, and in related brain stem noradrenergic nuclei. They project to every major region of the CNS. The release of noradrenalin from these projections has an arousing effect on the brain, promoting wakefulness, vigilance and responsiveness to novel stimuli.