Neurones and glia

What are the 4 main types of glia?

• oligodendrocytes

• astrocytes

• microglia

• ependymal cells

What are the key differences of glia from neurones?

• newly generated in adult brain

• don’t have excitable membrane so no APs

• don’t form synapses

What is the role of oligodendrocytes?

provide insulation to myelinated axons

How many axons do oligodendrocytes typically myelinate?

3-50

What is the role of microglia?

principal component of immune system of CNS and have similar role to macrophages

What is the main role of ependymal cells?

make CSF in choroid plexus and keep it circulating through ventricular system with cilia beating

What are the roles of astrocytes?

• maintain integrity of BBB

• CNS homeostasis

• take up & processing of neurotransmitters that spill over synapses

• regulating energy supply to neurons

• release gliotransmitters (e.g. ATP & adenosine)

• radial glia migration & axonal pathfinding during development

Where are astrocytes found?

extend processes to “fence in” neurones and oligodendrocytes, dendrites, synapses and nodes of Ranvier

What are dendrites generally specialised for?

input

What is convergence?

information input at synapses on dendrites

What are axons generally specialised for?

output

What is divergence?

information output at presynaptic terminals

What is the main, general role of neurones?

integrate and distribute information

1

apical dendrites 

2

inhibitory terminal

3

cell body

4

nucleus

5

excitatory terminal 

6

axon hillock

7

node of Ranvier

8

myelin sheath

9

axon

10

presynaptic terminal

11

synaptic cleft

12

postsynaptic dendrite

What is the membrane potential maintained by?

Na+/K+ pump

What does opening an ion channel do?

shift membrane potential towards equilibrium potential for that ion/ions

What are the 4 types of ion channel?

• ligand-gated

• phosphorylation-gated

• voltage-gated

• stretch or pressure-gated

What are key characteristics of chemical synapses?

• slow transmission (synaptic delay)

• essentially uni-directional

• amplification

• flexibility

• plasticity 

What are the 2 types of neurotransmitter receptors?

• ionotropic

• metabotropic

What are the key characteristics of ionotropic receptors?

• faster

• directly influence membrane potential

What type of receptor does this image show?

ionotropic

What are the key features of metabotropic receptors?

• slower

• may indirectly influence membrane potential

Do ionotropic receptors have a depolarising or hyperpolarising effect?

depolarising

Do metabotropic receptors have a depolarising or hyperpolarising effect?

hyperpolarising 

What type of receptor does this image show?

metabotropic

Assuming that membrane potential is -70mV, then what effect will ACh have on membrane potential via nicotinic (ionotropic) versus muscarinic (metabotropic) receptors?

Nicotinic - depolarise

Muscarinic - hyperpolarise

What does EPSP stand for?

excitatory postsynaptic potential

What does IPSP stand for?

inhibitory postsynaptic potential

Are nicotinic receptors EPSP or IPSP?

EPSP

Are muscarinic receptors EPSP or IPSP?

IPSP

What does the direction of change in membrane potential depend on?

ion permeability and starting membrane potential

What is the major fast excitatory neurotransmitter?

glutamate

What is the major fast inhibitory neurotransmitter in the brain?

GABA

What is the major fast inhibitory neurotransmitter in the spinal cord?

glycine

What are the major transmitters of the PNS?

noradrenaline and acetylcholine

In the CNS, what act as neuromodulators?

• noradrenaline

• acetylcholine

• dopamine

• serotonin

In the CNS, what do noradrenaline, acetylcholine, dopamine and serotonin act as?

neuromodulators

What determines how information is processed to produce an appropriate response?

• anatomical specificity of synaptic connections between neurons

• neurotransmitter specificity 

• receptor subtypes

What do neuromodulators lack?

anatomical specificity

What do neuromodulators modulate?

activity of whole neural circuits

Why are neurones connected into circuits?

• process information

• reduce appropriate responses

Does A (top) show temporal or spatial summation?

temporal

Does B (bottom) show temporal or spatial summation?

spatial

temporal summation

repetitive stimulation of same input at sufficient frequency, epsps summate to produce larger depolarisation

Spatial summation

sub-threshold epsps and ipsps from synapses at different inputs propagate passively to axon hillock where they summate

Inputs from distal regions of the dendritic tree will have ______ effects than inputs on the cell soma.

weaker

What is the likely effect on membrane potential if C is stimulated shortly after A + B?

reduced depolarisation

What is the membrane potential at the axon hillock influenced by? (spatial summation)

the sum of excitatory and inhibitory synaptic inputs to the neuron

What can release of neurotransmitters (e.g. noradrenaline) be inhibited by?

autoreceptor-mediated inhibitory feedback

What does presynaptic (axo-axonic) inhibition do?

reduces transmitter release from a presynaptic terminal & can selectively inhibit certain inputs to a neuron without affecting the synaptic integration of other inputs

What can regulate synaptic transmitter release?

pre-synaptic neurotransmitter receptors

What does high frequency presynaptic stimulation of certain glutamatergic synapses result in?

long-lasting enhancement of transmission - greater magnitude and slope of epsp

What does synaptic plasticity enable?

experience to change behavioural responses

What type of receptor is the NMDA receptor?

ligand- and voltage-gated

What can NMDA receptors detect?

coincident pre- and post-synaptic activity

What happens at normal resting potentials in the NMDA receptor?

Mg2+ ions bind to open channel, blocking ion flow

What happens when the NMDA receptor is partially depolarised?

Mg2+ is repelled

What is the open NMDA channel permeable to?

• Na+

• K+

• Ca2+

In the NMDA receptor, what does increased post-synaptic Ca2+ trigger?

series of changes resulting in LTP

What is Ca2+ influx via the NMDA receptor thought to be important in?

excitotoxic neuronal death during stroke

What can overactivity of NMDA receptors lead to?

neuronal death in stroke