Neurones And Glia

Question 1

What are components of the cns

Answer 1

• Network of neurones with supporting glia
• Neurones sense changes and communicate with other neurones
– around 1011 neurones
• Glia support, nourish and insulate neurones and remove ‘waste’
– around 1012 glia

Question 2

What are types of glial cells

Answer 2

• Astrocytes (several different types) – most abundant type of glial cell
– Supporters
  • Oligodendrocytes – Insulators
• Microglia
– immune respons

Question 3

What are the roles of astrocyted

Answer 3

• Structural support
• Help to provide nutrition for neurones
– glucose-lactateshuttle
• Remove neurotransmitters (uptake)
– control concentration of neurotransmitters (especially important for glutamate (toxic)
• Maintain ionic environment 
– K+ buffering
• HELP to form blood brain barrier

Question 4

Hwo do astrocytes provide energy for neurones

Answer 4

• Neurones do not store or
•produce glycogen
Astrocytes produce lactate which can be transferred to neurones
• Supplements their supply of glucose
• Glucose lactate shuttle
Lactate used to produce atp
Glycogen can be stored in astrocytes. Can produce pyruvate, lactate. Transporters can transport lactate
Intense neuronal activity - need some more energy (atp) can get lactose lactate shuttel
Can operate for 10-15 min

Question 5

How do astrocytes help to remove neurotransmitters

Answer 5

• Re-uptake
– Astrocyteshave transporters for transmitters such as glutamate
– Helps to keep the extracellular concentration low.

Question 6

How do astrocytes help to buffer k+ in brain ecf

Answer 6

• High levels of neuronal activity could lead to a rise in [K+] in brain ECF
• Astrocytes take up K+ to prevent this
Can get build up of K= in ecf. If it gets too high will depot the surrounding Europe’s - spontaneous electrical activity - too much glutamate - toxic.
Astrocytes perm to cl-, keep memb potential very negative, so they can take upk+ - inward movement of k+ though channels and transporters - work to keep a low k+ conc
Astrocytes can be coupled. So k+ moves between them to maintain low

Question 7

What are oligodendrocytes

Answer 7

• Responsible for myelinating axons in CNS
• Compare with PNS where Schwann cells are responsible for myelination
• Good time to revise ICPP Unit and myelination

Question 8

What are microglia

Answer 8

• Immunocompetent cells
• Recognise foreign material - activated
• Phagocytosis to remove debris and foreign material 
• Brain’s main defence system
Processes get wides when activated 
Mesodermal. Other glia are ectodermal a

Question 9

What is the bbb

Answer 9

• Limits diffusion of substances from the blood to the brain extracellular fluid
• Maintains the correct environment for neurones
• Brain capillaries have
– tight junctions between endothelial cells
– basement membrane surrounding capillary
– end feet of astrocyte processes

Blood is not a suitable environment for neurones as it can have changing levels of, e.g. aas, k+, etc

Endothelial cells from tight junctions- prevents charge molecules difficusing into the brain extracellular space. (Astrocytes do not form bbb but associate)

Question 10

Describe the pathways across the bbb

Answer 10

• Substances such as glucose and amino acids and potassium are transported across BBB.
• This allows the concentration to be controlled

Ions or small molecules rely on transporters and channels. Eg glucose in glut1. AAs are transported across - controlwhat crosses over into the brain ecf.

Question 11

How is the brain immune specialised

Answer 11

• Does not undergo rapid rejection of allografts
• Rigid skull will not tolerate volume expansion
– Too much inflammatory response would be harmful - pressure
• Microglia can act as antigen presenting cells
• T-cells can enter the CNS
• CNS inhibits the initiation of the pro-inflammatory T-cell response
• Immune privilege is not immune isolation, rather specialisation

Question 12

Descrbe neurotransmitter release at the synapse

Answer 12

• Depolarisation in the terminal opens voltage-gated Ca2+ channels. Ca2+ ions enter the terminal
• Vesicles fuse and release transmitter
• Neurotransmitter diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane

Question 13

Descrbe the postsynaptic response

Answer 13

• The response depends on – nature of transmitter
– nature of receptor
• Ligand-gated ion channels
• G-protein-coupled receptors

Question 14

What are the 3 chemical classes of neurotransmitters

Answer 14

AMINO ACIDS
glutamate, GABA, glycine

BIOGENIC AMINES
acetylcholine, noradrenalin dopamine, serotonin (5-HT), histamine,

PEPTIDES
dynorphin, enkephalins, substance P, somatostatin cholecystokinin neuropeptide Y

Question 15

Descrb amino aid neurotransmitters

Answer 15

• excitatory amino acids
– mainly glutamate
– major excitatory neurotransmitter
• over 70% of all CNS synapses are glutamatergic • present throughout the CNS
• inhibitory amino acids – GABA
– Glycine

Question 16

Desribe glutamate receptors

Answer 16

Ionotropic
AMPA Kainate NMDA
receptors receptors receptors Na+/K+ Na+/K+ Na+/K+
and Ca2+
Ion channel - permeable to Na+ and K+ (and in some cases Ca2+ ions)
Activation causes depolarisation – increased excitability
Metabotropic
mGluR1-7
G protein-coupled receptor
Linked to either:
• changes in IP3 and Ca2+ mobilisation
• or inhibition of adenylate cyclase and decreased cAMP levels

Question 17

Describe teh response at glutamate receptors

Answer 17

Fast excitatory responses
• Excitatory neurotransmitters cause depolarisation of the postsynaptic cell by
acting on ligand-gated ion channels.
- excitatory postsynaptic potential (EPSP)
- depolarisation causes more action potentials

Question 18

What are the fucntionsof different receptors at glutamierguc synapses

Answer 18

• Glutamatergic synapses have both AMPA and NMDA receptors
• AMPA receptors mediate the initial fast depolarisation
• NMDA receptors are permeable to Ca2+
• NMDA receptors need glutamate to bind and the cell to be depolarised to allow ion flow through the channel
– Also glycine acts as a co-agonist
Need ampa to depolarise to activate nomad.

Question 19

Descrive glutamate receptors, synaptic plasticity and excitotoxicity

Answer 19

• Glutamate receptors have an important role in learning and memory
– Activation of NMDA receptors (and mGluRs) can up-regulate AMPA
receptors
– Strong, high frequency stimulation causes long term potentiation (LTP)
– Ca2+ entry through NMDA receptors important for induction of LTP
• Too much Ca2+ entry through NMDA receptors causes excitotoxicity – Too much glutamate - excitotoxicity
Lip underlies leaning and memory

Calcium going in - activate downstream signalling - more ampa - more depopulated

Question 20

What are the main inhibitory amino acids

Answer 20

• GABA is the main inhibitory transmitter in the brain
GABA
• Glycine acts as an inhibitory neurotransmitter mostly in the brainstem and spinal cord

Question 21

How do gaba and glycine receptors work

Answer 21

• GABAA and glycine receptors have integral Cl- channels
• Opening the Cl- channel causes hyperpolarisation
– Inhibitory post-synaptic potential (IPSP)
• Decreased action potential firing

Question 22

How do barbiturates and benzodiazepines affect gaba receptors

Answer 22

• Barbiturates and benzodiazepines bind to GABAA receptors
• Both enhance the response to GABA - Both modulate the receptors to enhance the action city

– Barbiturates - anxiolytic and sedative actions, but not used for this now
• risk of fatal overdose also dependence and tolerance
• sometimes used as anti-epileptic drugs

– Benzodiazepines
– have sedative and anxiolytic effects
– used to treat anxiety, insomnia and epilepsy

Question 23

Where s glycine in high conc

Answer 23

Brainstem ad spinal cord

Question 24

What are bogenic amines and ach

Answer 24

• acetylcholine
• dopamine
• noradrenaline
• serotonin (5-HT)
• mostly act as neuromodulators • confined to specific pathways

Question 25

Descrbe ach as a neurotransmitter

Answer 25

• ACh
– neuromuscularjunction
– ganglion synapse in ANS
– postganglionic parasympathetic
• ACh is also a central neurotransmitter
– acts at both nicotinic and muscarinic receptors in the brain
– mainly excitatory
– receptors often present on presynaptic terminals to enhance the release of other transmitters

Question 26

Wha are cholinergic pathways i the cns

Answer 26

• Neurones originate in basal forebrain and brainstem
• Give diffuse projections to many parts of cortex and hippocampus (longterm potentiation in hippocampus)
• There are also local cholinergic interneurones
• eg in corpus striatum
• Involved in arousal, learning & memory, motor control
• Degeneration of cholinergic neurones in the nucleus basalis is associated with Alzheimer’s disease
• Cholinesterase inhibitors are used to alleviate symptoms of Alzheimer’s disease

Question 27

Describe dompanimeric pathways in the cns

Answer 27

Nigrostriatal pathway involved in movement control eg in Parkinson’s
Mesocortical pathwats - mood arousal and reward
Also tubero hypophyseal pathway

Question 28

What are conditions associated with dopamine dysfunction

Answer 28

• Parkinson’s disease
– associated with loss of dopaminergic neurones
– substantia nigra input to corpus striatum
• Can be treated with levodopa - converted to dopamine by DOPA decarboxylase (AADC)
• Schizophrenia
• May be due to release of too much dopamine
– amphetamine releases dopamine & noradrenaline
– produces schizophrenic like behaviour
– antipsychotic drugs are antagonists at dopamine D2 receptors
– Other neurotransmitters also implicated

Question 29

Descirb dopamine and the bbb

Answer 29

Ss

Question 30

Describe NA as a neurotransmitter

Answer 30

• Noradrenaline - transmitter at postganglionic – effector synapse in ANS
• Also acts as a neurotransmitter in the CNS
• Operates through G protein-coupled α- and β-adrenoceptors
• Receptors to noradrenaline in the brain are the same as in the periphery

Question 31

Describe Na pathways in the cns

Answer 31

Cell bodies of NA containing neurones are located in the brainstem (pons and medulla)
Diffuse release of NA throughout cortex, hypothalamus, amygdala and cerebellum

Question 32

Desribe noradrenaline and behavioural arousal

Answer 32

• Most NA in the brain comes from a group of neurones in the locus ceruleus
– LC neurones inactive during sleep
– activity increases during behavioural arousal
– amphetamines increases release of noradrenaline and dopamine and increase wakefulness
• Relationship between mood and state of arousal
– depression may be associated with a deficiency of NA

Question 33

Describe serotonergic pathways

Answer 33

Serotonin, 5-HT
• Similar distribution to noradrenergic
neurones
FUNCTIONS
• Sleep/wakefulness 
• Mood
• SSRIs (serotonin selective reuptake inhibitors) treatment of depression and anxiety disorders