S1+S2 - intro Flashcards
What does grey matter contain ? what is its role ?
Composed of cell bodies and dendrites, with a rich blood supply
• There are axons in grey matter, but volume is predominantly composed of cell bodies and
dendrites
• Most of the computation occurs here
• ‘Grey matter’ in the PNS is termed a ganglion (collection cell bodies)
What does white matter contain ? what is its role ?
- Composed of (myelinated and non-myelinated) axons with no cell bodies
- Myelin (a lipid emulsion like mayonnaise) is white
- White matter pathways connect areas of grey matter, like cables between components of a computer
- ‘White matter’ in the PNS is termed a nerve (or root)
read this one
• A sensory deficit in a dermatomal pattern suggests the lesion is at the level of dorsal roots or
spinal nerves
• A sensory deficit across multiple segments may suggest a cord lesion
• A sensory deficit in a homuncular pattern may suggest a lesion above the thalamus (see
sensory system)
define
funiculus
tract
fasiculus
A funiculus refers to a large block of white matter containing multiple distinct pathways
which both ascend and descend.
• A tract refers to an anatomically and functionally defined white matter pathway connecting
two distinct regions of grey matter. In a tract, impulses travel in a single direction only.
• A fasciculus is a subdivision of a tract that supplies a distinct body region. Examples include:
gracile fasciculus (subdivision of dorsal column tract supplying lower half of body) and
cuneate fasciculus (subdivision of dorsal column tract supplying upper half of body,
excluding the head)
what are the 3 types of fibers
what do they connect?
o Association fibres connect cortical regions within a hemisphere
o Commissural fibres connect the hemispheres
o Projection fibres usually connect cerebral hemispheres with the cord or brainstem
or vice versa
have a read of lectures 1 and 2 briefly, then do the quizes on them. also do session 2 quiz
do it
what is an astrocyte
Structural support • Help to provide nutrition for neurones • Astrocytes produce lactate which can be transferred to neurones • Supplements their supply of glucose - as the lactate is converted to glucose in the neuron – glucose-lactate shuttle
• Remove neurotransmitters (uptake)
– control concentration of neurotransmitters (especially
important for glutamate (toxic) - transporters reuptake to remove from the neurosynaptic cleft - keeping extracellular conc low
• Maintain ionic environment
– K+ buffering
they can uptake K that may build up if the brain has increased activity
• Help to form blood brain barrier
what is an oligodendrocyte
responsible for mylenating axons in the CNS
what are microglia
Immunocompetent cells
• Recognise foreign material - activated
• Phagocytosis to remove debris and foreign material
• Brain’s main defence system
outline the role of the blood brain barrier
• 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
glucose, amino acids and K+ need to be transported across the BBB - allowing for a controlled concentration
how is the CNS immune priviledged ?
• Rigid skull will not tolerate volume expansion
– Too much inflammatory response would be harmful
- Microglia can act as antigen presenting cells
- T-cells can enter the CNS
• CNS inhibits the initiation of the pro-inflammatory T-cell response
what are the three ways neurons can communicate at the synapse
The synapse
– fast excitatory neurotransmission - when depolaritsation of a ligand ion channel - depol will cause more action potentials - the excitatory postsynaptic potential
– fast inhibitory neurotransmission
– modulatory responses
breifly recap how we signal at the synapse with neurotransmitters
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
Postsynaptic response • The response depends on – nature of transmitter – nature of receptor • Ligand-gated ion channels • G-protein-coupled receptors
what is the major excitatory neurotransmitter ?
glutamate - an amino acid
what is the main inhibitory neurotransmitter ?
GABA - an amino acid
try and name the 4 types of glutamate receptors
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
Ionotropic AMPA receptors Kainate receptors NMDA receptors Ion channel - permeable to Na+ and K+ (and in some cases Ca2+ ions) Activation causes depolarisation – increased excitability
Bonus - glutamatergic synapses
Glutamatergic synapses have both AMPA and NMDA receptors
• AMPA receptors mediate the initial fast depolarisation
• NMDA receptors are permeable to Ca2+ - provide the large AP
• 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
how are glutamate receptors involved in memory ?
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
what is the inhibitory neurotransmitter for the brainstem and spinal cord ?
glycine
what are GABA and Glycine receptors ?
They have integral CL channels
opening them will cause a hyperpolarisation - decrease the AP fire rate
explain a patella reflex
hints the exitation signal where does it enter sends signals to contract where ? interneuron then a a signal where to prevent contraction ? via what neurotransmitters
4 other neurotransmitters are ?
seretonin
dopamine
noradrenaline
acetylcholine
outline seretonin in the brain
come from the Raphe nuclei
FUNCTIONS
• Sleep/wakefulness
• Mood
• SSRIs (serotonin selective reuptake
inhibitors) treatment of depression
and anxiety disorders
outline dopamine in the brain
Dopa comes from substantia niagra in brainstem
Nigrostrial pathway to striatum - for motor control
mesocortical - to frontal cortex and mesolimbic - to amygdala
both involved in the mood arousal and reward process
Conditions associated with dopamine dysfunction
• 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
outline acetylcholine in the brain
ACh as 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
neucleus basalis in forebrain supplies the cortex with ach
others supply the brainstem
involved in arousal, memory and learning and motor control
degentation of ach neurons in the neucleus basalis is associated with Alzheimer disease - give cholineresterase inhibitors to relive symptoms
outline noradrenaline in the brain
- 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
Cell bodies of NA containing neurones are located in the brainstem (pons and medulla) - locus cerelulus to brain and RF to cord
– 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
outline dopamine therapy and the BBB
we give L - Dopa to boost dopamine
in the periphery this would cause high DOPA and hence psychosis
so give carbidopa to inhibit this conversion of L-DOPA to dopamine via the AADC enzmye
carbidopa cant cross the BBB so still converted to Dopamine where it can help boost dopa, reliving Parkinsons
