Neurones, synapses and transmitters Flashcards
How many neurons are in the brain?
100 billion
How many neurons in the neocortex?
22.8 billion in men, 19.3 billion in women
How long are all the nerve fibres in our brain?
150,000-180,000km
How many synapses in the cortex
150,000 billion
At what rate are neurones lost?
1 a second or 86,000 a day
What is the ratio of glia to neurones?
10 glia for each neurone
What do glia offer neurones?
Physical support
Metabolic support
Electrical insulation
Guiding connections (in development)
Do glial cells send signals?
Yes
What is the central nervous system?
The brain and spinal cord
What is the peripheral nervous system made up of?
Sensory nervous system
Motor system
Autonomic nervous system
What is the autonomic nervous system made up of?
Sympathetic
Parasympathetic
Enteric
What is the opposite of the autonomic nervous system?
The somatic nervous system
What is the definition of the peripheral nervous system?
Neurones that extend from the CNS
How are neurones specialised for communication?
Dendrites - receive input from other neurones
Axon - impulse conduction
Synaptic bouton - release of neurotransmitter
How are neurons classified?
Number of processes coming off the cell body: uni-, bi-, multi-polar
Dendrites: shape, spines
Connections: motor, interneurons
Axon length: golgi type I or II
Neurotransmitter (can’t be seen on microscope)
What is a unipolar neurone?
Single axonal process
What is a bipolar neurone?
Two axonal processes
What is a multipolar neurone?
Multiple axonal processes
What is a pseudo-unipolar neurone?
Single axonal processes, cell body is on a stem
What is an electrical synapse?
(also known as gap junction)
Fastest and most primitive means of communication
Bi-directional transfer of information
How do gap junctions work?
A pore between two cells, it allows ions to move between two cells
What does a gap junction do?
Allow synchronous activity between neurons
Relatively rare (present in development)
Present in glia-neuron, glia-glia communication (cardiac myocytes)
What is a chemical synapse?
A uni-directional transfer of information
What is a synaptic cleft?
The gap between the pre and postsynaptic elements
What is an efferent neuron?
Information going out
What is an afferent neuron?
Information coming in
Explain what happens in a chemical synapse
Action potential invades nerve terminal
Depolarisation triggers Ca2+ channel opening
Ca2+ influx (chemical gradient)
Vesicle containing neurotransmitter moves to cell membrane and fuses
Neurotransmitter leaves cell
Diffuses across the synaptic cleft
Binds to receptor
How can a signal be terminated in a chemical synapse?
By re-uptake or enzymes in the synaptic cleft
Explain how re-uptake occurs
Presynaptic neurone takes up neurotransmitter and either repackages it or breaks it down with enzymes
Explain how enzymatic breakdown occurs
Enzymes present in the synaptic cleft breakdown the neurotransmitter
What are the 4 categories of neurotransmitters?
Amino acids: glutamate, GABA
Monoamines: noradrenaline, 5-HT
Acetylcholine
Neuroactive peptides
What are the two classifications of neurotransmitters?
Inhibitory
Excitatory
What are the receptors in synapses?
Membrane spanning protein molecules
Specific to a neurotransmitter
How do the receptors cause a signal?
Transmitter binding causes structural change, structural change = signal
How many receptors does a neurotransmitter have?
Several subtypes
How do we classify receptors?
Localisation: post or pre synaptic
What it responds to: autoreceptor, heteroreceptor
How do we name multiple receptor sub-types?
Based on most potent, selective agonist
e.g. for glutamatergic receptors we have: AMPA, NMDA, Kainate
Name the receptor signalling mechanisms
Ionotropic
Metabotropic
How does an ionotropic receptor work?
Ionotropic is receptor operated (ligand gated channels)
Transmitter binds: conformational change, channel opening, ion movement (Na+ in excitatory or Cl- in inhibitory)
How quick is an ionotropic receptor?
Fast
How does a metabotropic receptor work?
"G-coupled protein receptors" Transmitter binds Conformational change Activates G-protein Activates effector systems Has an indirect effect on excitability
How quick is a metabotropic receptor?
Slow, but its effect lasts longer
What can activated G-proteins do?
Open or close ion channels
Stimulate or inhibit enzymes/ secondary messenger systems
