Nervous system Flashcards
Three main classes of neurons
- Afferent/sensory
- Interneurons (entirely in CNS)
- Efferent neurons (somatic and autonomic)
How can you divide efferent autonomic neurons into?
Sympathetic and parasympathetic
What do somatic motor neurons control ?
Skeletal muscles
What do sympathetic and parasympathetic neurons control?
Smooth muscles
Cardiac muscle
Glands
What is the CNS made of?
Bran and spinal cord
Name one neurotrophic factor produced by Schwann cells
Nerve growing factor (ngf); potential solution to Alzheimer
What do Schwann cells do?
They form myelin sheaths in PNS and secrete neurotrophic factors
What do satellite cells do?
Cover the cell bodies in ganglia(outside cans) and support cell bodies
What do ependymal cells do?
They line the spaces in the brain called ventricles where you find cerebrospinal fluid
They are also a source of neural stem cells
What are ganglia?
They are clusters of cell bodies outside the CNS
What do oligodendrocytes do?
They produce myelin in CNS
What do microglia do?
Macrophage-type cells that protect the nerve cells
What do astrocytes do?
(in CNS)
Secrete neurotrophic factors.
Take up neurotransmitters, ions and water
Provide neutrons with substrates for ATP production
How are Schwann cells and oligodendrocytes different in myelination process?
Hundreds of Schwann cells may myelinated one single axon whereas one oligodendrocyte myelinates portions of several axons
What is the white matter?
Areas of CNS that contain a high number of myelinated axons
What is the grey matter?
Areas of CNS that contain cell bodies and unmyelinated axons
What does the membrane potential depend on?
- Concentration of positively and negatively charged ions on each side of the membrane
- Ion permeability of the membrane
What 3 types of channel can there be ?
- Voltage-gated : selective for particular ions
- Chemically gated: operand close in response to binding of ligands like neurotransmitters.
- Mechanically-gated: open and close in response to physical forces like vibration and stretch
Where do graded potentials usually happen?
Cell body and dendrites
Why do graded potentials lose strength ?
Because of current leaking across non-insulated membrane and because of resistance from cytoplasm
Where do action potentials happen?
Axon hillock
Can there be a summation of action potentials?
No, because of refractory period
Can there be a summation of graded potentials?
Yes and two or more graded potentials coming together might produce an action potential if they are suprathreshold
How does diameter relate to conduction?
Large diameter= faster conduction due to less resistance
Stages of action potential
- Resting membrane potential (-70mV)
- Depolarizing stimulus
- Membrane depolarises to threshold(-50). Voltage-gated Na+ channels open
- Na+ entry depolarises cell
- Na+ channels close. Voltage-gated K+ channels open
- K+ leaves the cell. Membrane returns to resting potential
- Membrane hyperpolarizes due to loss of k+
- K+ channels close
- Membrane potential restored
How is signal transmitted in electrical synapses?
Through gap junctions
How are gap junctions formed?
By docking two hemichannels from two cells.
What are the hemichannels composed of?
Connexin and innexin proteins
Classes of neurotransmitters
- CLASSICAL
- Acetylcholine
- Biogenic amines (noradrenaline, dopamine, histamine…)
- Amino Acid (glutamate) - PEPTIDES
- Substance P (sens. of pain)
- Opioids (endorphins..) - UNCONVENTIAL TRANSMITTERS
- Gases: Nitric oxide
- Purine: ATP
- Lipids: cannabinoids/anandamide
How does an excitatory transmitter act on postsynaptic neuron?
It depolarises the membrane and if it reaches threshold it will cause an. action potential
How does an inhibitory transmitter act on postsynaptic neuron?
It hyperpolarizes the membrane making it difficult to fire an action potential as it is farther away from the threshold
How many steps for production of Acetylcholine?
Just one enzymatic step
Where do substrates for Acetylcholine production come from?
Acetyl CoA comes from glucose metabolism
Choline comes from plasma
What enzyme makes Acetylcholine and how?
Choline acetyltransferase catalyses transfer of acetyl group from AcetylCoA to choline.
How is Acetylcholine degraded?
By enzyme acetylcholinesterase in ECS, which converts it into acetic acid and choline (recycled)
What protein is involved in regulated exocytosis of neutrontramsitters?
Synaptotagmins bind to calcium ions and trigger the vesicle to use snare proteins and fuse with membrane
What is an inotropic receptor?
A receptor that upon binding of neurotransmitter, opens an ion channel
What is a metabotropic receptor?
A receptor that upon binding of neurotransmitter, changes the concentration of intracellular metabolites (e.g. cAMP)
It does so via a G-protein linked effector molecule (e.g. adenylate cyclase)
What is a metabotropic receptor coupled to ?
A G-protein effector molecule
What is an agonist?
A substance that binds to and activates the receptor
What is an antagonist
A substance that interferes with transmitter binding
What kind of receptor is Nicotinic ACh receptor ?
Inotropic because the transmitter binding allows cations to enter the neuron
What kind of receptor is Muscarinic ACh receptor?
Metabotropic
What is the receptor for noradrenaline ?
Adrenergic receptor; metabotropic
What do the different subtypes of adrenergic receptors do?
alpha1: activates phospholipase C1…
alpha2: inhibits adenylate cyclase, decreasing cAMP
beta1-3: activate adenylate cyclase, increasing cAMP
How are transmitters removed?
- Enzymatic degradation in synaptic cleft
- Re-uptake into nerve terminal or glia followed by enzymatic metabolism
Is there an uptake mechanism for ACh?
No, although choline is recycled
Are biogenic amines uptaken?
Yes, in the nerve terminal
Are amino acids taken up?
Yes, by nerve terminal and glia
