BIOL125 - Nervous System

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  • Created by: Katherine
  • Created on: 19-04-16 13:13
What is the function of the nervous system?
To enable rapid and flexible response to changes in external and internal environment of the body?
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What is the sensory function of the nervous system?
To sense internal and external changes
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What is the integrative function of the nervous system?
To analyse and store the internal/external change information. It should make decisions on appropriate voluntary and involuntary responses.
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What is the motor function of the nervous system?
To initiate muscular activity or glandular secretions.
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What is an overview of the vertebrate nervous system?
The sensory receptor receives a stimulus. It travels along the sensory input to the CNS, in the brain and spinal cord where it is integrated to info. It travels to the PNS, resulting in motor output and a change in the effector.
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What is the PNS?
The peripheral nervous system.
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What is the purpose of the PNS?
To carry nerve impulses to and from CNS. To connect the CNS to sensory receptors, muscles and glands.
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What do the brain and spinal cord do?
Integrate sensory information. Generates thoughts and emotions. Stores memory. Makes decisions. Initiates motor activity.
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What type of cells are found in the nervous system?
Neurons and Glia
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What are neurons for?
They're specialised for cell signalling. Most don't divide, apart from a few stem cells which do.
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What are glia cells for?
They have diverse functions. They can divide, e.g. to form glial scars in brain damage or disease.
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Are there more neurons or glial cells in the brain?
There are considerably more glial cells in the brain.
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What does the neuron compose of?
Cell body, dendrites and Axon.
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What is the cell body?
It contains the normal cell organelles. It is the main site of protein synthesis and degrradation
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What are dendrites?
Shortt, bristle like highly branches processes which receive nerve input (synapses), they're not myelinated.
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What is the Axon?
Long thin projections, propagates nerve impuleses to another neuron, muscle fibre or gland. Often myelinated, by oligodendrocytes (CNS) or Schwann cells (PNS). They terminate at axon terminals/synapses
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How does axonal transport occur?
There can be very long axons so nerve terminals are remote from the cell body, which is the main site of protein synthesis and degradation. Materials are transported from the cell body to and from the axon terminals. They have a well defined cytoskel
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What are the components of the neuronal cytoskeleton?
Actin, Microtubules, Neurofilaments
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What is actin?
It is a meshwork under cell surface
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Microtubules and Neurofilaments are cross linked to themselves and each other by...
Microtubule associated proteins (e.g. tau)
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What does tau do?
It accumulates inside nerve cells in the brain in Alzheimer's disease, in the form of neurofibrillary tangles.
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What are microtubules composed of?
A tubulin and B tubulin.
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What is neurofilament?
A type of intermediate filament (10nm diameter). Not globular subunit, but long extended filaments.
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What are fast anterograde materials carried by axonal transport?
Small vesicles, enzymes for transmitter metabolism
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What are slow anterograde materials carried by axonal transport?
Tubulin, neurofilament proteins, tau protein
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What are fast retrograde materials carried by axonal transport?
Larger vesicles, nerve growth factor, can be hijacked by viruses and toxins (e.g. herpes, rabies, polio, tetanus), peroxide tracer
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What is the role of kinesin?
It
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What are the 3 different types of neuron?
Bipolar, unipolar and multipolar
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What is a bipolar neuron?
It has one main dendrite and one axon - e.g. retina of the eye, inner ear, olfactory area of brain.
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What is a unipolar neuron?
Just on process from cell body, which is part way down the aon - always sensory neurons (pain, temperature, touch, pressure)
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What is a multipolar neuron?
Many dendrites and one axon - most neurons in CNS
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What are the different types of Glial cells in the CNS?
Astrocyte, Oligodendrocytes, Microglial cells, Ependymal cells.
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What are astrocytes?
They syrround neurons and blood vessels, aid neuronal cell migration and axon growth; contribute to blood brain barrier, regulate ionic environment of nerve cells, take up transmitters, make GF, activated in diseases and can form glail scars.
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What are oligodendrocytes?
Source of CNS myelin; single cell can myelinate >50 acons with each myelin segment from a single oligodendrocyte.
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What are microglial cells?
Scavenger cells (macrophages) which can remove debris from dying neurons - may enter from blood
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What are ependymal cells?
Line fluid filled ventricles - produce and circulate cerebrospinal fluid.
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What types of Glial cells are in the PNS?
Schwann cells and Satellite cells
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What is a schwann cell?
It is a source of PNS myeline, each cell produces part of the myelin around only a single axon
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What is a satellite cell?
Flattened cells around cell bodies of neurons in PNS ganglia
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What does the myelin sheath wrap around?
The axon
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What are the 4 principal parts of the human brain?
1.) Brain stem 2.) Cerebellum 3.) Diencephalon 4.) Cerebrum
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What is the brain stem?
It is continuous with spinal cord, respirator with cardiovascuar control, swallowing and vomiting.
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What is the cerebellum?
It is behind the brain stem. Co-ordinates movement, balance, posture and maintains muscle tone.
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What is the diencephalon?
Principally the thalamus and hypothalamus, above brain stem. Pain, touch, pressure, hot/cold sensations, sound, taste, smell, thirst, sleep patterns.
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What is the cerebrum?
Surrounds Diencephalon and is very well developed in humans. Has sensory, motor and association areas (seat of intelligence, memory, and emotions), visual cortex.
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Where is the gray matter in the brain?
On the outside of he cerebrum.
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What consists of the gray matter?
Neuronal cell bodies, dendrites.
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Where is the white matter in the brain?
In the cerebrum
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What does the white matter consist of?
It consists of myelinated axons
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The cerebrum is divided into how many hemisphere? What are these connected by?
2 - Corpus callosum
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The cortex is highly convoluted with what
Sulci and gyri
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Each hemispere is divided into 4 lobes, what are these?
Frontal, parietal, occipital and temporal.
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The cerebral cortex is divided into 3 areas, what are these?
Somatosensory areas, motor areas, association cortex.
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Where do neurons receive information?
At dendrites.
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Information is transmitter along the axon in the form of...
Electrochemical signals or nerve impulses
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What are axon potential due to?
The flow of ions (Na+, K+) through specific protein channels in the membrane
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Are ion channels always open?
No, some are regulated or gated
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What type of gated ion channels are there?
Mechanically gated, ligand gated or voltage gated
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What are voltgage gated ion channels involved in?
They are involved in the generation and propagation of nerve impulses
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What are Ligand gated ion channels involved in?
They are involved in neurotransmission at the synapse
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What are mechanically gated ion channels involved in?
They are involved in perception of touch
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What does a ligand gated ion channel open in response to?
A ligand gated ion channel opens in response to binding of a messenger, or ligand (e.g. hormone or neurotransmitter)
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What are the two ways in which ions can leave and enter a cell?
Chemical driving force and electrical driving force
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What is the chemical driving force?
This is due to diffusion from a region of high concentration to a region of low concentration
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What is the electrical driving force?
The interior of cell is negatively charged so positively charged cations will be retained wherase negatively charged anions will be expelled.
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What is the electricalchemical driving force?
It is a combination of the chemical and electrical forces acting on any particular ion. It give the nett force that acts to drive an ion into or out of the cell, throguh an open membrane channel.
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What is the resting potential?
-70mV
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Tests on resting potential are carried out on...
Giant squid axons
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What is the resting membrane potential of a nerve cell?
It is the difference in voltage across the plasma membrane when the cell is at rest (i.e. when it is not receiving or sending any signals)
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What does the resting potential depend on?
Concentration gradients for multiple ions across the membrane, and on the relative permeability of the membrane of those ions.
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What are the most important ions?
Na+ and K+
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What is the equilibrium potential?
It is the membrane potention required to exactly counteract the chemical forces acting to move one particular ion across the membrane.
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What is the name of the equation that calculates the action potential
The Nerst equation
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As the Ena of sodium ions is +60, do the ions try and enter, or leave the cell?
They try and enter the cell
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In this, do chemical, electrical or both forces act in the same or different directions?
Both force act in the same direction
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As the Ek is -94, will potassium ions try and enter or leave the cell?
They try and move out of the cell
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In this, do chemical, electrical or both forces act in the same or different directions?
Different directions, but chemical force is greater
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Incoming signals from sensory stimulus can do what to a cell membrane?
Depolarise it
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The depolarisation causes the membrane potential to do what?
Rise from its resting potential of -70mv.
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What happens if the membrane potential is depolarised by a certain critical level?
An action potential is triggered in the axon
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What is the critical level?
-55mv
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What is it called when the membrane potential is made to decrease?
It is hyperpolarisation - it makes it less likely that an action potential will occur.
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What is the name of the zone where the action potential is initiated?
The trigger zone.
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An action potential is self...
Popagating, with no loss of signal intensity as it moves down the acon.
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What are the other properties of action potentials?
Each stimulus produces full action potential or none at all. Impulses jump from node (of ranvier) to node in myelinated axons at speeds p to 150m/s. Intensity of signal is conveyed by frequency of nerve impulse.
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What is the name of the time in which an action potential cannot be stimulated?
The refractory period
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Are synapses electrical or chemical?
Both, but usually chemcial
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Where are transmitters stored/
In membrane bound synaptic vesicles.
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What is the amount in one vesicle called?
A quantum
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What does the arrival of an action potential causes?
It causes influx of ca2+ then fusion of vesicles with pre-synaptic membrane and release of transmitter into synaptic cleft.
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What does the transmitter bind to?
Receptors on post synaptic membrane.
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The effect of the transmitter can be...
Excitatory or inhibitory
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What is the criteria for transmitter substances?
1.) Synthesised in the neuron 2.) Present at presynaptic terminals, packaged within synaptic vesicles 3.) Endogenous substance (drug) at reasonable concentration mimics eactly the action of endogenously released transmitter 4.) Specific mecahnsim rem
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What is acetlycholine?
It is found in the brain at the neuromuscular junction and in autonomic ganglia. Brain ACH is deficient in Alzheimer's disease.
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Wht is Acetylcholine synthesised by?
Choline acetly transferase
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Receptors can either be:
Nicotinic or muscarinic
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What is nicotinic?
Neuromuscular junction, brain, autonomic nerves
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What is muscarinic?
Smooth muscle, exocrine glands, brain
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What causes action to stop?
Acetlycholinesterase attached to the extracellular side of synaptic membranes (neuronal and glial)
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What is an agonist?
It binds to receptors and stimulate it (mimicks transmitter)
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What is an antagonist?
It binds to the receptor but doesn't stimulate it (blocks transmitter)
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What is an example of a nicotinic agonist?
Nicotine, from tobacco
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What is an example of a nicotinic antagonist?
Curare, dart poison used by south American indians
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What is an example of a muscarinic agonist?
Muscarine, from the toadstool
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What is an example of a muscarinic antagonist?
Atropine from deadly nightshade
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What is responsible for muscle contraction?
The axon terminal of a motor neuron and striated muscles fibres.
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In vertebrates, numerous ..... receptors are found at the NMJ?
Nicotinic acetylcholine receptors
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What is Alheimer's disease characterised by?
Loss of short term memory
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What are catecholamines synthesised from?
From tyrosine
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What are 3 examples of catecholamines?
Noradrenaline, adrenaline and dopamine.
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What is associated with motor function and is lost in Parkinson's disease?
Dopamine
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The brain lacks phenylalanine hydroxylase which converts Phe to Tyr, so what happens?
Tyr is transported into brain from blood.
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Catabolism involved enzymes:
Monoamine oxidase (MAO) and catechol 0-methyltransferase (COMT)
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What is the mean age of Parkinson's disease onset?
60 years
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What is Parkinson's characterised by?
Muscle rigidity, tremor, bradykinesia.
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It is a multifactorial disease, what does that mean?
It is attibuted to multiple factors, such as age, environment and genetics.
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What causes Parkinson's disease?
It is due to degeneration of pigmented cells in the basal ganglia.
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What does this result in?
It results in >50% depletion of the transmitter dopamine
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What is used to treat Parkinson's disease?
L-dopa
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What happens to L-dopa?
It is transported to the brain and converted into dopamine.
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L-dopa is simultaneously administered with what and why?
Dopa decarboxylase inhibitor (which cannot penetrate into the brain), which prevents metabolism to dopamine in the periphery.
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What else can be given to Parkison's sufferers?
Inhibitors of MAO and COMT can be given to inhibit dopamine degradation.
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What is serotonin synthesised from?
It is synthesised from tryptophan by tryptophan hydroxylase and 5 hydroxtryptophan (5 HTP) decarboxylase.
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How many different receptors does serotinin have?
Many, around 14.
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Hallucinogenic drugs such as LSD act as 5-HT ..... and mimick he action of serotonin at 5 HT receptors.
Agonists
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Can Serotonin be inactivated?
Yes, by MAO
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Are amino acids present at a higher or lower concentration in the CNS than other body tissues?
Higher
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Are the amino acids in the CNS essential or non essential?
Non essential - we don't need them in the diet as they are all mde.
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Which amino acids are excitatory and which are inhibitory?
Dicarboxylic amino acids (glutamate, aspartate) are excitatory and Glycine and GABA are inhibitory
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Which are major transmitters in the brain?
Glutamate and GABA
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Where is the most common type of neurotransmitter?
In the hypothalamus.
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Peptide transmitters are synthesised as large precursor proteins and transported to where?
To synaptic release site where they are activated by proteolytic cleavage.
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What do peptide transmitters do?
They slow post synaptic effects.
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The actions of peptide transmitters are terminated by what?
By extracellular proteases
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Give some examples of peptide transmitters:
Opioids (endorphines, enkephalins and dynorphins), vasoactive intestinal peptide (VIP), Neurotensin.
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What is a gas transmitter?
Nitric oxide
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Being a gas, NO is not stored in synaptic vesicles, so where does it come from?
It is made as required by an enzyyme (NOS), from arginine. NO simply diffuses from nerve terminals into adjacent cells, and forms covalent linkages to a multiplicity of targets.
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What is inactivation of NO?
Diffusion away.
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What are the two main types of transmitter receptors?
Either acts directly on an ion gated channel, or act indirectly of a G protein coupled receptor
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How do transmitters that act directly work?
Also called an ionotropic receptor. It is always stimulatory, it is fast.
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How do transmitters inditectly work?
Also called a metabotropic receptor. Can trigger opening or closing of a separate ion channel. Can also lead to many other effects on the cell. Slow - up to hours.
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What is the sequence of events when a G protein acts indirectly on an ion channel?
Agonist binds to receptor, GTP exchanges for GDP on the G protein a subunit. G protein dissociates from receptor - then ligand too. The 3 subunits of the G protein dissociate. The a subunit activates the ion channel. The a subunit inact by hydrolysis
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Some G proteins stimulate of inhibit enzyme targets instead of acting on what?
Ion channels
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What are the most common of these targets?
Adenylate cyclase, Guaylate cyclase, Phospholipase C
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Which enzymes make corresponding second messengers?
Ccylic AMP, Cyclic GMP, Inositol - which can then causes a slow response in the cell
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What is the structure of ligand gated receptors?
Composed of 4 or 5 different subunits arranged around a central pore in the membrane.
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What is an example?
Nicotinic acetlycholine, GABA, Glycine, 5 HT3 receptors.
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What is the structure of G protein coupled receptors?
Composed of a single protein with 7 membrane spanning regions ( a helices) = seven transmembrane receptor.
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What are some well known drug targets:
Tricylic antidepressants, SSRIs, Valium, MAO inhibitors, L-DOPA, Acetylcholinesterase inhibitors
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What do Tricylic antidepressants do?
They block neuradrenaline and serotonin re-uptake (depression)
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What do SSRIS do?
They also block serotonin re-uptake
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What does Valium do?
Activates GABA receptors
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What do MAO inhibitors do?
Block breakdown of biogenic amines
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What does L-DOPA do?
It is a dopamine precurose.
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What does Acetylcholinesterase inhibitors do?
Blocks breakdown of acetylcholine
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