The Nervous System Flashcards
How much of the total blood flow of the heart does the brain recieve, why?
20%. The brain cannot store glucose or extract energy without O2.
State the primary sources of arterial blood supply to the brain.
The vertebral arteries supply the caudal part and enter at the base of the skull. The internal carotid arteries supply the rostral part and ascend the left and right sides of the neck. These join to form the basilar artery.
What is a fissure?
A fissure is a deep cleft in the brain.
What is a sulcus?
A sulcus is a shallow cleft in the brain.
What is a gyrus?
A ridge in the brain.
What is the corpus callosum?
The corpus callosum is a bundle of nerve fibers that connect the hemishpheres of the brain.
Name the 4 lobes of the forebrain (telencephalon)?
Frontal, parietal, temporal, occipital
State the function of the thalamus.
The thalamus relays motor and sensory signals to the cerebral cortex. It also regulates sleep and alertness.
State the function of the hypothalamus.
The hypothalamus regulates homeostasis. It controls the autonomic nervous system and the endocrine system. It regulates behaviour.
How many nuclei is the hypothalamus comprised of?
22
What does the midbrain (mesencephalon) consist of?
The tectum and the tegmentum
State the function of the tectum.
Auditory (inferior) and visual (superior) processing
State the 3 regions of the tegmentum.
The red nucleus, periaqueductal grey and substantia nigra
State the function of the red nucleus of the tegmentum of the mesencephalon.
The RN coordinates sensorimotor information.
State the function of the periaqueductal grey of the tegmentum of the mesencephalon.
The PAG is involved in pain suppression due to a high concentration of endorphins.
State the function of the substantia nigra of the tegmentum of the mesencephalon.
The SN makes dopamine and projects to the basal ganglia.
State the structures that make up the hindbrain.
The hindbrain is made of the metencephalon (cerebellum and pons) as well as the myelencephalon (medulla oblongata and spinal cord).
State the function of the cerebellum.
The cerebellum receives signals from the muscles and the sensory and vestibular systems and coordinates this to produce smooth movements.
State the function of the pons.
The pons is a large bulge which is involved in sleep and arousal.
State the function of the spinal cord.
The spinal cord is a neuronal link between the PNS and the CNS. It is also an integrating center for spinal reflexes.
Name the 12 cranial nerves.
I=olfactory
II=optic
III=oculomotor
IV=trochlear
V=trigeminal
VI=abducens
VII=facial
VIII=vestibulocochlear
IX=glossopharyngeal
X=vagus
XI=spinal accessory
XII=hypoglossal
(oh,oh,oh, to touch and feel very good velvet, AH)
What is aphasia?
Aphasia is an impairment of the ability to communicate. Can be caused by strokes or brain tumours.
What is a resting membrane potential?
A resting membrane potential is the difference between the electric potential in the intracellular and extracellular matrices of the cell when it isn’t excited.
What is an action potential?
An action potential is a fast, transitory and propagating change of the resting membrane potential.
What is the equilibrium potential of an ion?
Equilibrium potential of an ion is the membrane potential that exactly balances the concentration gradient of the ion across the membrane.
A cell membrane is composed of a lipid bilayer. What composes this bilayer?
Phospholipids, glycolipids, cholesterol, membrane proteins
State Fick’s law.
Fick’s law states that the rate of diffusion is proportional to both the surface area and concentration difference and is inversely proportional to the thickness of the membrane.
What are the forces affecting the passage of ions across a membrane?
Electrical gradient: (+)ive ions flow towards (-)ive ions.
Chemical gradient: ions move from areas of high concentration to areas of low concentration.
How is separation of charge achieved across a membrane?
Only lipophilic molecules travel freely across a membrane, all others rely on transport proteins.
Describe the action of the sodium-potassium pump.
The sodium-potassium pump (Na+/K+ ATPase pump) is a transporter protein that utilises active transport to transport ions into the cytoplasm.
The pump binds to ATP and Na+. ATP is hydrolysed and the pump is phosphorylated. A conformational change occurs, exposing Na+ to the extracellular side. In the phosphorylated state, the pump has a low affinity for Na+, causing the ions to be released into the extracellular space. The pump then binds K+, which triggers its dephosphorylation, causing it to revert to its previous conformation and transport K+ into the cell. The unphosphorylated pump has a higher affinity for Na+ so K+ is released.
How many ions are transported across the membrane as a result of a cycle of the sodium-potassium pump?
One cycle of the sodium-potassium pump transports 3 Na+ ions outside the cell and transports 2 K+ ions inside the cell. In an act that defies the concentration gradient of the cytoplasm.
What is the normal osmolality of all body fluid compartments?
290 mOsmol
What is an electrochemical gradient?
An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane.
What is the function of the gating of ion channels?
The gating of ion channels is so that they have conducting and non-conducting states. They control ion selectivity.
What is the transition between states of an ion channel called?
Gating
What is gating influenced by?
Gating is influenced by changes in the membrane potential (voltage-gated channels), extracellular ligands (ligand-gated channels), mechanical stimulation and phosphorylation.
What is a graded potential?
A graded potential is the small change in membrane potential that is caused by the movement of ions across the membrane. These can be +/-ive, are transient and do not result from the opening of voltage-gated ion channels.
What is continuous conduction?
Continuous conduction is the conduction of action potentials in unmyelinated axons.
What is saltatory conduction?
Saltatory conduction is the conduction of action potentials in myelinated axons, where the action potentials seem to jump from one node of Ranvier to the next.
What do nerve conduction velocities depend on?
Resistance of the axonal membrane (insulation) and internal resistance of the axon (diameter)
What is neurotransmission?
Neurotransmission is the communication of information between neurons in the brain.
What is a neurotransmitter?
Neurotransmitters are chemicals that are released at a synapse by the presynaptic neuron and consequently affect the postsynaptic cell in a specific manner .
What are action potentials?
Action potentials are the electrical signals in neurons that convey information from the brain to organs.
What is ephaptic signalling?
Ephaptic signalling is when two axons are so close together that the current produced by one has a major effect on the adjacent axon.
What is volume transmission?
Volume transmission involves the extra-synaptic release of neurotransmitters. These neurotransmitters move by diffusion through the blood stream or by CSF.
What is chemical transmission?
Chemical transmission is communication between neurons that involves the rapid release of a chemical messenger that diffuses across to the receiving cell and causes a change in the postsynaptic cell’s properties.
State the 5 common neurotransmitters as well as their function.
Acetylcholine - voluntary movement of the muscles
Glutamate – major excitatory neurotransmitter, roles in memory and learning
Dopamine - motivation, pleasure
Serotonin - emotions, wakefulness and temperature regulation
GABA – the major inhibitory neurotransmitter
Where are neurotransmitters stored? Why?
Synaptic vesicles
To protect them from enzymatic degradation and to keep them ready for release.
Describe the movement of presynaptic vesicles in the terminal button.
When voltage-gated Ca+ channels are opened due to the depolarization of the synaptic terminal by an action potential, docking, priming and fusion of presynaptic vesicles occur.
Docking is the movement of vesicles from reserve pool to tight association with the plasma membrane. During this, SNARE proteins on vesicle and the membrane interact to prepare for fusion.
Priming are the reactions that convert the vesicle to a form that can fuse in response to an action potential. This step involves the assembly of the SNARE complex.
Fusion is the local elevation of calcium concentration that stimulates vesicle to fuse with the membrane. Synaptotagmin, a calcium-sensitive protein on the vesicle, acts as a calcium sensor. It allows the release of neurotransmitters into the synaptic cleft.
What are synaptic potentials?
Synaptic potentials are brief electrical responses caused by activated receptors.
How do ionotropic receptors work?
Specific neurotransmitters bind to the ionotropic receptor which causes a conformational change and the opening of the ion channel.
How do metabotropic receptors work?
Metabotropic receptors are indirectly coupled to ion channels via G-proteins, which activate second messenger cascades.
State the symptoms of the grinning death, what is it caused by?
Symptoms: risus sardonicus (rigid smile), trismus (lockjaw), opisthotonus (rigid, arched back)
Cause: tetanus toxin produced by clostridium tetani. It blocks the release of inhibitory neurotransmitters, causing spasms.
Describe the events that occur at the postsynaptic membrane.
Neurotransmitters bind to receptors which change the ion permeability of the postsynaptic cell membrane. Activation of receptors causes postsynaptic potentials which may be either excitatory or inhibitory. Postsynaptic potentials from dendrites spread passively and converge on the cell body. If postsynaptic potentials are above threshold, an action potential will arise.
Describe the localisation of iGluRs.
iGluRs include AMPARs, NMDARs and KainateRs. AMPARs and NMDARs are mostly co-localised at glutamatergic synapses where they mediate fast chemical synaptic transmission. NMDARs, AMPARs and KainateRs can be synaptic, extra-synaptic, presynaptic and postsynaptic.
Name the technique whereby micropipettes measure the opening of ion channels.
Patch-clamping (records a change in I)
Name two common morphological types of glutamatergic synaptic connection in the brain.
Type I: excitatory, located on the spine or shaft of a neuron
Type II: inhibitory: located on the soma or shaft of a neuron
What is the location and function of dendritic spines?
Dendritic spines are found are small protrusions on a dendritic shaft which increase the synaptic efficiency of the neuron.
Which are quicker iGluRs or mGluRs?
iGluRs
Describe the action of AMPARs.
AMPARs open and close quickly, and are thus responsible for most of the fast excitatory synaptic transmission in the central nervous system
What are AMPARs permeable to?
Na, K and Ca to a smaller extent
Name the subunits of AMPARs.
GluA1, GluA2, GluA3, GluA4
How can AMPARs be regulated?
Regulation of AMPAR subunits can arise through splicing and
post-translational changes in AMPAR subunits.
How can knowledge about AMPARs be applied clinically?
AMPAR antagonism can be used as anti-seizure medication.
How can NMDA receptors be activated?
NMDARs are ligand and voltage-sensitive receptors. Activation requires binding of glutamate and the co-agonist glycine. (slow)
What are the subunits of NMDARs?
GluN1 (glycine-binding site)
GluN2A/B/C/D (contains glutamate binding site and is responsible for the Mg block)
GluN3A/B (reduce inward currents)
Describe the action of the Mg block in NMDARs.
At resting membrane potential NMDARs carry little current, as magnesium ions block permeability to cations. The Mg block is relieved by depolarisation, this is the reason for slow activation and depolarisation.
What is potentiation?
Potentiation refers to the process by which the strength or efficacy of synaptic transmission is enhanced.
Classify the metabotrophic glutamate receptors.
Group I: mGluR1, mGluR5
Group II: mGluR2, mGluR3
Group III: mGluR4, mGluR6, mGluR7, mGluR8
State the function of each functional group of metabotrophic glutamate receptors.
Group I: increases synaptic function (excitatory)
Group II: decreases synaptic function
Group III: modulates synaptic input and regulates neurotransmitter release
Localise the 3 functional groups of mGluRs.
Group I: postsynaptic
Group II: presynaptic and glial
Group III: presynaptic
State the Group I mGluR pathway.
1) Glutamate binds to the group I receptor, which is coupled to PLC.
2) PLC cleaves PIP2 into IP3 and DAG.
3) IP3 diffuses to the cytoplasm and binds to ER which releases Ca2+.
What are the effects of activating the group I mGluR pathway?
Ca2+ is released and Ca is implicated in synaptic plasticity. Increase in protein kinase C which phosphorylates many synaptic proteins, enhancing NMDAR activity. The less negative membrane potential increases the probability of action potentials arising in a neuron. Homer protein is released which traffics mGluRs and functionally connects iGluRs and mGluRs.
What are the effects of activating the group II mGluR pathway?
Reduces voltage-gates Ca channels in presynaptic neurons. There is a dephosphorylation of proteins required in the signalling cascade for synaptic transmission. May release GABA.
What is excitotoxicity?
Excitotoxicity refers to the ability of glutamate and related compounds to destroy neurons by prolonged excitatory synaptic transmission. (In this way group II/III mGluRs are neuroprotective as they inhibit this transmission.)
