(PM3B) CNS Intro Flashcards
What is the sympathetic nervous system?
Autonomic - involuntary
(1) Mobilises
(2) Fight/ flight
What is the parasympathetic nervous system?
Autonomic - involuntary
(1) Conserves
(2) Rest/ digest
What is the coronal (frontal) plane?
Ear to ear
Splits front and back of body
What is the horizontal (transverse) plane?
Front to back
Splits top and bottom of body
What is the sagittal plane?
Left and right
Splits left side of body from right side of body
What is grey matter?
Brain tissue
Dense in neuronal cell bodies
Glial cells + neurophil
What is white matter?
Areas dense in myelinated axonal tracts
Fewer cell bodies
What is the cerebral cortex?
Contains 90% of brain’s total neurons
Responsible for:
(1) Abstract thought
(2) Judgement
(3) Memory
(4) Interpretation
(5) Integration of sensory input
Proportionally larger in humans than other mammals
Evolutionary young area
What are Brodmann areas?
Regions of the cerebral cortex
What is the frontal lobe?
A cortical lobe of the brain
Responsible for higher, executive function
What are the cortical lobes of the brain?
(1) Frontal lobe
(2) Parietal lobe
(3) Occipital lobe
(4) Temporal lobe
What is the parietal lobe?
A cortical lobe of the brain
Responsible for integration of sensory information
What is the occipital lobe?
A cortical lobe of the brain
Responsible for visual processing
What is the temporal lobe?
A cortical lobe of the brain
Responsible for processing sensory information
What is the limbic system?
Responsible for application of emotion to cognitive functioning (fear/ love/ rage/ pleasure)
Includes:
(1) Hypothalamus
(2) Amygdala
(3) Hippocampus
(4) Thalamic nuclei
(5) Olfactory region + others
What brain areas/ systems are responsible for determining overall behaviours?
Balance of cortical + limbic functions
What is the thalamus?
Area in the brain
In the limbic system
Pre-processor + relay for sensory information
Dysfunction can cause perceptual symptoms, e.g. hallucinations
What is the hypothalamus?
Area in the brain
In the limbic system
Coordinates nervous system with endocrine system (via pituitary) + sympathetic nervous system
What is the hippocampus?
Area in the brain
In the limbic system
Important for learning + memory
What is the amygdala?
Area in the brain
In the limbic system
Involved in fear processing + emotional memories
What are the basal ganglia?
Interconnected nuclei within the cerebrum
Responsible for coordinating voluntary motor activity between cerebellum + cortex
Maintenance of posture + muscle zone
What are the main components of the basal ganglia?
(1) Striatum
(2) Globus pallidus
(3) Subthalamic nuclei
(4) Substantia nigra
What can happen following basal ganglia dysfunction?
(1) Huntington’s disease
(2) Parkinson’s disease
What is the excitatory neurotransmitter in the basal ganglia?
Glutamate
What is the inhibitory neurotransmitter in the basal ganglia?
GABA
What is the modulatory neurotransmitter in the basal ganglia?
Dopamine
What is the brainstem?
Oldest part of the brain (in evolutionary terms)
Contains visual, auditory + motor centres
Responsible for involuntary motor functions
What are the components of the brainstem?
(1) Midbrain
(2) Pons
(3) Medulla
What are the main responsibilities of the brainstem?
(1) Respiration
(2) Cardiovascular control
(3) Pain sensitivity control
(4) Alertness
(5) Consciousness
What is the relay station in the brainstem?
Reticular formation monitors + influences CNS input + output
(1) Ascending: Carries information TO the brain
(2) Descending: Carries information AWAY from the brain
What does the ascending relay station do in the brainstem?
Carries information to the brain
From the periphery
What does the descending relay station do in the brainstem?
Carries information to the periphery
From the brain
Where are the majority of cell bodies for amine neurotransmitters contained?
Brainstem
What are the main neurotransmitters in the brainstem?
(1) Dopamine
(2) Noradrenaline
(3) 5-hydroxytryptamine (serotonin)
(4) Cholinergic neurons
What are neurons?
Principle signalling units of the NS
What are glia?
(1) Oligodendrocytes: Make myelin
(2) Astrocytes: Homestasis + synaptic modulation + BBB
(3) Microglia: Brain’s immune system
(4) Ependymal cells
What are astrocytes?
Type of glia
Stellate (fibrous + protoplasmic)
(1) Physical support for neurons
(2) Neurotransmitter uptake
(3) Ionic homeostasis
(4) Signalling to neurons
What are oligodendrocytes?
Type of glia
Myelinating cells of CNS
Each cell myelinates several axons
What are microglia?
Type of glia
Macrophage-like cells
Cells of the immune system in the CNS
Respond to CNS injury + inflammation
Phagocytose foreign bodies
Contribute to repair + injury
What is the blood brain barrier?
High-selective + partially permeable membrane
Barrier to protect brain from periphery
(1) Endothelial cells form tight junctions
(2) Tight junctions make the brain inaccessible for polar molecules (unless actively transported)
What is receptor mediated-transcytosis?
Mechanism by which some large molecules enter the CNS
What is the role of efflux transporters in the blood brain barrier?
Actively pump some molecules out of the brain
How do most drugs pass the blood brain barrier?
via diffusion
Needs low molecular weight + high lipid solubility
What are the key factors which determine if a molecule can diffuse through the blood brain barrier?
(1) Must be low molecular weight
(2) Must have high lipid solubility
What are the structural features of a neuron?
(1) Dendrites
- Basal
- Apical
(2) Cell body
(3) Axon
- Initial segment
- Hillock
- Myelin sheath
- Node of Ranvier
(4) Nerve terminals
- Presynaptic terminal
How can neurones differ morphologically?
(1) Shape
(2) Spines
(3) Myelinated/ unmyelinated
What percentage of neurons use glutamate as a neurotransmitter?
50%
What percentage of neurons use GABA as a neurotransmitter?
30%
What are some of the most common neurotransmitters used by neurons?
(1) Glutamate
(2) GABA
(3) Acetylcholine
(4) Neuropeptides
(5) Amines (serotonin/ noradrenaline)
Which structures within the neuron are responsible for processing?
(1) Dendrites
(2) Cell body
Which structures within the neuron are responsible for output?
(1) Axon
(2) Nerve (axon) terminals
What are some of the positive and negative charged ions used for transmission of an electrical signal?
(1) Cations:
- Na+
- Ca2+
- K+
(2) Anions:
- Cl-
- Protein anions
What is the approximate charge of the inside of a neuronal cell?
-70mV
In a neuronal cell, which ions are at high concentration extracellularly?
(1) Ca2+
(2) Na+
(3) Cl-
In a neuronal cell, which ions are at high concentration intracellularly?
(1) K+
(2) Protein-
What is another term for potential difference?
Voltage
What is another term for voltage?
Potential difference
How can ion channels be opened?
(1) Ligands – ligand-gated channels
(2) Changes in membrane potential – voltage-gated channels
What is the role of sodium (Na+) as an electrochemical transmitter?
To make the maximum voltage (Vm) more positive
(1) High concentration outside the cell
(2) Sodium channels are closed at resting membrane potential
(3) Channels open – Na+ enters neuron down concentration gradient
(4) Sodium can be pumped back out of the neuron in exchange for potassium ions (K+)
What is the role of potassium (K+) as an electrochemical transmitter?
To make the maximum voltage (Vm) more negative
(1) High concentration inside the cell
(2) Many K+ channels are open at rest to fine tune the resting potential (-70mV)
(3) Channels open – K+ moves out of neurons down concentration gradient
(4) K+ is pumped into the cell
What is the role of chloride (Cl-) as an electrochemical transmitter?
To make the maximum voltage (Vm) more negative
(1) High concentration outside the cell
(2) Most Cl- channels are ligand-gated (GABA + glycine receptors)
(3) Channels open – Cl- flows into neuron down the concentration gradient
(4) Cl- is pumped out of the cell by a co-transporter
What is the action potential of a neuron?
-70mV at rest – depolarisation drives the action potential towards + beyond 0mV
The binary unit of information transfer in the nervous system
Conveys information intRAcellularly
Initiates electrochemical transmission intERcellularly
Relies on voltage-activated ion channels
What are dendrites?
Receive signals from other neurons
How are post-synaptic potentials graded?
Volume of neurotransmitter present
What is an excitatory post-synaptic potential?
Due to influx of Na+ and Ca2+ ions
Depolarises the cell (makes it less negative)
What is an inhibitory post-synaptic potential?
Due to influx of negative ions (Cl-)
Hyperpolarises the cell (more negative)
What determines whether an action potential fires or not?
Overall contribution of excitatory post-synaptic potentials and inhibitory post-synaptic potentials
What is temporal summation?
When ≥2 post-synaptic potentials coincide
This has a much greater effect than 1 post-synaptic potential
This applies for both inhibitory and excitatory
What is spatial summation?
Thousands of inputs received by a neuron (excitatory/ inhibitory)
Gives rise to ‘spatial summation’
Determines whether an action potential fires or not
Why are some neurotransmitter receptors located presynaptically?
Activation decreases further release of neurotransmitter
Called autoreceptors
Self-regulate via negative feedback
What is the most common type of autoreceptor?
Metabotropic
e.g. 5-HT or dopamine
What is an autoreceptor?
Activation decreases further release of neurotransmitter
Located presynaptically
Self-regulate via negative feedback
What are some examples of neurotransmitter receptors?
(1) Glutamate + GABA receptors
(2) a1 + a2 adrenergic receptors (noradrenaline)
(3) 5-HT receptors
(4) D1 + D2 receptors (dopamine)
(5) H1 (histamine)
(6) M1 (acetylcholine)
Using glutamate as an example, state the stages of action potential propagation.
(1) Resting neuron membrane potential at -70mV
(2) Glutamate released from presynapse
(3) Activates AMPA/kainate receptors, influx of Na+ leading to depolarisation
(4) Cell depolarises (NMDARs slower and voltage-dependent)
(5) Resulting depolarisation called an excitatory postsynaptic potential (EPSP)
(6) Subsequent APs can occur before Vm returns to rest and summate
(7) If/when summated EPSPs reach the threshold for voltage-gated Na+ channel activation (~-55mV), allowing rapid entry Na+ and an action potential will fire, propagating the signal
(8) All or nothing mechanism of action (no partial action potentials)
Where are presynapses located?
Axon terminals
What are the types of postsynaptic cell receptor?
(1) Ionotropic – fast-acting channels/ pores
(2) Metabotropic – slower-acting via secondary messengers
What is glutamate?
(1) Most common excitatory neurotransmitter in the CNS (~50% of neurons)
(2) Acts on ionotropic + metabotropic receptors
What is GABA?
(1) y-amino-butyric acid
(2) Principal inhibitory neurotransmitter
(3) GABA(a) acts at ionotropic receptors
(4) GABA(b) acts at metabotropic receptors
How does an ionotropic receptor work?
(1) Ionotropic receptor activation opens channel to allow influx specific ions
(2) Glutamate receptors allow Ca2+ and Na+ ions, GABA(a) allow in Cl- ions
(3) Leads to depolarisation (e.g. glutamate) or hyperpolarisation (GABA)
How do metabotropic receptors work?
(1) Metabotropic neurotransmitter receptors are G-protein coupled (GPCRs)
(2) On binding ligand, get dissociation and activation of G-protein signalling
(3) Downstream effect depends on which G-protein type has been coupled
(4) Slower, receptor activates intracellular signals, may activate or close ion channels, may increase/decrease gene expression
What are some examples of small neurotransmitters?
(1) Amino acids (e.g. glutamate, GABA, glycine), typically fast-acting
(2) Monoamines (e.g. dopamine, noradrenaline, serotonin), diffuse effects, neurons of brainstem
(3) Soluble gases (Nitric oxide)
(4) Acetylcholine
What are some examples of large neurotransmitters?
Neuropeptides (e.g. endorphins, substance P, neuropeptide Y)
What are the types of glutamate receptors?
(1) Ionotropic: AMPAR (fast activation), NMDAR (slower, voltage-dependent block at resting), Kainate R
(2) Metabotropic: mGluR1-8 (Class I: mGluR1 & 5, Gq; Class II: mGluR2&3, Gi/G0; Class III mGluR4-8, Gi/G0)
