Chapter 13: The CNS Flashcards
What are the 4 characteristic parts of a neuron?
- Dendrites
- Soma
- Axon
- Presynaptic Terminals
What are some different types of neurons and where are they found?
Multipolar found in the CNS
What are the major neuronal cell types of the adult cerebral cortex?
What type of structure do astrocytes form in the brain?
Form a mesh sponge like matrix in which other cell types are embedded in.
What are the key features/functions of astrocytes?
- Astocytic processes do not overlap.
- A single astrocyte can ensheath >100, 000 synapses.
- Can modulate a significant area of brain almost instantaneously.
- Astrocytes can stimulate adjacent astrocytes leading to propagation of signals great distances to affect whole brain regions.
Function: Used to modulate many synapses by modulating 1 astrocyte.
What are the synapses called with astrocyte involvement?
Tripartite Synapses
Engulf whole synapse preventing the leaking out of Neurotransmitter.
All synapses in the CNS are Tripartite.
What are Microglia and what is their function?
- Constantly survey and respond to perturbation in their environment.
- They are the Immune Cells of the CNS.
What are Oligodendrocytes and what is their function?
Form Myelin in the CNS
1 Oligodendrocyte can Myelinate - 50 Axon Segments
1 Cell Myelinates Multiple Axons
Given that axons can terminate on different parts of the neuron,
What are the 5 different axon termination sites and what are they called?
- Axoaxonic
-
Axodentritic - Classic
* Axosomatic - Will have greatest effect on if AP will fire at hillock. - Dendrodentric
- Dendrosomatic
What are the steps in neurotransmission?
- DNA/RNA Synthesis
- Axo-Plasmic Transport
- Neurotransmitter Synthesis and Storage
- Action Potential (Tetrodotoxin)
- Membrane Depol Opens Ca Channels
- Neurotransmitter Release
- Neurotransmitter receptor coupling
- Neurotransmitter Removal - Reuptake and Metabolism.
What causes Up-Regulation (Sensitization)?
Sustained reduction in NT release of long-term use of antagonist.
What causes down regulation (Desensitization)?
Sustained bockade of NT reuptake or long-term use of agonist
How many principle NT does the CNS use?
2
Ach and NE
What are the principle NT of the CNS?
> 12
ACh, NE, 5-HT, DA, Glu, GABA
What is the definition of Neurotransmitter?
A substance released from the axon terminal of a presynaptic neuron on excitation which diffuses across the synaptic cleft to either excite or inhibit the target cell.
How long does NT Action last for?
Few Milliseconds
What is the definition of a Neuromodulator?
A substance that alters nerve impulse transmission.
- Alters by acting on receptors distance from the release site.
- A slow signal modulates other gast neurotransmitter signals on the same neuron.
- Affects astrocytes, pre and post synaptic neurons.
What parts does the brainstem consist of and what is its function?
Pons/Medulla/Midbrain
Functions
- Baroreceptor Reflex Maintains blood pressure and heart rate.
- Carbon Dioxide Sensors Maintain breathing.
- Chemoreceptive trigger zone reduces absorbtions of toxic compunds from the GI.
- Consciousness and sleep.
Physiological Survival Reflexes
What does the Diencephalon consist of and what is its function?
Thalamus/Hypothalamus
Functions
- The Thalamus has sensory and motor functions.
- Hypothalamus controls behaviors crucial for survival. (Agressive, defensive, consumatory, reproductive)
- Controls pituitary hormonal regulation of the body.
- Involved in thermoregulation and control of ANS.
Where is the cerebellum and what is its function?
Functions
- Receives input from multiple sources and outputs primarily to cerebral cortex via the thalamus.
- Coordinates voluntary movement in space and time.
- Maintains balance
- Controls Eye Movement
- Motor Learning
- Alcohol is toxic to the cerebellum affecting balance.
What is the function of the Cerebral Cortex?
- Controls sensory and motor activity.
- Responsible for language and concept manipulation.
- Generates thoughts, ideas, and consiousness.
- Stores Long Term Memories.
What does the Limbic system (emotional brain) consist of and what are its functions?
Amygdala, Hippocampus, Habenula and Septal Area
Functions
- Interprets and filters information relayed betwene the hypothalamus and the cortex.
- Responsible for judgement, evaluation and the inhibition of the output of inappropriate thoughts, ideas, behaviours.
- Helps to focus attention by inhibiting irrelevant sensory input and cognitive activity.
- Important in memory formation and emotions.
Hippocampus - Learning and Memory
Amygdala - Emotion, Fear, Memory
What is the Basal Ganglia; what does it consist of; what is its function?
A group of nuclei forming a functional unit.
Consists of the striatum, the globus pallidus, the substania nigra and subthalamic nucleus.
Functions
- Regulates voluntary motor control.
- Regulates the contraction of opposing muscle bundles allowing for smooth movements.
What is NE transmission and modulation involved in?
- The reticular activating system: Basic Arousal, alertness, wakefulness. insomnia.
- The limbic system: anxiety, depression, appropiateness.
- Central responses to stress.
- The hypothalamus: Feeding, Thermoregulation.
- Modulatory role: Focus, attention and performance.
What is shown to be activated when the NE system is stimulated.
Astrocytes
What is Dopamine Neurotransmission involved in?
- The extrapyramidal motor system: Parkinson’s Disease.
- The limbic system: Psychosis, anxiety, depression.
- The hypothalamus: Reward/Pleasure, Pituitary Secretion, Thermoregulation.
- The Chemoreceptive trigger zone: Emesis
What is serotonin neurotransmission involved in?
- The Limbic System: Psychosis, Anxietym Depression
- The hypothalamus: thermoregulation, pituitary secretion.
- Helps shape cortical circuits.
What is acetylcholine neurotransmission invovled in?
- The limbic system: Emotions, memory
- The extrapyramidal motor system: Parkinson’s Disease
- Helps shape neural Circuits.
What is Histamine neurotranmissioni involved in?
Reticular Activating system: Arousal
What is Glutamate neurotranmission involved in?
- The limbic System: Learning and Memory
- Everywhere - Main excitatory neurotransmitter.
- Neurodegeneration if excessive (Excitotoxicity)
What is GABA neurotransmission involved in?
The extrapyramidal motor system: Parkinsons and Huntingsons Disease
The limbic system: Psychosis, anxiety, depression.
Everywhere: The main inhibitory neurotransmitter, epilepsy.
What are the physical ways contributing to the BBB?
- Brain endothelial cells have tight intercellular junctions (No fenestra)
- Have layers of lipid rich membrans (endothelium, atrocytes, pericytes.
What are the chemical means contributing to the BBB?
Brain Endothelial cells have 5 times more mitochondia the Peripheral
Mitochondria have MAO enzymes - Prevent entry into the brain of neuroactive monamines in the the blood such as noradrenaline, adrenaline, serotonin, tyrmaine.
What determines passage through the BBB?
Lipophilicity
If not lipophilic - Can be actively carried across if brain needs them.
What type of drugs are transported into the brain?
Lipophilic/ Fat Soluble Drugs - Can cross BBB
Levo Dopa - Chemical precursor of dopamine, noradrenaline, and adrenaline. - Actively Transported
Levo Dopa only known compound to be actively transported into brain
What does the BBB consist of?
- Endothelial cells with tight junctions
- Pericytes and Astrocyte end Feet.
- Plasma protein Binding.
