Neuroscience II Flashcards
What are Neurons?
Basic functional units of the NS
What is the function of the Neuron?
Processes and trasmits info (electrical and chemical)
How is the Structure of a Neuron?
- Cell Body: contains organelles essential for survival
- Short, highly branched dendrites: receive info from other neurons
- Long, single axon: carries electric signal to target
What is a Bipolar Neuron?
Has 2 processes separated by a cell body in the middle
What is Unipolar Neuron?
Has 1 single elongated process with the cell body to the side
What is a Multipolar Neuron?
Has more than 2 processes; a single axon and multiple dendrites
What are Neuroglia?
Supporting neuronal function
How many % of the total cell population in the NS are Neuroglia?
~50%
What are the types of Neuroglia and their functions?
- Astrocytes: regulate chemical content of the ESF
- Myelinating Glia (Oligodendrocytes, Schwann Cells): Myelination of Neurons
- Microglia: phagocytic role
- Ependymal Cells: production of CSF
What type of tissues are Nerves and Muscle Cells?
Excitable tissue (Produce electric signals when excited)
Why are Electric Signals important for NS and MSK?
(NS) Receive, process, initiate and trasmit messages
(MSK) Initiate contraction
What happens to the membrane potential during depolarisation and hyperpolarisation?
(Depolarisation) Less -ve
(Hyperpolarisation) More -ve
What are the terms of Polarisation?
Polarisation: MP ≠ 0mV
Depolarisation: MP becomes less polarised than Resting Potential
Repolarisation: MP returns to RP
Hyperpolarisation: MP becomes more polarised than RP
How are Electric Signals produced?
By changes in ion movement
What is a triggering event?
An event that triggers a change in membrane potential, altering membrane permeability and thus, ion flow across membrane
What types of Membrane Channels are there?
- Leaky Channels
2. Gated Channels
What are the types of Gated Channels?
- Voltage gated
- Chemically gated
- Mechanically gated
- Thermally gated
What are Graded Potentials (GP)?
Local changes in MP occurring in varying grades
How are GPs spread?
By passive current flow BUT they die out over short distances
What is an Action Potential (AP)?
Brief, rapid, large changes in MP (100mV) when the inside of an excitable cell transiently becomes more than the outside
What leads to an AP?
Marked changes in membrane permeability and ion movement
What are the channels involved in AP?
Voltage-gated Na+ and K+ channels
Which channel has an inactivation gate?
Na+ channel
Describe how an AP is generated.
- RP (-70mV): all channels closed
- Threshold: Na+ channel OPEN
- Excessive Depolarisation (+30mV): Na+ enters ICF (Rising phase of AP)
- Peak of AP: Na+ channel INACTIVATED, K+ channel OPEN
- Repolarisation (-70mV): K+ leaves ICF (Falling phase of AP)
- Na+ channel resets to ‘closed but capable of opening’ state, ready to respond to triggering event
- Hyperpolarisation (-90mV): Further outward movement of K+ out of ICF
- K+ channel closes and MP = 70mV
What does the Na+-K+ pump do?
Gradually restore [ ] gradients disrupted by AP
From where to where are APs propagated?
From axon hillock to axon terminals
What are the different zones in the Neuron?
- Input zone
- Trigger zone
- Conducting zone
- Output zone
Where is and what is the function of the Input zone?
Dendrites; Receive incoming signals from other neurons
Where is and what is the function of the Trigger zone?
Axon hillock; Initiates AP
Where is and what is the function of the Conducting zone?
Axon; Conducts AP in undiminishing fashion, often over long distances
Where is and what is the function of the Output zone?
Axon terminals; Releases neurotransmitter that influences other cells
How long is a typical Axon?
1mm to more than 1m long
What is a Refractory Period?
AP cannot be initiated in a region that has just undergone an AP due to inactivation of Na+ channels
What is the purpose of a Refractory Period?
Ensures one-way propagation of AP and limits frequency
In what fashion does AP occur?
“All-or-none” fashion due to discrimination of stimuli
How is the strength of a stimulus coded?
By the frequency of AP (magnitude of each AP same)
How does Myelination influence the AP?
Increases the speed of conduction of AP
What does the fiber diameter influence?
Velocity of AP propagation
What is Myelin?
Thick layer of lipids
What is the function of Myelin?
Acts as an insulation to “electrical transmission” along the axon
What is Contiguous conduction?
Local current flow that depolarises adjacent inactive area from RP to Threshold Potential (TP)
What is Saltatory conduction?
Local current flow that depolarises adjacent inactive node from RP to TP
What is a Synapse?
Junction between Neurons
What are the types of Synapses?
- Electrical synapses: neurons connected directly by gap junctions
- Chemical synapses: chemical messenger transmits info one way across a space separating the 2 neurons
How is the Anatomy of a Chemical Synapse?
- Presynaptic Terminal
- Synaptic Cleft
- Postsynaptic Terminal
How does Synaptic Transmission?
- Depolarisation due to incoming AP from axon
- Influx of Ca2+ due to opening of voltage-gated Ca2+ channels
- Docking: Vesicles with neurotransmitter dock at protein
- Release of neurotransmitter
- Binding of neurotransmitter to receptor
What does the neurotransmitter do?
Carries the signal across a synapse
What are the different types of synapses based on its effects?
- Excitatory: Generation of EPSP
2. Inhibitory: Generation of IPSP
What can modify synaptic transmission?
Drugs and diseases
What are the types of pathways are neurons linked by?
- Convergence: Given neuron has many other neurons synapsing on it
- Divergence: Branching axon terminals so a single cell synapses and influences other cells
What are some examples of neurotransmitters?
- Acetylcholine
- Dopamine
- Glutamate
- Gamma-aminobutaryic acid (GABA)
What is the effect of Acetylcholine?
(PNS) Neuromuscular junctions, parasympathetic nerves
(CNS) Muscarinic and Ionotropic
What is the effect of Dopamine?
Many pathways in CNS
What is the effect of Glutamate?
EPSP in CNS
What is the effect of GABA?
IPSP in CNS
