Structure of Neurons Flashcards
What are the different regions of neurons?
Dendrites, soma (cell body), axon hillock and initial segment, axon, synapse
What is the function of dendrites?
Receive inputs from other neurons and convey graded electrical signals passively to the soma
What is the function of the soma?
Integrates electrical signals that are incoming via passive conduction to the axon hillock
What are some features of the soma?
Synthetic and metabolic centre
Contains nucleus, ribosomes, mitochondria and ER
What is the purpose of the axon hillock and initial segment?
Site of initiation of the all or nothing AP
What is the function of the axon?
Conducts output signals as APs to presynaptic terminal
Mediates transport of materials between soma and presynaptic terminal (anterograde direction) and vice versa
What is the function of the synapse?
Point of chemical communication between neurons or to other cells
What are the different classes of neurons?
Unipolar = one neurite, found in PNS Pseuodunipolar = one neurite that splits Bipolar = two neurites Multipolar = three or more neurites
What are the different functional regions of neurons?
Input region = electrical signals enter
Integrative region = all signals are assimilated
Conductile region = signal conducted away from soma
Output region = signal leaves neuron
Do all neurons have all of the functional units?
Yes, all four regions are present irrespective of function
When is an all or nothing AP generated?
Once threshold is reached
What is the overshoot period during AP generation?
Very brief period when polarity is reversed to inside positive
What do APs allow electrical signals to do?
Allows electrical signals to be conducted over large distances without degrading
What is the difference between passive signals and APs?
Passive signals diminish as they spread but APs have constant amplitude
What is the impact caused by the nerve cell membrane being leaky?
Passive signals don’t spread far due to current loss across the membrane accompanied by a reduced change in potential
What does the distance across which current spreads depend on?
Membrane resistance and axial resistance of axoplasm
What is passive conduction a factor in?
Propagation of the AP
What effect does increasing the length constant have on the local current spread?
It increases the local current spread = this in turn increases AP conduction velocity
How can you improve the spread of passive conduction?
Decrease axial resistance by increasing axon diameter
Increase membrane resistance by adding insulating material
How does insulation impact conduction?
Conduction in myelinated axons is much faster than in unmyelinated axons of the same diameter
What is salatory conduction?
AP jumps from one node of Ranvier to the next = occurs in myelinated axons
What are the steps in synaptic transmission?
Uptake of precursor Synthesis and storage of precursor Depolarisation by AP and Ca2+ influx Ca2+ induced release of transmitter Receptor activation Enzyme mediated inactivation or reuptake of transmitter
What separates pre and post synaptic membranes?
A narrow synaptic cleft
What does the synaptic cleft contain?
Matrix of fibrous extracellular protein that holds the membranes together
