Neurotransmission Flashcards
What do dendrites convey?
Graded electrical signals passively to the soma
What do dendrites receive inputs from?
Other neurones
What is the soma?
Synthetic and metabolic centre- containing nucleus, ribosomes, mitochondria, and ER.
What does the soma do?
Integrates incoming signals that are conducted passively to the axon hillock
What is the axon hillock and initial segment?
Site of initiation of the all or none ap
What does the axon do?
Conducts output signals as aps to other neurones (or cells).
Between what does the axon mediate transport of materials?
Soma and presynaptic terminal (anterograde direction) and vice versa (retrograde)
What is a synapse?
Point of chemical communication between neurones (or other cells)
What direction of transport do several virus’ exploit to infect neurones?
Retrograde
What are the 4 types of neurone?
Unipolar, pseudounipolar, bipolar, multipolar
Describe a unipolar neurone and give an example
One neurite. Peripheral autonomic neurone
Describe a bipolar neurone and give an example
Two neurites. Retinal bipolar neurone
Describe a pseudounipolar neurone and give an example
One neurite that bifurcates. Dorsal Root Ganglion (DRG) neurone
Describe a multipolar neurone and give an example
Three or more neurites. Lower motor neurone (LMN) (motoneurone)
What are the four functional regions of neurones?
Input, integrative, conductile, output
What are Golgi Type I and Type II axons?
Type I is long, type II is short
What is overshoot?
Brief period when polarity is reversed to inside postive
What occurs in the upstroke of the ap?
Opening of voltage activated Na+ channels and inward Na+ movement
What occurs in the downstroke of ap?
Opening of voltage activated K+ channels and outward movement of K+
Why do passive signals not spread far from their site of origin?
The nerve cell membrane is leaky (not a perfect insulator). This is due to current loss across the membrane
In the axon does the ap have a constant or variable amplitude?
Constant
What kind of process is the membrane potential change?
Passive neuronal process that decays exponentially with distance
What does the distance over which current spreads depend upon?
Membrane resistance (rm) and axial resistance of the axoplasm (ri)- increased rm/ri increased length constant
What does greater local current spread increase?
AP conduction velocity
What does the ap do to the charges on each side of the membrane?
Swaps them (-ve on outside, +ve on inside)
How would you decrease ri?
Increasing axonal diameter (not feasible though)
How would you increase rm?
Adding an insulating material - myelin- provided by Schwann cells in PNS and oligodendrocytes in CNS (both types of macroglia)
What is the length constant equation?
Lambda= (rm/ri)^0.5
What do many Schwann cells surround?
A single axon
What does one oligodendrocyte surround?
Many axons
What is saltatory conduction?
When an ap jumps from one node of Ranvier to the next
What is the definition of axodendritic?
Presynaptic cell synpases with the post synaptic cell on the back of its dendrite
What is the defintion of axosomatic?
Presynaptic axon synapses on the soma of the post synaptic cell
What is the defintion of axoaxonic?
Presynaptic terminal of one cell terminates upon one presynaptic terminal of another cell before that cell shows an axosomatic synapse upon a postsynapstic cell
What makes a synapse excitatory or inhibitory?
Transmitter used
What transmitter is used most in excitatory synpases in the CNS?
Glutamate
What does glutamate activate?
Postsynaptic, cation selective, ionotropic, glutaate receptors
What does glutamate generate?
Local graded excitatory (depolarising) response- the excitatory postsynaptic potential (epsp)
What transmitter is used most in inhibitory synpases in the CNS?
GABA, or glycine
What does GABA/glycine activate?
Postsynaptic, anion selective, ionotropic, GABAa or glycine receptors
What does GABA/Glycine generate?
Local graded, inhibitory (hyperpolarising) response- ipsp
What sequence is crucial to the computational capacity of the CNS?
Electrical-chemical-electrical
What is spatial summation?
Many inputs converge upon a neurone to determine its output
What is temporal summation?
A single input may modulate output by variation in ap frequency of that input
Where are amino acids and amines released from?
Synaptic vesicles
Where are peptides released from?
Secretory vesicles
What can glutamate, GABA, glycine, acetylcholine, and 5-HT activate?
Ionotropic ligand-gated ion channels (LGICs), and GPCR (excepet glycine)
What speed of neurotransmission do ionotropic ligand-gated ion channels (LGICs) mediate?
Fast
What speed of neurotransmission do metabotropic GPCRs mediate?
Slow
What are the stages of chemical neurotransmission?
- Uptake of precursor
- Synthesis of transmitter
- Storage of transmitter
- Depolarisation by ap
- Ca2+ influx
- Ca2+ induced release of transmitter (exocytosis)
- Receptor activation
- Enzyme mediated inactivation of transmitter
or - Reuptake of transmitter
What are secretory granules transported to the presynaptic terminal by?
Fast axoplasmic transport via microtubules
