Neurons & Neurotransmission Flashcards
Name the five key parts of the neuron
- dendrite
- cell body/soma
- axon hillock
- axon
- synapse
What is the function of a dendrite?
Receives inputs from other neurons and convey graded electrical signals passively to the soma
Describe the contents of the soma
Synthetic and metabolic centre it contains nucleus, ribosomes, mitochondria and ER
What is the function of the axon of hillock?
site of initiation of all or none action potentials
What is the function of the axon?
Conducts output signals as action potentials to the presynaptic terminal
In what direction do chemicals move in an axon?
Retrograde and anterograde
What happens at the synapse?
Point of chemical communication between neurons/other cells
How are neurons classified?
According to shape - number and conformation of processes (neurites)
State four types of neuron
- unipolar (one neurite)
- pseudounipolar (bifurcation of axon gives rise to two terminals)
- bipolar (two neurites)
- multipolar (three or more neurites, cell body gives rise to multiple dendrites)
Where are each type of neuron found?
Unipolar - peripheral autonomic neuron
Pseudounipolar - dorsal root ganglion
Bipolar - retinal ganglion
Multipolar - lower motor neuron
State four functional regions of a neuron
- input
- integrative (soma/axon of hillock)
- conductile
- output (release of neurotransmitter)
What leads to the shape of the action potential?
Upstroke - sodium influx
Down stroke - potassium efflux
What two factors affect how far an action potential will travel?
Membrane resistance (leakiness) Axial resistance (impedance)
What happens to the amplitude of the action potential as it moves along the axon?
Remains constant
Why do passive signals not travel far?
Membrane is leaky due to reduced change in potential
How do you increase the spread of an action potential?
Decrease axial resistance (axon diameter)
Increase membrane resistance (insulator)
Name two types of insulator cell
Schwann cell (PNS) Oligodendrocyte (CNS)
Describe the node of ranvier
Concentration of ion channels due to a gap in myelin sheath leads to saltatory conduction which action potentials jump between nodes
What is the general process of neurotransmission?
- Uptake of precursor
- Synthesis of transmitter
- Storage of transmitter
- Depolarisation by AP
- Ca2+ influx by voltage activated channels
- Ca2+ induced release of transmitter
- Receptor activation
- Enzyme mediated inactivation of transmitter or re-uptake of transmitter
Name the two membrane involved in a chemical synapse
pre synaptic and post synaptic
What holds the two synaptic membranes together?
Matrix of extracellular protein in the cleft
How can you distinguish between pre and post synaptic membranes?
Pre - vesicles that store neurotransmitter in active zones
Post - density containing lots of receptors
Name three types of synapse based on the location of the synapse
- axodendritic (very common)
- axosomatic (common)
- axoaxonic (rare)
Name two types of synapse based on function
Excitatory
Inhibitory
Describe and give an example of an excitatory synapse
CNS most frequently glutamate activates post synaptic cation selective ionotropic receptors and leads to local graded depolarisation
What causes an e.p.s.p?
Sodium influx
Describe and give an example of an inhibitory synapse
CNS most frequently GABA/glycine activates post synaptic anion ionotropic receptors to generate a local graded hyperpolarisation
What causes an i.p.s.p?
Chloride influx
State the two types of integration
Spatial
Temporal
Describe spatial integration
Many inputs converge upon a neuron to determine its output
Describe temporal integration
Single input may modulate output by variation in AP frequency of that input
Where are peptides released from?
Secretory vesicles
Where are amino acids/amines released from?
Synaptic vesicles
What type of channels mediate fast neurotransmission?
Ionotropic ligand gate ion channels
What type of receptor mediate slow neurotransmission?
G protein coupled receptors
Name the one neurotransmitter that does not activate G protein coupled receptors
Glycine
State the two key types of receptor
Ionotropic receptor
Metabotropic receptor
Describe the metabotropic receptor
Receptor and channel are distinct, slow and indirect
Name three artificial glutamate receptors
- AMPA
- Kainic Acid
- NMDA
Describe non-NMDA receptors
Sodium and potassium permeable channel that is fast and excitatory
Describe NMDA receptors
Sodium, potassium and calcium permeable, slow and excitatory
How do glutamate metabotropic receptors work?
By secondary messenger cascade, no specific ion channel but can be inhibitory
What are the two key types of supporting cell in the nervous system?
Ependymal
Glia
Describe ependymal cells
Ciliated cells that line the ventricles of the brain and central canal of the spinal cord.
What is the function of ependymal cells?
Contribute to formation and circulation of CSF and have a role in early development
Name two types of glial cells
Microglia
Macroglia
Describe microglia
Phagocytes that engulf debris and involved in the relationship between CNS and immune system
Name the four types of macroglia
- astrocytes
- oligodendrocytes
- schwann
- capsular
What do the astrocyte processes do?
- subpial end feet on the surface of the brain and spinal cord
- perivascular end feet at the capillaries of blood brain barrier
- contacts with neurons
State five functions of the astrocytes
- control electrolyte balance
- produce neurotrophins
- uptake neurotransmitters
- supply glutamine for synthesis of glutamate
- regulate tightness of BBB
Describe oligodendrocytes
Small cells with few processes - processes form myelin sheath around multiple CNS axons and produce neurotrophic factors that are important in repair of damaged axons in CNS
Describe Schwann cells
Each cell is only a short segment of one axon and cells spiral around the axon to form the lamella
What is the purpose of schwann cells?
Vital in regeneration of transected axons - they proliferate to form a tube which growth sprouts from the proximal end to re-innervate the de-innervated target
Where are capsular cells found?
Surround neuronal cell bodies in sensory and autonomic ganglion
Describe the structure of capsular cells
Flattened cells form an almost complete layer that separates ganglion cell bodies in the DRG and cranial nerves from the surrounding tissue and vasculature
Where are capsular cells found?
Autonomic ganglion particularly the sympathetic division
