Week 2 - finished Flashcards
How many neurons are there in the CNS?
Approx 100billion
Glial cells outnumber neurons in the CNS by how many to 1?
10
What is the function of glial cells?
Form the structural support for the neuronal network and make a massive contribution to the regulation of neuronal function.
What are the important parts/sections of the neuron? Describe briefly what each of these do.
Dendrites - receive stimuli through activation of chemically or mechanically gated ion channels. Sensory neurons produce generator or receptor potentials. Motor neurons produce excitatory (EPSP) or inhibitory (IPSP) postsynaptic potentials.
Cell body - receives stimuli and produces
Junction of axon hillock - trigger zone: integrates EPSP and IPSP and if the sum is a depolarisation threshold, it initiates an action potential.
Axon - propagates nerve impulse from initial segment (or from the dendrites in a sensory neuron) to the axon terminals in a self reinforcing manner (impulse amplitude doesn’t change as it propagates along the axon)
Axons, terminals and synaptic end bulbs - inflow of Ca++ caused by depolarisation phase of nerve impulse triggers neurotransmitter release via exocytosis of synaptic vesicles
What are the 2 fundamental types of cells that contribute to the central nervous system?
Glial cells
Neutrons
Are dendrites myelinated?
No
Where do dendrites typically extend from?
The apex of the cell body
What is the soma? What does it contain? It produces proteins that do what?
The central component of a neuron and contains the nucleus.
It produces proteins for:
Electrochemical transmission
Structural maintenance of the neuron itself
Neuroimmune regulation
Where does the axon extend between?
The axon hillock and the area of the soma
What cells form myelin in the PNS?
Schwann cells
What cells form myelin in the CNS?
Oligodendrocytes
What are the breaks in the neuron sheath called?
Nodes of ranvier
What are the functional classifications of neurons?
Afferent: sensory Efferent: motor Interneurons: - Neither motor nor sensory - Can be subdivided into: Golgi type 1: long/relay (corpus callousness) Golgi type 2: short, spinal (reflex)
What are the structural classifications of neurons?
Unipolar: autonomic ganglia
Bipolar: retina and most DRG
Multipolar: LMNs and cerebellum
What are some of the main functions of glial cells?
Ion buffering by uptake (vasomotor control, neuronal metabolic support)
Blood brain barrier
Glympatic system
Scavenger function (after cell damage)
Myelin sheathing
What are the types of glial cells? Briefly describe each of their functions.
Microglia: scavenger, clears debris. (Like a type of T cell)
Macroglia:
- Oligodendrocytes (myelin in CNS)
- Schwann cells (myelin in PNS)
- Astrocytes (blood brain barrier)
Is there regeneration potential in the CNS?
Little to none
How does glial scarring impact CNS regeneration?
Glial cells and neural tissue have little regeneration potential. Even when this tissue does regenerate the glial cell function is impaired and organisation within that area of the CNS is impacted.
Is regeneration possible in the PNS?
Yes but it is dependant on the distance from the lesion to the soma.
Glial cells clear debris but if the myelin sheath is in tact they glial cells can secrete proteins to promote and guide axons, extension and regeneration
What are the characteristics of action all potential transmission? What are they determined by?
Electrical or chemical (NMJ or chemical)
Excitatory or inhibitory
Determined by: Neurotransmitter Type of synapse Type of receptors Ions involved
What are the elements of a synapse?
Pre synaptic neuron
Synaptic cleft
Post synaptic neuron
What is the release of neurotransmitters reliant on?
The arrival of the action potential at the terminal button of the pre synaptic neuron
Describe the process of neurotransmitter release after an action potential reaches the pre synaptic neuron
Action potential reaches terminal button
Vesicles fuse to presynaptic membrane
Neurotransmitter is released into synaptic cleft
Neurotransmitter instigates a change in the neurotransmitter receptors of the post synaptic membrane
Post synaptic neuron either depolarises or hyperpolarises
What are the 2 types of post synaptic membrane receptors?
Those that form a channel through the membrane
Those that don’t (eg. G- protein coupled receptor)
Describe the steps the an action potential
Influx of ions through a channel
Changes the neurons membrane potential
Na+ gives hyperpolarisatioon, neuron fires (EPSP)
Cl- gives hyper polarisation, neuron is taken further from firing (IPSP)
What will an influx of Na+ into a neuron do in terms of action potential?
It will depolarise the neuron
What will an influx of Cl- into a neuron do in terms of action potential?
It will hyperpolarise the neuron
When an EPSP is created, what does this mean?
The neuron has been sent an excitatory or depolarisation potential
What an IPSP is created, what does this mean?
The neuron has been sent an inhibitory or hyperpolarisation potential
What is a synapse?
The junction between the processes of 2 neurons by which those neurons can communicate via chemical or neurotransmitter means.
What is an axo-somatic synapse? Describe a little about them (e.g. are they inhibitory or excitatory?)
A synapse between the axon of one neuron and the body of another neuron.
Grays type 2
Often inhibitory
Very powerful
Typically uses GABA
What kind of synapses are axo-axonic and axo-dendritic
Type 1
What is a Grays type 1 synapse?
Typically excitatory synapse
Some axo-axonic can be inhibitory
Typically uses glutamine
What type of conduction do myelinated axons allow?
Saltatory. Slower. Domino effect.
What type of conduction do unmyelinated axons allow?
Continuous. Faster and jumps from node to node.
What do receptor agonists do? What are some examples of them?
They enhance or prolong neurotransmitter activity.
eg. SSRI’s
Endophins and enkephalins
Morphine
What do receptor antagonists do? What are some examples of them?
Block transmitter uptake and therefore hinder NT activity.
eg. Narcan use in opiod overdose
ACE inhibitors for hypertension and cardiac failure.
