Chapter 4 Flashcards
What is a promotor?
A region of DNA that initiates a transcription of a particular gene.
What do promotors indicate?
They indicate what kind of cells should read the gene and when
When are promotors located?
Just before the gene
How many genes does the human genome contain for the voltage gated potassium channel?
40 distinct genes
When did distinct genes for the voltage gated potassiums channel appear? Before what?
They first appeared over a billion years ago. Before the evolution of multicellular organisms
When was the last time the gene variants have changed for the voltage gated potassium channels? Since the evolution of what?
Hundreds of millions of years. Since the evolution of the nervous system in bilateral creatures
Is there a perfect voltage gated potassium channel? If not, how many are there?
No, there’s 40
How do cells make their voltage gated potassium channels?
They can choose to express one or any combination of them to optimize cell function
What are the supporting cells of the nervous system?
- Neuroglia/Glial cells
- Astrocyte
- Microglia
- Oligodendrocytes
What do Neuroglia/glial cells do?
They help traffic nutrients and maintain molecular (ionic) stability. They support many functions of the nervous system
Where are glia found?
They are found all around neurons , and even encapsulate some parts of them.
By how much do glia cells outnumber neurons in the brain?
Somewhere between 2:1 and 5:1
What is an astrocyte?
It is a glial cell that provides physical support and cleans up debris in the brain through phagocytosis
What do astrocytes do?
They control the chemical composition of the surrounding environment and help nourish neurons
What are microglia?
The smallest of glial cells.
What do microglia do?
They provide and immune system for the brain and protect the brain from invading microorganisms
What does an oligodendrocyte do?
Produce myelin sheath, which encapsulates axons
Is sheath continuous?
No, it is a series of segments.
What is the exposed axon called?
The node of ranvier
What do oligodendrocytes form during the development of the CNS?
They form processes shaped something like canoe paddles
How do the paddle shaped processes form myelin?
It wraps itself many times around the segment of an axon and while doing so, produces layers of myelin that make up part of the axon’s myelin sheath
What do excess ions do?
They hug the membrane
Where do myelinated axons come into contact with extracellular fluid?
The node of ranvier: because the axon is naked
Are there many ion channels in myelinated areas? If there is, what happens?
There are almost no ion channels. The ones that are there have no consequences because there is no extracellular fluid outside the membrane
What is saltatory conduction?
The conduction of action potentials by myelinated axons
What do action potentials do in regards to the node of ranvier? What happens to the strength of the signal?
They jump from one node of ranvier to the next? The strength of the signal is regenerated with additional voltage gated Na+ channels
What is a synapse?
A junction between the axon terminal of the sending neuron and the cell membrane of the receiving neuron
How is the communication across the synapse acheived? What’s this molecule called?
By the release of a molecule from an axon terminal.
The molecule is called a neurotransmitter.
What kind of effects can a neurotransmitter have?
Simple excitatory or inhibitory effect or a complex modulatory effect on the receiving neuron.
What are synaptic vesicles?
They contain molecule of neurotransmitter. They attach to the presynaptic membrane and release neurotransmitter into the synaptic cleft.
What is the synaptic cleft?
The space between the pre and post synaptic membranes.
What is the synaptic cleft filled with?
Extracellular fluid
What is the presynaptic membrane?
The membrane of the terminal bouton (the sending cell). This is where the neurotransmitter is released from.
What is the postsynaptic membrane?
The membrane of the receiving cell that is opposite the axon terminal
What does electron Microscopy allow us to do?
It allows us to see small anatomical structures using a special electron microscope.
What is the size of a mitochondria?
1 um
What is the size of a typical protein?
3 nm
What are ligands?
Signaling molecules that bind to protein receptors
What does most cell signaling and cell communication occur through?
Through ligand receptor interactions
What are the two categories of neurotransmitter receptors?
Ionotropic and metabotropic
What are ionotropic receptors?
Ion channels
What are metabotropic receptors?
They are g protein coupled receptors that can open ion channels through an intracellular signaling cascade.
Where can receptors be located?
surface receptors:
intracellular pool of receptors
Surface receptors: on the cell membrane
Intracellular pool of receptors: Inside the cell
Are neurotransmitter receptors usually surface or intracellular pool of receptors?
Generally surface receptors
Where are post and presynaptic receptors located?
Presynaptic: presynaptic membrane
Postsynaptic: postsynaptic membrane
Where are extra synaptic receptors located?
Somewhere near but outside the synapse
What is a ligand? Give an example of a ligand?
A signaling molecule that binds to the binding site of a receptor. Neurotransmitters.
What is a binding site?
Location on a receptor protein to which a ligand binds
What is a postsynaptic receptor?
A receptor protein in postsynaptic membrane of a synapse that contains a binding site for a neurotransmitter
What is a ligand gated ion channel?
A receptor that is an ion channel. Aka ionotropic receptor. The ion channel opens when the ligand binds to it.
How is neurotransmitter signaling in the synapse kept brief?
The two mechanisms:
enzymatic deactivation
reuptake
What’s enzymatic deactivation?
Destruction of a neurotransmitter by enzyme after its release
What’s reuptake?
Re entry of a neurotransmitter just liberated by a terminal button back through its membrane, thus terminating postsynaptic potential.
Whats postsynaptic potential? What produces it?
Alterations in the membrane potential of a post synaptic neuron, produced by neurotransmitter release into the synapse and receptor activation
What are the two different types of post synaptic potentials? How do they work?
excitatory: influx of positive sodium ion depolarize the cell
inhibitory: influx of negative chloride ion hyper polarize the cell
What’s depolarization?
When the membrane potential of a cell becomes less negative than it normally is at rest
What’s hyperpolarization?
When the membrane potential of a cell becomes more negative than it normally is at resr
What causes EPSP (excitatory post synaptic potential)?
It is caused by a neurotransmitter binding to a post synaptic receptor protein
What are EPSPs mediated by? Why?
Receptor proteins that open ion channels permeable to sodium.
Making the membrane more permeable to sodium will depolarize the cell
What happens if only a couple EPSP’s are occuring at one time? Why?
The influx of sodium ions will not likely cause an action potential.
The depolarizing effect of the incoming sodium will be counteracted by an increase in the outflow of potassium ions through the leak channels
What has to happen to trigger an action potential?
Many EPSPs have to occur at nearly the same times.
Sodium ions have to come in at a faster rate than potassium ions can leave in order to depolarize he membrane to the threshold of activation.
The depolarization has to reach the beginning of the axon, where voltage gated sodium channels are congregated and can trigger an action potential.
What causes IPSP? (inhibitory post synaptic potential)
It is caused by the neurotransmitter binding to a postsynaptic receptor protein
What are IPSPs mediated by? Why?
Receptor proteins that open ion channels permeable to chloride. Making the membrane more permeable to chloride will hyper polarize the cell.
What is neural integration called?
The interaction of excitatory and inhibitory synapses on a particular neuron
What happens when EPSPs and IPSPs occur at the same time?
The influx of negatively charged chloride ions diminish the impact of the positively charged sodium ions. IPSPs decrease the likelihood that the cell will fire, EPSP increases the likelihood that the cell will fire
What can postsynaptic potentials be?
Depolarizing (excitatory) or hyper-polarizing (inhibitory)
What determines the direction of the postsynaptic potential (EPSP vs IPSP)?
The receptor
Some serontonin receptors cause EPSPs and some cause IPSPs, what is up to determine how it wants to respond to the signaling molecule?
It is up to the Postsynaptic cell
Whats an ionotropic receptor?
A neurotransmitter receptor that is an ion channel.
What determines whether an ion channel will cause EPSPs or IPSPs?
The properties of the pore of the ion channel
What causes an EPSP?
The neurotransmitter activation of ionotropic receptors that let in positively charged sodium ions
What causes an IPSP?
The neurotransmitter activation of ionotropic receptors that let in negatively charged chloride ions
What happens when the dendrites of a sensory neuron are stimulated by a noxious stimulus (like a hot object)?
It sends messages down the axon to terminal buttons located in spinal cord.
The sensory neuron will activate an interneuron, which in turn will activate a motor neuron and cause a withdrawl reflex
What happens when a neuron deep in the brain is activated? For example : a cortical neuron?
cortical neuron - action potential (in spinal cord)- excite inhibitory interneuron - induce IPSCs (in motor neuron and block the withdrawl reflex)
