Neurons and Synapses [W2] Flashcards
Location of Ogliodentrocytes
central nervous system (CNS)
location of Schwann Cells
peripheral nervous system (PNS)
Location of astrocytes
brain + spinal cord, CNS
location of microglia
brain + spinal cord, CNS
Function of ogliodentrocytes
Create myelin sheath for axons in the CNS (can do multiple instead of one just single axons like Schwann cells)
function of Schwann cells
Create myelin sheath for individual axons in the PNS; help with axon regrowth in PNS
Function of astrocytes
regulate blood brain barrier, provide structural support, maintain env’t around synapses; also, involved in uptake and release of transmitters, modulate synaptic transmission and help repair nervous system
function of microglia
brain’s immune cells, remove/repair damaged tissue, release anti-inflammatory agents
function of protein channels in cell membrane
regulate mvmt of substances in/out neuron
Function of axons
transmits signals across distances
function of synaptic terminals
neurotransmitter release
function of dendrites
receive inputs from other neurons
Explain Galvani (1791). Importance?
electricity made frog’s leg twitch. helped est. electrical properties of neurons
Explain Helmholtz (1850). Importance?
Measured speed of nerve impulse @ 90ft/sec. helped est. electrical properties of neurons
Explain Young (1936). Importance?
Recorded electrical impulses in the axon (1mm diameter) of a giant squid. Helped est. electrical properties of neurons
Explain Hodgkin & Huxley (1952). Importance?
negative resting potential in squid axon; found that applying electrical stimulus triggers an action potential–> trigger was voltage change from - to + (depolarization)
What 4 main ions contribute to resting potential?
Na+, Cl–, K+, negatively charged proteins
What are the steps/stages that occur in action potential?
Opens Na+ channels –> Na+ enters cell, changing membrane potential –> K+ channel opens, K+ exits cell –>Na+ channels close, K+ ions still exiting ==> Repolarisation –> K+ channel closes slowly==>hyperpolarisation from too much K+ outside cell –> all channels close, return to resting potential
What is the negative resting potential?
-70mV
all neurons have a _______resting potential
negative
Which part of a neuron receives input from other neurons?
dendrites receive information from other neurons via synapses
As an action potential passes along the axon, the interior of the axon is first depolarized by the entry of________ and then repolarized by the exit of ___________
sodium ions; potassium ions
The conduction of an action potential along an axon is mediated by __________
voltage-gated ion channels
What are the Nodes of Ranvier?
spaces along the axon where there is no myelin sheath
The process of neurotransmitter release is called ________
exocitosis
What is the most prevalent excitatory neurotransmitter in the nervous system?
glutamate
What is the most prevalent inhibitory neurotransmitter in the nervous system?
GABA
What is a direct agonist drug?
A drug that activates post-synaptic receptors
What is a direct antagonist drug?
A drug that blocks post-synaptic receptors
What is the endogenous neurotransmitter that acts at cannabinoid receptors in the brain?
anandamide
What is are vesicles?
spherical structures at the presynaptic terminal that contain neurotransmitters ready to send out
What causes the release of the neurotransmitter into the synapse?
Depolarisation from action potential opens calcium channels in the presynaptic membrane. Calcium then travels to presynaptic terminals where it interacts with the vesicle and triggers the vesicles to fuse with presynaptic membrane, releasing the neurotransmitters into the synapse.
What happens to excess neurotransmitters?
Either degraded by enzymes or removed via transporter proteins
what is the function of autoreceptors?
They feedback whether there is too much or too little of a neurotransmitter being produced/released
How are neurotransmitters made?
Synthesized in soma or presynaptic terminal; all required different “ingredients” based on which neurotransmitter is being synthesized
What are metabotropic receptors? Do they respond quickly or slowly to transmitters?
receptors that are opened through a sequence of chemical events; responds more slowly to transmitters because of intermediate step
Example of a ionotropic receptor
GABA receptor
what are ionotropic receptors? Do they respond quickly or slowly to transmitters?
receptor that is part of a ligand-gated ion channel, binding of neurotransmitter causes the channel to open so ions can flow through.
What is saltatory conduction? Why is it beneficial?
When action potential jumps from one Node of Ranvier to the next. Beneficial bc it speeds up impulse and requires less energy to restore resting potential
Explain the experiment by Otto Loewi (1921). What does this evidence?
simulated heart beat in heart in second chamber sharing same surrounding fluid but otherwise not touching. Is evidence that chemical exchange allows neurons to connect with each other.
What is the voltage change as action potential passes?
-70mV to +30mV
What is kiss and run fusion?
When transmitters are released through transient fusion with pore in cell membrane. Vesicle retains its shape, entire contents may not be released.
What is full fusion (vesicles)?
Vesicle and membrane merge and entire contents of vesicle spill into synaptic gap. Takes longer to regenerate a vesicle than reuse
Explain the ‘lifecycle’ of a neurotransmitter, from synthesis to release.
neurotransmitters are synthesised in the soma or the presynaptic terminal. They are packaged into vesicles and transported through microtubules to the presynaptic terminal, where they stay until they are released through fusion into the synaptic cleft.
what is the soma of a cell?
the cell body, contains nucleus and mitochondria
what are dendrites?
extensions from the cell that receive information from other cells
what are glia?
non-neuronal cells found in the CNS and PNS
What are the notable glia in the CNS?
astrocytes, microglia, oligodendrocytes, radial glial cells, and ependymal cells
what are microglia? Function?
small cells that act as the immune system for brain; repair and remove damaged tissue
What are astrocytes? Function?
star shaped cells that provide structural support in the CNS, and regulate the blood brain barrier
What are ogliodendrocytes? Function?
cells that provide myelin insulation for axons in the brain
What are Schwann cells? Function?
cells that provide myelin insulation for peripheral neurons
How does action potential move along axon?
Self-perpetuates
def: concentration gradient
unequal distribution of particles/ions between intra and extra cellular fluids
Explain the effects of voltage and concentration gradient on Cl- and Na+ re: cell membrane
Cl- channels allow Cl- to pass through the cell membrane, but it’s harder for Na+ to cross the membrane. Concentration gradient pulls Cl- ions through channels in cell membrane but voltage gradient draws them back until the ions are in balance
What ions are more concentrated outside the cell?
Na+ and Cl-
What ions are more concentrated inside the cell?
K+, but can move freely
Can proteins move freely through cell membrane? Why/Why not?
No; too large
Depolarisation allows ___ ions to flow through, ___________ polarisation.
Na+, enhances/increases
def: neutrons
neutral atoms; no pos or neg charge
def: electrons
negatively charged particles that orbit atoms
def; protons
positively charged atoms
def: ion
An atom that has either a positive or negative charge (not neutral)
def: phospholipids
two lipids (hydrophobic) and phosphorus heads (hydrophilic)
How do molecules pass through the cellular membrane?
protein channels in the phospholipid layer
Cl-
Chloride ion
Na+
Sodium ion
K+
Potassium ion
What are the three components of a neuron?
soma, axon, dendrites
What does ATP stand for?
Adenosine Triphosphate
What is ATP?
molecules that capture energy and transport it to where it is needed in the body
Function and location of ependymal cells
cells that make up the epithelial lining of cerebral ventricles; produce and secrete CSF; cilia help direct flow of CSF, which allows them to move nutrients and filter out potentially harmful substances as needed
Myelin sheath (what + function)
“insulation” for the axon; prevents loss of electric current to extracellular fluid
What does ‘white matter’ mean?
highly myelinated sections of the brain –> myelin is white
what is meant by ‘grey matter’?
cell bodies and dendrites in the brain, unmyelinated areas
function of Nodes of Ravier
ionic exchange happens at NoR; action potential is generated
Explain Multiple Sclerosis (MS)
autoimmune inflammatory disorder; attacks + degenerates the myelin on axons; demyelination causes neurological symptoms; demyelination affects how fast electrical impulses can travel
Cause(s) of MS
not fully known; suspected that it is part environmental and part genetic predisposition
Symptoms of MS
fatigue, blurred vision, tingling/numbness, muscle weakness/tightness, problems with mobility and balance, etc.; symptoms depend on what part of the brain is affected
types of neuronal structures
multipolar, bipolar and unipolar/monopolar
def: bipolar neuron
a single dendrite is connected to the cell body, then info travels down the axon to the presynaptic terminal
def: unipolar/monopolar neuron
dendrites are combined into an axon-like structure before connecting to the cell body; info is then send through an axon to a presynaptic terminal
def: multipolar neuron
many dendrites are connected to the cell body; they are then combined at the axon hillock, which connects to the axon. Info is then sent down axon to presynaptic terminal
def: efferent pathway
the pathway through which neural information travels to effect behaviour (efferent = exit, effector) away from CNS
def: afferent pathway
pathway though which sensory information travels toward CNS
how is information communicated within the neuron?
electrical signals
how is information communicated between neurons?
chemical or synaptic signals
Why do we use a squid axon to study electrical properties of neurons?
comparatively large compared to other axons, 1mm
What mediates the movement of ions in/out of the cell?
diffusion along concentration gradient; electrostatic pressure
def: cations
positively charged ions
def: anions
negatively charged ions
What are the two options for the electrical potential of an axon?
Resting potential, action potential
def: membrane potential
the difference between the charges of intra and extra cellular fluid
how do ions move through the cell membrane?
through ion channels; channels only let certain ions through
which gates are voltage sensitive?
outside gates for Na+ and K+
Which gates are not voltage sensitive ?
inside Na+ gate
What happens during depolarisation?
Opens voltage gated channels so Na+ flows into the neuron. This enhances depolarisation.
What happens re: depolarisation along the axon?
once triggered, it moves along the axon like a wave of depolarisation opening one channel and then the next and the next, like dominoes
What triggers action potential?
Excitatory neurotransmitters binding to the receptors of a neuron, this allows some Na+ into the cell, which helps it rise to it’s threshold. Once it reaches the threshold, action potential is triggered
When does action potential happen after depolarisation?
When the neuron reaches its threshold membrane potential, ~ -55mV
What is the rising phase of the action potential?
when the neuron reaches it’s threshold membrane potential, Na+ channels open and Na+ rushes in which causes significant depolarisation, bringing membrane potential past 0, to +30mV
What creates the electrical signal of the action potential?
influx of positive ions
What happens when Na+ reaches it’s peak (about +30mV)?
Na+ channels close and K+ channels open. K+ flows out of the neuron causing repolarisation
What is the falling phase of the action potential?
repolarisation, when K+ ions flow out of the cell
What is the relative refractory period of the action potential? Why is it important?
After the falling phase, when too much K+ leaves the neuron and it becomes hyperpolarised to -90mV. Stops the neuron from being able to fire again too quickly.
What ion is predominantly outside the cell (neuron)?
Na+
What ion is predominantly inside the cell (neuron)?
K+
What are the intra and extra cellular charges of a neuron at rest?
Inside is negative, outside is positive
How do you restore a neuron to resting potential (after action potential)?
Sodium-potassium pump works to rebalance ions
What does the Sodium-potassium pump do?
Pump out three Na+ ions and pump in two K+ ions to help restore/maintain concentration gradient
How is action potential impacted by Nodes of Ranvier?
Action potential jumps from one NoR to the next, on and on and on, which speeds up action potential moving through the axon and means that less energy is required to restore resting potential
how is information transmitted from one neuron to another?
Action potential passes along the axon to the post synaptic neuron. Action potential opens voltage-gated Calcium channels (Ca2+) in the presynaptic terminal. Calcium triggers vesicles to fuse with the presynaptic membrane (exocytosis). Neurotransmitters are released into the synaptic cleft, travel through the cleft to the postsynaptic terminal and bind to receptors
def: ionotropic receptors
neurotransmitter binds directly to the receptor to open/close the ion channel
def: metabotropic receptors
neurotransmitter triggers a sequence of chemical events which open/close ion channels
Explain how a metabotropic receptor works to open an ion channel
neurotransmitter binds to receptor, which activates an enzyme. Enzyme triggers the production of cAMP (messenger), which then opens the ion channel
what are excitatory presynaptic potentials (EPSPs)?
slight depolarisation of the postsynaptic membrane (caused by influx of positive ions) that, when summed with other inputs (EPSPs/IPSPs) at the axon hillock, can cause an action potential to be generated if they cumulatively take the membrane potential to/over the membrane threshold
What are inhibitory presynaptic potentials (IPSPs)?
a slight hyperpolarisation in the postsynaptic membrane (caused by influx of negative ions) that decreases the likelihood of an action potential being generated. Summer with other inputs (EPSPs/IPSPs) at the axon hillock
What are the two types of vesicle fusion?
kiss and run fusion, full fusion
def: full fusion
vesicle fuses with membrane and empties its entire contents into the synaptic cleft
def: full fusion
vesicle fuses with membrane and empties its entire contents into the synaptic cleft
Are EPSPs or IPSPs stronger? Why? Significance?
IPSPs are stronger. They’re closer to the soma and fewer of them are needed to stop an action potential from being generated
What triggers the synaptic terminals to release neurotransmitters?
Voltage change that occurs when the action potential reaches the presynaptic terminal
Where are ion channels located?
On dendrites
Where does drug action/modification of transmission occur?
synapses
def: acetylcholine (ACh)
neurotransmitter in PNS and at neuromuscular junctions
def: cholinergic synapse
synapse that uses ACh as a neurotransmitter
What drugs affect cholinergic synapses?
Caffeine, botox, curare, atropine
What does caffeine do to cholinergic receptors?
activates cholinergic receptors
What does atropine do to cholinergic receptors?
block receptors (e.x., belladonna dilates pupils)
What does curare do to cholinergic receptors?
block receptors causing muscle paralysis (e.x., used on tips of arrows by traditional South American tribes)
What does botox do to cholinergic receptors?
blocks the release of acetylcholine (ACh)
def: agonist drug
a drug that mimics the action of a neurotransmitter and binds to and activates a receptor
def: antagonist drug
a drug that blocks the neurotransmitter from binding to a receptor but doesn’t activate the receptor; blocks the action of the neurotransmitter
def: indirect drug action
a drug that doesn’t directly act on the receptor but acts on another part of the process like production or deactivation
Effects of agonist drugs
increases the synthesis of neurotransmitters; blocks the reuptake of neurotransmitters/blocks them from being destroyed by enzymes, thus increasing the number of neurotransmitters; destroys degrading enzymes so they don’t destroy neurotransmitters in presynaptic terminal; binds to autoreceptors to block their negative feedback;
Effect of antagonist drugs
stop neurotransmitters from being released; acts on the receptors to block neurotransmitters; cause neurotransmitters to leak from vesicles in presynaptic neuron, which causes them to be degraded by enzymes and unusable; blocks neurotransmitters from being synthesized by destroying synthesizing enzymes; drug activates autoreceptors to stop the release of neurotransmitters
What are autoreceptors? What do they do?
receptor located on the presynaptic terminal that responds to that presynaptic neuron’s own neurotransmitter. Serve as part of a negative feedback loop to essentially recognise when to stop releasing the neurotransmitter
What happens to excessive neurotransmitters?
They’re either degraded by enzymes or they’re removed via transporter proteins. If removed via transporter proteins, they’re either further degraded by enzymes or they’re repackaged into vesicles for release at a later point.
What enzyme degrades ACh
Acetylcholinesterase
Example of a drug that blocks acetylcholinesterase
Physostigmine, organophosphates (like in insecticides)
Why is physostigmine dangerous?
Can cause excess production of neurotransmitter at neuromuscular junction which can be poisonous
subcategories of monoamines incl. examples for each
catecholamines (dopamine, noradrenaline); indolamine (5HT/serotonin)
def: monoamines
neurotransmitters synthesized from a single amino acids that is in a small group of neurons in the brain stem
What is 5HT/serotonin involved in?
brain arousal and mood
What is dopamine involved in?
movement, motivation, addiction
What is noradrenaline involved in?
brain arousal
how is dopamine deactivated?
reuptake
how is noradrenaline deactivated?
reuptake
What drugs have block dopamine and noradrenaline reuptake?
cocaine and amphetamines block reuptake therefore increase the action of dopamine and noradrenaline
subcategories of neurotransmitters incl. examples for each
amino acids(GABA and glutamate); neuropeptides (endorphins, opioid peptides, etc.); soluble gasses (nitric oxide, carbon monoxide, nitrogen monoxide,etc.); endocannabinoids (anandamide, etc.)
What does GABA stand for?
gamma-aminobutyric acid
What is gamma-aminobutyric acid (GABA)?
most common inhibitory neurotransmitter
Example of drugs that work on GABA receptors?
benzodiazepine anti-anxiety drugs
def: amino acids (neurotransmitters)
small, fast-acting neurotransmitters; found in simple organisms so likely first neurotransmitters to have evolved
GABA receptor is a __________ receptor
ionotropic
explain what happens with GABA receptor to open the ion channel
GABA binds to receptor, opens chloride (Cl-) ion channel
def: neuropeptides (neurotransmitters)
bigger than other neurotransmitters and tend to be modulatory rather than direct and fast acting; lots of different types
Why is anandamide unusual compared to other neurotransmitters ?
acts on the pre-synaptic neuron instead of post
How do soluble gasses get released as neurotransmitters?
diffuse out through the cell membrane and diffuse into receiving cell through the cell membrane, instead of transmission through vesicles. Transmit feedback from post to pre-synaptic neurons
how many neurotransmitters are generally used by a single neuron?
one
what are ligand-gated channels
ionotropic receptors
def: temporal summation
multiple pre-synaptic neurons act together to reach the membrane threshold and trigger an action potential
def: spatial summation
a single pre-synaptic neuron releases neurotransmitter that build up over time to reach the membrane threshold which then triggers an action potential
Where are IPSPs and EPSPs summed?
Axon hillock
def: receptive field (visual)
retinal ganglion cells have a small spaces where, when stimulated, they detect spots of light. Those spots are the receptive field of the ganglion cells.
What part of the eye detects light and where is it located in the eye?
retina, back of the eye
What generates an action potential re: visual field and retinal ganglion cells?
When all the ganglion cells connected to a single neuron are stimulated, it creates EPSPs. If all signals are EPSPs, then the action potential is triggered. if there is a mix of IPSPs and EPSPs, no action potential
how do neurons process information?
Dendrites receive information from other neurons or sensory receptors. This information travels through the soma to the axon hillock where it is summed. If the membrane potential threshold is reached (-55mV) then an action potential is generated. The action potential travels down the axon to the pre-synaptic terminal. The voltage change at the terminal triggers the release of neurotransmitters into the synaptic cleft. Neurotransmitters bind to receptors on the post-synaptic terminal, which triggers the same events in the receiving neuron
