Neurophysiology Flashcards
What is the overall job of the nervous system?
To control and communicate internally and externally via electrical signals and received sensory inputs
Why does the nervous system use electrical signals?
They give rapid and immediate responses
What is an Astrocyte?
A neuroglial cell that clings to neurons, regulates extracellular compartments, and contributes to the Blood Brain Barrier
What is the function of a microglial cell?
They are the macrophages of the immune system. IE They run defense.
What is the function of ependymal cells?
To line ventricles in the CNS and regulate the CSF
What cells create myelin sheaths in the CNS?
Oligodendrocytes
What is the Blood Brain Barrier?
A membrane that allows only certain compounds to enter the brain. It is formed by tight junctions between the capillary wall & the foot process of astrocytes
What are the parts of a typical neuron?
SOMA- A cell body with a large nucleus and large ER
DENDRITES - Short, branched connected to the cell body
AXON HILLOCK - The mound from which the axon extends
AXON - One, maybe two long wire-like
MYELIN SHEATH - Adipose tissue coating Schwann cells
THE NODE IF RANVIER - The unmyelnated parts of the axon
What part of a neuron has the most ligand-gated channels?
Dendrites
What does -lemma mean?
Membrane
What is the myelin sheath made of and what is its purpose?
Adipose tissue (lipids), provides insulation to speed the signal along an axon
What are the classifications of FUNCTIONAL neurons?
SENSORY/AFFERENT - Carries from receptors in the Periphery to the CNS
MOTOR/EFFERENT - Carries signals from CNS to muscles, glands, organs
ASSOCIATION/INTERNEURONS - Short, interpretative neurons (more of this kind than others)
What are the different classifications of STRUCTURAL neurons?
Pseudounipolar - SENSORY neurons, look like they have a little guy growing off
Bipolar - SENSE SENSORY NEURONS (visual, olfactory) Two processes (one dendrite, one axon) on either side of a soma
Multipolar - MOTOR NEURONS - many processes branching off of the soma
What is an axonal transport and what are the types?
Microtubules along which large and insoluble compounds can move
Note: access method for viruses (like polio) and toxins
Anterograde - Cell body to end of terminal
Retrograde - Terminal to cell body
How is a nerve repaired?
The portion distal of the damage degenerates and is phagocytised and the proximal end regenerates into tubes of Schwann cells which very slowly grow and get mylenated.
Note: This does not happen in the brain
What is the name for axon bundles in the Periphery Nervous System?
Nerves
What is the name for axon bundles in the Central Nervous System?
Tracts
What is a synapse?
The space that serves as communication point between a neuron and its target.
It is really 3 things: a pre-synaptic neuron, the cleft, and the post-synaptic neuron
How many synapses does the average neuron have?
1,000
What are the different types of ion channels found in neurolemma (plasma membrane)?
Ligand-Gated - chemically opened (by neuritransmitters)
Mechanically Operated - Sensing pressure, hearing
Voltage-Gated - Many types, but Na+ channels are of particular note
Leaky Channels - Spewing out K+ all the damn time. Always open
What is the difference between electricity and voltage?
Electricity - When opposite charges are separated they contain potential energy, when they come together that energy is released.
Voltage is the measurement of the difference in potential energy creates bu charge separation
What is membrane potential?
The imbalance between inside and outside of a cell’s plasma membrane
Where are ions concentrated in relation to the plasma membrane?
Intracellular (More inside)
Potassium (K+)
Proteins (-)
Extracellular (More outside)
Sodium (Na+)
Calcium (Ca2+)
Chlorine (Cl-)
What is the chemical gradient across the plasma membrane?
Low permeability for proteins and K+ inside the cell and Na+ outside the cell creates a gradient of concentration
What is the Electrical Gradient?
The charge is negative inside a cell from trapped proteins and the K+ trying to move out and Na+ on the outside create a difference in concentration of charge
How do gradients affect an ion’s behavior across the plasma membrane?
In other words, what creates membrane potential?
The unequal amounts of sodium and potassium pumping in and out of the cell (3K Out, 2Na in) create potential across the membrane
What does equilibrium potential tell us?
Which direction one ion moves
What is RMP and what are the factors contributing to Resting Membrane Potential?
When a neuron is not receiving input or sending output it is considered reating and has a voltage of -70 mV
- Fixed anions inside the cell
- Concentration different of ATPase pump
- Permeability of membrane causing K leaks
Define depolarization
When potential goes less negative than -70mV (the charge increases toward -55)
Define hyperpolarization
When potential goes lower than -70 (toward -70, caused by voltes gates closing very slowly)
Define repolarization
When potential returns to -70 as K+ ions diffuse out of a neuron
What is a stimulus?
Anything that activates something
What happens when a stimulus comes to a neuron?
Neurotransmitters bind to ligand-gates channels on dendrites
OR
mechanical stress stimulates pumps
OR
temperature change is communicated
What is graded action potential, where does it happen, what does it tell us and how is its magnitude detemined?
A small, localized, change in the membrane potential, telling us the frequency and amplitude of a stimulus
It happens mostly in the dendrites and soma
The magnitude depends on the number of open Na+ channels
Ex. Receptor cells, post-synaptic potentials, motor-end plate neurons
True or False: The further away a graded potential response gets from the stimulus the stronger it gets.
False. The response gets smaller and more dissipated as it moves across the membrane.
What is threshold potential?
-55mV The trigger zone where voltage-gated channels open (Na+ in particular)
What is action potential?
AKA nerve impulse, a brief reversal of membrane potential to +30 mV propagated down the entire length if the exon (very not localized) to axon terminal
What is the rule of All or None?
If a stimulus hits the -55mV threshold then action potential pops off. It is always excitatory (meaning it makes the charge more positive)
If it does not hit that threshold then nothing happens
What are the phases of action potential?
- RMP
- A depolarizing stimulus occurs
- Membrane depolarizes to Threshold
- Rapid Na+ entry depolarizes cell
- Na+ channels close, K+ channels open
- K+ moves from cell to extracellular fluid
- K+ channels stay open, repolarizing cell
- K+ channels close, K+ continues to leak
- Cell returns to RMP
What is the difference between absolute and relative refractory periods?
Why are absolute periods like that?
When is the relative period?
Absolute - No matter how strong the neuron cannot respond to the next stimulus due to INACTIVATION OF Na+ CHANNELS
Relative - Neuron can respond if the the stimulus is strong enough, membrane potential is going from -70mV to -90mV
What is saltatory conduction?
Voltage “jumps” from one chunk of myelin to the next over the node of Rainvier, increasing conduction velocity
What are the factors that contribute to/against the conduction velocity of an axon?
Myelination - increases impulse rate/prevents charge leakage
Diameter of axon - larger diameters have increased velocity due to less resistance
Alcohol, Sedatives, Anesthetics - Slow or block impulses by reducing permeability of Na+. Pain is present but brain can’t detect it
Insufficient Blood Flow - Cold or pressure slows impulses
What is the physiological name for cell communication?
Synaptic Transmission
What happens in a presynaptic axon terminal during synaptic transmission?
An action potential moves down an axon and it is excited (depolarizes)
Voltage-gated Ca2+ channels open
These channels release an excitatory NT
What happens in a postsynaptic membrane during synaptic transmission?
-Dendrites and cell bodies open chemically gates channels
-Inward diffusion causes depolarization
-Summation occurs (all potentials are added at axon hillock)
-When threshold is crossed voltage-gates channels open
-Axon conducts action potential
-NTs bind to their receptors, causing ion channels to open
What is the difference between Excitatory Post-Synaptic Potential and Inhibitory Post-Synaptic Potential?
EPSP - Exictatory - Na+ channels cause DEpolarization. Moves toward less negative than RMP.
IPSP - Inhibitory - Binding of NTs causes HYPERpolarization of membrane and away from theshold
What is temporal summation?
A PREsynaptic neuron increases the frequency of impulses and releases more NT in quick succession which causes Action Potential
(tapping a button quickly in QTE)
What is spatial summation?
Post-synaptic neurons are stimulated by multiple pre-synaptic neurons at the same time and combine their DEpolarization
(think QTE and hit both buttons at once)
What do modulator neurons do?
Affect the effectiveness (inhibit OR enhance) of the presynaptic input without affecting input from other neurons
Ex. Eventually get used to the noise of a crowded bar, stop noticing the texture of clothes
What is the difference between pre-synaptic and post-synaptic inhibition?
Presynaptic - The amount of NT released from one target (Neuron A) is decreased by an inhibitory neuron (Neuron B) which blocks the NT release at a synapse
Postsynaptic - All targets are equally inhibited by a silencing neuron
What is presynaptic facilitation?
The amount of NT released from Neuron A is enhanced
What is Synaptic Plasticity?
Repeated use of a synapse can increase or decrease ease of transmission over longterm potentiation
Note: This is the molecular mechanism for learning
What are the different Circuits of Neuronal Pools?
Divergent - One incoming fiber stimulates multiple fibers, often amplifying circuits
Convergent - Results from multiple strong stimulations, ie many inputs converge on one output
Ex. Balance
Reverberating - A chain of neurons containing collateral synapses chain together
Ex. Short term memory
Parallel After-Discharge - Incoming neurons stimulate several neurons aling parallel arrays
Ex. A plexus
Note: Helpful if a neuron gets damaged
What are neurotransmitters? (List em)
A neurotransmitter (NT) is a signaling molecule secreted by a neuron to affect another cell across a synapse
-Acetylcholine
-Biogenic amines (catechloamine, seratonin)
-Amino acids (glutamate, glycine, GABA)
-Peptides (endorphins, substance P)
-Messengers (ATP, dissolves gases like NO)
How are neurotransmitters classified? What is the difference between direct and indirect NT receptors?
By function: exhibitory or inhibitory (and some are both, eg ACh is exhibitory at neuromuscular junctions and inhibitory at cardiac muscle)
By receptor mechanisms
Direct - Open ion channels
Ex. ACh
Indirect - Act through secondary messengers but effect lasts longer
Ex. Biogenic amines, peptides, gases
How do neurotransmitters do their actions and how are they deactivated?
- Re-uptake by presynaptic axon terminals or astrocytes
- By enzymes or by diffusing away from synaptic cleft
Describe Acetylcholine
Most widely used NT
Two subtypes: Nicotinic and Muscarinic
-Nicotinic: Produces depolarization, EPSP
-Muscarinic: Activates G-protein cascade (which opens K+ channels, opening some - Depolarization, closing others - Hyperpolarization)
What deactivates Acetylcholine?
Deactivated by acetylcholinesterase (AChE), breaking it down to Cholone and AcetylCoA (which gets recycled back into pre-synaptic terminal)
Describe the catecholamines:
What do they activate, how are they inactivated?
Monoamines:
Serotonin, Norepinephrine, Epinephrine
Activates G-protein cascades to ion channels and increase cyclic AMP
Inactivated by presynaptic reuptakes and breakdown by MAO (monoamine oxidase)
What are the characteristics of serotonin?
Involved in the regulation of mood, appetite, cerebral circulation, behavior (similar on structure to LSD)
NOTE: SSRIs are Specific antidepressants that Inhibit the Reuptake of Seratonin (Prozac, Zoloft, Pacil)
What are the the two major systems of dopamine?
- Nigrostatial Dopamine System from substantia nigra, involved in motor control
Note - Degeneration of this system causes Parkinson’s - Mesolimbic Dopamine System involved in behavior and emotional reward.
Note - Addiction works on this tract. Overactivity contributes to schizophrenia
What is the most common inhibitory NT?
GABA
Glycine is another big one
What is the difference between PNS norepinephrine and CNS norepinephrine?
PNS - Adrenergic Alpha and Beta Receptors
CNS - Amphetamines
What do the gaseous NTs do?
Nitrous Oxide and Carbon Monoxide act through the cGMP second messenger systems
NO causes smooth muscle relaxtion
What does botox do?
blocks ACh release at NT junctions, which causes flacid paralysis
What is Potassium-Equilibrium Potential?
-90mV. The charge of a membrane after a membrane potential
