Fundamentals of NS and Neurophysiology Flashcards
Oct 14
Supporting Cells of PNS and function
Supporting Cells of CNS and function
Schwann Cell: PNS/ myelinates axons of axons in PNS
Satellite Cell: CNS/myelinates cell body (soma) of neurons in PNS
Astrocytes: CNS/ Maintain chemical balance of brain
Microglia: CNS/ Phagocytic, remove foreign micro-orgs and dead tiss.
Ependymal: CNS/ Line epith of brain ventricles and cavities
Oligodendrocytes: CNS/ myelinate axons in CNS
What is a neuron?
Excitable Nerve cell that transmit elec signal
3 main parts of a neuron and their functions
- Dendrite: receptive area/ receives graded potential from axon terminal of another neuron
- Cell Body/Soma: Bio synthetic part of the neuron. Contains the nucleus which makes proteins
- Axon: Transmits elec signal (action potentials) from cell body to another cell. Has the mylelin sheath
Myelin Sheath: About and function
increases conduction rate of impulses/protects & insulates axons
Electrical Disequilibrium: definition
The difference in concentration/charge on either side of the cell membrane by separation of ions.
Graded Potential: Definition and function
Local change in membrane potential that varies w/ the intensity of the stimulus. The more intense the stim, the further the current flows
Action Potential: Definition and function
All or nothing (yes or no) signal that travels along the axon and triggers release of neurotransmitters at the axon terminal
Propagation of an action potential
A positive feedback loop
As voltage gated Na+ channels open, ICF depolarizes which opens more voltage gated Na+ gates, which further depolarizes cell.
Conduction Velocities of Axons
A. Axon Diameter: what does it do re: conduction velocity?
B. Myelin Sheath: what does it do re: conduction velocity?
A. The larger the diameter of the axon, the faster conduction is. The larger the axon diameter the lesser the resistance to elec current
Myelin Sheath: insulates fibers, faster signal conduction, prevents leakage of charge
Nerve Fibers: What are the 3 groups and what are the function and conduction rates of each
Group A Fibers: Large diameter/ Girthly myelinated/ conduct rates: 15- 150 meters p/ second (fastest)
Group B: Intermediate diameter/ lightly myelinated/ conduction rates: 3-15 meters p/sec (second fastest)
Group C: Small unmyelinated. conduction rate 1 meter p/ sec (slowest)
- How are Neurons grouped functionally? What are the 3 types?
According to the direction the impulse travels in relation to the CNS.
The three types are:
1) Sensory/Afferent Neurons
2) Motor/Efferent Neurons
3) Interneurons
Describe each of the 3 Functional type of Neurons and their functions
- Sensory Afferent Neurons: Axons travel toward CNS. Carry impulses toward CNS. Cell bodies located outside CNS (in ganglia). Unipolar
- Motor Efferent Neurons: Axons travel away from CNS. Carry impulses to effectors. Cell bodies located in CNS ( in grey matter). Multipolar
- Interneurons: Located between sensory and efferent neurons and are confined to CNS. Function is integrate information
Synapse: definition
Junction site where neurons communicate/ exchange information.
Presynaptic Neuron vs Post synaptic neuron
Presynaptic: the neuron that is sending the info to the other
Postsynaptic: the neuron that is receiving the info from the previous neuron. Graded potentials happen here.
Axodendritic Synapse
Synapses between axon ending of 1 neuron and dendrites of another.
Axosomatic Synapse
Synapse between axon ending of 1 neuron and cell body (soma) of another
General vs Special Senses of Sensory Division
General Senses: touch, pressure, proprioception, temperature, anything sensed by visceral organs
Special Senses: taste, smell, senses that req special organs (eye, ears)
Axon Hillock: Location and function
Located at end of cell body on neuron.
Function: decides whether action potential will or will not fire. -55 mV threshold required)
Electrical DIsequilibrium
Cells separate ions creating different concentrations on either side of the membrane
Ion Concentration on each side of membrane
(ICF vs ECF) for Na+, K+, Cl-
Na+: in ECF: 140 mM
in ICF: 14mM
(Na+ wants to move from outside cell to inside of cell/ high to low concentration
K+: in ECF: 4 mM
in ICF 140 mM
(K+ wants to move from inside to outside cell/ high to low concentration)
Cl-: in ECF: 110 mM
in ICF: 7 mM
Cl-wants to move from outside to inside the cell (high to low concentration)
Resting Membrane Potential
Potential difference across the membrane. It is -70mV.
It represents a source of potential stored energy.
Concentration Differences of Ions across the membrane are a result of what 3 factor?
- Electrical Attraction by FIXED ANIONS (neg chg proteins inside the cell) that cannot cross the cross membrane
- Resting membrane is more permeable to K+ than to Na+. K+ able to leak out of of cell into ECF
- Active Transport by Na+/K+ ATPase Pump: Actively pumps 3 Na+ out while also pumping 2 K- back in to cell. Requires energy ea time used
Na+/K+ ATPase Pump: function
To maintain resting membrane potential of -70mV & to actively pump 3 Na+ out of cell and actively pump 2 K+ back into cell.
Nerve: Definition
A bundle of Axons
Action potential. What is happening when membrane potential is at -70 mV?
- Resting Membrane Potential
- No gated channels are open
- Membrane Polarized
Absolute Refractory Period
Ensures each AP is a separate all or nothing event.
Na+ inactivation gates closed. Channels can’t respond to new stimulus
What happens when membrane potential is at -55mV?
- AP threshold reached, Axon hillock initiates AP.
- Na+ channels open
- Na+ inactivation gates close 1 mS after Na+ channel opens
- Depolarization/ inside of membrane less negative
- Absolute Refractory Period: happening during depolarization to repolarization on either side
What happens at +30mV?
- Peak Depolarization/ Action potential max output
- K+ channels open (+20mV to +30) K+ leaves cell
3.Na+activation gates close - Membrane starts to repolarize as k+ leaves cell
What happens at less than -70mV?
- K+ channels close around -90mV
- Hyperpolarization of cell membrane
- Inside of membrane is more negative (lower than -70mV)
- Membrane is at Relative Refractory Period
Chemically Gated Channels
open and close when exposed to the correct neurotransmitter
Example: Ligand gated channels
Voltage Gated Channels
open & close when voltage threshold is crossed
These are the most common
Mechanically Gated Channels
open when a membrane is deformed/physically stretched to open
What is an Ion
A charged molecule
Relative Charge Scale
RMP measured by assigned ECF value of zero, then measuring the difference between the 2 sides of the membrane
How can non charged molecules/ ions move across a membrane?
Only with a concentration gradient or active transport
How do molecules/ions without a concentration gradient and with passive transport move across the membrane?
Because ions are charged and can be either attracted or repelled across the membrane
How come ions cannot reach equilibrium even though a typical cell is permeable to K+?
Because the chemical gradient favors K+ leaking from the cell and the Electrical gradient favors attracting K+ in the cell.
Relative Refractory Period
Na+ activation gates closed/closing but Na+ inactivation gates are open. A strong enough stimulation can re-open activation gates & depolarize membrane & produce a 2nd AP
Polarization
membrane is at rest (-70mV). no gated channels open. ICF more negatively charged than ECF.
Depolarization
Membrane potential moves higher than -70 mV to ward zero or higher
Inside of membrane becomes LESS negative
Hyperpolarization
Membrane potential moves even lower than -70mV. Inside of membrane become MORE negatively charged
When do Na+ activation gates open
@ -55mV
When do Na+ inactivation gates close?
Shortly after +30mV
When do K+ activation gates open?
@+30+mV
Stimulus Strengh
Intensity is coded in frequency of AP (how often they happen) and not the intensity
Chemical Synapses: Function and about
Allow for release and reception of neurotransmitters
Consist of axon terminal, synaptic cleft, and a receptor region
opening ion channels on post synaptic membrane can have either excitatory or inhibitory effect on post synaptic neuron.
Binding of neuro -T either drives them toward threshold or away fromn
Chemical Synapses: Step 1:
AP opens Ca2+ channels in the axon terminal
Chemical Synapse Step 2:
Ca2+ enters membrane and initiates V-Snare/T-Snare protein DOCKING
Chemical Synapse Step 3:
V-Snare/ T-Snare interaction allows vesicle FUSION to membrane. Vesicles contain neurotransmitters.
Step 4: Chemical Synapse
Fusion results in NEUROTRANSMITTER RELEASE into synapse via EXOCYTOSIS. Complexes move away from each other and create pores in axonal membrane
Step 5: Chemical Synapse
Released Neuro T’s cross synapse and bind w/ postsynaptic receptor channels
Step 6: Chemical Synapse
Ion channels open on post synaptic membrane
(as result of Neuro T’s binding to receptors)
Electrical Synapses: Function and location
Function:
Synchronize activity of all interconnected neurons
Allow direct rapid communication between adjacent cells through gap junctions.
They are faster than chemical synapses
Location:
Found in embryo, cardiac and smooth muscle and brain
Chemical Synapse can be either____or____?
Can be either excitatory or inhibitory
Excitatory: opens Na+ channels, drives toward threshold
(depolarization)
Inhibitory: opens K+ or Cl-, drives away from threshold (hyperpolarization)
Structural Classification of Neurons (3)
- Unipolar: 1 long axon w/ cell body attached via stalk. most commonly are sensory(afferent) neurons.
- Bipolar: cell body in middle and 2 long processes extended from ea end of soma. Only found in special sensory receptors (retinas, olfactory bulb)
- Multipolar: (most common) many dendrites & only 1 axon that extend from soma. Mostly are motor (efferent) neurons and interneurons.
What are the 3 ways Neurotransmitters are terminated?
- Degraded by the receptor terminal
- Are re-sequestered back into the presynaptic terminal
- Diffuse away from the synapse and broken
down/destroyed by glial cells
Excitatory Synapses
- Neuro-T binds to CHEMICALLY GATED channels &
pushes them open. These are Chemically gated
channels, (NOT voltage gated channels!). - Open gates/allow Ion diffusion (Na+ in & K+ out)
simultaneously (more Na+ in than K+ out) - Na+ follow electrochemical gradient.
K+ follows chemical gradient - Results in local depolarization cell from the above
activity. This is called Excitatory Post Synaptic
Potentials aka “EPSP”. - These graded potentials vary in amplitude depending on amt of N. T. that binds. If the EPSP’s reaching the
hillock are strong enough to reach threshold, then an
AP will result
What is an EPSP?
Excitatory Post Synaptic Potential
It is the local depolarization of membrane from charged Ions entering membrane as result of an excitatory synapse.
It is a graded potential
How will an EPSP result in an AP?
EPSP’s vary in amplitude (strength) depending on the amt of NT that binds. If the EPSP’s that reach the Hillock are strong enough they will trigger an AP.
What gradient does Na+ follow and what gradient does K+ follow?
Na+ follows an electrochemical gradient
K+ follow a chemical gradient
Inhibitory Synapse (Function & how it happens)
Function: Reduces RMP potential resulting in hyperpolarization.
How: when inhibitory N.T.’s bind & open K+ and Cl- channels, Cl- enters resulting in hyperpolarization of membrane.
IPSP: Inhibitory Post synaptic potential: the resulting hyperpolarization of the post synaptic membrane from opened K+ and Cl- channels
Na+ channels are not affected
How are EPSP’s and IPSP’s generated at the post synaptic receptors?
By either a DIRECT CHEMICAL GATES or an INDIRECT CHEMICAL GATES
DIRECT EFFECTS
Direct Effects: when a N.T. directly opens a channel.
Ex: Acetylcholine
Results in rapid, short acting synaptic potentials
INDIRECT EFFECTS
Indirect Effects: Depend on a 2nd messenger (G-protein or enzyme) to either open a channel or change metabolic activity inside cell.
Ex of G-Protein: Norepinephrine (opens channel)
Ex of Enzyme: Nitric Oxide
Results in slow, long term effect on synaptic potential
Summation
1 single EPSP cannot induce an AP but they can summate/ add up (multiple EPSP’s) enough impulses to trigger at Hillock - That is summation
What are the 2 types of summation?
Temporal Summation:
Multiple impulses travel down a (1) presynaptic neuron (1 terminal) in rapid order and add up (summate)
Spatial Summation: impulses from large # of terminals stimulate post synaptic membrane.
Synaptic Potentiation
Hint: “Potent”
The repeated use of a synapse enhances the ability of postsynaptic excitation, producing larger post synaptic potentials (repetition of the stroke = a “Potent” blast )
Presynaptic Inhibition
Hint: “Pre-mature…moms knocking the door”
When another neuron inhibits excitatory release via axoaxonic synapse, it leads to decreased amount of NT release.
