Nervous system: action potentials, graded potentials, and synaptic transmission

steps of synaptic transmission

1. action potential arrives 2. VG Ca2+ open, increasing intracellular Ca2+ 3. Causes vesicles with neurotransmitter to exocytose, releasing neurotransmitters to synaptic cleft 4. neurotransmitters binds, leading to change in ion permeability in post-synaptic cell 5. degradation enzymes OR reuptake proteins on pre-synaptic cell diminish neurotransmitter concentration in synapse

steps of action potential

1. initial depolarization; if sufficient enough, VG Na+ will open 2. VG Na+ open, Na+ rushes in 3. VG K+ open but its effects are unseen since VG Na+ are still open 4. VG Na+ inactivate 5. VG K+ still open and can see its effects as K+ rushes out 6. VG K+ inactivate. Na/K pump causes return back to resting membrane potential

why is propagation unidirectional?

At each site of depolarization there is a refractory period such that when its neighboring ion channels open, it does not cause them to re-open again.

what if there a potential much larger than threshold?

actions retains same amplitude, same type of action potential

open state of VG channels

allows ions to pass through down electrochemical gradient

myelinating cells

assist with conductance of electrical messages, insulate axons with fatty myelin sheaths

anterograde transport

away from soma

where in the neuron does it decide whether to fire an action potential?

axon hillock; has highest amount of VG channels

relative refractory period

bigger depolarization is required to get to threshold; number of available VG Na+ channels still isn't 100%

central nervous system

brain and spinal cord, processes incoming information

afferents

carry information to CNS

connexins

collection of 6 connexons. forms basis of these gap junctions found at electrical synapses

importance of cytoskeleton in neuron

critical for maintaining physical features, helps to quickly move material from one soma to other parts of neuron

spatial summation

different synapses are active at the same time; could be all EPSPs, all IPSPs, or a mix of both

peripheral nervous system

everything that's not brain and spinal cord, carries information to CNS and deliver motor commands to the rest of the body

myelinated axon propagation (saltatory conduction)

faster, leak channels are covered by the myelin, electrical signals stay stronger over longer distances, less interactions with membrane

neuron

functional unit of the nervous system; use changes in membrane potential to conduct information both within same cell and between cells, communicate information, process incoming sensory information, initiate changes in physiology and body movement

propagation

how information spreads down length of axon, regeneration of action potentials

inhibitory post-synaptic potential (IPSP)

hyperpolarization/maintain resting membrane potential in post-synaptic cell (increases in K+ or Cl- permeability)

both action potentials and graded potentials

ion movement, changes in membrane potentials

synapse

junction between neuron and target cell. there's electrical and chemical synapses (latter is more common in body)

depolarization

less negative than rest, moving more positive from rest

action potential

long distance, actively regenerated, all or nothing response to depolarization at the axon, large and standard changes in membrane potential, require voltage-gated ion channels, systemic opening of Na+ VG channels

astrocytes

monitor nutrients/waste, maintaining proper ECF ion concenetrations

absolute refractory period

most of VG Na+ are inactive; no way for Na+ to move across membrane; exists as we climb action potential and persists until close to rest

repolarization

moves back to rest following depolarization

hyperpolarization

moves more negative from rest

oligodendrocytes

myelinating cells of the CNS

Schwann cells

myelinating cells of the PNS

interneurons

neurons that are completely within the CNS, involved in processing of information

why are membrane potentials important to a neuron?

neurons use changes away from resting membrane potential to transmit electrical information within and between cells; presence of various voltage-gated ion channels are embedded within membrane

what if there's not a large enough depolarization to open VG Na+?

no action potential; only sub-threshold potentials

inactive state of VG channels

no ion movement because it's closed and not allowed to open

closed state of VG channels

no ion movement but can still be opened with stimulus

excitatory post-synaptic potential (EPSP)

post-synaptic cell experiences depolarization (increases in Na+ permeability, could generate action potential)

gap junctions

protein tunnels that interact with each other; extend from each cell

post-synaptic density

proteins just beneath dendrites of post-synaptic cell that help stabilize receptors and anchor them

ionotropic receptors

receptor and ion channel are the same protein, quick

metabotropic receptrs

receptor and the ion channel it influences are two different proteins, utilize G proteins, takes longer, slower response to neurotransmitter binding, effects are longer lasting/acting

temporal summation

same synapse is active very close in time; either all EPSPs or all IPSPs because it's the same synapse

graded potential

short distances, not actively regenerated, decay pretty rapidly, most found in dendrites, caused by the opening of ion channels, magnitude depends on stimulus strength (smaller stimulus = smaller magnitude), confined to small region on membrane, decay quickly with space and time

unmyelinated axons propagation

slower, entire membrane works to regenerate actin potential because leak channels allow signal to dissipate quickly

microglia

specific to neural tissue; immune-like cells

glial cells

support neurons, 90% of the nervous system

summation

synaptic integration; process by which the axon hillock takes into account all incoming inputs

efferents

take information away from CNS

retrograde transport

toward soma

chemical synapse

translates electrical messages to chemical messages that diffuse to post-synaptic cell; information becomes electrical again in post-synaptic cell, slower, greater flexibility due to physical disconnection

electrical synapse

travels directly from cytosol of pre-synaptic cell to post-synaptic cell cytosol via gap junctions, fast, found where info transmission has to be quick, less flexible

axon hillock

where a neuron decides whether to send an action potential