Neuronal Signaling Flashcards
Cell membrane: Structure
Lipid Bilayer
Composed of phospholipids, not permeable to ions, establishes concentration gradients, and is able to store opposite sign charges but they can’t cross membrane (forms electrical gradient)
Cell membrane: Structure
Proteins
-Either associated with the outer or inner layer of the lipid bilayer or incorporated within and spanning the lipid bilayer (more common)
Cell membrane: Structure
Proteins-Types
- Transporters
a) Carriers-actively move ions into or out of cells against their concentration gradients
b) Ion channels-allow only certain kinds of ions to cross the cell membrane in the direction of their concentration gradients - Others-Receptors, Structural, Enzymes, and Adhesion
Cell membrane: Structure
Glycocalyx
-External surface of the cell composed of carbohydrates
Cell membrane: Function
- Selective Barrier: separates intracellular and extracellular compartments
- Intercellular Communication: cell recognition and attachment to other cells and extracellular molecules
- Signal Transduction
Resting Membrane Potential
- Electrical potentials are generated across the cell membranes of neurons due to:
1) differences in ion concentrations
2) selective permeability of membranes to ions
Resting Membrane Potential: Ionic Basis
a. Na+-K+ pump: keeps [Na+] low and [K+] high
b. cell membrane is selectively permeable to K+ due to open K+ channels–>K+ leaks out of cell
c. excess positive charge outside cell and excess negative charge inside cell
Resting Membrane Potential: Properties
a. the resting membrane potential of neurons ranges from -40mV to -90mV (~65mV)
b. uniform throughout the cell
Alterations in Resting Membrane Potential
a. Depolarization-reduction in the resting membrane potential (more +, influx of Na+); excitatory for AP
b. Hyperpolarization-an increase in the resting membrane potential (more -, influx of Cl-); inhibitory for AP
Signals within Neurons (Electrochemical Basis of Nerve Function):
Signals (4)
- to produce a behavior each participating neuron sequentially generates four different signals within a cell:
1) input, 2) trigger, conducting, and 3) output
Signals within Neurons (Electrochemical Basis of Nerve Function):
Function Components of 4 Signals
- -four functional components or regions, which generate the four signals:
1) receptive, 2) summing or integrative, 3) 1ong-range conducting or signaling, and 4) secretory
Signals within Neurons (Electrochemical Basis of Nerve Function): Input Component-Region
- Sensory neurons-sensory receptors that respond to various sensory stimuli
- Motor neurons and interneurons- postsynaptic membrane receptors that respond to communication from other cells
Signals within Neurons (Electrochemical Basis of Nerve Function): Input Component-Signal
a. Ionic basis: brief change in the resting membrane potential due to the alteration of membrane permeability to ions; either excitatory or inhibitory
b. Properties: graded in amplitude and duration, proportional to amplitude and duration of stimulus; propagation is passive–decreases in amplitude with distance
Signals within Neurons (Electrochemical Basis of Nerve Function): Trigger Component
- Region-highest concentration of voltage-gated Na+ channels, located adjacent to the neurons input component–sensory: myelinated axon of first node of Ranvier; motor: axon hillock
- Signal- the activity of all the receptor’s AP are summed–threshold–AP
Action Potential: Ionic basis
- Upstroke (or Rapid Depolarization): Increase in Na+ permeability
- Overshoot (or Reversal of MP): Increase in [Na+]
- Repolariztion: Decrease in Na+ permeability and increase in K+/ efflux of K+
- Hyperpolarization: K+ permeability remains for a prolonged period of time, until the MP is more negative than RMP
Acton Potential: Properties
- All or None: NOT graded or local
- the amplitude and duration of the input signal influence the frequency and number of AP
- Absolute Refractory Period: stimulus CANNOT elicit a second AP
- Relative Refractory Period: only a suprathreshold stimulus can elicit at second AP
Signals within Neurons (Electrochemical Basis of Nerve Function): Conducting Component-Properties
- Propagation is active = does NOT decrease in amplitude with distance; periodically regenerated
- Unidirectional: once AP passes, Na+ channels are in inactivated state and are refractory to further stimulation
- Conduction velocity is dependent of the axon diameter and myelination status–larger and more myelin = faster
Signals within Neurons (Electrochemical Basis of Nerve Function): Output Component-Region
Presynaptic Terminal-Active Zones
Signals within Neurons (Electrochemical Basis of Nerve Function): Output Component-Signal
Release of NT at synapse of effector cell or a second neuron
Signals within Neurons (Electrochemical Basis of Nerve Function): Output Component-Signal
Ionic Basis
AP reaches presynaptic terminal–stimulates Ca2+ channels to open–causes synaptic vessels to migrate to presynaptic membrane–release NT via exocytosis
Signals within Neurons (Electrochemical Basis of Nerve Function): Output Component-Signal
Properties
- NT are released as discrete units, called quanta
- total amount of NT released is dependent on the amount Ca2+ which enters the presynaptic terminal (dependent on frequency + number of APs)
- total amount of NT released can be regulated from outside the cell
Signals Between Neurons
Occur b/w part of one neuron and part of a second neuron or effector cell via synapes
Signals Between Neurons:
Synapses
- Functional contacts b/w cells
- Information carried by AP–the message of an AP is determined by the neural pathway that it carries***
- Occur between a neuron’s axon and another neuron’s dendrite, cell body, or axon
Signals Between Neurons:
Synapses: Electrical-Structure
Gap Junctions: specialized membrane channels with pores that connect the pre and postsynaptic cell membranes
Signals Between Neurons:
Synapses: Electrical-Function
Mechanism of Signal Transmission:
- Ions (an other molecules) can diffuse with pores that connect the from pre- to postsynaptic cell
- Rapid
- No threshold for signal transduction
- Uni-directional or bi-directional flow of info
Signals Between Neurons:
Synapses: Chemical-Structure
- Presynaptic terminal- contains synaptic vessels filled with NT concentrated active zones along the presynaptic membrane
- Synaptic Cleft-space b/w pre- and postsynaptic membrane
- Postsynaptic Membrane-contains receptors, target molecules that exhibit an affinity for individual NTs
Signals Between Neurons:
Synapses: Chemical-Function
Function- same as above-Mechanism of Signal Transmission
1) Synaptic delay
2) Threshold for signal transduction
3) Uni-directional flow of information
Signals Between Neurons:
Neurotransmitters
- chemicals localized to and released from a presynaptic terminal that bind to receptors in the postsynaptic membrane–>effector function in target cell
- > 100 different agents
- many types of neurons synthesize and release two or more NTs
- activity is limited by diffusion away from the post-synaptic membrane, enzymatic degradation in the synaptic cleft and re-uptake across the cell membrane and surrounding glial cells
- effects (excitatory or inhibitory) depend on the receptors; most NTs have more than one efffect
Signals Between Neurons:
Neurotransmitters-Types
- Small molecules- tend to mediate rapid synaptic transmission (ex. Amino acids, Biogenic Amines-seretonin, dopamine, histamine, NEP, and EP, and Nitric Oxide)
- Neuropeptides-tend to mediate slow synaptic transmission (ex. Opioid peptides, posterior pituitary peptides, Tachykinins (Substance-P), Glucagon-related peptides, Pancreatic Polypeptide-Related Peptides
