Chap 4: Neural Conduction & Synaptic Transmission Flashcards
Microelectrodes
Their tips are less than 1000th of a millimeter in a diameter much too small to be see by the naked eye
Membrane potential
The difference in electrical charge between the inside and the outside of a cell
Resting membrane potential
When both electrode tips are in the extracellular fluid, the voltage difference between them is zero
Resting potential
In its resting state with the -70 mV charge built up across its membrane a neuron is said to be polarized
Ionic basis of the resting potential
Like all salts in solution the salts in neural tissue separate into positively and negatively charged particles called ions
Concentration gradients
That is, they are more likely to move from areas of high concentration to areas of low concentration than vice versa
Electrostatic pressure
Any accumulation of charges, positive or negative in one area tends to be dispersed by the repulsion among the like charges in the vicinity and the attraction of opposite charges concentrated elsewhere
Neurotransmitter
Which diffuse across the synaptic clefts and interact with specialized receptor molecules on the receptive membranes of the next neurons in the circuit
Depolarize
The receptive membrane (decrease the resting membrane potential, from -70 to -66 mV
Hyperpolarize
Increase the resting membrane potential from -70 to -72 mV
Excitatory post synaptic potentials (EPSPs)
Known as post synaptic depolarization, they increase the likelihood that the neuron will fire
Inhibitory postsynaptic potentials (IPSPs)
Known as postsynaptic hyperpolarization, they decrease the likelihood that the neuron will fire
Graded responses
The amplitudes of EPSPs & IPSPs are proportional to the intensity of the signals that elicit them
Axon hillock
The conical structure at the junction between the cell body and the axon, but they are actually generated in the adjacent section of the axon
Threshold excitation
If the sum of the depolarizations and hyperpolarizations reaching the section of the axon adjacent to the axon hillock at any time is sufficient to the dispel arise the membrane
Action potential (AP)
Is massive but momentary lasting for 1 millisecond reversal of the membrane the potential from about -70 to +50 mV
Integration
Adding or combing a number of individual signals into one overall signal
Temporal summation
Shows how post synaptic potentials produced in rapid succession at the same synapse sum to form a greater signal
Voltage activated ion channels
Ion channels that open or close in response to changes in the level of the membrane potential
Refractory periods
Th
Refractory periods
There is a brief period of about 1 to 2 milliseconds after the initiation of an action potential during which it is impossible to elicit a second one
Relative refractory period
The period during which it is possible to fire the neuron again, but only by applying higher than normal levels of stimulation
Antidromic conduction
When electrical stimulation of sufficient intensity is applied to the terminal end of an axon, an action potential will be generated and will travel along the axon back to the cell body
Orthodromic conduction
Axonal conduction in the natural direction from cell body to terminal buttons
Nodes of ranvier
The gaps between adjacent myelin segments
Saltatory conduction
It’s the transmission of action potentials in myelinated axons
Dendritic spines
Nodules of various shapes that are located on the surfaces of many dendrites
Also common are axosomatic synapses-synapses of axon terminal buttons on somas (cell bodies)
Directed synapses
Supynapses at which the site of neurotransmitter release and the site of neurotransmitter reception are in close proximity
Nondirected synapses
Are synapses at which the site of release is at some distance from the site of reception
Neuropeptides
Are short amino acid chains comprising between 3 and 36 amino acids, in effect they are short proteins
Synaptic vesicles
Small molecule neurotransmitter are typically synthesized in the cytoplasm of the terminal button
Coexistence
When neurons contain two neurotransmitter
Exocyctosis
The process of neurotransmitter release
When a neuron is at rest, synaptic vesicles that contain small molecule neurotransmitters tend to congregate near sections of the presynaptic membrane that are particularly rich in voltage activated calcium channels
Receptors
Is a protein that contains binding sites for only particular neurotransmitters and it can influence only those cells that have receptors for it
Ligand
Any molecule that binds to another
Receptor subtypes
The different types of receptors to which a particular neurotransmitter can bind
Ionotropic receptors
Are those receptors that are associated with ligand activated ion channels
Metabotropic receptors
Are those receptors that are associated with signal proteins and G proteins
Second messenger
The subunit may move along the inside surface of the membrane and bind to a nearby ion channel thereby inducing an EPSP or IPSP or it may trigger the synthesis of a chemical
Autoreceptors
Are metabotropic receptors that have two unconventional characteristics
Enzymatic degradation
Reuptake is the more common of the two deactivating mechanisms
The majority of neurotransmitter once released are drawn back into the presynaptic
Acetylcholinesterase
One of the few neurotransmitters for which enzymatic degradation is the main mechanism of synaptic deactivation
Gap junction
Are narrow spaces between adjacent neurons that are bridged by fine tubular channels called connexins that contain cytoplasm
Amino acid neurotransmitters
Glutamate, aspartate, glycine, and gamma aminobutyric acid GABA
The three classes of conventional neurotransmitter
The amino acids, the monoamines, and the acetylcholine
Acetylcholine
Is a small molecule neurotransmitter that is in one major respect like a professor who is late for a lecture
Soluble gas neurotransmitter
Includes nitric oxide and carbon monoxide, these neurotransmitters are produced in the neural cytoplasm and immediately diffuse through the cell membrane into the extracellular fluid and then into nearby cells
Endocannabinoids
Are neurotransmitters that are similar to delta 9 tetrahydrocannabinol
Pituitary peptides
Contains neuropeptides that were first identified as hormones released by the pituitary
Hypothalamic peptides
Contains neuropeptides that were first identified as hormones released by the hypothalamus
Brain gut peptides
Contains neuropeptides that were first discovered in the gut
Opioid peptides
Contains neuropeptides that are similar in structure to the active ingredients of opium
Miscellaneous peptides
Is a catch all category that contains all of the neuropeptide transmitters that do not fit into one of the other four categories
Agonists
Drugs that facilitate e effects of a particular neurotransmitter
Antagonists
Drugs that inhibit the effects of a particular neurotransmitter
Receptor blockers
Bind to postsynaptic receptors without activating them and in so doing block the access of the usual neurotransmitter
Atropine
Which is the main active ingredient of belladonna is a receptor blocker that exerts its antagonist effect by binding to muscarinic receptors
Botox
A neurotoxin released by a bacterium often found in spoiled food, is another nicotine antagonist
Endogenous
Occurring naturally within the body opioids have been discovered
Enkephalins means in the head
Endorphins which is a contraction of endogenous morphine
