Lecture 11 Flashcards
what are neurons?
-nerve cells that transfer information within the body
what are the 2 types of signals neurons use to communicate?
-electrical signals
-chemical signals
what are the features of electrical signals?
-long distance
-mostly intracellular (within cells)
what are the features of chemical signals?
-short distance
-intercellular (outside/between cells)
what does interpreting signals involve?
-sorting complex sets of paths and connections
where does the processing of information take place?
-ganglia
-brain
what are ganglia?
-simple clusters of neurons
what is the brain?
-complex organization of neurons
what do neurons exemplify?
-the relationship between form and function that arises during evolution
where are most of the neurons organelles?
-cell body (soma)
what are the main parts of a neuron?
-body
-axon
-axon hillock
-dendrites
-synaptic terminals
what are dendrites?
-highly branched extensions that receive signals from other neurons
what is the axon?
-a longer extension that transmits signals to other cells at synapses
what is the axon hillcock?
-cone shaped base of an axon
-connects the axon to the cell body
what do synaptic terminals do?
-pass information across the synapse as chemical messengers
-chemical messengers are neurotransmitters
what is a synapse?
-junction between an axon and another cell
what is the basic path of where information is transmitted?
-from a presynaptic cell to a postsynaptic cell
what is a presynaptic cell?
-neuron
what is a postsynaptic cell?
-neuron
-muscle cell
-gland cell
what nourishes or insulates most neurons?
-glial cells
what are the 3 processes that the nervous system goes through to process information?
-sensory input
-integration
-motor output
what is the role of sensors?
-detect external stimuli and internal conditions
-transmit information along sensory neurons
where is sensory information sent? what occurs at this stage?
-the brain or ganglia
-interneurons integrate the information
-a motor output is created
how does the motor output leave the brain/ganglia? what does this output trigger?
-leaves via motor neurons
-triggers muscle or gland activity
what are the features of the central nervous system?
-includes the brain and nerve cord (spinal cord)
-where integration takes place
what are the features of the peripheral nervous system?
-includes everything else
-carries information in and out of the CNS
what do the bundled neurons of the PNS form?
-nerves
what is membrane potential?
-the voltage across a cell’s plasma membrane
what is voltage?
-difference in electrical charge
what is resting potential?
-the membrane potential of a neuron that is not sending signals
what do changes in membrane potential act as?
-signals
-transmitting and processing of information
what are the concentrations of ions in and out of a mammalian neuron at resting potential?
-[] of K+ is highest inside the cell
-[] of Na+ and Cl- is highest outside the cell
how are the K+ and Na+ gradients maintained? what do they represent?
-sodium-potassium pumps using ATP
-represent chemical potential energy
what converts chemical potential to electrical potential?
-the opening of ion channels in the plasma membrane
what are the relative amounts of open K+ and open Na+ channels in a neuron at resting potential?
-many open K+ channels
-few open Na+ channels
what results from the many open K+ channels?
-K+ is diffused out of the cell
-results in a buildup of negative charge and negatively charged proteins within the neuron
-act as a major source of membrane potential
at equilibrium what gradients are balanced?
-electrical and chemical
what is the equilibrium potential? what equation calculates this
-the membrane voltage for a particular ion at equilibrium
-nernst equation
is the equilibrium potential of K+ positive or negative? what about Na+
-K+ is negative
-Na+ is positive
what is known about the K+ and Na+ currents in a resting neuron? what about the resting potential?
-they are equal and opposite each other
-the resting potential across the membrane is steady
why do membrane potential changes occur?
-neurons contain gated ion channels
-they open or close in response to stimuli
who measures and how is membrane potential measured?
-electrophysiologists
-intracellular recording
what does the resting membrane potential of a neuron depend on?
-the net movement of ions in and out of the cell
what happens to the membrane when positive ions move in to cell (negative ions move out)? give an example.
-membrane becomes less polarized/depolarized
-Na+ channels open and Na+ moves in to the cell
what happens to the membrane when positive ions move out of the cell (negative ions move in)? give an example.
-membrane becomes more polarized/hyperpolarized
-K+ channels open and K+ moves out of the cell
what are graded potentials?
-changes in polarization where the magnitude of the change varies with the strength of the stimulus
-NOT NERVE SIGNALS
what will graded potentials have an effect on?
-the generation of nerve signals
what creates an action potential?
-a depolarization that shifts the membrane potential sufficiently
-massive change in membrane voltage
what are features of action potentials?
-constant magnitude
-all or none
-transmit signals over long distances
how do action potentials arise?
-some ion channels are voltage gated
what does it mean for an ion channel to be voltage gated?
-open or close when the membrane potential passes a certain level
what is the first stage of generating an action potential?
-most voltage gated sodium and potassium channels are closed
-at resting potential
what is the third stage of generating an action potential?
-the threshold is crossed
-membrane potential increases
what is the second stage of generating an action potential?
-voltage gated sodium channels open first
-sodium flows into the cell
-rising phase
what is the fourth stage of generating an action potential?
-voltage gated sodium channels inactivate
-voltage gated potassium channels open
-potassium flows out of the cell
-falling phase
what is the fifth stage of generating an action potential?
-membrane permeability to potassium is higher than at rest
-voltage gated potassium channels close
-resting potential is restored
-the undershoot
what is the refractory period? what does it result from?
-period after an action potential where a second action potential cannot be initiated
-results from sodium channel inactivation
where is an action potential usually generated?
-the axon hillock
where do action potentials travel?
-toward the synaptic terminals
-only travels in one direction
what happens to the neighbouring region of the axon membrane during action potential conduction?
-an electrical current depolarizes it
what prevents the action potential from travelling backwards?
-inactivated sodium channels behind the depolarization zone
what will increase the speed of an action potential?
-an increase in the axons diameter
-insulation
what insulates axons in vertebrates?
-myelin sheath
what forms the myelin sheath?
-glial cells
-oligodendrocytes in the CNS
-schwann cells in the PNS
in which regions of the axon are action potentials formed? why here?
-nodes of ranvier
-voltage gated sodium channels are found here
what are nodes of ranvier?
-gaps in the myelin sheath
what saltatory conduction?
-the process that describes how action potentials skip from node to node
what occurs at electrical synapses?
-electrical current flows from one neuron to another through gap junctions
what occurs at chemical synapses?
-a chemical neurotransmitter carries information between neurons
what type of synapses are most common?
-chemical synapses
what is the pathway of the neurotransmitter from the presynaptic to postsynaptic?
-presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles
-neurotransmitter will diffuse across the synaptic cleft and be received by the postsynaptic cell
where are synaptic vesicles located?
-in the synaptic terminal
what causes the release of the neurotransmitter in order for it to be received by the postsynaptic cell?
-the action potential
what does direct synaptic transmission involve?
-binding of neurotransmitters to ligand-gated ion channels in the postsynaptic cell
what causes the generation of a postsynaptic potential?
-the neurotransmitter binding
-it will open ion channels
what are the two categories of postsynaptic potentials?
-excitatory postsynaptic potentials (EPSPs)
-inhibitory postsynaptic potentials (IPSPs)
what are excitatory postsynaptic potentials?
-depolarizations that bring the membrane potential toward the threshold
what are inhibitory postsynaptic potentials?
-hyperpolarizations that bring the membrane potential farther from the threshold
what is typical of most neurons to have on their dendrites and cell body?
-many synapses
what will happen if a single EPSP is produced?
-nothing usually
-too small to trigger an action potential in the postsynaptic neuron
what will happen if 2 EPSP’s are produced?
-if produced in rapid succession, an effect called temporal summation occurs
what is the difference between temporal summation and spatial summation?
-temporal summation = same synapses on the same postsynaptic neuron in rapid succession
-spatial summation = different synapses on the same postsynaptic neuron produced simultaneously
what will trigger an action potential in terms of EPSPs?
-a combination of EPSPs through spatial and temporal summation
what will an IPSP do through summation?
-counter the effect of an EPSP
what determines whether an axon hillock will reach threshold and generate an action potential?
-the summed effect of EPSPs and IPSPs
how are neurotransmitters cleared from the synaptic cleft?
-inactivation by enzymatic hydrolysis
-recapture by the presynaptic neuron
what can be said about a molecules shape?
-very important to its function
-determined by the position of its atoms valence orbitals
what happens when a neurotransmitter binds to a receptor that is metatropic?
-movement of ion channels now depend on one or more metabolic steps
-activates a signal transduction pathway in the postsynaptic cell which involved a second messenger
how do ligand-gated channels compare to second messenger systems?
-the effects of second messenger systems have a slower onset but last longer
how many different receptors may a single neurotransmitter bind to?
-more than a dozen
what two effects can neurotransmitters have on postsynaptic cells?
-excite postsynaptic cells
-inhibit postsynaptic cells
what is acetylcholine?
-common neurotransmitter in vertebrates and invertebrates
-for muscle stimulation
-for memory formation
-for learning
what are the two major classes of acetylcholine receptors in vertebrates?
-ligand gated receptor
-metabotropic receptor
what toxins disrupt acetylcholine?
-nerve gas
-sarin
-botulism toxin (produced by certain bacteria)
what are 4 classes of neurotransmitters?
-amino acids
-biogenic amines
-neuropeptides
-gases
where are amino acid neurotransmitters active? what are some examples?
-active in the CNS + PNS
-ex: glutamate, GABA, Glycine (all active in the CNS)
where are biogenic amines active? what are some examples?
-active in the CNS + PNS
-ex: epinephrine, norepinephrine, dopamine, serotonin
what are neuropeptides? what are their key aspects?
-relatively short amino acid chains
-include substance P and endorphins (affect pain perception)
what will bind to the same receptors as endorphins and act as painkillers?
-opiates
what neurotransmitter gases are active in the PNS? what are their key aspects?
-nitric oxide (NO) + carbon monoxide (CO) (local regulators)
-NO is not stored in cytoplasmic vesicles, synthesized on demand
-broken down soon after production
-vertebrates synthesize small amounts of CO (deadly to inhale it normally)
where are most neurotransmitters stored?
-cytoplasmic vesicles
what does neuron organization and structure reflect?
-function in information transfer
what establishes the resting membrane potential of a neuron?
-ion pumps + channels
where do neurons communicate with each other?
-at synapses
