Nerve impulses and synaptic transmission Flashcards
What are the 3 overlapping functions of the nervous system? Explain them.
- Sensory input. The nervous system uses its millions of sensory receptors to monitor changes occurring both inside and outside the body.
- Integration. The nervous system processes and interprets sensory input and decides what should be done at each moment
- Motor output. The nervous system activates effector organs—the muscles and glands—to cause a response, called motor output.
What are the different types of membrane channels?
- Leakage or nongated channels: are always open.
- Gated channels: changes shape to open and close the channel in response to specific signals
What are the 3 main types of gated channels? Explain them.
- Chemically gated channels; also known as ligand-gated channels, open when the appropriate chemical (in this case a neurotransmitter) binds
- Voltage-gated channels; open and close in response to changes in the membrane potential
- Mechanically gated channels; open in response to physical deformation of the receptor (as in sensory receptors for touch and pressure).
Generating a resting membrane potential depends on what?
(1) differences in K+ and Na+ concentrations inside and outside cells
(2) differences in permeability of the plasma membrane to these ions.
When do membrane potential changes occur?
- Concentrations of ions across membrane change
- Membrane permeability to ions changes
The terms depolarization and hyperpolarization describe changes in membrane potential relative … ?
to resting membrane potential
What are the two types of signals that changes in membrane potential can produce?
- Graded potentials—usually incoming signals operating over short distances that have variable (graded) strength
- Action potentials—long-distance signals of axons that always have the same strength
What is depolarization?
- A decrease in membrane potential
- The inside of the membrane becomes less negative (moves closer to zero) than the resting potential
What is hyperpolarization?
- an increase in membrane potential
- The inside of the membrane becomes more negative than the resting potential.
What is the membrane potential at rest within a neuron?
-70mV
If the membrane potential goes from -70mV to -95mV, is the neuron depolarized or hyperpolarized?
hyperpolarized since it became more negative
If the membrane potential goes from -70mV to 60mV, is the neuron depolarized or hyperpolarized?
depolarized because it became less negative
Why are graded potentials called “graded” ?
- Because their magnitude varies directly with stimulus strength.
- The stronger the stimulus, the more the voltage changes and the farther the current flows.
How are graded potentials triggered?
- by some change (a stimulus) in the neuron’s environment that opens gated ion channels.
T or F. A graded potential can only be depolarized but not hyperpolarized.
False. They can be either depolarized or hyperpolarized
Between graded potentials and action potentials, which is “brief, long-distance signals within a neuron” and which is “short-lived, localized changes in membrane potential”
Action potential - brief, long- distance signals within a neuron
Graded potential - short-lived, localized changes in membrane potential
Does strength decrease with distance during an action potential?
No, Strength does not decrease with distance because it is constantly being regenerated
What is the location of event of graded potentials?
Cell body and dendrites
What is the location of event of action potentials?
Axon
How does the central nervous system differ between weak and strong impulses?
by the frequency of impulses
*high frequency = stronger stimulus
Rate of Action Potential propagation (spread) depends on what two factors?
- Axon diameter - Larger-diameter fibers have less resistance to local current flow, so have faster impulse conduction
- Degree of myelination - Two types of conduction depending on presence or absence of myelin
What is the difference between continuous conduction and saltatory conduction?
- Continuous conduction: slow conduction that occurs in nonmyelinated axons
- Saltatory conduction: occurs only in myelinated axons and is about 30 times faster
Where are voltage-gated Na+ channels located?
At myelin sheath gaps
What is the role of myelin sheaths during action potentials?
to insulate and prevent leakage of charge
What are the three groups of nerve fibers? Describe them.
Group A fibers
- Largest diameter
- Myelinated somatic sensory and motor fibers of skin, skeletal muscles, and joints
- Transmit at 150 m/s (~300 mph)
Group B fibers
- Intermediate diameter
- Lightly myelinated fibers
- Transmit at 15 m/s (~30 mph)
Group C fibers
- Smallest diameter
- Unmyelinated
- Transmit at 1 m/s (~2 mph)
Which groups of nerve fibers include the ANS, visceral motor, and sensory fibers that serve visceral organs?
Group B and C
What is a synapse?
a junction that mediates information transfer from one neuron to the next or from a neuron to an effector cell
The neuron conducting impulses toward the synapse is the _____ _____, and the neuron transmitting the electrical signal away from the synapse is the ____ ____.
- presynaptic neuron
- postsynaptic neuron
What are the most common synapses?
- Axodendritic synapses: Synapses between the axon endings of one neuron and the dendrites of other neurons.
- Axosomatic synapses: Those between axon endings of one neuron and the cell body (soma) of another neuron
What are the less common synapses?
- Axoaxonal: synapses between axons
- Dendrodendritic: synapses between dendrites
- Somatodendritic: synapses between cell bodies and dendrites
What are the two types of synapses?
- Electrical synapses: are much less common than chemical synapses
- Chemical synapses: neuromuscular junction
How do chemical synapses transfer signals?
They convert electrical signals to chemical signals (neurotransmitters) that travel across the synapse to the postsynaptic cells, where they are converted back into electrical signals.
How are chemical synapses specialized?
specialized to allow the release and reception of neurotransmitters.
What are the two parts of a chemical synapse?
- An axon terminal (presynapse) that contains membrane-bound synaptic vesicles, that have neurotransmitter molecules
- A neurotransmitter receptor (postsynapse) located on a dendrite or the cell body
What are the first 3 steps (out of 6) of information transfer across chemical synapses?
- Action potential arrives at presynaptic axon terminal
- Depolarization of the membrane by AP opens the Na+ and voltage-gated Ca2+ channels
- Ca2+ entry causes synaptic vesicles fuse with the axon membrane to release neurotransmitter by exocytosis into the synaptic cleft.
What are the last 3 steps (out of 6) of information transfer across chemical synapses?
- Neurotransmitter bind to specific receptors on the postsynaptic membrane.
- This opens ion channels, creating graded potentials (either excited or inhibited).
- Neurotransmitter effects are terminated.
What is the difference between excitatory and inhibitory neurotransmitters?
- When neurotransmitters are excitatory (cause depolarization)
- neurotransmitters are inhibitory (cause hyperpolarization)
Which is inhibitory and which is excitatory between: GABA, glutamate, and glycine?
- GABA and glycine are inhibitory,
- Glutamate is excitatory.
What results in local net graded potential depolarization called EPSP
When the Na+ influx greater than K+ efflux
An EPSP is a local ___ of the postsynaptic membrane
depolarization
- EPSPs bring the neurons closer to the action potential threshold
An IPSP is a local ___ of the postsynaptic membrane
hyperpolarization
- IPSPs bring the neurons away from the action potential threshold
What happens to the postsynaptic membrane during an IPSP
Makes postsynaptic membrane more permeable to K+ or Cl–. This reduces postsynaptic neuron’s ability to produce an AP.
- If K+ channels open, it moves out of cell
- If Cl– channels open, it moves into cell
What is the difference between a direct and indirect postsynaptic receptor structure?
- Direct action: neurotransmitter binds directly to and opens ion channels
- Promotes rapid responses by altering membrane potential
- Indirect action: neurotransmitter acts through intracellular second messengers, usually G-protein pathways
- Broader, longer-lasting effects similar to hormones
What are the receptors involved in cell signaling?
- Channel-linked receptors
- G protein–coupled receptors
How does depolarization and hyperpolarization differ in channel-linked receptors?
- Depolarization : Channel-linked receptors are cation channels that allow small cations (Na+, K+, Ca2+) to pass, but Na+ entry contributes most to membrane depolarization.
- hyperpolarization : Channel-linked receptors that respond to GABA, glycine, and Cl− to pass, mediate fast inhibition (hyperpolarization).
Which cell synaptic transmission is faster between Channel-Linked Receptors and G protein–coupled receptors
Channel-linked receptors
What are some examples of G protein-linked receptors?
- Muscarinic ACh receptors
- Receptors that bind biogenic amines
- Receptors that bind neuropeptides
What happens when a neurotransmitter binds to a G protein–linked receptor
- Activating of G protein once the neurotransmitter binds
- Activated G protein controls production of second messengers, such as cyclic AMP, cyclic GMP, diacylglycerol, or Ca2+
- The second messengers can then:
– Open or close ion channels
– Activate kinase enzymes
– Phosphorylate channel proteins
– Activate genes and induce protein synthesis
What is the difference between the facilitated and discharge zone of neuronal pools
- Postsynaptic neurons in the discharge zone receive more synapses and are more likely to generate APs.
- Postsynaptic neurons in the facilitated zone receive fewer synapses and are facilitated (brought closer to threshold).
Describe serial processing.
- Input travels along one pathway to a specific destination
- System works in all-or-none manner to produce specific, anticipated response
- Example : spinal reflex
Describe parallel processing.
- Input travels along several pathways
- One stimulus promotes numerous responses
- Example: A sensed smell may remind one of an odor and any associated experiences
What are circuits? What are the four types of circuits?
- patterns of synaptic connections in neuronal pools
- Diverging
- Converging
- Reverberating
- Parallel after-discharge
What a diverging curcuit?
- When one input leads to many outputs
- an amplifying circuit
- a single neuron can activate 100s of motor neurons in the spinal cord which leads to 1000s of skeletal muscle fibers
What a converging curcuit?
- Many inputs lead to one out put
- a concentrating circuit
- Different sensory stimuli can all elicit the same memory
What a reverberating curcuit?
- Signal travels through a chain of neurons, each feeding back to previous neurons
- An oscillating ciruits
- Controls rhythmic activity
- Example: involved in breathing, sleep-wake cycle etc.
What is a parallel after-discharge circuit?
- A signal stimulates neurons arranged in parallel arrays that eventually converge on a single output cell.
- impulses reach output cell at different times
- The olfactory tracts have two destinations :
i) the olfactory cortex (inferior frontal lobe) smells are interpreted and identified and
ii) the limbic system (amygdala, and hippocampus) where memories and emotions associated with the smell are activated
