Lesson 7 Nervous System Flashcards
What is the definition of Resting Membrane Potential (RMP)?
The baseline electrical potential difference across a cell membrane when the cell is at rest, typically -70 mV in neurons.
RMP is influenced by ion gradients and selective permeability of the membrane.
What mechanisms maintain the Resting Membrane Potential?
- Ion Gradients maintained by the Na⁺/K⁺ ATPase pump
- Selective Permeability of the membrane, primarily to K⁺
The Na⁺/K⁺ pump moves 3 Na⁺ out and 2 K⁺ in.
What is the absolute refractory period?
A period during which no action potential is possible due to inactivated Na⁺ channels.
This ensures unidirectional propagation and limits action potential frequency.
What is the role of neurotransmitters at a chemical synapse?
They are chemical messengers that bind to receptors on the postsynaptic membrane, causing graded potentials.
Neurotransmitter release is triggered by action potentials arriving at the presynaptic terminal.
What are the two types of synapses?
- Electrical synapses
- Chemical synapses
Electrical synapses allow direct current flow, while chemical synapses involve neurotransmitter release.
What characterizes Type A nerve fibers?
Large-diameter, myelinated fibers that conduct at 15 to 120 m/s.
They are responsible for motor neurons supplying skeletal muscles and most sensory neurons.
Fill in the blank: The process of _______ allows action potentials to be conducted rapidly between adjacent cells in electrical synapses.
gap junctions
Gap junctions are formed by connexons that allow graded current to flow.
What is spatial summation?
The process where multiple inputs lead to a graded potential that can reach action potential threshold.
It involves simultaneous stimulation from different neurons.
True or False: Hyperkalemia can lead to muscle weakness due to inactivation of Na⁺ channels.
True
Initially, hyperkalemia causes hyperexcitability, but severe cases can lead to muscle weakness.
What happens during depolarization in action potentials?
Voltage-gated Na⁺ channels open, allowing rapid influx of Na⁺.
This typically occurs when the membrane potential reaches the threshold of -55 mV.
What is the effect of neurotransmitter binding to ligand-gated ion channels?
It can produce either a depolarizing or hyperpolarizing graded potential in the postsynaptic membrane.
The effect depends on the type of ion channel that opens.
What is a local current in the context of action potentials?
A local current refers to the flow of ions that depolarizes adjacent areas of the axon, propagating the action potential.
This occurs due to the influx of Na⁺ in the depolarization phase.
What is the primary effect of local anesthetics like lidocaine?
They block Na⁺ channels, preventing action potentials in pain neurons.
This results in loss of sensation in the affected area.
What are graded potentials?
Local, variable-strength changes in membrane potential that can be depolarizing or hyperpolarizing.
They summate to trigger action potentials if the threshold is reached.
Describe the phases of action potentials.
- Depolarization
- Repolarization
- Hyperpolarization
- Return to RMP
Each phase corresponds to specific ion channel activities.
What determines the maximum frequency of action potential generation?
The refractory periods of the neuron.
Absolute refractory period prevents any action potentials, while relative refractory period allows them with stronger stimuli.
What is the clinical significance of multiple sclerosis (MS)?
Demyelination slows action potential conduction, leading to symptoms like optic neuritis and limb numbness.
MS affects the myelin sheaths of neurons in the central nervous system.
What neurotransmitter is predominantly affected in Myasthenia Gravis?
Acetylcholine (ACh)
Autoantibodies in Myasthenia Gravis destroy ACh receptors, reducing excitatory postsynaptic potentials.
What is the function of the Na⁺/K⁺ pump?
It maintains ion gradients by moving 3 Na⁺ ions out and 2 K⁺ ions in.
This is crucial for establishing and maintaining the resting membrane potential.
What is the significance of the synaptic cleft?
It is the space between the presynaptic terminal and the postsynaptic membrane where neurotransmitters diffuse.
This diffusion is essential for communication between neurons.
What are the three classification criteria for neurotransmitters?
Chemical structure, effect on the postsynaptic membrane, mechanism of action at their target.
What are the two main effects neurotransmitters can have?
- Excitatory
- Inhibitory
What is the ionotropic effect?
Binding to ion channels.
What is the metabotropic effect?
Binding to G-protein-linked receptors.
Which neurotransmitter is considered the best understood and most common?
Acetylcholine (ACh).
Name two classes of biogenic amines.
- Catecholamines
- Indoleamines
Provide examples of amino acid neurotransmitters.
- GABA
- Glycine
- Glutamate
What are purines in the context of neurotransmitters?
Nitrogen-containing compounds derived from nucleic acids; examples include adenosine and ATP.
What are neuropeptides?
Short chains of amino acids; include Substance P and endorphins.
What are gasotransmitters?
Examples include nitric oxide and carbon monoxide.
What is a key characteristic of neurotransmitter receptor molecules in synapses?
Neurotransmitter only ‘fits’ in one receptor.
True or False: Neurotransmitters affect all cells in the body.
False.
What happens to norepinephrine after it is released into the synaptic cleft?
It is taken up by the presynaptic terminal, preventing further binding to its receptor.
What enzyme breaks down some norepinephrine molecules?
Monoamine oxidase (MAO).
How does myelination affect the speed of conduction in neurons?
Faster in myelinated than in non-myelinated due to jumping from one node of Ranvier to the next.
What is saltatory conduction?
The action potential seems to jump from node to node, increasing the speed of conduction.
What causes local currents in myelinated axons?
An action potential at a node of Ranvier generates local currents.
What is the absolute refractory period?
No action potential can be produced by a stimulus, no matter how strong.
What is the significance of the relative refractory period?
A stronger-than-threshold stimulus can initiate another action potential.
Fill in the blank: The size of a graded potential is proportional to the strength of the _______.
[stimulus]
What are the four phases of action potentials?
- Depolarization
- Repolarization
- Afterpotential
- Return to resting potential
What is the all-or-none principle in action potentials?
As long as the stimulus is greater than threshold, an action potential will occur, regardless of stimulus strength.
What happens during depolarization of an action potential?
Increased membrane permeability to Na+ and movement of Na+ into the cell.
What is the role of voltage-gated Na+ channels during repolarization?
They close, stopping Na+ movement into the cell and increasing K+ movement out of the cell.
What is afterpotential?
A period of hyperpolarization that occurs because voltage-gated K+ channels remain open longer than needed.
What is the mechanism for hyperpolarization due to chloride ions?
Chloride ions diffuse into the cell, adding negative charges.
What determines the frequency of action potentials?
Stimulus strength.
What is the difference between a threshold stimulus and a subthreshold stimulus?
Threshold stimulus causes a graded potential that initiates an action potential; subthreshold does not.
What is the effect of botulism?
Inhibition of ACh secretion
ACh stands for acetylcholine, a neurotransmitter involved in muscle activation.
What is the effect of tetanus?
Inhibition of ACh breakdown
This leads to sustained muscle contractions.
What type of neurotransmitter is serotonin?
Biogenic amine
Primarily acts as an inhibitory neurotransmitter in CNS synapses.
What is the primary function of dopamine in the CNS?
Mood regulation
Dopamine can have excitatory or inhibitory effects depending on the synapse.
How does cocaine affect dopamine levels?
Increases extracellular dopamine levels by blocking reuptake
This leads to feelings of euphoria.
What is norepinephrine’s role in the nervous system?
Excitatory neurotransmitter in some CNS and ANS synapses
Most sympathetic targets respond to norepinephrine.
What is the effect of amphetamines on norepinephrine?
Increase extracellular norepinephrine and dopamine levels by blocking reuptake
This also leads to feelings of euphoria.
What type of neurotransmitter is GABA?
Amino acid, mostly inhibitory
GABA receptors can be ionotropic or metabotropic.
What is the effect of alcohol on GABA receptors?
Makes GABA receptors less sensitive
This can worsen withdrawal symptoms such as anxiety and tremors.
What neurotransmitter is glycine and its function?
Inhibitory amino acid in CNS synapses
Its inhibition can lead to increased excitability of neurons.
What is the main excitatory neurotransmitter in the brain?
Glutamate
Important for learning and memory.
What is the role of adenosine in the CNS?
Inhibitory neurotransmitter important in learning and memory
Prevents glutamate release during a stroke, providing a neuroprotective effect.
What is the function of substance P?
Excitatory neurotransmitter in descending pain pathways
Morphine can block the release of substance P, reducing pain.
How do endorphins affect pain?
Inhibitory neurotransmitters that reduce pain by blocking substance P release
They also produce feelings of euphoria.
What is the effect of nitric oxide (NO) on blood vessels?
Causes vasodilation
This effect is important for erectile function and is targeted by medications like Viagra.
What are endocannabinoids and their role?
Inhibitory neurotransmitters important in learning, memory, appetite, and nausea control
They are targeted by the active ingredient in marijuana.
What occurs during an excitatory postsynaptic potential (EPSP)?
Depolarization occurs and response is stimulatory
This may lead to action potential if threshold is reached.
What is the resting membrane potential of a neuron?
-70 millivolts
This is the typical voltage when a neuron is not actively firing.
What happens during depolarization?
Membrane potential moves toward zero, potentially producing an action potential
This involves the influx of sodium ions.
What is repolarization in the context of action potentials?
Return of membrane potential to resting state after depolarization
Potassium ions exit the cell during this phase.
What is the refractory period?
Time during which a neuron cannot fire another action potential
Divided into absolute and relative refractory periods.
What is graded potential?
Changes in membrane potential that vary in size
These can summate to trigger an action potential.
What is the role of voltage-gated ion channels?
Regulate the flow of ions across the membrane during action potentials
Sodium and potassium channels are crucial for depolarization and repolarization.
What is the relationship between stimulus strength and action potential frequency?
Higher stimulus strength increases the frequency of action potentials
This relationship is critical for signal transmission in neurons.
What initiates the communication between neurons?
Graded potential generated at the synapse
This occurs before depolarization at the axon hillock.
What happens at the synapse during neurotransmitter release?
Neurotransmitters cross the synaptic cleft to bind with postsynaptic receptors
This initiates a response in the target neuron.
What is the first step in the norepinephrine release process?
The released norepinephrine crosses the synaptic cleft and enters the presynaptic terminal with a sodium ion.
What happens to some norepinephrine after its release?
Some norepinephrine is reused; it enters the synaptic vesicle and is expressed out into the synaptic cleft.
What role does MAO play in norepinephrine metabolism?
MAO breaks down some norepinephrine, which becomes inactive metabolites.
What is the first step in the acetylcholine (ACh) release process?
The release of ACh from the channels in the postsynaptic membrane.
What enzyme breaks down ACh in the postsynaptic membrane?
Acetylcholinesterase.
What are the products of ACh breakdown?
Choline and acetic acid.
How is new ACh formed in the presynaptic terminal?
Choline and sodium ions enter the presynaptic terminal and combine with Acetyl-CoA.
What is the structure of a chemical synapse?
It consists of a presynaptic terminal, synaptic cleft, and postsynaptic membrane.
What is the function of voltage-gated calcium ion channels in the presynaptic terminal?
They allow calcium ions to enter the presynaptic terminal when the action potential arrives.
What happens when neurotransmitters reach the postsynaptic membrane?
They bind to receptor sites and can open chemically gated sodium channels.
What is a gap junction?
A space between two plasma membranes connected by connexons.
What is the function of connexons in electrical synapses?
They allow the action potential to pass directly from one cell to another.
What is saltatory conduction?
The propagation of action potentials along myelinated axons, jumping from node to node.
What is the role of the Nodes of Ranvier in saltatory conduction?
They are the points where action potentials are generated in a myelinated axon.
What occurs during the absolute refractory period in an axon?
It prevents another action potential from occurring towards the site of the next action potential.
What is the resting membrane potential?
The electrical potential difference across the cell membrane when a neuron is at rest.
What is the role of astrocytes in the central nervous system?
They provide structural support and regulate the movement of substances from blood to tissue.
What are the functions of ependymal cells?
They line ventricles of the brain and the central canal of the spinal cord, helping to move and secrete cerebrospinal fluid.
What are the types of neuronal pathways?
- Serial pathway
- Convergent pathways
- Divergent pathways
- Reverberating circuit
- Parallel after-discharge circuit
What is a convergent pathway?
A pathway where multiple inputs funnel into one neuron for integration and decision-making.
What is a divergent pathway?
A pathway where one neuron synapses with many other neurons, amplifying the signal.
What is a reverberating circuit?
A circuit that causes reciprocal activation, essential for processes like breathing.
What is a parallel after-discharge circuit?
A circuit where a single neuron sends impulses through multiple parallel pathways converging on a common output neuron.
What is temporal summation?
The process where two action potentials arrive in close succession at the presynaptic membrane.
What is spatial summation?
The process where action potentials from different presynaptic neurons combine to produce a graded potential.
What is the role of neuromodulators?
They influence the likelihood of an action potential being produced in the postsynaptic cell.
What is presynaptic inhibition?
The reduction in the amount of neurotransmitter released from the presynaptic terminal.
What is presynaptic facilitation?
The increase in the amount of neurotransmitter released from the presynaptic terminal.
What characterizes an inhibitory postsynaptic potential (IPSP)?
Hyperpolarization that decreases the likelihood of an action potential.
What is the difference between myelinated and unmyelinated axons?
Myelinated axons have a myelin sheath that increases conduction speed, while unmyelinated axons do not.
What is a multipolar neuron?
A neuron with many dendrites and one axon.
What is a bipolar neuron?
A neuron with one dendrite and one axon.
What is a pseudo-unipolar neuron?
A neuron that appears to have an axon and no dendrites.
What is an anaxonic neuron?
A neuron with multiple dendrites but no axon.
What is an anaxonic neuron?
An anaxonic neuron has multiple dendrites but no axon.
What are the main components of a neuron?
Neuron cell body, dendrites, axon.
What is the function of dendritic spines?
Dendritic spines are small projections in the dendrites that receive synaptic inputs.
What is the role of the Golgi apparatus in a neuron?
The Golgi apparatus is involved in processing and packaging proteins.
What is the function of mitochondria in neurons?
Mitochondria provide energy through ATP production.
What are Nissl bodies?
Nissl bodies are rough endoplasmic reticulum and ribosomes involved in protein synthesis.
Where does the axon emerge from the neuron?
The axon emerges from the axon hillock.
What is the myelin sheath?
The myelin sheath is a protective covering that insulates the axon.
What are Schwann cells?
Schwann cells are responsible for forming the myelin sheath in the peripheral nervous system.
What is the node of Ranvier?
The node of Ranvier is the space between segments of the myelin sheath where the axon is exposed.
What is the function of presynaptic terminals?
Presynaptic terminals release neurotransmitters into the synaptic cleft.
What does the central nervous system (CNS) consist of?
The CNS consists of the brain and spinal cord.
What is the function of the sensory division of the peripheral nervous system (PNS)?
It receives sensory input and transfers it to the CNS.
What are the two divisions of the motor division of the PNS?
- Somatic nervous system
- Autonomic nervous system
What is the role of the somatic nervous system?
The somatic nervous system controls voluntary movements of skeletal muscles.
What is the function of the autonomic nervous system (ANS)?
The ANS regulates involuntary functions such as heart rate and digestion.
Fill in the blank: The major influence on the resting membrane potential is _______.
potassium ions
What is depolarization?
Depolarization is a change in membrane potential that makes the inside of the cell more positive.
What are astrocytes?
Astrocytes are star-shaped glial cells that support neurons and regulate extracellular fluid composition.
What is the function of ependymal cells?
Ependymal cells line brain ventricles and secrete cerebrospinal fluid.
What is the role of oligodendrocytes?
Oligodendrocytes form myelin sheaths around axons in the CNS.
What are microglia?
Microglia are specialized macrophages in the CNS that respond to inflammation.
What are the three functional classifications of neurons?
- Sensory (afferent)
- Motor (efferent)
- Interneurons
What is a multipolar neuron?
Multipolar neurons have multiple dendrites and are the most common type in the CNS.
What is unique about bipolar neurons?
Bipolar neurons have two processes and are often found in sensory organs like the retina.
What does retrograde transport in neurons involve?
Retrograde transport moves substances from the axon terminals back to the cell body.
What is the primary concern in oligodendrocyte pathology?
Demyelination, which can occur in conditions like Multiple Sclerosis.
What is Guillain-Barré Syndrome?
An acute autoimmune disorder that attacks peripheral nerves and leads to demyelination.
What is Guillain-Barré Syndrome (GBS)?
An acute autoimmune disorder where the immune system mistakenly attacks peripheral nerves’ Schwann cells, leading to demyelination.
Symptoms include rapid onset of weakness, sensory changes, and potential respiratory failure, often following an infection.
What are voltage-gated ion channels?
Channels that open or close in response to specific, small voltage changes across the cell membrane.
At rest, the membrane is negative inside relative to outside.
What is the function of ligand-gated ion channels?
They open or close in response to a ligand such as a neurotransmitter or hormone binding to receptor protein.
Receptor proteins are usually glycoproteins.
What are leak ion channels?
Also called nongated ion channels; always open and responsible for permeability when the membrane is at rest.
More leak ion channels are present for potassium than for sodium.
What does the sodium-potassium pump do?
It actively pumps sodium out of the cell and potassium into the cell for each ATP molecule used.
Neurons expend ATP to maintain the uneven distribution of ions across the membrane.
What establishes the resting membrane potential?
The resting membrane potential exists due to:
* Permeability characteristics of the membrane
* Differences in ion concentrations on each side of the membrane.
The potential difference ranges from −70 to −90 mV.
What occurs during depolarization?
The inside of the cell becomes more positive, for example, from −70mV to −55mV.
Sodium ions are the most common factor leading to depolarization.
What is the primary characteristic responsible for the resting membrane potential?
The plasma membrane is 50–100 times more permeable to potassium ions (K+) than to sodium ions (Na+).
This is due to the presence of K+ leak channels.
Fill in the blank: The sodium-potassium pump maintains the uneven distribution of ______ across the plasma membrane.
ions
True or False: The outside of the plasma membrane becomes negatively charged due to the sodium-potassium pump.
False.
The outside becomes more positively charged.
What are the two types of axons discussed?
Myelinated axons and unmyelinated axons.
Myelinated axons are insulated and speed up transmission, while unmyelinated axons rest in invaginations of glial cells.
What is the function of Schwann cells?
They wrap around portions of only one axon to form myelin sheath and provide support, nutrients, and protection.
The outer layer is the neurilemma.
What changes occur in a cut nerve?
Degenerative changes include:
* The axon distal from the cut breaks into segments
* Macrophages invade to phagocytize the myelin
* Schwann cells enlarge and form a column for regeneration.
Regeneration in the CNS is limited compared to the PNS.
What is gray matter composed of?
Unmyelinated axons, cell bodies, and dendrites.
It is involved in integrative functions.
What is white matter composed of?
Myelinated axons that propagate action potentials.
It consists of axon tracts connecting different areas of gray matter.
What role do oligodendrocytes play in the CNS?
They produce and maintain the myelin sheath around axons.
Oligodendrocytes do not produce columns of cells to guide growing axons like Schwann cells do.
What determines the ionic concentration differences across a membrane?
The sodium-potassium pump and membrane permeability.
High concentrations of sodium ions are outside the cell, while potassium and proteins are inside.
