CNS and Action Potentials Flashcards
What are the two branches of the nervous system and what do they consist of?
Central: Brain and spinal cord
Peripheral: afferent and efferent neurons.
What is the difference between afferent and efferent neurons?
Afferent: stimulated by external stimulus to send signal to CNS for integration
Efferent: sends information to CNS through motor neurons to target cells
What is a neuron’s structure and function?
Structure: Soma (cell body) from which dendrites or axons protrude, high density of ion channels.
Function: Receive and send electrical signals and secrete signalling molecules (neurotransmitters and neurohormones)
How do nerve cells develop?
- Neurostem cells originating from the ectodermal layer mature into common progenitors.
- Common progenitors are stimulated to differentiate into either neuronal progenitors or glial progenitors
- Neuronal progenitors develop into neurons and glial progenitors develop into astrocytes or oligodendrocytes
What is the difference between a dendrite and an axon?
Dendrite: receive incoming signals, branched for high surface area for reception
Axons: carry outgoing electrical signals starting originating at the axon hillock
What are the type of neuron shapes?
Multipolar: many dendrites and branched axons
Pseudounipolar: Cell body located off one side of a long process due to fusion of dendrite with axon
Bipolar: single axon and dendrite coming off the cell body
Axonic: Lack identifiable axon but have numerous branched dendrites
How do afferent neurons, interneurons, and efferent neurons differ in function and structure?
Afferent: carry info about stimuli from receptors to CNS; pseudounipolar with cell bodies close to CNS
Interneurons: Site of integration between sensory and motor neurons; axonic/multipolar with complex branching axons and dendrites
Efferent: Send signal from CNS to target cells to perform a response; Multipolar with long sheathed axon.
What is found at the end of axons?
collateral: divisions of axon
Axon terminal: enlarged endings that store and release neurotransmitter
Varicosities: enlarged regions along axon of autonomic neurons that store and release neurotransmitter.
What is the difference between sensory nerves, motor nerves, and mixed nerves?
Sensory: bundles of afferent axons
Motor: bundles of efferent axons
Mixed: bundles of both afferent and efferent axons
What is axonal transport?
Motor protein (dynein) walking from soma ER along microtubule holding proteins in vesicles to transport the axon.
What are glial cells and what kinds are there?
Communicate with neurons and provide biochemical and structural support.
CNS: ependymal cells, astrocytes, microglia, oligodendrocytes,
PNS: schwann cells, satellite cells
What do schwann cells and oligodendrocytes do?
Support and insulate axons by forming myelin by squeezing out glial cytoplasm and wrapping around the axon. Gap junctions connect the membrane layers of myelin and allow the flow of nutrients and information from layer to layer.
What is the difference between an oligodendrocyte and a schwann cell?
Schwann cell: singular cell makes a singular myelin sheath, found in PNS
Oligodendrocyte: singular cell makes many segments of myelin, found in CNS
What is a satellite cell?
Nonmyelinating Schwann cell in PNS that form capsules around nerve cell bodies in ganglia.
What is an astrocyte?
Highly branched CNS glial cells that have many functions:
- surround blood vessels and become part of blood brain barrier
- produce trophic factors
- take up excess water and K+
-act as neural stem cells - pass lactate to neurons
What are microglia?
Specialized immune cells that reside in CNS that remove damaged cells and foreign invaders.
What do ependymal cells do?
Specialized cells that create a selectively permeable epithelial layer that separates the fluid compartments (ventricles) of the CNS and make neural stem cells.
What are trophic factors?
Chemicals for nourishment and promotion of growth and survival
What are two factors that influence the membrane potential?
Uneven distribution of ions and differing membrane permeability of those ions
What are the three categories of channels that act in response to stimuli and where do you find them?
Mechanically gated ion channels: found in sensory neurons and act in response to physical stimulus
Chemically gated ion channels: found in most neurons and bind to many ligands
Voltage gated ion channels: respond to changes in cell’s membrane potential
What is a graded potential?
Depolarization/hyperpolarization that travel over short distances and lose strength as they travel. Used for short distance communication (postsynaptic potentials), can be summed and long lasting, and intensity reflects the size of the stimulus with
What are action potentials?
Very fast and large depolarization that travel for long distances without losing strength and are used for their rapid signalling over long distances.
What is the difference between subthreshold and suprathreshold graded potential?
Sub: Graded potential starts above threshold, and by the time it reaches axon hillock, it is below the threshold and does not initiate action potential.
Supra: Graded potential starts above threshold and by the time it reaches axon hillock, it is still above the threshold and will initiate action potential.
What is local current flow? How does it relate to the loss of strength of graded potentials?
Local current flow is the wave of depolarization via entry of Na+. The depolarization dies out because of positive ion leakage channels as well as cytoplasmic resistance.
What are the steps of an action potential?
- Resting membrane potential
- Cell is depolarized at axon by graded potential due to stimulus
- Membrane depolarizes to threshold at axon hillock causing Voltage Na+ channels to open quickly and let Na+ in, and slowly opening K+ channels.
- Rapid entry of Na+ depolarizes cell greatly
- Na+ channels inactivate and K+ channels fully open due to positive voltage.
- K+ shoots out of cell, repolarizing the membrane
- remain open after repolarization, causing afrerhyperpolarization
- K+ channels close due to negative voltage and Na+ channels begin to recover
- Cell returns to resting ion permeability and resting membrane potential as Na_ channels fully recover.
What is the difference between the two gates on a voltage gated sodium channel?
In response to depolarization, activation gate opens and allows sodium into the cell. Inactivation gate closes after a delay and prevent Na+ from entering
What are the three patterns of action potentials and how are they formed?
Single AP: one action potential
Tonic AP: constant firing of action potential
Bursting AP: Few action potentials at once
How are action potentials conducted?
- From initial state of -70mV, Na+ from graded potential enters a trigger zone in axon hillock.
- Depolarization opens voltage gated Na+ channels which enter the axon and the initial segment of axon depolarizes
- Positive charge from depolarized trigger zone spreads via local current flow to adjacent sections of the membrane
- Membrane distal to trigger zone depolarizes from local current flow, Na+ channels open and allows Na+ into cell
- Refractory period prevents backwards conduction
What is the difference between hyperkalemia and hypokalemia?
Hyperkalemia: increase in blood K+ concentration results in a less negative membrane potential, bringing it closer to threshold mV which makes it more reactive.
Hypokalemia: decrease in blood K+ concentration results in a more negative membrane potential, bringing it farther from threshold mV which makes it less reactive.
Why is
unmyelinated: Na+ is attracted to nearby areas due to local flow and open more Na+ channels, but may leak. SLOWER.
myelinated: Na+ is released in one node of ranvier and must rush to another node of ranvier to open the Na+ gate. FASTER
Why is conduction faster in myelinated axons?
Myelin prevents leakage of Na+, keeping the momentum of the charge as it travels via local current flow.
What are two ways action potentials are conducted faster?
- Saltatory Conduction: Insulation separating voltage gated channels into nodes of Ranvier allowing the jump of action potential from one node to another.
- Larger diameter of axon allows no resistance form the membrane
What is Multiple Sclerosis?
Autoimmune disease characterized by the demyelination of CNS axons, causing multiple patterns of progression including relapsing-remitting and progressive phases. Some things thought to cause MS is the environment, viruses, genetics, and cerebral blood flow.
What are the symptoms and treatments of multiple sclerosis?
Symptoms: loss of balance, loss of speech, loss of vision, abnormal pupil reflexes, numbness, and pain.
Treatments: immunosuppressants, drugs to manage symptoms
What is the Guillain Barre syndrome?
Autoimmune disease characterized by the demyelination of PNS axons, resulting in the slowing and or loss of AP conduction that may take months to years to recover form. Caused by GI/lung infection and may be associated with chronic illness like lupus and HIV.
What are the symptoms and treatments of Guillain Barre syndrome?
Symptoms: tingling, weakness, pain in hands/feet, inability ot speak, paralysis, respiratory distress
Treatment: Plasmapheresis (removing antibodies from blood), immunoglobulin G (inactivate antibodies)
What is fugu poison?
Tetrodotoxin is an antagonist of voltage gated Na+ channels with high affinity, high specificity, efficiacy, and potency. It prevents entry of Na+ into cells through voltage gated channels.
What are the symptoms of fugu poison?
Intoxication 1: Numbness of lips and tongue, paraesthesia, headache, nausea, diarrhea, vomiting, reeling/walking issues.
Intoxication 2: increasing paralysis, respiratory distress, inability to speak, dyspnea, hypotension, convulsions, mental impairment, cardiac arrhythmia, death within 20min - 8 hours.
