CNS And Action Potentials Flashcards
What are specialized for communication in the nervous system
Neurons
Glia
The nervous system consists of ____ and____
The peripheral nervous system
The central nervous system
The peripheral nervous system consists of what
Sensory division
Efferent division
Sensory division sends ____
Efferent division takes ___
Information to the CNS through afferent neurons
Information from the CNS to target cells via efferent neurons
Define neurons
Specialized to carry electrical signals and communicate with other cells
High density of ion channels
Special transport mechanisms to move materials from one end to the other
Secrete signalling molecules (neurotransmitter and neurohormones)
What are the four types of neurons
Pseudounipolar (sensory neurons)
Bipolar (sensory neurons)
Anaxonic (interneurons)
Multipolar (efferent and interneurons)
What are the types of glia in the CNS
Oligodendrocytes
Ependymal cells
Microglia
Astrocytes
What are the types of glia in the PNS
Satellite cells
Schwann cells
Oligodendrocytes
Myelinate axons
Line ventricles and make neural stem cells
Ependymal cells
What are the immune cells of the CNS
Microglia
Astrocytes
Blood brain barrier
Trophic factors
Take up excess water and K
Neural stem cells
Pass lactate to neurons
What do Schwann cells do
Myelinate axons
What do satellite cells do
Trophic factors
Membrane potential will change if ion channels _____ and allow _____
Open
Ions to move across the cell membrane
How are ion channels on neurons classified according to
Ions they carry
Where on the cell they are located
Gating mechanisms
What are the 5 ion channel gating mechanisms
1) voltage gated ion channel
2) receptor channels
3) phosphorylation gated
4) stretch gated
5) temperature gated
What are voltage gated ion channels
Changes in membrane potential open the channel
What are receptor channels
(Ligand gated ion channels)
Gate when they bind a ligand
Opening and closing of ion channels causes ___
Rapid changes in membrane potential
Explain graded potentials
Signals communicated from one neuron to the next are graded potentials
Small subthreshold changes in membrane potential
Can be depolarizing or hyperpolarizing
Passive
Proportional to the size of the stimulus
Caused by the flow of ions through a few ion channels
Gradually dissipate as they travel through a cell
Can be summed
Postsynaptic potentials
Signals communicated from one neuron to the next are graded potentials
The graded potential travels like a ripple on a pond and it moves ____ from the source and degrades as it moves ___ away
Outward
Farther
Takes time to get from synapse to the axon hillock
Why does the signal degrade (eventually to nothing)
Electrical resistance in the cytoplasm
The cell membrane is leaky to ions
Explain action potentials
Wave of depolarization that propagates across neuronal membrane (regenerative)
All of one
FAST (often called a spike AP)
Large amplitude about 100 mV
Always depolarizing
Requires the membrane be depolarized past a threshold
There is a refractory period
CANNOT BE SUMMED
In neurons site of AP generation is the axon hillock
Explain the ionic basis of the action potential
Starts at RMP (-70) Cell is depolarized by graded potential Membrane depolarizes to threshold (-55) - voltage gated Na channels open quickly and Na enters - voltage gated K channels open slowly The rapid Na entry depolarized the cell Na channels stop and K channels open fully K Leaves the cell K channels hyperpolarizes the cell K closes and Na recoverers
What causes repolarization
Or hyperpolarization
When K leaves the cell
What is the absolute refractory phase
What is the relative refractory phase
Rising and falling phase
Recovery phase
How will changes in extracellular K influence transmission of action potentials
Hyperkalemia
Hypokalemia
Hyperkalemia
- RMP is depolarized
- smaller stimulus will bring cell to threshold
Hypokalemia
- RMP is hyperpolarized
- requires larger stimulus to bring cell to threshold
The action potential is conducted from the ___ to the ___
Soma
Terminals
What is local current flow (unmylenated axons)
A section of axon depolarizes
Positive charges move by local current flow into adjacent sections of the cytoplasm
On the extracellular surface current flows towards the depolarized region
Initial state of unmylenated action potentials
Normal ion gradients RPM -80
Very high density of Na channels at the axon hillock
Voltage gated Na and K channels distributed along the axon
What is the trigger zone on an unmylenated axon
Axon hillock
Once the initial state of AP on unmylenated axons occur what happens
Voltage gated Na channels open and Na enters the axon (causing depolarization)
Positive charge flows into adjacent sections of the axon by local current flow
Local current flow from the active region causes new sections of the membrane to depolarize
How does the depolarization occur on an unmylenated axon
Some Na is attracted to the nearby areas (LOCAL CURRENT FLOW)
This causes depolarization of the nearby axon to its threshold (the hillock is now refractory)
Na enters the axon causing depolarization and this depolarizes ____ to the threshold
The adjacent segment
Myelin is formed from concentric layers of _____ cell membrane and they are excellent __
Glial
Insulators
What does Mylen do for the axon
Increases electrical efficiency of the axons
What are the Mylenations separated by
Nodes of ranvier
What are found at the nodes of ranvier
Very high density Na channels
K channels are found nearby
What type of conduction do AP travel on mylenated axons
Saltatory conduction
What does saltatory conduction mean
The action potential travels by jumping node to node (instead of travelling like a wave)
What are demylenated diseases (what happens)
Degeneration of the mylen sheath
Conduction slows when the current leaks out
What are the two ways to speed up velocity of AP along an axon
Increase axon diameter
Mylenation
How does increasing the axon diameter help AP move faster
Increases velocity because as the axon radius becomes larger internal resistance decreases
How does mylenation make AP move faster
Increases velocity because insulted areas mean less leakage of Na and K
Also means less ATP used
Mylenation allows axons to be smaller so you can fit more into a space
What is demyelination disease
Multiple sclerosis
Guillain barre syndrome
What is multiple sclerosis
Autoimmune disease
Unknown cause
Demyelination of CNS axons
Multiple patterns of progression
What are symptoms of multiple sclerosis
What are treatments
Loss of balance loss of speech loss of vision abnormal pupil reflexes numbness pain
Immunosuppressants and other drugs as indicated by symptoms
What is guillain barre syndrome
Autoimmune days after a seemingly minor GI or lung infection
May also be associated with chronic illness such as lupus HIV
Demyelination of sensory and motor and autonomic axons (PNS)
Slowing or loss of AP conduction
What are symptoms of guillain barre syndrome
Tingling weakness pain in hands and feet
Inability to speak paralysis and respiratory distress
What are treatments of guillain barre syndrome
Plasmapheresis (to remove antibodies from blood) and immunoglobulin G to inactivate circulating antibodies
Most people survive but recovery may take months to years
What is fugu poisoning
Kills 30-100 people a year
Tetrodotoxin comes from pufferfish and several other species
Fugu is a very specific antagonist of voltage gated Na channels
Prevents entry of Na into cells
Prevents AP in neurons and muscles
What other anesthetic also block voltage gated Na channels
Lidocaine
Benzocaine
