Unit 1 Nerve Cells and Impulses Flashcards
What is the absolute refinery period?
a time when the membrane is unable to produce an action potential because sodium channels are closed. It is the first phase of the refractory period.
Define action potential
all-or-none message sent by an axon.
all-or-non law
principle that the amplitude and velocity of an action potential are independent of the stimulus that initiated it
concentration gradient
difference in distribution of ions across the neuron’s membrane. it is one of the forces that acts on the sodium and potassium ions
depolarize/depolarization
to reduce polarization toward zero across a membrane. Happens right before action potential peal when NA+ channels open, and rushes into the neuron.
Electrical Gradient
a difference in electrical charge between the inside and outside of the cell
Graded potential and when does it happen
a membrane potential that varies in magnitude in proportion to the intensity of the stimulus (happens when a local neuron receives information from other neurons)
Hyperpolarization and when does it happen in the actional potential process
increased polarization (increasing neg charge inside neuron) final stage of action potential due to potassium leaving
local anesthetic
drugs, such as Novocain, that attaches to the sodium channels of the membrane, stopping action potentials
Local Neurons
Neurons without an axon, and neurons that don’t follow the all-or-none law
Myelin
an insulating material composed of fats and proteins
myelinated axons
axons covered with myelin sheaths
polarization
difference in electrical charges between the inside and outside of the cell
propagation of the action potential
transmission of an action potential down an axon
Refractory period
time when the cell resists the production of further action potentials, results of sodium gates shutting at peak of action potential
prevents continuous action potentials
relative refractory period
2nd part of refractory period/time after absolute refractory period that requires a stronger stimulus to initiate an action potential due to potassium (K+) flowing out at a higher rate
resting potential
condition of a neuron’s membrane when it has not been stimulated or inhibited
saltatory condition
the jumping of action potentials from node to node
selective permeability
ability of some chemicals to pass more freely than others through a membrane
sodium-potassium pump
Protein complex that actively transports sodium ions out of the cell while drawing in two potassium ions,
threshold
minimum amount of membrane depolarization necessary to trigger an action potential
voltage gated channels
membrane channel whose permeability to sodium (or some other ion) depends on the voltage difference across the membrane
active transport
a protein mediated process that expends energy to pump chemicals (i.e. glucose, amino acids, vitamins, iron) from the blood into the brain
afferent axon
a type of axon that brings information INTO the structure (**remember/HINT ** = admit)
astrocytes
star shaped glia that wrap around synapes of functionally related axons, pass chemicals back and forth beween neurons, and blood among neighbouring neurons
axon
thin fiber of constant diameter that conveys impulse toward other neurons, an organ, or muscle
neurons
receive information and transmit it to other cells
glia
serve many functions, such as supporting neurons, regulation, recovery, homeostasis, and myelin production
membrane
a structure that separates the inside of the cell from the outside environment
nucleus
structure that contains the chromosomes
mitochondrion
the structure that performs metabolic activities, providing the energy that the cell uses for all activities
ribosomes
sites within a cell that synthesize new protein molecules
endoplasmic reticulum
a net work of thin tubes that transport newly synthesized proteins to other locations
soma (cell body)
structure containing the nucleus, ribosomes, and mitochondria
dendrites
branching fibers that get narrower near their ends, surface is lined with specialized synaptic receptors
dendritic spines
short outgrowths that increase the surface area available for synapses
blood brain barrier
mechanisms that excludes most chemicals form the vertebrate brain (brains immune defense)
efferent axons
carries info AWAY from a structure (exit)
synaptic receptors
where dendrite receives info from other neurons
presynaptic terminal
end of each axon branch, where axon releases chemicals that cross through the junction between that neuron and another cell
nodes of Ranvier
interruptions in the myelin sheath that are essential for transmission of electrical impulses
intrinsic neuron/ interneuron
neuron whose axons and dendrites are all confined within a given structure
types of glia
astrocytes, microglia, oligodendrocytes, Schwann Cells, Radial glia
glucose
a simple sugar, vertebrate neurons require it
tripartite synapes
a hypothesis that states the tip of an axon releases chemicals that cause the neighbouring astrocyte to release chemicals of its own, modifying message to next neuron
microglia
act as the part of the immune system, removing viruses and fungi from the brain
Oligodendrocytes:
are in the brain + spinal cord, build myelin sheaths that surround and insulate necessary for proper functioning, produce myelin sheaths that insulate certain vertebrate axons in the central nervous system
Schwann Cells
in periphery of the body, build myelin sheaths that surround and insulate necessary for proper functioning
Radial Glia
guide the migration of neurons and their axons and dendrites during embryonic development, most differentiate into neurons
why do vertebrate neurons depend on glucose
b/c its the only nutrient that crosses blood brain barrier (BBB) in large quantities
Why do we need the BBB
Immune system fights viruses by killing infected cells (suited for replaceable cells like skin & blood)
Brain cannot easily replace neurons, therefor has a barrier to block harmful invaders
What substances freely cross the BBB and by what mechanism
small uncharged molecules (oxygen, CO2) and fat soluble molecules (i.e. vitamins A & D, psychiatric drugs, illegal drugs)
active transport
thiamine
vit B1 that helps body convert food into energy, required to process glucose (prevalent in chronic alcoholism)
what are the forces involves with the maintenance f the action potential
electrochemical gradient (NA+ more concentrated outside, K+ more concentrated outside making neuron more neg charged at rest attracting positive NA+ inside cell)
Selective Permeability of Membrane (prevents depolarization)
Sodium-Potassium Pump ( NA+ out and K+ in, helps restore and maintain resting membrane potential)
Voltage Gated Ion Channels (depolarization, repolarization, and hyperpolarization)
describe the function of an action potential
to enable neural communications, allows neurons to send signals to other neurons, muscles, glands, playing a crucial role in sensory perception, movement, and cognition
What is the molecular basis of the action potential (stages)
Resting potential (inside neg charge, NA+ mostly inside, K+ mostly out)
depolarization (NA+ channels open, NA+ rushes inside making cell more positive)
action potential peak (Neuron becomes highly positive, NA+ channels close)
repolarization (K+ channels open, K+ leaves the cell, restoring neg charge)
hyperpolarization (too much K+ leaves, making neuron extra neg)
recovery/resting potential (sodium potassium pump restores balance by pushing NA+ out, and K+ in)
why does saltatory conduction preserve energy
Because depolarization (Letting K+ in) only happens at nodes
Describe the propagation of the action potential
AP moves along axon as a wave due to sequential opening of ion channels
AP begins at first Node of Ranvier
After AP, NA+ enter axon and diffuse, pushing a chain of positive charge along the axon to the next node, where they regenerate a new AP
what moves sodium (NA+) into the cell when the membrane is at rest
the concentration gradient and the electrical gradient
what mechanisms moves K+ in and out when membrane is at rest
concentration gradient: moves K+ OUT (bc potassium is more concentrated on the inside than outside)
electrical gradient: moves K+ INTO (because they are positively charged, and inside is neg charged)
