chapter 2: structure and function of cells in the nervous system Flashcards
cells of the nervous system, communication within neurons, and communication between neurons
what does the central nervous system (CNS) consist of?
the brain and spinal cord
what does the peripheral nervous system (PNS) consist of?
nerves and most of the sensory organs
nerve
bundle of thousands of individual neurons wrapped in a tough protective membrane
nerve fibers
transmit messages through the nerves from sensory organs to the brain or from the brain to muscles and glands
sensory neurons
process sensory information gathered from the environment
motor neurons
control motor behavior and muscle contractions
interneurons
lie entirely within the CNS integrating sensory and motor stimuli
local interneurons
communicate with nearby neurons to analyze small pieces of information
relay interneurons
connect circuits of local interneurons between brain regions
neurons
primary information-processing cells that transmit signals throughout the brain and body
soma
cell body of a neuron which contains the nucleus
dendrites
tree branches extending from the soma that receive messages transmitted across the synapse
axon
a long thin tube thats outside surface carries information from the soma to the terminal buttons
anterograde axonal transport
relies on kinesin to move information toward the terminal buttons
retrograde axonal transport
relies on dynein to move information toward the soma at half the rate of anterograde axonal transport
myelin sheath
a protective layer of fats and proteins covering the axon that allows efficient transmission of action potentials
multiple sclerosis
deterioration of the myelin sheath that can lead to slower nerve transmission and axonal degeneration
terminal buttons
knobs at the end of the axon terminal that secrete neurotransmitters
synapses
small spaces in between the terminal buttons of one neuron and the dendrites of another
glia
supporting cells of the nervous system that provide protection and nutrients, fight and remove pathogens and dead neurons, facilitate communication, and assist with the growth and repair of cells
astrocytes
star-shaped glial cells that surround soma and dendritic membranes to nourish neurons and perform phagocytosis, ingesting dead cells and replacing the vacant area with scar tissue, as well as maintain the blood brain barrier
oligodendrocytes
glial cells that form the myelin sheath with segments of space for faster transport along axons, and provide immune support and respond to inflammation after injury
nodes of ranvier
uncoated portions of axons between segments of myelin sheath
microglia
smallest of the glial cells that provides immune support by protecting the brain against invading microorganisms, responsible for neuroinflammation after injury, act as phagocytes that enable astrocytes to remove dead cells
schwann cells
glial cells in the PNS that serve the same function as oligodendrocytes, while promoting regrowth by digesting dying axons after nerve damage and forming cylinders to guide axonal regrowth
paul ehrlish
-discovered the blood brain barrier by injecting blue dye into the bloodstream that tinted all tissue except the brain and spinal cord
-when he injected the dye into the ventricles in the brain, the CNS turned blue
blood brain barrier
-a selectively permeable barrier between the blood and the fluid that surrounds the cells of the brain regulating the composition of fluid within and outside of neurons
-lined with capillaries that carry blood into the CNS
what is one reason the permeability of the blood brain barrier differs throughout the brain?
in the area postrema, neurons can enter and detect toxic substances in the blood that can induce vomiting
how do cells communicate with each other?
through electrical signals
what is the resting potential of an axon?
-70 mV
depolarization
membrane potential becomes more positive increasing the likelihood of an action potential
action potential
a burst of rapid depolarization that facilitates communication between neurons, followed by hyperpolarization back to resting potential
what two forces can change the membrane potential of a neuron?
diffusion and electrostatic pressure
what ions are present in the intracellular and extracellular fluid of a neuron and what are their charges?
sodium (Na+)
potassium (K+)
chloride (Cl-)
organic anions (A-)
which of the ions present in a neuron cannot leave the neuron and contributes to its negative internal charge?
organic anions (A-)
what is the role of sodium in depolarization?
sodium from the extracellular fluid enters the cell through diffusion and remains there due to electrostatic pressure
what is the role of potassium in depolarization?
potassium from the intracellular fluid exits the cell through diffusion but is pushed back in due to electrostatic pressure
what is the role of chloride in depolarization?
chloride from the extracellular fluid enters the cell through diffusion but is pushed back out due to electrostatic pressure
what is the purpose of the sodium-potassium pump?
it keeps the intracellular concentration of sodium low
how does the sodium-potassium pump work?
for every two potassium ions pushed in, three sodium ions are pushed out of the cell
all-or-none law
an action potential either occurs or doesn’t, the size is always constant
rate law
an axon’s firing rate represents varying information
saltatory conduction
messages get smaller as they pass down the axon but are still large enough to trigger action potentials at the next node
what are the six steps of an action potential?
- membrane potential reaches the threshold of excitation, where the sodium channels open and sodium rushes into the cell
- potassium channels open and potassium rushes out of the cell
- sodium channels become refractory
- potassium continues to leave the cell until the membrane returns to resting potential
- potassium channels close and sodium channels reset
- membrane becomes briefly more negative than resting potential while the sodium potassium pump gathers potassium
what are the two advantages of saltatory conduction?
less energy is required and action potentials are conducted faster
how do neurons communicate with each other?
neurotransmitters are released from the terminal buttons of the presynaptic neuron and attach to the binding sites of the postsynaptic neuron
ligand
a chemical that binds to a receptor site
what can binding to a receptor trigger?
opening of ion channels that all ions can use to enter and exit the cell
synaptic vesicle
small, round structures that are packaged by transport proteins with several neurotransmitters, peptides, or other ligands to be taken across the synaptic cleft by trafficking proteins
what are the four types of synapses?
axo-dentritic, axo-somatic, axo-axonic, and dendro-dendritic
exocytosis
mechanism of active transport by which molecules are released from the cell through calcium channels that are opened by depolarization during action potentials
ionotropic (direct) receptor
ligands bind to receptor site and ion channel opens
metabotropic (indirect) receptor
ligands bind to receptor site which activates a g-protein to activate second messengers to induce ion release
excitatory postsynaptic potential
sodium and calcium channels are opened to increase the likelihood action potentials by depolarizing the postsynaptic cell
inhibitory postsynaptic potential
potassium and chloride channels are opened to hyperpolarize the postsynaptic cell and decrease the likelihood of action potentials
reuptake
the rapid removal of neurotransmitters from the synaptic cleft back into the terminal buttons of the presynaptic neuron by transporter molecules
enzymatic degradation
enzymes break apart neurotransmitters released from terminal buttons to prevent the overstimulation of postsynaptic cells and excessive firing
autoreceptor
located on the terminal button of the presynaptic cell and regulates the amount of neurotransmitters released
neuromodulators
chemicals released that alter the transmission of signals between neurons, helping or inhibiting receptors
hormones
neuromodulators secreted into extracellular fluid by endocrine glands or cells in various organs and bound to target cells
peptide hormones
bind to metabotropic receptors and alter the physiology of a cell
steroid hormones
alter protein production of cell because they are smaller and more fat soluble than peptide hormones
