Exam 2: Ch 5 Book Background Info Flashcards
what is a neuron
a nerve cell that communicates information using a combination of electrical and chemical signals
convey electrical signals rapidly and accurately to organize and direct physiological responses
most neurons are ____ excitable
electrically
what does being electrically excitable mean
electrical signals can be generated across the plasma membrane
these signals are transmitted across the cell’s length without losing signal strength b/c of the movement of ions
glial cells
supportive cells of the nervous system that fill the spaces between neurons
10-50x more glia than neurons
what does the nervous system do
collects and processes information, analyzes it, and generates outputs to control responses
why is studying neurons useful
electrical properties easily studied with tools from the physical sciences
neurons function similarly in all animals so results from one species are applicable to many others
neurons process info in a complex manner but in doing so they rely on a surprisingly _____ number of basic physical and chemical properties
small
soma
cell body of a neuron
responsible for metabolic maintenance
nerve processes
thin fibers that arise from the soma
2 types: dendrites and axons
dendrites
branched nerve processes that extend from the soma and serve as receivers that gather signals from other neurons
transmit signals toward the soma
cells with a complex dendritic tree…
typically receive input from many other neurons
axons (nerve fibers)
a specialized nerve process that conducts signals away from the soma
may be very long (spine to muscles)
axon terminal
a region at the end of the axon that allows signals to be sent simultaneously to many other neurons (to glands, to muscle fibers)
many vertebrate axons are surrounded by supporting cells that provide an insulating layer called the ….
myelin sheath
during embryonic development and maintenance through life…
dendrites and the axon grow outward from the soma
maintenance of these fibers depends on a steady flow of proteins and other constituents that are synthesized in the soma and transported down the processes
what happens if an axon in an adult animal is severed?
degenerates back to the soma within days or weeks
regeneration of axons in mammals
limited to nerves in the periphery of the body
in cold-blooded vertebrates some regeneration may happen in the CNS
damaged neurons in invertebrates
many times they will regenerate and reestablish connections with their original targets
what does a spinal motor neuron do?
carries signals from soma in spinal cord to skeletal muscle fibers
spike-initiating zone
an area located at or near the junction between the axon and soma (axon hillock)
integrates signals from many input neurons to determine whether an action potential is created
actions potential originate in the spike-initiating zone
action potential (spike, nerve impulse)
voltage across plasma membrane rapidly rises then falls
where does the axon carry the action potential?
from the spike-initiating zone to the axon terminals, which transmit the signal to other cells
axon hillock
the junction between the axon and soma
the spike-initiating zone is often found here
much of the physiological behavior of the neuron depends on ______ _____ ____ such as ____ and _____
passive electrical properties
capacitance and resistance
neurons also possess active electrical properties that allow them to…
conduct electrical signals without loss of strength
depends on the presence of proteins in the plasma membrane called voltage-gated ion channels
voltage-gated ion channels
proteins in the cell membrane that allow ions to cross in a regulated fashion
located in regions of specialized signaling function
open when the plasma membrane is depolarized to make an AP
what voltage-gated ion channels are found in the axonal membrane
Na and K
what voltage-gated ion channels are found in the axon terminals
Ca
the axon of a sensory neuron is called?
an afferent fiber
what does afferent fiber mean
it conducts signals inward toward higher processing centers in the brain
interneuron
the most numerous type of neuron found only in the CNS
link and carry information between other neurons
synapse
a specialized region between the axon of a neuron and the dendrites of another
types of effector organ
muscles and glands
efferent neuron
neurons that carry information from the processing regions of the CNS outward to effectors
neuronal circuit
afferent neurons, interneurons, and efferent neurons
a cell that passes information to a particular neuron is said to be _____
presynaptic
a cell that receives information transmitted across a synapse is said to be _____
postsynaptic
most synaptic transmission is carried by chemical _________
neurotransmitters
neuronal circuit cockroach example
afferent neurons in the wind receptors in the tail contact large interneurons in the CNS
the interneurons contact efferent motor leg neurons
stimulus causes the cockroach to run away
the plasma membrane of the postsynaptic neuron’s dendrites and soma contain…
ligand-gated ion channels that bind neurotransmitters
these cause the postsynaptic cell to respond to the presence of the chemical signal
all or none signals
signals whose amplitude is invariant
APs
graded signals
signals whose amplitude is variable
depends on stimulus strength or another variable
sensory neruons
transmit info collected from external stimuli (sound, light, pressure) or respond to internal stimuli (blood oxygen level, the orientation of the head, position of a joint)
motor neurons
carry signals to effector organs
cause contraction of muscles or secretion by gland cells
central nervous system
brain and nerve cord
ganglia
neuronal stomata distributed along the nerve cord
typically control local regions of the animal’s body
vertebrate vs invertebrate spinal cord
vertebrate: located along dorsal midline
invertebrate: ventral midline
oligodendrocytes
glia found in the CNS
schwann cells
glia in the periphery that wrap axons in myelin
myelin sheath
an insulating coating around axons that contributes to reliable and rapid transmission of APs
functions of glial cells
regulate [K+], pH in fluid filled spaces
remove neurotransmitters from extracellular space
provide structural and metabolic support
glial cell membranes are highly permeable to
K+
coupled by junctions that allow K+ to flow between
this flux allows glial cells to take up and redistribute extracellular K+, which could otherwise buildup
voltage
electrical potential difference
although a stable voltage exists across the plasma membranes of all cells, only the membranes of ______ ______ _____ can respond to changes in their transmembrane potential difference by generating APs
electrically excitable cells
ex. neurons, muscle fibers
how are membrane potentials measured
as electrical current
detected directly by using two electrodes to measure change caused by current flow across the membrane
where are the sensing electrodes placed
one in electrical contact with the cytosol
the other in contact with the extracellular medium
this is so any potential difference can be measured (membrane potential Vm) and amplified and displaced on a recording instrument like a computer or oscilloscope
membrane potential Vm units
volts
what did Hodgkin and Huxley study in the 40s and 50s
membrane potentials from squid giant axons
resting potential (Vrest)
the steady inside-negative potential recorded when no APs or postsynaptic events are occurring
expressed in millivolts (usually between -20 - -100)
the cytoplasm of the cell is ___potential
isopotential
calculate the strength of the electric field across the plasma membrane
E = V/d
E = strength of electric field
V = volts
d = distance in meters (5nm b/c plasma membrane)
how to measure passive electrical properties of the plasma membrane
put two microelectrodes into one cell
current delivered from a current generator to the current electrode
recording electrode records this effect on membrane potenetial
current generator effects
current in form of migrating ions
flow if from positivity to negativity
if positive current, flows into cytosol and out the cell
if negative current, positive charge is drawn out of the cytosol and into the electrode
hyperpolarization
when the interior of the cell becomes even more negative, which increases the size of the potential difference across the plasma membrane
ex. -60 mV to -70 mV
depolarization
if the current electrode adds positive charge to the interior of the cell it diminishes the potential difference across the membane
ex. -60 mV to -20 mV
as the amount of applied positive current increases, the ____ __ ________ also increases
degree of depolarization
what can depolarization cause?
some voltage-gated Na+ ion channels to open
causes an AP
threshold potential
the value of the membrane potential at which an AP is triggered 50% of the time
ion selectivity in channels
most channels allow only one or a few ionic species to cross the membrane
movement driven by electrochemical gradient
what is responsible for the dramatic depolarization during an AP
simultaneous opening of many voltage-gated Na channels when initial depolarization reaches the threshold potential
what is responsible for the passive change in membrane potential in response to hyperpolarizing current?
K+ selective leak channels that are always open
maintain resting potential and are uniformly distributed in the plasma membrane
ligand-gated channels
ion channels that open when messenger molecules like neurotransmitters bind to receptor proteins in the cell surgace
electrochemical potential
the voltage difference across the plasma membrane described as Vm (the membrane potential)
what does electrochemical potential depend on
concentrations of several ion species inside the cell being different than outside the cell (gradient)
ion channels being selectively permeable
equilibrium potential
a potential difference across a membrane established by one ion being permeable vs. another impermeable ion
formed when a permeable ion diffuses down its concentration gradient until a repulsive electrical potential balances the concentration gradient
ex. Cl- impermeable and K+ permeable
electromotive force (emf)
force due to electric potential difference across the membrane
can offset concentration gradient
steady state
system remains invariant
maintenance requires no expenditure of energy
