The Nervous System Flashcards
neurons
specialized cells capable of transmitting electrical impulses, and then translating those electrical impulses to chemical signals
shape matches its function, dictated by the other cells with which it interacts
cell body (soma)
where nucleus of neuron is located
location of the endoplasmic reticulum and ribosomes
dendrites
appendages of neuron emanating directly from the soma
receive incoming messages from other cells
axon hillock
integrates incoming signals
plays an important role in action potentials
sums signals in order to determine whether excitatory enough to initiate an action potential
action potentials
transmission of electrical impulses down the axon
signals can be either excitatory or inhibitory–if excitatory enough, will initiate these
relay electrical impulses down the axon to the synaptic bouton
all-or-nothing messages
cause the release of neurotransmitters into the synaptic cleft
axon
long appendage of neuron that terminates in close proximity to a target structure (a muscle, glad, or other neuron)
myelin
insulates most mammalian nerve fibers to prevent signal loss or crossing of signals
increases the speed of conduction in the axon
produced by oligodendrocytes (CNS) or Schwann cells (PNS)
myelin sheath
maintains the electric signal within one neuron
oligodendrocytes
produce myelin in CNS
Schwann cells
produce myelin in PNS
nodes of Ranvier
at certain intervals along the axon, there are small breaks in the myelin sheath with exposed areas of axon membrane
critical for rapid signal conduction
nerve terminal/ synaptic bouton (knob)
at the end of the axon
enlarged and flattened to maximize neurotransmission to the next neuron and ensure proper release of neurotransmitters
neurotransmitters
chemicals that transmit information between neurons
synaptic cleft
small space between neurons into which the terminal portion of the axon releases neurotransmitters which bind to the dendrites of the postsynaptic neuron
synapse
collectively, the nerve terminal, synaptic cleft, and postsynaptic membrane
nerve
multiple neurons bundled together in the PNS
may be sensory, motor, or mixed
tracts
axons bundled together in CNS
nuclei
how cell bodies of neurons in the same tract are grouped (CNS)
glial cells/ neuroglia
play both structural and supportive roles
- astrocytes
- ependymal cells
- microglia
- oligodendrocytes (CNS) & Schwann cells (PNS)
astrocytes
nourish neurons and form the blood-brain barrier, which controls the transmission of solutes from the bloodstream into nervous tissue
ependymal cells
line the ventricles of the brain and produce cerebrospinal fluid, which physically supports the brain and serves as a shock absorber
microglia
phagocytic cells that ingest and break down waste products and pathogens in the CNS
resting membrane potential
-70 mV
inside of neuron negative relative to outside
use selective permeability to ions and Na+/K+ ATPase to maintain this negative internal environment
electrical potential difference (voltage) between inside of the neuron and extracellular space
Na+/K+ ATPase
maintains resting membrane potential at -70 mV by moving 3 Na+ ions out of the cell for every 2 K+ ions moved into the cell
important for restoring gradient after action potentials have been fired (energy necessary to move ions against their gradients)
active transport
depolarization
caused by excitatory input (raises the membrane potential, Vm, from its resting potential
makes neuron more likely to fire an action potential
hyperpolarization
caused by inhibitory input (lowers the membrane potential from its resting potential)
makes neuron less likely to fire an action potential
threshold
usually in the range of -55 to -40 mV
if enough excitatory input to be depolarized to this point, action potential will be triggered (opening of voltage-gated sodium channels in membrane)
therefore, not every stimulus generates a response
summation
additive effects of multiple signals
temporal and spatial
temporal summation
multiple signals integrated during a relatively short period of time
spatial summation
additive effects are based on the number and location of incoming signals
electrochemical gradient
promotes the migration of sodium into the cell
interior of cell more negative than exterior of cell, which favors the movement of positively charged sodium cations into the cell
higher conc of sodium outside the cell than inside, which also favors movement of sodium into the cell
depolarization
occurs when membrane potential becomes more positive as sodium passes through ion channels into the cell
inactivated sodium channels
occurs when Vm approaches +35 mV
have to be brought back near the resting potential to be reversed
closed sodium channels
before the cell reaches threshold, and after inactivation has been reversed
open sodium channels
from threshold to approximately +35 mV
inactive sodium channels
from approximately +35 mV to the resting potential
repolarization
restoration of the negative membrane potential as positively charged potassium cations are driven out of the cell
hyperpolarization
efflux of K+ causes an overshoot of resting membrane potential
serves an important function: makes the neuron refractory to further action potentials
refractory periods
absolute and relative
absolute refractory period
no amount of stimulation can cause another action potential to occur
relative refractory period
there must be greater than normal stimulation to cause an action potential because the membrane is starting from a potential that is more negative than its resting value
impulse propagation
for a signal to be conveyed to another neuron, the action potential must travel down the axon and initiate neurotransmitter release
information can only flow in one direction
saltatory conduction
process by which an electrical signal jumps across the nodes of Ranvier to travel down the axon
neurotransmitters
released into synapse at nerve terminal
when action potential arrives, voltage-gated calcium channels open
influx of calcium causes fusion of vesicles filled with these with the presynaptic membrane, resulting in exocytosis of these into synaptic cleft
bind to receptors on the postsynaptic cell, which may be ligand-gated ion channels or G protein-coupled receptors
must be cleared from postsynaptic receptors to stop the propagation of the signal
can be enzymatically broken down, can be absorbed back into presynaptic cell, can diffuse out of synaptic cleft
reuptake channels
absorb neurotransmitters back into the presynaptic cell
white matter
in CNS, consists of myelinated axons–in brain, deeper than grey matter; in spinal cord, grey matter deeper
grey matter
in CNS, consists of unmyelinated cell bodies and dendrites
somatic NS
voluntary
autonomic NS
automatic
divided into parasympathetic NS and sympathetic NS
parasympathetic NS
rest-and-digest
sympathetic NS
fight-or-flight
reflex arcs
use ability of interneurons in spinal cord to relay information to the source of stimuli while simultaneously routing it to the brain
monosynaptic reflex arc
sensory (afferent, presynaptic) neuron fires directly onto motor (efferent, postsynaptic) neuron
polysynaptic reflex arc
sensory neuron may fire onto motor neuron as well as interneurons that fire onto other motor neurons
