CHAPTER 45 ~ Neurons and Nervous System Flashcards
two types of cells in neuron system
neurons and glial cells
neurons
excitable and generate action potentials
glial cells
support neurons physically, immunologically and metabolically. There are oligodendrocytes in CNS and Shwann cells in PNS that myelinate. And astrocytes in blood brain barrier
effectors
who nervous system communicates to; are muscles, glands, etc
simplest neuronal network consists of
a sensory neuron connected to a motor neuron connected to a muscle cell.
Afferent neurons
carry information INTO nervous system –> info comes from sensory neurons, so afferent neuron is usually a sensory neuron
Efferent neurons
carry commands to physiological and behavioral effectors such as muscles and glands => motor neuron
Interneurons
integrate and store info; communicate between afferent and efferent neurons
ganglia
clusters of neurons, (can have different functions throughout body), usually one pair is larger and more central = brain
CNS
Brain + Spinal cord; site of MOST info processing, storage, and retrieval
PNS
neurons that extend or reside outside brain and spinal cord (bring info TO CNS though)
dendrites
projections that sprout from cell body of neuron; bring inputs from other neurons or sensory cells to the body
axon hillock
integrates info from dendrites and initiates or inhibits action potentials based on these inputs. Lots of Na+ channels here.
axon
carry action potentials away from cell body and towards the synapse with target cell
axon terminal
forms synapses with target cell
membrane potential
difference in voltage across plasma membrane
resting potential
in an unstimulated neuron; -60mV
action potential
caused by the sudden opening and closing of ion channels (Na+ and K+) causing large, swift changes in membrane potentials.
at resting potential:
K + leak channels always open, voltage Na+ and K+ closed –> -60 mV (HIGH K+ inside, HIGH Na+ outside)
during Depolarization:
K+ leak channels and Sodium/potassium pump both open, SOME Na+ voltage open, K+ closed –> -50 mV (threshold) when ALL Na+ open, cell becomes more positive as action potential fires –> +50 mV
during Repolarization/Hyperpolarization:
K+ leak and sodium/potassium pump open, Na+ voltage close, K+ voltage open, K+ FLOOD OUT = membrane potential becomes negative again + undershoot
threshold potential
opens up voltage gated ion channels 5-10 mV above the resting potential
refractory period
voltage Na+ channels cannot open again for 1-2 milliseconds = no action potential (in Na+ voltage channel: activation gates closed, inactivation gates opened)
why are action potentials an “all or nothing” event?
because it is a chain reaction; slight depolarization of membrane involves SOME Na+ voltage channels opening, whose influx of Na+ ions triggers further depolarization, which in turn causes MORE Na+ gates to open until membrane reaches threshold and generates action potential –> positive feedback, so action potential always rises to max value
saltatory conduction
impulse propagation from node to node–> “jumping”
oligodendrocytes
glial cells, myelinate axons in CNS
Shwann cells
glial cells, myelinate neurons in PNS
astrocytes
glial cells, contribute to blood-brain barrier which protects brain from toxic chemicals in blood; surround smallest blood vessels in the brain; are permeable to fat soluble molecules such as alcohol = drunkness
Multiple Sclerosis (MS)
gradual demyelination - destruction of myelin via immune response; affect 400,000 americans, 2.5 million worldwide. Onset ~ 20-40 years old
patch clamping
process that allows single ion channels to be studied
Mechanism of MS
myelinated fibers demyelinated via inflammatory process, this causes conduction block. Na+ channels redistribute to restore conduction, and remyelination occurs = clinical remission
Synapses
an axon terminal that contains many chemical filled vesicles; enable nervous system to process and integrate info.
neuromuscular junction
chemical synapse between a motor neuron and a muscle cell
Acetylcholine (ACh)
neurotransmitter used by vertebrate neuromuscular synapses
Mechanism of Action Potential @ Synapse:
as action potential reaches synapse, Na+ influx triggers opening of Ca2+ voltage gated channels; influx of Ca2+ triggers fusion of ACh-containing vesicles to membrane, releasing ACh into synaptic cleft. ACh binds to receptors on post-synaptic cell, opening Na+ channels and depolarizing motor end plate = Action Potential. ACh-esterase comes and digests ACh, taking back the monomers to the pre-synaptic cell for use in synthesis of new ACh molecules.
Acetylcholinesterase
breaks down ACh fused to ACh gated channels on post-synaptic cell. Brings back by-products to pre-synaptic cell to be remade into ACh
synapses between motor neurons and muscle cells
are always excitatory = respond to ACh with a graded potential
if receptor on post-synaptic cell is a Cl- channel opened by a neurotransmitter..
Cl- influx = hyperpolarization of cell and thus no action potential
synapse is EXCITATORY
if post-synaptic neuron responds by chemical stimulus by depolarizing
synapse is INHIBITORY
if post-synaptic neuron responds by hyperpolarizing
ACh –> Na+ –> depolarization = excitatory
GABA or Glycine –> Cl- –>hyperpolarization = inhibitory
all excitatory/inhibitory inputs go to axon hillock, excitatory and inhibitory inputs summed over space and time - if resulting combined potential depolarize axon hillock to threshold…
axon fires action potential
Spatial summation
adds up simultaneous influences of synapses at diff sites of post synaptic cell
Temporal Summation
adds up post-synaptic potentials generated at same site in rapid sequence
ionotropic receptors
ion channels; neurotransmitter binding to these receptors cause a direct change in ion movement across the plasma membrane of post-synaptic membrane = these proteins enable fast, short-lived responses
metrabotropic receptors
not ion channels, but induce signalling cascades in postsynaptic cell that secondarily lead to changes in ion channels = response is slower and longer-lived tan those by ionotropic receptors
