Chapter 8 Flashcards
3 types of neurons
sensory interneuron motor neuron
anaxonic neuron
a bunch of afferent processes, but no axon typically CNS interneurons
bipolar neuron
processes –> cell body–> axon typically a sensory neuron
pseudounipolar neuron
one single elongate process, with the cell body situated on one side typically a sensory neuron
multipolar neuron
“typical” neuron that you think of a bunch of dendrites –> cell body –> axon typically a motor neuron
node of ranvier
in between area of connecting schwann cells covered in myelin sheath.
cell body
soma
dendritic spines
specialized little processes that increase dendritic surface area, increases communication ability of the neuron. a micro-anatomical feature
axonal growth cone
during embryogeneis, axons seek out targets and grow out. also involved in neural-regeneration should damage and re-growth occur responds to growth factors extracellular matrix molecules and membrane proteins
axon hillock
region where the cell body meets the axon
Glial cells in CNS
ependymal cells astrocytes microglia oligodendrocytes
Glial cells in PNS
Schwann cells satellite cells
Ependymal cells
create barriers between compartments source of natural stem cells
astrocytes
Highly branded glial cell make up large portion of the brain communicate w/each other via gap junctions for rapid communication source of neural stem cells take up K, water and NTs secrete neurotropic factors *help form the blood brain barrier* provide substrates for ATP production if there is a nerve injury, will start forming scar tissue, interferes with regeneration and repair
Microglia
modified immune cells- not actually nerve cells act as scavengers when activated, remove damaged cells and foreign invaders
oligodendrocytes
form myelin sheets branch to myelinate several axons
schwann cells
form myelin sheets one schwann cell associates with one axon secrete neurotropic factors
satellite cells
support cell bodies located in ganglia essentially non-myelinating schwann cells
Multiple sclerosis
de-myelination, exposing naked nerve fiber autoimmune, in part. affects skeletal muscle, but there are also bladder and bowel dysfunction, respiratory issue, parathesia, optic disturbances, depression, paranoia, mental changes phenotype varies greatly
ganglia
nerve cell bodies located outside of CNS
nerve regeneration in CNS
can’t happen b/c of astrocyte inhibition
conductance
ease of which an ion flows through a channel
voltage gated ion channels
respond in change to cells membrane potential Na and K channels along the axon
current
I the flow of electrical charge caries by an ion direction depends on the electrochemical gradient of the ion
- K+ : moves into the cell
- Na+, Cl- and Ca2+ : move out of the cell
electrical signal created by
the net flow of ions across the membrane, depolarizing or hyper polarizing the cell
current flow (I) follows ohms law
I= V / R I is directly proportional to the voltage difference and inversely proportional to the resistance
axonal transport
moves proteins and organelles between cell body and axon terminal
Slow axonal transport
rate of protein being synthesized and being moved along mt transport is slow
fast axonal transport
can be bi-directional, vessels can be used again.
synapse development
depends on neurotrophic factors
resting membrane potential of a neuron
~-70mV
the major contributor to the resting membrane potential
K
the resting membrane is more permeable to K, and there is more K inside the cell
Nearnst equation
describes the membrane potential that would result if the membrane were permeable to only one ion
E ion(in mV) = 61 / Z x log [ion] out/ [ion] in
•Z is the electrical charge on the ion (1+ for K+)
Predicted E K+ = -90mV
actual E K+ is -70mV
why not the same?
other ions must be contributing to the membrane potential
•neurons at rest are slightly permeable to Na+
(Na+ leaks in)
•Goldman-Hodgkin-Katz equation (GHK)
•Calculates the membrane potential that results from all ions that can cross the membrane
•
•Accounts for membrane permeability of each ion
For mammalian cells:
Na+, K+ and Cl- have largest effect on resting membrane potential
each ion’s contribution is inversely proportional to its ability to cross the membrane
Dependent on:
•the combined contributions of concentration gradient ([out]/[in]) (add these together)
- membrane permeability (P ion) for each ion
- If a membrane is not permeable to an ion, it drops out of the equation (eg Ca2+)
if a membrane becomes more permeable to Na+
will get membrane depolarization
if a membrane becomes more permeable to K+
will get membrane hyperpolerization
4 major types of gated channels in neurons:
. Na+ channels
- K+ channels
- Ca2+ channels
- Cl- channels
Conductance
ease at which an ion flows through a channel
•varies with the gating state and the protein isoform
•
•eg: K+ leak channels are open most of the time; others open or close in response to stimuli
mechanically gated ion channels
found in sensory neurons, open in response to physical forces such as pressure or stretch
chemically gated ion channels
respond to a variety of ligands, such as ECF neurotransmitters, ICF signal molecules
voltage gated ion channels
respond to changes in the cell’s membrane potential
eg: Na+ and K+ channels along the axon
biological electricity resistance comes from 2 sources
Rm: resistance of the cell membrane
Ri: internal resistance of the cytoplasm
(and the diameter of the cell)
Rm and Ri together comprise the length constant for a given neuron
graded potentials
•Variable strength signals
•
•travel short distances
•
•lose strength as they travel through the cell
•
•used for short distance communication
•
•if strong enough, can initiate an action potential
Action potentials
•Very brief, large depolarizations
•
•Travel for long distances through a neuron without losing strength
•
•Rapid signaling over long distances
___ follows an action potential
refractory period
No RF, would lose gradients, signals would not be coordinated
The membrane cannot be excited to get an AP at the RF
The excitability factor steadily increases in the RF period
Current flow
the depolarized section has + on inside and – on outside
Nonpolarized area of cell is – on inside and + on outside
action potential is UNIDIRECTIONAL
trigger zone
the area where Na channels are open and Na enters the cell
Saltatory conduction
Action potentials appear to jump from one node of Ranvier to the next.
Only the nodes have voltage-gated Na+ channels
Demyelinating diseases reduce or block conduction when current leaks out of
the previously insulated regions between the nodes.
NT termination
NTs returned to axon terminals for reuse or transported to glial cells
enzymes inactivate NTs
or NTs diffuse out of synaptic cleft
