Part 7 Flashcards
describe the function of a Cell body ?
Genetic and metabolic machinery for neurotransmitter synthesis. necessary for a cell to exist.
what are the structural features of a neuron?
Cell body, Axon, Dendrite, synapse
what is the function of an Axon?
propagates action potential
describe a dendrite?
filamentous extensions of cell body
what is a synapse?
axon terminal
what are cell bodies called in the CNS and PNS?
CNS - Nucleus
PNS - Ganglion
what are axons called in the CNS and PNS?
CNS - tract
PNS - nerve
all neurons in the PNS are surrounded by ?
Glia (Schwann Cells)
Gaps between Schwann Cells are called?
Nodes of Ranvier
4 Types of connective tissue surrounding nerves ?
Epineruium
perineurium
endoneurium
basement membrane
Epineurium ?
surrounds the whole nerve
Perineurium ?
surrounds fascicles of nerve fibers
endoneurium ?
surrounds individual axons
Basement Membrane ?
protein matrix secreted by Schwann cells
• forms a protein interface between Schwann cells and endoneurium
Nerve Fascicles ?
Bundles of axons that target single muscles or skin regions
Nervi Nervorum ?
bundles of axons that innervate CT layers of nerves
Vasa Nervorum?
Blood vessels to CT, axons and Glia in nerves
What is Neuropathy ?
Neural disease due to damage to axons or glial cells
What are some common causes of Neuropathy ?
Diabetes, kidney failure, alcoholism, nutritional deficiency, trauma,auto immune disease.
How does Axonal degeneration progress?
damage begins at the hands and feet distally and moves proximally
Explain demyelination
degeneration of glia and the unwinding of myelin sheaths around axons
what is Guillain-Barre ?
Demyelination of motor fibers due to an autoimmune response to infection, surgery or immunization
What is Multiple Sclerosis?
demyelination disease in the CNS
what is paresthesia ?
burning or tingling (pins and needles) feeling due to neuropathy
what is hyperalgesia ?
exaggerated pain response to normally painless stimuli
Explain sprouting in relation to Nerve regeneration
Branching by axon proximal to injury.
Basement membrane tunnels, created by Schwann cells, guide axons, using laminin.
What is Laminin?
neurite promoting glycoprotein, component of the basement membrane that is increased on the surface of schwann cells
Whats the speed of Axon regrowth for PNS and CNS?
PNS - 1mm/day
CNS - minimal due to lack of basement membrane
Gray matter is made up of ?
H shaped region of cell bodies dendrites and axons
why is White matter ‘White’?
myelin, glial cells surround many axons making it look ‘white’
rootlets extend out from ?
dorsal and ventral horns and converge into roots
dorsal and ventral roots exit the vertebral column and unite to become ?
the spinal nerve
Spinal nerve splits into two rami?
Dorsal and Ventral rami (aka Peripheral nerves)
Where is the cell body found in the sensory neurons and motor neurons?
Sensory neuron - Dorsal root ganglion
Motor neuron - Ventral horn
sympathetic neurons are found in nearly all nerves. they have two types of cell bodies
preganglionic - found in gray matter, projects axon to sympathetic ganglion
postganglionic - forms sympathetic ganglion, projects axons to periphery.
this membrane constituent can increase permeability to water soluble molecules and stiffens membranes to help form lipid rafts
cholesterol
types of membrane proteins?
transmembrane (alpha helix, beta barrel)
membrane associated
lipid linked
protein attached
what are the benefits to carbohydrates connecting transmembrane proteins to the ECM?
carbohydrates bind lectins which mediate cell-cell adhesions
ex. blood clotting and inflammation.
the most common transmembrane protein that crosses the membrane bilayer?
alpha helix
the alpha helix can make multiple crossings or a single crossing across the membrane, explain the difference?
multiple crossings - create a pore used as an ion channel
single crossing- acts as a signal receptor
Ion specificity of a channel depends on ?
- charge distribution: positive channel will only allow negative through.
- diameter and shape of channel: (size of ion is determined more by hydration shell than size of atom)
what causes the sodium potassium pump to alter conformation?
donation of phosphate by ATP
membrane polarization created by a single ion is known as?
equilibrium potential
this potential is generated by the net flux of all ions?
membrane potential (Vm)
product of net driving force and permiability
net flux
sum of concentration and electrical gradients
net driving force
ease of flux through a channel
permeability
this ion has a high net flux, high permeability and concentration and electrical gradients are in opposite directions, reducing net driving force.
K+
this ion has a low net flux, low permeability and concentration and electrical gradients are in the same directions, increasing net driving force.
Na+
3 types of ion gaiting properties ?
Voltage gated
ligand gated
mechanically gated
Voltage gated ion channels are located at ? and work by ?
Location : axion hillock and nodes of Ranvier
stimulus : de/hyper polarizing current which changes conformation and permeability
ligand gated ion channels are located at ? and work by ?
location: neural or other cell surfaces
stimulus: neurotransmitters, ligands
mechanically gated ion channels are located at ? and work by ?
location: skin, retina..etc
stimulus : pressure, touch, light..
Receptor Stimulus increases Na+ permeability yielding?
a graded depolarization of the membrane potential
At what location does the triggering of the all or none action potential take place?
nodes of Ranvier
what mechanism causes the all or none action potential at the nodes of Ranvier?
influx of Na+ ions from the receptor potential depolarizes and opens Na+ gated ion channels.
briefly explain the 4 phases of action potential
- Incoming positive ionic current depolarizes membrane to threshold level of voltage.
- At threshold, rapid depolarization to positive value,~50mV (Na)
- Repolarization to initial potential
- Hyperpolarization, ~-70mV (K)
what happens during depolarization?
Na channel opens in response to depolarization (at threshold)
• Potential almost reaches +50mV (Na)
what causes repolarization?
Na channel spontaneously inactivates
• K channels opens
what happens during hyperpolarization
- K channel still open; K flux happens through both leak & volt-gated channels
- Potential almost reaches >-70mV (K)
what type of channels do not participate in action potentials?
non gated, leakage K+ channels
internal depolarization causes the protein configuration to?
open the outer portion of the channel
initial depolarization and overshoot is strong because ?
Na influx has a high driving force
why does Na+ have a high driving force?
both concentration and electrical gradients are in the same direction and summate.
what is excitability?
sensitivity of the cells ability to produce an action potential
what two variables can alter excitability?
– Concentration gradient
– Channel permeability and/or threshold
potential
how does hyperkalemia (increasing extracellular K+ level) affect concentration gradient?
causes prolonged depolarization, Na+ channels are inactivated, the threshold is raised and the cell becomes less excitable.
• Decreasing extracellular K+ has reverse effect
channel permeability can be altered by ?
channel blocking and protein reconfiguration. (lidocaine is an example of channel blocking)
describe the refractory period
only happens in unmyelinated axons. the period of time after an action potential during which the membrane channels are less responsive to stimuli
whats the difference between an absolute refractory period and a relative refractory period?
Absolute - channels cannot be activated
relative - takes a greater stimulus to create action potential.
describe conduction in a myelinated axon.
AP’s are only produced in nodes of Ranvier and the axon hillock because this is where the voltage-gated channels are.
What is Saltatory conduction?
refers to the skipping of AP generation from one node to the next.
Why does amplitude decrease along a myelinated area of an axon?
because current leaks out through non-gated K+ channels.
demyelination occurs due to Guullian - barre and MS, what does this due to conduction
conduction is slowed or halted because excess current leaks out through non-gated K channels.
This reduces the available current for the next node of Ranvier.
How many axons does a neuron usually have?
One
How many dendrites does a neuron usually have?
Many
Na-K pump pumps __ Na ions out and __ K ions in against their concentration gradients. This results in what?
3; 2; Results in a net loss if one charge.
