BIOMED 10/10b Organization of PNS Flashcards
Define neuron
cell that helps with transmission and integration of information
Structure of a neuron
- Cell Body
- Axon
- Dendrites (receive information from multiple sources and transmits info to other neurons)
4 main functional regions of a neuron
- input
- integrative
- conductive
- output
what is contained within the cell body of the neuron?
- cell body is the main integrative unit of neuron and supports basic metabolism of the neuron
- Nucleus stores the DNA ***
- ER has rough and smooth, responsible for synthesis of lipids and proteins and synaptic vesicles
- lysosomes digest compounds and change glycogen to glucose; form part of the axoplasmic transport system
- mitochondria produce ATP
- golgi apparatus stores lipids and proteins
- microtubules are free way of neurons that carry the axoplasmic axonal transport system
Cell body of peripheral sensory neuron lies
dorsal root ganglia (slightly outside the spinal cord) - afferent
cell body of the peripheral motor neuron lies
within the spinal cord - efferent
axon main functions
- transmission of information: propagation of action potential
- transportation of metabolically important materials to and from the soma to the axonal end
A. anterograde axonal transport takes vesicles from soma to presynaptic terminal
B. retrograde transport system takes metabolites from presynaptic terminal back to the neuron
example of a disorder that relies on the axonal transport system
Tetanus: injury in a non-hygienic environment where there are micro-bacteria that sit on RETROGRADE axonal system that goes to the neuron and causes cytoxic cascades that lead to tetanic contractions
Myelination of axons
- myelinated: schwann cell concentric circles (300 layers)
- unmyelinated: surrounded by a single schwann cell that doesn’t wrap around axon multiple times and provides trophic support
schwann cells
wrap around axon in concentric circles to form a myelin sheath
- protection
- insulation
multiple unmyelinated axons are covered by one single schwann cell (T/F)
TRUE
how do neurons transmit information?
- within neuron (dendrites to axon - Action Potential)
- between neurons (synapse)
how do neurons transmit information on a cellular level?
- resting membrane potential
- post synaptic potential
- action potential
how do neurons transmit information with synaptic mechanisms?
- convergence
2. divergence
how do neurons transmit information with behavioral mechanisms?
- feedback
2. feedforward
resting membrane potential
- difference in the charge/charges across a particular membrane
- (-)70mV on the inside, making it more negative
example of when a patient has issues with resting membrane potential?
- epilepsy is unwanted activity of the neurons
- the membrane potential is not stable, so there is a lot of unwanted activity in the brain
neuronal cell membrane
- phospholipid bilayer
- lipids arranged so that it is partially/semi permeable to some ions
- physical barrier that keeps the ions separate
what are charges?
ions carry a charge and in order to keep them separate, there needs to be a barrier – aka the neuronal cell membrane
two main forces trying to move the ions in and out of the cell body
- Electrostatic Forces - like charges repel each other, so if a negatively charged ion is inside, it is going to try to move outside
- Diffusion Forces: relies on the concentration of ions, so if there is more sodium outside and less inside, it travels from outside to in
which type of force plays a higher role in generation of an action potential?
Diffusion Forces
extracellular vs intracellular ion concentrations
Extracellular:
- high Na+ outside (moves inward)
- high Cl- outside (moves inward)
- More positive than inside
Intracellular
- high K+ (moves outward)
- high proteins
- More negative than outside
different mechanisms for ion transport
- ion channels
2. activated mechanisms
Ion Channels
- movement of ions from intra to extra or extra to intra.
- specific to certain kinds of ions
- channels are gated, but some are leakage
- gated depending on multiple factors
different kinds of gated ion channels
- ligand gated
- mechanical gated
- voltage gated
- leakage gated
what does a ligand gated channel do?
has a receptor on one end, when a neurotransmitter sits on the receptor side, the channel opens (Ach molecule )
what is a mechanical gated channel?
if there is a mechanical stress applied at the level of the receptors/channels, that opens the gate
what is a voltage gated channel?
only opens when there is a specific potential difference across the cell membrane. sensitive to opening and closing
what is a leakage gated channel?
open for the most part, passively allow leakage of the ion
in the cellular membrane there are more _____ leakage channels than ______
K+, Na+
active mechanism for ion transport
require ATP
-sodium-potassium pump
what does the Na+/K+ pump do?
-it transports 3 Na+ from inside to outside
-it transports 2 K+ from outside to inside
-in the process, ATP gets changed into 1 ADP + 1 P
there is more sodium outside and it transports sodium outside
there is more potassium inside and it transports potassium inside
THUS, it moves against the concentration gradient and requires ATP for energy
net charge of the Na+/K+ pump?
3+ out 2+ in, so 1 net negative charge on the inside of the membrane
what maintains the resting membrane potential?
- high K+ INSIDE and a lot of potassium leak channels, so potassium leaves and cell becomes more negative
- high Cl- OUTSIDE and open leak channels (not as many as potassium) so more Cl- enters and cell becomes even more negative
- high Na+ OUTSIDE and very few leak channels, most of closed. So, not a lot of sodium able to enter the cell so small amount of positive coming in.
- Sodium Potassium Pump works against gradient and sends Na+ out and K+ in, developing a net negative charge again.
If the leakage channels and sodium potassium pump are altered, what happens?
this is caused by a neural signal!
Change in resting membrane potential causes
- depolarization
2. hyperpolarization
depolarization
inside becomes less negative, normal polarity is being lost, thus depolarization occurs
hyperpolarization
inside becomes more negative, more polar than normal polarity, so hyperpolarization occurs
Post Synaptic Potential
- a graded potential: small change in potential then it goes back to resting
- after the synapse, the change leads to a change in the potential of the neuron
what are two features of a graded potential?
- Excitatory Synapse: EPSP, inside becomes more positive than resting, membrane becomes DEPOLARIZATION
- Inhibitory Synapse: IPSP, inside becomes more negative than resting, the membrane becomes HYPERPOLARIZATION
If RMP is -70mV, -50mV, or -100mV, what grade is the membrane potential?
a. polarized
b. depolarized - EPSP
c. hyperpolarized - IPSP
phases of the spike of the action potential
after EPSP, there is a
- depolarizing phase
- repolarizing phase
what causes the spike of the action potential?
- neuron signals
- synpase
- synapse releases neurotransmitters
- post synaptic neuron takes neurotransmitters
- uptake of neurotransmitters changes the permeability of the post synaptic membrane
- with the permeability change, calcium enters and helps open Na+ channels.
- thus membrane potential raises and leads to EPSP
- if change is strong enough (high concentration of neurotransmitter vesicles), mechanically gated channels open too!
action potential mechanisms
- Voltage gated sodium channels only open at -55mV, before that it could be ligand gated channels. Then we get the spike in action potential
- At +30, the voltage gated sodium channels close and voltage gated potassium channels open and potassium starts leaving the cell and the inside gets more negative
- As it reaches repol, sodium-potassium pump gets reactivated
- Potassium channels are slow and sluggish
- Sodium channels are fast
- When voltage gets back to resting potentials, potassium channels are slower to close and so they remain pushing out potassium and leads to a hyperpolarization
Action Potential Propagation
- Axons conduct information by propagation of the action potential
- Diffusion of sodium ions cause depolarization of the surrounding axon is the basis of AP propagation
- Myelin acts as an electrical insulator so the charge can accumulate at the node of ranvier in between two schwann cells. When the sodium channels open there is a huge concentration of the ions that rush in and get sucked into the next node of ranvier
- Hyperpolarization prevents sodium from moving back instead of forward throughout the myelin
- Partially stimulate an axon and the action potential travels both towards the dendrite and cell body
when do voltage gated channels open?
only at -55mV
before the voltage gated channels open, what channels are open
could be ligand, leak, mechanical, etc
peripheral nervous system
spinal nerves and cranial nerves
31 pairs
both sensory and motor
longitudinal organization (starts at the brain/skull and goes all the way to L2 vertebrae
action potential propagation
diffusion of sodium ions that cause depolarization of ions
nerve roots of the spinal peripheral nerve
cross section of spinal cord = spinal segment
broader gray matter is the ventral (efferent)
–motor from spinal to muscle
Balloon nerve root is dorsal (afferent)
–sensory to spinal cord from periphery
what would happen when the dorsal root is cut?
there would be sensory loss, but the abulity to generate a contraction would be there
what would happen if the ventral root is cut?
paralysis
