Ch. 2: Physical/Electrical Properties of CNS Cells Flashcards
Anterograde Transfer
Movement of proteins from cell body to end of axon
Types of Neurons
- Bipolar
- Pseudo-unipolar
- Multipolar
Axon Hillock
- proximal part of axon against cell body
- where new action potentials get started
- voltage gated channels located here in motor neurons and bipolar neurons)
Axoplasmic Transfer
constant movment of proteins in neuron (axon)
Anterograde
Retrograde
Retrograde Transfer
Movement of proteins from end of axon toward cell body
Bipolar neuron
- 2 Major poles
- Dendrite and axon
Example: retina cells
chemical signals
- transmission of signal between neurons (one to next)
- chemicals start new electrical signal
4 Membrane Channels
- Ligand gated
- Voltage gated
- Non-gated
- Modality gated
Pseudo-Unipolar Neuron
- One major trunk with 2 parts:
- the peripheral axon (acts like dendrite)
- the central axon
Example: somatosensation
Multipolar Neuron
- many major trunks but only one axon
- receive many signals and consolidates into 1
example: motor neurons
Electrical Signals
Transmission of info within 1 neuron
Non-gated Channels
open hole in membrane that’s always open and leaks based on concentration gradients
Modality-Gated Channels
- Open in response to modalities (touch/temp/body chemicals)
- Located at ends of sensory neurons
Resting potential
-70mV inside the cell
Depolarization
Makes inside of neuron less negative so it’s more likely to create an action potential
excitatory
Ligand-gated channels
- opens to neurotransmitters
- located on post-synaptic membrane/dendrite
Voltage-gated channels
- opens in response to change in membrane voltage
- located all along axon (any nerve cell)
- Send messages long distances
3 Factors that maintain resting potential:
- Na+/K+ pump (3Na+ out/2K+ in)
- Large negative molecules trapped inside soma
- Passive diffusion through non-gated channels
Hyperpolarization
- makes inner neuron more negative
- less likely to create action potential
- inhibitory
Graded Potential
more stimuli or more frequent stimuli open more channels and cause more depol/hyperpol
local potential
small change over short distances
summation of local potentials
- small polarity changes added together to make large polarity change
- Temporal vs Spatial
Spatial summation
2 or more stimuli arriving at same time are added together
Temporals Summation
Repetition of a single stimulus adds together
Action Potential
- a big change over a long distance
- very large change in membrane potential
Passive Propogation
- Change in polarity because ions spill in through open gates
- Local potential changes
Active Propogation
- new action potentials get started along membrane
- one action potential starts another which starts another etc
Axon Hillock
- Spot where voltage-gated channels are located for multipolar neurons
- action potentials start here
- (Synaptic Potentials)
Threshold Depolarization
-point where there are enough local potential depol to open voltage-gated channels to start an action potential
Trigger Zone
- Spot where voltage-gated channels are located for sensory neurons
- (receptor potentials)
Action Potential sequence
- Local Potential
- Threshold depolarization
- Action potential
- refractory period
- propogation
Refractory Period
-temporary hyperpolarization that prevents depolarization from traveling backwards to ensure one way signal
The “size” principle
-Large diameter neurons have faster conduction because they have less internal resistance
3 types of macroglia
Astrocytes
Oligodendrocytes
Schwann Cells
Saltatory Conduction
- Action potential jumps from one node of ranvier to the next on myelinated neurons
- fast!
Astrocytes & cell signaling
- Ca++ storage and movement
- release of glutamate
- can increase or decrease communication by moving Ca++ or glutamate
Ca++
primary ion of depolarization in the CNS
Function of glia
- supporting cells
- structure for neurons
- assist with transmission
- possible role in pathogenesis
Oligodendrocytes
- Fatty insulators
- protective insulation of CNS neurons
- insulate several neurons
- white matter
Glutamate
Primary ligand of depolarization in the CNS
Neuroinflammation
response of CNS to infection, disease and injury
Electrical communication in neurons requires:
- Resting potential difference
- ATP (energy)
- Electrolytes
6 Characteristics of local potentials
- result of opening of modality or ligand gated channels
- small change in polarity
- graded
- depol or hyperpol
- passive propogation
- small distances
Synaptic Potential
generated by ligand-gated channels on post-synaptic membrane
2 Types of Local Potentials
- Receptor potentials
- Synaptic potentials
Receptor Potential
generated by modality-gated channels at distal end of sensory neurons
5 characteristic of action potentials
- Result of opening voltage-gated channels
- large change in polarity and long distance
- all or none
- depol only (can’t inhibit)
- passive and active propogation
Schwann cells
- Fatty insulators
- protective insulation of PNS neurons
- Insulate 1 neuron with layered covering (myelinated)
- insulate many neurons with simple covering (unmyelinated)
- Phagocytic with peripheral injury
Benefits of neuro-inflammation
- Reactive Microglia + when they:
1. remove debris
2. produce neurotrophic factors to supoprt axonal regeneration and remyelination
3. Mobilize astrocytes to reseal blood brain barrier and provide trophic effect
There may be a coorrelation between_____
Abnormal glial activity & neural damage in stroke, alzheimer’s, MS and parkinsons
Disadvantages of Neuro-inflammation
- Can cause death of neurons and oligodendrocytes and inhibit neural regeneration
- microglias and astrocytes can be overactive and release toxins into neural environment (HIV can activate this)
Astrocytes
- Primary external scaffold
- most direct role in cell signaling
- scavenger (K+ and NT)
- connect neurons to capillaries (blood brain barrier)
- Pathway for migrating neurons in development
Microglia
- phagocytic with injury
- destroy aging neurons
- may have started as immune cell during development
- abnormal activation–>brain disease
Guillain-Barre
- Autoimmune attack on schwann cells (PNS)
- Demyelination of Nn–>weakness, sensory loss (can affect throat and breathing muscles)
- remyelination usually follows
neural stem cells
Primitive stem cells:
- Self-renew
- Differentiate
- Populate
May help in NS diseases
MS
- CNS autoimmune attack on oligodendrocytes
- S/Sx: motor, sensory, autonomic
- No remyelination; gradual and progressive
- “better” periods due to decreased inflammation (not remyelination)
Divergence
One neuron communicating with many
Convergence
- many neurons communicating with one
- post synaptic neuron consolidates signals to one and relays it
