Flashcards in Neurons Deck (91):
What are the two major divisions of the nervous system?
CNS - brain and spinal cord - surrounded by bone
PNS - nerves and neurons - not surround by bone
2 classes of cells
Glial cells and neurons
Glial cells are _____ of NS, 4 functions, *
Structural units like glue
Firmness and structure
Provide nutrients to neurons
Scavengers - remove debris
* no function in electrical transmission
Neurons are ____ of NS, 5 parts and functions
Functional units/basic signaling units of NS
Dendrites/branching - input mechanism
Cell body/soma - integrative centre of neurons
Axon hillock - site of action potential generation
Axon/conducting unit - myelin and nodes of ranvier to have signals go faster
Terminal branch - output mechanism from collaterals
Where do neurons make connections
At synapses with one another
Area where neurons communicate with another cell
Neuron that sends msg
Post synaptic neuron
Cell that receives msg
Fluid filled gap separating pre and post synaptic membranes
3 different types of synapses
Axo dendritic synapse - between axon of presynaptic neuron and dendritic branch of postsynaptic neuron
Axo somatic - between axon of presynaptic neuron and cell body of postsynaptic neuron
Axo axonic - between axon of presynaptic neuron and axon of postsynaptic neuron
Contraction for movement
Action opposing agonist
Works with agonist
Same muscle for sensory and contracting
Motor nerve - efferent or afferent?
Sensory nerve - efferent or afferent?
Single axon rule
If a neuron has an axon, then it has only one
3 structural classification of neurons for mammalian
Single process emerges from soma, splits into two processes
Goes to periphery and spinal cord
Sensory neuron that travels to the dorsal root ganglia
Soma give rise to 2 processes - 1 actual axon
Special sense organs
Single axon and many dendritic branches
Motor neurons controlling skeletal muscles
3 functional classification of neurons
Sensory neurons - 2
respond to stimuli
input neurons of NS
Sends signals to cells outside of NS
output neurons of NS
Carry information between sensory and motor neurons
Cell membrane consists of? What’s selectivity?
Lipd/protein belayer to separate intra/extra cellular environments, semipermeable to some ions
What dictates the electrical signalling properties of neurons?
Relative concentration of ions between intra and extra cellular environments - membrane potential
What exists across a neuron’s cell membrane?
What is a potential difference?
Difference in electrical potential across the membrane where electrical potential reflects ionic concentration (Na, K, Cl, Ca)
Voltage value describing the potential difference across the membrane at any point of time
What ions are outside?
Sodium and chloride
What ions are inside?
Potassium and aspartame
Neuron resting membrane potential
Muscle cell RMP
2 sources of alteration of membrane permeability
Activity of surround neurons - by neurontransmitters
Electrical current - lab
Why is RMP negative?
Inside of cell is negatively charged relative to the outside
At rest what is the membrane imperable to? How does it make it negative?
Na, more K leak channels making the inside negative at -65mV, then pumps regulate that
What do inputs from other neurons do to the membrane
Depolarize Or hyperpolarize
Alteration in membrane permeability will alter
Stimulation leads to influx of Na - membrane potential becomes more positive - depolarization
Stimulation makes membrane impermeable to Na - MP becomes more negative
Neurons send signals to other neurons via their axons in 2 ways
Passive conduction and active propagation
Charged particles move to equalize potential difference, this will continue to do so as long as potential difference exists - but this cant go far because distance matters
Process that requires metabolic energy
Involves voltage gated ion channels
Action potential - cellular ATP
Intracellular recording vs extracellular recording of AP
Microelectrode to see the potential difference across the membrane
Extracellular recording of AP uses two electro heads outside of the axon and see the potential difference between electrodes - starting from 0 because there is not resting membrane electrode
APs are generated when the cell membrane is?
Membrane potential will change in response to stimulus, but it will return to rest values unless ...
We reach the membrane/firing threshold
At a given membrane potential/threshold, membrane respons with? Different threshold for neurons and muscles?
Sudden change in potential
Neurons = -55mV
Muslce cells = -75mV
Principle of neurons producing APs in response to excitatory synaptic inputs
Stimulus that moves membrane potential closer to threshold increases probability for AP firing known as excitatory stimulus so the sodium can rush in.
What does a hyperpolarizing stimulus work and what is it always on known as?
Closing sodium ions - inhibitory stimulus
Events of depolarization
Signal generated near axon hillock
Sodium channels open and depolarization happens, it goes up to 30mV, sodium channel closes and K channels open to depolarize - keep on going until less than -65mV which all voltage gates close
Neurophysiological perspective of an action potential
A standard brief pattern of change in membrane potential
Functional perspective of action potential
Unit of information transmission within and amongst excitable tissues
5 essential principles of action potential
All or nothing
Initiated only at one site
Velocity depends on neuron characteristics
All or nothing
Each AP looks the same, it either gets created or not
All APs produced in the particular neuron all reach the same max value, thus, they are either generated as a whole (ALL) or they are not generated at all (nothing) because the number of channels would be the same like firing a gun
Initiated at only one site
APs are generated only at the axon hillock where there is a high density of Na channels
APs are dynamic and travel along the neuron axon/muslce fibre
- how it is preserved
AP propagation is unidirectional and travel away from soma (ORTHODROMIC)
Refractory period of axon (inactive Na channels post AP firing)
Varying levels of excitability along axon (due to density of Na channels)
Absolute refractory period - when is that and could an AP be generated?
Na open then close and K opens - hyperpolarizes and no AP can be generated
Can you have initiate an AP during the relative refractory period?
Larger than normal stimulus can initiate a new AP
What would interfere with this?
High density Na channels at the nodes of ranvier which allows them to “jump” and increase conduction velocity - we dont have to generate as many APs as it flows passively under the myelin sheath
Demyelination disease reduce/block conduction and current leaks out the previously insulated axons
Purpose of unmyelinated vs myelinated axons
Glandular control vs balance information
Once generated will the AP propagate through the entire axon?
2 characteristics of the neuron that are largely responsible for differences in propagation speed
Whether the axon is myelinated or not
Thickness of the axon - thicker means faster
AP velocity depends on neuron characteristics such as - 3
Neuronal fibre types, health of neuron, avg conduction velocity
Muscle spindle type and conduction velocity
Ia - 80-120m/s
Golgi tendon organ type and conduction velocity
Ib - 80-120 m/s
Muscle spindle type and conduction velocity
Pressure receptor type and conduction velocity
Nocireceptor type and conduction velocity
IV - 0.5-2m/s
How to calculate the velocity of conduction?
Skeletal muscle motor neuron type and conduction velocity
Alpha = 100m/s
Muslce spindle and the 2 types of neurons and their conduction velocity
Two outcomes of synaptic transmission
EPSP & IPSP
Excitatory post synaptic potential : Depolarization - membrane becomes more permeable to Na
Inhibitory post synaptic potential - membrane becomes less permeable to Na = hyperpolarization
Two ways of summing the effects of subthreshold potentials
Temporal summation and spatial summation
Sum effects of several APs from same synapse
- EPSPs are superimposed, leading to larger EPSP, several APs arrive successively at presynaptic membrane before it gets back to its resting levels
Several APs (stimuli) from diff synapses arrive simultaneously - AP generated
If you want more output, what would you increase?
AP firing frequency which is increased by stimulus durationm but not intensity
Patterns of neural connectivity
Neurons can be connected directly to each other or connected via other neurons
Monosynaptic - two neurons directly connected
Disynaptic - 2 neurons connected via intermediate neuron
Trisynaptic - 2 connected via 2 intermediate neurons/polysynaptic
Different populations of neurons connect to other population via two pathways
Convergence - multiple neurons in source population connect to smaller number in target population - one postsynaptic cell from multiple presynaptic cells - intermediate neurons consolidate the info into one msg.
Divergence - fewer neurons in source population connect to a larger number in target population - one presynaptic cell that makes the message to multiple postsynaptic
Information only moves forwards from input neurons to output neurons
2 types of feedback connectivity
- how does it happen?
Feedback excitation - presynaptic excites postsynaptic
Fdbk inhibition - neg fdbk which maintains homeostasis
There’s a collateral that goes back to the presynaptic cell
Principle of skilled human movement
Internal processes associated with practice/experiment that lead to changes in capability for movement
Changes in movement resulting from maturation
Regulated and coordinated movement from the info from receptors/perception