Nerve Physiology Flashcards
RMP of nerve
-70 mv
Firing level of nerve
-55mv
How is firing level attained
By giving threshold stimulus
Features of local potential (differentiate with action potential)
By sub threshold stimulus Graded response Decremental Not self propagated Can be depolarising/hyperpolarising May/may not be followed by action Summation present
Features of action potential
Differentiate with local potential
By threshold/suprathreshold stimulus All or none response Travel without decrement Self propogated Always depolarising Followed by action Summation absent
Types of summation
Spatial
Temporal
Eg of spatial summation
EPSP
IPSP
Receptor potential
Motor end plate potential
Phases of action potential
Depolarisation
Repolarisation
After depolarisation
Hyperpolarisation
Pls know why and how it happens ;)
Why does hyperpolarisation happen
Due to slow closure of K+ channels
Features of Na and K channels
Na - fast to open and fast to close
K- slow to open and slow to close
Both open in voltage range from -70mv to +30 mv
Types of refractory period
Absolute refractory period
Relative refractory period
What is Absolute refractory period and when
Stimulus will not elicit another action potential
From firing level till repolarisation is 1/3rd complete
What is relative refractory period and when
Stronger stimulus will elicit another A P
From when repolarisation is 1/3rd complete till start of depolarisation phase
Neuron is least excitable in which phase of action potential
Depolarisation phase
Membrane Conductance of potassium at rest compare to membrane conductance of sodium at rest
Membrane conductance of potassium is more then membrane conductance of sodium
Membrane conductance graph of sodium and potassium during action potential
Please check the book
Relationship between strength of stimulus to the time taken for response (action potential)
The increase in strength of stimulus the decrease in the time taken for response (action potential)
What is rheobase
Minimum strength of stimulus (electric current) which when applied for prolonged duration produces response (Action potential)
Utilisation time
Time taken by Rheobase current to produce response
What is chronaxie
Time taken by current which is twice the rheobase to produce response
Relationship between chronaxie and excitability of tissue
Lesser the chronaxie more excitable the tissue
Different sized neurons and their chronaxie
Bigger neurons lesser chronaxie
Larger diameter - larger surface area- more number of sodium channels
Chronaxie relationship between Skeletal Muscle, cardiac muscle, smooth muscle
Chronaxie of Skeletal muscle
Chronaxie after nerve injury
Increased chronaxie
As nerve regenerates chronaxie?
Chronaxie decreased
Site of generation of action potential in spinal motor neurons
Initial segment > axon hillock
Why is this site of the action potential initial segment in spinal motor neurons
initial segment has high concentration of sodium channels per unit area
Which is the site of highest concentration of sodium channels
Nodes of Ranvier
2000-12000 channels/sq micrometer
Axon hillock and initial segment have how many sodium channels/sq micrometer
Axon hillock -350
Initial segment - 500 / sq micrometer
Dendrites and Soma how many sodium channels
50–75
Site of generation of action potential in sensory neuron is
Initial nodes of ranvier
Spinal motor neuron and sensory neuron difference
Features of just spinal motor neuron
Spinal motor neuron
Aalpha motor neuron/lower motor neuron/anterior horn neuron
Multipolar neuron
Cell body lies in anterior horn of spinal cord
Spinal motor neuron carries impulses from spinal cord to muscle
Site of generation of action potential is initial segment
Spinal motor neuron and sensory neuron difference
Features of just sensory neuron
Sensory neuron
Dorsal root ganglion cell
Pseudo unipolar
Cell body lies in the dorsal root ganglion
DRG cell carries impulse from skin to spinal cord
Site of generation of action potential is 1st node of ranvier
Factors affecting velocity of conduction of a nerve impulse
Diameter
Myelin
Larger the diameter of nerve fibre Ra (axonal resistance)is ?
Lower Ra higher velocity
Know why :P
What produces myelin in PNS and CNS
PNS - Schwann cells
CNS- oligodendrocytes
Saltatory conduction
Jumping of impulse at nodes of ranvier
More Myelinated nerve fibres the membrane resistance is ?
More myelinated more membrane resistance
Large myelinated nerve fibres have ______ Ra and ______ Rm
Low Ra
High Rm
Maximum velocity is present in nerve fibres with _____ Rm/Ra ratio
High
What does myelin do to membrane resistance and membrane capacitance
Increases membrane resistance
Decreases membrane capacitance
Large diameter myelinated nerve fibres have ______ Ra, _______ Rm and ________ capacitance
Low Ra
High Rm
Low capacitance
Maximum velocity is present in nerve fibres with ______ resistance and ________ capacitance
High resistance (Rm) Low capacitance
Demyelinating disorder ______ Rm and _______ membrane capacitance
Decrease Rm
Increase membrane capacitance
What are the two classification of nerve fibres and their types
Erlanger and gasser classification-A(alpha,beta,gamma,delta),B and c [sensory,motor,autonomic]
Lloyd and hunts numerical classification- I,II,III,IV [sensory]
Know what each type of nerve fibres carry
Just know it (check the notes)
A,B,C nerve fibres diameter and velocity
Decreasing diameter and velocity (from A-C)
Most numerous type of nerve fibre
C
Aalpha carries (corresponding to type IA AND IB)
Spinal motor nerve
Proprioception
IA- sensory fibre from muscle spindle
IB-golgi tendon organ
Abeta carries (corresponding to type II)
Fine touch,vibration,deep pressure(poking),proprioception(muscle spindle)
Agamma carries
Motor nerve to muscle spindle
Adelta carries (corresponding to type III)
Fast pain,temperature (cold),some mechanoreceptor
B fibres carry
Preganglionic autonomic
Type c fibres carry
Postganglionic autonomic
Crude touch,itch,tickle,pressure,slow pain,temperature (cold,warmth)
Most unmyelinated nerve fibre
Type IV
Afferent/sensory from muscle spindle
IA and II
Motor to extrafusal muscle fibres
Aalpha
Motor to intrafusal muscle fibres
Agamma
Susceptibility to pressure
Which nerve fibre gets affected by pressure the most to least
A>B>C
Susceptibility to hypoxia
Which nerve fibre gets affected by hypoxia the most to least
B>A>C
Susceptibility to local anaesthetic
Which nerve fibre gets affected by LA the most to least
A>B>C
Types of intrafusal muscle fibres
Nuclear bag (1-3) and nuclear chain (4-5)
Types of nuclear bag fibres
Nuclear bag dynamic and nuclear bag static
Sensory fibres of nuclear bag dynamic /
Sensory fibres for dynamic response
IA fibres
Sensory fibres of nuclear bag static and nuclear chain static /
Sensory fibres for static response
IA and II
Motor nerve fibre of nuclear bag and nuclear chain
Agamma fibres
Two ways a muscle spindle can be stimulated
Increase in muscle length
Increase in Agamma motor nerve discharge
What is axoplasmic transport
Physical transport of substances through axoplasm
Name some molecular motors of axoplasm
Kinesin
Dynenin
Myosin-V
Types of axoplasmic transport
Fast -anterograde and retrograde
Slow -always anterograde
Eg of fast anterograde transport
Vesicles,neuropeptides,mitochondria,reticulum,lysosome
Eg of retrograde fast transport
Neurotropic viruses (rabies)
Tetanus toxin
Nerve growth factor
Eg of small molecule rapidly acting neurotransmitter
Class I,II,III,IV
Pls see notes
Sympathetic pre ganglion secretes
Acetylcholine
Sympathetic post ganglion secreted
Norepinephrine
Except sweat glands- Ach,renal blood vessel-dopamine
Parasympathetic preganglion and postganglion secretes
ACh and ACh
Fast response (fast EPSP) What is secreted and what is the receptor
ACh
Nicotine receptor
(Millisecond)
Slow response (slow EPSP)
What is secreted and what is the receptor
ACh
M1
(Second)
Slow response (late slow EPSP)
GnRH
Peptide receptor
(Min)
Slow response (slow IPSP)
ACh
M2
(Sec)
Types of synapses (two)
Chemical and electrical Excitatory Types (EPSP in post-synaptic membrane)and inhibitory (IPSP in post-synaptic membrane)
Types of Inhibition/Inhibitory synapses
Post synaptic (direct) inhibition Presynaptic inhibition Feed forward inhibition Feedback inhibition Lateral inhibition
Know what they are -.-
Types of GABA receptors present on presynaptic membrane
Ionotropic receptor (GABAa,GABAc) Metabotropic receptor (GABAb)
Why is there a spastic paralysis in tetanus toxin
Because tetanus toxin inhibits release of GABA Which Increases the release of glutamate
Hence more excitation
Examples of feedforward inhibition
In cerebellum
Granule cells excite basket cell and stellate cells
Basket cells and stellate cells are inhibitory to purkinje cells
Lateral inhibition examples
Between photo receptors
Two point discrimination
Minimum separable distance in two point discrimination on fingertips and back
Fingertips – 2 mm
Back – 65 mm
Seddons classification of nerve injury
Neuopraxia
Axontemesis
Neurontemesis
Know what they are -.-
Wallerian degeneration
Changes in cell body
24–48 hours –chromatolysis (Disappearance of Nissl’s granules)
Nucleus moves to periphery
Wallerian degeneration
Changes in distal segment
Few hours – swelling of axis cylinder
3 to 5 days – axonal degeneration is complete
8th day -myelin degeneration starts
32nd day – myelin degeneration complete
Nissl’s granule composed of
Ribosomes and mRNA
Empty tube of neurilemma also called
Ghost tube
Wallerian Degeneration
Changes in proximal segment
Similar to distal segment of nearest node of Ranvier
Prerequisite for regeneration of nerve
Neurilemma is intact
Distance between cut ends is less than 3 mm
What is the rate of regeneration of nerves
1 mm/dead or 1 inch per month
Regeneration is usually complete by one year
