Neurophysiology Flashcards
The transfer of information along and between the neurons can be done in two ways.
Electrical : Action potential
Chemical : Neurotransmitters
The cell body communicates with its terminal using electrical impulses: action potentials
Action potentials are ‘all-or-none’ signals
Action potentials cause ________________
depolarization of the terminal and release of neurotransmitters
Steps in propagation of AP through a synapse:
- impulse arrives at pre-sm
- VGCC open, Ca2+ enters pre-sn
- synaptic vesicles carrying nt’s arrive at pre-sm and bind to docking protein.
- they release their nt’s into the synaptic cleft
- nt’s diffuse and bind to receptor at post-sm
- impulse continues
RMP concentrations of ions:
Na+ (and Cl-) are concentrated outside
K+ (and A-) are concentrated inside.
The ionic charge between inside and outside is unequal
Inside is negative to outside (-60 to -90mV)
Neurones are special because _______
they can rapidly alter their membrane potential.
This depends on voltage-gated ion channels
Electrical signalling importance:
Physiological:
- Transfer along neurones (long distance/fast)
- Summation/integration of inputs
Pharmacological:
1. Site for drug action (local anaesthetics, anticonvulsants)
Puffer fish contains tetrodotoxin (TTX). Why is it bad?
TTX is very potent toxic, works by blocking VGNC necessary to produce action potential!
Chemical transmission by -
Ligand-gated channels i.e. eg neurotransmitters
Not all synapses are chemical. they can also be
Electrical synapses.
action potential can move through gap junction channel and become coupling potential
Process of chemical transmission:
Action potential arrives at axon terminals and depolarizes the membrane
Voltage-gated Ca2+ channels are opened and Ca2+ flows in
Ca2+ influx triggers the synaptic vesicles to release neurotransmitters
Neurotansmitters binds to the target receptor on postsynaptic neuron
Chemical transmission importance
Physiological:
Communication between neurones (short distance/slow)
Complex signalling
Pharmacological:
Sites for drug action
Myelination is the process of ____________ to allow ________________
Process of forming a myelin sheath around a nerve to allow nerve impulses to move faster.
Myelin is formed by: _____1_____
in the peripheral nervous system (PNS)
and by __________ in the central nervous system (CNS)
- Schwann cells
2. Oligodendrocytes
Difference between Schwann cells and oligodendrocytes?
Each Schwann cell forms a single myelin sheath around an axon. In contrast, each oligodendrocyte forms multiple sheaths (up to 30 or more) around different axons. Along the same axon, sequential myelin sheaths are formed by different oligodendrocytes.
How is myelination done?
Schwann cellsin the PNS form individual myelin sheaths (blue) aroundaxons(orange), whereasoligodendrocytes in the CNS form multiple myelin sheaths (purple), each on separate axons. Schwann cell nuclei are located on the outside of the sheath. One myelinating Schwann cell is shown partially unrolled: the light central area is the topological equivalent of the compact myelin sheath, and the darker edges represent belts of cytoplasm along the cell border. In the CNS, a stretch of unmyelinated axon is shown in agreement with recent evidence that some axons are inconsistently myelinated.
A cross-section of a myelin sheath is illustrated at the bottom demonstrating the origin of the intraperiod line, formed by apposition of the extracellular leaflets of theglialplasma membrane, and the major dense line, formed by the tight apposition of the cytoplasmic leaflets. Myelin grows by the spiral wrapping of the inner turn (arrow) around the axon.
Role of myelin in normal neurone - 4 points:
- insulation for axons
- fast, saltatory impulse propagation
- Promoting rapid, efficient nerve conduction
- Axon maintenance and function
Clinical implications of myelin sheath formation?
Multiple sclerosis is an autoimmune disease in which the immune system attacks myelin in the CNS. What effect will MS have on the conduction of AP in the nervous system?
it will slow down nerve impulse conduction
Relationship between extent of myelination, axon diameter and conduction velocity.
more diameter, and myelination = faster impulse velocity.
conductionvelocity = root of diameterofaxon
Which one has the fastest impulse velocity?
Greater cell diameter, myelinated.
There are 3 types of nerves: Efferent which carry ________
and afferent which carry ________, and mixed nerve.
Efferent = motor nerve fibers carrying impulses from the CNS to the effector organs, such as muscles and glands
Afferent = sensory nerve fibers (axons) grouped together to carry impulses from receptors to the CNS
SAME (Sensory Afferent, Motor Efferent)
- Mixed nerve
Erlanger Gasser Classification:
groups nerve fibres according to decreasing order of size and speed, and hence in the sensitivity of their work.
all myelinated except for C.
Order:
A - alpha beta gamma delta
B
C
ERLANGER-GASSER CLASSIFICATION nerve fibres functions
A alpha - Proprioception: somatic motor
A beta - vibration, sensory axons
A gamma - motor to muscle spindles
A delta - pain, cold, touch
B - sympathetic preganglionic motor axons
C - crude touch, pain, and temperature sensation.
Different nerve endings: Specialized sensory receptors on cutaneous and subcutaneous tissue – highly diverse! Their morphology is of 2 types: Free ending nerve, encapsulated nerves
Name the 6 examples along with their basic functions.
Merkel disk receptor, meissener corpuscle = Mechanoreceptors
Nociceptors = Free Nerve ending
Thermoreceptors = Ruffini ending, sweat gland, pacinian corpuscle.
Receptor adaptation
Quality of stimulus is determined by ______________ and ______________
the properties of the relevant receptors
and
the location of their central targets
Quantity/strength of the stimulus is conveyed by the rate of AP discharge triggered by the receptor potential.
There can be 2 types of action potential generated:
Rapid firing then fall silent in the presence of continued stimulation (“adapt” to stimulus)
Sustained discharge in the presence of ongoing stimulus
There can be two types of receptor adaptations:
- Rapidly adapting/phasic receptors: respond maximally but briefly to maintained stimuli
Response decreases if the stimulus is maintained - Slowly adapting/tonic receptors: keep firing as long as the stimulus is present
2 examples of Slowly adapting fibers
Merkel disk receptor (stimulus - steady pressure, texture)
Ruffini ending (stimulus - stretch)
2 examples of Rapidly adapting fibers
Meissner - strokiing flutter
Pacinian - vibration
