Neurophysiology
- basic principles Tutorial
II_autumn
Most neurons share a group of traits:
• derive from ectoderm
• four morphological regions – dendrites, body, axon,
synaptic terminals
Most neurons share a group of traits:
• derive from ectoderm
• four morphological regions – dendrites, body, axon,
synaptic terminals
Most neurons share a group of traits:
• four functional components – input, integrative,
conductive, output
• generate electrical potentials
• communication with another neurons
Axonal transport
• apparatus for the protein synthesis in the cell body
• orthograde/antegrade transport
Glial cells
Microglial cells
• arise from macrophages
• scavenger cells (remove debris resulting from injury,
infection, …)
Macroglial cells
• Schwann cells (PNS), oligodendrocytes (CNS) - myelin
CNS PNS
Glial cells
Microglial cells
• arise from macrophages
• scavenger cells (remove debris resulting from injury,
infection, …)
Macroglial cells
• Schwann cells (PNS), oligodendrocytes (CNS) - myelin
- blood vessels (tight junction formation → blood-brain barrier)
- synapses and surface of nerve cells (produce tropic
substances, maintain appropriate concentration of ions and
neurotransmitters)
• astrocytes – send processes to:
Astrocytes
• metabolic functions: K+, pH, oxidative stress (GSH),
energy storage (glycogen), glutamate-glutamin shuttle
• modulation of synaptic activity, tissue repair
Cerebral
Compartments
Ganong´s Review of Medical Physiology, 23rd edition
Blood-brain barrier
cerebral capillaries – tight inter-endothelial connections
circumventricular organs
Cerebrospinal fluid
- production rate
of production: 450-550 ml/day
(70 % come from plexus choriodei)
circulating volume: 130-150 ml
CSF pressure in supine position in
lumbar region:
70-180 mmH2O
Cerebrospinal fluid
- composition clear
and colorless, up
to 4 cells/μl, little
amount of proteins
Cerebrospinal fluid: circulation
Cerebrospinal fluid: absorption
Resting membrane potential
A difference in the electrical potential (=voltage) across
the plasma membrane of an unstimulated excitable
cell.
Resting membrane potential
the difference in electrical potential when the cell is at
rest results from two factors:
(1) the unequal distribution of electrically charged
ions, in particular, the positively charged Na+ and
K+ ions and the negatively charged amino acids and
proteins, on either side of the cell membrane,
(Na+-K+ pump)
(2) the selective permeability of the membrane to K+
(ion channels).
3 Na+
2 K+
nondiffusible
anionts (proteins)
+ + + + + + + + + + + + + +
- - - - - - - - - - - - - - - - - -
[Na+]e
[Na+]i»
[K+]e [K+]i« K+
Resting membrane potential
Resting membrane potential
► Nernst equation
Resting membrane potential
3 Na+
2 K+
nondiffusible
anionts (proteins)
+ + + + + + + + + + + + + +
- - - - - - - - - - - - - - - - - -
[Na+]e
[Na+]i»
[K+]e [K+]i« K+
► Goldmann equation
Na+
Cl-
[Cl-]e
[Cl-]i
Resting membrane potential
Electrotonic potentials, local response
… passive changes of membrane polarity caused by addition
or removal of the charge by an electrode
Electrotonic potentials, local response
Action potential
Guyton & Hall. Textbook of Medical Physiology
Action potential
… propagated electrical response of a nerve fiber (or other
excitable cells), all-or-non character
Action potential
Action potential
Action potential
… propagated electrical response of a nerve fiber (or other
excitable cells), all-or-non character
Action potential
Conduction
orthodromic conduction
saltatory conduction
antidromic conduction
Nerve fibres
• … divided based on axonal diameter, conduction
velocity, and function
Synapses
Many different axons converge
on the neuron, and their
terminal boutons form
axodendritic and axosomatic
synapses.
Synapses - structure
presynaptic membrane
synaptic cleft
postsynaptic membrane
Synapses - types
• electrical synapses
• chemical synapses
• excitatory synapses
• inhibitory synapses
• axo-dendritic, axo-somatic, axo-axonal synapses
Synapses
Excitatory postsynaptic
potential (EPSP)
Inhibitory postsynaptic
potential (IPSP)
Synapses
Synapses - neurotransmitters
Small molecule transmitters
• large number of neuropeptides (substance P, enkephalin,
vasopressin, etc.)
Large molecule transmitters
• monoamines (acetylcholine, serotonin, histamine)
• catecholamines (dopamine, norepinephrine, epinephrine)
• amino acids (glutamate, GABA, glycine)
Synapses – neurotransmitters - receptors
• Each neurotransmitter (ligand) has many subtypes of
receptors – effects differ in cells.
Synapses – neurotransmitters - receptors
• Each neurotransmitter (ligand) has many subtypes of
receptors – effects differ in cells.
• Receptors are also on presynaptic membrane
(autoreceptors) – feeback control (negative, less often
positive).
• Receptors tend to group in large families (structure and
function) – ionotropic (ionic channel), metabotropic (Gproteins
and proteinkinases)
Synapses – neurotransmitters - receptors
• Each neurotransmitter (ligand) has many subtypes of
receptors – effects differ in cells.
• Receptors are also on presynaptic membrane
(autoreceptors) – feeback control (negative, less often
positive).
• Receptors tend to group in large families (structure and
function) – ionotropic (ionic channel), metabotropic (Gproteins
and proteinkinases)
• Receptors are concentrated in clusters in postsynaptic
membrane close to the place where the neurotransmitter
is released.
• Prolonged exposure to ligands results in desensitization of
the receptors – homologous and hereologous.
Synapses - neurotransmitters
Monoamines
• Intrinsic signals – e.g. rapid firing of the neuron
• Extrinsic signals – e.g. direct synaptic input from other
neurons, or diffuse action of neuromodulators
Synapses – synaptic plasticity
• Presynaptic modification – alteration of the neurotransmitter
release
• Postsynaptic modification – modulation of response to the
neurotransmitter
• Both pre- and postsynaptic modification at the same time
• Short-term changes
• Long-term changes – crucial to development and learning
• Potentiation
• posttetanic potentiation – increased size of EPSP during and
after a repetitive (tetanic) stimulation of the presynaptic
neuron (due to accumulation of Ca2+ and increased release of
the transmitter)
• may be long-term → long-term potentiation (learning)
Synapses – synaptic plasticity
• Potentiation
Synapses – synaptic plasticity
• Synaptic depression
Synapses – synaptic plasticity
• after a prolonged high-frequency stimulation - result from a
temporary depletion of the store of releasable synaptic
vesicles
• Postsynaptic inhibition/facilitation
Synapses – synaptic plasticity
• release of excitatory/inhibitory neurotransmitter on the
synapse → the probability of firing of the postsynaptic cell is
increased/decreased
• Presynaptic inhibition/facilitation
Synapses – synaptic plasticity
axo-axonal synapses
Neuromuscular junction
Neuromuscular junction
Neuromuscular junction
End-plate potential
• local depolarizing potential due to increased Na+ conductance