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45 Organization of the
Nervous System, BasicFunctions of Synapses, “Transmitter Substances”
Dr. A.R. Jamshidi Fard2011
The Central Nervous System
• CNS
Brain
Spinal cord ~
Peripheral Nervous System
• Somatic Nervous System - SNS
Sensory & Motor
• Autonomic Nervous System - ANS Sympathetic Division
Parasympathetic Division
• Cranial Nerves - 12 Pair
• Spinal Nerves - 31 Pair ~
A typical neuron
Action potentials in the squid giant axon
Electrical signals are propagated by voltage-dependent channels
• A threshold depolarisation causes adjacent sodium channels to open– Signals move along axons >>>> DOMINO
The properties of single ion channels can be observed and manipulated using the patch-clamp method
Myelinated nerve cells have much faster rates of transmission
Passive diffusion of Na+ ions triggers voltage-dependent gates at the next node of Ranvier
Simple circuits – the knee-jerk response
REFLEX
ARCH
Central Nervous System Neuron: The BasicFunctional Unit
1- Sensory Part of the Nervous SystemSensory Receptors
3- Processing of Information—“Integrative” Function of theNervous System
4 -Storage of Information—Memory
2- Motor Part of the Nervous SystemEffectors
Major Levels of CentralNervous System Function
First Neuron Order
Second Neuron Order
Third Neuron Order
Comparison ofthe Nervous System with a Computer
Types of Synapses:Chemicaland Electrical
Ca
Ca
Ca
CaCa
“Second Messenger” System in the Postsynaptic Neuron
Inhibition1. Opening of chloride ion channels through the postsynaptic neuronal membrane. 2. Increase in conductance of potassium ions out of the neuron.3. Activation of receptor enzymes that inhibit cellular metabolic functions that increase the number of inhibitory synaptic receptors or decrease the number of excitatory receptors.
Excitation1. Opening of sodium channels 2. Depressed conduction through chloride or potassium channels, or both. 3. Various changes in the internal metabolism
of the postsynaptic neuron to excite cell activity or,
, , , increase the number of excitatory
membrane receptors or decrease the number of inhibitory
membrane receptors.
IPSPs
Or
EPSPs
Small-Molecule, Rapidly Acting TransmittersClass I AcetylcholineClass II: The Amines Norepinephrine Epinephrine Dopamine Serotonin HistamineClass III: Amino Acids Gamma-aminobutyric acid (GABA) Glycine Glutamate AspartateClass IV Nitric oxide (NO)
Neuropeptide, Slowly Acting Transmitters or Growth Factors
Hypothalamic-releasing hormones Thyrotropin-releasing hormone
Luteinizing hormone–releasing hormone Somatostatin (growth hormone inhibitory factor)
Pituitary peptides Adrenocorticotropic hormone (ACTH)
b-Endorphin a-Melanocyte-stimulating hormone
Prolactin Luteinizing hormone
Thyrotropin
Growth hormoneVasopressinOxytocinPeptides that act on gut and brainLeucine enkephalinMethionine enkephalinSubstance PGastrinCholecystokininVasoactive intestinal polypeptide (VIP)Nerve growth factorBrain-derived neurotropic factorNeurotensinInsulinGlucagonFrom other tissuesAngiotensin IIBradykininCarnosineSleep peptidesCalcitonin
“Spatial Summation” “Temporal Summation”
“Excitatory State”
Some Special Characteristics of Synaptic Transmission
Fatigue of Synaptic Transmission.
Effect of Acidosis or Alkalosis on Synaptic Transmission.
Synaptic Delay.
Effect of Hypoxia on Synaptic Transmission.
Effect of Drugs on Synaptic Transmission.