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.