VPT 321: Veterinary Neuropharmacology (2+1) copy 1

NEUROANATOMY AND NEUROPHYSIOLOGY

• The CNS consists of brain and spinal cord.
• The CNS is involved with control and co-ordination of movement and higher functions such as consciousness and memory.
• The basic functional unit of the nervous system is the nerve cell. The neuron has three parts:
  • a cell body
  • a dendritic tree and
  • an axon.
    • Soma or the cell body is responsible for metabolic functions. The soma plays a role in protein synthesis that includes the synthesis of peptide neurotransmitters or the “prohormone” form the peptide neurotransmitter. Electrical signals from synapses all over the dendrites and cell body are temporarily and spatially summated to yield a net signal that may be transmitted to other neurons via the axon and the dendrites. Thus the cell body has an integral function. The soma contains some synapses and voltage sensitive ion channels.
    • Dendrites are neuronal processes extending from the soma that contain the majority of the synapses in the CNS. Synapses are typically located on short processes called spines. The synaptic structure is generally referred to as a button. A button contains both pre and postsynaptic specializations. Dendrites contain voltage sensitive Na⁺ and Ca²⁺ ion channels.
    • Axons are also called as fibers. Within the CNS bundles of axons are called tracts or stria whereas in the periphery they are called nerves. Neurons are grouped into categories depending upon the length of their axons as:
      • projection neurons – long axon
      • intermediate neurons – intermediate axon and
      • local-circuit neurons – short axon.

• The CNS comprises of billions of neurons, many of which are linked to form diffuse network. Because of the complex arrangements of these transmission lines, an impulse may be
  • blocked in its transmission from one neuron to another
  • changed from a single impulse into repetitive impulses or
  • integrated with impulses from other neurons to result in highly intricate patterns of impulses in subsequent neurons.
• The basic processes of synaptic transmission in the central nervous system are essentially similar to those operating in the periphery.
• Glial cells, particularly astrocytes participate in chemical signaling, functioning essentially as ‘inexcitable neurons’.
• Nerve impulses are transmitted from one neuron to the next via specialized structures called synapses. These are chemically mediated in the vast majority of cases in the CNS.
• An important characteristic of chemically mediated synapses is that they always transmit signals in one direction.
• Transmission is initiated when the first neuron releases a chemical substance known as neurotransmitter, which impinges on the surface of the other cell.
• Usually the cell body or dendritic region is the receiving end of the neuron and the axon terminals are the transmitting ends of the cell.