BS2550 - Neuronal and Cellular Signalling Lecture 1 Main Components of the Nervous System The Nervous System is an information processing system. The CNS consists of the brain and spinal cord. PNS = sensory neurons that link sensory receptors with circuits in the CNS: o Somatic motor division = motor axons that connect the brain and spinal cord to skeletal muscles. o Autonomic motor division = cells and axons that innervate the smooth/cardiac muscle and glands. Cells of the NS can be divided into: - Nerve cells (neurons) - specialised for long distance electrical signalling. - Glial cells - support signalling functions of neurons, function in the developing and adult NS, repair NS damage, can act as stem cells in some brain areas - promote regrowth. Neurons Neurons are specialised for long distance electrical signalling and intercellular communication via synapses. They have an obvious morphology = axon, dendrites, and branching. - Axons = most neurons only have one axon (away from cell body) - this can be branched. - Short axons are a feature of interneurons - projection neurons feature very long axons. - Dendrites = primary targets for synaptic input from axon terminals of other neurons. - The size and branching on dendrites can vary - neurons lacking many dendrites will have a limited capacity to relay information (will receive less complex input from fewer axons) - neurons with more complex dendrites allow for greater integration of information. There are 3 functional classes of neurons: - Motor (efferent) - away from the CNS. - Sensory (afferent) - towards the CNS. - Interneurons relay or connect sensory and motor neurons.
Presynaptic and postsynaptic neurons communicate via the secretion of molecules from the pre terminal - these bind to the adjacent post receptors on target cell. - Neurotransmitters - must diffuse through the synaptic cleft - these are secreted from the presynaptic terminal in synaptic vesicles by exocytosis. - Number of inputs to a single neuron = convergence. - Number of targets innervated by a single neuron = divergence. They convey electrical signals over long distances via a self-generating wave of electrical activity called an action potential (AP) - these are all-or-nothing changes in the electrical potential across the nerve cell membrane. - Information encoded by APs is passed on at the synapse = synaptic transmission. - Most abundant type of synapse = chemical - electrical synapses exist too (mediated by gap junctions). Glial Cells Glial cells are support cells; they are physically connected to neurons but do not directly participate in electrical signalling. They do not directly participate in synaptic transmission - support signalling function of neurons. List of functions: - Modulate the rate of nerve signal propagation, - Control uptake and metabolism of NTs at/near the synaptic cleft, - Provide an interface between the brain and immune system. There are 3 types of glial cells: - Astrocytes = only in CNS - main function is to maintain appropriate chemical environment for neurons - involved in formation of blood brain