Neuronal and Cellular Signalling Lecture 1 Notes: Principles of Signalling in the Nervous System Neuronal Cells - The nervous system is an information processing system - There are 2 functional classes of neurons: (a) Motor (efferent, away from the CNS) (b) Sensory (afferent, toward the CNS) (c) Interneurons - Spinal nerves are mixed (i.e. each contain motor and sensory nerve fibres - Similarly, cranial nerves are mixed, or they an be purely sensory or motor. - Interneurons are 'relay/connector' neurons that connect sensory and motor neurons in the CNS (e.g. reflex circuit interneurons). - Cells of the nervous system include neurons and glia - Neurons consist of a receptive ('input') component (dendrites and cell body), transmission component (axon) and effector ('output') component (axon terminals). Sometimes, information can bypass the dendrites and travel directly to the cell body. - Most of the cells in the brain are granule cells (small cell bodies) - Neuronal cells are morphologically diverse, examples include: (a) Cortical (multipolar) neuron (b) Motor neuron (cat spinal cord) (c) Cerebellar (multipolar) neuron (d) Sensory neuron (pseudo-unipolar), found in the ventral spinal nerve cord (e) Unipolar MN (fly VNC) - Makram et al (2015, Blue Brain Project) analysed 0.3mm3 of a rat neocortex (around 300,000 neurons) to identify functional classes and morphological differences. They identified 207 morpho-electrical neuron sub-types in this small area in the brain. This was used to digitally reconstruct and simulate a part of the rat neocortex. Central nervous system Peripheral nervous system Brain Cranial nerves Spinal cord Spinal nerves Cerebral hemispheres, diencephalon, cerebellum, brainstem, and spinal cord (analysis and integration of sensory and motor information) nervous system Central Sensory components Sensory ganglia and nerves Sensory receptors (at surface and within the body) Motor components Visceral motor system Somatic motor system (sympathetic, parasympathetic, nervous system Peripheral and enteric divisions) Motor nerves Autonomic ganglia and nerves Internal and external environment Effectors Smooth muscles, cardiac muscles, and glands Skeletal (striated) muscles dendrite cell body axon myelin sheath axon terminal Nerve fibre (axon) Perincerisas Epiecerium ???? - Nerves are bundles of sensory and motor axons (nerve fibres) in the PNS. 5-6 fascicles form one nerve fibre (axon). Fascicle Porieuriun Epinwarium Perineurium Eddonaurium
- Glial cells (glia) are 'support' cells physically connected to neurons. Glia do not directly participate in electrical signalling. - The main types of glia include: (a) Astrocytes (CNS) (b) Oligodendrocytes (CNS) (c) Microglia (CNS) (d) Schwann cells (PNS) - Astrocytes provide structural and metabolic support to neurons. Synaptic transmission occurs via Glu and GABA transporters. Have an ionic composition and have some role in neuronal repair ('glial scars', e.g. regrowth of axons following spinal cord injury, possible involvement in dementia and AD). - Oligodendrocytes and Schwann cells myelinate glia which insulates the axons (lipid-rich myelin) to increase speed of transmission. This also provides metabolic support of the axons. - Multiple sclerosis (MS) is a disease which destroys the CNS myelin/oligodendrocytes. Therapy may be possible for this disease using the stimulation of OD stem cells. - Microglia are