Neurophysiology

• The central nervous system consists of the brain and spinal cord.
• The peripheral nervous system consists of all other parts of the nervous system, including the somatic nervous system and the autonomic nervous system.
• The somatic nervous system is part of the peripheral nervous system.
• The brainstem consists of three parts: midbrain, pons, and medulla oblongata.
• The autonomic nervous system is also part of the peripheral nervous system.
• Microglia are not neuronal origin (small), migrate to the brain, and remain dormant until brain injury occurs.
• Schwann cells perform the same function as oligodendrocytes for the PNS, forming myelin sheaths and insulating axons, moving things quicker and enabling depolarisation to happen in the membrane.
• Axons transmit outgoing electrical signals from the integrating centre of a neuron to target cells at the end of the axon.
• Astrocytes provide a structural scaffold to neurons, are sensitive to the same neurotransmitter, and are connected to the syncytium via gap junctions, assisting in mopping up neurotransmitters released by neighbouring neurons.
• Neurotransmitters are chemical messengers which are secreted from the presynaptic membrane of a neuron, diffuse across the synaptic cleft, and temporarily bind receptors on the post synaptic membrane, propagating action potentials.
• EFFERENT NEURONS divide their axons into branches called collaterals, which are enlarged endings called axon terminals.
• Multiple sclerosis is about the lack of myelin sheath, which affects astrocytes, oligodendrocytes, and Schwann cells in their formation of the myelin sheath.
• Myelin sheaths insulate axons by insulating cells wrapping around axons, not continuous along axon, and are separated by nodes of Ranvier, enabling action potential to effectively jump between nodes, increasing the conduction velocity of action potential.
• Oligodendrocytes form myelin sheaths around some neurons, have fewer and thinner projections than astrocytes, and are not neuronal origin (small), migrating to the brain and remaining dormant until brain injury occurs.
• Glial cells are a type of support cell with four main cell types: astrocytes, DNS, type schwann, and oligodendrocytes.
• Axon cytoplasm is filled with fibers and filaments, lacking ribosomes and endoplasmic reticulum proteins.
• Dendrites increase the surface area of a neuron, allowing it to receive communication from other neurons.
• The cell body of a neuron resembles a typical cell, with a nucleus and organelles, and has an extensive cytoskeleton that extends outward into the axon.
• Neurotransmitter links to receptor, changing which may or may not open certain gated channels.
• Post-synaptic depolarisation of the membrane may occur, but not necessarily result in an action potential.
• Depolarisation of the membrane is called an action potential.
• An action potential is generated by an excitable cell, with a resting membrane potential of -70mV.
• The formation of a ligand/receptor complex in an excitatory neurone acts to depolarise the post-synaptic membrane.
• Neurotransmitter binds to receptor to depolarise, causing a synaptic transmission.
• If sufficient stimulus is applied to the post-synaptic membrane, it will depolarise the threshold of the post-synaptic membrane, causing an action potential.
• A stimulus of larger than normal magnitude would be able to limit the frequency of action potentials, ensuring unidirectional travel of an action potential.
• Relative refractory period can cause further depolarisation, lasts 2-3ms.
• Some neurons perform excitatory functions, some have inhibitory functions, and others may have both.
• The refractory period is the time when a neurone is unable to generate an action potential.
• Classical neurotransmitters include acetylcholine, monoamines (adrenaline, noradrenalin, dopamine, histamine, serotonin), and amino acids (aspartate, GABA, glycine).
• Peptides include adrenocorticotrophic hormone, antidiuretic hormone, angiotensin II, calcitonin gene-related peptide, glucagon, etc.
• Other small-molecule neurotransmitters include purines (Cadenosine, ATP) or gases (nitric oxide, carbon monoxide).
• Neurotransmitters are synthesized in the endoplasmic reticulum of neurons, stored in neurosecretory vesicles until synaptic release, and then merge with the membrane releasing their contents into the synaptic cleft via exocytosis.
• Absolute refractory period is when voltage gate Na channels are in the inactive phase, no stimulation.
• An action potential will only be generated once threshold voltage is reached.
• An increase in sympathetic activity will be accompanied by a complementary decrease in parasympathetic activity.
• The spinal cord consists of dorsal ventral roots protruding from both sides, with dorsal roots carrying afferent signals and the ventral roots carrying efferent signals.
• The sympathetic nervous system generally has short preganglionic neurons and long postganglionic neurons, while the parasympathetic nervous system possesses long preganglionic neurons and short postganglionic neurons.
• The autonomic nervous system provides an interface between the environment and the Central Nervous System (CNS) for sensory information flowing to the CNS.
• The sensory pathways start with receptors, transduction process leads to an electrical response in the primary afferent called receptor potential.