Physiology

• The brain is encased in the bony skull known as the Cranium
• The spinal cord runs through the vertebral column, which consists of bony vertebrae
• Gray matter in the CNS contains unmyelinated nerve cell bodies and clusters of cell bodies known as nuclei
• White matter in the CNS consists of myelinated axons and axon bundles that contain very few cell bodies
• Myelin is a lipid-rich substance that forms around nerves (axons)
• Cerebrospinal fluid (CSF) is produced in the choroid plexus in the ventricles and surrounds the entire brain
• Neurons require a constant supply of oxygen and glucose, with the brain receiving 15% of pumped blood
• The blood-brain barrier has highly selective permeability and protects the brain from toxic water-soluble compounds and pathogens
• Ascending tracks carry sensory information to the brain, while descending tracks carry commands to motor neurons
• The brain stem includes the Medulla oblongata for involuntary functions, the Pons for control of breathing, and the Midbrain for eye movement, hearing, and seeing reflexes
• The Vagus nerve is mixed, carrying sensory and efferents to many internal organs, muscles, and glands
• The Diencephalon includes the Thalamus as a sensory relay station, the Pineal gland for melatonin production, the Hypothalamus for control of homeostasis, and the Pituitary for endocrine function control
• The Cerebrum consists of two hemispheres connected by the Corpus callosum, with gray matter including the Cerebral cortex, Basal ganglia, and Limbic system
• The Motor system involves skeletal muscle movement, neuroendocrine signals, and visceral responses coordinated in the hypothalamus and medulla
• The Autonomic division controls smooth muscle, cardiac muscle, glands, and some adipose tissue, with the Parasympathetic system dominating during rest-and-digest activities and the Sympathetic system during fight-or-flight responses
• The Autonomic nervous system includes the Sympathetic system for "fight or flight" responses and the Parasympathetic system for rest, with the Vagus nerve containing about 75% of all parasympathetic fibers
• The Adrenal medulla is part of the sympathetic nervous system and releases epinephrine into the bloodstream
• Chemical signals are molecules secreted by cells into the extracellular fluid, with target cells responding to these signals
• Four basic methods of cell-to-cell communication include local communication, contact-dependent signals, and long-distance communication using hormones and neurocrine molecules
• Ligands are signal molecules that bind to receptor proteins to initiate a response in the target cell
• Receptor proteins are necessary for a cell to respond to a particular chemical signal, and the response can lead to modifying existing proteins or initiating the synthesis of new proteins
• Lipid-soluble ligands include steroid hormones like cortisol and water-soluble ligands such as neurotransmitters and lipophobic hormones like insulin and adrenaline
• Signals can be hydrophobic or hydrophilic, with lipophilic compounds able to diffuse through the membrane and bind to receptors in the cytosol
• Lipophilic ligands, such as cortisol, bind to intracellular receptors
• Extracellular receptors bind lipophobic ligands like adrenaline and insulin
• Four types of membrane receptors: channel, receptor + G-protein, receptor + enzyme, integrin
• Primary ligands or agonists activate receptors, while antagonists block receptor activity
• Competitive antagonists compete for the same binding site, causing orthosteric modulation
• Non-competitive antagonists bind to a different spot, leading to allosteric modulation
• GABA is an inhibitor allowing chlorine to flow inside the cell, decreasing the chance for an action potential to happen
• Dendrite is the acceptor-part of the neuron, while the cell body leads to the myelinated axon segments
• If depolarization reaches the synapse, calcium channels are opened (voltage dependent), allowing calcium to move into the neuron and activate the fusion of vesicle with neurotransmitter with presynaptic membrane to release contents
• Resting membrane potential: K+ chemical force somewhat higher than the electrical force needed to counteract this (-90mV)
• Neuron is very permeable to K+, leading to leakage of K+ out of the cell
• For every 3 Na+ ions pumped out, 2 K+ ions are pumped in
• Refractory period is rate-limiting to action potentials and allows one-way travel
• Sodium channels open first and fast, potassium channels open slower and later, causing hyperpolarization
• Axons are myelinated in parts, a node of Ranvier disturbs the myelinated coverage, decreasing leakage of the potential
• Calcium is an important 2nd messenger, AMPA receptors are responsible for Na+ uptake, NMDA receptors are responsible for Ca2+ uptake
• GPCR (G-protein coupled receptor) signal transduction involves Adenylyl cyclase-cAMP pathway