Neurophysiology: Homeostasis, Synaptic Transmission, and Muscle Function

Homeostasis and AllostasisPage 1

Homeostasis is the maintenance of physiological stability (temperature, blood pressure, blood glucose, pH). Allostasis refers to the body's adaptive response to restore homeostasis. Regulatory systems include feed-forward mechanisms (anticipatory) and feedback loops (negative and positive).

Ionic Channels and Membrane PotentialPage 2

Cell membranes are semi-permeable lipid bilayers requiring ion channels and pumps. Ion pumps (active transport) like the Na+/K+ ATPase maintain gradients. Voltage-gated and ligand-gated channels facilitate passive ionic flow. The resting membrane potential (approx. -70 mV) is defined by ionic permeability and is characterized by the Nernst and Goldman equations.

Action Potentials and ConductionPage 5

Action potentials are all-or-nothing depolarizations used for cell communication. The process involves Na+ influx (depolarization) and K+ efflux (repolarization). Conduction speed is increased by myelin sheaths and Nodes of Ranvier, while demyelinating diseases like Multiple Sclerosis impair signal transmission.

Synaptic TransmissionPage 10

Communication occurs at synapses (electrical or chemical). Chemical synapses involve neurotransmitter release via calcium-dependent exocytosis. Ionotropic receptors provide fast responses, while metabotropic (G-protein coupled) receptors provide slower, biochemical modulation.

Synaptic PlasticityPage 20

Synaptic efficacy is modified by experience through short-term and long-term plasticity. Long-term potentiation (LTP) and depression (LTD) are activity-dependent processes involving NMDA receptors and calcium signaling, fundamental to learning and memory. Synaptic scaling serves an homeostatic role to stabilize overall neuronal excitability.

Muscle ContractionPage 25

Muscle contraction follows the sliding filament theory, driven by the cyclic interaction of actin and myosin (crossbridge cycle) fueled by ATP and calcium. Skeletal muscle is regulated by troponin/tropomyosin, while smooth muscle relies on calcium-calmodulin and myosin phosphorylation. The heart utilizes the Frank-Starling mechanism to regulate its pumping capacity.

Sleep PhysiologyPage 37

Sleep consists of NREM and REM stages, regulated by systemic changes in cerebral metabolic activity and thalamocortical gating. NREM is characterized by slow oscillations, whereas REM shows high cerebral activity despite muscle paralysis, serving critical roles in cognitive restoration and brain homeostasis.