Human Physiology Lecture 12: Nervous System

Nervous System

• The nervous system is responsible for rapid transmission of signals from cell to cell, ensuring coordinated function and maintenance of homeostasis in the body.
• It consists of two major subsystems: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

Central Nervous System (CNS)

• Consists of the brain and spinal cord.
• Receives and sorts out information from the environment and inside the body, determining the appropriate response.

Peripheral Nervous System (PNS)

• Made up of nerves that extend throughout the body.
• Enables communication between the CNS and body tissues.
• Comprised of the Somatic Nervous System and Autonomic Nervous System.

Neuron Structure

• Cell Body: contains the nucleus with genetic information.
• Dendrites: receive information.
• Axon: carries information over long distances; may be myelinated.
• Axon Terminals: transmit information.

Universal Properties of Neurons

• Excitability (irritability): ability to respond to environmental changes (stimuli).
• Conductivity: production of traveling electrical signals that quickly reach other cells.
• Secretion: release of chemical neurotransmitters that stimulate other cells.

Resting Membrane Potential

• Unequal distribution of ions (sodium and potassium) on either side of the nerve cell membrane.
• Results in a potential difference of approximately -70 mV, with the inside being negative relative to the outside.

Action Potential

• Rapid change in membrane potential (from -70 mV to +30 mV) in response to stimulation.
• Occurs only in areas with a high density of voltage-regulated ion gates.
• Threshold stimulus: minimum stimulus required to generate an action potential.

Synaptic Transmission

• Three kinds of synapses with different modes of action: excitatory cholinergic, inhibitory GABA-ergic, and excitatory adrenergic.
• Synaptic delay: time from arrival of signal at axon terminal to beginning of action potential in postsynaptic cell (approximately 0.5 msec).

Excitatory Cholinergic Synapse

• Employs acetylcholine (ACh) as its neurotransmitter.
• ACh excites some postsynaptic cells and inhibits others.
• Description of excitatory action:
  • Voltage-regulated calcium gates open, allowing calcium influx.
  • Exocytosis of synaptic vesicles releasing ACh.
  • ACh binds to ligand-regulated gates on the postsynaptic neuron, allowing sodium influx and potassium efflux.
  • Depolarization of postsynaptic neuron, potentially leading to an action potential.

Inhibitory GABA-ergic Synapse

• Employs γ-aminobutyric acid (GABA) as its neurotransmitter.
• GABA receptors are chloride channels.
• Cl- influx makes the inside of the postsynaptic neuron more negative than the resting membrane potential, inhibiting it.

Excitatory Adrenergic Synapse

• Employs norepinephrine (NE) as its neurotransmitter.
• Receptor is a transmembrane protein associated with a G protein.
• NE binds to the receptor, causing the G protein to dissociate and activate adenylate cyclase.
• This leads to the production of cyclic AMP (cAMP), which can induce various effects, including:
  • Opening of ligand-regulated ion gates from the inside of the membrane.
  • Activation of cytoplasmic enzymes leading to diverse metabolic changes.
  • Induction of genetic transcription.

Understanding the nervous system's role in maintaining homeostasis and communication within the body. Covers the importance of cell coordination and the difference between nervous and endocrine systems.