Introduction to the Physiology of the Nervous System

Nervous System Physiology Introduction

Issues and Communication
  • For unanswered questions, message on WhatsApp.
  • Ensure phone is working to hear the lecture.
  • Minimize distractions and focus.
  • Slides are a guide; take notes.
  • Research topics mentioned during the lecture after class.
Lecture Overview
  • Substance transport in nerves.
  • Neuron structures and functions.
  • Clinical correlations.
  • Neuronal circuits.
  • Nervous tissue supporting cells (neuroglia).
  • Ion channels: leaked, gated, and voltage-gated.
Nervous System Function
  • Enables talking, walking via impulse transmission.
  • Impairments (e.g., stroke) disrupt these transmissions.
  • Reading and comprehension rely on neurotransmission.
  • Electrochemical impulses: electrical (voltages) and chemical (neurotransmitters).
  • Neuroglia cells: Supporting cells (astrocytes, oligodendrocytes, Schwann cells, ependymal cells, satellite cells).
  • Nervous tissue = neurons + supporting cells.
Basic Functions
  • Sensory activities.
  • Interpretation of sensory input at integrative centers.
  • Motor output (response).
  • Pain experience requires information sent to integrative centers.
  • Examples: Muscular contraction, glandular secretions are because of motor output.
Functional Overview
  • Central Nervous System (CNS): brain, spinal cord (integrative areas).
  • Peripheral Nervous System (PNS): everything outside the brain and spinal cord. Anything outside the central nervous system is considered to be peripheral nervous system.
Neurons
  • Basic functional unit of the nervous system.
  • Capable of producing action potentials.
  • Nervous tissue comprises neurons and supporting (neuroglia) cells.
Neuron Structure
  • Cell Body (soma): Contains nucleus, cytoplasm.
  • Nissl bodies: Rough endoplasmic reticulum, compacted with ribosomes (protein synthesis).
  • Mitochondria and microtubules are present.
  • Dendrites: Projections from cell body membrane, receive sensory input.
  • Dendritic spines: Projections with receptors (mechanical, thermal, ligand-gated).
  • Axon: Long shaft where action potentials occur.
  • Axon Hillock: Triangular area where voltage determines channel opening.
  • Axon Terminals: End of axon, contain terminal buttons (synaptic terminals/knobs).
  • Two processes: dendrites and axon.
  • Cannot undergo mitosis (no centrioles).
  • Limited cellular division makes neural damage difficult to repair in CNS.
Protein Synthesis and Transport
  • Genetic material (DNA) in nucleus transcribes into mRNA.
  • mRNA moves to cytoplasm and is translated into proteins by ribosomes in Nissl bodies.
  • Proteins: cell membrane proteins (ion channels), neurotransmitters (GABA, acetylcholine, glycine, glutamate).
  • Golgi apparatus packages proteins into vesicles for transport.
  • Microtubules: Organelles in axon for transport, use motor proteins.
  • Motor Proteins:
    • Kinesin: Anterograde axonal transport (cell body to terminal buttons).
    • Transports organelles and synthesized proteins.
    • Dynein: Retrograde axonal transport (terminal buttons to cell body).
  • Transports organelles back to cell body. (Retrograde transport moves virus particle to cell body, for replication).
Terminal Button
  • Kinesin transports mitochondria and vesicles containing neurotransmitters.
  • SNARE proteins: On vesicles (v-SNAREs) and terminal button membrane (t-SNAREs).
  • Essential for neurotransmitter release.
  • t-SNAREs: SNAP-25, syntaxin.
  • v-SNAREs: synaptobrevin, synaptotagmin.
  • Calcium facilitates SNARE protein binding to pull vesicle to membrane, enabling exocytosis.
Neurotransmitter Release
  • Synaptic vesicles contain neurotransmitters
  • Requires SNARE proteins, the SNARE proteins are on vesicle (v-SNAREs) & terminal button membrane (t-SNAREs)
  • Example, Acetylcholine and glutamate, are excitatory neurotransmitters. Also you need the presence of calcium.
  • Exocytosis follows docking.
SNARE Proteins
  • Are critical for binding the vesicle to the terminal membrane, in the presence of calcium.
  • Without the Snares there will be no neurotransmitters release.
  • Different SNARE proteins are, on the vesicle (v-SNAREs) & terminal button membrane (t-SNAREs)
  • Botulinum = Destroys SNARE Proteins.
Clostridium tetani vs. Botulinum

  • Clostridium tetani: Destroys SNARE proteins of inhibitory neurotransmitters, leading to continuous muscle contraction (spasms).

  • Botulinum: Destroys SNARE proteins of excitatory neurotransmitters, leading to flaccid muscles (paralysis).

Neuron Classification
  • Structural: based on physical structure.
  • Functional: based on function.
Structural Classification of Neurons
  1. Multipolar: Many dendrites, one axon (common in CNS).
  2. Bipolar: One dendrite, one axon (retina, inner ear, olfactory nerve).
  3. Unipolar (Pseudo-unipolar): Single process (sensory neurons); cell bodies in ganglia.
Functional Classification of Neurons
  1. Sensory Neurons: Transmit information to the brain and spinal cord.
  2. Interneurons (Association Neurons): Relay neurons within the brain and spinal cord.
  3. Motor Neurons: Transmit information from the brain and spinal cord to effector organs (muscles, glands).