Nervous System Organization Quiz

Nervous System Organization

• The nervous system has three components: sensory, integration, and response.
• The sensory component receives information from sensory organs and transmits it through sensory neurons.
• The integration component processes information in the spinal cord and brain.
• The response component transmits signals from the CNS via motor neurons to effector organs like muscles and glands.

Peripheral Nervous System

• The peripheral nervous system (PNS) is the interface between the central nervous system (CNS) and the environment.
• It includes sensory and motor neurons.
• Sensory fibers carry information from receptor organs like skin, viscera, and proprioceptors to the CNS.
• Motor fibers are further divided into somatic motor (voluntary) and autonomic nerves (sympathetic and parasympathetic).

Central Nervous System

• The central nervous system (CNS) comprises the brain and spinal cord.

Neuron Structure

• The neuron is the functional unit of the nervous system.
• The axon is the long, slender projection that transmits signals away from the cell body.
• The axon terminal is the endpoint of the axon responsible for releasing neurotransmitters.
• The cell body contains the nucleus and other organelles.
• The dendrites are branched extensions that receive signals from other neurons.

Neuroglia

• Neurons coexist with neuroglia, which provide support and protection for neurons.

Membrane Structure

• The cell membrane is composed of a phospholipid bilayer.
• Proteins embedded in the membrane play crucial roles:
  • Receptor proteins: bind neurotransmitters.
  • Channel proteins: form pores for ion movement.
  • Transport proteins: bind and transfer ions (K+ and Na+).

Resting Membrane Potential

• The resting membrane potential (RMP) is created by the uneven distribution of charged particles across the membrane.
• The RMP is typically -75mV.
• It is maintained by the sodium-potassium pump, which actively moves Na+ out of the cell and K+ into the cell.
• Selective permeability: The membrane is more permeable to K+ than Na+, contributing to the RMP.

Action Potential Generation

• An action potential (AP) is a rapid change in membrane potential that allows for nerve impulse transmission.
• The AP occurs in three stages:
  • Depolarization: Stimulation increases Na+ permeability, raising the membrane potential.
  • Threshold: When the membrane potential reaches a critical voltage (+30mV), voltage-sensitive Na+ and K+ channels open.
  • Repolarization: Na+ channels close, and K+ channels fully open, allowing K+ to flow out, returning the membrane potential to negative.

Action Potential Propagation

• The AP propagates down the axon.
• Myelination: Insulation provided by myelin sheaths increases the speed of conduction by reducing ion leaks.
• Nodes of Ranvier: Gaps in the myelin sheath that allow for rapid ion diffusion, enabling "saltatory conduction."
• Diameter of fibers: Larger diameter fibers have greater surface area for ion diffusion, resulting in faster conduction velocity.

Synapse

• A synapse is the junction between two neurons or between a neuron and an effector organ.
• It allows for the transmission of signals from one cell to another.
• Pre-synaptic terminal: The axon terminal of the presynaptic neuron, releases neurotransmitters.
• Post-synaptic terminal: The receptive area on the dendrite or cell body of the postsynaptic neuron.
• Synaptic cleft: The narrow space between the pre- and post-synaptic terminals where neurotransmitters diffuse.

Signal Transduction at the Synapse

• Signal transmission at the synapse involves the following steps:
  1. Arrival of an Action Potential (AP) at the pre-synaptic terminal.
  2. Calcium influx into the pre-synaptic terminal.
  3. Fusion of synaptic vesicles with the pre-synaptic membrane.
  4. Exocytosis of neurotransmitters into the synaptic cleft.
  5. Diffusion of neurotransmitters across the synaptic cleft and binding to receptors on the post-synaptic membrane.
  6. Receptor activation triggers a response in the postsynaptic neuron.
  7. Removal of neurotransmitters by either enzymatic breakdown or reuptake into the pre-synaptic terminal for recycling.

Neurotransmitters

• Neurotransmitters (NTs) are chemical messengers that transmit signals across synapses.
• They can be excitatory, inhibitory, or modulatory.
• Key neurotransmitters:
  • Acetylcholine (Ach): Released at neuromuscular junctions and in the autonomic nervous system (ANS). Has both nicotinic and muscarinic receptors.
  • Catecholamines:
    • Norepinephrine (Noradrenaline): Acts on α1, α2, β1, and β2 adrenoceptors.
  • Glutamate: Excitatory within the brain.
  • Glycine: Inhibitory within the spinal cord.
  • Gama-aminobutyric acid (GABA): Inhibitory within the CNS.
  • Others: Serotonin, Dopamine, and neuropeptides.

Acetylcholine Receptors

• Nicotinic receptors: Found at the NMJ and in pre-ganglionic neurons of the ANS.
• Muscarinic receptors: Found in post-ganglionic neurons of the parasympathetic nervous system.

Adrenergic Receptors

• β1 receptors: Located in the myocardium; excitatory effect.
• β2 receptors: Located in smooth muscle; relaxation effect.
• α1 receptors: Located in smooth muscle; contraction effect.

Synthesis, Storage, Release, and Deactivation of Neurotransmitters

• Neurotransmitter synthesis: Takes place in the cell body, axon, or axon terminal.
• Neurotransmitter storage: Granules or vesicles in the axon terminal.
• Neurotransmitter release: Calcium influx triggers exocytosis of neurotransmitters into the synaptic cleft.
• Neurotransmitter deactivation: Enzymatic breakdown, reuptake into the pre-synaptic terminal for reuse, or degradation and removal.

One Health Relevance

• Animal health and welfare: The nervous system controls complex physiological and biochemical processes in animals, affecting their behavior and overall health.
• Public health: Nervous system dysfunction can directly or indirectly impact behavior, productivity, and the Human-Animal bond.
• Ecosystem health and sustainability: The nervous system influences animal feeding patterns, behavior, and locomotion, impacting the food chain.

Test your understanding of the nervous system, including its organization, components, and functions. This quiz covers the sensory, integration, and response components, alongside the roles of the peripheral and central nervous systems. Dive deep into the structure and function of neurons as well!