Nervous System Overview

Learning Outcomes

• Understand the CNS and PNS in relation to afferent and efferent signals.
• Illustrate input, integration, and output signals of the nervous system.
• Compare and contrast somatic and visceral nervous systems.

Central and Peripheral Nervous Systems

• CNS: Brain (cerebrum, cerebellum, brainstem) and spinal cord.
• PNS: 12 pairs of cranial nerves and 31 pairs of spinal nerves.
  • Afferent (sensory) and efferent (motor) components.
  • Subdivided into somatic (voluntary) and autonomic (involuntary) divisions.
  • Includes ganglia and sensory receptors.

Autonomic Nervous System

• Sympathetic: Increases heart rate (fight or flight).
• Parasympathetic: Slows heart rate (rest and digest).
• Enteric: Neurons in the GI tract, monitors GI wall stretching.

Functions of the Nervous System

1. Sensory Function: Detection via receptors.
2. Integration: Analyzing and decision-making in CNS.
3. Motor Function: Initiating action, targeting muscles/glands.
4. Homeostasis: Coordination between CNS and PNS.

Sensory and Motor Neurons

• Sensory (Afferent) Neurons: Signals to CNS.
• Motor (Efferent) Neurons: Signals from CNS to PNS effectors.

Cells of the Nervous System

Neuron Structure

• Cell Body: Contains nucleus and organelles.
• Dendrites: Receive information.
• Axon: Conducts impulses.
• Synapse: Contact point between neurons.

Neuron Classification

• Structural: Unipolar, bipolar, multipolar.
• Functional: Sensory, association, motor.

Neuroglia Types

• CNS: Astrocytes, oligodendrocytes, microglia, ependymal cells.
• PNS: Schwann cells, satellite cells.

Clinical Applications

• Multiple Sclerosis: CNS demyelination.
• Guillain-Barré Syndrome: PNS demyelination.

Myelin Sheath

• Produced by oligodendrocytes (CNS) and Schwann cells (PNS).
• Insulates for faster signal transmission.
• Nodes of Ranvier: Gaps in myelin sheath.

Membrane Potentials

Pumps and Channels

• Ion concentration via pumps (Na+/K+, Ca++).
• Types: Leakage, ligand-gated, voltage-gated, mechanically-gated.

Resting Membrane Potential

• Nonconducting neuron potential: ~-70mV.
• Determined by ion distribution and membrane permeability.

Graded and Action Potentials

• Graded Potentials: Varying response.
• Action Potentials: Rapid depolarization and repolarization.
• Propagation: Continuous (unmyelinated) vs. saltatory (myelinated).

Synapses and Neurotransmitters

Synapse Types

• Electrical: Gap junctions.
• Chemical: One-way transfer.

Neurotransmitters

• Receptors: Ionotropic and metabotropic.
• Small Molecules: Acetylcholine, amino acids, etc.

Neural Integration and Circuits

• Excitatory/Inhibitory Postsynaptic Potentials: Affect action potential initiation.
• Circuit Types: Converging, diverging, reverberating, parallel-after-discharge.

Clinical Applications

• Neuropathy: Disorders of cranial/spinal nerves.
• Diseases: Parkinson’s, Alzheimer’s, Stroke, ALS, Lyme Disease, Spina Bifida.

This high-level overview captures the key components and functions of the nervous system, focusing on structure, function, and related disorders.