The Nervous System and Nervous Tissue

The Nervous System Overview

  • Nervous System Functions: Master control and communication system of the body

    • Communicates through electrical and chemical signals

    • Rapid, specific responses with immediate effects

Functions of the Nervous System

  1. Sensory Input: Gathering information from sensory receptors about internal and external changes

  2. Integration: Processing and interpreting sensory input at a control center

  3. Motor Output: Activating effectors (muscles and glands) to produce a response

Structure of the Nervous System

  • Central Nervous System (CNS): Composed of the brain and spinal cord

    • Integrates sensory input and dictates motor output

  • Peripheral Nervous System (PNS): All nerves that lie outside the CNS

    • Includes spinal nerves, cranial nerves, and the enteric nervous system

PNS Functional Divisions

  • Sensory (Afferent) Division:

    • Somatic sensory fibers from skin, muscles, and joints to CNS

    • Visceral sensory fibers from visceral organs to CNS

  • Motor (Efferent) Division:

    • Transmits impulses from CNS to effectors

    • Includes somatic and autonomic nervous systems

Neuroglia and Neurons

  • Neuroglia (Glial Cells): Support and protect neurons

    • Types in CNS: Astrocytes, Microglial cells, Ependymal cells, Oligodendrocytes

    • Types in PNS: Satellite cells and Schwann cells

  • Neurons: Conduct electrical impulses, characterized by longevity, high metabolic demands, and loss of division ability

Neuron Structure

  • Cell Body: Contains nucleus and organelles for metabolic activities

  • Dendrites: Receptive regions that convey incoming signals toward the cell body

  • Axon: Conducting region that generates and transmits impulses away from the cell body

    • Myelination increases the speed of impulse transmission

Membrane Potentials and Action Potentials

  • Resting Membrane Potential: The electrical charge difference across the plasma membrane

    • Generated by differences in ionic composition and permeability of the membrane

  • Action Potentials: Rapid reversal of membrane potential used for long-distance signal transmission

    • Triggered when membrane depolarization reaches a threshold

  • Refractory Periods: Periods when it is impossible or difficult to generate another action potential

Synapses

  • Synapse: Junctions mediating information transfer between neurons or neurons and effectors

    • Signal transmission occurs through electrical or chemical synapses

  • Chemical Synapses: Involve neurotransmitter release and receptors

    • Steps: Arrival of AP, neurotransmitter release, receptor binding, graded potentials in postsynaptic neuron

    • Termination of signal through reuptake, degradation, or diffusion away

Neurotransmitter Types and Functions

  • Chemical Classification: Include acetylcholine, biogenic amines, amino acids, peptides, purines, and gases

  • Functional Classification: Distinguish between excitatory and inhibitory effects based on receptor binding

    • Example: ACh can be both excitatory (at neuromuscular junctions) and inhibitory (in cardiac muscle)

Neural Integration

  • Integration: Neurons functioning together in groups for broader neural functions

  • Processing Patterns:

    1. Serial Processing: Input along one pathway; typical in reflex actions

    2. Parallel Processing: Input along multiple pathways; allows for simultaneous processing and responses.