Fundamentals of the Nervous System and Nervous Tissue: Study Notes

Chapter 11: Fundamentals of the Nervous System and Nervous Tissue

Introduction to the Nervous System

The nervous system is the master controlling and communicating system of the body. It is responsible for receiving, integrating, and responding to information from both internal and external environments.

• Functions: Sensory input, integration, and motor output

• Communication: Uses electrical and chemical signals

• Response: Produces rapid and specific immediate responses

Organization of the Nervous System

• Central Nervous System (CNS): Brain and spinal cord; integration and command center

• Peripheral Nervous System (PNS): Cranial and spinal nerves; communication lines between CNS and the rest of the body

Functional Divisions of the PNS

• Sensory (Afferent) Division: Conveys impulses from sensory receptors to CNS

• Motor (Efferent) Division: Transmits impulses from CNS to effector organs (muscles and glands)

Motor Division Subdivisions

• Somatic Nervous System: Voluntary control of skeletal muscles

• Autonomic Nervous System (ANS): Involuntary control of smooth muscle, cardiac muscle, and glands

• ANS Subdivisions: Sympathetic (activates body systems) and Parasympathetic (conserves energy, promotes housekeeping functions)

Neuroglia (Glial Cells)

Neuroglia are supporting cells in the nervous system that provide structural and functional support to neurons.

• Types in the CNS: Astrocytes, microglia, ependymal cells, oligodendrocytes

• Types in the PNS: Satellite cells, Schwann cells

Functions of Neuroglia

• Astrocytes: Support neurons, regulate exchanges between capillaries and neurons, control chemical environment, influence neuronal functioning

• Microglia: Monitor neuron health, act as phagocytes

• Ependymal Cells: Line cavities of brain and spinal cord, circulate cerebrospinal fluid

• Oligodendrocytes: Form myelin sheaths in CNS

• Satellite Cells: Surround neuron cell bodies in PNS, similar function to astrocytes

• Schwann Cells: Form myelin sheaths in PNS, vital for regeneration of damaged peripheral nerve fibers

Neurons (Nerve Cells)

Neurons are the structural and functional units of the nervous system, specialized to conduct impulses.

• Special Characteristics: Longevity, amitotic (do not divide), high metabolic rate

• Structure: Cell body (soma), dendrites, axon

Neuron Cell Body

• Contains nucleus and organelles

• Major biosynthetic center

• Clusters in CNS: nuclei; clusters in PNS: ganglia

Neuron Processes

• Dendrites: Receive input, convey graded potentials toward cell body

• Axon: Generates and transmits nerve impulses (action potentials) away from cell body

• Axon terminals release neurotransmitters

• Bundles of axons in CNS: tracts; in PNS: nerves

Myelin Sheath

• Whitish, fatty substance that insulates axons and increases speed of impulse transmission

• Formed by oligodendrocytes in CNS and Schwann cells in PNS

• Gaps in sheath: Nodes of Ranvier

Classification of Neurons

• Structural: Based on number of processes extending from cell body

  • Multipolar: Many processes (most common)

  • Bipolar: Two processes (rare, e.g., retina)

  • Unipolar: Single process (mainly in PNS as sensory neurons)

• Functional: Based on direction of impulse conduction

  • Sensory (Afferent): Transmit impulses toward CNS

  • Motor (Efferent): Carry impulses from CNS to effectors

  • Interneurons: Connect sensory and motor neurons, integration in CNS

Structural Class	Processes	Location
Multipolar	3 or more	Most CNS neurons
Bipolar	2	Retina, olfactory mucosa
Unipolar	1	Mainly PNS (sensory)

Basic Principles of Electricity in Neurons

• Voltage (V): Measure of potential energy generated by separated charge

• Current (I): Flow of electrical charge between two points

• Resistance (R): Hindrance to charge flow

• Ohm's Law:

$I = \frac{V}{R}$

• Greater voltage = greater current; greater resistance = smaller current

Membrane Potentials

• Neurons have a resting membrane potential (typically -70 mV)

• Potential difference across membrane due to ion distribution

• Changes in membrane potential are essential for nerve impulse transmission

Ion Channels

• Leakage Channels: Always open

• Gated Channels: Open/close in response to signals

  • Chemically gated: Open with binding of specific neurotransmitter

  • Voltage-gated: Open/close in response to membrane potential changes

  • Mechanically gated: Open/close in response to physical deformation

Summary Table: Comparison of Structural Classes of Neurons

Type	Processes	Location	Function
Multipolar	3 or more	CNS	Motor, interneurons
Bipolar	2	Retina, olfactory mucosa	Sensory
Unipolar	1	PNS	Sensory

Key Terms and Definitions

• Neuron: Nerve cell, basic functional unit of the nervous system

• Neuroglia: Supporting cells in nervous tissue

• Action Potential: Electrical impulse carried along axon

• Synapse: Junction between two neurons or a neuron and effector cell

• Myelin: Fatty substance insulating axons, increasing conduction speed

Additional info:

• Some content inferred and expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.