Neurophysiology: Organization and Structure of the Nervous System

Chapter 8. Neurophysiology

Synonyms in Neuroscience

Understanding terminology is essential in neurophysiology, as many terms have synonyms used interchangeably in textbooks and scientific literature.

Term Used in This Book	Synonym(s)
Action potential	Spike, nerve impulse, conduction signal
Autonomic nervous system	Visceral nervous system
Axon	Nerve fiber
Axonal transport	Axoplasmic flow
Axon terminal	Synaptic knob, synaptic bouton, presynaptic terminal
Axoplasm	Cytoplasm of an axon
Cell body	Cell soma, nerve cell body
Cell membrane of an axon	Axolemma
Glial cells	Neuroglia, glia
Interneuron	Association neuron
Rough endoplasmic reticulum	Nissl substance, Nissl body
Sensory neuron	Afferent neuron, afferent

Organization of the Nervous System

The nervous system is divided into central and peripheral components, each with specialized functions in processing and responding to stimuli.

• Central Nervous System (CNS): Consists of the brain and spinal cord. Responsible for integrating sensory information and coordinating responses.

• Peripheral Nervous System (PNS): Includes all neural structures outside the CNS, such as nerves and ganglia. Transmits signals between the CNS and the rest of the body.

• Afferent Pathway: Sensory neurons carry information from receptors to the CNS.

• Efferent Pathway: Motor neurons transmit commands from the CNS to effectors (muscles and glands).

• Somatic Motor Division: Controls voluntary movements via skeletal muscles.

• Autonomic (Visceral) Motor Division: Regulates involuntary functions, such as cardiac and smooth muscle activity, and glandular secretion. Subdivided into sympathetic and parasympathetic branches.

• Effectors: Target tissues that respond to neural commands, including muscles and glands.

Example: When you touch a hot surface, sensory receptors send signals via afferent neurons to the CNS, which processes the information and sends a response through efferent neurons to contract muscles and withdraw your hand.

Neurons and Nerves

Neurons are the fundamental units of the nervous system, while nerves are bundles of axons found in the peripheral nervous system.

• Neuron: A single nerve cell specialized for transmitting electrical signals. Components include dendrites, cell body (soma), axon, axon hillock, and axon terminals.

• Nerve: A collection of axons bundled together in the PNS. Nerves do not contain neuron cell bodies; those are located in ganglia or the CNS.

• Ganglia: Clusters of neuron cell bodies located in the PNS.

• Example: The median and ulnar nerves in the arm are bundles of axons that transmit motor and sensory information.

Additional info: The distinction between nerves and neurons is crucial for understanding neural pathways and clinical conditions affecting the nervous system.

Types of Neurons

Neurons are classified based on their function and location within the nervous system.

• Sensory (Afferent) Neurons: Transmit sensory information from receptors to the CNS.

• Motor (Efferent) Neurons: Carry commands from the CNS to effectors such as muscles and glands.

• Interneurons: Found only in the CNS; integrate information from afferent neurons and send responses to efferent neurons.

Example: Interneurons in the spinal cord process sensory input and coordinate reflex actions.

Summary Table: Neuron Types

Type	Location	Function
Sensory (Afferent)	PNS to CNS	Transmit sensory input
Motor (Efferent)	CNS to PNS	Transmit motor commands
Interneuron	CNS	Integrate and process information

Key Definitions

• Axon: The long, slender projection of a neuron that conducts electrical impulses away from the cell body.

• Dendrite: Branch-like extensions that receive signals from other neurons.

• Ganglion: A cluster of neuron cell bodies in the PNS.

• Effector: A muscle or gland that responds to neural stimulation.

Additional info: Understanding the structural and functional organization of the nervous system is foundational for studying neurophysiology and related clinical disorders.