Anatomy of the Nervous System: Systems, Structures, and Cells

Chapter 3 – The Anatomy of the Nervous System

Overview

This chapter introduces the major systems, structures, and cell types that comprise the human nervous system. Understanding the organization and function of the nervous system is foundational for psychology and neuroscience students.

General Layout of the Nervous System

Main Divisions

• Central Nervous System (CNS): Consists of the brain and spinal cord. It is encased in bone (skull and vertebral column) and is responsible for processing and integrating information.

• Peripheral Nervous System (PNS): Located outside the skull and spine. It brings sensory information into the CNS and carries motor signals out to the body.

Peripheral Nervous System

Subdivisions

• Somatic Nervous System (SNS): Interacts with the external environment. It transmits sensory information from the skin, muscles, and joints to the CNS and carries motor commands from the CNS to skeletal muscles.

• Autonomic Nervous System (ANS): Regulates involuntary bodily functions such as heart rate, digestion, and breathing. It controls the activity of internal organs and glands.

Somatic Nervous System

• Afferent nerves: Carry sensory signals to the CNS from the body.

• Efferent nerves: Carry motor signals from the CNS to the muscles.

• Example: Touching a hot surface sends afferent signals to the CNS, which then sends efferent signals to withdraw the hand.

Autonomic Nervous System

• Afferent nerves: Carry sensory information from internal organs to the CNS.

• Efferent nerves: Carry motor commands from the CNS to internal organs.

• The ANS is further divided into two branches: Sympathetic and Parasympathetic nervous systems.

Organization of the Nervous System

Division	Subdivisions	Functions
Central Nervous System	Brain, Spinal Cord	Integration and processing of information
Peripheral Nervous System	Somatic NS (Afferent/Efferent), Autonomic NS (Afferent/Efferent)	Communication between CNS and body
Autonomic NS	Sympathetic, Parasympathetic	Regulation of involuntary functions

Sympathetic vs. Parasympathetic Nervous System

Sympathetic Nervous System

• Activates the fight or flight response during stressful situations.

• Increases heart rate, accelerates breathing, dilates pupils, and inhibits digestion.

• Prepares the body for rapid action.

• Example: Encountering a threat causes sympathetic activation, leading to increased alertness and energy mobilization.

Parasympathetic Nervous System

• Promotes rest and digest functions after stress has passed.

• Slows heart rate and breathing, constricts pupils, and stimulates digestion.

• Restores the body to a state of calm.

• Example: After a stressful event, parasympathetic activity helps the body recover and conserve energy.

Comparison Table: Sympathetic vs. Parasympathetic Effects

Organ/System	Sympathetic Effect	Parasympathetic Effect
Pupil	Dilates	Constricts
Heart	Accelerates rate	Slows rate
Digestive Tract	Inhibits motility/secretion	Stimulates motility/secretion
Bladder	Relaxes	Contracts
Sexual Function	Stimulates ejaculation	Stimulates erection

Neural Pathways and Exit Points

• Both sympathetic and parasympathetic systems use two-stage neural pathways (preganglionic and postganglionic neurons).

• Sympathetic: Synapse close to the spinal cord, then travel far to target organ. Exit from thoracic and lumbar regions.

• Parasympathetic: Synapse far from the spinal cord, then travel a short distance to target organ. Exit from cranial and sacral regions.

Key Terms and Definitions

• Central Nervous System (CNS): The brain and spinal cord; the main control center for processing information.

• Peripheral Nervous System (PNS): All neural structures outside the CNS; connects the CNS to limbs and organs.

• Somatic Nervous System: Controls voluntary movements and transmits sensory information.

• Autonomic Nervous System: Regulates involuntary bodily functions.

• Sympathetic Nervous System: Mobilizes body resources during stress.

• Parasympathetic Nervous System: Conserves energy and restores the body to a resting state.

• Afferent Nerves: Carry signals toward the CNS.

• Efferent Nerves: Carry signals away from the CNS.

Diagram: Organization of the Nervous System

Additional info: The diagram in the materials visually represents the hierarchical structure of the nervous system, showing the CNS and PNS, and further subdivisions into somatic/autonomic systems and their respective afferent/efferent nerves.

Summary

• The nervous system is divided into the CNS and PNS, each with distinct roles.

• The PNS is further divided into the somatic and autonomic systems, which control voluntary and involuntary functions, respectively.

• The autonomic system consists of the sympathetic and parasympathetic branches, which generally have opposite effects on organ systems.

• Understanding these divisions is essential for studying brain function, behavior, and psychological processes.