Nervous System Overview

Introduction to the Nervous System

The nervous system is a complex network responsible for coordinating the body's activities by transmitting signals to and from different parts of the body. It is essential for sensation, movement, and homeostasis.

• Functions: Sensory input, integration, motor output

• Major Divisions: Central Nervous System (CNS) and Peripheral Nervous System (PNS)

• Central Nervous System (CNS): Consists of the brain and spinal cord; responsible for processing and integrating information.

• Peripheral Nervous System (PNS): Includes all neural tissue outside the CNS; connects the CNS to limbs and organs.

Organization of the Nervous System

Structural and Functional Divisions

The nervous system is organized structurally and functionally to efficiently process and respond to information.

• Structural Divisions: CNS and PNS

• Functional Divisions: Sensory (afferent) division and Motor (efferent) division

• Sensory Division: Transmits information from sensory receptors to the CNS.

• Motor Division: Transmits commands from the CNS to effector organs (muscles and glands).

• Somatic Nervous System: Controls voluntary movements of skeletal muscles.

• Autonomic Nervous System (ANS): Regulates involuntary functions (e.g., heart rate, digestion).

Cells of the Nervous System

Neurons

Neurons are the primary functional units of the nervous system, specialized for the transmission of electrical signals.

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

• Function: Receive, process, and transmit information

• Types of Neurons: Sensory neurons, motor neurons, interneurons

• Synapse: Junction between two neurons where communication occurs via neurotransmitters

Neuroglia (Glial Cells)

Neuroglia are supporting cells that provide structural and metabolic support to neurons.

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

• Types in PNS: Schwann cells, satellite cells

• Functions: Support, insulation, protection, and maintenance of the neural environment

Functional Properties of Neurons

Membrane Potential

Neurons maintain a resting membrane potential due to differences in ion concentrations across the cell membrane.

• Resting Membrane Potential: Typically around -70 mV in neurons

• Generated by: Sodium-potassium pump and differential permeability of the membrane to ions

Action Potentials

An action potential is a rapid change in membrane potential that travels along the axon, allowing neurons to transmit signals over long distances.

• Phases: Depolarization, repolarization, hyperpolarization

• Threshold: The minimum stimulus required to initiate an action potential

• All-or-None Principle: An action potential either occurs fully or not at all

Equation for Resting Membrane Potential (Nernst Equation):

Synaptic Transmission

Chemical Synapses

At chemical synapses, neurotransmitters are released from the presynaptic neuron and bind to receptors on the postsynaptic cell, leading to signal transmission.

• Neurotransmitters: Chemical messengers such as acetylcholine, dopamine, serotonin

• Synaptic Cleft: The small gap between neurons at a synapse

• Postsynaptic Potential: Change in membrane potential of the postsynaptic cell

Organization of the Peripheral Nervous System

Sensory (Afferent) Division

The sensory division carries information from sensory receptors to the CNS.

• Somatic Sensory Fibers: Convey impulses from skin, skeletal muscles, and joints

• Visceral Sensory Fibers: Convey impulses from visceral organs

Motor (Efferent) Division

The motor division transmits impulses from the CNS to effector organs.

• Somatic Nervous System: Voluntary control of skeletal muscles

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

Autonomic Nervous System (ANS)

Divisions of the ANS

The ANS is divided into the sympathetic and parasympathetic divisions, which generally have opposing effects on target organs.

• Sympathetic Division: Prepares the body for 'fight or flight' responses

• Parasympathetic Division: Promotes 'rest and digest' activities

Comparison of Sympathetic and Parasympathetic Divisions

Reflex Arcs

Components of a Reflex Arc

A reflex arc is the neural pathway that mediates a reflex action.

• Components: Receptor, sensory neuron, integration center, motor neuron, effector

• Example: Knee-jerk reflex

Summary Table: Organization of the Nervous System

Additional info:

• Some diagrams and tables were inferred based on standard Anatomy & Physiology content for the nervous system.

• Images were not included as none were 100% clearly and directly relevant to the adjacent explanations.