Central and Peripheral Nervous System: Structure, Function, and Sensory Integration

Central and Peripheral Nervous System

Overview

The nervous system is a complex network responsible for integrating sensory information, coordinating voluntary and involuntary actions, and maintaining homeostasis. It is divided into the central nervous system (CNS) and the peripheral nervous system (PNS), each with specialized structures and functions.

Major Functions of the CNS

Key Roles

• Integration Center: The CNS processes and interprets sensory input, making decisions and issuing commands.

• Coordination of Voluntary Movement: The CNS initiates and controls voluntary muscle activity.

• Homeostasis: The CNS regulates internal environment, including temperature, pH, and other vital parameters.

• Higher Mental Functions: Responsible for consciousness, memory, learning, and emotion.

Brain Structure and Function

Major Brain Regions

• Cerebrum: Largest part, responsible for higher brain functions such as thought, memory, and voluntary movement.

• Cerebellum: Coordinates movement and balance.

• Brainstem: Controls basic life functions (breathing, heart rate).

• Diencephalon: Includes thalamus and hypothalamus, involved in sensory relay and homeostasis.

Functional Areas of the Cerebral Cortex

• Motor Areas: Control voluntary muscle movements.

• Sensory Areas: Receive and interpret sensory information.

• Association Areas: Integrate information for complex functions such as reasoning and language.

Peripheral Nervous System (PNS)

Divisions

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

• Efferent Division: Carries motor commands from the CNS to effectors (muscles and glands).

Special Senses

• Vision, Hearing, Taste, Smell, Touch: Each sense has specialized receptors and neural pathways.

• Example: Photoreceptors in the retina convert light into electrical signals for vision.

Neural Pathways and Synaptic Transmission

Key Concepts

• Reflex Arcs: Simple neural circuits that mediate reflex actions.

• Synaptic Transmission: Communication between neurons via neurotransmitters across synapses.

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

Homeostasis and the Nervous System

Role in Regulation

• Autonomic Nervous System (ANS): Subdivision of the PNS that regulates involuntary functions (e.g., heart rate, digestion).

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

• Parasympathetic Division: Promotes 'rest and digest' activities.

Muscle Physiology

Types of Muscle Tissue

• Skeletal Muscle: Voluntary, striated muscle attached to bones.

• Cardiac Muscle: Involuntary, striated muscle found in the heart.

• Smooth Muscle: Involuntary, non-striated muscle in walls of hollow organs.

Muscle Contraction

• Sliding Filament Theory: Muscle contraction occurs when actin and myosin filaments slide past each other.

• Role of Calcium: Calcium ions trigger contraction by enabling cross-bridge formation between actin and myosin.

• ATP: Provides energy for muscle contraction and relaxation.

Key Terms and Definitions

• Neuron: Basic functional unit of the nervous system, specialized for signal transmission.

• Action Potential: Rapid change in membrane potential that propagates along the axon.

• Receptor: Specialized cell or structure that detects stimuli.

• Effector: Muscle or gland that carries out the response to neural signals.

Sample Table: Comparison of CNS and PNS

Feature	CNS	PNS
Main Components	Brain, Spinal Cord	Cranial and Spinal Nerves
Function	Integration, Processing	Transmission of Signals
Protection	Skull, Vertebral Column, Meninges	Minimal (connective tissue coverings)
Regeneration	Limited	Possible (especially in axons)

Sample Equations

• Resting Membrane Potential:

$V_m = V_{inside} - V_{outside}$

• Ohm's Law (applied to neural conduction):

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

Clinical Reasoning and Application

• Example: Damage to the left side of the brain often results in deficits on the right side of the body due to the crossing of motor pathways.

• Application: Understanding sensory and motor pathways aids in diagnosing neurological disorders.

Summary

The nervous system's structure and function are foundational to understanding human physiology. Mastery of these concepts is essential for further study in anatomy, physiology, and clinical practice.