Central and Peripheral Nervous System: Structure and Function

The Nervous System

Overview

The nervous system is a complex network responsible for coordinating all bodily functions and responses to internal and external stimuli. It is divided into two main parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

• Central Nervous System (CNS): Consists of the brain and spinal cord. It processes information and directs responses.

• Peripheral Nervous System (PNS): Composed of nerves outside the CNS, connecting it to limbs and organs.

Central Nervous System (CNS)

Major Components

• Brain: The control center of the body, responsible for processing sensory information, thoughts, emotions, and motor functions.

• Spinal Cord: Transmits signals between the brain and the rest of the body; involved in reflex actions.

Parts of the Brain

The brain is divided into several major regions, each with specialized functions:

• Cerebrum: The largest part, responsible for higher brain functions such as thought, action, and sensory processing.

• Cerebellum: Located under the cerebrum, it coordinates voluntary movements, balance, and posture.

• Brainstem: Connects the brain to the spinal cord and controls vital functions such as breathing, heart rate, and digestion.

Cerebrum

The cerebrum is the largest part of the brain, composed of two hemispheres. It contains billions of neurons and is involved in complex processes such as reasoning, problem-solving, and voluntary movement.

• Gray Matter: Contains neuron cell bodies; involved in processing and cognition.

• White Matter: Made up of myelinated axons; transmits signals between different brain regions.

Lobes of the Cerebrum

The cerebrum is divided into four main lobes, each with distinct functions:

• Frontal Lobe: Executive functions, motor control, problem-solving.

• Parietal Lobe: Sensory processing, spatial orientation.

• Temporal Lobe: Hearing, language, memory.

• Occipital Lobe: Visual processing.

Major Fissures and Sulci

• Longitudinal Fissure: Separates the right and left cerebral hemispheres.

• Central Sulcus: Divides the frontal and parietal lobes.

• Lateral Fissure: Separates the temporal lobe from the frontal and parietal lobes.

• Parieto-Occipital Fissure: Separates the parietal and occipital lobes.

Peripheral Nervous System (PNS)

Structure and Function

The PNS connects the CNS to the limbs and organs. It is essential for transmitting sensory and motor information.

• Cranial Nerves: Emerge directly from the brain; control senses and muscle movements in the head and neck.

• Spinal Nerves: Emerge from the spinal cord; serve the rest of the body.

Types of Receptors

Receptors in the PNS detect changes in the environment and relay information to the CNS.

• Chemoreceptors: Detect chemical stimuli (e.g., taste, smell).

• Osmoreceptors: Respond to changes in solute concentrations in body fluids.

• Thermoreceptors: Sense temperature changes.

• Mechanoreceptors: Detect pressure, vibration, and body position.

• Nociceptors: Sense pain from chemical or physical damage.

Protective Structures of the CNS

Meninges

The brain and spinal cord are protected by three layers of connective tissue called meninges:

• Dura Mater: Outermost, tough layer.

• Arachnoid Mater: Middle, web-like layer.

• Pia Mater: Innermost, delicate layer that nourishes the CNS.

Functional Organization

Gray and White Matter

• Gray Matter: Contains neuron cell bodies and synapses; found in the cortex and deeper brain structures.

• White Matter: Composed of myelinated axons; forms tracts for communication within the CNS.

Spinal Cord Organization

• Dorsal Roots: Carry sensory information to the CNS.

• Ventral Roots: Carry motor information from the CNS to muscles.

• Spinal Nerves: Formed by the fusion of dorsal and ventral roots.

Reflexes

Reflex Arc

A reflex arc is the pathway by which a reflex action occurs, typically involving sensory neurons, interneurons, and motor neurons.

• Monosynaptic Reflex: Involves a single synapse between a sensory and motor neuron; fastest type (e.g., knee-jerk reflex).

• Polysynaptic Reflex: Involves multiple synapses; slower but allows for more complex responses.

Examples of Reflexes

• Muscle Spindle Reflex: Maintains muscle tone and posture.

• Tendon Reflex: Prevents muscle damage from excessive tension.

• Babinski Reflex: Used to assess neurological function; normal in infants, abnormal in adults.

Summary Table: CNS vs. PNS

Feature	Central Nervous System (CNS)	Peripheral Nervous System (PNS)
Main Components	Brain, Spinal Cord	Cranial Nerves, Spinal Nerves
Function	Processing, integration, coordination	Transmission of signals to/from CNS
Protection	Skull, vertebrae, meninges	Connective tissue coverings
Types of Matter	Gray and White Matter	Nerve fibers

Key Terms and Definitions

• Neuron: A nerve cell; the basic unit of the nervous system.

• Synapse: Junction between two neurons where communication occurs.

• Myelin: Fatty substance that insulates axons, increasing signal speed.

• Corpus Callosum: Large bundle of nerve fibers connecting the two cerebral hemispheres.

• Hydrocephalus: Accumulation of cerebrospinal fluid (CSF) in the brain, causing increased pressure.

Important Equations

• Nerve Conduction Velocity: $v = \frac{d}{t}$ where $v$ is velocity, $d$ is distance, and $t$ is time.

Additional info:

• Some details about the organization of the spinal cord and reflexes were inferred from standard anatomy and physiology knowledge.

• Images referenced in the notes illustrate the anatomical structures described.