Central Nervous System: Structure, Function, and Protection (Ch. 11 & 12a) Study Guide

CH 11. Nervous System and Tissue

Action Potentials in Neurons

The generation and propagation of action potentials are fundamental processes in neuronal communication. Action potentials are rapid electrical signals that travel along the axon of a neuron, allowing for the transmission of information throughout the nervous system.

• Generation: Initiated when a neuron's membrane potential reaches a threshold, causing voltage-gated sodium channels to open and sodium ions to rush into the cell, depolarizing the membrane.

• Propagation: The depolarization spreads along the axon as adjacent voltage-gated channels open, creating a wave of electrical activity. Repolarization follows as potassium channels open, restoring the resting potential.

• Example: Sensory neurons transmit pain signals from the skin to the spinal cord via action potentials.

Additional info: The refractory period ensures unidirectional propagation and limits the frequency of action potentials.

CH 12a. Central Nervous System – The Brain

Structural and Functional Divisions of the Nervous System

The nervous system is divided into central and peripheral components, each with distinct roles in processing and transmitting information.

• 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 tissue outside the CNS; subdivided into sensory (afferent) and motor (efferent) divisions.

• Functional Divisions: The motor division is further divided into the somatic (voluntary control of skeletal muscles) and autonomic (involuntary control of smooth muscle, cardiac muscle, and glands) nervous systems.

Major Regions of the Adult Brain

The adult brain is organized into several major regions, each with specialized functions.

• Cerebrum: Largest part, responsible for higher cognitive functions.

• Diencephalon: Contains structures such as the thalamus and hypothalamus.

• Brain Stem: Includes the midbrain, pons, and medulla oblongata; controls basic life functions.

• Cerebellum: Coordinates movement and balance.

Lobes, Fissures, and Functional Areas of the Cerebral Cortex

The cerebral cortex is divided into lobes and functional areas, separated by prominent fissures.

• Lobes: Frontal, parietal, temporal, and occipital.

• Fissures: Longitudinal fissure (separates hemispheres), central sulcus (separates frontal and parietal lobes), lateral sulcus (separates temporal from frontal and parietal).

• Functional Areas: Motor areas (control movement), sensory areas (process sensory input), association areas (integrate information).

Lateralization of Cortical Function

Lateralization refers to the specialization of certain functions in either the left or right cerebral hemisphere.

• Left Hemisphere: Typically dominant for language, math, and logic.

• Right Hemisphere: Involved in spatial abilities, face recognition, and creativity.

• Example: Broca's area (speech production) is usually located in the left hemisphere.

Primary Motor Cortex and Somatosensory Cortex: The Homunculus

The primary motor cortex (precentral gyrus) and primary somatosensory cortex (postcentral gyrus) are mapped according to the body regions they control or receive input from, forming a 'homunculus' or body map.

• Motor Homunculus: Represents the distribution of motor control; areas with fine motor skills (e.g., hands, face) occupy larger regions.

• Somatosensory Homunculus: Represents the distribution of sensory input; areas with greater sensitivity have larger cortical representation.

Major Regions of the Brain Stem and Their Functions

The brain stem is composed of three main regions, each with essential functions for survival.

• Midbrain: Controls visual and auditory reflexes.

• Pons: Relays information between the cerebrum and cerebellum; regulates breathing.

• Medulla Oblongata: Controls heart rate, blood pressure, and respiratory rhythm.

Structure and Function of the Cerebellum

The cerebellum is located at the back of the brain and is crucial for motor coordination and balance.

• Structure: Two hemispheres with a highly folded surface (folia).

• Function: Integrates sensory input and fine-tunes voluntary movements; maintains posture and equilibrium.

Diencephalon: Location, Subdivisions, and Functions

The diencephalon is situated between the brain stem and cerebrum and consists of several important structures.

• Thalamus: Relay station for sensory information.

• Hypothalamus: Regulates homeostasis, endocrine activity, and autonomic functions.

• Epithalamus: Includes the pineal gland, which secretes melatonin.

Ventricles of the Brain

The brain contains four interconnected ventricles filled with cerebrospinal fluid (CSF).

• Lateral Ventricles (2): Located in each cerebral hemisphere.

• Third Ventricle: Located in the diencephalon.

• Fourth Ventricle: Located between the brain stem and cerebellum.

Formation and Circulation of Cerebrospinal Fluid (CSF)

CSF is produced by the choroid plexuses in the ventricles and circulates through the ventricular system and subarachnoid space.

• Formation: Produced by filtration of blood plasma through ependymal cells in the choroid plexus.

• Circulation Pathway: Lateral ventricles → third ventricle → fourth ventricle → subarachnoid space → absorbed into venous blood via arachnoid granulations.

Protection of the CNS: Meninges, CSF, and Blood Brain Barrier

The central nervous system is protected by several physical and chemical barriers.

• Meninges: Three connective tissue membranes (dura mater, arachnoid mater, pia mater) that cover the brain and spinal cord.

• Cerebrospinal Fluid (CSF): Cushions the brain, provides nutrients, and removes waste.

• Blood Brain Barrier: Selective permeability barrier formed by endothelial cells; protects the brain from toxins and pathogens while allowing essential nutrients to pass.