Human Nervous System Structure and Cognitive Brain Areas

Description of the Nervous System

Central and Peripheral Systems

Basic description of the nervous system: The nervous system consists of two major anatomically distinct but interconnected divisions.

• Peripheral nervous system (PNS): composed of groups of neurons called ganglia and peripheral nerves that lie outside the spinal cord and brain (encéfalo). These structures transmit sensory and motor information between the body and the central nervous system.
• Central nervous system (CNS): consists of the brain and the spinal cord (espinal). The CNS integrates information and coordinates activity across the organism.

Spinal Cord and Brainstem

The spinal cord extends from the base of the skull to approximately the first lumbar vertebra and contains motor neurons (motoneuronas) that mediate reflexes and convey motor commands. The brainstem includes several structures continuous with or adjacent to the spinal cord:

• Medulla oblongata (medulla): a caudal prolongation of the spinal cord that shares many structural and functional features with it.
• Pons (Varolii's bridge): adjacent to the medulla oblongata; contains a large number of neurons that distribute information from the cerebral hemispheres to the cerebellum.
• Midbrain (mesencephalon): located above the pons; participates in eye movement control and in coordinating movements of skeletal muscles.

Cerebellum and Diencephalon

Cerebellum: receives sensory information from the spinal cord, input from the motor cortex, and balance information from the inner ear (vestibular organs). It is essential for coordination and fine-tuning of movement.

Diencephalon: composed mainly of the thalamus and hypothalamus. The thalamus processes and distributes motor and sensory information that reaches the cortex, while the hypothalamus regulates autonomic functions and many homeostatic processes.

Cerebral Hemispheres and Cortex

The cerebral hemispheres are two large regions of the brain composed of white matter and neuronal nuclei. These nuclei form systems such as the basal ganglia, and other limbic structures including the hippocampal formation and amygdala, in addition to the cerebral cortex.

The cerebral cortex is divided into four lobes: frontal, parietal, temporal, and occipital.

Brain Areas for Cognition

Association Cortex Regions

The cognitive functions are located in specific areas of the brain. Three major association cortex regions are commonly distinguished:

1. Prefrontal and premotor association cortex:

   This region receives input from several higher-order sensory cortices. These connections allow sensory information to influence the planning and execution of complex, coordinated movements.

2. Parieto-temporo-occipital association cortex:

   Consists of several interspersed functional areas that lie between semantic, visual, and auditory regions and that receive projections from those sensory areas. It is important for integrating multimodal sensory information.

3. Limbic association cortex:

   Located in the medial and ventral frontal lobes. It receives projections from higher-level sensory areas and sends projections to other cortical and subcortical regions, contributing to affective, memory-related, and motivational aspects of cognition.

Note: Terminology in the original text (for example, Spanish terms such as encéfalo, espinal, and motoneuronas) has been retained in parentheses where appropriate to preserve the original content while correcting grammar and spelling and improving clarity.