The Central Nervous System: Structure and Function of the Brain and Cerebral Cortex

The Central Nervous System

Overview

The central nervous system (CNS) is composed of the brain and spinal cord, serving as the primary control center for the body. It integrates sensory information and coordinates bodily functions.

• Brain: Divided into four main regions—cerebral hemispheres, diencephalon, brain stem, and cerebellum.

• Spinal Cord: Connects the brain to the peripheral nervous system and transmits neural signals.

Regions and Organization of the CNS

Spinal Cord

• Central cavity surrounded by gray matter.

• External white matter composed of myelinated fiber tracts.

Brain

• Similar pattern to spinal cord, but with additional areas of gray matter in cerebral hemispheres and cerebellum.

• Outer gray matter called cortex.

Cerebral Hemispheres

Surface Features

The cerebral hemispheres are characterized by ridges (gyri), shallow grooves (sulci), and deep grooves (fissures).

• Longitudinal fissure: Separates left and right hemispheres.

• Transverse cerebral fissure: Separates cerebrum from cerebellum.

Lobes of the Cerebral Hemispheres

Five Lobes
Frontal
Parietal
Temporal
Occipital
Insula

Major Sulci

• Central sulcus: Separates frontal and parietal lobes.

• Parieto-occipital sulcus: Separates parietal and occipital lobes.

• Lateral sulcus: Outlines temporal lobes.

Cerebral Cortex

Structure and Function

The cerebral cortex is the thin (2–4 mm) superficial layer of gray matter, accounting for about 40% of the brain's mass. It is the site of conscious mind functions, including:

• Sensory perception

• Voluntary motor initiation

• Communication

• Memory storage

• Understanding

General Considerations

• Three types of functional areas:

  1. Motor areas: Control voluntary movement.

  2. Sensory areas: Conscious awareness of sensation.

  3. Association areas: Integrate diverse information.

• Each hemisphere is concerned with the contralateral side of the body.

• Lateralization of cortical function exists.

• Conscious behavior involves the entire cortex.

Motor Areas of the Cerebral Cortex

Primary Motor Cortex

• Located in the precentral gyrus of the frontal lobe.

• Controls precise, skilled, voluntary movements.

• Contains large pyramidal cells (upper motor neurons).

Premotor Cortex

• Helps plan movements.

• Controls learned, repetitive, or patterned motor skills.

• Coordinates simultaneous or sequential actions.

• Controls voluntary actions dependent on sensory feedback.

Broca's Area

• Present in one hemisphere (usually the left).

• Motor speech area that directs muscles of speech production.

• Active in planning speech and voluntary motor activities.

Sensory Areas of the Cerebral Cortex

Primary Somatosensory Cortex

• Located in the postcentral gyrus of the parietal lobe.

• Receives sensory information from skin, skeletal muscles, and joints.

• Capable of spatial discrimination.

Somatosensory Association Cortex

• Integrates sensory input for understanding objects.

• Determines size, texture, and relationship of parts of objects being felt.

Visual Areas

• Primary visual (striate) cortex: Located in the occipital lobe; receives visual information from the retina.

• Visual association area: Surrounds the primary visual cortex; interprets visual stimuli (e.g., color, form, movement).

Auditory Areas

• Primary auditory cortex: Located in the superior margin of the temporal lobe; interprets information from inner ear as pitch, loudness, and location.

• Auditory association area: Located posterior to the primary auditory cortex; stores memories of sounds and permits perception of sound stimuli.

Vestibular Cortex

• Located in the posterior part of the insula and adjacent parietal cortex.

• Responsible for conscious awareness of balance (position of head in space).

Olfactory Cortex

• Primary olfactory (smell) cortex: Located in the medial aspect of temporal lobes; region of conscious awareness of odors.

Gustatory Cortex

• Located in the insula just deep to the temporal lobe.

• Involved in perception of taste.

Visceral Sensory Area

• Posterior to gustatory cortex.

• Conscious perception of visceral sensations (e.g., upset stomach, full bladder).

Multimodal Association Areas

Overview

Multimodal association areas receive inputs from multiple sensory areas and send outputs to multiple areas, including the premotor cortex. They allow meaning to be assigned to information, store it in memory, tie it to previous experience, and decide on actions.

• Sensations, thoughts, and emotions become conscious—makes us who we are.

Three Broad Parts

1. Anterior association area (prefrontal cortex): Involved with intellect, cognition, recall, and personality. Contains working memory for abstract ideas, judgment, reasoning, persistence, and planning. Development depends on feedback from social environment.

2. Posterior association area: Large region in temporal, parietal, and occipital lobes. Plays a role in recognizing patterns and faces, localizing us in space, and binding different sensory inputs. Involved in understanding written and spoken language (Wernicke's area).

3. Limbic association area: Part of the limbic system; includes cingulate gyrus, parahippocampal gyrus, and hippocampus. Provides emotional impact that helps establish memories.

Summary Table: Major Functional Areas of the Cerebral Cortex

Area	Location	Main Function
Primary Motor Cortex	Precentral gyrus (frontal lobe)	Voluntary movement control
Premotor Cortex	Anterior to precentral gyrus	Planning and coordination of movements
Broca's Area	Frontal lobe (usually left)	Speech production
Primary Somatosensory Cortex	Postcentral gyrus (parietal lobe)	Sensory input from skin, muscles, joints
Visual Cortex	Occipital lobe	Visual information processing
Auditory Cortex	Temporal lobe	Auditory information processing
Vestibular Cortex	Insula/parietal cortex	Balance awareness
Olfactory Cortex	Temporal lobe	Smell perception
Gustatory Cortex	Insula	Taste perception
Visceral Sensory Area	Insula	Visceral sensation awareness
Prefrontal Cortex	Frontal lobe	Intellect, cognition, personality
Posterior Association Area	Temporal, parietal, occipital lobes	Pattern recognition, spatial awareness
Limbic Association Area	Limbic system	Emotion, memory

Key Terms and Definitions

• Gyri: Elevated ridges of the brain surface.

• Sulci: Shallow grooves separating gyri.

• Fissures: Deep grooves separating large regions of the brain.

• Cortex: Outer layer of gray matter in the brain.

• Contralateral: Refers to the opposite side; each hemisphere controls the opposite side of the body.

• Lateralization: Specialization of function in each hemisphere.

Additional info:

• Functional areas of the cerebral cortex are highly interconnected, allowing for complex behaviors and integration of sensory and motor information.

• Damage to specific cortical areas can result in loss of particular functions, such as speech, movement, or sensory perception.