L1 The Brain: Anatomy and Functional Areas

Department: Department of Anatomy & Neuroscience, University College Cork (UCC), Ireland (Coláiste na hOllscoile Corcaigh).
Lecture Title: L1 The Brain.
Modules: NU3047 and NU3089.
Lecturer: Aonghus Lavelle.
Primary Textbook References: - Gray’s Anatomy for Students (Drake et al.), Churchill Livingstone/Elsevier. - Seeley’s Anatomy and Physiology (VanPutte et al.), McGraw Hill. - Atlas of Human Anatomy (Netter et al.), Elsevier.

Brain Components: - Cerebrum: Consists of the cerebral hemispheres. - Diencephalon Area: Contains the following structures: - Thalamus. - Hypothalamus. - Pineal body. - Brainstem: Serves as the structural connection between the brain and the spinal cord. - Cerebellum: Located posterior to the pons and attached directly to the brainstem.
The Cerebrum: - This is the largest portion of the brain. - It is divided into the Right and Left hemispheres. - Gray Matter Structures: - Nuclei: Clusters of gray matter located deep within the brain. - Cortex: The outer surface layer of the brain. - Surface Topography: - Gyri: The elevated folds or ridges on the surface. - Sulci: The shallow depressions or grooves between gyri. - Fissure: A particularly deep sulcus.

Lobes of the Cerebrum: The lobes are generally named after the overlying cranial bones: - Frontal Lobe (associated with the Frontal bone). - Parietal Lobe (associated with the Parietal bone). - Occipital Lobe (associated with the Occipital bone). - Temporal Lobe (associated with the Temporal bone).
Major Sulci and Fissures: - Longitudinal Fissure: The deep groove that separates the two cerebral hemispheres. - Lateral Sulcus: The groove that separates the temporal lobe from the overlying frontal and parietal lobes. - Central Sulcus: The groove that specifically separates the frontal lobe from the parietal lobe. - Precentral Gyrus: Located in the frontal lobe; functions as the primary motor cortex. - Postcentral Gyrus: Located in the parietal lobe; functions as the primary somatic sensory cortex. - Central Sulcus Position: This sulcus is situated exactly between the precentral and postcentral gyri.

White Matter: - Composition: Myelinated axons. - Tracts: Bundles of axons that travel together to similar destinations within the Central Nervous System (CNS).
Gray Matter: - Composition: Unmyelinated axons, cell bodies, dendrites, and neuroglia.
Structural Distribution: - In the Brain: - Gray matter is found on the outer surface (cortex) and in localized internal clusters (nuclei). - White matter is located deeper than the cortex. - In the Spinal Cord: - White matter is found on the outer surface. - Gray matter is located deeper and exhibits a characteristic "H-shape."
Inter-hemispheric Connection: - Corpus Callosum: A substantial bundle of nerve fibers that connects the right and left cerebral hemispheres, allowing for communication between them.

Functional Asymmetry: While hemispheres appear identical, certain functions (e.g., language) are not shared equally between sides.
Dominant Hemisphere: Usually the Left side. - Statistical Prevalence: Dominant in $95\%$ of right-handed individuals and more than $50\%$ of left-handed individuals. - Major Functions: Mathematics and speech.
Nondominant Hemisphere: Usually the Right side. - Major Functions: Three-dimensional (3-D) or spatial perception, recognition of faces, and musical ability.

Primary Motor Cortex (Motor Area 1): - Location: Frontal lobe, specifically the Precentral gyrus. - Cellular Composition: Contains the nerve cell bodies of Upper Motor Neurons (UMN) of the Pyramidal tracts. - Function: Responsible for the voluntary contraction of skeletal muscles. - Motor Homunculus: - Controls the movement of the opposite (contralateral) side of the body. - The body is represented "upside down" on the cortex. - The cortical area size is proportional to the precision of movement; larger areas are dedicated to parts requiring fine motor control, such as hand muscles and the tongue.
Premotor Area (Motor Area 2): - Location: Frontal lobe, anterior to the primary motor area. - Cellular Composition: Contains extrapyramidal neurons. - Function: Controls skilled, learned motor activities of a repetitive nature (e.g., typing).
Broca's Area (Motor Area 3): - Location: Frontal lobe, anterior to the lower premotor area; found in the dominant hemisphere (usually the left). - Function: Motor speech; it sends messages to the appropriate muscles required to actually produce sounds.

Primary Somatic Sensory Cortex (Sensory Area 1): - Location: Parietal lobe, specifically the Postcentral gyrus. - Function: Receives general sensory information. - Sensory Homunculus: - Provides a map of the opposite (contralateral) side of the body. - The body is represented "upside down." - The size of the cortical region is related to the density of sensory receptors in that specific body area (e.g., large regions for the hands and lips).
Other Primary Sensory Cortices: - Primary Taste Cortex: Located in the parietal lobe. - Primary Olfactory Cortex: Located in the temporal lobe. - Primary Auditory Cortex: Located in the temporal lobe. - Primary Visual Cortex: Located in the occipital lobe.

Wernicke’s Area (Sensory Area 6): - Location: Dominant hemisphere (usually the left). - Function: Sensory speech; involved in understanding heard language and thinking of what to say.
Speech Pathology Terms: - Dysphasia / Aphasia: Refers to absent or defective speech or language comprehension (the ability to understand spoken language). - Etiology: Caused by a lesion located somewhere in the speech pathway. - Pathological Sites: Damage may include Broca’s area, Wernicke’s area, or the connections between them.