Med 7107: The Cerebrum Lecture 1

Lecture 1: The Cerebrum

• The lecture is on the cerebrum, part of the neuroscience course (Med 7107).
• The instructor is Savannah Newell, PhD, Assistant Professor of Anatomical Sciences at Edward Via College of Osteopathic Medicine (VCOM) in Louisiana.
• The lecture date is Block 3, 2025.

Learning Objectives

• Students will recall the cerebrum's function within the nervous system's macroscopic organization.
• Students will locate lobes of the cerebral hemisphere.
• Students will recognize major gyri and sulci of the cerebral cortex.
• Students will recognize the histological organization of the cortex.
• Students will recognize the concept of Brodmann areas.
• Students will identify primary motor, primary somatosensory, and association areas of the cortex.
• Students will recognize somatotropic organization of the somatosensory cortex.
• Students will recognize the somatotropic organization of the primary motor cortex.
• Students will locate the subcortical gray matter (basal ganglia).
• Students will recognize white matter fiber tracts connecting cortical areas.
• Students will recognize the somatotopic organization of fibers traversing the internal capsule.
• Students will learn directional, descriptive, and laterality terms in relation to the nervous system and clinical imaging.
• Recommended reading materials include Moore, Dalley, and Agur (pp. 886); Blumenfeld (pp. 24-32); and Schuenke, et al. (pp. 266-269).

Announcements

• Clinical cases and quizzes continue with the same expectations as Block 2.
• Ultrasound content will be added.
• A detailed schedule for ultrasound will be provided soon.
• Invitations to use "Butterfly" ultrasound technology, housed in the Sim Center, have been sent.
• Images from ultrasound are part of the exam material.

Structural Division of the Nervous System

• The Central Nervous System (CNS) processes information and includes the brain, brainstem, cerebellum, diencephalon (thalamus and hypothalamus), and basal ganglia, and spinal cord.
• The Peripheral Nervous System (PNS) communicates with the CNS and organs, with minimal processing occurring in ganglia. It includes cranial nerves, spinal nerves, autonomic ganglia, and sensory ganglia and splanchnic and pelvic splanchnic nerves.

Gray Matter & White Matter

• Gray Matter: Contains nerve cell bodies, responsible for neural processing, includes nuclei (clusters of nerve cell bodies in the CNS) and ganglia (clusters of nerve cell bodies outside the CNS).
• White Matter: Facilitates conduction using axons (bundles of nerve fibers in the CNS) organized as tracts (axons connecting neighboring or distant nuclei of the cerebral cortex).

Overview of the Brain

• The forebrain is composed of the cerebrum (telencephalon) and the diencephalon (thalamus, hypothalamus).
• The cerebellum is located at the back of the brain.
• The brainstem includes the midbrain, pons, and medulla.

Overview of the Cerebrum

• The cerebrum has two hemispheres (R+L) connected by the corpus callosum.
• Four paired lobes: frontal, parietal, temporal, and occipital.
• Sulci are grooves, gyri are ridges on the cortex.
• The cerebellum has two hemispheres connected by the vermis.

Direction in the CNS

• Forel Axis: Refers to the cerebrum.
• Maynert Axis: Refers to the spinal cord, brainstem, and cerebellum.
• Directions in the CNS: Cranial/oral/rostral/anterior, caudal/posterior, dorsal/superior, and ventral/inferior.

Cerebrum (Detailed)

• Contains two hemispheres (R and L), connected by the corpus callosum.
• Four major paired lobes (frontal, parietal, temporal, occipital), plus limbic lobe and insular cortex.
• Sulci and gyri are the grooves and ridges in the cerebral cortex.
• White matter, grey matter, and deep nuclei compose the cerebrum's components.

Lobes of the Cerebrum (Detailed)

• The frontal lobe extends from the frontal pole to the central sulcus.
• The lateral sulcus separates the frontal from the temporal lobe.
• The frontal lobe's orbital part is inferior.
• The parietal lobe starts at the central sulcus and extends to the imaginary line connecting the top parietooccipital sulcus to the pre-occipital notch.
• The lateral sulcus, extending inferiorly, forms a boundary for the parietal lobe.
• The medial surface of the parietal lobe is bounded by the subparietal sulcus, parietooccipital sulcus, marginal branch of cingulate sulcus, and part of the calcarine sulcus.
• The temporal lobe's superior boundary is formed by the superior lateral sulcus and the inferior boundary from the parietal boundary.
• The line connecting the parietooccipital sulcus and the pre-occipital notch defines a posterior boundary.
• The medial surface moves toward the corpus callosum’s splenium.
• The collateral sulcus is superior to the medial surface.
• The occipital lobe extends from the posterior boundary to the anterior boundary, limited by the parietal lobe.
• The lateral surface includes occipital gyri, and the Cuneus is wedge-shaped, located between the parietooccipital sulcus and calcarine sulcus.
• The lingual gyrus is located on the temporal lobe, inferior to the calcarine sulcus, connecting with the parahippocampal gyrus.

Limbic Lobe (Cortex)

• The limbic lobe encircles the telencephalon-diencephalon junction.
• It is located on the medial surface of the temporal lobe.
• It's bordered by the corpus callosum and other lobes.
• It includes the cingulate gyrus, parahippocampal gyrus, and subparietal sulcus.

Insula

• The insula is also known as the insular cortex or lobe.
• It is within the lateral fissure.
• The insula is covered by the frontal, temporal, and parietal opercula.

The Cerebral Cortex

• It is a thin layer of gray matter.
• Has a surface area of 1800 cm².
• Comprises approximately half the brain's weight.
• Contains about 25 billion nerve cells and a substantial amount of axons (around 100,000 km).
• The neocortex is the major part of the cerebral cortex and consists of six distinct cortical layers.
• The mesocortex and allocortex also exist in other areas of the brain, differing in internal layer structures.

Histological Organization of the Cortex

• The neocortex has six distinct layers of horizontal lamination.
• The relative thickness of cortical layers can vary depending on the brain area's function.
• The cortical layers exhibit their own internal vertical bundles.
• Layer I is the most superficial, with layer VI being the deepest.
• Layers II-V demonstrate a variation in cell structures (small, medium, and large pyramidal cells).

Layers of the Cortex

• Layer I consists of few neurons, mainly axons, and dendrites from deeper cortical layers.
• Layers II and III contain small to medium-sized neurons connecting to other cortical areas.
• Layer IV receives input primarily from the thalamus.
• Large pyramidal neurons, composing layer V, project to subcortical structures (e.g., brainstem, spinal cord, and basal ganglia).
• Layer VI neurons project to the thalamus.

Korbinian Brodmann

• Brodmann categorized brain regions based on neuron shape and arrangement.
• A map of the brain, established in 1909, classified brain regions based on cytoarchitecture.
• The map comprises 52 distinct regions; many correlate with specific brain functions, called Brodmann areas.

Brodmann Areas (Detailed)

• The Brodmann areas are divisions of the cerebral cortex based on cytoarchitectural features.
• The numbers correlate with specific functions in the brain.

Primary Motor & Sensory Cortexes

• The primary motor cortex, located in the precentral gyrus, controls voluntary movements.
• The primary somatosensory cortex, in the postcentral gyrus, processes sensory information.
• Both areas have somatotopic organization, meaning areas of the cerebral cortex correspond to specific body areas.

Somatotopic Organization of Primary Motor Cortex, Somatosensory Cortex

• Precentral gyrus (area 4) contains the primary motor cortex, organizing body parts for motor functions. The areas in this region correlate with the parts of the body controlled.
• Postcentral gyrus (areas 3, 1, and 2) contains the primary somatosensory cortex, involved in sensory information processing. Specific regions correlate to specific body areas.

Subcortical Grey Matter

• Basal ganglia, deep brain clusters, are associated with motor control and limbic systems.
• Major components of basal ganglia include the caudate nucleus, putamen, globus pallidus, substantia nigra, and subthalamic nucleus.

White Matter Connections

• White matter forms fasciculi based on connections (association and commissural).
• Association fibers connect areas within the same hemisphere.
• Commissural fibers connect to the opposite hemisphere.
• Projection fibers connect cortical areas with subcortical structures.

White Matter Connections (Detailed)

• Association fibers include short U-fibers (connecting gyri within a hemisphere) and long, named fasciculi (connecting different lobes—frontal, parietal, occipital, temporal).
• Commissural fibers are long bundles connecting the two hemispheres, including the corpus callosum (largest) and anterior and posterior commissures.
• Projection fibers connect the cortex to other parts of the CNS (e.g., brainstem, spinal cord, thalamus, or other structures outside the cortex).

Projection Fibers

• Corona radiata: descending and ascending axons from cortical neurons and lower areas to the cortex, respectively.
• Internal capsule: converging fibers from the corona radiata coming to the brainstem.
• Cerebral peduncles: contain the corona radiata and connect to subcortical structures.

Somatotopic Organization of Internal Capsule

• Internal capsule is organized somatotopically and contains ascending and descending projection fibers.
• It connects the frontal lobe to lower brain structures; different nuclei of the basal ganglia and other fibers.
• Anterior limb: contains motor fibers (face, arm, and legs) from the primary motor cortex to respective body areas.
• Posterior limb: contains sensory fibers (face, arm, and legs) from the thalamus to the sensory cortex.

References

• A list of recommended neuroanatomy textbooks and articles for further study is included in the slides.

This quiz covers the cerebrum and its significant anatomical features within the neuroscience course (Med 7107). It focuses on the functions, lobes, gyri, sulci, histological organization, and the important concepts of Brodmann areas. Prepare to identify the primary motor and somatosensory areas, as well as the organization of the cerebral cortex.