Neuroscience Chapter: Neurons and Hemispheres

Parts of a Neuron

• Dendrites: Tapered extensions of the cell body that collect information from other neurons.
• Soma (cell body): Contains the nucleus and other organelles, responsible for synthesizing macromolecules and integrating electrical signals.
• Axon: A single, cylindrical extension that can be myelinated or unmyelinated. It conducts information to other neurons.
• Axon terminals (synaptic endings): Vesicle-filled structures at the end of the axon that transmit information to other neurons.

Cerebral Hemispheres

• Cerebral cortex: The outer surface of the brain composed of six layers of cell bodies (gray matter).
• White matter: Contains myelinated axonal processes of neurons, found deeper within the cerebral hemispheres.
• Gyri: Elevations on the surface of the cerebral hemispheres, increasing the surface area.
• Sulci: Infoldings on the surface of the cerebral hemispheres.
• Four lobes: Frontal, parietal, occipital, and temporal lobes.

Ventricular System

• Lateral ventricles: Two C-shaped fluid-filled cavities within the cerebral hemispheres.
• Third ventricle: A slit-like cavity surrounded by the thalamus and hypothalamus.
• Fourth ventricle: Located between the pons and medulla anteriorly and the cerebellum posteriorly.
• Cerebrospinal fluid (CSF): Produced by the choroid plexus, circulates through the ventricular system.

Meninges

• Dura mater: The outermost layer of the meninges, composed of two layers: periosteal and meningeal.
• Arachnoid mater: The middle layer of the meninges, with a thin outer layer and strands of connective tissue extending to the pia mater.
• Pia mater: The innermost layer of the meninges, a thin layer that closely follows the brain's surface.
• Subarachnoid space: The space between the arachnoid and pia mater, filled with CSF and major blood vessels.

Cerebral Vasculature

• Anterior circulation: Supplied by the internal carotid arteries.
• Posterior circulation: Supplied by the vertebral arteries.
• Internal carotid arteries: Course through the neck and enter the skull through the carotid canal.
• Anterior cerebral arteries (ACAs): Supply the medial aspect of the brain.
• Middle cerebral artery (MCA): Supply the lateral aspect of the brain.

Spaces in the Cranial Meninges

• Epidural space: Potential space between the dura mater and the skull.
• Subdural space: Potential space between the dura mater and the arachnoid mater.
• Subarachnoid space: Normally present CSF-filled space.

Cerebral Arteries

• Cerebral arteries are numbered 1 through 38, with most located along the center.
• The arteries are numbered 3, 38, 36, 3, 7, 33, 6, 8, 9, 12, 14, 15, 17, 21, and 24.
• The posterior cerebral cortex is supplied by the vertebrobasilar system.
• The vertebrobasilar system begins bilaterally with the vertebral arteries, which branch off from the subclavian arteries and ascend through the foramen transversarium of the cervical vertebrae.
• The vertebral arteries join to form the basilar artery which courses along the ventral brainstem.
• The basilar artery supplies the posterior cerebral artery (PCA) at the level of the midbrain.
• The PCA perfuses the inferior and medial temporal and occipital lobes.
• The posterior communicating artery branches off from the PCA and connects to the internal carotid artery.

Circle of Willis

• The Circle of Willis is a circulatory anastomosis at the base of the brain.
• The Circle of Willis is formed by the anterior and posterior communicating arteries.
• The anterior cerebral artery (ACA), internal carotid artery (ICA), middle cerebral artery (MCA), and posterior cerebral artery (PCA) are key components of the Circle of Willis.

Cerebral Veins

• Cerebral veins drain into the internal jugular vein.
• Superficial and deep veins connect to the dural sinuses.
• The superior sagittal sinus runs along the superior edge of the falx cerebri.
• The superior sagittal sinus drains into the transverse sinuses.
• The transverse sinus forms the sigmoid sinus, which exits the jugular foramen to become the internal jugular vein.
• The inferior sagittal sinus runs along the inferior margin of the falx cerebri.
• The inferior sagittal sinus joins the great vein of Galen to form the straight sinus.
• The confluence of the sinuses, where the straight sinus, superior sagittal sinus, and occipital sinus join, is drained by the transverse sinuses.
• The cavernous sinus is a plexus of veins located on either side of the hypophysial fossa.
• The cavernous sinus receives drainage from the ophthalmic veins.
• The cavernous sinus is drained by the superior petrosal sinus (drains into the transverse sinus) and inferior petrosal sinus (drains into the internal jugular vein).

Superficial Veins

• The superficial middle cerebral vein is positioned parallel to the lateral fissure, draining the temporal lobe into the cavernous sinus.
• The superior anastomotic vein (of Trolard) connects to the superficial middle cerebral vein perpendicularly.
• The superior anastomotic vein courses superiorly across the parietal lobe to drain into the superior sagittal sinus.
• The inferior anastomotic vein (of Labbé) connects to the superficial middle cerebral vein perpendicularly.
• The inferior anastomotic vein passes inferiorly along the temporal lobe to drain into the transverse sinus.

Deep Veins

• Deep veins are more constant in their organization.
• Deep veins drain into the great cerebral vein (of Galen), which enters the dural venous sinuses.
• The anterior cerebral vein and deep middle cerebral vein travel adjacent to the ACA and MCA, respectively.
• The anterior cerebral vein and deep middle cerebral vein join to form the basal vein (of Rosenthal), which continues around the lateral aspect of the midbrain.
• The internal cerebral veins are formed at the interventricular foramen by the joining of the septal and thalamostriate veins bilaterally.
• The internal cerebral veins and basal veins join posterior to the midbrain to form the great cerebral vein (of Galen).
• The great cerebral vein joins the inferior sagittal sinus to form the straight sinus.

Thalamus

• The thalamus is a large, egg-shaped mass of gray matter located in the diencephalon.
• The thalamus acts as a synaptic relay for pathways projecting to the cerebral cortex.
• The thalamus acts as a gatekeeper, preventing or enhancing information transfer based on behavioral state.
• Sensory, motor, limbic, and modulatory signals from behavioral and arousal circuits have synaptic relays within the thalamic nuclei.
• The thalamus is located deep within the brain, neighboring several structures and portions of the ventricular system.
• The thalamus extends anteriorly to contact the interventricular foramen.
• The thalamic nuclear masses and the ventrally located hypothalamus comprise the lateral walls of the third ventricle.
• The thalamus is located immediately lateral to the posterior limb of the internal capsule.
• The thalamus is related to the dorsal aspect of the body of the lateral ventricle.
• The thalamus extends caudally to the midbrain portion of the brainstem.
• The thalamus is interconnected across the midline of the third ventricle by the interthalamic adhesion.
• The thalamic nuclei are classified into four groups based on their relationship to the internal medullary lamina: anterior, medial, lateral, and intralaminar.
• The thalamic nuclei are divided into three major functional classes: relay, intralaminar, and reticular.
• Most of the thalamus is composed of relay nuclei, which have reciprocal excitatory connections with the cortex.
• Relay nuclei are subdivided into specific and nonspecific based on their projections to specific areas of the primary sensory and motor cortex or more diffuse cortical projections.
• Specific relay nuclei primarily reside in the lateral thalamus.
• All sensory modalities, with the exception of olfaction, have relays in the lateral thalamus before reaching their primary cortical target.
• Vascular supply to the thalamus arises from penetrating branches from the ACA, anterior choroidal artery (branching from the internal carotid), lenticulostriate arteries of the MCA, and thalamoperforator arteries from the PCAs.

Test your knowledge on the fundamental structures of neurons and the components of cerebral hemispheres. This quiz covers key parts like dendrites, axons, and the four lobes of the brain. Perfect for students studying neuroscience or biology.