Brain

EXERCISE 13: GROSS ANATOMY OF THE BRAIN

Overview of Cephalization

  • Definition: Cephalization is the concentration of neural tissue in a central location within the body, most commonly observed in the head when present.

  • Significance: This trait is characteristic of all higher animals, differentiating them from simpler organisms like sponges.

  • Evolutionary Insight: Animals more complex than sponges—such as worms, snails, and reptiles—possess structures that can be classified as ganglia (nerve cell clusters) or actual brains.

  • Mammalian Brain: In mammals, the brain's structure, complexity, and functional flexibility reach their apex.

Objectives

  1. Identify larger brain structures using charts, models, and dissection specimens.

  2. Explain anatomical relationships between major brain components.

  3. Conduct a dissection of the sheep brain and pinpoint its major structures.

Procedure I: Identification of Human Brain Structures

  1. Examine a model of the human brain. Use lab charts and following diagrams to identify the structures listed below.

  2. Refer to the glossary of terms for anatomical part descriptions.

External Structures of the Brain

  • Longitudinal cerebral fissure

  • Optic nerve

  • Central sulcus

  • Transverse cerebral fissure

  • Optic chiasma

  • Lateral sulcus

  • Cerebral hemispheres

  • Optic tracts

  • Spinal cord

  • Frontal lobe

  • Pituitary gland

  • Olfactory bulbs

  • Parietal lobe

  • Infundibulum

  • Olfactory tracts

  • Temporal lobe

  • Mammillary bodies

  • Medulla oblongata

  • Occipital lobe

  • Cerebral peduncles

  • Pyramids

  • Corpora quadrigemina

  • Cerebellum

  • Pons

Internal Structures of the Brain

  • Corpus callosum

  • Thalamus

  • Septum pellucidum

  • Fornix

  • Hypothalamus

  • Infundibulum

  • Lateral ventricle

  • Pituitary gland

  • Third ventricle

  • Cerebral peduncles

Lobes and Fissures of the Cerebral Hemispheres

  • Frontal Lobe

  • Parietal Lobe

  • Occipital Lobe

  • Temporal Lobe

  • Central Sulcus

  • Lateral Sulcus

  • Gyri: Folds of the cerebral cortex

  • Sulci: Shallow grooves between gyri

Inferior View of the Brain

  • Observations on the ventral surface:
       - Olfactory tract
       - Optic chiasm
       - Cranial Nerves:      - Olfactory bulb (I)
         - Optic nerve (II)
         - Oculomotor nerve (III)
         - Trochlear nerve (IV)
         - Trigeminal nerve (V)
         - Abducens nerve (VI)
         - Facial nerve (VII)
         - Vestibulocochlear nerve (VIII)
         - Glossopharyngeal nerve (IX)
         - Vagus nerve (X)
         - Accessory nerve (XI)
         - Hypoglossal nerve (XII)

Midsagittal Section of the Cerebellum and Brain Stem

  • White matter (Arbor vitae)

  • Gray matter

Frontal Section of the Brain

  • Cingulate gyrus

  • Corpus callosum

  • Thalamus

  • Hypothalamus

  • Pituitary gland

Internal Anatomy

  1. Position the brain with the dorsal surface facing up.

  2. Perform a clean midsagittal section along the longitudinal fissure from the anterior to the cerebellum and brain stem.

  3. Identify the following structures using lab charts:
       - Cerebral hemispheres
       - Corpus callosum
       - Septum pellucidum
       - Forix
       - Choroid plexus
       - Thalamus
       - Hypothalamus
       - Infundibulum
       - Pons
       - Cerebellum
       - Medulla oblongata

Cranial Nerves

  • Definition: Paired peripheral nerves that originate directly from the brain.

  • Identification: Cranial nerves are identified by both a name and a Roman numeral. They primarily innervate the head and neck region; exceptions include the Vagus nerve, which affects involuntary organs in the thorax and abdomen.

Terminology

  • Arachnoid mater: The middle layer of the three meninges.

  • Arbor vitae: Tree-like arrangement of white matter in the cerebellum.

  • Central sulcus: A shallow groove separating the frontal and parietal lobes.

  • Cerebellum: The second largest part of the brain located dorsal to the brain stem.

  • Cerebral aqueduct: A passage linking the third and fourth ventricles.

  • Cerebral hemispheres: The right and left halves of the cerebrum, the largest part of the brain.

  • Cerebral peduncles: Large tracts on the ventral surface of the midbrain.

  • Choroid plexus: A capillary network located inside the ventricles.

  • Corpor quadrigemina: Area in the dorsal midbrain consisting of superior and inferior colliculi.

  • Corpus callosum: A white matter tract situated just superior to the lateral ventricles.

  • Cranial nerves: Peripheral nerves branching from the brain.

  • Decussation of the pyramids: The crossover point for most motor pathways on the ventral surface of the medulla oblongata.

  • Dura mater: The tough outer layer of the meninges.

  • Falx cerebri: A thick partition of dura mater located in the longitudinal fissure.

  • Fissure: A deep groove that separates major brain and spinal cord regions.

  • Fornix: A white matter tract located inferior and medial to the lateral ventricles.

  • Fourth ventricle: Cavity located between the pons and cerebellum.

  • Frontal lobe: The anterior region of the cerebral cortex.

  • Gray matter: CNS tissue composed mainly of cell bodies, unmyelinated axons, and dendrites.

  • Gyrus: A fold in the cerebral cortex.

  • Hypothalamus: Region just below the thalamus and third ventricle.

  • Infundibulum: A stalk-like structure connecting the hypothalamus and pituitary gland, located posterior to the optic chiasma.

  • Lateral sulcus: A groove that separates the frontal and temporal lobes.

  • Longitudinal fissure: The deep groove separating the cerebral hemispheres.

  • Mammillary bodies: Rounded structures located just posterior to the infundibulum on the ventral brain surface.

  • Medulla oblongata: The lower extension of the brain where it meets the spinal cord.

  • Meninges: The three-layer protective covering around the CNS.

  • Occipital lobe: The most posterior cerebral cortex lobe.

  • Olfactory bulb: An elliptical structure located on the ventral surface of the frontal lobe.

  • Olfactory tract: A white matter tract extending posteriorly from the olfactory bulb.

  • Optic chiasma: The junction where optic nerves and tracts converge anterior to the infundibulum.

  • Optic nerve: Cranial nerve II, connecting the retina to the optic chiasma.

  • Optic tract: The posteriorly extending white matter tract from the optic chiasma.

  • Parietal lobe: The cerebral cortex lobe located anterior to the occipital lobe and posterior to the frontal lobe.

  • Pia mater: The thin inner layer of the meninges that closely adheres to the CNS.

  • Pineal body: A small, unpaired structure anterior to the corpora quadrigemina and superior to the thalamus.

  • Pituitary gland (Hypophysis): The bulbous structure found outside the dura mater, posterior to the optic chiasma.

  • Pons: The brain structure situated between the cerebral peduncles and the medulla, below the cerebellum and ventral to the fourth ventricle.

  • Postcentral gyrus: The cerebral cortex fold located posterior to the central sulcus.

  • Precentral gyrus: The fold of cerebral cortex situated anterior to the central sulcus.

  • Pyramids of the medulla: Cone-shaped columns of white matter on the medulla's ventral side.

  • Septum pellucidum: A thin membrane that separates the lateral ventricles.

  • Sulcus: A shallow groove that separates gyri.

  • Temporal lobe: The lateral lobe of the cerebral cortex.

  • Tentorium cerebelli: A dural partition lying in the transverse fissure, separating the cerebellum and cerebrum.

  • Thalamus: The brain area surrounding the third ventricle, found inferiorly to the cerebrum's white matter and superiorly to the hypothalamus.

  • Third ventricle: Midline cavity found medial and inferior to the lateral ventricles, encircled by the thalamus.

  • Transverse fissure: A deep groove separating the cerebellum from the cerebrum.

  • White matter: CNS areas primarily consisting of myelinated processes, appearing white in fresh specimens.