Anatomy II and Anatomy III

Brain Anatomy – Transcript-Derived Study Notes

• The brain is comprised of the 3 major components: the cerebrum, cerebellum, and brainstem.

Cerebrum and hemispheres

• The cerebrum is the most prominent region of the brain and is divided into left and right hemispheres.

• Hemispheres share many functions, but some functions show laterality (e.g., language is primarily controlled on one side).

• The cerebral hemispheres have many folds to increase surface area. Ridges are called gyri and grooves are called sulci; large grooves are called fissures.

• The cerebral hemispheres are divided into 4 lobes:

  • Frontal lobes: most rostral, located at the front. Responsibilities include higher-level executive functions (attention, critical thinking, impulse control). They are the last brain region to fully develop, not completing development until individuals reach their 20s. The frontal lobes also contain the primary motor cortex, located in the precentral gyrus.

  • Parietal lobes: the central sulcus lies caudal to the frontal lobe and divides the frontal lobes from the parietal lobes. They are important for processing sensory information. The primary somatosensory cortex is located in the postcentral gyrus and is responsible for the perception of touch and pain. The parietal lobes also perform higher-level visual processing.

  • Temporal lobes: located on the side of the brain, separated from the frontal and parietal lobes by the lateral fissure. They process hearing, smell, taste, and higher-level visual processing. The temporal lobe is also important for speech and memory.

  • Beneath the cerebral cortex, the hippocampus and amygdala lie deep in the temporal lobes; these are two regions of the limbic system, a circuit important for emotion and memory.

  • Occipital lobes: the most caudal lobes located at the back of the brain; their primary function is processing visual information.

Non-Cerebral Components

• The cerebellum lies inferior to the occipital lobes and is divided into two hemispheres, like the cerebral cortex. It is best known for regulation and control of movement, but it is also involved in cognitive functions like emotions.

• The brainstem is located between the cerebrum and the spinal cord. It regulates critical functions like heart rate, breathing, and sleep, and it is the location of most cranial nerves.

• The spinal cord is part of the central nervous system but not part of the brain. It receives sensory information from the body and sends motor information to the body. Involuntary motor reflexes are a function of the spinal cord, indicating that the spinal cord can process information independently from the brain.

Views of the brain

Dorsal View (viewing from above)

• The brain shows bilateral symmetry of the left and right cerebral hemispheres, separated by the longitudinal fissure.

• Frontal, parietal, and occipital lobes are visible.

• The central sulcus divides the frontal lobe from the parietal lobe.

• The precentral gyrus (location of the primary motor cortex) sits rostral to the central sulcus; the postcentral gyrus (location of the primary somatosensory cortex) lies caudal to the central sulcus.

Ventral View (underside)

• The frontal and temporal lobes are visible, as is the cerebellum.

• The longitudinal fissure divides the cerebrum into right and left hemispheres.

• The pons and medulla (brainstem components) connect the cerebrum to the spinal cord.

• Cranial nerves are visible on the ventral surface.

• The olfactory tract leads out to the olfactory bulb, which connects to the olfactory nerve.

• The optic tract crosses the midline at the optic chiasm, and then the optic nerve projects to the retina.

• Other cranial nerves enter or leave the brain at the level of the brainstem.

• The hypothalamus is located caudal to the pons, and the mammillary bodies project out from the hypothalamus.

Mid-sagittal View

• A mid-sagittal section slices the brain through the longitudinal fissure and separates the right hemisphere from the left.

• In this view, all 4 cortical lobes are visible.

• The frontal lobe is separated from the parietal lobe by the central sulcus; the occipital lobe is in the posterior region; the temporal lobe lies behind the brainstem.

• The cerebellum, pons, medulla, and spinal cord are caudal to the cerebrum.

• The midbrain is visible superior to the pons and consists of two regions: the tegmentum and the tectum.

• The corpus callosum is a white matter bundle located in the center of the cerebrum and crosses from one hemisphere to the other.

• Surrounding the corpus callosum is the cingulate gyrus, a region important for emotion.

Diencephalon and Limbic System

• The diencephalon consists of regions around the thalamus and hypothalamus. It is located inferior to the fornix and lateral ventricle, posterior to the anterior commissure, and superior to the brainstem.

• The fornix is a nerve fiber bundle containing primarily output from the hippocampus.

• The anterior commissure sits above the hypothalamus and is a white matter tract, like the corpus callosum, that allows information to cross from one hemisphere to the other.

• The thalamus is best known for its role as a relay and processing location for the sensory and motor systems.

• The hypothalamus has a variety of functions including control of stress and the “fight or flight” response of the autonomic nervous system, reproduction, sleep, thirst, hunger, and other homeostatic functions.

• The mammillary bodies lie in the posterior part of the hypothalamus and are important for memory.

• The optic nerves from the retina cross at the optic chiasm, and the optic tracts continue back into the diencephalon.

Brainstem, midbrain, and sensory pathways

• In the brainstem, the tectum of the midbrain consists of the superior and inferior colliculi, which are important for vision and hearing, respectively.

• The reticular formation is located throughout the brainstem. Networks within the reticular formation regulate sleep and consciousness, pain, and motor control.

• The fourth ventricle lies between the brainstem and the cerebellum.

Coronal sections and deep structures

• Coronal sections allow deep tissue structures to be visible.

• A cut through the anterior portion of the temporal lobe shows the amygdala, a region important for emotion, located in the medial temporal lobe.

• The regions of the basal ganglia are visible: the striatum, which consists of the caudate and the putamen, and the globus pallidus.

• The basal ganglia have multiple functions but are best known for their role in the regulation of movement.

• The lateral ventricle sits medial to the basal ganglia, and above the lateral ventricle is the corpus callosum.

• The third ventricle is located in the middle of the brain, inferior to the lateral ventricle, and the optic chiasm lies inferior to the third ventricle.

• The longitudinal fissure separates the left and right cerebral hemispheres, and the lateral sulcus is the border between the frontal and temporal lobes.

Quick reference terms

• Gyri: ridges on the cerebral cortex.

• Sulci: grooves between gyri.

• Fissures: large sulci.

• Precentral gyrus: location of the primary motor cortex.

• Postcentral gyrus: location of the primary somatosensory cortex.

• Central sulcus: divides frontal and parietal lobes.

• Lateral fissure (Sylvian fissure): separates temporal lobe from frontal and parietal lobes.

• Fornix, anterior commissure, corpus callosum: major white matter tracts connecting hemispheres or linking hippocampal outputs.

• Thalamus: sensory/motor relay station.

• Hypothalamus: homeostasis and autonomic control.

• Mammillary bodies: memory-related structures within the hypothalamus.

• Amygdala: emotion.

• Hippocampus: memory (noted as a part of the limbic system within the temporal lobe).

• Basal ganglia: movement regulation (caudate, putamen, globus pallidus).

• Ventricles: lateral, third, and fourth ventricles.