Brain and Cranial Nerves - Chapter 14

Brain and Cranial Nerves

• Chapter 14 covers the brain and cranial nerves.
• The brain has three main parts: cerebrum, cerebellum, and brainstem.
• The cerebrum is the largest part of the brain (83% of brain volume) with hemispheres, gyri (thick folds), sulci (shallow grooves), and longitudinal fissure (deep groove separating hemispheres), and corpus callosum (thick nerve bundle connecting the hemispheres).
• The cerebellum is the second largest part (about 50% of neurons), located in the posterior cranial fossa.
• The brainstem is the portion remaining when the cerebrum and cerebellum are removed, containing the diencephalon, midbrain, pons, and medulla oblongata.
• Cranial nerves are numbered, and some begin or end in the medulla (IX, X, XI, XII).
• The medulla oblongata controls cardiac and vasomotor centers, regulating heart rate, blood vessel diameter, and breathing. It also has reflex centers controlling actions like coughing and swallowing.
• The pons is an anterior bulge in the brainstem. It works with other structures for various functions including pathways to and from the cerebellum, cranial nerves V, VI, VII, and VIII (hearing, equilibrium, taste, facial sensations), and eye movement, facial expressions, chewing, swallowing, and secretions. It also manages aspects of sleep, respiration, and posture.
• The midbrain is a short segment connecting the hindbrain and forebrain. It contains the cerebral aqueduct, continuations of medial lemniscus and reticular formation, and nuclei of cranial nerves III (oculomotor) and IV (trochlear) controlling eye movements. The tectum includes superior and inferior colliculus handling visual and auditory information. The substantia nigra manages motor functions, and cerebral crus contains fibers connecting the cerebrum to the pons, including corticospinal tracts.
• The reticular formation is a loosely organized web of gray matter scattered through the brainstem. It handles somatic motor control (muscle tone, balance, posture), relaying signals to the cerebellum, integrating visual, auditory, and balance information, and controlling the gaze center to track and fixate on objects. The reticular formation has roles in cardiovascular control (including cardiovascular centers in the medulla), pain modulation, sleep, and consciousness, and habituation.
• The cerebellum is responsible for motor coordination, including evaluating sensory input (textures, spatial perception). The cerebellum aids in monitoring muscle contractions, spatial perception, timekeeping for movement prediction, and compensating for head movements. Its function also includes hearing, planning and scheduling tasks.
• The forebrain is made up of the diencephalon (encloses the third ventricle, containing the thalamus, hypothalamus) and telencephalon (primarily the cerebrum).
• The thalamus is a major part of the diencephalon, an ovoid mass on each side, being part of a major relay center to the cerebral cortex. It plays a key role in motor control through relaying signals from the cerebellum to the cerebrum and providing feedback loops to basal nuclei. It is also involved in memory and emotional function.
• The hypothalamus is part of the diencephalon, extending from the optic chiasm to the mammillary bodies. The hypothalamus manages hormone secretion, influencing the anterior pituitary. It's a major center for the autonomic nervous system regulating heart rate, blood pressure, and gastrointestinal activity. It controls thermoregulation, food and water intake, sleep and waking cycles, and emotions.
• The epithalamus forms the roof of the third ventricle. It includes the pineal gland (an endocrine gland) and habenula (a relay center to the midbrain).
• The telencephalon primarily develops into the cerebrum. The cerebrum is divided into hemispheres connected by the corpus callosum. It handles sensory perception, memory, thought, judgment, and voluntary motor actions. It is divided into lobes (frontal, parietal, temporal, occipital), and the insula (hidden by other lobes). Each lobe has specialized functions.
• Basal nuclei are masses of cerebral gray matter buried deep in the white matter, lateral to the thalamus. These nuclei interact with the substantia nigra and motor cortex, playing a role in motor control. Key nuclei include the caudate nucleus, putamen, and globus pallidus.
• The limbic system is a complex of structures in the cerebrum playing a major part in emotion and learning. Key components include the cingulate gyrus, arching above the corpus callosum, the hippocampus (in the medial temporal lobe for memory) and the amygdala (immediately rostral to the hippocampus processing emotion). These structures interact through fiber tracts allowing feedback loops

Major Landmarks

• Longitudinal fissure- separates cerebral hemispheres
• Gyri- thick folds in the cerebral cortex
• Sulci- shallow grooves in the cerebral cortex
• Corpus callosum- thick nerve bundle connecting cerebral hemispheres at the bottom of the longitudinal fissure.