Cerebrum Anatomy

• The cerebrum constitutes the largest part of the brain, located in the anterior and middle cranial fossa.
• A deep cleft, known as the longitudinal cerebral fissure, divides the cerebrum into right and left hemispheres.
• Each hemisphere contains a lateral ventricle, part of a four-ventricle system that produces and circulates cerebrospinal fluid (CSF) for cushioning, protection, and waste removal.
• The corpus callosum, a mass of white matter composed of myelinated nerve fibers, connects the two hemispheres deep within the brain.
• Peripheral cerebrum consists of nerve cell bodies or gray matter, forming the cerebral cortex; gray matter is on the outer surface, with white matter beneath it.
• Cerebral cortex features many infoldings or furrows, called convolutions, that increase the surface area.
• Each cerebral hemisphere is divided into lobes named after the cranial bones they underlie: frontal, parietal, temporal, and occipital.
• Deep sulci (fissures) define the boundaries of these lobes.
• Tracts of nerve fibers, or white matter, connect the lobes within the cerebrum.
• The internal capsule contains projection fibers, which connect the cerebral cortex with lower brain regions and the spinal cord, and lies between the basal nuclei and the thalamus.
• The internal capsule carries many nerve impulses to and from the cerebral cortex.

Functions

• The cerebral cortex is responsible for higher mental activities, including memory, intelligence, thinking, reasoning, moral sense, and learning.
• Sensory perception of pain, temperature, touch, sight, hearing, taste, and smell occurs in the cerebral cortex.
• The cerebral cortex initiates and controls skeletal (voluntary) muscle contraction.

Other Areas

• Important masses of gray matter deep within the cerebral hemispheres include the basal nuclei, thalamus, and hypothalamus.
• Basal nuclei connect to the cerebral cortex and thalamus and are involved in initiating muscle tone for slow, coordinated movements; inadequate control results in jerky, clumsy movements.
• The thalamus, consisting of nerve cells and fibers, resides within the cerebral hemispheres below the corpus callosum
• Before redistribution to the cerebrum, sensory input from skin, viscera, and special sense organs is transmitted to the thalamus
• The hypothalamus is below and in front of the thalamus, above the pituitary gland, and is linked to the posterior pituitary by nerve fibers and to the anterior pituitary by a complex vascular system.
• Through these connections, the hypothalamus regulates hormone output from both lobes of the pituitary gland.
• Other functions include the control of the autonomic nervous system, appetite, thirst, water balance, body temperature, circadian rhythms, and emotional reactions.

Brain Stem

• The brain stem connects the cerebrum to the spinal cord and controls basic life-sustaining functions and reflexes.
• The brainstem consists of three parts: the midbrain, pons, and medulla oblongata.

Midbrain

• The midbrain is situated around the cerebral aqueduct between the cerebrum and the pons.
• It contains cell bodies and nerve fibres which connect the cerebrum with lower parts of the brain and with the spinal cord.
• The cell bodies act as relay stations for ascending and descending nerve fibres.

Pons

• The pons is situated in front of the cerebellum, below the midbrain, and above the medulla oblongata.
• It consists mainly of nerve fibres that form a bridge between the two hemispheres of the cerebellum and of fibres passing between the brain and the spinal cord.
• Groups of cells within the pons act as relay stations, some associated with cranial nerves.
• Anatomically, the pons differs from the cerebrum in that cell bodies (grey matter) lie deeply.
• White matter lies on the surface.

Medulla Oblongata

• The medulla oblongata connects the brainstem and the spinal cord, extending from the pons to the spinal cord, and is about 2.5 cm long.
• The outer aspect is composed of white matter which passes between the brain and the spinal cord, and grey matter lies centrally.
• Vital centres of autonomic reflex activity lie in deeper structures.
• The cardiac centre controls the rate and force of cardiac contraction through sympathetic (increased rate/force) and parasympathetic (decreased rate/force) nerve fibres.
• The respiratory centre controls the rate and depth of respiration by stimulating the diaphragm and intercostal muscles, with stimulation from excess carbon dioxide or deficient oxygen in the blood.
• The vasomotor centre controls blood vessel diameter, especially in small arteries and arterioles, via the autonomic nervous system; stimulation can cause constriction or dilatation.
• The vasomotor center is stimulated by body temperature and emotions; pain typically causes vasoconstriction, although severe pain can cause vasodilatation, leading to a drop in blood pressure and fainting.
• Reflex centers are stimulated by irritating substances, sending impulses to the medulla oblongata to initiate vomiting, coughing, or sneezing to expel the irritant.

Cerebellum

• The cerebellum resides behind the pons, below the posterior cerebrum, and consists of two hemispheres separated by the vermis.
• Grey matter forms the surface, with white matter lying deep.

Functions

• The cerebellum coordinates voluntary muscular movement, posture, and balance.
• It ensures smooth, even, and precise actions by coordinating various muscle groups.
• Sensory input from muscles, joints, eyes, and ears informs the cerebellum's control of balance and equilibrium.
• The cerebellum influences skeletal muscle contraction to maintain balance and posture.
• Damage to the cerebellum results in clumsy, uncoordinated movement, staggering gait, and inability to perform smooth, steady, precise movements.