Brain Regions and Functions

Brain Regions and Functions

• The spinal cord contains neurons, which are surrounded by fibers that run up to and down from the brain.
• It houses the major systems responsible for controlling body movement, including somatic motoneurons and sympathetic preganglionic neurons.
• It receives somatosensory afferent information from the body and skin and some visceral afferent signals; this information is sent to the brain via ascending pathways and also used to generate reflexes.
• The spinal cord in mammals and humans is mainly subordinate to the brain, but acts autonomously in some functions.

The Brainstem

• The brainstem is composed of the hindbrain (medulla and pons) and midbrain.
• All cranial nerves except the olfactory (I) and optic (II) emerge from the brainstem.
• The brainstem manages many basic autonomic functions, such as respiration and cardiovascular control.
• The brainstem also controls the overall activity (arousal state) of the forebrain.

The Hindbrain

• The medulla oblongata and pons house major regulatory systems for the body.
• Functions of the medulla oblongata and pons can be maintained in the absence of the forebrain.
• Irreversible loss of brainstem function is the criterion for diagnosing death.
• The pons is expanded ventrally by bundles of fibers that bridge the midline on the ventral surface, which are the axons of cells with inputs from the cerebral cortex that are destined for the cerebellum.

The Cerebellum

• The cerebellum is found in all vertebrates and grows in size with phylogeny.
• It plays a significant role in the control of movement by learning how to plan movements.
• Its contributions to non-motor functions (e.g., cognition) are currently debated.

The Midbrain

• The midbrain is the smallest of the brain divisions in mammals.
• The dorsal surface of the midbrain (often called the tectum in non-mammalian vertebrates) contains two pairs of bulges: the superior (rostral) and inferior (caudal) colliculi.
• The colliculi are areas that receive and process visual and auditory information, respectively.
• In reptiles, amphibians, and fish, these are the principal processing areas for these senses (alternatively called the optic and auditory tectum, respectively).
• In mammals, the colliculi are important for initiating rapid movement in response to sensory stimuli and as pre-cerebral sensory processing centers, but visual and auditory processing for perception is primarily handled by the cerebral cortex.

The Forebrain

• The forebrain consists of two anatomical subdivisions: the diencephalon and the telencephalon, which are not functionally simple.
• The diencephalon consists of the thalamus and the hypothalamus.
• The diencephalon is essential for regulating homeostasis, controlling the endocrine system via the pituitary gland, and managing the autonomic nervous system through the brainstem.

The Hypothalamus

• The hypothalamus connects to other forebrain structures, including regions of the cerebral cortex, and drives motivated behaviors.

The Thalamus

• The thalamus works closely with the cerebral cortex, with specific regions of the cortex reciprocally interlinked with corresponding parts of the thalamus.
• The thalamus plays an essential role in sleep and wakefulness, attention, and motivation.

The Cerebral Hemispheres

• The two cerebral hemispheres make up the largest part of the brain in mammals and are essential for higher-order brain functions, including consciousness.
• The hemispheres contain complex circuitry with connections between the layers of cortex and between different regions.
• The hemispheres are interconnected by the corpus callosum, a massive bundle of fibers that cross the midline.

Ventricular System

• The ventricular system is a series of fluid-filled cavities within the brain.
• The ventricular system forms during development, and the fluid it contains is called cerebrospinal fluid (CSF).
• The two largest ventricles are the lateral ventricles within the cerebral hemispheres.

Development of the Brain

• The brain develops from the neural tube, which differentiates into three major divisions: the hindbrain, midbrain, and forebrain.
• The hindbrain further divides into the medulla oblongata and the pons.
• The forebrain divides into the diencephalon and the telencephalon, giving rise to the cerebral hemispheres.
• Structures within the brain grow disproportionately during development.
• Due to the limited intracranial space, many brain structures fold and bend.
• The cerebral hemispheres and cerebellum expand into two-dimensional sheets with a layered structure that buckles and folds to fit within the skull.