Chapter 13

Overview of the Brain

  • The brain is a crucial part of the central nervous system (CNS) located within the cranial cavity.

  • Four major divisions of the brain are:

    • Brainstem

    • Cerebellum

    • Diencephalon

    • Cerebrum

Brain Regions
Diencephalon

  • Central core between the brainstem and cerebrum including:

    • Thalamus: Major sensory relay center; influences mood and movement.

    • Hypothalamus: Controls homeostasis and autonomic functions; regulates the endocrine system and emotional responses, including hunger, thirst, and circadian rhythms.

Brainstem

  • Composed of:

    • Medulla Oblongata: Pathway for ascending/descending nerve tracts; governs reflex centers for heart rate, breathing, swallowing, and vomiting.

    • Pons: Contains tracts relaying information between the cerebellum and cerebrum; helps initiate REM sleep.

    • Midbrain: Contains cranial nerve nuclei and nerve tracts for sensory processing and coordination, especially reflexes concerning vision and hearing.

    • Reticular Formation: Interconnected nuclei throughout the brainstem that control arousal, awareness, and sleep-wake cycles.

Cerebrum

  • Largest brain part made up of the right and left hemispheres.

  • Distinct regions include:

    • Cerebral Cortex: Oversees perception, thought, memory, and voluntary movement. Organized into layers of various neuron types.

    • Basal Nuclei: Responsible for motor control and inhibition of unintended movements; includes caudate nucleus, lentiform nucleus (putamen, globus pallidus), and substantia nigra.

Meninges and Cerebrospinal Fluid (CSF)

  • The brain is protected by layers called meninges:

    • Dura Mater: Tough outer layer.

    • Arachnoid Mater: Middle layer below the dura mater.

    • Pia Mater: Delicate innermost layer tightly bound to the brain.

  • CSF functions:

    • Provides chemical stability and support for the brain and spinal cord.

Blood Supply to the Brain

  • Receives 15 to 20% of cardiac output; blood flows via internal carotids and vertebral arteries, forming the circle of Willis.

Cranial Nerves

  • Twelve pairs of cranial nerves (CN I to XII) serve sensory, somatic motor, and autonomic functions:

    • CN I: Olfactory

    • CN II: Optic

    • CN III: Oculomotor

    • CN IV: Trochlear

    • CN V: Trigeminal

    • CN VI: Abducens

    • CN VII: Facial

    • CN VIII: Vestibulocochlear

    • CN IX: Glossopharyngeal

    • CN X: Vagus

    • CN XI: Accessory

    • CN XII: Hypoglossal

Clinical Relevance

  • Traumatic Brain Injuries: Causes and effects on CNS function.

  • Hydrocephalus: Conditions causing fluid buildup in ventricles; interpretation of impacts.

  • Representative diseases and disorders of the CNS and cranial nerves.