Neuroanatomy and Brain Metabolism — Notes OmpathStudy

Neuroanatomy and Brain Metabolism 1. Functional Anatomy of the Brain Lobes Frontal Lobe Functions: Executive functions (decision-making, planning), motor control (primary motor cortex), speech production (Broca's area), and personality/social behavior. Lesions: Result in personality changes (impulsivity), impaired judgment, hemiparesis, and Broca's aphasia. Parietal Lobe Functions: Sensory perception (touch, pain, proprioception), spatial awareness, and integration of sensory stimuli. Lesions: Result in sensory deficits, spatial disorientation, and apraxia (impaired motor planning). Occipital Lobe Functions: Primary visual processing, visual recognition of objects/faces, and depth/color perception. Lesions: Result in visual field deficits (e.g., homonymous hemianopia), visual agnosia, or cortical blindness. Temporal Lobe Functions: Auditory processing (primary auditory cortex), memory formation (hippocampus), emotional regulation (amygdala), and language comprehension (Wernicke's area). Lesions: Result in auditory deficits, Wernicke's aphasia, memory impairment (anterograde/retrograde amnesia), and emotional disturbances. 2. Subcortical and Brainstem Structures Cerebellum: Coordinates voluntary movement, balance, and motor learning. Lesions cause ataxia, intention tremors, and dysmetria. Brainstem: Controls vital functions (respiration, heart rate, BP). Lesions can cause altered consciousness or respiratory arrest. Thalamus: The primary sensory relay station (except olfaction) and regulator of sleep/wakefulness. Hypothalamus: Maintains homeostasis (temperature, hunger, thirst) and controls the endocrine system via the pituitary gland. Basal Ganglia: Regulates voluntary motor movements and motor learning. Dysfunction leads to Parkinson's disease (rigidity, bradykinesia) or Huntington's (chorea). Amygdala: Processes emotions, particularly fear and aggression. 3. Cerebral Blood Supply Internal Carotid System Anterior Cerebral Artery (ACA): Supplies medial surfaces of frontal and parietal lobes. Middle Cerebral Artery (MCA): Supplies lateral aspects of frontal, parietal, and temporal lobes. Most common site for ischemic stroke. Vertebrobasilar System Vertebral Arteries: Supply the cerebellum and brainstem. Basilar Artery: Formed by the junction of vertebral arteries; supplies the pons and midbrain. Posterior Cerebral Artery (PCA): Supplies the occipital lobe. Circle of Willis An anastomotic ring at the base of the brain providing collateral circulation. It includes the anterior/posterior communicating arteries, ACA, internal carotids, and PCA. 4. Brain Metabolism and Energy Utilization Glucose Metabolism High Demand: The brain consumes ~60% of blood glucose. Energy is primarily used by Na+/K+-ATPase to maintain membrane potentials. Sensitivity: Neurons lack glycogen stores and are highly sensitive to hypoxia; irreversible damage occurs within ~5 minutes of oxygen deprivation. Enzymatic Limitation: The brain lacks glucose-6-phosphatase , making it dependent on hepatic glycogenolysis and gluconeogenesis for glucose supply during fasting. Metabolism During Starvation Ketogenesis: During prolonged fasting, the liver produces ketone bodies: acetoacetate and beta-hydroxybutyrate . Preference: The brain prefers beta-hydroxybutyrate over acetoacetate because its oxidation yields an additional NADH, producing more ATP. Clinical Note: Excessive ketone production can lead to ketoacidosis, lowering blood pH and causing metabolic distress.