Cerebrum & Diencephalon

Nervous System Overview

• Central Nervous System (CNS): Consists of the brain and spinal cord. It integrates sensory information and coordinates body functions.

• Peripheral Nervous System (PNS): Includes all neural tissue outside the CNS. It connects the CNS to the limbs and organs.

  • Somatic nervous system: Controls voluntary movements by innervating skeletal muscles; responsible for conscious control.

  • Autonomic nervous system (ANS): Regulates involuntary functions by supplying internal organs. Operates unconsciously to maintain homeostasis.

  • Sympathetic: Mediates the "Fight or flight" response, preparing the body for stress by increasing heart rate, dilating pupils, and redirecting blood flow.

  • Parasympathetic: Promotes "Rest and digest" functions, conserving energy by slowing heart rate, increasing intestinal and gland activity, and relaxing sphincter muscles.

Cerebrum

• Directional Terms: Rostral (toward the nose), Dorsal (toward the back), Ventral (toward the belly), Caudal (toward the tail)

• Key Structures:

  • Longitudinal fissure: Deep groove that divides the two cerebral hemispheres.

  • Gyri: Elevated ridges on the surface of the cerebrum, increasing surface area for cortical processing.

  • Sulci: Grooves on the surface of the cerebrum, separating the gyri.

  • Lateral sulcus/fissure: Prominent groove that separates the temporal lobe from the frontal and parietal lobes.

  • Central sulcus: Groove that separates the frontal lobe from the parietal lobe.

  • Pre-central gyrus: Ridge located anterior to the central sulcus; contains the primary motor cortex.

  • Post-central gyrus: Ridge located posterior to the central sulcus; contains the primary somatosensory cortex.

• Lobes:

  • Frontal: Controls executive functions, motor control, and speech production.

  • Parietal: Processes sensory information, spatial orientation, and navigation.

  • Temporal: Involved in auditory processing, memory formation, and language comprehension.

  • Occipital: Responsible for visual processing.

  • Limbic: Regulates emotions, memory, and motivation.

  • Insula: Involved in taste, visceral sensation, and autonomic control.

• Cortical Areas:

  • Primary motor cortex: Controls voluntary movements.

  • Primary somatosensory cortex: Processes tactile information, including touch, pressure, and pain.

  • Primary auditory cortex: Processes auditory information.

  • Primary visual cortex: Processes visual information.

  • Broca's area: Critical for speech production, located in the frontal lobe.

  • Wernicke's area: Essential for language comprehension, located in the temporal lobe.

• Brodmann's Areas:

  • Primary motor cortex: $4$

  • Premotor cortex: $6$

  • Primary Somatosensory cortex: $3, 1, 2$

  • Broca’s area: $44, 45$

  • Wernicke's area: $22$

• Grey and White Matter

  • Outer grey matter: Cerebral cortex; contains neuronal cell bodies and dendrites.

  • White matter: Axons; facilitates communication between brain regions.

  • Deep grey matter: Nuclei; clusters of neuron cell bodies located deep within the cerebrum.

• White Matter Classifications:

  • Projection fibers: Connect the cerebral cortex to the brainstem and spinal cord; includes the Internal capsule.

  • Commissural fibers: Connect the two cerebral hemispheres; includes the Corpus callosum, anterior & posterior commissure.

  • Association fibers: Connect different areas within the same hemisphere. Includes Short fibers (adjacent gyri), Cingulum (frontal, parietal, temporal), Uncinate fasciculus (frontal & temporal), Superior longitudinal fasciculus (all lobes), Inferior longitudinal fasciculus (temporal & occipital).

Diencephalon

• Components:

  • Thalamus

  • Hypothalamus

  • Epithalamus

  • Subthalamus

• Thalamus

  • Bilateral structure surrounding the third ventricle and medial to the internal capsule.

  • Relay center interconnected with the CNS. Integrates information from the cerebellum and basal ganglia, as well as sensory tracts.

  • Relay Nuclei:

  • Basal ganglia to Ventral anterior nuclei: Relays motor information to motor areas.

  • Cerebellum to Ventral lateral nuclei: Relays motor information to motor areas.

  • Ascending tracts to Ventral posterolateral nuclei: Relays body somatic sensory information to the somatosensory cortex.

  • Trigeminal nerve to Ventral posteromedial nuclei: Relays face somatic sensory information to the somatosensory cortex.

  • Inferior colliculi to Medial geniculate nucleus: Relays auditory information to the auditory cortex.

  • Optic tract to Lateral geniculate nucleus: Relays visual information to the visual cortex.

• Epithalamus

  • Pineal gland: Regulates circadian rhythms by secreting melatonin.

• Hypothalamus

  • Homeostasis: Regulates body temperature, metabolic rate, blood pressure, water intake/excretion, and digestion to maintain internal balance.

  • Reproductive and defensive behaviors

  • Emotional expression.

  • Endocrine regulation.

• Subthalamus

  • Ventral to thalamus, superior to substantia nigra.

  • Subthalamic nuclei part of basal ganglia; involved in motor control.

Other Subcortical Structures

• Basal ganglia: Involved in motor control, learning, and executive functions.

• Hippocampus: Critical for memory formation and spatial navigation; particularly involved in forming new long-term memories.

• Amygdala: Processes emotional responses, including anxiety, fear, and rage; also involved in emotional learning and memory.