12.1-12.2

Chapter Overview

  • Chapter 12: Focus on the central nervous system (CNS), primarily the brain and spinal cord.
      - Central Nervous System Functions: Integrates sensory information and initiates motor responses.
      - Two lectures dedicated to the brain and one to the spinal cord.

Structure of the Nervous System

  • Key Figures from Chapter 11: Used figures to explain structural divisions.

  • CNS Division:
      - Central Nervous System Components: Brain and spinal cord.
      - Functional Role: Integrating sensory input and initiating motor output.

Sensory and Motor Pathways

  • Integration of Signals: Majority of signals (99%) are filtered out by the CNS.

  • Neuron Functions:
      - Afferent: Sensory input to the CNS.
      - Efferent: Motor output from the CNS.

  • Dorsal vs Ventral:
      - Dorsal: Location of sensory neurons, synonymous with posterior in humans.
      - Ventral: Location of motor neurons, synonymous with anterior in humans.

Brain Characteristics

  • Brain Weight: Approximately 2-3 pounds (0.9-1.4 kg), described as mushy and comparable to uncooked tofu.

  • Blood Flow: Receives about 20% of total blood flow despite being a small part of body weight.

Main Parts of the Brain

  1. Cerebrum: Largest outer portion, comprises most of the brain mass.
       - Visual Appearance: Recognizable wrinkly structure.

  2. Diencephalon: Contains four main components.

  3. Cerebellum: Located at the back, below the occipital lobe; referred to as the 'little brain'.

  4. Brain Stem: Comprises three parts:
       - Midbrain: Top part of the brain stem.
       - Pons: Middle part, connecting the cerebrum and cerebellum.
       - Medulla Oblongata: Long, oblong shape, transitions into the spinal cord.

Spinal Cord Overview

  • Location: Extends from foramen magnum to about lumbar vertebrae 2.

  • Spinal Cord Diameter: Comparable to a dime.

Neural Structures and Functions

  • Gray Matter vs. White Matter:
      - Gray Matter: Contains neuron cell bodies, located in outer cortex of the brain.
      - White Matter: Composed of myelinated axons (neural highways) located deeper in the brain.

  • Spinal Cord Arrangement: Flipped layout compared to the brain; gray matter is centrally located, and white matter is peripheral.

  • Neural Tissue: Both brain and spinal cord share similar types of neurons and supportive cells (neuroglia).

Development of the Nervous System

  • Neural Tube Formation:
      - Early embryonic stages, neural tube develops into brain structures after four weeks post-fertilization.

  • Segmentation of Brain:
      - Forebrain = Telencephalon + Diencephalon.
      - Midbrain = Mesencephalon.
      - Hindbrain = Metencephalon (pons, cerebellum) + Myelencephalon (medulla oblongata).

Brain Anatomy: Sulci and Gyri

  • Sulci: Shallow grooves on the brain; indentation areas.

  • Gyri: Bumps or ridges formed by sulci.

  • Longitudinal Fissure: Deep groove separating left and right hemispheres.

Brain Hemispheres and Lobes

  • Two Hemispheres: Left and right, each controlling opposite sides of the body.

  • Five Lobes per hemisphere:
      1. Frontal
      2. Parietal
      3. Temporal
      4. Occipital
      5. Insula (buried under the lateral fissure).

Lobes Functionality

  • Frontal Lobe: Involved in motor functions and behaviors.

  • Parietal Lobe: Processes sensory information.

  • Temporal Lobe: Responsible for auditory processing.

  • Occipital Lobe: Visual processing area.

  • Insula: Associated with taste (gustatory functions).

Functional Areas in the Cortex

  • Motor Cortex: Located in the precentral gyrus of the frontal lobe, initiates skeletal muscle movement.

  • Somatosensory Cortex: Located in the postcentral gyrus of the parietal lobe, processes sensory information.

  • Association Areas: Majority of the cerebral cortex dedicated to integrating complex ideas and linking sensory inputs (e.g., recognizing sounds associated with visual images).

Language and Communication

  • Broca’s Area: Responsible for speech production, located in the frontal lobe.

  • Wernicke’s Area: Responsible for understanding and interpreting speech, located in the temporal lobe.

Thalamus and Hypothalamus Functions

  • Thalamus: Relays sensory information to corresponding cortical areas, except for smell.

  • Hypothalamus: Regulates autonomic nervous system functions, control of body homeostasis, and biological drives (hunger, thirst, temperature).

  • Epithalamus (Pineal Gland): Regulates sleep-wake cycles through the secretion of melatonin.

Conclusion and Next Steps

  • Diencephalon Details: Future discussions will delve deeper into functions of thalamus, hypothalamus, and epithalamus, aligning with chapter learnings.

Important Terminology

  • Decussation: Crossover of neural pathways between hemispheres.

  • Afferent: Capacities concerning sensory input.

  • Efferent: Capacities relating to motor output.