Brain Areas and Spinal Cord Notes

Diencephalon

• Includes the thalamus and hypothalamus.

Thalamus

• Gateway for sensory information.
• All sensory information travels through the thalamus.
• Directs information to the appropriate brain area.
• Example:
  • Visual information from the retina travels to the thalamus and then to the occipital lobe.
  • Information from the skin travels through the thalamus and then to the somatosensory area in the parietal lobe.
• Sensory information can be from various sources such as:
  • Skin (temperature, pressure).
  • Eyes.
  • Other special senses.

Hypothalamus

• Connected to the pituitary gland via a stalk.
• Critical for the endocrine system.
• Controls many bodily functions such as:
  • Metabolism.
  • Menstrual cycle function.
  • Sperm production.
• Controls the autonomic nervous system.
  • Balances parasympathetic and sympathetic systems.
• Regulates body temperature.
• Involved with hunger and thirst.
  • Osmoreceptors detect changes in blood osmolarity (solute concentration, e.g., sodium).
  • High sodium concentration stimulates thirst and the release of antidiuretic hormone.
• Involved with emotions.
  • Feelings of pleasure, rage, and fear.
  • Relays information to other parts involved in emotion generation, such as the amygdala as part of the limbic system.

Brain Stem

• Involved with basic vital functions critical to homeostasis.
• Consists of:
  • Midbrain.
  • Pons.
  • Medulla oblongata.
• Controls breathing and blood pressure.
  • Control centers regulate breathing, including the drive to breathe in (inspiration).
  • Control centers regulate blood pressure via the baroreflex.
  • Information from baroreceptors in the carotid arteries and aorta is processed here.

Cerebral White Matter

• Consists of myelinated fibers bundled into large tracts.
• Types of fibers:
  • Commissural fibers: Connect gray areas of the two hemispheres.
    • Primarily travel through the corpus callosum.
    • Link the left and right hemispheres.
    • Other structures that carry commissural fibers include the anterior commissure (to a lesser extent).
  • Association fibers: Connect areas within the same hemisphere.
  • Projection fibers: Connect hemispheres with lower brain regions or the spinal cord.
    • Example: Fibers from the primary motor area control voluntary movement of skeletal muscle.
    • Information is relayed from the primary motor cortex to the skeletal muscle.
    • Can be very long neurons/axons (e.g., from the motor cortex to the foot).

Spinal Cord

• Directly connected to the brain stem.
• Travels within the vertebral column for protection.
• Gives rise to spinal nerves.
  • Cervical spinal nerves: Originate from spaces between the vertebrae.
    • Continue as part of the peripheral nervous system.
    • Take information away from the spinal cord and bring sensory information back.
  • Thoracic spinal nerves: Refer to the thoracic cavity and rib cage.
  • Lumbar spinal nerves.
  • Sacral spinal nerves: Originate at the level of the sacrum.
• The spinal cord ends at the conus medullaris, just below the rib cage (around the first or second lumbar vertebrae).
• Nerves extend from the end of the spinal cord, forming the cauda equina (horse's tail).
  • These nerves arise from their respective gaps in between the vertebral bodies.
• Filum terminale: A protective layer (pia mater) that anchors the spinal cord to the sacrum.

Cross Section of Spinal Cord

• Arrangement similar to that in the brain, with gray and white matter.
• Gray matter: Inner part, shaped like a butterfly.
  • Composed of cell bodies, dendrites, and small unmyelinated axons.
  • The central canal is in the middle and is filled with fluid.
• White matter: Outer part, composed of myelinated fibers.
  • Contains myelinated fibers and tracts.
  • Ascending tracts: Take sensory information towards the brain (e.g., to the primary somatosensory area).
  • Descending tracts: Take motor information away from the brain.
    • Example: Information from the primary motor area travels via descending tracts.