Fisiología del Sistema Nervioso

Functions of the Nervous System

• Receives and regulates changes: Afferent signals from internal and external environments.
• Processes afferent inputs: Integration of the information received.
• Generates responses: Efferent signals activate the relevant organs to enact responses.

Organization of the Nervous System

• Central Nervous System (CNS): Brain and Spinal Cord, protected by bony encasement.
• Peripheral Nervous System (PNS): Includes cranial nerves (except optic), spinal nerves, and autonomic nerves associated with Schwann cells.
• Continuity: The CNS and PNS are structurally and functionally continuous at various levels:
  • Structural level: Continuity from epineurium to the dural sheath.
  • Electrical level: Neurons transmit electrical impulses continuously.
  • Chemical level: Similar neurotransmitters in both CNS and PNS.

Types of Cells in the Nervous System

• Neurons: Specialized nerve cells that transmit electrical impulses.
• Glial Cells: Supportive cells that outnumber neurons.
  • Macroglia: Consists of astrocytes, oligodendrocytes, Schwann cells, ependymal cells.
  • Microglia: Act as immune cells in the CNS, involved in removing debris and responding to injury.

Astrocytes

• Types:
  • Fibrous: Found in white matter, with long, thin extensions.
  • Protoplasmic: Found in gray matter, shorter and more branched.
• Functions:
  • Maintain spatial organization of neurons.
  • Guide neuronal migration during development.
  • Form the blood-brain barrier (BBB) via perivascular feet.
  • Support neurons by storing glycogen and providing nutrients.
  • Assist in the repair process following neuronal death.

Oligodendrocytes

• Key function: Formation of myelin sheaths in the CNS.
• May myelinate multiple axons.
• Myelination begins around 16 weeks of gestation and continues until the child begins walking.

Ependymal Cells

• Line the cavities of the brain and spinal cord; aid in the movement of cerebrospinal fluid (CSF).

Protective Barriers of the CNS

Meninges

• Three layers (from superficial to deep):
  • Dura Mater: Tough, outer layer that protects CNS.
  • Arachnoid Mater: Middle layer containing CSF.
  • Pia Mater: Thin, inner layer that adheres to the surface of the CNS.

Cerebrospinal Fluid (CSF)

• Functions:
  • Provides nutrients and removes waste from neural tissue.
  • Acts as a cushion for the CNS against trauma.
• Continuously formed and reabsorbed, maintaining a volume of 100-150 ml.

Blood-Brain Barrier (BBB)

• Formed by tight junctions between astrocytes and capillaries, allowing selective permeability.
• Essential substances (e.g., glucose, oxygen) can pass easily, while toxins are excluded.

Structural Organization of the CNS

Spinal Cord

• Gray Matter: Contains neuron cell bodies, forms an 'H' shape in cross-section.
  • Dorsal Horn: Contains sensory neuron bodies (afferent).
  • Ventral Horn: Contains motor neuron bodies (efferent).
• White Matter: Composed of myelinated axons organized into tract pathways.

Brain Stem

• Connects spinal cord to cerebrum; contains vital centers for autonomic functions.
• Houses cranial nerve nuclei that control sensory and motor functions.

Cerebellum

• Coordinates voluntary movement and balance.
• Divided into three lobes: vermis and two hemispheres.
• Interconnected with the brain stem and other cerebellar structures by peduncles.

Functions of the Cerebellum

• Maintains balance and posture.
• Regulates the force, timing, and fluidity of movements.

Diencephalon

Thalamus

• Acts as a relay station for sensory information (excluding olfaction) to the cortex.
• Damage can lead to loss of sensation or altered sensitivity.

Hypothalamus

• Regulates homeostatic functions, including temperature, thirst, and appetite.
• Controls the autonomic nervous system and endocrine activities.

Cerebral Cortex

• Composed of gray matter with varied thickness (3-5 mm).
• Organized into four lobes: frontal, temporal, parietal, occipital.
• Divided functionally into sensory, motor, and association areas.

Functions of the Frontal Lobe

• Responsible for voluntary movement planning and execution.

Cortex Layers

• Neurons organized in layers facilitating communication across regions.

Anatomy and Function of Basal Ganglia

• Involved in the control of voluntary motor movements.
• Composed of nuclei that work together to execute complex motor functions without conscious control.