Structure and Function of the Nervous System

Structure of the Nervous System

• The nervous system is divided into the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).
• The CNS includes the brain and spinal cord, responsible for interpreting sensory input and directing responses.
• The PNS incorporates cranial and spinal nerves, ganglia, and sensory receptors; it carries signals to and from the CNS.

Functions of Neurons and Neuroglia

• Neurons are the functional units of nervous tissue, transmitting nerve impulses.
• Neuroglia (glial cells) support neurons, act as phagocytes, and maintain homeostasis, protecting against pathogens.
• CNS neurons cannot regenerate or multiply, leading to lasting damage from injuries.

Types of Neurons

• Bipolar neurons: Two processes, involved in sensory functions like vision and smell.
• Unipolar neurons: Primarily sensory, carry information to the CNS in one direction from sensory receptors.
• Multipolar neurons: Most common type, involved in motor functions and complex processing; carry impulses from the CNS to muscles and glands.
• Interneurons: Located only in the CNS, connecting sensory and motor neurons. Crucial for reflexes and complex thought processes.

Structure and Function of Nerves

• Nerves are bundles of axons. In the CNS, these are called tracts; in the PNS, they are called nerves.
• Fascicles: Bundles of nerve fibers within a nerve, surrounded by connective tissue layers.
  • Endoneurium: Surrounds each individual axon.
  • Perineurium: Surrounds a fascicle of axons.
  • Epineurium: The outermost layer surrounding the entire nerve.

Types of Nerves

• Sensory (Afferent) nerves: Conduct impulses from sensory receptors to the CNS.
• Motor (Efferent) nerves: Carry impulses from the CNS to muscles or glands.
• Mixed nerves: Contain both sensory and motor fibers; most peripheral nerves, including spinal nerves, are mixed.

Pathophysiology of the Nervous System

• Stroke: Results from a blood clot disrupting brain blood flow, damaging neurons and the blood-brain barrier. High stroke death rates are linked to the critical roles of affected brain regions.
• Myelin and nerve impulse transmission: Myelin is an insulating layer around axons; it speeds up nerve impulse transmission. Myelinated neurons transmit signals faster than unmyelinated neurons.