115. Functional Organization of Nervous System – Quiz

📌 Professor’s Notes: Quick Revision

High-yield revision notes for rapid review before university examinations.

• The nervous system is the body’s communication and control system. It receives sensory information, processes it, and generates appropriate motor, autonomic, and behavioral responses to maintain homeostasis.
• The nervous system is divided into:
  • Central nervous system (CNS): Brain and spinal cord.
  • Peripheral nervous system (PNS): Cranial nerves, spinal nerves, and ganglia.
  • Autonomic nervous system (ANS): Sympathetic and parasympathetic divisions regulating visceral organs, glands, smooth muscle, and cardiac muscle.
• The brain is divided into:
  • Forebrain (Prosencephalon): Telencephalon (cerebral hemispheres) for sensory perception, learning, memory, cognition, and voluntary movements; diencephalon containing thalamus (major sensory relay) and hypothalamus (autonomic and endocrine regulation).
  • Midbrain (Mesencephalon): Controls posture, locomotion, and visual and auditory reflexes.
  • Hindbrain (Rhombencephalon): Pons, cerebellum, and medulla. Together with the midbrain, they form the brainstem, which regulates cardiovascular, respiratory, visceral, and sleep-wake functions.
• The spinal cord consists of 31 segments, giving rise to 31 pairs of spinal nerves. It contains ascending sensory and descending motor tracts and acts as the center for spinal reflexes. The subarachnoid space below its termination is the site for lumbar puncture.
• The nervous system functions through three basic steps:
  • Sensory input: Receptors detect mechanical, chemical, thermal, light, sound, or electrical stimuli and convert them into nerve impulses (sensory transduction).
  • Integration: The CNS processes information, often through the thalamus and cerebral cortex, compares it with stored memory, and plans an appropriate response.
  • Motor output: Somatic, autonomic, or behavioral responses are produced through effector organs.
• The CNS contains two major cell types:
  • Neurons: Structural and functional units that generate and conduct action potentials.
  • Glial cells (neuroglia): Provide structural, metabolic, protective, and supportive functions.
• Types of glial cells:
  • Astrocytes: Structural support, metabolic support, regulation of extracellular ions, maintenance of the blood-brain barrier, and regulation of cerebral blood flow.
  • Oligodendrocytes: Form the myelin sheath in the CNS; one cell can myelinate multiple axons.
  • Microglia: Phagocytic immune cells that remove damaged tissue and microorganisms.
  • Ependymal cells: Line the ventricles and central canal and participate in cerebrospinal fluid (CSF) production in the choroid plexus.
  • Schwann cells perform myelination in the PNS.
• A neuron consists of a cell body (soma), dendrites, and an axon.
  • Nissl bodies (rough endoplasmic reticulum) are present in the soma and proximal dendrites but absent in the axon hillock and axon.
  • The axon hillock and initial segment are the usual sites of action potential generation.
  • Myelination increases the speed of impulse conduction by enabling saltatory conduction.
• Classification of neurons:
  • By processes: Unipolar, pseudounipolar (dorsal root ganglion), bipolar (retina, olfactory epithelium), and multipolar (most common; spinal motor neurons).
  • By axon length: Golgi type I (long axon) and Golgi type II (short interneurons).