Neuroanatomy 1

Nervous System: Neuroanatomy

• The nervous system's main function is maintaining homeostasis, a stable internal environment.
• It achieves this by receiving, integrating, and analyzing information.
• This includes making decisions and sending instructions to control voluntary movement and influence endocrine function.
• The nervous system also regulates unconscious activities.

Nervous System Divisions

• The nervous system comprises the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).
• The CNS includes the brain and spinal cord.
  • The brain processes information, controls responses, sensations, movement, emotions, communication, thought, and memory.
  • The spinal cord transmits information from the brain to the rest of the body and vice versa.
• The PNS includes nerve fibres located outside the brain and spinal cord.
  • Nerve fibres carry information to and from the CNS.

Nervous System Divisions for Pain

• The CNS and PNS are fundamental to processing and understanding pain information.
• The afferent division carries information to the CNS, while the efferent division carries information from the CNS.
• The Somatic Sensory and Visceral Sensory branches are part of this afferent division, and provide information on touch, pressure, vibration, temperature, pain, sight, smell, taste, and equilibrium.

Cells of the Nervous System

• Neurons: Diverse structural types (pseudo-unipolar, bipolar, anaxonic, multipolar) with various functions (sensory, interneurons, motor). They form circuits to process information.
• Glial cells: Support neurons. In the CNS include oligodendrocytes, astrocytes, microglia, and ependymal cells. In the PNS include Schwann cells and satellite cells.

Nerve Cells and Nerve Communication

• Impulses are transferred between nerve cells electrically along the axon.
• Signals are transferred chemically at synapses.

Glial Cells in CNS and PNS

• CNS: Oligodendrocytes myelinate neurons, astrocytes connect neurons to capillaries, microglia remove debris and have immune functions, and ependymal cells create cerebrospinal fluid.
• PNS: Schwann cells myelinate neurons, and satellite cells surround neuron cell bodies.

Bundles of Axons

• Axons are bundled into nerves (PNS) or tracts (CNS).
• Axons and their Schwann cells are surrounded by a basal lamina in the PNS.
• Fascicles are bundles of axons surrounded by perineurium and form nerves surrounded by epineurium.

Ways to Divide the Nervous System/Neurons

• Categorization by direction (afferent or efferent). Afferent neurons carry information to the brain and spinal cord, while efferent neurons carry information from the brain and spinal cord.
• Categorization by type (sensory or motor). Motor neurons control muscles, while sensory neurons respond to stimuli.
• Categorization by function (autonomic or voluntary), and anatomy (CNS vs PNS). Somatic nervous system controls voluntary functions, while the autonomic nervous system controls involuntary functions.

CNS: Brain

• The brain develops from an embryonic tube and folds to create complex tissue structures.
• Structures include the cerebral cortex, cerebral nuclei (basal ganglia, amygdala, basal forebrain), thalamus, hypothalamus, retina, midbrain structures (superior and inferior colliculi, red nucleus, substantia nigra), pons, medulla oblongata, cerebellum.

CNS: Spinal Cord

• The spinal cord consists of gray and white matter.
• Transverse histological sections show different levels of cervical, thoracic, lumbar and sacral regions.
• Sections can be processed to simulate myelin staining.

PNS: Spinal Nerves and Cranial Nerves

• Spinal nerves carry signals to and from the spinal cord.
• Cranial nerves link the brain to sensory organs and muscles in the head and neck.

Spinal Cord and Spinal Nerves

• Sensory information enters the spinal cord through dorsal roots, and motor commands travel through ventral roots.
• Sensory and motor axons travel together in spinal nerves.

Meninges

• The brain and spinal cord are covered by the dura mater, arachnoid mater, and pia mater, in layers.

CNS Fluid Compartments

• Cerebrospinal fluid (CSF), interstitial fluid, and intracellular fluid are interlinked compartments. They support constant chemical environment and have barriers.

Brain Vasculature

• Blood vessels branch to supply the brain.
• Arteries branch into arterioles, providing capillaries for exchange.
• Venules collect waste and return blood to the heart.

Blood Brain Barrier

• A system regulating substances entering the brain.
• Tight junctions between endothelial cells prevent leakage.

Cerebrospinal Fluid

• Produced by the choroid plexus and circulates in the ventricals, central canal, and subarachnoid space.
• CSF protects and maintains a constant chemical environment.

Sensation and Sensory Processing

• Sensory receptors transduce external and internal environment energies into nerve signals.
• Sensory information travels through afferent nerves to the brain.

Sensory Systems

• Sensory systems include somatosensory, visual, auditory, vestibular (balance), olfactory (smell), and gustatory (taste)—specific to their organs and functions.