Anatomy

• Neuroanatomy


  The study of the structure and organization of the nervous system
• Nervous system


  • Controls and coordinates the activities of the body both voluntary and involuntary
  • Made up of specialized cells, whose function is to receive sensory stimuli and to transmit them to effector organs, whether muscular or glandular
• Parts of the nervous system


  • Central nervous system (brain and spinal cord)
  • Peripheral nervous system (cranial and spinal nerves and their associated ganglia)
• Components of the nervous system

  • Neurons (nerve cells)
  • Neuroglia (glia cells)
• Neuron


  The basic and functional unit of the nervous system, enables communication between different brain areas, also between the brain, the spinal cord, and the entire body through chemical or electrical signals
• Neuron


  • Cell body (perikaryon/soma)
  • Dendrites
  • Axon and its terminals
• Cell body


  The core/metabolic centre of the cell, contains the nucleus, carries genetic information, maintains the neuron's structure, and provides energy to drive activities
• Axon hillock


  A specialized region where the axon joins to the cell body, area for the initiation of action potential
• Dendrite


  Fibrous roots that branch out from the nerve cell body, play an important role in the transmission of nerve impulses by increasing overall surface area, receive electrical impulses from axons of other nerve cells which in turn accumulate in the cell body before being sent to the axon hillock
• Axon


  A single elongated structure that extends from the axon hillock to the axon terminal, contains microtubules and specialized insulating substances on its surface called myelin which boost the transmission of nerve impulses
• Node of Ranvier


  The gap between each pair of successive myelin sheath
• Cells that form the myelin sheath

  • Oligodendrocytes (in the central nervous system)
  • Schwann cells (in the peripheral nervous system)
• Classification of neurons based on function

  • Sensory neurons
  • Motor neurons
  • Interneurons
• Sensory neurons


  Carry information from the body's periphery into the nervous system for the purpose of both perception and motor coordination
• Motor neurons


  Carry commands from the brain or spinal cord to muscles and glands
• Interneurons


  Constitute the largest class, consisting of all nerve cells that are not specifically sensory or motor
• Classification of neurons based on structure

  • Unipolar
  • Bipolar
  • Pseudo-unipolar
  • Multipolar
  • Anaxonic
• Nerve impulse


  An action potential, also called a nerve impulse, is an electrical charge that travels along the membrane of a neuron, can be generated when a neuron's membrane potential is changed by chemical signals from a nearby cell
• Neurotransmission


  Transfer of signals from one neuron to another, or between a neuron and an effector organ, communication between neurons or between neurons and target tissues, occurs at a synapse
• Synapse


  • Junctions formed with other nerve cells where the presynaptic terminal of one cell's axon comes in contact with the postsynaptic membrane (dendrite) of another (axon-dendrite), can also be axon-to-axon, dendrite-to-dendrite, and axon-to-cell body synapses, has three components: presynaptic cell, synaptic cleft, and postsynaptic cell
• Types of synapses


  • Axosomatic synapse
  • Axoaxonal synapse
  • Dendro-axonic or dendro-dendritic synapse
  • Somato-dendritic synapse
• Neuroglia


  • Non conducting cells of the nervous systems, provide mechanical support to neurons, surround the cell bodies, axons, and dendrites of neurons, serve as insulators and prevent neuronal impulses from spreading in unwanted directions, about 10 to 50 times more than neurons in the CNS
• Types of neuroglia


  • Macroglia (larger: insulate, protect, and help neurons to develop and migrate)
  • Microglia (smaller: have phagocytic properties, digesting foreign particles)
• Ependymal cells


  Line cavities and produce cerebrospinal fluid
• Microglia

  • Small, star-shaped cells that help protect the CNS, originate from macrophages, the brain's resident immune cells, serve as the first line of defense against invading pathogens or disease-causing agents, highly dynamic, moving constantly to actively survey the parenchyma in the resting healthy brain, become activated & recruited during infection, injury or seizure
• Macroglia

  • Oligodendrocytes (in the CNS)
  • Astrocytes (in the CNS)
  • Ependymal cells (in the CNS)
  • Satellite cells (in the PNS)
  • Schwann cells (in the PNS)
  • Enteric glia (in the PNS)
• Oligodendrocytes

  • Located in the CNS, are small cells with few processes, in white matter, they provide myelin and in gray matter, surround and support the cell bodies of neurons, a single oligodendrocyte can wrap its membranous processes around many axons, insulating them with myelin sheath
• Astrocytes

  • The most numerous glia cell, irregular, rough star-like shape cell bodies and processes that attach to both capillaries and neurons in the central nervous system, form blood-brain barrier, provide nutrients and other substances to neurons, regulate concentrations of ions and chemicals in the extracellular fluid
• Ependymal cells


  • Columnal/cuboid cells (ependymocytes) lining the fluid-filled ventricles of the brain and the central canal of the spinal cord, apical ends sometimes have cilia or long microvilli, basal ends are elongated and extend branching process, they are involved in the production of cerebrospinal fluid
• Schwann cells


  • Also known as neurolemmocyte, produced from the neural crest, each Schwann cell positioned along length of single axon forms segment of myelin sheath about 1mm long, the interval between segments of myelin are known as node of Ranvier
• Satellite cells


  • Derivative of embryonic neural crest, cells form an intimate covering layer over the layer
• The nervous system is functionally divided into autonomic and somatic nervous systems
• Divisions of the nervous system

  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)
  • Brain
  • Spinal Cord
  • Spinal Nerves
  • Cranial Nerves
  • Ganglia
  • Autonomic Nervous System (ANS)
  • Somatic Nervous System (SNS)
• Autonomic Nervous System


  The part of the nervous system concerned with the innervation of involuntary structures, such as the heart, smooth muscle, and glands within the body
• Divisions of the Autonomic Nervous System

  • Sympathetic
  • Parasympathetic
  • Enteric
• Somatic Nervous System


  It is composed of somatic parts of the CNS and PNS, providing sensory and motor innervation to all parts of the body except the viscera in the body cavities, smooth muscle, and glands
• Components of the Somatic Nervous System

  • Somatic Sensory System
  • Somatic Motor System
• Somatic Sensory System


  Transmits sensations of touch, pain, temperature, and position from sensory receptors
• Somatic Motor System


  Innervates only skeletal muscle, stimulating voluntary and reflexive movement by causing the muscle to contract
• The spinal cord is the major reflex center and conduction pathway between the body and brain