Neuroanatomy

• The amygdala plays a key role in processing emotions, especially fear and aggression.
• The spinal cord extends from the base of the skull to the lumbar region of the vertebrae.
• The brainstem consists of the medulla oblongata, pons, midbrain, and diencephalon (thalamus).
• The spinothalamic tract transmits crude touch, pressure, pain, temperature sensation.
• The dorsal column-medial lemniscus pathway primarily transmits fine touch, proprioception, and fine muscle movements.
• Functions of the nervous system:

  • Receive information from the external world and internal organs
  • Transduce signals through depolarization of nervous cells
  • Transfer information from periphery to center and vice versa through conduction and communication
  • Integration: putting together information and deciding what to do
  • Response: motor response, secretory response, modification of internal circuitry
• Neurons:

  • Excitable cells with high amounts of ion channels and ion pumps
  • Have long prolongments called axons with specialized endings (axon terminals) forming synaptic contacts with dendrites, cell bodies, muscle cells, and other axons
  • Communication is largely chemical through the release of neurotransmitters from the presynaptic side
• Division of the nervous system:

  • Central Nervous System (CNS) protected by bony structures, includes the brain and spinal cord
  • Peripheral Nervous System (PNS) includes cranial nerves, spinal nerves, dorsal root ganglia, sympathetic and parasympathetic nerves and ganglia
• Central Nervous System:

  • Contains the majority of neuronal cell bodies
  • Grey matter: collections of cell bodies, white matter: grouped axons
  • Layers of protection: skin, connective tissue, muscle, periosteum, skull, meninges, cerebrospinal fluid
  • Organization in the brain with cerebral cortex, white matter, and nuclei; in the spinal cord with white matter and gray matter
• Meninges:

  • Three layers covering and protecting the brain: dura mater, arachnoid mater, pia mater
  • Spaces within the meninges: epidural, subdural, subarachnoid filled with cerebrospinal fluid
• Topographic classification:

  • Dura mater forms septa dividing the cranial cavity into compartments
  • Falx cerebri and tentorium cerebelli divide the cranial cavity into supratentorial and infratentorial compartments
• Neurons:

  • Basic unit of the signaling system composed of cell body, dendrites, and axons
  • Neurons vary in shape and size: multipolar, bipolar, pseudounipolar, unipolar
  • Supporting glia cells include astrocytes, oligodendrocytes, ependymal cells, microglia
• Synapses:

  • Junctions between neurons carrying information
  • Chemical synapses release neurotransmitters, electrical synapses communicate through electrical coupling
• Neurotransmitters:

  • Acetylcholine, norepinephrine, dopamine, serotonin, GABA
  • Important for muscle contraction, sympathetic nervous system, motor circuits, central circuits
• Development of the CNS:

  • Arises from the neural tube formed from ectodermal cells
  • Neurulation process involves the formation of the neural plate, neural groove, neural tube, and neural crest
  • Differentiation into spinal cord and brain with three main divisions: forebrain, midbrain, hindbrain
• Fetal time:

  • Expansion of cerebral hemispheres into small cavity
• Fetal development:

  • The cylindrical formation of the neural tube will form the spinal cord
  • Expansion of the cerebral hemispheres into a small cavity causes the formation of folding that give origin to the sulci and gyri
  • Formation of interhemispheric commissures
• At birth:

  • There are 80 - 100 billion neurons
  • The brain is very heavy (300 - 400 g), more than 10% of the body weight and 1/4th of the adult brain
• Chronology of brain development:

  • Neurogenesis (formation of neurons) occurs only during the embryo-fetal period till about week 19
  • Synaptogenesis (formation of circuits) starts at about week 20 and continues for the whole life, reaching peak between 2nd and 4th year
  • Myelination starts at the end of fetal life around week 29 and continues for the whole life
  • Competitive elimination of neurons starts at 4th month and continues for the whole life, where unused neurons get eliminated
• • Maturation ends at about 20 years (18 for females and 21 for males) under the action of sex hormones (estrogens for females and androgens for males)
• The Diencephalon:

  • Oldest part of the cerebrum
  • Composed of two hemispheres and a central diencephalon
  • Positioned between the mesencephalon and the corpus callosum
  • Thalamus represents 80% of the diencephalon and is a nuclear complex
  • Thalamus is bordered laterally by an internal capsule and anteriorly extends from the anterior pole to the anterior part of the optic chiasm
  • Primary arterial supply is from the posterior cerebral artery
  • Ventral view allows observation of optic pathways, pituitary stalk and tuber cinereum, mamillary bodies, and posterior perforated substance
• Thalamus:

  • Large, grey, ovoid mass of nuclei, mostly relay nuclei
  • Located at the lateral surface of the 3rd ventricle
  • Divided into three groups of nuclei: anterior, medial, and lateral nuclei
  • Each nucleus projects on a specific part of the cerebral cortex
  • Anterior thalamic tubercle is found in the rostral thalamus
• Hypothalamus:

  • Very small structure located ventrally and inferiorly to the thalamus
  • Forms the lateral walls and floor of the third ventricle
  • Vascularization by the anterior and posterior branches of the circle of Willis and the superior hypophyseal artery
  • Contains many small nuclei involved in vital homeostatic functions
  • Nuclei can be divided into magnocellular and parvocellular nuclei
• Magnocellular nuclei:

  • Big nucleus body and long prolongments
  • More active in synthesis and delivery of proteins
• Parvocellular nuclei:

  • Pre optic nuclei
  • Embryologically from the telencephalon
  • Important in thermoregulation and sexual activity
• Hypothalamus:

  • Contains many nuclei with various functions like control of the endocrine system, thermoregulation, control of circadian rhythms and cooling
  • Preoptic area and suprachiasmatic nuclei of the supraoptic region are involved
• Subthalamus:

  • Located inferior to the thalamus and lateral to the hypothalamus
  • Vascularization mainly from the perforating branches of the anterior choroidal artery and the posterior communicating artery
  • Contains small nuclei, with the subthalamic nucleus of Luys being the most important
• Epithalamus:

  • Posterior part of the prolongment of the third ventricle
  • Consists of the habenular trigone and the epiphysis
  • Important for circadian rhythm, inducing sleep, and regulation of gonadal activity
• Metathalamus:

  • Contains the geniculate bodies
  • Located posterior to the inferior side of the thalamus
  • Acts as a relay station for the acoustic and optic pathways
• Telencephalon:

  • Formed by two cerebral hemispheres
  • Most superior and largest part of the brain
  • Composed of the cerebral cortex, white matter, deep nuclei, and lateral ventricles
• Lobes of the Telencephalon:

  • Frontal, parietal, temporal, occipital, insular, and limbic lobes
  • Characterized by gyri and sulci that demarcate functional centers
• Cerebral Cortex:

  • Phylogenetically subdivided into allocortex (older) and isocortex (newer)
  • Three functional divisions: projection neurons, association neurons, commissural neurons
  • Histological subdivisions: pyramidal and fusiform cells, non-pyramidal cells
• Gyri and Sulci:

  • Form important landmarks that allow separation of the brain into functional centers
  • Sulci separate gyri and demarcate lobes
  • Longitudinal fissure divides the hemispheres into right and left lobes
• Non-spiny non-pyramidal cells are interneurons
• Stellate (granular) cells:

  • Real afferent cells
  • Similar to granular cells of the cerebellar cortex
  • Contact with Mossi fibers
  • Receive important afferent information from the thalamus
• Double bouquet cells:

  • Important interneurons involved in vertical distribution along all cerebral cortex
• Horizontal cells of Cajal:

  • Have a trans-horizontal position with dendrites involved in horizontal irradiation
  • Important for horizontal communication with other neurons
• Chandelier cells/Cells of Retzius:

  • Small neurons with short axons and dendrites
  • Important in horizontal communication
• Cells of Martinotti:

  • Multipolar neurons
  • Related to vertical communication between different neurons
  • Dendrites can spread above and below
  • Cerebral cortex can be subdivided into 6 layers
• Cerebral cortex layers can be distinguished from a functional point of view:

  • Supragranular layers (I, II, III) contain many interneurons, primary origin and termination of intracortical connections
  • Internal granular layer (IV) contains the largest number of granular cells, related to the collection of thalamic information
  • Infragranular layers (V-VI) contain pyramidal and fusiform neurons, connecting the cerebral cortex with subcortical regions