Structure and Function of the CNS

• Derivatives of telencephalon

  • olfactory lobes
  • hippocampus
  • cerebrum
• Derivatives of diencephalon

  • retina
  • epithalamus
  • thalamus
  • hypothalamus
• Derivatives of mesencephalon

  • mesencephalon
• Derivatives of metencephalon

  • cerebellum
  • pons
• Derivatives of myelencephalon

  • medulla
• Neural tube flexures

  • two ventrally directed
  • mesencephalic (cephalic) flexure - centred at midbrain
  • cervical flexure - located near the junction between the myelencephalon and the spinal cord
  • one dorsally directed
  • pontine flexure - located at the region of the pons
• The cerebral hemisphere is the largest part of the forebrain. It is divided into four lobes:

  • frontal
  • parietal
  • temporal
  • occipital
• The nerve cell bodies which form the grey matter are located on the outer layer of the cerebral cortex and brainstem. The nerve fibres that form the white matter are located in the inner layer. Aggregates of nerve cell bodies called nuclei are also contained within the inner layer of the cerebral cortex and brainstem.
• A collection of nerve fibre bundle that serve a particular function is called nerve tract. Nerve tracts run within the white matter.
• The outer superficial layer of the cerebral hemisphere is the grey matter, called the cerebral cortex or pallium. It has a complex pattern of convoluted ridges, gyri and furrows, sulci to maximise its surface area.
• The deep layer of the cerebral hemispheres is the white matter formed by axons (fibres) from cells of the cerebral cortex.
• The vast majority of the axons that pass between the cerebral cortex and subcortical structures form a condensed broad sheet of white matter called the internal capsule.
• The two cerebral hemispheres are incompletely separated by a deep cleft called the great longitudinal fissure. In the depth of the great longitudinal fissure, the two hemispheres are united by nerve fibres called the corpus callosum.
• Between the internal capsule and the cerebral cortex are radiating nerve fibres in a fan-like arrangement called the corona radiata
• Buried within the white matter are a number of nuclear masses:

  • basal ganglia or corpus striatum
  • caudate nucleus
  • putamen
  • globus pallidus
• The cerebral cortex is involved in conscious awareness, thought, memory and intellect. All s
• All sensory modalities relay to the cerebral cortex mostly via the thalamus for conscious perception and experiential interpretation.
• The cerebral cortex serves as the highest level for the representation of the motor system for the conception and initiation of actions.
• The constituent parts of the nervous system - the central nervous system and peripheral nervous systems; the brain and spinal cord, and the autonomic nervous system and the peripheral nerves.
• The primary embryological germ layer called the ectoderm gives rise to the neural tube that forms the primary and secondary brain vesicles, which give rise to the definitive adult structures of the central nervous system.
• The cerebral cortex is divided into four lobes, frontal, parietal, temporal and occipital, and an insula cortex.
• The key features of the cerebral hemispheres include the complex convolutions of the cortex forming gyri and sulci, the great longitudinal fissure, the central sulcus, parieto-occipital fissure, lateral fissure, cingulate gyrus and sulcus and calcarine sulcus.
• The nerve cell bodies form the outer layer of the grey matter of the brain and brainstem, while the axons form the inner layer called the white matter.
• Within the white matter are located neural nuclear masses; the bundle of fibres called internal capsule and corona radiata.
• The cerebral cortex is involved in conscious awareness, thought, memory and intellect, and sensory perception and motor functions of the brain.
• The posterior part of the cerebral cortex which include parietal lobe for somatosensory, occipital lobe for vision, and temporal lobe for hearing, are involved in receiving sensory information from the outside environment.
• The adjacent association cortices elaborate the information in a multimodal and spatial modality - specific perception - touch, sight and hearing
• The anterior part (frontal lobe) is involved with the organisation of movements (primary motor, pre-motor and supplementary motor areas) and strategic guidance of complex motor behaviours over time (pre-frontal area).
• Frontal lobe syndrome

  • difficulty initiating behaviour
  • inability to stop a behavioural pattern
  • difficulties in planning and problem solving
  • incapable of creative thinking
• Apraxia: difficulty with planning and performing motor activities
• Agnosia: inability to recognise objects, faces, smells or sound
• Aphasia: difficulty with production and comprehension of language or speech, read or write
• Amnesia: memory loss - difficulty forming new memory, recognise familiar faces or places
• Broca's aphasia

  • loss of ability to produce spoken and written language (not due to muscle impairment)
  • comprehension only mildly to moderately affected
  • patients know what they want to say but cannot express it
  • 12% of stroke patients
• Wernicke's aphasia

  • speech is fluent
  • loss of language comprehension
  • can't produce meaningful speech
  • damage to left posterior superior temporal gyrus
• Right side parietal lobe

  • attention to stimuli
  • dressing
  • drawing
  • feeling shape and texture
  • finding one's way around
  • spatial imaging
• Right occipital lobe

  • interpreting vision
• RIght frontal lobe

  • voluntary movement
  • personality and mood
  • initiative
  • planning
  • social behaviour
  • strategies for new situation
  • bladder control
  • concentration
• Right temporal lobe

  • visual memory
  • facial recognition
  • music appreciation
  • hearing
  • mood (aggression)
  • non-language
• In majority of individuals, which is said to have left hemisphere dominance for language, areas of association cortex in the frontal, parietal and temporal lobes of the left hemisphere are responsible for the comprehension and expression of language.