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Introduction

  • The telencephalon/cerebral hemispheres are made up of cerebral cortex, lateral ventricles, white matter and deep nuclei
    • Deep nuclei include the corpus striatum and amygdala
  • Thickest cortex is the occipital cortex (visual centres)

Lateral ventricles

  • Lateral ventricles form a C-shaped cavity in each hemisphere
    • Several parts:
      • Body – adjacent to thalamus
      • Anterior horn – anterior to thalamus
      • Inferior horn – temporal lobe
      • Posterior horn – occipital lobe
      • Collateral trigone (atrium) – behind the thalamus where body, posterior and inferior horns meet
    • Choroid plexus produces CSF
  • Located: medial boundaries of the body, the trigone and inferior horn
    • Septum pellucidum – medial wall of the anterior horn and body
  • The thalamus forms part of the floor of the lateral ventricle

Deep grey matter

  • Corpus striatum is made up of the caudate nucleus and the lentiform nucleus
    • Caudate nucleus - swirly tail thing
      • Occupies the lateral wall of the lateral ventricle and the anterior horn
      • Parts:
        • Head – bulges into the anterior horn
        • Body – in body of ventricle
        • Tail – curves to the back of the thalamus into the inferior horn. Amygdala is a small blob attached to the end of the tail of the caudate nucleus
    • Lentiform nucleus - made of globus pallidus (deep) and putamen (laterally; tucked in behind the insula). These fibres separate the caudate nucleus and the putamen, and these fibres are called the internal capsule: projection fibres (connecting cortex and subcortical structures)
      • Wedge-shaped structure (brazil nut size)
      • Embedded in cerebral white matter
      • Narrow part of wedge is the globus pallidus (medially)
      • Extension superiorly, posteriorly and anteriorly is the putamen
    • Nucleus accumbens = the area where the putamen and caudate nucleus meet
  • Outside the lentiform nucleus
    • Lateral – external capsule (white matter)
      • claustrum (grey matter)
      • extreme capsule (white matter)
    • Medial – internal capsule (white matter) 􏰁 thalamus 􏰁 ventricle
  • Amygdala (amygdaloid body)
    • Found in front of the inferior horn of the lateral ventricle
    • Deep to the uncus (primary olfactory area in temporal lobe) o Part of the limbic system involved in control of emotions
  • Hippocampus
    • Cortex
    • Found on the medial edge of the temporal lobe, where the cortex rolls inwards on itself
    • Forms the medial wall of the inferior horn of the lateral ventricle
    • Part of the limbic system. It's needed for converting memories from short to long term
  • Basal ganglia includes the subthalamic nucleus (diencephalon), substantia nigra midbrain), the caudate and lentiform nuclei (telencephalon)

White matter: projection fibres

  • Connect the cortex to subcortical structures
    • Subcortical structures: thalamus, basal ganglia, brainstem, spinal cord (run in both directions)
    • Forms the internal, external capsules and the corona radiata; external capsule is pretty thin unlike internal capsule. These two wrap the lentiform nucleus, and intersect at the top of the putamen in what is called the corona radiata.
  • Internal capsule (NB: optic radiation is an extension of the internal capsule)
    • Fibres converge from all parts of the cortex forming the internal capsule
      • Laterally: lentiform nucleus
      • Medially: caudate nucleus (note head and tail in horizontal section) and thalamus
      • Inferiorly: continues into the brainstem as the cerebral peduncle
      • Superiorly: fibres fan out forming the corona radiata
    • 5 parts:
      • Anterior limb – between the head of the caudate and the lentiform
        • Includes:
          • Anterior thalamic radiation – fibres from the thalamus and prefrontal and cingulate cortex
            • Frontopontine fibres – pass from the frontal lobe to the pontine nuclei
      • Posterior limb (lenticulothalamic part) – between thalamus and lentiform nucleus. Most common site in brain for strokes (lacunar infarcts).
        • Includes
          • Middle (superior) thalamic radiation – fibres from thalamus and motor and somatosensory areas of cortex, corticospinal, corticobulbar and corticopontine tracts; (contains ascending somatosensory information too - more extensive effects than lesions in the cortex)
      • Genu – junction between anterior and posterior
      • Retrolenticular part – behind the lentiform nucleus
        • Contains optic radiation and corticopontine fibres. Note that fibres of the optic radiation are heavily myelinated
      • Sublenticular part – fibres pass beneath the lentiform nucleus
        • Contains the auditory radiation – fibres passing to the auditory cortex (temporal lobe)
        • Also some fibres to the optic radiation (Meyer’s loop fibres)
    • Clinical significance
      • Most common site of cerebral haemorrhage
      • Supplied by perforating branches of the anterior and middle cerebral arteries
        • Anterior cerebral (via anterior choroidal) supplies the anterior limb
        • Middle cerebral (via lateral striate arteries) supplies the rest of the internal capsule
      • Problems:
        • These arteries are susceptible to rupture with a sudden rise in BP
        • This area is susceptible to embolic blockage
      • Posterior limb is most commonly affected
        • Results in contralateral spastic hemiplegia and hemiasthesia
        • Infarct may extend into the retrolenticular part and cause hemianopia
  • External capsule
    • Thin sheet of white matter covering lateral surface of the lentiform nucleus
    • Mostly made up of fibres from the cortex to the putamen (corticostriate fibres)
    • Borders up against the insula
  • Corona Radiata
    • Above the caudate nucleus
    • Superior continuation of the internal and external capsules

Association fibres

  • Confined to one hemisphere
    • Connect different parts of the cortex
  • Short association fibres (arcuate) pass from one gyrus to the next
    • Located directly beneath the cortex
  • Long association fibres connect lobes and important functional areas
    • Form distinct bundles
    • Eg: the arcuate fasciculus (superior longitudinal) connects the auditory receptive speech area (Wernicke’s) and the motor speech area (Broca’s)

Commissural fibres

  • Interconnect corresponding parts of the hemispheres
  • Gather in 3 distinct bundles at the midline
    • Corpus callosum
      • Contains 200-300 million fibres (larger in females)
      • Consists of a rostrum, genu (connecting prefrontal), body and splenium (connecting occipital)
      • Sometimes cut in patients with severe epilepsy
    • Anterior commissure
      • Contains about 1 million fibres
      • Beneath the rostrum of corpus callosum
      • Connects the inferior parts of the temporal lobes (including the olfactory areas)
    • Hippocampal commissure and fornix
      • Axons from the hippocampus form a bundle called the fornix
  • The fornix passes from the posterior hippocampus over the back of the thalamus and approaches the midline (following the concavity of the ventricle)
  • Beneath the splenium, some fibres cross the midline and enter the opposite fornix
    • Form the hippocampal commissure (junction of posterior fornices together)
  • From here, the body of the fornix passes forward to the front of the thalamus
  • The two forinces intersect
    • Now it turns ventrally and forms the anterior boundary of the interventricular foramen
  • Thus it enters the hypothalamus and terminates
    • Fimbria are projections of the fornix onto the hippocampus
  • Fornix's anterior projections wrap around the anterior horn of the lateral ventricle to meet the mammillary body
  • Choroid plexus attaches fornix to the thalamus
  • Interventricular foramen is between the fornix in front and thalamus behind.