2 Neuroscience2.6 Neuroanatomy

2.6 Neuroanatomy

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Written by Resident Doctor Committee · Published

Basal ganglia

  • The striatum, made up of the caudate and putamen, is the main cortical input to the basal ganglia.

  • The internal globus pallidus and substantia nigra pars reticulata are the main output nuclei.

  • The loop runs from cortex to striatum, pallidum and thalamus, then back to cortex.

  • The lentiform nucleus is the putamen laterally and the globus pallidus medially.

  • The globus pallidus looks pale because of its myelinated fibres, and a lamina divides it into external and internal segments.

  • The ventral striatum lies beneath the internal capsule, where the caudate and putamen merge; its main component is the nucleus accumbens.

  • The ventral striatum receives dopamine from the ventral tegmental area and responds to expected reward.

Dorsal loops serve movement, habit and executive control; ventral loops serve reward, motivation and salience.

Limbic system

Papez's circuit runs in this order:

  1. The hippocampus projects through the fornix to the mammillary bodies.

  2. The mammillothalamic tract carries the circuit from the mammillary bodies to the anterior thalamic nucleus.

  3. The anterior thalamic nucleus projects to the cingulate gyrus.

  4. The cingulum carries the circuit from the cingulate gyrus back to the hippocampus via the parahippocampal gyrus and entorhinal cortex.

Follow the loop from the hippocampal subiculum through the fornix to the mammillary bodies, along the mammillothalamic tract to the anterior thalamic nucleus, up to the cingulate gyrus, and back by the cingulum through the parahippocampal gyrus and entorhinal cortex; the mammillary bodies and anterior thalamus are the diencephalic links damaged in Korsakoff syndrome. NotMySecondOpinion, Public domain, via Wikimedia Commons

  • Korsakoff syndrome damages the diencephalic parts of the circuit, the mammillary bodies and thalamus, and causes amnesia.

  • The hippocampus supports declarative memory.

  • The amygdala lies deep to the uncus at the front of the medial temporal lobe, anterior to the hippocampus.

  • The amygdala processes emotional significance and recruits autonomic and endocrine responses.

  • The amygdala was not part of Papez's circuit; it joined the limbic system when MacLean broadened the concept in 1952.

Visual cortex

  • Posterior cerebral artery occlusion infarcts the calcarine visual cortex and gives a contralateral homonymous hemianopia with macular sparing.

  • The macula is spared because the occipital pole also has a middle cerebral artery supply.

  • A bitemporal hemianopia localises instead to the optic chiasm, for example from a pituitary mass.

Revision material for the MRCPsych examinations. Not clinical guidance, and not for use in patient care.