NS18 - Forebrain 2 - Cerebrum

NS18 - Forebrain 2 - Cerebrum

1. Consists of......

   • Cerebral cortex (Neocortex)
     • = grey matter on surface of cerebral hemispheres
   • Basal nuclei (subcortical)
     • = Grey matter deep in cerebral hemispheres involved in extrapyramidal motor system
   • Limbic system (Archicortex)
     • = Complex set of brain structures located on both sides of thalamus. For behaviour, emotion, memory.
   • Olfactory bulb (Paleocortex)
     • = Ancient sensory system for sense of smell

2. FUNCTIONS

   • Interpretation of sensory impulses
   • Motor function
   • Planning & Organisaiton

3. CEREBRAL CORTEX

   • Lobes
     • Frontal: Association & motor cortex
     • Parietal: Sensory processing
       • Somatosensory cortex
         • Each region within somatosensory cortex receives sensory input from a specific area of body
           • Greater sensory input from an area = Greater size of the corresponding area in somatosensory cortex
         • E.g. Rabbits: mostly mouth & forelimb
     • Occipital: Visual processing
     • Temporal: Auditory processing, Memory
     • NB: *Cruciate sulcus* separates motor cortex (Frontal) from somatosensory cortex (Parietal)
       • But parietal lobe starts *caudal* to the cruciate sulcus (that's because parietal lobe starts where the parietal *bone* starts!)
     • Rhinocephalon (smell brain) is NOT part of neocortex - but it's large so ~ lobe

4. SUBCORTICAL BASAL NUCLEI

   • CAUDATE NUCLEUS, Putamen, Globus pallidus
   • see previous lectures!
   • Substantia nigra - is in midbrain

5. LIMBIC SYSTEM - Behaviour & Memory

   • = A group of interconnected telencephalic gyri & nuclei surrounding thalamus (common to all mammals)
     • SEE DIAGRAMS IN NOTES!!!
   • Involved in BEHAVIOUR, EMOTION, olfaction, motivation & various autonomic functions
     • Limbic system & Olfactory cortex are closely associated - hence so are smell & memomry
   • Found @ limbus (border) between cerebrum & thalamus
   • Components
     • E.g. Cingulate gyrus
     • E.g. Hippocampus (Inside out: grey matter is on the inside!)

6. ASCENDING RETICULAR ACTIVATING SYSTEM (ARAS)

   • = Part of brainstem.
   • Determines arousal (Consciousness/Awareness) levels & Regulates sleep
   • Stimulated by collateral axons of most sensory fibres travelling to thalamus
     • E.g. from spinal cord & cranial nerves
     • ARAS then projects into cortex to wake it up
   • Functions as a TRIAGE system - Ranks incoming info in terms of importance
     • E.g. Mothers wouldn't sleep through a baby crying because ARAS recognises that it's important
   • Hypocretin (neurotransmitter) = important in controlling sleep-wake cycle
     • If deficient -> Narcolepsy-Cataplexy

7. OLFACTORY CORTEX

   • First order neurones = Olfactory receptors @ olfactory EPT
     • Second order neurones = @ Olfactory bulb
       • Their axons project to amygdala in rostral piriform lobe (i.e. olfactory cortex)
   • Olfactory pathway reaches cortex w/o being relayed by thalamic nuclei!
   • Pathway: Olfactory neurones in nasal cavity synapse @ olfactory bulb
     • Send axons through lateral olfactory tract to piriform lobe
       • then connections to L&R

8. FOREBRAIN WHITE MATTER

   • = Myelinated axons connecting cerebral cortex w/ other brain regions
   • 3 types
     • 1. Projection fibres
       • Leave cerebrum to join/become internal capsule
     • 2. Commissural fibres
       • Connect cortices of L&R cerebral hemispheres
       • E.g. Corpus callosum (largest), Rostral commissures (Olfaction)
     • 3. Association fibres
       • Connect regions of cerebral cortex within 1 hemisphere
         • E.g. Occipital cortex & Motor cortex for visual reflexes

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