Neuroanatomy & Psychiatric Disorders - prereading

<<Planes of the brain<<

• White matter": Mainly axons due to myelination (lipid/ fatty sheath)
• Grey matter: neuronal cell bodies

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}}Main regions of the brian}}

]]Embryology]]

• Refer back to case 7 embryology on the formation of the spinal cord

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• The neural tube then splits into the main parts of the brain

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]]Rhombencephalon]]

• Brain stem
• Cranial nerves + normal nerves run from the medulla
• The cerebellum + pons are important in co-ordinating movements + responding to external stimuli

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{{Cerebellum - divided i nto 3 lobes:{{

1. Flocculonodular lobe

   • Vestibulocerebellum/ archicerebellum
   • Regulates balance + co-ordination (oldest)

2. Posterior lobe

3. Anterior lobe

4. Contains Purkinjie + granule cells

   

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• Areas closest to the vermis- spinocerebellum/ paleocerebellum
• Spinocerebellum: regulates body temperature + limb movement
• Laterally- neocerebellum
• Neocerebellum:

regulates planning,

sensory movement for action

]]Cerebellar Disorders]]

• Damage of the neocerebellum causes ataxic gait e.g. stroke or alcohol-related

• Cerebellum has a complex arterial supply

• Therefore, it is important in cases of stroke or vertebral/ basilar artery dissection (present with cerebellar signs

  

  

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]]Pontine disorders]]

• locked-in syndrome
• Central pontine myelinolysis
• Progressive Supranuclear Palsy (Steele-Richardson-Olszewski):
  • Supranuclear ophthalmoplegia
  • Neck dystonia
  • Parkinsonism
  • Pseudobulbar palsy
  • Behavioural impairment
  • Imbalance
  • Frequently falls

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]]Reticular formation]]

• Allows for communication of the brain to the rest of the body

• A hub for the synthesis of neurotransmitters and wake/sleep state

• Ascending/ descending through the brainstem

• Includes ascending reticular activating system- role in arousal

  

<<Mesencephalon<<

• Midbrain
• Acts as a connector between different parts of the brain
• links everything together
• Don’t worry too much about the next info

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Parts of the midbrain

• Tectum (dorsal part) splits into:

• Superior colliculus- visual processing + eye movement control

• Inferior colliculus- auditory processing

  

]]Disorders of the mesencephalon]]

• Parkinson’s - reduction in dopaminergic neurones in substantia nigra
• Schizophrenia- increased dopamine in substantia nigra
• Multi-system atrophy- degeneration of striatum and substantia nigra
• Ventral tegmental area- primary sites of addictive drugs (heroin, cocaine, alcohol, nicotine)

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]]Diencephalon]]

Contains:

• Thalamus
• Hypothalamus
• Pineal Body
• Subthalamus
• Epithalamus
• Mammillary bodies

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Limbic system:

• Connects cortical control to memory / sensory/ secretory areas
• Involved in motivation, visceral processes + rewards
• Systems of emotions
• Connects a group of structures surrounding the brainstem (cingulate gyrus, hippocampus, hypothalamus + anterior thalamic nuclei)
• Connecting these structures enables cortical control of emotion + plays a role in storing memory

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]]Telencephalon]]

• higher functions such as smell, memory + Intelligence

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Hippocampus

• Medial temporal lobe
• Short-term memory to long term memory
• Spatial memory
• Includes dentate gyrus + granule cells - formation of new episodic memories, site of neurogenesis, affected in depression
• Alzheimer’s + dementia → hippocampal atrophy → memory symptoms

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Cortex

• Memory
• attention
• Cognition
• awareness
• thought
• language
• consciousness
• 4 lobes, gyrus (fold) + sulcus

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Frontal lobe

• Superior frontal gyrus = self-awareness/ laughter
• Middle frontal gyrus
• Inferior frontal gyrus = language processing, Broca’s area
• Medial frontal gyrus = executive mechanism
• Paraolfactory area= limbic
• Orbitofrontal cortex= stimulus-reward, stimulus/outcome, addiction
• Ventromedial prefrontal cortex- decision making, emotion regulation, addiction
• frontotemporal dementia/ Pick’s disease = genetic + accumulation of tau + frontal symptoms

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Prefrontal cortex

• Planning + executing actions
• One of the last to develop
• lesions:
  • Dramatic changes in personality
  • Loss of spontaneity/ problems with initiating speech/ movements
  • inability to make + carry out sequences of actions/plans

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Parietal lobe

• Integrates sensory information

• Dominant hemisphere lesions:

  • Dysphasia, aphasia
  • Dyscalculia- difficulty learning, doing calculations
  • Dyslexia
  • Apraxia- ability to execute or carry out skilled movements and gestures, despite having the desire and the physical ability to perform them.
  • Agnosia- inability to recognize and identify objects or persons.
  • Gerstmann syndrome- Dyscalculia, Dysphasia, finger agnosia, LR disorientation

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• Non- dominant hemisphere lesions:

  • Spatial disorientation
  • Constructional apraxia
  • Dressing apraxia
  • anosognosia- unaware of their own health problems

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Temporal lobe

• Transeverse temporal gyri - Heschl’s gyri
• Superior temporal gyrus= auditory context with TTG. Pricess perception of sound + apply comprehension.
• Posterior STG = wernicke’s area
• Middle temporal gyrus
• Fusiform gyrus = FACIAL RECOGNITION, synaesthesia, dyslexia, prosopagnosia
• Inferior temporal gyrus= visual object recognition

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Occipital lobe

• Lingual gyrus
  • role in vision + dreaming
  • Visuo-limbic integration
  • encoding complex images
  • word processing
• Cuneus - basic visual processing
• Calcarine sulcus/fissure
  • primary visual cortex
  • takes signals from geniculate nucleus via thalamus

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Tracts- only for reference

• Arcuate fasciculus- links Broca’s + Wernicks area
• Uncinate fasciculus
  • Links temporal inferior frontal gyrus + frontal lobe
  • Hippocampus + amygdala with orbitofrontal cortex
  • implicated in several psych conditions
• 2 visual streams hypothesis:
  • dorsal - where?
  • ventral- what?

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Central dopamine hypothesis

• Meso-cortical pathway
• Meso-limbic pathway
• Nigrostriatal pathway
• Affected in schizophrenia + other psych disorders
• Medications for scz work on this pathway
• Side effects of these meds are linked to these pathways (e.g. cog-wheel rigidity like that seen in parkinson’s/ galactorrhea due to pituitary stimulation)

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]]Alzheimer’s Dementia]]

• Microscopic accumulations of peptide amyloid-β – plaques → cause loss of synapses, then neurons.
• Progressive degeneration
• Early changes in the hippocampus (first to be damaged)

Generalised shrinking and enlarged ventricles follow

• In severe depression, the dentate gyrus don’t light up in the scans which means they don’t form many memories.

]]Drug misuse]]

• The reward system is based on dopamine.

• It activates all dopamine pathways, particularly the mesolimbic pathway.

• Dopamine is produced in the Vental Tegmental Area (VTA).

• The mesolimbic pathway links this to the Nucleus Accumbens (motivation/ reward).

• If we do something good, or use an addictive drug, this pathway is stimulated.

• The mesocortical pathway is also activated.

• This links to the Prefrontal Cortex (PFC).

• This changes how you prioritise and plan.

  

  

]]Disorders]]

Case 1- depression after frontal tumour

• 56 year old female

• Progressive apathy

• Social withdrawal

• Poor self-care for part 3 years

• Admitted to a psychiatric facility for depression

• unresponsive to antidepressants so CT was conducted

  

• 8cm medial bifrontal mass

• Total excision benign transitional-type meningioma → rapid improvement

• 4 months after the operation was cheerful + motivated

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Case 2- Psychosis after temporal tumour

• 18-year-old female

• Referred form school to a psychosis clinic (high risk)

• 2 years of withdrawal from social activities + resent from work groups or talking in public

• 1 year later became concerned about unknown people stating + laughing at her for no reason

• Feeling the world around her has changed

• She is concerned that people are intimidating her + that there are special messages in TV for her

• She is neurologically normal + an average IQ

• Initial diagnosis: prodromal syndrome of schizophrenia but symptoms became more rapidly severe

• Routine MRI conducted

  

• Tumour in the left temporal lobe - dysembryoplastic neuroepithelial tumour (DNET)- usually benign glial neural neoplasm

• Surgically remove

• Psychotic symptoms improved with the help of other treatments- risperidone + CBT

• However, remained socially withdrawn

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Case 3- bipolar effective disorder due to Wilsons disease

• Middle aged female

• Detained + admitted under section 2 of the Mental Health Act (MHA) 2007- decline in her mental state

• Initially aggressive behaviour + required restrain by the Emergency Department security + police

• Quietly spoken

• voicing paranoid persecutory delusions

• euthymic with labile affect

• alternating between anger

• tearfulness

• displaying disinhibited affection

• Doesn’t know why she was presented

• CT

  

• Hypodensity in the putamen, worse on the left

• No mass, infarct or infectious process to explain the lesions

• Consistent with the MRI from a couple of months ago which demonstrates hyperintensity of both putamina

• Associated with Wilson’s disease

• final diagnosis: psychosis secondary to neurological Wilson’s Disease

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Case 4- Psychiatric syndromes associated with neurological disease

• 63-year-old male

• paranoia

• impaired anterograde memory + fatigue

• FLAIR scan shows bilateral hyperintensities in the hippocampus (arrows) → shows inflammatory process

• Blood tests revealed anti-voltage gated potassium channel antibodies