Neuroanatomy & Psychiatric Disorders - prereading

<<Planes of the brain<<

 

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

}}Main regions of the brian}}

 

]]Embryology]]

  • Refer back to case 7 embryology on the formation of the spinal cord
  • The neural tube then splits into the main parts of the brain

 

]]Rhombencephalon]]

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

{{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

 

 

 

  • 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

 

 

]]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

]]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

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)

]]Diencephalon]]

Contains:

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

 

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

]]Telencephalon]]

  • higher functions such as smell, memory + Intelligence

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

Cortex

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

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

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

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

  • Non- dominant hemisphere lesions:
      * Spatial disorientation
      * Constructional apraxia
      * Dressing apraxia
      * anosognosia- unaware of their own health problems

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

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

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?

 

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)

]]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

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

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

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