Forebrain 3 Flashcards
What does the neocortex do?
- Has the idea for a movement
What does the direct pathway do as part of motor control?
- Through the basal ganglia it facilitates the appropriate pattern of motor activity
- Allowing it to acheive the desired movement
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What happens with the information after the basal ganglia?
- Information sent via the thalamus to the supplementary motor area
- This communicates with the motor cortex (M1)
- M1 controls motor neurones via the corticospinal tract
What does the cerebellum do in terms of motor control?
- Identifies & corrects errors in movement
What does the indirect pathway do to movement?
- Brings an end to a movement
Explain the motor pathway in the brain, form the idea to execution of a movement.
- Neocortex –> has idea for a movement
- Direct Pathway via the Basal Ganglia –> facilitates appropriate patterns of motor activity to achieve desired movement
- Information sent via thalamus to SMA
- SMA communicates with M1
- M1 controls motor neurones via corticospinal tract
- Cerebellum –> identifies & correct errors in movement
- Indirect Pathway –> brings an end to the movement
What is the thalamus part of?
- Diencephalon
What 3 pathways synapse in the thalamus on their way to the cerebral cortex?
- Basal Ganglia (usually globus pallidus internal segment)
- Dentate Nucleus of Cerebellum
- Somatosensory Pathways (spinothalamic tract & lateral meniscal pathway)
NB: All pathways carrying specific information to the cerebral cortex synapses in the thalamus
NB: Thalamus is a sort of translation centre (translating incoming excitatory signals for cortex)
This information goes to the thalamus to be relayed to the cortex
Where is the thalamus found?
- Either side of the 3rd Ventricle
Which part of the globus pallidus has an outflow to the thalamus?
- Internal Segment
NB: Most things that need to go to the thalamus/cortex from the basal ganglia go via the globus pallidus internal segment
What is the only information type that goes to the cerebral cortex that is not relayed by the thalamus?
- Smell
What is important about the connection between the thalamus & cerebral cortex?
- Each nucleus of the thalamus –> has reciprical connections with a specific area of cerebral cortex
- Informaton can also be passed between cortical areas via the thalamus
What is communication between region of cortex called?
- Direct Association Neurones (main way of communication)
NB: They can also communicate with other regions via the thalamus (however this is not the main way)
Important point about the thalamus.
- Different types of information –> go to different nuclei in the thalamus
What is the superior colliculus important for?
- Eye Movement
What is the inferior colliculus important for?
- Auditory Pathway
Where is the hypothalamic sulcus found between?
Groove between:
- Intraventricular Foramen
- Opening of the Aqueduct
What is above & below the hypothalamic sulcus?
- Anything Below –> HYPOTHALAMUS
- Anything Above –> THALAMUS (on the side of the 3rd ventricle)
NB: Thalamus is further back than 3rrd ventricle but forms a large part of the 3rd ventricle wall
Where is the internal medullary lamina (intramedullary) found and what is it?
- Sheet of White Matter
- Found in the middle of the thalamus (which is mostly grey) which divides at the front (fork)
Where is the anterior nucleus found?
- Between the 2 branches of the internal medullary lamina (front fork)
- Front of the Thalamus
Where is the dorsal medial nucleus found?
- Nucleus on the medial side of the internal medullary lamina
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Where is the pulvinar nucleus found?
- Expanded nucleus at the back
What 2 areas does the pulvinar nucleus have lots of connections with?
- Parietal Lobe (more)
- Occipital Lobe (less)
NB: Enlarged in primates
Where is the intralaminar nuclei?
- Found inside the internal medullary lamina
- Group of nuclei found here (middle of thalamus)
How many lateral nuclei are there?
What are they called?
- 3 nuclei
- Ventral-Posterior Lateral Nucleus (back)
- Ventral-Lateral Lateral Nucleus (side)
- Ventral-Anterior Lateral Nucleus (front - besides anterior nucleus)
NB: Each are important with specific connections with specific places of the brain
Which pathway is the lateral geniculate nuclei involved in?
- Visual Pathway
Which pathway is the medial geniculate nuclei involved in?
- Auditory Pathway
Where are the lateral & medial geniculate nuclei found?
- These sit at the bottom of the thalamus
- They look like ‘pimples’
Where is the thalamic reticular nucleus found?
What is its function?
- Around the lateral sides of the thalamus
- This is different from the rest of the thalamus
- Receives collaterals from fibres that come in & out of the thalamus
- Function –> Counsciousness
What is the claustrum important for?
- It is the seat of consciousness
What sensory modalities does the dorsal column / medial lemniscal pathway relay?
- Discriminative Touch
- Conscious Propioception
- Vibration Sense
What sensory modalities does the spinothalamic tract relay?
- Nociception
- Temperature
- Light Touch
Where in the brain do all somatosensory fibres relay before going to the cerebral cortex?
- Thalamus
NB: All somatosensory fibres do this
Which nucleus do somatosensory fibres relay through in the thalamus?
- Ventral-Posterior Nucleus
What is the main somatosensory nucleus of the thalamus?
- Ventral-Posterior Nucleus of the Thalamus
What arrangement is the ventral-posterior nucleus in?
Roughly how is it organised?
- Somatotopic Arrangement
- Head Sensory Information –> Medial Part of VP Nucleus
- Rest of Body Sensory Information –> Lateral Part of VP Nucleus
What is the ventral-posterior nucleus of the thalamus important for?
- Somatosensory relay
- Connected to the somatosensory cortex (post-central gyrus)
What syndrome can arise from damage to the somatosensory nuclei in the thalamus?
- Thalamic Syndrome
Occlusion in which blood supply can cause thalamic syndrome?
- Posterior Cerebral Artery (supplies thalamus)
Where do the blood supply to the thalamus come from?
- Posterior Cerebral Artery (PCA)
How does damage to the thalamus usually arise?
- Vascular Problem
How is the ventral-posterior nucleus specifically supplied?
- Small blood vessels from the PCA
These can be blocked –> causing variable effects –> however somatosensation is almost always affected
What are the effects of thalamic syndrome?
- All somatosensory activity from the contralateral side –> is interpreted as painful
- Will not feel other somatosensation
- Numb but painful feeling
- This will be ongoing (24 hours a day)
NB: Pain is like being immersed in boiling hot water continuously
What is a big issue with thalamic syndrome?
- Pain is ongoing
- Very painful
- High rate of suicide (due to pain)
What are the effects of prefrontal lobotomy on pain?
- Patients could still feel pain
- However –> they were no longer worried about the pain (thus no longer suicidal)
No prefrontal lobe –> means you cannot plan for the future –> therefore you do not worry for the rest of your life
NB: Pain is a construct of the cerebral cortex
Good diagram of the brain blood supply
Describe the pathway of the PCA and the supply to the thalamus.
- Winds around the midbrain
- Gives off lots of small branches at the base of the brain
- Some Branches –> penetrating central branches –> supplying thalamus
What is the main output from the cerebellum?
- Dentate Nucleus
NB: Helps to coordinate movements via 2 nuclei in the thalamus
Which 2 nuclei are the destinations of the main output from the cerebellum (dentate nucleus)?
- Ventral-Lateral Nuclei
- Ventral-Anterior Nuclei
NB: These then have recipricol connections with the pre-motor & motor cortex
What part of the brain activates when planning movements?
- Supplementary Motor Area
- Active Bilaterally (even if the movement is one sided)
What are the 2 main motor nuclei in the thalamus which relay motor information to the motor cortex?
- Ventral-Anterior Nucleus
- Ventral-Lateral Nucleus
What is the general function of the corpus striatum?
- Part of the basal ganglia
- Selects appropriate programs for producing movements that your cortex desires
What are the 2 main functions of the cerebellum?
- Coordination of Movement
- Correction of Errors
Where does the basal ganglia particularly relay information up to?
Where does it go via?
- Supplementary Motor Area (SMA)
- Thalamus
Where does the optic tract go via to get to Area V1?
- Lateral Geniculate Nucleus
What are 2 other names for area V1?
- Brodmann Area 17
- Calcarine Cortex
Discribe briefly the path from the retina to the brain.
- Retinal Ganglia –> send information down the optic nerve
- It goes the lateral geniculate nucleus (LGN)
- LGN –> has recipricol connection with V1 in the calcirine cortex
Outline the auditory pathway in the brain from the cochlear nuclei.
- Fibre from the Cochlea –> synapses onto the Inferior Colliculus
- Fibres from here go to the Medial Geniculate Nucleus of the Thalamus
- Medial Geniculate Nucleus –> fibres go to the Primary Auditory Cortex
Cochlea –> Inferior Colliclus –> Medial Geniculate Nucleus –> Primary Auditory Cortex
Where is the primary auditory cortex found?
- Buried in the Lateral Fissure on the Superior Surface of the Temporal Lobe
Where does the fibre from the cochlea first synapse?
- Inferior Colliculus
Which part of the thalamus is involved in the auditory pathway?
- Medial Geniculate Nucleus
Which nucleus in the thalamus is involved with emotions & personality?
- Dorsal Medial Nucleus
What is the pathway for emotions? (generally)
- Amygdala –> Dorsomedial Nucleus (Thalamus) –> Prefrontal Cortex
NB: Recipricol connection always between thalamus & cortex
Via what part of the internal capsule do the fibres go to the prefrontal cortex?
- Anterior Limb of the Internal Capsule
NB: Recipiricol connection
What are the effects of the amygdala when its stimulated and when its ablated?
- Stimulated –> Anger & Fright
- Ablated (Bilaterally) –> Placcidity
What is the intralaminar nuclei important for?
- Consciousness
What type of monoamine does the locus ceruleus send?
- Noradrenaline (NA)
NB: Found at the base of the brain (fibres go everywhere)
Where is the locus ceruleus found?
- Pons
What does the locus ceruleus & noradrenaline fibres do?
- Activates the cerebral cortex
What monoamine does the nucleus basalis send all over the neocortex?
- Cholinergic Fibres
What nucleus can the reticular fibres activate?
- Nucleus Basalis (ACh)
What function are the following involved in?
- Locus Ceruleus (pons)
- Reticular Fibres
- Nucleus Basalis
- Hypothalamic Nuclei
- Consciousness (keep you alert)
Where are the reticular formation found? (2 places)
- Medial part of the Rostral Pons
- Midbrain
Damage to what 3 places can cause a profound coma to be induced?
- Reticular Formation (medial part of the rostral pons)
- Reticular Formation (midbrain)
- Intralaminer Nuclei in the Thalamus (bilaterally)
Damage/distruption to this system –> means the cerebral cortex is not stimulated/woken up –> giving rise to a coma
Where do fibres from the intralaminer nuclei go?
- Cerebral Cortex
- Non-specific (unlike other nuclei in the thalamus)
- Widespread excitatory neurones
- Collaterals going all over to large areas of neocortex
What is the main input into the intralaminer nuclei?
Why is this pathway important?
- Information from the Reticular Formation in the Brainstem
- Lots of Nociceptive Inputs go to the Reticular Formation
Therefore painful stimuli go to reticular formation –> then to intralaminer nuclei –> which then goes to widespread areas of cortex –> important in consciousness
- Allows you to be awoken in cortex if there is pain
- Protective function
What 2 places do axon collaterals go to from the intralaminer nuclei?
Why is this needed?
- Cerebral Cortex
- Striatum
Allows the striatum & cortex to be prepared & ready to organise movements in response to a nasty stimulus
NB: Cold object on your face whilst you are asleep
Other than the brainstem reticular formation, from where else does the intralaminer nuclei get inputs from?
- Spinothalamic Tract (nociceptive pathway) - directly
What procedure may be able to help patients with damage to these alertness centres restore consciousness?
What does the procedure involve?
- Deep brain stimulation
- Electrodes placed in the central part of the thalamus
- Stimulate the intralaminer nucleus in the thalamus
NB: Very important nucleus in consciousness
Name the 6 structures which make up the limbic system
- Amygdala
- Hippocampus
- Thalamus
- Hypothalamus
- Basal Ganglia
- Cingulate Gyrus
What is the overall function of the amygdala?
- Emotion centre of the brain
What is the overall hippocampus function?
- Essential role in forming new memories about past experiences
Where is the limbic cortex?
- Anterior part of the cingulate gyrus
- Continous with the parahippocampal gyrus (via isthmus)
- Ends at the uncus (medial temporal lobe part for smell)
Where is the cingulate gyrus found? (generally)
- Goes around the corpus callosum
What are the main 2 functions of the limbic cortex?
- Memory
- Controlling ANS
NB: Complicated functions
NB: When forming memory information goes from the anterior cingulate gyrus to the parahippocampus (centre for memory)
Where is the high micturition centre?
- Anterior part of the cingulate gyrus
What is the high mictruition centre responsible for?
- Enables what & when & where it is appropriate for you to empty your bladder
- Anterior part of the cingulate gyrus
- It must be functioning on at least 1 side of the brain
What condition can affect the cingulate gyrus area?
- Meningioma
What effect does nocieption have on the anterior cingulate gyrus?
- It activates the ANS system (e.g. sympathetic)
Schematic of the medial side of the brain hemisphere.
What is the cingulum?
- Bundle of axons connecting the cingulate cortex with the entorhinal cortex + parahippocampal gyrus
Where is the entorhinal cortex found?
- Anterior part of the parahippocampal gyrus
To where does the entorhinal cortex send axons?
NB: Entorhinal cortex = anterior part of the parahippocampal gyrus
- Hippocampus
What is the overall general pathway of the limbic system?
Cingulate Gyrus –> Parahippocampal Gyrus + Entorhinal Cortex –> Hippocampus
What do the 3 red arrows point to on this scan?
What is found in the inferomedial temporal lobe?
- Hippocampus & Adjacent Cortex
What is the important function of the inferomedial temporal lobe?
- Needed for Episodic Memory formation
NB: New events about past memories (who, what, where etc.)
In which fossa is the hippocampus situated in?
- Middle Cranial Fossa
What pathology can happen in the middle cranial fossa and what part of the brain could this affect?
- Infection can accumulate
- Can affect Hippocampus
Where is the hippocampus found?
- Deep in the medial temporal lobe
What do you need for episodic memory?
- Hippocampus (medial temporal lobe) on at least one side
What condition do you get from bilateral ablation of the hippocampus (medial temporal lobe)?
What is this condition?
- Anterograde Amnesia
- Cannot put new memories into your memory stores –> thus cannot make long-term memories (does not affect short-term memory)
NB: It is necessary on one side of the brain to form episodic memory
What condition can commonly affect the medial temporal lobe in the middle cranial fossa?
How does it happen?
What is affected?
- Meningitis
- Common
- Lots of bacteria found in the subarachnoid space
- Subarachnoid space contains CSF and is found all around the brain
- Bacteria settles down in the middle temporal fossa around medial temporal lobe (hippocampus region)
- This damage causes inability to form episodic memory
What types of neurones are found in the hippocampus?
- Pyramidal Neurones
How is the hippocampus shaped?
What divisions is it divided into?
- Medial surface of the temporal lobe –> the cortex is folded in
- Forms the hippocampus
- Divided into CA1
What 2 other structures are part of the hippocampus?
- Fornix (white matter from hippocampal formation)
- Dentate gyrus
How many layers are there in the hippocampus and what is the middle layer called?
- 3 layers
- Middle –> Pyramidal Cell Layer
Learn this diagram
What does the septal nucleus do in terms of the hippocampus?
- Sends cholinergic neurones back to the hippocampus along the same pathway through the fornix
- Cholinergic fibres –> do not carry specific information –> they help synaptic activity everywhere
Where is the mammilary body found?
- Bump on the bottom of the hypothalamus
What are the 2 sources of afferent input into the hippocampus called?
- Perforant path
- Septohippocampal
What do the the septohippocampal carry?
- Cholinergic fibres (from septal nuclei)
- Carries ACh (non-specific information) –> to improve & speed up information processing –> this promotes synaptic activity
- Comes from the septal nuclei
NB: Septal nuclei afferents go all over the hippocampus
What is the perforant pathway?
- Path from the entorhinal cortex to the dentate gyrus
- Carries specific information about what things are going into the memory stores
- Axons perforate the cortex –> enter dentate gyrus
- Mossy fibres then go to CA3 (hippocampus)
Entorhinal Cortex –> Dentate Gyrus –> Hippocampus
What is the path from the septal nuclei to the hippocampus?
How does it help?
- Sends cholinergic fibres through the fornix –> into hippocampus
- Promotes synaptic activity –> helps memorisation
What disease involves problems with the septal nuclei?
- Alzeihmers
What are the 2 possible output directions form the hippocampal formation?
- Via fornix
- Via Entorhinal Cortex (back the way they came)
Describe the hippocampal output pathway via fornix.
Which nucleus of the thalamus does it synapse into?
- Output from the hippocampus
- Runs along the pathway to mammary body (all the way around)
- Synapses into the anterior nucleus of the thalamus
Where does CA1 output go?
- Entorhinal Cortex
Name the 3 pointed structures.
What happens to the mammilary body in alcoholics?
Why?
How can this be stopped or maybe reveresed?
- Shrivels up & dies
- Lack thymine in the diet
- Giving thymine supplements
Learn this summary of tracts.
What is so important about this circuit of papez?
- Necessary on at least one side of the brain in order to form a memory
NB: Hippocampus & medial temporal lobe are needed on at least one side for forming memory
What happens if there is bilateral damage to the circuit of papez?
- Loss of episodic memory
What happened to patient NA?
- Fencing foil –> whent up his nose straight into thalamus
- Destroyed mammillary bodies (hypothalamus) & mammalothalamic tract
- These are part of the circuit of papez
- Bilateral damage –> meant lose of ability to form episodic memory
He kept things around him to try and remind of places he had been & had lists around the house of things he needed to remember
There were no cognitive deficiences
What can cause bilateral damage to medial temporal lobes?
- Infections
- Accumulate bilaterally in the medial cranial fossa
NB: Bilateral stroke can also cause this but this is very unlikely
What happened to patient HM?
- Bilateral removal of medial temporal lobes
- No cognitive effects
- Could not remember new events again (episodic memory)
What is the syndrome called when you have bilateral damage to the temporal lobes?
- Kluver-Bucy Syndrome
- Loss of anterior temporal lobe bilaterally
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What are the effects of Kluver-Bucy syndrome?
- Profound amnesia (inability to form episodic memory) –> anterograde (new events)
- Hypersexuality (amygdala removed)
- Placidity (amygdala removed)
- Taste everything
- Visual agnosia (loss of visual association cortex)
How is the temporal lobe involved in vision?
- Temporal lobe –> part of visual association cortex
- Involved in identifying objects in the visual field (‘what’ stream)
NB: FFA is also part of the temporal lobe
What are the effects of losing vision areas in temporal lobe?
- Inability to recognise things
- Visual agonsia (if bilateral)
- Mix up a tree with a b
What causes Korsakoff’s syndrome? (2 things)
- Mammillary nuclei degeneration
- Anterior thalamus degeneration
What causes Korsakoff’s syndrome?
Among who is it common?
- Loss of Vitamin B1 Intake
- Causes degeneration of mammillary body & anterior nucleus
- Common among alcoholics & vitamin deficiency
What are the effects of Korsakoff’s syndrome?
- Profound retrograde amnesia (loss of memmory from before event)
- Confabulation
What is the hypothalamus in charge of?
- Hormones!
- Top centre that controls ANS & Hormones
What are the hypothalamic nuerones involved in?
- Neurosecretion from Posterior Pituitary Gland
- Production of Release Factors that regulate hormone release from Anterior Pituitary Gland
What happens in terms of body temperature if the hypothalamus is damaged?
- No control over body temperature
- Constantly need to measure it
- Go into cold & warm places to change it
- Cold-Blooded
Name the 7 things that the hypothalamus regulates?
- Sleep & wakefulness
- Body temperature
- Food intake
- Water intake & loss (hormones & behaviour)
- Other aspects of ANS
- Sex & reproduction (hormones & behaviour)
- Direct stress response (influences blood flow to specific tissues bya cting as 1st step in stimulation of secretion of adrenal stress hormones)
Where is histamine released from?
What is its affect on consciousness?
- Histaminergic neurones found in the hypothalamus
- Controls sleep/day cycle
- More Histamine –> More Awake
- Less histamine is released during sleep
What is a common side effect of anti-histamines?
Does this always happen?
- Sleepiness
- Only if it penetrates the blood-brain barrier (thus affects brain)
