Cerebral cortex and limbic system

Question 1

What does the cerebrum consist of? What is it separated by?

Answer 1

Cerebrum consists of two hemispheres Separated by longitudinal fissures.

Question 2

Lable the image

Answer 2

Question 3

What are brodmann areas based on?

What the areas outside the primary cortices and what do they allow?

Answer 3

• Brodmann areas are based on cell histology and cytoarchitecture which separates them into different functional regions.
• Areas outside the primary cortices are association areas- they allow higher cognitive processing and interpretation and integration of information.

Question 4

Describe the areas of the cortex that are shown and their function

Answer 4

• Area 4 = primary motor cortex on the precentral gyrus (rostral to central sulcus). Controls motor output to contralateral side of body.
• Area 6 = supplementary motor area (medial) and premotor cortex (lateral). Involved in motor planning/ motor program retrieval, sequencing of motor activities
• Area 1= primary somatosensory cortex on post central gyrus- receives contralateral sensory input - including taste
• Area 7 = posterior parietal cortex- integrates sensory input - loss leads to stereognosis (inability to percieve objects through tactile information).
• Area 17 = primary visual cortex - receives contralateral visual field information from both eyes
• Area 41 = primary auditory cortex, receives bilateral auditory sensory input.

Question 5

Describe the presentation of injury to each of the areas shown

Answer 5

• Area 6- premotor cortex and supplementary motor area:
  
  • inability to act out movements (e.g. using a hammer/ waving goodbye). Called ideomotor apraxia.
• Area 4 - primary motor cortex:
  
  • ​​​UMN lesion signs to contralateral side of the body (hyperreflexia, spastic paralysis, no muscle atrophy, babinski’s sign/ extensor plantar reflex).
• Area 1- Primary somatosensory cortex:
  
  • contralateral sensory loss and paresthesia
  • asterognosia - inability to identify objects by hand without visual/ other sensory information
• Area 17 - primary visual cortex:
  
  • damage to the tip of the striate cortex leads to central sclotoma
  • damage to entire cortex- inability to process visual field information from both eyes
• Area 41- primary auditory cortex:
  
  • ​Injury causes reduction in hearing acuity on contralateral side
• Area 22 - superior temporal gyrus association area, wernickes area - language processing
  
  • Damage leads to receptive aphasia
  • loss of ability to distinguish/recognise sound - i.e whether speech/ door opening
• Area 46- Prefrontal cortex:
  
  • ​changes in emotional behaviour and processing
  • flat personality
  • memory problems

Question 6

Describe the injury presentation if there is damage to the posterior parietal cortex?

Answer 6

• Posterior parietal cortex also called the superior lobule - integrates sensory inputs, controls perception of the contralateral body/environment
• Damage to this area presents with Hemispatial neglect:
  
  • ​Neuropsychological condition in which damage to the posterior parietal cortex of 1 hemisphere leads to deficit in the attention and awareness of 1 side of the field of vision
• most often due to right sided damage
• patient will ignore the contralateral side of the world
• walk into objects
• contralateral asterognosia –> inability to identify object by touch of the hands without additional sensory/ visual input.

Question 7

What is the word for inability to recognise faces?

What is the brain region involved?

What is the word for inability to recognise colours?

Region involved?

Answer 7

• Prosapagnosia= inability to recognise faces
• Area involved is the fusiform gyrus in the medial occipital and temporal lobe
• Achromatopsia = inability to recognise colours
• again area involved is the medial occipital and temporal lobe.

Question 8

What key cortices are located in the medial occipital and temporal lobes?

Answer 8

• cortices for facial recognition, shape recognition and colour recognition

Question 9

Describe the associative neural interconnections between these different cortical areas and the function of each area

Describe what would happen if there was damage to that region

Answer 9

• Area 17 - primary visual cortex which allows us to see the object, receives contralateral visual field information. Damage here can lead to central scotoma (if at tip of striate cortex) or could lead to general inability to receive contralateral visual field information.
• Area 18 - secondary visual cortex, association area. Allows us to figure out what the object is. Damage here can lead to:
  
  • Associative agnosia - sees the object but unable to distinguish/ recognise the object
  • Apperceptive agnosia- unable to percieve or see the object
• Area 19 - extrastriate cortex - sensitive to motion and perception of human bodies. Enables us to see if the object is moving. If there is damage here there will be an inability to detect movement- can only recognise objects when they are stationary.
• Frontal eye fields in the frontal cortex - allow voluntary eye movements, allowing us to track a moving object. Project to extraocular muscles via another pathway. Damage here leads to eye deviation towards the damaged side.

Question 10

Define dysphasia/ aphasia

Answer 10

• Inability to express oneself via speech or inability to understand written or spoken language

Question 11

What hemisphere is normally dominant for speech and language?

Answer 11

• Left hemisphere normally dominant for speech and language
• language functions such as grammar, vocabulary and literal meaning are typically lateralised to the left hemisphere
• Broca’s and Wernicke’s are typically located in the left hemisphere in around 95% of right handers.

Question 12

What are the areas of the cortex shown below?

What is the effect if there is damage?

Answer 12

• Red - Broca’s area (brodmann area 44/45) - involved in the production of speech/ motor control of speech. Damage here leads to expressive aphasia, where patient can fully understand written/ spoken language but has difficulty producing speech/ effortful speech, slow, short sentences and missing grammar.
• Orange - Wernicke’s area - brodmann area 22 - involved in the comprehension of written and spoken language. Damage here leads to receptive aphasia, where patient unable to understand what has been communicated to them but is able to produce speech that is gramatically correct, normal rate/ fluent speech but often has inappropriate content.
• Green - angular gyrus: dysfunction here can lead to 1) alexia - inability to recognise/ read written words or letters. 2) agraphia - inability to write
• Blue - primary auditory cortex - damage here leads to reduction of hearing sensitivity in both ears - mostly contralateral- and loss of stereo perception of sound origin.

Question 13

what cerebral artery supplies hearing/ speech/language areas?

Answer 13

middle cerebral artery

Question 14

What do complex cerebral functions require?

What is a fasciculus?

Answer 14

• Complex cerebral functions require different parts of the cortex to be interconnected
• A fasciculus = bundle of fibres sharing a similar function and route of travel

Question 15

Fill in the blanks and explain the neural pathway from seeing text and explaining what is says

Answer 15

• Visually see the text via primary visual cortex
• this is then processed in the angular gyrus which allows us to understand the writing/ letters
• damage inbetween the interconnection between primary visual cortex and angular gyrus leads to alexia (inability to understand written words or letters)) without agraphia (patient still able to spontaneously write, agraphia = inability to write).
• This information is passed to Wernicke’s area (Brod 22) which allows comprehension of the written text, damage leads to receptive aphasia.
• From wernickes area the information is passed to Broca’s area (Brod 44/45) which is involved in motor planning of speech.
• information passes along the arcuate fasciculus –> damage here leads to conductive aphasia where the patient understands written and spoken word, has fluent speech but poor speech repetition –> unable to repeat phrases spoken to them.
• Damage to Broca’s area (Brod 44/45) leads to expressive aphasia - speech that is slow, short, lacking grammar but appropriate content.

Question 16

what connects the R and L hemispheres?

why would damage to this tract matter?

Answer 16

• R and L hemispheres connected via the Corpus callosum
• Damage to this white matter tract matters as information being received by one cerebral hemisphere may need to be processed by a region in the other hemisphere - i.e processed by language centre which is in the L hemisphere. (lateralised functions.)
• Damage to corpus callosum - inability to name objects that are held in the left hand - as sensory information would be processed in the right somatosensory cortex and needs to be passed to the left to name what is in the hand.
• Inability to read via left half of visual field (visual path ok from left eye to right visual cortex but cant get to left side).

Question 17

How long would it take for a person to become unconcious after a vessel occlusion to the brain?

What can compromise arterial blood supply to the CNS?

Answer 17

• Takes only 10 seconds for a person to become unconcious if a vessel supplying the brain becomes occluded.
• Compromise arterial blood supply to CNS:
  
  • vessel occlusion - either thrombus or embolus
  • extradural haematoma - cresecent shaped, pressure on underlying cerebrum
  • intracerebral haemorrhage - often due to a burst aneurysm or vessel wall degeneration
  • Aneurysm - often at sites of arterial branching

Question 18

What is a stroke?

What cranial nerves are affected by a carotid artery aneurysm?

Answer 18

• A stroke is a persistent neural deficit of vascular origin
• Carotid aneurysm can compress cranial nerves 3/4/6.

Question 19

What are the two main blood vessels that supply the brain?

Where do they branch from, how do they enter the skull?

What do they supply?

Answer 19

• Blood supply via 1) vertebral arteries 2) internal carotid artery
• Vertebral arteries branch directly off the subclavian arteries
• Travel via the foramen transversarium of the vertebral column, then enter the skull via the foramen magnum.
• Supplies the brainstem, cerebellum, posterior/inferior cerebrum, proximal spinal cord.
• Internal carotid branches directly off common carotid
• enters the skull via the carotid canal, surrounded by a symapathetic plexus (internal carotid plexus) that innervates the superior tarsal muscle and pupillary dilator muscles.
• supplies the majority of the cerebral hemispheres and the eye.

Question 20

Describe the circle of willis

Answer 20

• Circle of willis is formed by the internal carotids and branches that come off
• Internal carotids give off posteriorly- the posterior communicating artery which joins the posterior cerebral artery (PCA) and middle cerebral artery (MCA).
• The ICA continues itself as the MCA
• Anteriorly it gives off the anterior cerebral arteries which are joined by the anterior communicating artery.
• Posteriorly the circle of willis is joined to the basilar artery formed by the union of the two vertebral arteries.

Question 21

Describe the branches of the internal carotid arteries and what they supply

Answer 21

• The internal carotid arteries give off anteriorly the anterior cerebral artery, connected by the anterior communicating artery. ACA supplies the anteromedial aspect of the cerebrum.
• Posteriorly they give off the posterior communicating artery, which connects the MCA and PCA
• The PCA supplies the lateral and medial portions of the posterior portion of the brain.
• The MCA comes directly off the internal carotid artery and supplies the lateral aspects of the cerebrum
• The opthalmic artery comes off medially and goes to supply the orbit
• The anterior choroidal artery comes off the internal carotid laterally and supplies parts of the brain important for vision and motor control:
  
  • supplies optic tract and chiasm
  • supplies the lateral geniculate nucleus and lateral thalamus
  • posterior limb of internal capsule
  • the choroid plexus of the temporal horns of the lateral ventricles
  • lateral midbrain

Question 22

Describe the branches of the vertebral arteries

Answer 22

• vertebral artery travels up to the brainstem via the foramen transversarium and enters via the foramen magnum
• before uniting as the basilar artery and running over the pons it gives off the anterior spinal branch anteriorly, which runs over the anterior spinal cord. It also gives off the two posterior spinal arteries that run down the posterior aspect of the spinal cord.
• Each vertebral artery also gives off a posterior inferior cerebellar artery.
• Once they unite as the basilar artery, it then gives off the anterior inferior cerebellar artery.
• Basilar artery continues up over the pons, giving off pontine arteries.
• It continues up over the midbrain and gives off the superior cerebellar artery.
• Just after this it gives off the posterior cerebral arteries. (PCA)

Question 23

label the image:

what do the communicating vessels act as?

Answer 23

• The communicating vessels in the circle of willis act as potential routes for collateral circulation
  *

Question 24

Describe the overall pattern of blood supply to the different regions of the cerebral hemispheres

Which arteries (vertebral/ internal carotid) give which cerebral arteries?

Answer 24

• Anterior cerebral artery does the anteromedial surface of the cerebrum
• Middle cerebral artery does most of the lateral surface of the cerebral hemispheres, up to superior/ middle temporal gyrus of the temporal lobe.
• Posterior cerebral artery supplies the lateral and medial regions of the posterior cerebrum.
• Remember the internal carotid arteries give off the ACA and MCA.
• The vertebral arteries unite as the basilar, then bifurcate to give the PCA.

Question 25

Why might the posterior cerebral artery be particularly susceptible to raised intracranial pressure?

Answer 25

* Posterior cerebral artery is particularly susceptible to raised intracranial pressure as it runs directly over the tentorium cerebelli. * May become occluded with raised intracranial pressure leading to a defecit in supply to the posterior lateral and medial portions of the cerebrum

Question 26

What are the deep penetrating branches of the ACA/MCA/PCA what regions do they supply?

Answer 26

* The ACA gives off the medial striate arteries that supply above the corpus callosum and the head of the caudate nucleus * The MCA gives off the lateral striate artery, also known as the lenticulostriate arteries. Supplies the lentiform nucleus (globus pallidus + putamen) and the striatum (putamen and caudate). * The PCA gives off the thalamogeniculate arteries which supply the thalamus and geniculate nuclei (both medial and lateral).

Question 27

What is the blood supply to the basal ganglia?

Answer 27

* Blood supply to the basal ganglia is via the anterior choroidal (direct branch off internal carotid) , the ACA and MCA. * The ACA gives off medial striate arteries * MCA gives off lateral striate arteries

Question 28

What is the blood supply to the internal capsule? Describe the somatotopic mapping of the internal capsule

Answer 28

* Anterior limb supplied by lenticulostriate arteries (lateral striate) off MCA plus recurrent artery of Heubner (medial striate) off ACA. * Genu supplied by lenticulostriate artery * Posterior limb supplied by lenticulostriate arteries and anterior choroidal artery (directly off ICA). * Somatotopic mapping: anterior limb formed by descending tracts from cortex to thalamus and pons (frontopontine and frontothalamic). * Genu = head of motor tracts, then follow back onto the posterior limb with arms/trunk/legs. * Posterior limb carries on with similar somatotopic map of sensory ascending tracts * Retrolenticular limb carries auditory and visual fibres

Question 29

How would an infarct of the internal capsule present?

Answer 29

* Infarct of the internal capsule could present with widespread contralateral symptoms- could present with motor, sensory, visual or auditory symptoms.

Question 30

Describe the choroidal circulation and what each branch supplies

Answer 30

* There are two choroidal arteries, 1) anterior choroidal artery coming directly off the ICA and 2) the posterior choroidal artery coming off the PCA, both at the circle of willis. * Anterior choroidal artery supplies: * Posterior limb internal capsule * optic tract * lateral geniculate nucleus and lateral thalamus * lateral midbrain * choroid plexus of lateral ventricles * limbic system * Posterior choroidal artery supplies: * posterior choroidal actually multiple branches * supplies 3rd and lateral ventricles, parts of limbic system, cerebral peduncles and caudate.

Question 31

How can infarction of the brainstem present with different motor lesions?

Answer 31

* Infarction of the brainstem will present with LMN lesion for the cranial nerves (as LMN's exit brainstem). * Will present with UMN lesion symptoms for the arms and legs as the corticospinal tract travels through the brainstem and down to its appropriate spinal level to synapse with a LMN in the ventral horn of the spinal cord.

Question 32

What main cerebral artery supplies regions associated with aphasia?

Answer 32

* Middle cerebral artery supplies the temporal lobe- wernickes area- and the lateral cortex (brocas area).

Question 33

What is the limbic system? how is it arranged around the diencephalon?

Answer 33

* **The limbic system= epicentre emotional and behaviour expression.** * Concerned with **sensations of emotion, visceral responses to emotion and memory.** * Limbic system has both a **cortical component** and **subcortical component.** * Cortical component --\> consists of neocortex (cortex concerned with sight/ hearing), orbitofrontal cortex (part of preF cortex, decision making), hippocampus, insular cortex, cingulate gyrus. * Subcortical component --\> amygdala, olfactory bulb, hypothalamus (final output of limbic system), anterior and dorsomedial nuclei of thalamus, septal nuclei. * many of the structures **form a ring around the diencephalon** **(thalamus and hypothalamus and epithalamus).**

Question 34

What are the functions of the limbic system?

Answer 34

Think of the 5 F's: Feeding --\> satiety and hunger Forgetting --\> memory Fighting --\> emotional responses Family --\> reproduction and maternal instinct Fornicating --\> sexual arousal

Question 35

What makes up the limbic system?

Answer 35

* Cortical component: * neocortex (concerned with sight and hearing) * Orbitofrontal cortex (part of prefrontal cortex concerned with decision making) * hippocampus --\> memory * insular lobe * cingulate gyrus * Subcortical component: * amygdala --\> fear and anxiety * nucleus accumbens --\> reward P/W, pleasure * Septal nuclei --\> front of corpus callosum, pleasure * olfactory bulb * hypothalamus --\> final output of the limbic system * Anterior and dorsomedial nuclei of thalamus

Question 36

Label the image

Answer 36

Question 37

What is the papez circuit? what is it formed of?

Answer 37

Papez circuit is the fundamental medial circuit of the limbic system that allows emotional expression, closed neural circuit that starts and ends in the hippocampus. Formed of the hippocampus, fornix, mamillary bodies, mamillothalamic fibres, anterior nucleus of thalamus, cingulate gyrus, entorhinal cortex. (entorhinal cortex adjacent cortex to hippocampus).

Question 38

What is the flow of information in the papez circuit?

Answer 38

* Hippocampus --\> fornix --\> mamillary bodies ---\> mamillothalamic fibres --\> anterior nucleus thalamus --\> cingulate gyrus --\> entorhinal cortex ---\> hippocampus

Question 39

What is the fornix?

Answer 39

* C shaped bundle of nerve fibres forming the major output tract of the hippocampus connecting to the mamillary bodies of the hypothalamus and anterior nucleus of the thalamus.

Question 40

What is the hippocampus involved in? where is the hippocampus located? What would damage to this structure lead to?

Answer 40

* Hippocampus is involved in memory formation and recall * Located in the inferomedial temporal lobe * Damage would lead to anterograde amnesia * No problem with long term memory but unable to form new memories * Hippocampus also involved in memories involving visuospatial tasks and language

Question 41

What are the different types of memory?

Answer 41

* Short term memory --\> short duration (under 1 hr) * Declarative/ explicit memory --\> recall fact/ event/ knowledge (Takes effort) * Implicit/ procedural --\> learned skill, writing, motor skills and language

Question 42

What is Korsakoff's psychosis? How can it occur? What is damaged? How can it present? What is Wernicke Korsakoff syndrome?

Answer 42

* Korsakoff's psychosis refers to damage to the mamillary bodies and thalamus due to metabolic damage or alcohol abuse * Metabolic damage from a thiamine (B1) deficiency * Presents with anterograde and often retrograde amnesia * confabulation --\> patient inserts fabricated "memories" of long term events into current conversation * Hallucinations * Wernicke korsakoff syndrome = korsakoff syndrome + ataxia, opthalmoplegia (paralysis of the extraocular muscles) and dementia

Question 43

Describe the different regions of the cingulate gyrus

Answer 43

* Anterior gyrus: Autonomic area: * cardiorespiratory and digestion * visceral response to emotion * bladder control * emotional modulation of pain * Posterior gyrus: * Vocal area for correct sentence construction * memory * cognition

Question 44

What are the inputs to the amygdala?

Answer 44

* Visual and auditory cortex * Solitary tract (taste) * olfactory and limbic system * hypothalamic * sensory from the body

Question 45

What are the outputs of the amygdala? What can this bring about?

Answer 45

* Outputs: * hypothalamus * Hippocampus * Multiple areas of cortex * Can bring about --\> fear and anger --\> behavioural emotions --\> recognise emotional content of faces --\> impulsivity --\> sexual behaviour and emotion

Question 46

What are the physiological effects of amygdala activation?

Answer 46

* increased HR and BP * increased GI motility * reduced saliva * irritability * increase muscle tension * pupil dilation

Question 47

What is Kluver bucy syndrome?

Answer 47

* Kluver Bucy syndrome occurs with bilateral damage to the amygdala: * docile, lack of fear and anger * Increased appetite * hypersexual behaviour * exploratory with hands and mouth * visual agnosia and memory disorder

Question 48

What can an overactive amygdala lead to?

Answer 48

Anxiety, stress, anger

Question 49

What are the septal and nucleus accumbens nuclei involved in?

Answer 49

* Septal and accumbens nuclei both involved in pleasure (sexual orgasm and sensations) , dopamine reward pathways, intense sense of well being