Lecture 12: Cerebrum Flashcards
Where is cortical information housed?
In the gyri
Why are the gyri important?
Because they are where cortical information is housed
What is in the outer part of gray matter?
Cortical neuronal cell bodies extending axons to different places
Where can cortical neurons extent their axons?
*From one gyrus to another
*One lobe to another
*To the other hemisphere
*Down to the spinal cord
Where do short association fibers go?
From one gyrus to another gyrus in the the same lobe (or a gyrus close by)
Where do long association fibers go?
From one lobe to another lobe and stay on the same side of the cortex
Where do commissural fibers go?
From one hemisphere to the other (through the corpus callosum)
Where do Projection fibers go?
Down the spinal cord
What are the for types of association fibers?
*Short association fibers
*Long association fibers
*Commissural fibers
*Projection fibers
What association fibres go from gyrus to gyrus?
Short association fibers
What association fibres go from lobe to lobe?
Long association fibers
What association fibres go from hemisphere to hemisphere?
Commissural fibers
What association fibres go down the spinal cord?
Projection fibres
What are the main projection fibers that go down the spinal cord?
*Corticospinal
*Corticobulbar
*Spinothalamic
*Dorsal Columns Medial Lemniscal
What is the internal capsule?
The white matter tracts that travel between the thalamus and basal ganglia in the brain
What are the three parts of the internal capsule?
Anterior Limb
Genu
Posterior Limb
What are the parts of the basal ganglia?
*Caudate
*Putamen
*Globus Pallidus
What is in the anterior limb of the Internal Capsule?
Thalamocortical projects (all sensory afferents except for afferents)
What pathways are part of the thalamocortical projects that go through the anterior limb of the internal capsule?
*Spinothalamic tract
*Dorsal Columns Medial Lemniscus
*Trigeminothalamic tract
What pathways are part of the Posterior Limb?
Corticospinal tracts for conscious movements of the lower limbs
What is the Corticobulbar tracts?
Motor tracts for conscious movement of the muscles of the face
What is housed in the genu of the Internal Capsule?
The Corticobulbar tracts
What are the nuclei associated with the corticobulbar tracts?
*Oculomotor nucleus
*Abducens
*Trochlear
*Trigeminal
*Facial
Why is a stroke or lesion the the internal capsule important?
Because the internal capsule houses many axon tracts
What is found in layer I of the cortex?
- Few nerve cell bodies
- Many dendritic and axonal processes in synaptic interaction
What is found in layer II of the cortex?
- Small neurons which establish intracortical connections
What is found in layer III of the cortex?
- Medium-sized neurons giving rise to association and commissural fibres
What is found in layer IV of the cortex?
Termination of afferent fibres from the thalamus
What is found in layer V of the cortex?
- The origin of projection fibres to extracortical targets, such as BG, thalamus, brainstem and spinal cord
- In the primary motor cortex of the frontal lobe, this layer contains corticospinal tract cell bodies
What is found in layer VI of the cortex?
Association and projection fibers
In what layer of the cortex is association and projection fibers found?
Layer VI
In what layer of the cortex are:
- Few nerve cell bodies
- Many dendritic and axonal processes in synaptic interaction
Layer I
In what layer of the cortex are:
- Small neurons which establish intracortical connections
Layer II
In what layer of the cortex are:
- Medium-sized neurons giving rise to association and commissural fibres
Layer III
In what layer of the cortex are:
- Termination of afferent fibres from the thalamus
Layer IV
In what layer of the cortex are:
- The origin of projection fibres to extracortical targets, such as BG, thalamus, brainstem and spinal cord
- In the primary motor cortex of the frontal lobe, this layer contains corticospinal tract cell bodies
Layer V
What is functionally located in the Frontal Lobe?
- Higher cognitive function
- Motor planning and execution
- Language
What is functionally located in the Parietal Lobe?
- Somatic sense of body image
- 3D localization of self and targets in space
- Language
What is functionally located in the Occipital lobe?
Vision
What is functionally located in the temporal lobe?
- Short-term memory
- Learning
- Auditory
Where is:
- Higher cognitive function
- Motor planning and execution
- Language
Frontal Lobe
Where is:
- Somatic sense of body image
- 3D localization of self and targets in space
- Language
Parietal Lobe
Where is:
- Vision
Occipital lobe
Where is:
- Short-term memory
- Learning
- Auditory
Temporal Lobe
What is stored in the Limbic system?
Emotional, social and sexual behavior
Where is:
Emotional, social and sexual behavior
Limbic system
What is information on functional localization mostly from?
- Stimulation and ablation studies
- Electrophysiological recording
- Observations of regional blood flow
- Post mortem studies of patients with known lesions
What is the Montreal surgery?
Stimulating the brain with electrical probes while patients were conscious to observe their responses. This led to the cortical homunculus
What led to homunculus?
The Montreal surgery where they stimulated brains of conscious people and observed responses
What led to Broca’s area?
The post-mortem study of patient ‘Tan’ who could understand everything but could only speak the word Tan
What was discovered in patient Tan?
A lesion in the left inferior frontal lobe - the orbital triangular and opercular which makes up Broca’s speech area
What area of the brain is Broca’s speech area?
Left inferior frontal lobe - the orbital triangular and opercular
Where is Wernicke’s area?
The posterior portion of the left temporal lobe
What happens if there is a lesion in Wernicke’s area?
People cannot understand what is being said to them and their speech is often incoherent and makes no sense**
What is the function of the Primary Auditory Cortex?
Sound Localization
Where is the primary auditory cortex located?
Heschl’s gyrus
What is housed in Heschl’s gyrus?
The primary auditory cortex
Where is information carry from Heschl’s gyrus?
Short association fibres carry information to neighbouring gyri like Wernicke’s area and Broca’s area
What is the function of Wernicke’s sensory speech area?
Comprehension of sound
What will a lesion to Wernicke’s sensory speech area cause?
Sensory and Receptive Aphasia
What is Sensory Aphasia?
Inability to understand spoken word
What is receptive aphasia?
When someone is able to speak well and use long sentences, but what they say may not make sense
What may cause sensory and receptive aphasia?
A lesion to Wernicke’s sensory speech area
What is the function of Broca’s Motor Speech Area?
Formulation of the motor movements for speech
What can a lesion to Broca’s area cause?
Broca’s aphasia, motor aphasia or expressive aphasia - can understand what they are hearing but can’t reply
What is Broca’s aphasia, motor aphasia, or expressive aphasia?
Issues with producing speech
What may cause issues with producing the motor movements for speech?
A lesion to Broca’s area
What is the Arcuate Fasciculus?
A white matter tract that runs from Wernicke’s to Broca’s area
What is the Arcuate Fasciculus used for?
When a person is asked to repeat after another person
What can a lesion to the Arcuate Fasciculus cause?
Conduction aphasia, but they are good with spontaneous speech
What is conduction aphasia?
The inability to repeat words or phrases
What may cause conduction aphasia?
The inability to repeat words or phrases
What are the steps to verbally respond to a question?
- Listen (primary auditory cortex)
- Comprehend (Wernicke’s area)
- Send association fibres through the Arcuate Fasciculus
- Broca’s motor speech area to formulate speech
- Activate UMN for speech muscles
What are the three operation system of the brain?
- Sensory systems
- Association systems
- Motor systema
What do the Sensory systems do?
Create the internal representation of the outside world
What do association systems do?
Integration of diverse sensory information for planning purposeful action
What is the Topography of the Primary Sensory Cortex?
The Homonculus
What is the Homunculus essential for?
Recognition and localization of sensory stimuli
What is the each primary sensory area surround by?
A larger zone of association cortex that interpret that sensation
What is an association cortex?
An area that interprets the incoming signals and is appropriately connected to other parts of the cerebral cortex
What do Lesions to Association cortices cause?
- Agnosias
- Aphasias
- Apraxias
What are Agnosia’s?
The inability to recognize common objects (parietal lobe)
What lobe are Agnosia’s associated with?
The Parietal lobe
What are aphasias?
The inability to understand/vocalize speech
What are aphasia associated with?
Wernicke’s or Broca’s area
What are Apraxias?
The inability to execute purposeful movements (motor planning disorder)
What may a lesion in the Primary Sensory Cortex cause?
Tingling and numbness
What is the Posterior Parietal Cortex?
The association cortex for the Primary Sensory Cortex
What can a lesion in the Posterior Parietal Cortex cause?
Agnosia - won’t be able to identify something by touch
Neglect - Won’t understand that their own body is a part of themselves
What may cause Agnosia and Neglect?
A lesion to the Posterior Parietal Cortex
What may a lesion to the Primary Visual Cortex cause?
Visual Field Defects
What may a lesion to the Visual Association Cortex cause?
Visual Agnosia - Issues interpreting what is seen
What may cause visual agnosia?
A lesion to the Visual Association Cortex
What may a lesion to the Primary Auditory Cortex cause?
Inability for sound localization
What may cause the inability for sound localization?
A lesion to the primary auditory cortex
What may a lesion to Wernicke’s sensory speech area cause?
Sensory and receptive aphasia - inability to comprehend
What can lesions to the Parietal, temporal and Occipital association cause?
Different agnosias
What can lesiona to the Limbic association cortex cause?
Schizophrenia and depressive illness
What may cause Schizophrenia and depressive illness?
Lesions to the Limbic Association Cortex
What do Lesions to the Prefrontal Association Cortex cause?
Personality and behavior disorders
What causes personality and behaviour disorders?
Lesions to the prefrontal cortex
What makes up the Primary Olfacotry area?
The uncus, parts of the insula and the frontal gyri
What are lesions to the parietal association cortex usually like?
They are often incomplete and the ability to feel an object may be present but there may be a defect in the ability to interpret this sensation
What is Tactile Agnosia?
The inability to interpret a touch sensation due to a lesion in the parietal association cortex
What is Astereognosis?
The loss of awareness of the spatial relation of parts of the contralateral side of the body (can’t discriminate shape)
What is another name for Astereognosis?
Tactile amnesia
What is Cortical Neglect?
An extreme form of astereognosis in which the patient ignores/denies one side of the body and corresponding visual field
What is the ventral stream of the Visual association cortex for?
- Color
- Letters
- Faces
-Visual memories
What is the Dorsal Stream of the Visual Association Cortex for?
- 3D visual understanding of an object
- Motion of an object
What does a lesion to the Ventral stream cause?
Prosopagnosia
What causes Prospopagnosia?
A lesion to the ventral stream
What is Prosopagnosia?
Cannot recognize faces
Which visual association stream recognizes:
- Color
- Letters
- Faces
- Visual memories
Ventral Stream
Which Stream recognizes:
- 3D visual understanding of an object
- Motion of an object
Dorsal Stream
Which lobe is the Dorsal Stream apart of?
The occipital and parietal lobe
What does a lesion to the primary auditory cortex cause?
Wernicke’s aphasia
What is Wernicke’s aphasia?
When you can’t understand the difference between someone’s voice and other sounds
What is Amusia?
A right side lesion in the Primary Auditory cortex leading to inability to recognize previously ‘familiar’ voices and music
What causes Amusia?
A right side lesion in the primary auditory cortex
What is unique about the olfactory and gustatory association cortices?
They intermix
What is the function of the Olfactory and Gustatory cortices?
They allow us to smell and identify taste
Why do the Olfactory and Gustatory cortices send association fibers?
To get an emotional response to a smell or taste and to acquire memories associated with smell
What can a lesion to the olfactory and gustatory cortex cause?
Anosmia - loss of smell which leads to lack of taste
What causes Anosmia?
A lesion to the olfactory and gustatory association cortices
What is localized in the left hemisphere?
- Broca’s motor speech area (frontal lobe)
- Wernicke’s sensory speech area
What is the Premotor cortex responsible for?
Telling upper motor neurons when to fire
How do the Premotor cortex and the Supplementary Motor cortex work?
They receive feedback from basal ganglia, reticular formation, and the limbic system, which they integrate in order to tell the primary motor cortex when to fire
Where is sensory information in the motor system coming from?
- Understanding your surroundings - Posterior parietal Cortex
- Visual info - Primary Visual Cortex
What are the three main steps in motor movements?
- Identification of body in space - posterior parietal cortex
- Formulation of plan - Premotor cortex
- Execution of movement - Primary motor cortex
What are the descending motor pathways?
- Corticospinal
- Corticobulbar
- Corticoreticular
- Reticulospinal
- Vestibulospinal
- Rubrospinal
What are the two conscious descending motor pathways?
Corticospinal and corticobulbar
What two things can an UMN do to a LMN?
It can excite or inhibit the LMN
What does a lesion to the UMN cause?
Disinhibition of the LMN causing spastic paralysis
What causes spastic paralysis?
A lesion to the UMN
What does a lesion to the LMN cause?
Flaccid paralysis so the LMN won’t contract
What is the Hierarchy of the Descending Motor Pathways?
- Corticobulbar and Corticospinal (pyramidal tracts)
- Corticoreticular, reticulospinal, vestibulospinal, rubrospinal (extrapyramidal tracts)
Describe the Corticospinal and Corticobulbar tract?
The allow for voluntary control of LMNs but they receive input from the basal ganglia and cerebellum o ensure smooth, coordinated, purposeful movement
What are the Corticospinal and Corticobulbar tract modulated by?
The basal ganglia and cerebellum
What do the basal ganglia and cerebellum do for the Corticospinal and Corticobulbar tracts?
Ensure smooth, coordinated and purposeful movement
What can a basal ganglia lesion causes?
Parkinson’s disease
Huntington’s Chorea
What does a Cerebellar lesion cause?
Ipsilateral ataxia
Why are the extrapyramidal tracts important?
Because they work behind the scene to allow conscious movements to occur in the right way so that we don’t need to think about multiple movements
What are the four extrapyramidal tracts?
- Corticoreticulospinal tract
- Vestibulospinal tract
- Rubrospinal tract
- Tectospinal tract
What does the Corticoreticulospinal tract do?
Excitatory to leg extensors and arm flexors
What does the Vestibulospinal tract do?
Excitatory to arm and leg extensors and inhibitory to arm and leg flexors
What does the Rubrospinal tract do?
Inhibitory to arm extensors and excitatory to arm flexors. No effect on leg muscles
What does the Tectospinal tract do?
Influences leg muscles
Which descending motor pathway is excitatory to leg extensors and arm flexors?
The Corticoreticulospinal tract
Which descending motor pathway is excitatory to arm and leg extensors and inhibitory to arm and leg flexors?
The vestibulospinal tract
What descending motor pathway is inhibitory to arm extensors and excitatory to arm flexors with no effect on leg muscles?
The Rubrospinal tract
What descending motor pathway influences the neck muscles?
The tectospinal tract
How does the tectospinal tract influence the neck muscles?
Turns the head with you see something in the visual field or when someone whispers in the ear etc
What are the two types of posturing?
Decorticate posturing
Decerebrate posturing
Where in the brain is a lesion that causes Decorticate Posturing?
The lesion is below the cerebral cortex and at the very top of the midbrain
What are the characteristics of the tracts in Decorticate Posturing?
The extrapyramidal tracts are all functional
- The rubrospinal tract flexes the upper body
- The corticoreticular tract flexes upper body and extends lower body
- The vestibulospinal tract is excitatory to arm/leg extensors and arm extensors are overruled by corticospinal and rubrospinal tracts
What are the characteristics of the limbs in Decorticate Posturing?
Arms flexed and legs extended
What are the characteristics of the limbs in deceberate posturing?
Arms and legs extended
What are the characteristics of the pathways in Decerebrate Posturing?
- CST and Rubrospinal tract are not active
- Corticoreticulospinal tract want to flex upper body (overruled by VST) and extend lower body
-Vestibulospinal tract is excitatory to arm and leg extensors and inhibitory to arm and leg flexors with extends upper body
As a brainstem lesion gets lower what happens to the posturing?
Can change a decorticate to a decebreate Posturing
