Cortical organisation and function Flashcards
Where is the primary motor cortex
In front of the central sulcus. Broadman’s area 4
Where is the primary somatosensory cortex
Behind the central sulcus. Broadman’s areas 1,2,3
What are the functions of the Parietal lobe
Sensation: touch pain
Sensory aspects of language
Spatial orientation and self perception
What are the functions of the Frontal lobe
Regulating and initiating motor function
Language
Cognitive functions (executive function eg planning)
Attention
Memory
Eg someone with frontal lobe defects could have major changes in personality
What are the functions of the occipital lobe
Processing visual information
What are the functions of the temporal lobe
Processing auditory information
Emotions
Memories
what does the limbic lobe (limbic system include)
Amygdala, hippocampus, mamillary body, and cingulate gyrus
What are the functions of the limbic lobe
Learning
Memory
Emotion
Motivation
Reward
Where is the insular cortex
behind the lateral fissure
What is the function of the insular cortex
Visceral sensations (sensations from inside the body)
Autonomic control
Interoception
Auditory processing
visual-vestibular integration (world not behaving the way you think its behaving) eg diziness
(eg sense of hunger and thirst etc)
what is the grey matter made up of
Neuronal cell bodies and glial cells (around 85 billion of each)
What does the white matter contain
Myelinated neuronal axons arranged in tracts
What are white matter tracts
connect cortical areas within the same hemisphere and between hemispheres
What are association fibres
connect areas within the same hemisphere
What are Commissural fibres
Connect homologous structures in the left and right hemispheres. Also present in the spinal cord
What are projection fibres?
Connect cortex with lower brain structures (thalamus, brain stem, spinal cord).
Types of fibres
If asked what are the type of fibres then answer is association fibre if asked what is the name of the fibre then give name of tract eg superior longitudinal fasiculus
What are the different types of association fibres
Long fibres and short fibres
name the different Association fibre tracts
Superior longitudinal fibres: connects frontal and occipital lobes
Arcuate fasciculus: connects frontal and temporal lobes (arcuate means arching)
Inferior longitudinal Fasciculus connects temporal and occipital lobes
Uncinate faciculus connects anterior frontal and temporal lobes
this is why different areas may have same functions as they are connected by fibres
What are the types of Commissural fibres
Corpus Callosum
Anterior commissure
In which condition is the corpus callosum disconnected
Intractable epilepsy (untreatable) (corpus callosotomy)
To stop the spreading of seziures from one hemisphere to the other hemisphere. this is sometimes known as a hemispherectomy
What are afferent projection fibres
Going towards the cortex
What are efferent projection fibres
Going away from the cortex
What is the corona radiata
A specific region of projection fibres deep to the cortex (on their way down from the cortex going to the lower structures).
where do the projection fibres converger
Converge through internal capsule between thalamus and basal ganglia
what area is the rectangle
internal capsule. Inbetween the thalamus and basal ganglia
What are the outlines areas
internal capsule
What does the basal ganglia do
Coordinates movement
What are association cortices
they surrounded the primary cortices
function less predictable
not organised topographically
left right symmetry week or ansent
What are primary cortices
Function predictable
Organised topographically
Symmetry between left and right
What are the areas denoted by the red arrows
What are the primary and supplementary motor areas of the frontal lobe
Primary :
controls fine, discrete, precise voluntary movements.
Provides descending signals to execute movements.
Supplementary
Involved in planning complex movements (e.g. internally cued (eg sppech))
Premotor area
involved in planning movements (e.g. externally cued (reacting to something you have seen in the outside world like reaching for an object and picking it up)
(less predictable but more complex-if you stimulate the supplementary and premotor area, complex sequences of movements can occur, if you stimulate the primary motor cortex a few muscles will twitch
What happens if you have a cortical lesion affecting the primary motor cortex
you will lose dextrous (fine precise movement)
will have functional deficit in a part of the body or limb on the opposite side (about 85% of fibres cross overr to the other side)
What are the areas denoted by the arrows
What are the primary and supplemtary areas in the parietal lobe and what is their function
Primary somatosensory
processes somatic sensations arising from receptors in the body (e.g. fine touch, vibration, two-point discrimination, proprioception, pain and temperature.
(So basically if you put a finger on a pin the brain will know exactly which finger and what part of the finger has been put on there)
Somatosensory association
Interpret significance of sensory information, e.g. recognizing an object placed in the hand.
Awareness of self and awareness of personal space
(eg the primary cortex will say thats your little finger but the interpretation of what the sensation is is done by the somatosensory association)
What are the primary and supplementary areas in the Occipital lobe and what is their function
Primary visual: processes visualstimuli
Visual association
Gives meaning and interpretation of visual input
What are the primary and supplementary areas in the Tempral lobe and what is their function
What is tonotopic
Particular frequencies of sounds are represented in particular regions of the primary auditory complex.
What are the other association areas in the brain? and what are their function
What are the other association areas in the brain
Prefrontal cortex
Attention
adjusting social behaviour
planning
personality expression
decision making
brocas area
Production of language
Wernickes area
Understanding of language
What happens to cortical function after lesions in parietal lobe
eg lesion in right hemisphere
contrallateral neglect
lack of awareness of self on left side (may not shave left side, or wear the left side of trouser etc)
lack of awareness of left side of extrapersonal space (eg if asked to circle letter A from letters on paper may only circle those on the right side. if asked to draw flower, may only draw right half of flower)
What is agnosia
Inability to recognise
What is anterograde amnesia
Cannot form new memories
What happens to cortical function after temporal lobe disorders
Inability to recognise, form new memories (anterograde amnesia)
What is the effect of lesion to Brockas or Wernickes areas?
Broca’s area
Expressive aphasia – poor production of speech, comprehension intact
Wernicke’s area
Receptive aphasia – poor comprehension of speech, production is fine
What is the effect of lesion to the occipital cortex
What is prosopagnasia
face blindness (inability to recognise familiar faces or learn new faces)
face blindness (inability to recognise familiar faces or learn new faces)
What is prosopagnasia
How do you assess cortical fuinction
Positron emission tomography (PET)
Functional magnetic resonance imaging ( fMRI)
Electroencephalography (EEG) (measure elect4ri signals measured by the brain)
Magnetoencephalography (measures magnetic signals produced by the brain)
What is one common use of EEG
to diagnose Epilepsy
What are evoked-potentials Event-related potentials
you can evoke events and see what the responses are to those events (flashing images in front of peoples eyes)
In EEG electrodes are placed in a particular way called the 10 20 system. odd numbers are on ine side of scal and even number on the other side of the scalp.
Then compare this with that of patterns in healthy people
What are evoked-potentials Event-related potentials
you can evoke events and see what the responses are to those events
In EEG electrodes are placed in a particular way called the 10 20 system. odd numbers are on ine side of scal and even number on the other side of the scalp
What is the visual pathway
Visual Pathway transmits signal from eye to the visual cortex
What are Visual Pathway Landmarks
Eye
Optic Nerve – Ganglion Nerve Fibres
Optic Chiasm – Half of the nerve fibres cross here
Optic Tract – Ganglion nerve fibres exit as optic tract
Lateral Geniculate Nucleus – Ganglion nerve fibres synapse at Lateral Geniculate Nucleus
Optic Radiation – 4th order neuron
Primary Visual Cortex or Striate Cortes – within the Occipital Lobe
What are the first order neuron
The phot receptors Rod and cones detect light
What are the second order neurons
Retinal biploar cells.
Photo-receptors synapse upon bipolar cells,
forming the second order neurons.
What are the third order neurins
Retinal Ganglion Cells relay visual information out of the eye,
to the brain along the optic nerve.
When do the retinal ganglion cells get myelinated and why
after entering the optic nerve.
To improve signal transmission,
What happens at the optic chiasma. What is it known as
Half of the Retina Ganglion Nerve Fibres cross to the opposite side at the Optic Chiasma. (53%)
This is known as Decussation.
The crossed fibres originate from the nasal retina,
responsible for the temporal half of the visual field in each eye.
The uncrossed fibres predominantly originate from the temporal retina,
responsible for the nasal half of the visual field in each eye.
Where do Retinal Ganglion Fibres terminate
at the Lateral Geniculate Ganglion,
and synapse upon the fourth order neurons, or Optic Radiation.
What will Lesions occurring anterior to the Optic Chiasma affect
affect visual field in one eye only.
Lesion occurring posterior to the Optic Chiasma affect
will affect visual field simultaneously in both eyes,
Right sided lesion – Left Homonymous Hemianopia in Both Eyes
Left sided lesion – Right Homonymous Hemianopia in Both Eyes
As a rule, visual pathway lesion posterior to the chiasma produces contralateral Homonymous Hemianopia in both eyes.
This is an useful tool in predicting the location of potential brain lesion from visual field examination.
Lesion occurring posterios to the Optic Chiasma affect
will affect visual field simultaneously in both eyes,
because of the fibre crossing at the chiasma.
This is an useful tool in predicting the location of potential brain lesion from visual field examination.
What happens when there is a lesion at the optic chiasma
Damages crossed ganglion fibres from nasal retina in both eyes
Temporal Field Deficit in Both Eyes – Bitemporal Hemianopia
What happens if there is transection to optic nerve
Monocular blindness
What happens if there is lesion at optic chiasma
Bitemporal hemianopia
What happens if there is lesion only affecting the non crossed fibres
Nasal hemianopia on that side as only the temporal side fibres will be interrupted
What happens if there is lesion on optic tract
Homonymous hemianopia as fibres from both eyes will not reach brain
IF you have damage closer to the cortex
Quadrantanopia because the fibres spread wider in the brain as only some part of the fibres will be affected.
if damage occurs towards the occipital cortex
Homonymous hemianopia with macular sparing because information travels to the brain from the macula will be spread on widest part of occipital cortex and a good part will be spared
What are the causes of bitemporal Hemianopia
Typically caused by enlargement of Pituitary Gland Tumour
Pituitary Gland sits under Optic Chiasma
What are the causes of Homonymous Hemianopia
Stroke (Cerebrovascular Accident)
If you have visual field defect that doesn’t cross the vertical midline what is it related to
related to neurological condition
If you have visual field defect that doesn’t cross the horizontal midline what is it related to
eye condition most common being galucoma
What is damage to primary visual cortex caused by
Usually strokr
What happens in damage to primary visual cortex
Leads to Contralateral Homonymous Hemianopia of contralateral side with Macula Sparing
Area representing the Macula receives dual blood supply from Posterior Cerebral Arteries from both sides
What happens to the pupil in light
the iris circular muscle contracts,
and constricts the pupillary aperture.
decreases spherical aberrations and glare and increases depth of vision
Small pupil reduces the amount of light entering into the eye,
and thus reduces the rate of photo-pigment bleaching.
This action is mediated by the parasympathetic nerve,
within the 3rd Cranial Nerve.
What happens to the pupil in the dark
Pupil dilates in response to dark environment.
radial muscles contract
This is mediated by the sympathetic nerve,
activating the iris radial muscle.
It increases the amount of light entering into the eye.
What are the two pathways in the pupillary reflex
Afferent
Efferent
What happens in afferent pathway
Rod and Cone Photoreceptors synapsing on Bipolar Cells synapsing on Retinal Ganglion Cells
Pupil-specific ganglion cells exits at posterior third of optic tract before entering the Lateral Geniculate Nucleus
Afferent (incoming) pathway from each eye synapses on Edinger-Westphal Nuclei on both sides in the brainstem
In the diagramme the red and green is the afferent pathway and blue is efferent
What happens in efferent pathway
Edinger-Westphal Nucleus -> Oculomotor Nerve Efferent ->
Synapses at Ciliary ganglion ->
Short Posterior Ciliary Nerve -> Pupillary Sphincter
The Short Posterior Ciliary Nerve innervates directly on the iris Pupillary Sphincter.
Does the afferent pathway from one eye stimulate the efferent pathway in one eye or both eyes
that afferent pathway from either eye,
stimulates the efferent pathway on both eyes.
This means only one eye needs to be stimulated with light,
to elicit pupillary constriction response in both eyes.
