🧠Neurology🧠 - Cerebral Cortex Flashcards
Where is the cerebral cortex found?
Covering the entire surface of the brain
How is the cerebral cortex organised?
Organised into lobes
Highly folded with gyri and sulci
What type of neural matter does the cortex consist of?
Grey matter - consisting of cell nuclei and glial cells
How is the cerebral cortex organised microscopically?
Organised into layers and columns
How many regions of the brain are there and what are they based on?
52 distinct regions identified by Korbinian Brodmann
Based on cytoarchitecture
Where is the primary motor cortex located?
Pre-central gyrus
Where is the primary somatosensory cortex located?
Post-central gyrus
Name the 4 lobes of the brain
Frontal, parietal, temporal, occipital
What are the roles associated with the frontal lobe?(5)
Regulating and initiating motor function
Language
Cognitive functions(executive function such as planning etc…)
Attention
Memory
What are the roles associated with the parietal lobe?
Sensation - touch, pain
Sensory aspects of language
Spatial orientation and self-perception
What is the main role of the occipital lobe?
Processing visual information
What are the roles associated with the temporal lobe?(3)
Processing auditory information
Emotions
Memories
What are the structures found within the limbic lobe?(4)
Amygdala
Hippocampus
Mamillary body
Cingulate gyrus
What are the main functions associated with the limbic lobe?(4)
Learning
Memory
Emotion
Motivation and reward
What is associated with the insular cortex?(5)
Visceral sensations
Autonomic control
Interoception
Auditory processing
Visual-vestibular integration
Where is the insular cortex located?
Lies deep, within the lateral fissure
What are the 2 types of matter located in the brain
Grey and white matter
What is contained within grey matter?
Neuronal cell bodies/nuclei and glial cell (~85 billion of each)
What is contained within white matter?
Myelinated neuronal axons, arranged in tracts
What is the function of the white matter tracts?
To connect cortical areas
What are association fibres?
Connect areas within the same hemisphere
Have both long and short fibres
What are commissural fibres?
Connect homologous structures in the left and right hemispheres
What are projection fibres?
Connect the cortex with lower brain structures (e.g. thalamus, brain stem, spinal cord etc…)
What does the superior longitudinal fasciculus connect?
The frontal and occipital lobes
What does the arcuate fasciculus connect?
The frontal and temporal lobes
(specifically Broca’s and Wernicke’s areas)
What does the inferior longitudinal fasciculus connect?
The temporal and occipital lobes
What does the uncinate fasciculus connect?
The anterior frontal and temporal lobes
Name the 2 most significant commissural fibre tracts
Corpus callosum
Anterior commissure
What are the 2 classifications of projection fibres?
Afferent - towards cortex
Efferent - away from cortex
What path do the projection fibres follow?
Forms the corona radiata deep to the cortex
Converge through the internal capsule between the thalamus and the basal ganglia
Outline the differences of functions controlled by primary and secondary cortices
Primary cortices:
Predictable function
Organised topographically
Symmetry between left or right
Secondary cortices:
Less predictable functions
Not organised topographically, and little symmetry between left and right
What movements are controlled by the primary motor cortex?
Controls fine, discrete, precise voluntary movements
Provides descending signals to execute movements
What movements are controlled in the premotor area?
Slightly more complicated, planned movements
Externally cued
(something like picking up an object)
What movements are controlled in the supplementary area?
Involved in planning the most complex movements
Internally cued
(something like speech)
What are the main sensory areas of the parietal lobe?
Primary somatosensory
Somatosensory association
What is the function of the primary somatosensory?
Processes somatic sensations arising from receptors
(e.g. fine touch, vibration, two -point discrimination, proprioception, pain and temperature)
What is the function of the somatosensory association?
Interpret significance of sensory information
(e.g. recognising an object placed in the hand)
Awareness of self and personal space
What are the main sections of the occipital lobe?
Primary visual
Visual association
What is the function of the primary visual?
Processes visual stimuli
What is the function of the visual association?
Gives meaning and interpretation of visual input
What are the mains sections of the temporal lobe?
Primary auditory
Auditory association
What is the function of the primary auditory?
Processes auditory stimuli
What is the function of the auditory association?
Gives meaning and interpretation of auditory input
Name the other 3 association areas
Prefontal cortex
Broca’s area
Wernicke’s area
What is the function of the prefrontal cortex?(5)
Attention
Adjusting social behaviour
Planning
Personality expression
Decision making
What is the function of Broca’s area?
Production of language
What is the function of Wernicke’s area?
Understanding of language
What can result from frontal lobe lesions?
Changes in personality
Inappropriate behaviour
What can result from parietal lobe lesions?
Contralateral (opposite side) neglect
Lack of awareness of opposite side of body
Lack of awareness of opposite side of extrapersonal space
(left side of the body or world doesn’t exist/isn’t registered)
What can result from temporal lobe lesions
Lateral section - leads to agnosia, inability to recognise
Medial section - cannot form new memories, anterograde amnesia
What can lesions to Broca’s or Wernicke’s areas cause?
Broca’s area - expressive aphasia
(inability to produce speech, comprehension is intact)
Wernicke’s area - receptive aphasia
(inability to comprehend speech, production is intact
What can lesions to the primary visual cortex lead to?
Blindness in the corresponding area of the visual field
What can lesions in the visual association lead to?
Difficulties in interpretation of visual information
e.g. Prosopagnosia - inability to recognise faces or learn new ones
How can cortical function be assessed?
Electroencephalography (EEG)
Measures electrical signals produced by the brain
Magnetoencephalography (MEG)
Measure magnetic signals produced by the brain
How can cortical function be assessed practically?
Transcranial direct current stimulation (tDCS)
Uses low direct current over the scalp to increase or decrease neuronal firing rates
What type of disease is MS?
Autoimmune inflammatory demyelinating disease
Progressive, can show patterns of flare ups and remission
What is multiple sclerosis (MS)?
An autoimmune condition that affects the myelin sheath of neurones in the brain and spinal cord
What is the difference between unmyelinated and demyelinated neurones?
Unmyelinated never had myelin, demyelinated had myelin that has been removed/damaged
Unmyelinated can occur naturally, demyelinated should never occur
Demyelination means pathology
Which cells are responsible for myelination and in which part of the nervous system?
Oligodendrocytes in the CNS
Schwann cells in the PNS
What cells are affected in MS?
Oligodendrocytes
What are the main symptoms of MS?
Fatigue - one of the most common and disabling symptoms
Muscle weakness
Paresthesia - particularly in extremities, limbs, face and sometimes trunk
Vision problems - if MS is affecting the optic nerve
Muscle spasticity
Neuropathic pain
Cognitive difficulties
How can brain/nerve stimulation be used to confirm the presence of MS?
Increased conduction time/decreased conduction speed - indicates demyelination of nerves
Define orthodromic and antidromic
Orthodromic - an impulse travelling in the normal direction in a nerve fibre
Antidromic - travelling in the opposite direction to normal in a nerve fibre
What does an M-wave on an EMG correspond to?
The direct motor response, evoked by electrical stimulation of peripheral motor nerves
What is an H-reflex?
Activation of the sensory neurons causing muscle contraction
Action potentials travel along sensory neurons to the spinal cord, causing the motor neurons to become activated in the lower spinal cord
These action potentials can travel along the motor neuron to the muscle, causing a contraction
This is a reflex
What is an F-wave?
The F-wave is generated by electrically stimulating a peripheral nerve, causing a back-and-forth response in the motor neuron pathway. After the electrical stimulus, a small percentage of the impulse travels back up the motor nerve to the spinal cord and then returns to the muscle (an antidromic response)
How can the cortex of the brain by stimulated?
Transcranial magnetic stimulation (TMS)
What does transcranial magnetic stimulation involve?
Activation of the upper motor neurons, resulting in action potentials traveling across the entire motor pathway (upper and lower motor neurons) causing muscular contraction
This EMG response is known as a motor evoked potential (MEP)
What is TMCT, PMCT and CMCT
Total motor conduction time - time from brain to muscle (equivalent to MEP latency)
Peripheral motor conduction time - time from spinal cord to muscle
Central motor conduction time - time from brain to spinal cord
What is the definition of latencies?
the time delay between the delivery of a stimulus (usually an electrical impulse) to a nerve and the onset of the corresponding response, such as muscle contraction
What latencies is the PMCT equal to?
(M latency + F latency-1)/2
(-1 is explained in a later card)
Why does this “(M latency + F latency-1)/2” correspond to PMCT?
Nerve will be stimulated half way along its length, so M latency is time for impulse to travel half its length, F latency (once 1 second is taken off) corresponds to 1 and a half lengths travelled, so equals 2 lengths when the 2 times are added - only want the time for 1 length to be travelled hence divided by 2
-1 corresponds to the estimated amount of time for the antidromic action potential to turn around once arriving at the lower motor neuron
How is CMCT calculated?
TMCT - PMCT
What effect would MS have on MEP and the various conduction times?
Brain stimulation - MEP latency would be longer than usual - TMCT delayed
Peripheral stimulation - Normal F wave latency so normal PMCT
Therefore, delayed CMCT - so the problem is in the CNS
