Cortex & pyramidal motor system Flashcards
What are the features of the cortex?
- 2-4mm thick (very thin) layer that covers the whole of the brain
- When spread out flat it is around 1m^2 (large SA), folds to inc SA
- Cortex lines all of the white matter
What makes up most of white matter?
Myelin (oligodendrocytes) is the main componenet - makes it white
Define the cortex
A thin mantle of cells that make up the outer surfacde of the brain
What is the cortex composed of?
Grey matter (cell bodies)
Many of these cells are neurones, whose myelinated projections constitute the cerebral white matter
What is the most abundant cell in the cortex?
Pyramid cells (75-85%)
Where are pyramidal cells found?
- Abundant in the cortex (75-85%)
- Also in other structures (hippocampus)
Cell bodies make up cortex surrounding brain Their axons =white matter
What is the structure of pyramidal cells?
- Pretty large
- Soma 10-50um
- Have one rlly large dendrite that grows upwards & many others that branch off
- Appear spiny as they have many projections off of the dendrites to communicate w many other cells
Are pyramidal cells exitatory or inhibitory?
Excitatory (glutamergic)
It is a major cortical output
Where are granule cells found?
In other structures (cerebellum)
What is the structure of granule cells like?
- Soma is <10um
- Have a smooth stellate (no spines)
- Small round shaped body
Are granule cells inhibitory or excitatory?
Inhibitory cells –> GABAergic interneurones (many inhibitory neurones are called interneurones)
Name 3 types of glial cells:
- Astrocytes
- Microglia
- Oligodendrocytes
What is the structure of astrocytes like?
- Characteristic star shape
- Many dendrites & large cell body
- Very abundant in brain
What is the role of astrocytes?
- Maintian homeostasis (sequestering K+ ions and glutamine)
- End feet –> maintain BBB & contribute to blood flow reg
- Reapir & scarring in brain
What is the structure of microglia cells like?
Smaller than astrocytes –> can swell when they are activated by something negative
What is the role of microglia?
- Resident immune cells, fine processes during rest
- Ramified amoeboid (can swell), mobile when activated
What is the structure of oligodendrocytes?
Small cells whose processes form individual nodes of myelin around axon
What is the role of oligodendrocytes?
Make up the white matter as they ensheath axons
What are the 6 cortical layers?
1 - Molecular
2 - External granular
3 - External pyramidal
4 - Internal granular
5 - Internal pyramidal
6 - Multiform
What is found in the molecular (1) cortical layer?
Neurons
Glial cells
Apical dendrites
What is found in the external granular (2) cortical layer?
Small pyramidal
Granual neurons
What is found in the external pyramidal (3) cortical layer?
Small and medium pyramidal cells & granular cells
What is found in the Internal granular (4) cortical layer?
Mostly stellate neutrons, but some pyramidal cells
What is found in the internal pyramidal (5) cortical layer?
Large pyramidal neurons
Apical & basilar dendrites
Projections neurons
What is the multiform (6) cortical layer?
Small spindle like pyramidal neurons
What does golgi stain do?
Impregnates some cells, not all cells but will impregnate the whole cell
What does nissle stain do?
Stains all cells but only DNA material so we see the cell body
What are the main ones of Brodmann’s areas we need to know?
1-3
4
5&7
6
22
41
44,45
What is the location and name/function of Brodmann’s area 1-3?
Location = Postcentral gyrus
Name/function = Primary somatosensory area
What is the location and name/function of Brodmann’s area 4?
Location = Precentral gyrus
Name/function = Primary motor area
What is the location and name/function of Brodmann’s area 5, 7?
Location = Superior parietal lobule, supramarginal gyrus
Name/function = Somatosensory association areas
What is the location and name/function of Brodmann’s area 6?
Location = Middle frontal gyrus
Name/function = Premotor area
What is the location and name/function of Brodmann’s area 22?
Location = Superior temporal gyrus
Name/function = Wernicke’s area
What is the location and name/function of Brodmann’s area 41?
Location = Superior temporal gyrus
Name/function = Primary auditory area
What is the location and name/function of Brodmann’s area 44, 45?
Location = Inferior frontal gyrus
Name/function = Broca’s area
What is the order of signals around the motor areas of the brain?
- Primary somatosensory (1-3)
- Then to secondary somatosensory cortices (5,7)
- The to prefrontal cortex (8-10)
- To premotor cortex (6)
- Then motor cortex (4)
What happens in the primary somatosensory cortex?
The sensory info arrives here
What happens in the secondary somatosensory cortex?
Info is recieved from the primary somatosensory cortex & sends onto the Prefrontal cortex
What does the prefrontal cortex do?
Recieves info from secodnary somatosensory cortices
Plans movement
What does the premotor cortex do?
Recieves info from the prefronal cortex
Organises movement
What happens in the motor cortex?
Recieves info from the premotor cortex
Produces movement
How many layers do the motor & sensory cortex have?
6 each
What is layer 4 of the motor & sensory cortices, and how do they differ?
Input of sensory info
Layer 4 is a granular layer
It’s much larger in the sensory cortex as this is where the sensory info enters
What is layer 5 of the motor & sensory cortices, and how do they differ?
Output to other parts of the brain
Much larger in the motor cortex as this is where movement is produced so more cells needed here
What is another name for the primary motor cortex?
Precentral gyrus
What is another name for the primary sensory cortex?
Postcentral gyrus
What is the role of these following 5 brain areas:
Prefrontal -
Premotor -
Primary motor -
Primary somatosensory -
Secondary somatosensory -
Prefrontal - Planning movement
Premotor - Organising movement
Primary motor - Producing movement
Primary somatosensory - Recieving sensation
Secondary somatosensory - Interpreting sensation
How are the motor and somatosensory cortices layers arranged?
In cellular layers & are organised SOMATOTOPICALLY in an inverted fashion
What is Aphasia?
Disruption of lanuage and/or speech
What are the 2 main language centres we focus on?
Broca’s and Wernicke’s area
What sort of aphasia happens in Broca’s area?
Expressive aphasia
Failure to formulate
What sort of aphasia happens in Wernicke’s area?
Receptive aphasia
Failure to comprehend
How did Broca discover Broca’s area in the brain?
He was studying patients suffering from aphasia - language was appropriate but speech was choppy, some words come out abnormally & they were aware of this
He noticed damage in motor cortex (production of movement) & failure to formulate speech properly
How was the role of Wernicke’s area discovered?
Patients would use completely inappropriate language - had no idea what they were saying was inappropriate
Next to primary auditory cortex so auditory processing was wrong
How does brain lateralisation work?
There is a tendancy towards lateralisation of some functions in the human brain
Give 2 examples of lateralisation:
Handedness & language abilities
- 70% of ppl are right-handed
- 95% of right handed ppl have left hemisphere lang dominance
- 60-70% of left-handed ppl have left hemisphere language dominance
What is the role of Wernicke’s area?
Interprets spoken word
What is the role of Broca’s area?
Produces speech
What is multiple sclerosis (MS)?
Auto immune disease that attacks the myelin & thus can produce symptoms of upper & lower motor neurone sydromes
How many people does MS affect?
160/100 000 people
What are the symptoms of MS?
Can vary dramatically & can include tingling in the legs, fatigue, balance & coordination problems, blurred vision, diffculties speaking or swallowing
What is the most common form of MS?
It results symptomatic & asymtomatic periods
What is the order of info travelling around the motor system?
1 - Visual info req to locate target
2 - Frontal-lobe motor areas plan the reach & command the movement
3 - Spinal cord carries
4 - Motor neurons carry message to muscles of the hand and forearm
5 - Sensory receptors on the fingers send message to sensory cortex saying that the cup has been grasped
6 - Spinal cord carries sensory info to brain
7 - Basal ganglia judge grasp forces & cerebellum correct movement errors
8 - Sensory cortex recieves the message that the cup has been grasped
What does the cortex do?
It integrates info & produces movement via the pyramidal system
What carries motor signals?
They’re carried by upper motor neurones
These synapse w lower motor neurons in the brain stem & spinal cord
What do lower motor neurons do?
Bring motor signals to the muscles
What are some components of extrapyramidal systems?
Basal ganglia & cerebellum
What are the pyramidal tracts?
They are projection fibres (also upper motor neurons) that originate in layer 5 of pri,ary motor cortex
Revise the motor system compartments diagram
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Look at brain scans of white matter
fnjfonow
What are the 3 types of white matter tracts?
- Association fibres
- Commissural fibres
- Projection fibres
What does white matter refer to?
Myelinated axons & groups of myelinated axons that form white matter tracts
What are association fibres?
Exchange info within one hemisphere (ipsilateral)
What are commissural fibres?
Exchange info between hemispheres (contralateral)
What are projection fibres?
Carry info from the cortex to other regions of the brain & spinal cord (upper motor neurons)
What type of cells form white matter?
Oligodendrocytes
Name some key association fibres
- Cingulum
- Cingulum (parahippocampal)
- Superior longitudinal fasciculus
- Inferior longitudinal fasciculus
- Fasciculus occipito-frontalis
- Uncinate fasciculus
Where are association fibres found?
Only in a single hemisphere, not between them
Where are commissural fibres found?
Connect the cortices of the two hemispheres
Give an example of some commissural fibres?
- Corpus callosum
- Fornix
- Anterior commissure
- Posterior commissure
What is the main commissural fibre?
The corpus callosum
Runs anterior to posterior direction
Largest of white matter structures
What does the corpus callosum do?
Connects the cortices
What does the fornix do?
Connects the hippocampus (temporal lobe) to the hypothalamus & mammillary bodies near the diencephalon
Ppts in memory
What does the anterior commissure do?
Connects the temporal lobes (amygdala), puts in emotion
What does the posterior commissure do?
Connects bilateral midbrain nuclei, ppts in the pupillary light reflex
What do projection fibres do?
Connect the cortices to the other brain structures & the spinal cord
This includes the upper motor neurons
What are the pyramidal tracts?
Are a sub-population of upper motor neurons that produce movement
Where do the pyramidal tracts originate?
In layer 5 of the primary motor cortex & converge to form the INTERNAL CAPSULE b4 cont to spinal cord
Why are cerebral penducles important for the motor pathway?
Its where all the motor neurones converge & project to rest of body
What is the internal capsule a part of ?
Part of the pyramidal tracts
All motor fibres merge here –> 2nd largest white matter area
Strokes happen here often & can severly affect movement
Where do pyramidal tracts originate, pass thru & go to?
In the primary motor cortex
Descend & converge into the internal capsule
Pass thru midbrain (cerebral peduncles)
Synapes w lower motor neurons in brain stem & spinal cord
Where do pyramidal tracts originate?
Layer V of pirmary motor cortex
1 million nerve fibres w a conduction velocity of 60m/s
Which 2 tracts make up the pyramidal tracts?
- Corticobulbar tract
- Corticospinal tract
What is the corticobulbar tract?
Terminates in the brain stem
Produces head, neck & face movement
What is the corticospinal tract?
Terminates in the spinal cord
Lateral –> crosses over
Ventral –> remains on the same side
Where does corticobulbar tract run?
Come from face, head, tongue etc
All motor pathways pass thru cerebral peduncles
Terminates in brain stem & priduces head, brain etc movements
Where does the corticospinal tract run?
80% crosses over to the other side of body when it reaches spine
How is white & grey matter arranged in the spinal cord?
White matter on outside & grey matter on inside
How are the dorsal and ventral orientations of the spine arranaged & what do they do?
Doral = back (motor info) –> flexors
Ventral = front –> extensors
Both make connections in the lower motor neurons
What does the lateral corticospinal tract do?
Synapses with interneurons & motor neurons that invigorate muscles of the LIMBS and DIDGITS
What does the ventral corticospinal tract do?
Synapses w interneurons & motor neurons that inntevate the TRUNK (midline of the body)
What are some symptoms of upper motor neuron sydrome?
- Muscle weakness and/or stiffness
- Inc muscle tone (hypertonia)
- Exaggerated stretch reflexes & clonus (invol contractions), or spasticity (velocity sep reactions)
What are some symptoms of lower motor neuron sydrome?
- Muscle weakness
- Dec muscle tone
- Inhibited stretch reflexes & spontaneuos firing that cause individual muscle fibre contractions (recordable) & potentially twitching
What is amytrophic lateral sclerosis (ALS)?
Degeneration of upper & lower motor neurons
What is primary lateral sclerosis?
Slow degeneration of the corticospinal tract
Begins as weakness & stiffness of the legs that causes balance & walking problems
What is pseudobulbar palsy?
Degeneration of the cortcobbulbar tract
Facial paralysis, inl the tongue, persistant dribbling or difficulty w speaking, chewing & swallowing
What is progressive muscluar atrophy?
Lower motor neuron degeneration
Begins as weakness & stiffness of the hands that spreads to the lower body & muscles lose tone
How is the spinal cord ventral horn generally organised?
Organised topographically
Medial aspects innervate proximal & lateral aspects innervate distal muscles
