Nervous System Flashcards
What are the three components of the brainstem in order?
Midbrain, Pons, Medulla
What does the cerebellum take part in?
Coordination of movement
What are the three components that make up the hind brain?
Cerebellum, medulla, pons
What are the folds of the brain called?
Gyrus/gyri
What are the gaps between folds of the brain called?
Sulci
What are the folds made up of?
Grey matter 6-7 mm thick with a layer of white matter underneath.
What are the 3 key sulci?
Central sulcus, parieto-occipital sulcus, lateral sulcus (fissure)
What is the name of the important notch in the brain?
Preoccipital notch
What does the central sulcus separate?
Frontal and parietal lobe
What are the four gyri of the frontal lobe?
Superior frontal gyrus, middle frontal gyrus, inferior frontal gyrus, precentral gyrus
What lies beneath the lateral fissure?
Temporal lobe
What are the three longitudinal gyri of the temporal lobe?
Superior, middle and inferior temporal gyrus
What is behind the temporal lobe?
Occipital lobe
What lobe lies between the frontal, occipital and temporal lobe?
Parietal lobe
What is the name of the sulcus which separates the parietal lobe into an upper and lower part?
Intraparietal sulcus
What is the parietal lobe split into?
Superior and inferior parietal lobule
What are the names of the two gyri found on the inferior parietal lobule? What is special about them?
Supramarginal gyrus and angular gyrus. They are connected to form an m shape.
What is the other singular gyrus of the parietal lobe?
Postcentral gyrus
What does the precentral gyrus correspond with? What does it control?
Primary motor cortex. Controls muscles on the other side of the body.
What is the primary motor cortex dominated by?
The face and hands
What is meant by somatotopical?
Organised by body region. Increasing complexity requires more brain cells and a larger region of the cortex.
What is meant by primary and motor of primary motor cortex?
Primary: critical role
Motor: movement
What does the postcentral gyrus correspond with? What is it involved with?
Primary somatosensory cortex. Where you consciously appreciate every touch on your skin.
Large areas of the primary somatosensory cortex are devoted to ________ ____________ regions of the body.
Highly discriminatory
What is the purpose of the primary visual cortex?
Allows you to see the world.
What surrounds the primary visual cortex?
The calcarine sulcus
How is the primary visual cortex organised?
Visuotopically organised (retinotopically)
Why don’t we see a line down the middle of the world?
Visual cortex on one side communicates with the visual cortex on the other.
What do the areas around the primary visual cortex do? What are they called?
Add value (shape and colour) to the original picture. Supplementary/secondary visual cortices
From where does the primary auditory area get input from?
Gets input from the ear on the opposite side.
In which gyrus is the primary auditory area located?
The transverse gyrus of Heschl, deep within the brain.
How is the sound received by the primary auditory area organised
High tones and frequencies at one end whilst low tones and frequencies at the other. Tonotopically organised.
What does Wernicke’s speech area allow us to do?
Understand what is being said.
What happens when a person gets a stroke/tumour at Wernicke’s speech area?
Disorder of speech: a fluent/sensory aphasia. Can hear but not understand spoken word.
What is meant by an aphasia?
Disorder of speech associated with the brain.
What does Wernicke’s speech area communicate with? By what?
Broca’s speech area through a large bundle of fibres called the arcuate fasciculus.
What is the Wernicke’s and Broca’s speech areas associated with
W: sensory aspect of speech recognition.
B: motor aspect of speech recognition.
What does Broca’s speech area do?
Allows us to pronounce words by communicating with muscles that control speech.
What happens when we get a lesion on the Broca’s speech area?
Can’t pronounce words: non-fluent aphasia
What happens when the arculate fasciculus is broken?
Give an example.
A conduction aphasia. E.g. What did you have for lunch today? It’s going to rain outside.
What are the supramarginal and angular gyri responsible for?
Reading and writing
Which area controls which muscles are to be activated during writing?
Exner’s area
What is the non dominant right hemisphere responsible for in comparison with verbal language on the left side?
Non-verbal language: Body language Emotional expression Spatial skills Conceptual understanding Artistic/musical skills
What are the effects of injury on the non-dominant hemisphere?
Spatial disorientation Inability to recognise familiar objects Loss of musical appreciation Speech lacks emotion Loss of non-verbal language
What are the functions of the frontal association cortex?
Intelligence Personality Behaviour Mood Cognitive function
What are the functions of the parietal association cortex?
Spatial skills
3D recognition: shapes, faces, written words, concepts, abstract perception.
Wernicke’s area is larger on the _______ side.
Left
What information does Broca’s speech area contain?
How to pronounce words
What are the functions of the temporal association cortex?
Memory, mood, aggression, intelligence
What does Exner’s area do?
Drives muscles for writing.
Verbal language areas are concentrated mainly in the _________ hemisphere.
Left
In the right hemisphere, the general areas of verbal language of the left hemisphere are instead replaced by _________.
Non verbal language areas
What regions add value to the original visual cortex?
Supplementary visual cortices
Which regions are most highly developed in humans?
Complex association areas
What types of nerves are in the first upper region of the spinal cord? How many pairs are there?
Cervical (neck) nerves
8 pairs
What does the spinal cord extend down?
The middle of the vertebral column
Coming away from the spinal cord are ________
Nerves on each side called spinal nerves
How many pairs of spinal nerves are there?
31
What nerves are underneath the cervical nerves?
Thoracic spinal nerves
12 pairs
What spinal nerves are underneath the thoracic spinal nerves? How many?
Lumbar nerves
5 pairs
Each spinal nerve goes out towards ______
An area of the skin
What spinal nerves are under the lumbar nerves? How many?
Sacral nerves
5 pairs
Which pair of spinal nerves does not go towards the skin?
C1
What spinal nerves are at the very bottom of the spinal cord? How many?
Coccygeal nerves
1 pair
What would happen if one of the spinal nerves was cut?
The area that is goes towards would be numb.
What is meant by a dermatome?
A region of skin innervated by a spinal nerve.
How many dermatomes are there?
30
What are the two roots going into and out of the spinal cord?
Dorsal root
Ventral root
What are the functions of the dorsal and ventral root?
Dorsal: Receives sensory information
Ventral: Sends motor information to muscles
What do the dorsal and ventral roots join up to form?
Spinal nerve
What are the two major sets of information from the skin?
Touch and pressure
Pain and temperature
What two special types of receptor sit right under the skin?
Touch: Meissner corpuscles
Pressure: Pacinian corpuscles
What type of receptor is used for discriminative sensation?
Encapsulated receptors (more dense on lips and hands)
How are nerves of encapsulated receptors activated?
The receptor is depressed and nerve at centre is activated.
Where are the cell bodies of the nerves entering the dorsal root located?
In a swelling called the ganglion.
What area of the spinal cord do sensory nerves go to?
Dorsal area
What is considered discriminative sensation?
Touch and pressure
There are more nerves going to the _____ than the _____ (chest/hand)
hand
chest
How fast do nerves travel along myelinated fibres?
50 m/s
How fast do signals travel along non-myelinated fibres?
1 m/s
What is considered non-discriminative sensation?
Pain and temperature
What type of sensation occurs through free nerve endings?
Non-discriminative
What are free nerve endings?
Terminations of the nerve fibres. Very sensitive to pain and temperature.
How are non-discriminative fibres different to discriminative fibres?
Thinner, non-myelinated
Pain and temperature sensation is not as _______ as touch and pressure.
Precise / regionally specific
Where do non-discriminated nerves terminate?
The most dorsal part of the dorsal area specialised for receiving information about pain and temperature.
Where does the ventral root convey information?
Towards muscles
Where can we find very large motor neurones?
In the ventral horn of the grey matter
What neurotransmitter is released at the muscle?
Acetyl choline (fast conducting)
What is the lower motor neurone made up of?
Cell body and the axon passing out
Are lower motor neurones myelinated?
YES
What is paraplegia?
Loss of sensation as well as paralysis of the lower half of the body due to the compression of the spinal cord that is caused by severing e.g. T10
What is quadriplegia?
Loss of sensation of most of body as well as paralysis due to severing e.g. C2
How far is the skin from the brain?
About 1 metre
How many neurones are involved in passing the impulse from skin to brain?
3 - the information can be modified at each synapse
What is the pathway of the first-order neurones?
Passes from receptor through root ganglion and up the spinal cord in the dorsal column.
Where do the first-order neurones from the arm lie in the dorsal column?
Just lateral to those coming from the leg
What is the pathway of second-order neurone?
From the dorsal column nuclei (cuneate and gracile fasciculus). Passes up to the brainstem in a big bundle of fibres called the medial lemniscus. Terminates in the thalamus.
What must all information going to the cerebral cortex go through?
Thalamus
What occurs to the information passing through the thalamus?
It is further modified
Sensations can be _______ or _______. Why? What is this called?
Suppressed or highlighted because there are fibres that modulate the information reaching your sensory cortex at each level. Sensory modulation
The collection of fibres coming from receptors ______ as we ascend the spinal cord. What is this called?
Increases in size. Posterior/dorsal column
What are the two tracts of the posterior column?
Gracile tract (medial), Cuneate tract (lateral)
When does the cuneate fasciculus appear?
At the level of the arm
When do the first-order discriminate neurones from the skin terminate?
At the junction between the spinal cord and brain.
What do the gracile and cuneate tracts contain?
Millions of nuclei that receive all the terminals coming up from the discriminative pathway.
Where do neurones cross over in the discriminative pathway? What is this called?
Second-order neurones cross over immediately after the gracile and cuneate nuclei are reached. Decussation
Where are the second-order neurones collected up after decussation?
Medial lemniscus
What area of the thalamus is specialised for receiving, processing, suppressing, highlighting signals?
Ventroposterior nucleus
What does the ventroposterior nucleus do?
Receives, processes, suppresses, highlights, modifies the signal.
What is the motorway that the third-order neurones travel through to reach the cortex?
Internal capsule
What would happen if there was a lesion in the spinal cord for the discriminative pathway?
Lose touch and pressure sensation on the same side of the body
What would happen if there was a tumour somewhere in between the medial lemniscus to the sensory cortex?
Lose touch and pressure sensation on the opposite side of the body.
Where do the pain and temperature first-order neurones terminate?
Dorsal part of the posterior grey horn
Which neurones decussate in the non-discrimnative pathway? Where does this occur?
Second-order
Spinal cord - anterior white commissure
What does commissure mean?
Crossing
Where do the second-order neurones of the non-discriminative pathway collect?
Lateral spinothalamic tract
Why is the lateral spinothalamic tract called as such?
Lies in a lateral position
Goes from spinal cord up to the thalamus
What will be the first and last impulses to arrive at the thalamus in the non-discriminative pathway?
First - leg area
Last - neck area
The neurones from the discriminative and non-discriminative pathway travel to the _______ area of the thalamus.
Same (ventroposterior nucleus)
Does the lateral spinothalamic tract join up with the medial lemniscus? Where?
Yes
Pons
If there is a lesion in the spinal cord, what happens to the non-discriminative pathway?
Lose pain and temperature sensation on the opposite side of the body.
What happen when there is a lesion on the right side of the brain/brainstem? What is this called?
Loss of touch and pressure and pain and temperature sensation on the left. Associative sensory loss
What happens when there is a lesion on the left side of the spinal cord? What is this called?
Loss of touch and pressure sensation on the left and loss of pain and temperature sensation on the right. Dissociative sensory loss.
The upper motor neurone talks to the ________
Lower motor neurone
Describe motor homunculus
Degree of representation is associated with the degree of activity of these cells and the number of cells involved with control of movement.
Where is the corticospinal tract biggest?
At the top
Is the motor pathway myelinated? How fast is conduction?
Yes 50m/s
How does the UMN get past the thalamus?
Via the internal capsule
What is a capsule?
A fibre bundle
Why is the pyramidal tract named such?
The cross-section is pyramid shaped.
What is a better name for pyramidal tract?
Corticospinal tract
Where do most motor neurones decussate? What is this called?
At the junction between the brain and the spinal cord.
Pyramidal decussation
What is the motor pathway called after decussation?
Lateral corticospinal tract.
What happens to the corticospinal tract when it reaches the pons?
Breaks up into a number of fascicles, which come back together again in the pyramid of the medulla.
The UMN’s terminate on an LMN either _________ or via an __________.
Directly (main)
Via an interneurone
Where do 10-30% of the motor fibres decussate? What is this pathway called?
At the spinal cord
Ventral corticospinal tract
The __________ _______ fibres peel off and terminate on a LMN.
Innermost UMN
Where do the LMN’s lie in the spinal cord?
Ventral grey horn
How are LMN’s grouped?
By the muscles which they supply
What happens when upper motor neurones are damaged at any point in the pathway from the brain to spinal cord? What are the symptoms?
Spastic paralysis of the region of the body that the fibres would have innervated.
Can no longer do precise fine voluntary movements. Can only do crude movements. Tone in the muscles has increased a lot so reflexes are exaggerated.
What happens when there is a lesion of the LMN’s?
Flaccid paralysis.
Muscle no longer gets any impulses, so no tone, reflexes or movement and unable to use it. There are no neural pathways to cause the muscle to contract. Results in disuse atrophy.
What does the Polio virus target? How does it affect the LMN’s?
LMN’s. It enters the LMN, replicates and kills it.
What two systems tell the UMN’s when and how many to fire?
Basal ganglia and cerebellum
From where does the information telling UMN’s what to do come from?
The region of the thalamus called VA-VL (ventro anterior-ventro lateral) nucleus. Talk to the motor cortex in a very precise way.
What are the four major nuclei of the basal ganglia?
Striatum, globus pallidus, substantia niagra (group of nuclei), sub-thalamic nucleus
What is the striatum made up of?
Caudate nucleus and putamen
They are the same structure but have been subdivided by the internal capsule.
Why is the globus pallidus called such?
It is a pale globe
What are the two parts of the globus pallidus?
The outer part (external segment) called the GPe (externus)
The inner part (internal segment) called the GPi (internus)
What nucleus liess underneath the thalamus? What is it a part of?
Sub-thalamic nucleus (SUT), which is a part of the basal ganglia.
What are the two parts of the substantia nigra?
Substantia nigra pars compacta (SNc)
Substantia nigra pars reticulata (SNr)
Distinguish between the SNc and SNr.
SNc: contains pigmented cells
SNr: cells are dispersed and not pigmented
Which part of the substantia nigra is visible?
SNc
What does the striatum get input from?
The pigmented cells of the pars compacta
Where do the cells in the striatum project to?
The globus pallidus externus and internus
Where does the output from the basal ganglia go from? What do these fibres release?
From the globus pallidus to the thalamus
GABA - inhibitory
What are the important functions of the basal ganglia?
1) Initiating movement
2) Keeping muscle tone in the right state for movement or in a state of contraction at rest
3) Memory and planning of movement (Frontal cortex -> basal ganglia
4) Mood and movement
What is meant by mood and movement?
The degree of movement is controlled by mood. We can express our emotion through the muscles of our body. There is an emotional mood component in all our movements.
What symptoms appear in people with diseases affecting the basal ganglia?
Problems with: Initiating movement Muscle tone Remembering how to start movements Flat emotions Involuntary movements (tremor for Parkinson's)
The release of what influences the UMN’s?
Release of GABA in VA-VL
What are the large cells of the cerebellum called? How are they positioned?
Purkinje cells are perfectly aligned
About __% of the brain’s cells lie in the cerebellum
90% because a lot of the cells are very small and are packed
What is the function of the cerebellum?
Posture, balance, coordinates your movements as you move
What is unique about the cerebellum
Each half of the cerebellum coordinates the movements of the same side.
Where does the cerebellum feed into?
The same region of the thalamus (VA-VL) as the basal ganglia.
What does the cerebellum release into the VA-VL?
An excitatory neurotransmitter called glutamate.
What does the balance between the cerebellar input and the basal ganglia input into the thalamus cause?
Causes the cells to fire in the thalamus and stimulate the UMN’s in a precise way to produce smooth movement.
What does a person with cerebellar disease have?
Ataxia: uncoordinated movements and loss of balance.
If the right side of the cerebellum is damaged, which side of the body is affected?
The right side
What are the symptoms of Parkinson’s Disease?
- Pill-rolling tremor at rest, which starts on one side
- Difficulty starting to walk (often stooped) - increasing speed until falling over
- Muscles show cogwheel rigidity due to increased muscle tone
- Slow movements (Brady/hypokinesia)
- Problems with conveying mood - appear emotionally flat
Which area of the basal ganglia is affected by Parkinson’s disease?
Substantia Nigra Pars Compacta, which lies in the midbrain
What types of fibres come out of the SNc?
Lightly myelinated thin fibres going towards the striatum
What do the fibres from the SNc release at the striatum?
Dopamine in very high concentrations
What do we refer to the pathway from the SN and the striatum as?
Nigro-striatal pathway or Dopanergic nigro-striatal pathway
What causes Parkinson’s disease?
Lack of dopamine in the striatum when these SN cells degenerate. Output of the cells in the striatum is affected.
What are the effects of dopamine on the striatum? Why are there different effects?
Sometimes excitatory, sometimes inhibitory, because we have D1 and D2 receptors.
What percentage of SN cells in the brain have degenerated before a person starts showing symptoms?
60%
If degeneration of SN cells mainly occurs on the right, where are the symptoms of Parkinson’s seen? What tends to happen at later stages?
Mainly on the left
Symptoms slowly pass to the other side.
Which cells are tonically active?
Those in the globus pallidus internus
What is meant by tonically active?
They fire continuously at their normal resting state. Thus releasing GABA into the VA-VL continuously.
What is the effect of dopamine on the GPi?
These cells are less inhibited (hyperactive) so they end up firing more.
What are the consequences of hyperactivity of the GPi?
More GABA occurs in the thalamus and therefore more inhibition of the cells firing to the UMN’s occurs. The impulses passing to the UMN’s decrease in both intensity and frequency. This results in less excitation of UMN’s and therefore slow movement and difficulty in initiating movements.
What was the first method invented to reduce the effects of Parkinson’s? How well did it work?
Give dopamine tablets to patients.
This did not have any effect at all because dopamine is broken down and degraded in the stomach and is not absorbed into the blood as dopamine.
What was given instead of dopamine tablets to patients with Parkinson’s disease? What effect did this have?
A precursor chemical that is converted into dopamine in the body: L-Dopa. This had a miraculous effect.
Describe the path of L-Dopa in the body.
L-Dopa is injected into the patient. It is absorbed into the bloodstream, crosses the blood-brain barrier and diffuses into the brain. Sufficient gets into the striatum, where it is converted into active dopamine.
As time progresses, the dosage of L-Dopa given to Parkinson’s disease patients must ________.
Increase
How have pharmaceutical companies modified L-Dopa injections to make them more effective?
They give compounds with L-Dopa which help to prolong its effects in the brain.
What is the main treatment method of Parkinson’s disease at the moment?
L-Dopa
What are some of the long-term negative side effects of L-Dopa?
- Nausea and vomiting
- Dyskinesia: continuous unusual voluntary movements that can be worse than the original disease.
- May hasten the degenerative effects of the remaining dopamine neurones that are still functional.
- Dopamine reaches all areas of the brain and can effect these areas in different ways.
What is the tendency now to attempt to reduce the negative effects of L-Dopa?
Keep the patients off the drug for as long as possible. Gradually increase the dose and watch out for the side effects.
What was the first surgical treatment of Parkinson’s?
Pallidotomy
Freezing the tip or injecting a chemical into the GPi to remove the cells of that area. Those cells on the edges of the lesion would recover because they would only be partially frozen.
What are the conditions under which a pallidotomy is undergone?
Under local anaesthesia injected into the skull. Patient is awake so that the freezing is done to the extent that the tremor disappears.
What does the area frozen during a pallidotomy lie in? Why does this make a pallidotomy difficult and risky?
Tiger country: the GPi is quite a small target. Lying underneath it is the optic nerve crossing over and near it is the big corticospinal tract. If the electrodes are not in exactly the right place or the lesion is too big, there can be visual changes or a major stroke.
Why was a pallidotomy less popular in its early stages?
MRI was not available so imaging the area was difficult during the operation.
What was the second discovered surgical treatment of Parkinson’s disease?
Thalamotomy: putting a lesion in the VA-VL of the thalamus.
How did thalamotomy compare with pallidotomy?
Both very successful but thalamotomy had less complications because it was a bigger target.
Over the last ten years, due to the development of MRI, what surgical treatment are we now more inclined to do?
We are now able to target the GP much better, so pallidotomy has become more popular again.
How did stimulations of areas during pallidotomies aid treatment?
Could make sure that they weren’t affecting areas of the corticospinal tract. These stimulations also improve the patient.
Instead of killing brain cells, what method involving electricity do surgeons now use?
Deep brain stimulation. Pass and leave an electrode sitting in the globus pallidus internus or the subthalamic nucleus (now more common). Bring the wire out to a pacemaker (stimulator). A remote control can control the frequency and magnitude of stimulation.
What is a major advantage of deep brain stimulation
It is a reversible treatment
What is an empirical treatment? Give an example of one.
When you try and it works so you go with it. Deep brain stimulation.
Does deep brain stimulation usually occur to one side or both sides of the brain?
One side
Two sides can lead to many complications - speech disorders etc.
What are the two novel new treatments for Parkinson’s disease?
Cell replacement/transplantation of dopamine producing cells Gene therapy (Viral vectors)
What are the four types of cells that can be used for cell replacement/transplantation to treat Parkinson’s disease?
1) Immature neurones (fetal)
2) Genetically engineered, cultured neurones from brain tumours
3) Embryonic stem cells
4) Adult stem cells
What are the problems associated with using immature neurones for cell replacement when treating Parkinson’s disease?
Major ethics - must use cells from aborted fetuses
Technical - can form tumours
So not the main form of treatment
Where are adult stem cells found?
In the ventricular margin - subventricular zone
What is involved with gene therapy?
Putting genes in the cells of the subthalamic nucleus which make GABA to inhibit the cells in the SUT to help decrease the activity in the GPi.
