CNS Flashcards
Where are the sensory, motor and autonomic synapses found?
Sensory - dorsal horn.
Motor - ventral horn.
Autonomic - lateral horn.
What is the most common membranous origin in a meningoma?
Arachnoid mater.
What are the grey and white matter equivalents in the PNS?
Grey - ganglion.
White - peripheral nerve.
What is a nucleus and what is the cortex? State the difference between a nucleus and ganglia.
Nucleus - a collection of functionally related cell bodies. A nucleus is found in the CNS, whereas a ganglia is found in the PNS.
Cortex - folded sheet of cell bodies found on the surface of the brain, around 1-5mm thick.
Identify the central sulcus, pre- and post-central gyrus, lateral fissure, parieto-occipital sulcus and clacarine sulcus on the following.
Identify the corpus callosum, thalamus, cingulate gyrus, hypothalamus, fornix, tectum and cerebellar tonsil on the following.
How can a lack of CSF present clinically?
Headaches that are worse when standing up.
How much CSF is produced per day?
600-700ml.
What is the pathway of CSF?
Synthesised in the choroid plexus.
Drains from the lateral ventricles into the 3rd ventricle through the interventricular foramen.
Drain from the 3rd ventricle into the 4th ventricle via the aqueduct of the midbrain.
Drains from the 4th ventricle into the subarachnoid space via the median aperature, the 2 lateral aperatures and a small amount via the central canal.
It is then taken up into the venous sinuses via the arachnoid granulations.
What is the notochord derived from?
Mesoderm, made from the primitive node.
At what day does neurulation begin, and when and where does the neural tube first close?
It begins at day 18.
At day 21, the neural tube first closes in the cervical region.
When do the anterior and posterior neuropores close?
Anterior - day 25.
Posterior - day 28.
What is the neural tube formed from, and what do these cells form?
Formed from neuroepithelial cells.
These cells form glial and neuronal cells.
What do neuroblasts, intermediate zone and marginal zone form?
Neuroblasts - nerve cell precursors.
Intermediate zone - future grey matter.
Marginal zone - future white matter.
How does dorsal-ventral patterning occur?
Signals that are sent from the surface ectoderm, paraxial mesoderm and notochord.
What morphogens are released and what are their functions?
Sonic hedgehog (Shh, from the notochord) induces floor plate production via ventralisation.
BMPs induce roof plate production via dorsalisation.
What are the alar and basal plates’ products?
Alar - sensory and interneurons.
Basal - motor neurons.
What do the lumbosacral, cranial and trunk neural crest cells become?
Lumbosacral - parasympathetic neurons and enteric nervous system.
Cranial - sensory cranial nerve nuclei, parasympathetic ganglia, and facial skeleton.
Trunk - sympathetic neurons.
How do neural crest cells help form spinal nerves?
What are the risk factors for neural tube defects?
Older and younger mothers age.
Folic acid deficiency.
Maternal diabetes/ obesity.
What is cranial bifida?
Failure of the cranial neuropore to close, leading to meninges and/or parts of the brain herniating through the fontanelles.
What are the two types of neural crest defects?
Defective migration or mophogenesis.
Tumours derived - teratomas.
How many segments composes the spinal cord?
31.
How do sensory deficits at the level of dorsal root/ spinal nerve, cord and above the thalamus present?
Dorsal root - dermatomal.
Cord - multiple dermatomes.
Above the thalamus - homuncular pattern.
What is the impulse direction in a funiculus and tract?
Funiculus - bidirectional.
Tract - singular direction.
What are the functions of the:
- Cerebellar peduncles.
- Substantia nigra.
- Red nucleus.
- Periaqueductal grey matter.
Cerebellar peduncles - descending corticospinal fibres from the ipsilateral hemisphere.
Substantia nigra - dopaminergic neurones.
Red nucleus - unconscious movement.
Periaqueductal grey matter - pain transmission and mictuition.
What can a basilar artery occlusion cause and why?
Locked in syndrome.
The corticospinal fibres travel ventrally.
What is the relevance of the visual cortex around the clacarine sulcus?
Above the sulcus provides the contralateral inferior field.
Below the sulcus provides the contralateral superior view.
What is the optic chiasm?
The site at which nasal retinae - lateral fields - decussate.
What are the metabolic and mechanical functions of the CSF?
Metabolic - contains glucose.
Mechanical - shock absorption.
What do the 3 swellings of the neural tube form, and how are these further subdivided?
Diencephalon also forms the optic nerves.
What are the sensory and motor parts of the medulla and midbrain?
Medulla:
- Sensory; lemnisci.
- Motor; pyramids.
Midbrain:
- Sensory; colliculi.
- Motor; cerebral peduncles.
How does the brainstem form?
It is pulled down by the cord as the vertebra grow faster than the spinal cord.
Which chromosome is affected in Di George syndrome?
Chromosome 22.
Explain the glucose-lactate shuttle.
Glycogen in the astrocyte is broken down into lactate.
Lactate is then shuttled across the astrocyte and into the neuron via MCT1 and MCT2 transporters, respectively.
The lactate is then converted into pyruvate via lactate dehydrogenase, where the pyruvate then enters glycolysis.
NOTE: it only occurs when the neurons are active or there is disrupted blood supply, inhibiting glucose transport.
Explain the transport of glucose into neurons.
Glucose from the brain capillaries is transported into the interstitial space across endothelial cells via the GLUT1 transporter.
The glucose is then transported into the neuron via the GLUT3 transporter.
Why do astrocytes remove neurotransmitters, and how?
Excess glutamate causes toxicity.
Termination of depolarisation.
Re-uptake.
What is the benefit of the coupling of astrocytes?
Ions can move between them, allowing for the potassium to be buffered much more greatly, in the brain extracellular fluid.
How are microglia activated?
State the outcome.
Recognition of foreign material via the dendrites of the microglia causes swelling and formation of phagocytic cells.
These can also act as antigen presenting cells.
What does the post-synaptic response depend on?
The nature of the transmitter.
The nature of the receptor.
What are the different types of ionotropic glutamate receptors, and what are their functions?
AMPA - facilitates the influx of sodium and potassium.
Kainate - facilitates the influx of sodium and potassium.
NMDA - facilitates the influx of sodium, potassium and calcium.
How do glutamate metabotropics function?
GPCR:
- changes in IP3 and Ca2+ mobilisation.
- inhibition of adenylate cyclase and decreased cAMP.
What does the activation of NMDA receptors cause?
Up-regulation of AMPA receptors.
Induction of long term potentiation through calcium ion entry, if strong, high frequency stimulation.
What is long term potentiation and what is the function of it?
Increased strength of synaptic connections between neurons.
Related to learning and long-term memory formation.
How is long term potentiation inhibited?
Long term depression weakens the synaptic strength over time.
What are the difference between the GABA receptors?
GABAa - LGIC for chloride.
GABAb - GPCR, which has a modulatory role.
How does ACh produce its effects in the CNS?
Acts at both nAChR and mAChRs.
Excitatory.
Often act on pre-synaptic terminals to enhance the release of other transmitters.
Where is ACh released from in the CNS, where does it act and what is its functions?
Released from the nucleus basalis.
It acts on cerebral cortex and hippocampus.
Has arousal, learning, memory and motor functions.
What is the first neuronal degeneration in Alzheimer’s and how is this treated?
Degeneration of the nucleus basalis.
Cholinesterase inhibitors increased the amount of ACh released, alleviating symptoms.
What are the 3 main dopamine pathways?
Nigrostriatal - substantia nigra to the striatum.
Neocortical - midbrain to the cerebral cortex.
Mesolimbic - midbrain to the limbic system (hippocampus, amygdala, etc.).
What are the functions of the nigrostriatal, mesocortical and mesolimbic pathways?
Nigrostriatal - motor control.
Mesocortical - mood, arousal and reward.
Mesolimbic - mood, arousal and reward.
What receptors do antipsychotic drugs act on?
Dopamine D2 receptors.
Where is noradrenaline mainly released from in the CNS, and where does it act to have what action?
Cell bodies found in the brainstem - locus coerulus.
It projects widely to act on the cortex, limbic system and cerebellum.
It has effects on mood and arousal.
Where is serotonin released from in the CNS and what are its functions?
Raphe nuclei.
It has an effect in sleep/ wakefulness and mood.
Which cell in the CNS can help to form scar tissue and repair damage?
Astrocytes.
How do astrocytes have a function in contributing to cognition?
They are connected to each other via gap junctions, forming a syncytium, allowing calcium waves to propagate through it.
When and where is glycine released, and what is its function?
It is released during REM sleep, in the spinal cord.
It inhibits lower motor neurons, causing paralysis.
Which dopaminergic pathway can contribute to the development of schizophrenia?
The mesolimbic pathway.
What is the role of histamine in the CNS?
Stimulates the cortex to maintain wakefulness.
Sleep.
What are the functions of the following peptides:
- Dynorphin.
- Encephalins.
- Orexin/ hypocretin.
Dynorphin - pain transmission.
Encephalins - pain transmission.
Orexin/ hypocretin - has a role in narcolepsy.
How do ESPS function?
The depolarisation in post-synaptic terminals causes an ESPS.
If the ESPS exceeds the threshold, action potentials are triggered with increased frequency.
What can cause a ‘glove and stocking’ paraesthesia?
Diabetic neuropathy, toxins, renal failure.
Demyelination of the axons.
Where in the spinal cord does subacute degeneration of the cord affect?
The dorsal column.
What is sensory ataxia? State some symptoms.
Impairment of somatosensory nerves, interrupting sensory feedback signals to the brain.
Lack of coordination and postural instability - worsens when vision is impaired.
What is syringomyelia?
CSF-filled cyst within the central canal of the spinal cord that grows anteriorly and laterally.
What is a chiari malformation?
Where the brain tissue, usually the cerebellar tonsil, pushes into the spinal canal, causing syringomyelia.
Which sensory tract can be affected by an expanding syringomyelia, and how is the increasing distribution seen in patients?
The spinothalamic tract - as the cyst grows laterally, it affects the cervical, thoracic, lumbar and then sacral dermatomes.
What are some causes of insensitivities to pain?
Peripheral vascular disease.
Diabetes neuropathy.
FAAH-OUT gene mutation.
Congenital insensitivity to pain.
Where in the spinal cord is Lissauer’s tract located?
Off the tip of the dorsal horn.
What order of neuron forms the dorsal-column and spinothalamic pathways?
Dorsal-column - first order neuron.
Spinothalamic - second order neuron.
What are the functions of A and C fibres?
A fibres carry impulses from mechanoreceptors in the skin.
C fibres carry pain, from nociceptors.
What are the type and characteristics of first order neurones?
They are pseudounipolar neurons.
They have their cell body in the DRG (or trigeminal ganglion, for the trigeminal nerve, etc.).
They receive information from one type of receptor, and collect information from a single dermatome (usually).
They project ipsilaterally into the spinal cord, to the cell body.
They synapse onto secondary neurons.
What is the function of pseudounipolar neurones, and how are they adapted for this?
They are sensory neurons.
Their cell body does not interrupt the continuous axon, allowing impulses to travel rapidly.
What are the characteristics of second order neurons?
Their cell bodies are found in the dorsal horn or medulla.
They decussate.
They project into the thalamus.
What are the characteristics of third order neurons?
Their cell bodies are in the thalamus.
They project to the primary sensory cortex.
What is the process of binding?
The ability of the CNS to bring the different senses together for perception.
What does the type of sensation depend on?
The receptor type.
What is a receptive field?
An area of skin that a primary sensory neurone supplies - it can span across more than one dermatome.
What is somatotropy/ topographical representation?
The organisation of the sensory system, converting dermatomal sensory information into homuncular sensory information, with great efficiency, through the exchange of information between primary, secondary and tertiary sensory neurones.
What does the sensation from T6 and above, and T7 and below run in, in the dorsal column pathway?
T6 and above - cuneate fasciculus.
T7 and below - gracile fasciculus.
Where do the second order neurones decussate in the spinothalamic tract?
The ventral white commissure.
How does the neural level differ between the dorsal column and spinothalamic tracts?
Dorsal column loses ipsilateral sensation at the level of the lesion and below.
Spinothalamic loses contralateral sensation at 1-2 spinal levels below the level of the lesion, and below.
What is the strength of the receptor activation based on?
The level of ion flux during the generator potential.
Through what structure do second order neurones project from the gracile/ cuneate nucleus (medulla oblongata) to the contralateral thalamus?
Medial lemniscus.
Where do thalamic neurones from the superior and inferior parts of the body project to?
Superior projects to the lateral somatosensory cortex.
Inferior projects to the medial somatosensory cortex.
How does rubbing a painful area of the body relieve the pain?
Mechanoreceptors are stimulated and the information is conveyed along ABeta fibres (sensory).
These ABeta neurones stimulate inhibitory enkephalinergic interneurones, which inhibits the transmission of pain from the second order neurone cell body.
How can there be cortical modulation of pain?
Cortical neurones project down to the midbrain - periaqueductal grey, stimulating the neurones there.
These neurones then stimulate the neurones in the nucleus raphe Magnus, within the medulla (part of the reticular formation).
These neurones then descend and inhibit the second order sensory pain neurones via activation of the inhibitory enkephalinergic interneurones.
How do inhibitory interneurones inhibit the second order sensory pain neurones?
Through the release of enkephalin.
How does the light pass through the retina and how does this correlate to the function of the retina?
Light has to pass through the superficial neurosensory structures before reaching the pigmented layer.
The impulses then travel from the pigmented layer, superficially, to the retinal ganglion cells.
What are the functions of the following:
- Pigmented layer.
- Photoreceptors.
- Horizontal cells.
- Bipolar cells.
Pigmented layer - absorbs excess light, preventing the light from scattering and glare, moderating the amount of light being processed. It also anchors the photoreceptors.
Photoreceptors - rods are for black and white vision, and cones are for coloured vision and high visual acuity.
Horizontal cells - lateral inhibition, inhibiting signals from adjacent photoreceptors.
Bipolar cells - allows for communication between photoreceptor cells and retinal ganglion cells.
Where is the primary visual cortex found?
Found around the calcarine fissure in the occipital lobe.
What is binocular vision?
Vision using two eyes with overlapping fields of vision, allowing for good perception of depth.
Which artery prevents central vision from being lost?
The middle cerebral artery - macular sparing.
What is the function of the vestibular nuclei?
To send projections through the medial longitudinal fasciculus and descending down into the spinal cord, allowing for the position of the head to be compensated for when the body is at different angles.
What are the posterior spinal and anterior spinal arteries supplied by, generally?
Segmental vessels from the aorta.
What does the adamkiewicz artery do?
Gives branches to the anterior and posterior spinal arteries around the lower spinal cord.
What does the anterior spinal artery arise from?
Vertebral arteries.
What does the anterior spinal artery reside in?
The anterior sulcus of the spinal cord.
What is the damage distribution in an anterior spinal artery occlusion?
Bilateral symptoms, where there is damage to the ventral horns, corticospinal tracts, spinothalamic tracts and part of the dorsal horns.
Anterior 2/3rds of the spinal cord.
What is the damage distribution in a posterior spinal artery occlusion?
Ipsilateral symptoms as there is one on each side:
- most of the dorsal horn.
- dorsal column pathway.
Posterior 1/3rd of the spinal cord.
Why does a basilar artery occlusion cause locked-in syndrome?
State why the eyes can move.
The pontine arteries branch from the basilar artery.
The pontine arteries supply the corticospinal tracts.
The eyes can still move as the midbrain is preserved, so CNs III and IV can still function.
Which cerebellar arteries supply the midbrain, pons and medulla?
Midbrain - superior cerebellar arteries (and posterior cerebral).
Pons - anterior inferior cerebellar artery.
Medulla - posterior inferior cerebellar artery.
Which other artery has a significant blood supply to the medulla?
Vertebral arteries.
What is the projection of the middle cerebral arteries?
They travel laterally, and give off lenticulostriate branches.
As they emerge through the lateral fissure, it gives a superior and an inferior division.
What are the branches of posterior cerebral artery and what do these supply?
Quadrigeminal artery supplying the midbrain.
Anterior and posterior temporal arteries, supplying the inferior temporal lobe.
Calcarine artery supplying the occipital lobe.
Thalamoperforating artery supplying the thalamus.
Thalamogeniculate artery supplying the medial and lateral geniculate nuclei, of the thalamus.
What artery can be occluded by a sub-falcine herniation, and why?
Raised intracranial pressure can lead to the cingulate gyrus herniating under the falx cerebri, compressing the anterior cerebral artery.
What does the uvea consist of?
Choroid layer and its associated vasculature.
Ciliary body and iris, anteriorly.
Which artery is a direct continuation of the internal carotid artery?
The middle cerebral artery.
What are the major areas that the posterior cerebral artery supplies?
Occipital lobe.
Inferior temporal lobe.
Thalamus.
What is the damage to the visual system associated with a middle cerebral artery occlusion, affecting both optic radiations?
Macular splitting - a homonymous hemianopia.
What do the medullary pyramids contain?
Upper motor neurones that form the corticospinal tracts.
Where do the leg, trunk and arm run, within the internal capsule?
Leg most posteriorly.
Arm most anteriorly.
Trunk in the middle.
All located within the posterior limb of the internal capsule.
What is the innervation to the trigeminal and vagus nuclei?
State why.
Bilateral innervation - contains innervation of upper motor neurones from the ipsilateral and contralateral sides.
They are important features which, if compromised, could potentially be fatal, and so have a ‘fail-safe’ mechanism, protecting from strokes.
What is the nucleus of the vagus nerve called?
The nucleus ambiguous.
What are the surrounding structures of the internal capsule?
Give further details.
Surrounding the posterior limb:
- Thalamus is medial.
- Lentiform nucleus is lateral - immediately lateral is the globus pallidum, and slightly more lateral is the putamen.
Where within the internal capsule is the corticobullar tract found, and what is its function?
Within the genu.
It contains upper motor neurone axons that go to supply the lower motor neurones that supply the muscles of the face.
What are the different aspects of the posterior limb of the internal capsule?
Medial - ascending third order sensory fibres of the somatosensory tract.
Lateral - descending upper motor neurones supplying the arm, trunk and leg.
This means that it is a bidirectional pathway.
What do each of the colours of the midbrain represent, and what are their functions?
Red - cerebral peduncles, which connects the cerebral hemispheres to the midbrain, containing upper motor neurones.
Blue - substantia nigra, which produces dopamine.
Green - red nucleus which has some motor control and produces a coarse tremor if damaged.
Pink - spinothalamic and medial lemniscus (containing dorsal column second order neurones).
Black - oculomotor and edingerwestphal nuclei.
Yellow - peri-aqueductal grey, involved in micturition and pain.
Light green - cerebral aqueduct, which allows CSF to drain from the 3rd to 4th ventricle.
Superior colliculi - reflex actions of the visual system.
What do each of the following colours represent, in regards to the corticospinal tract?
Green - UMNs which synapse onto LMNs supplying the axial musculature.
Blue - UMNs which synapse onto LMNs supplying the limb girdles.
Yellow - UMNs which synapse onto LMNs supplying the intrinsic muscles of the limbs.
Red - UMNs which synapse onto LMNs supplying the distal limb muscles.
Where in the corticospinal tract can the following conditions effect:
- Multiple sclerosis.
- Guillain-Barré syndrome.
MS - lower motor neurones or the cell bodies/ proximal axons of the upper motor neurones in the CNS.
GBS - lower motor neurone axons in the PNS, the peripheral nerves.
What does the medial longitudinal fasciculus do?
Connects different cranial nerve nuclei together (CNs III, IV, VI), to allow the for the extra-ocular muscles to move in a conjugate manner - prevents the lateral movement of the eyes forming diplopia.
How are spinal reflexes modulated?
State what can occur if these are damaged.
Descending influences from the brain - strokes affecting the modulatory fibres can lead to different manifestations of the reflexes, such as Babinski’s sign.
Why do atrophy and fasiculations occur in lower motor neurone damage?
Atrophy - lower motor neurones deliver growth factors and action potentials to the muscle, so a decrease in these leads to a decrease in muscle mass.
Fasciculations - up-regulation of nAChRs means that the muscles become over-sensitive to circulating ACh, leading to uncoordinated contraction of muscles.
What is the rubrospinal?
A motor pathway that originates from the red nucleus to around C1-C2.
What is the reticulospinal tract?
A motor pathway from the reticular formation, that helps control muscle tone. It causes paralysis during REM sleep.
What is the vestibulospinal tract?
Input to the spinal tract from the semicircular canals, to help keep the head stationary.
What is the tectospinal tract?
From the colliculi to the tectum, giving reflexive information regarding the:
- Superior = visual.
- Inferior = auditory.
What is the corona radiata?
White matter of the cerebral hemispheres that aggregate to form the internal capsule.
What is clasp knife rigidity?
Where the resistance to moving a limb is high until the Golgi tendon organs detect the high degree of stretch, and then stimulate inhibitory interneurones causing relaxation.
What does the anterior limb of the internal capsule do?
Connects the axons of motor cortex with the cerebellum.
How does damage to the basal ganglia cause contralateral symptoms?
The corticostriatal pathway projects from the cortex to the striatum (putamen and caudate nucleus), sending the motor plan to the basal ganglia.
Impulses are then sent from the globus pallidus to the thalamus, and from the thalamus to the motor cortex on the ipsilateral side - the pallidothalamocortical pathway - mediating and adapting the motor plan.
Dopamine is provided to the basal ganglia via the nigrostriatal pathway.
This means that the basal ganglia is unilateral, and so damage to the basal ganglia will lead to damage to the upper motor neurones before they decussate.
How does damage to the cerebellum cause ipsilateral symptoms?
The input from the cerebella are through the pontine nucleus, via the corticopontine pathway, and then the pontocerebellar pathway, which decussates. Together, this is the corticopontocerebellar pathway.
The cerebellum then communicates with the contralateral thalamus, via the cerebellothalamo pathway, and then the thalamus communicates with the cortex via the thalamocortico pathway. Together, this is the cerebello-thalamo-cortical pathway.
This means there is a double decussation and so there is ipsilateral symptoms.
Furthermore, the spinocerebellar tract is ipsilateral, sending sensory information from the muscle spindle to the cerebellum, and so damage to this pathway also leads to ipsilateral symptoms.
How does the direct pathway cause excitation of the cortex?
The substantia nigra pars compacta sends excitatory dopaminergic connections to the putamen, stimulating the putamen.
The putamen then inhibits the globus pallidus internal segment.
This decreases the inhibition of the thalamus, leading to stimulation of the cerebral cortex.
How does the indirect pathway cause excitation of the cortex?
The substantia nigra pars compacta sends inhibitory dopaminergic connections to the putamen, inhibiting the putamen.
The inhibitory stimulations of the putamen to the globus pallidus external (GPe) are therefore inhibited, so there is less inhibition of the GPe.
This means there is more inhibitory stimulations sent from the GPe to the sub-thalamic nucleus.
The inhibition of the sub-thalamic nucleus leads to less stimulation of the globus pallidus internal.
Less stimulation of the globus pallidus interna means there is less inhibition of the thalamus, leading to increased excitation of the cortex.
What do the superior, middle and inferior cerebellar peduncles connect to?
What are the different outputs to the cortical regions and their associated neurotransmitters?
Thalamus - glutamate.
Hypothalamus - histamine.
Basal forebrain nuclei - acetylcholine.
What is seen on an EEG in REM sleep and when awake, and when the eyes are closed?
Beta-waves - low voltage, thus synchronicity, but high frequency.
Alpha-waves - slightly increased synchronicity as there is less sensory input, but still high frequency.
What is seen in the 4 stages of non-REM sleep, on an EEG?
Stage 1 - theta waves.
Stage 2/3 - theta waves, sleep spindles and k-complexes.
Stage 4 - delta waves.
As the stages increase, the amplitude (thus, synchronicity) increases, and the frequency decreases.
What cerebral artery is most commonly affected by emboli?
Middle cerebral artery - increased risk of atherosclerosis here.
What are some different types of primary CNS tumours?
What are the treatments for delirium?
What are some differences between delirium and dementia?
Label the following:
What are some physical symptoms of anxiety disorders?
GI, respiratory, cardiovascular, genitourinary, neuromuscular, sleep.
