All content Flashcards
Define Grey matter within the CNS.
Composed of cell bodies and dendrites
Define White matter within the CNS.
The axons of the cells, very fatty due to myelin sheaths
Describe the pattern of Grey and White matter within the brain, starting from the centre.
Grey matter in the centre, surrounded by white matter, with a grey matter layer around the outside.
Same in Spinal cord, without the extra grey matter layer.
Define the meaning of a “tract” within the spine
A white matter pathway between two grey matter regions. Sensory tracts ascend to the brain, motor descend from the brain.
Define a funiculus
A collection of white matter pathways (tracts)
What is the Cerebral Cortex?
A collection of grey matter structures found on the surface of the brain
What is a Commissural Fibre (Axon)?
A white matter axon that connects right and left hemispheres of the brain
What is a Projection Fibre (Axon)?
A white matter axon that connects the cerebral hemispheres to the spinal cord/brainstem
What is an Association Fibre (Axon)?
A white matter pathway that connects two cortical regions within the same hemisphere
Name the parts of the Brainstem in order
Midbrain, Pons, Medulla
What are the roles of the Midbrain?
Eye movements and responses to sound and vision
What are the roles of the Pons?
Feeding/Sleeping
What are the roles of the Medulla?
CVS and Resp centre management and major motor pathway location (medullary pyramids)
What is the Pre-central Gyrus?
Location of the Primary Motor Cortex
What is the Post-central Gyrus?
Location of the Primary Sensory Cortex
What is the Sylvian Fissure?
Separates the Frontal and Temporal lobes
What is the Calcarine sulcus?
Located within the occipital lobe, surrounded by the Primary Visual Cortex
What is the Optic Chiasm?
The location where the Optic nerves meet and visual systems cross over
What is the Uncus?
A part of the temporal lobe, located by the Optic Chiasm, which can herniate down through the foramen magnum and impinge on the brainstem, causing death. Important in olfaction.
What are the Medullary Pyramids?
Location of descending motor fibres
What is the Parahippocampal Gyrus?
Located right next to the Uncus, important for encoding long term memory in the hippocampus.
What is the Corpus Callosum?
The fibres connecting the two hemispheres of the brain
What is the Thalamus?
Relays sensory signals to the cerebral cortex and important in consciousness, sleep and alertness.
What is the Cingulate Gyrus?
The area of the brain around the Corpus Callosum, important for emotion and memory.
What is the Hypothalamus?
Centre for homeostasis (eg. Pituitary control), located in front of the thalamus.
What is the Hippocampus, where is it and what is its exit pathway called?
The Hippocampus is part of the Limbic system associated with new memory storage. Located below the Thalmus, with the exit pathway being the fornix.
What is the Tectum?
The dorsum of the midbrain, involved in response to sound/visuals.
What are the Cerebellar Tonsils?
Bottom of the Cerebellum that can herniate and compress the Medulla. Leads to “Coning” and death.
How much CSF is made per day and by what?
600ml, by the choroid plexus cells. Most is made in the lateral ventricles.
Name and describe the passage of the Ventricles.
Lateral Ventricles connect to the Third Ventricle in the centre via the interventricular foramen, which is in the midline. The third ventricle is connected to the Fourth Ventricle via the Cerebral Aqueduct. This then leads to the Subarachnoid Space.
What is on either side of the Third Ventricle?
The Thalamus.
Blockage of the Cerebral Aqueduct leads to what?
Hydrocephalus
How does the CSF leave the Fourth Ventricle to enter the Subarachnoid space?
Via the Foramens of Luschka and Magdendie. It enters the vertebrae via the Central Canal.
What week does Neurulation occur in?
Week 4
What is the role of the Notochord?
It causes conversion of overlying ectoderm into neuroectoderm, which forms the neural plate and folds into the neural tube.
What can failure of the neural tube to fuse lead to?
Anencephaly and Spina Bifida, depending on where the fusion failed to occur.
What does a Cranial neural tube fusion defect lead to?
Anencephaly
What does a Caudal neural tube fusion defect lead to?
Spina Bifida
What is Spina Bifida?
Failure of the neural tube to close caudally. Usually manifests in the lumbosacral region. Leads to neurological defects, no cognitive delay, always leads to hydrocephalus. A lump appears with CSF leaking from the spinal cord.
What does Spina Bifida lead to?
Neurological defects, no cognitive delay, always leads to hydrocephalus.
What are the types of Spine Bifida, in order of severity?
Occulta - least bad
Cystica:
- Meningocoele
- Myelomeningocoele - worst type, spinal cord exits the vertebrae
What is Anencephaly?
Failure of the neural tube to close cranially. Incompatible with life, will not have a brain.
How can a Neural Tube Defect (NTD) be detected?
Via raised Serum a-fetoprotein in the mother’s serum. Can also do a USS.
How can a Neural Tube Defect (NTD) be prevented?
Folic acid given pre-conceptually for 3 months and in first trimester.
What develops from the Cranial portion of the neural tube?
The brain - the 5 main components of the brain (cerebral hemispheres, thalamus, midbrain, pons/cerebellum, medulla oblongata)
What develops from the Caudal portion of the neural tube?
The spinal cord
What develops from the Lumen of the neural tube?
The ventricles of the brain (CSF)
What are the boundaries of the Cauda Equina?
L2-S5
Name the 3 Primary Brain Vesicles from the development of the Neural tube.
Forebrain - Prosencephalon
Midbrain - Mesencephalon
Hundbrain - Rhombencephalon
Name the 5 Secondary Brain Vesicles and their pre-decessors.
Prosencephalon -> Telencephalon and Diencephalon
Mesencephalon -> Mesencephalon
Rhombencephalon -> Metencephalon and Myencephalon
Name the 5 mature brain components that mature from the Secondary Brain Vesicles.
Telencephalon - Cerebral hemispheres Diencephelon - Thalamus Mesencephalon - Midbrain Metencephalon - Pons/Cerebellum Myencephalon - Medulla Oblongata
Name the two flexures of the brain and where they are located.
Cervical flexure = at spinal cord attachment to brain
Cephalic flexure = at the midbrain
Name the main ventricular system abnormality, who it is most common in and how to treat it.
Hydrocephalus - most common in newborns, suffering from Spina Bifida and treatable with a shunt. Usually due to cerebral aqueduct blockage.
What do the Alar plate and Basal plate of the primitive neural tube associate with in an adult?
Alar plate = Sensory, therefore Dorsal (DS)
Basal plate = Motor, therefore Ventral
What are neural crest cells?
Cells of the lateral borders of the neuroectoderm tube that undergo epithelial to mesenchymal transition (become functional body components eg. Glial cells).
Name one reason for neural crest defects to occur.
Alcohol - very sensitive.
Name 2 conditions of neural crest cell migration failure.
Single structures: Hirschsprung’s disease - no nerves to muscles of colon
Multiple structures: DiGeorge - no thyroid gland, cardiac defects
What spinal cord levels mediate the knee jerk reflex?
L2-L4
Describe the process of the knee jerk reflex
Muscle spindles (normal stretch) and the Golgi organ (extreme stretch) detect the tendon hammer hit. These transfer this information the motor ventral horn via the sensory fibres. The motor fibres from the ventral horn go to the knee flexors.
What is the Jendrassik manoeuvre?
Hands are held together and teeth clenched to increase the reflex response.
Why do seizures always manifest in the hands first?
Hands have a disproportionate representation within the somaesthetic cortex, in terms of size (humunculus).
What is a meningioma?
Benign, white matter, non-glial tumour of the meninges
Describe the difference between a T1 and T2 MRI.
T1 - White matter (fat) bright
T2 - Water bright (H2O = mnemonic)
What does Gd being visible on a T1 MRI mean.
Gd is usually not permeable to the BBB. If it is present on a scan, the BBB has been breached.
What is the role of Astrocytes within the CNS? (5 marks)
Most common glial cell. They support the NS by:
- Providing structural support
- Providing nutrition via glucose-lactate shuttle (convert blood glucose to lactate for the neuronal cells) - neurones do not store glycogen
- Removing neurotransmitters (uptake) eg. glutamate
- Forming the BBB
- Maintaining the ionic environment via K+ buffering (keep low by taking it in)
What is the role of Oligodendrocytes within the CNS?
Myelinate multiple axons at once - instead of Schwann cells in the PNS.
What is the role of Microglia within the CNS?
Immune cells of the CNS - can phagocytose foreign bodies and debris. Must be “activated” to become phagocytic.
Describe the makeup of the Blood Brain Barrier.
Endothelial cells with tight junctions and a basement membrane - astrocytes sen signals to endothelial cells to form tight junctions.
What must transported across the Blood Brain Barrier to control its concentration?
Glucose (glucose-lactate shuttle via Astrocytes/GLUT 1 channel) and Amino acids
Describe how the brain is immune privileged.
Will not get attacked. T cells can enter the BBB, but the T cell pro-inflammatory response is inhibited. Microglia act as antigen presenting cells.
Name the amino acid neurotransmitters.
Excitatory: Glutamate
Inhibitory: GABA, Glycine
Name the excitatory neurotransmitter/s of the CNS.
Glutamate.
Name the inhibitory neurotransmitter/s of the CNS.
GABA/Glycine
What are the two types of excitatory receptor for Glutamate?
AMPA and NMDA
Describe the MOA of excitatory receptors within the CNS.
AMPA = initial fast depolarisation (fast synaptic transmission) via Na+/K+
NMDA = allow ion flow through the channel after glutamate binding AND are permeable to Ca2+ (AMPA aren’t)
NMDA receptors up-regulate AMPA receptors
Describe the role of excitatory receptors within synaptic plasticity and excitotoxicity.
NMDA activation leads to up-regulation of AMPA receptors.
High frequency stimulation leads to long-term potentiation (learning).
Ca2+ entry through NMDA is important for this - however too much Ca2+ can lead to excitotoxicity (Ca2+ activates many processes within cells, destroying them).
What is the main inhibitory neurotransmitter within the brain?
GABA
What is the main inhibitory neurotransmitter within the spinal cord?
Glycine
What is the MOA of GABA and Glycine receptor channels in being inhibitory?
There receptor channels allow Cl- through. These lead to hyperpolarisation and decreased action potential firing - the inhibitory post-synaptic potential.
Name two drugs that target GABA receptors within the brain and their MOA.
Enhance the response of receptors to GABA:
Barbiturates - sedatives, risk of fatal overdose
Benzodiazepines - sedative/anxiolytic, treats anxiety, insomnia and epilespy
What do inhibitory interneurones within the spine release?
Glycine
Name the 4 main modulatory neurotransmitters within the CNS.
AcH
Dopamine
Noradrenaline
Serotonin (5-HT)
Describe the role of AcH as a modulatory neurotransmitter within the CNS.
Excitatory mainly. Acts on nicotinic and muscarinic neurotransmitters - these are mainly on pre-synaptic terminals to enhance the release of other neurotransmitters (eg. Glutamate).
Involved in memory, learning and motor.
How is Alzheimer’s disease linked to AcH. What is a treatment of Alzheimer’s that is based around this?
Degeneration of the cholinergic neurones in the nucleus basalis seen in Alzheimer’s - AcHesterase inhibitors are given to treat SYMPTOMS of Alzheimer’s.
What conditions are associated with Dopamine dysfunction and describe the basic pathophysiology.
Parkinson’s - loss of dopaminergic neurones in the substantia nigra - treated with Levodopa.
Schizophrenia - too much dopamine released - anti-psychotic drugs are dopamine antagonists of D2 receptors
What is the role of NA within the CNS and where is it primarily found?
Created mainly in the Locus Ceruleus (this area is inactive during sleep) - excitatory, leads to behaviour arousal.
Amphetamines increase NA release and increase wakefulness.
Define Somatic sensation.
Conscious body sensation.
Name the two somatosensory modalities.
“Spinothalamic” and “Dorsal Column Medial Lemniscus” system.
What can the Spinothalamic modality feel?
- Temperature (thermoreceptors)
- Pain (nociceptors)
- Pressure/Crude touch (mechanoreceptors)
What can the Dorsal Column Medial Lemniscus modality feel?
- Vibration
- Proprioception (Joint position sense from Golgi tendon/ Muscle spindles)
- Fine touch
- Two point discrimination
What can the Spinothalamic modality feel?
- Temperature (thermoreceptors)
- Pain (nociceptors)
- Pressure/Crude touch (mechanoreceptors)
What can the Dorsal Column Medial Lemniscus modality feel?
- Vibration
- Proprioception (Joint position sense from Golgi tendon/ Muscle spindles)
- Fine touch
- Two point discrimination
In the Spinothalamic System: What is a Primary (1st Order) Sensory Neurone and where is its cell body?
A primary sensory neurone transmits sensory information from a sensory receptor to their cell body in the Dorsal Root Ganglion (not Dorsal Horn), ipsilaterally.
Name the two sensory receptor types, give an example of each and describe them.
Rapidly adapting - eg. Mechanoreceptors - frequency of firing diminishes quickly after initial stimulus (explains why cannot feel clothes on skin)
Slowly adapting - eg. Nociceptors - do not change frequency of firing after initial stimulus (means pain can be persistent and not go away)
What is a “Receptive Field”?
An area of skin supplied by a single primary sensory neurone, connected to multiple sensory receptors.
Define the Acuity of a Receptive Field and its relationship with the size of the Receptive Field.
Acuity = how small a change/movement can be felt - two point discrimination
A larger receptive field = a lower acuity (inversely proportional)
Fields can overlap, leading to fuzzy dermatome boundaries
Give examples of a high and low acuity area of the body.
High acuity area = fingertip
Low acuity area = skin of the back
Describe the layout of the Homunculus in Primary Sensory Cortex in relation to the limbs, medial to lateral.
Medial: Lower limb
Lateral: Upper limb
Extra lateral: Hand
Extra-extra lateral: Face
How many neurones are there in the somatosensory neurone chain?
3 - Primary, Secondary, Tertiary
In the Spinothalamic System: What is a Secondary (2nd Order) Sensory Neurone and where is its cell body and where does it travel to?
From 1st order neurone, has cell body in dorsal horn and decussates in the Ventral White Commisure. Travels to the Thalamus via the Spinothalamic Tract.
In the Spinothalamic System: What is a Third (3rd Order) Sensory Neurone and where is its cell body and where does it travel to?
From Thalamus, cell body in the Thalamus. Projects to Primary Sensory Cortex in the post-central gyrus.
Inferior parts of the body: Medial
Superior part of the body: Lateral
Why is the hand disproportionately likely to be affected by a tumour?
Hand has a disproportionately large representation in the Homunculus of the Primary Sensory Cortex.
How does Somatotopy link to the Homunculus?
Every part of the body has a corresponding part of the brain within the Homunculus.
In the DCML System: What is a Primary (1st Order) Sensory Neurone and how/where does it ascend?
From Lower body: ascend through the Gracile Fasciculus to the Gracile Nucleus in the medulla
From Upper body: ascend through the Cuneate Fasciculus to the Cuneate Nucleus in the medulla
In the DCML System: What is a Secondary (2nd Order) Sensory Neurone and how/where does it ascend?
From Lower Body: Gracile Nucleus to contralateral Thalamus in the Medial Lemniscus.
From Upper Body: Cuneate Nucleus to contralateral Thalamus in the Medial Lemniscus.
In the DCML System: What is a Tertiary (3rd Order) Sensory Neurone and how/where does it ascend?
From Lower Body: Project to the Medial part of the Primary Sensory Cortex.
From Upper Body: Project to the Lateral part of the Primary Sensory Cortex.
In the DCML system: where do axons from the lower and upper body run up to the brain? (which is medial and which is lateral)
Lower body: Medial
Upper body: added Laterally
In the Spinothalamic system: where do axons from the lower and upper body run up to the brain? (which is medial and which is lateral)
Lower body: Laterally
Upper body: Medially - due to decussations
Describe Brown-Sequard syndrome.
Complete hemisection destruction of the spinal cord (destruction on one side) - dorsal and ventral horns and all white matter pathways destroyed.
Will lead to:
- Ipsilateral DCML modalities below the destroyed segment
- Contralateral Spinothalamic modalities below the destroyed segment
- Segmental anaesthesia ipsilaterally in a single dermatome
Describe the process of pain modulation, including the fibres involved.
A fibres = mechanoreceptors - when activated, inhibits C fibres via adrenaline mediated response
C fibres = carry pain
Describe B12 deficiency’s effect on the body.
B12 is only from meat.
Leads to demyelination of the spinal cord - will get loss of peripheral sensation, as well as megaloblastic anaemia.
List 2 causes for insensitivity to pain.
- Drugs
- Diabetes
Describe how bilateral symptoms of pain can occur,
Central canal swelling will lead to:
- Spinothalamic system Upper Limbs is fucked first, as Ventral White Commissure taken out first (decussating fibres lost)
- Gracile Fasciculus lost next, so DCML lost
- Finally Spinothalamic tracts of Lower Limbs (lateral) would be lost
What is the role of the Pigmented layer of the retina?
Prevents glare.
Why do people with albinism struggle to see in bright sunlight?
They do not have Melanin - the retinal pigment cells contain Melanin. Will not prevent glare.
What is Uveitis?
Inflammation of the Choroid layer of the eye.
What are Bipolar cells within the eye?
First Order Neurones of the eye - interact with retinal ganglion cells.
What is the process of viewing the retina of the eye?
A fundoscopy.
What is the white disc on a fundoscopy and how many photoreceptors does it have?
The Optic nerve and 0.
What is the dark circle on a fundoscopy? (2 things)
Macula and the Fovea. The fovea of the macula has the cones with the highest resolution
What is darker on a fundoscopy, an artery or a vein?
Vein
What is papilloedema?
Inflammation of the Optic nerve due to raised ICP.
Describe the optic pathway in words, from the eye, the journey of the optic nerve and where it ends up (including radiations and lobes)
- Optic nerve travels to optic chiasm.
- Nasal fibres decussate at chiasm, Temporal fibres do not.
- The optic fibres travel down the optic tract to the Lateral Geniculate Nucleus.
- From the Lateral Geniculate Nucleus, the fibres travel down the optic radiations to the Primary Visual Cortex in the Occipital Lobe.
Via:
- Superior radiations - Parietal (GB Adv SP)
- Inferior radiations - Temporal
Name the two sides of Visual field.
Temporal - lateral, but seen by Nasal fibres
Nasal - medial, but seen by Temporal fibres
What fibres (Nasal or Temporal) are responsible for seeing the Temporal viewing field?
The Nasal (alternate)
Which fibres decussate at the Optic chiasm?
Nasal
Which fibres do not decussate at the Optic chiasm?
Temporal
From the Optic chiasm, where do the fibres go and via which tract?
The fibres travel from the Optic chiasm to the Lateral Geniculate Nucleus via the Optic Tracts.
Describe how Monocular Blindness can occur and what it is. Give a cause.
Loss of all fields in one eye only.
Must have compression or loss pre-Optic-chiasm.
Retinal detachment or occlusion of a retinal artery or vein.
CN 2 lesion is most likely.
Describe how Bitemporal Hemianopia can occur and what it is. Give a cause.
Loss of Temporal fields on both eyes.
This means Nasal fibres lost (to see Temporal visual field). Most likely at the Optic Chiasm, as this is where the Nasal Fibres decussate.
Cause: Pituitary Adenoma.
Describe how Homonymous Hemianopia can occur (no-radiations) and what it is. Give a cause.
Loss of Left or Right side of vision of both eyes (one Nasal, one Temporal lost).
Damage to the Optic Tract on one side, so loss of one Nasal (contralateral) and one Temporal (ipsilateral).
Named based on which side of vision is lost.
Caused by Stroke/Tumour.
What quadrant of vision are the Superior Radiations responsible for?
The inferior quadrant.
What quadrant of vision are the Inferior Radiations responsible for?
The superior quadrant.
What lobe do the Superior radiations travel through?
The Parietal lobe (SP)
What lobe do the Inferior radiations travel through?
The Temporal lobe
Where do the Optic Radiations all end up?
The Occipital lobe, Primary Visual Cortex.
Describe how a right-sided Homonymous Inferior Quadrantinopia can occur and what it is. Give a cause.
Lesion of the right Superior Optic Radiation (Parietal Lobe):
- Loss of ipsilateral (right) Temporal fibre, supplying Inferior Nasal visual field
- Loss of contralateral (left) Nasal fibre, supplying Inferior Temporal visual field
Overall: Lost inferior right nasal field, lost inferior left temporal field
Describe how a right-sided Homonymous Superior Quadrantinopia can occur and what it is. Give a cause.
Lesion of the right Inferior Optic Radiation (Temporal Lobe):
- Loss of ipsilateral (right) Temporal fibre, supplying Superior Nasal visual field
- Loss of contralateral (left) Nasal fibre, supplying Superior Temporal visual field
Overall: Lost superior right nasal field, lost superior left temporal field
Describe how a Right Homonymous Hemianopia can occur (radiations cause) and what it is. Give a cause.
Loss of both optic radiations on one side (Left)
Happens only in stroke.
Describe Macular Sparing.
Only relevant to vascular lesions.
The occipital lobe has a dual blood supply:
- PCA
- MCA - supplies occipital pole
If PCA stroke occurs, macula will be okay, as supplied by MCA
Describe the Pupillary Light Reflex.
- Light enters eye, travels down Optic nerve to Lateral Geniculate Nucleus.
- Also travels to Pretectal Nucleus, which feeds into Edinger Westphal Nucleus.
- This stimulates Direct and Consensual Light reflexes.
Describe the Accomodation Reflex.
Required for near vision. 3 Cs: - Convergence of the eyes to a point - Constriction of the iris - Contraction of the lens by the ciliary *muscle*
Describe the role of the Medial Longitudinal Fasciculus.
Lies in the brainstem - makes the nerves that supply motor to the eye communicate with eachother.
What supplies blood to the anterior portion of the brain?
Internal Carotid Artery
What supplies blood to the posterior portion of the brain?
Vertebral Arteries
What structure/s are supplied by the anterior circulation of the Circle of Willis?
The cerebral hemispheres.
What structures are supplied by the posterior circulation of the Circle of Willis?
The brainstem, cerebellum and some of the temporal and occipital lobes.
What does the anterior cerebral artery supply and what is it a branch of?
Frontal and Parietal lobes medially - can affect homunculi if blocked.
Branch of ICA.
Name the branches of the ICA within the Circle of Willis.
Ophthalmic artery, anterior choroidal artery, Middle Cerebral Artery, Anterior Cerebral Artery, Posterior Communicating Artery (not PCA)
What important structure does the Posterior cerebral artery supply?
Thalamus
What does a PCA occlusion lead to in the eyes?
Homomymous hemianopia - Macular Sparing
Name the Cerebellar arteries.
Superior Cerebellar
Anterior Inferior Cerebellar
Posterior Inferior Cerebellar (branch of vertebral arteries)
Describe what the Middle Cerebral Artery supplies.
The *lateral* part of the cerebral hemispheres (eg. Parietal/Temporal) Deep branches (lenticulostriate arteries) supply lentiform/caudate nuclei and the internal capsule
Describe what the Anterior Cerebral Artery supplies.
Medial aspect of Frontal and Parietal lobes.
Describe what the Basilar artery supplies (and its branches - from below posterior communicating artery).
- Posterior Cerebral Artery - supplies Occipital Lobe, Temporal Lobe medially and Thalamus, as well as Midbrain (en-passant)
- Superior Cerebellar Artery - superior Cerebellum and Midbrain (en-passant)
- Potine arteries - Pons
- Anterior Inferior Cerebellar Artery - anterior inferior Cerebellum and Pons (en-passant)
Describe the branches of the Vertebral arteries and what they supply.
- Posterior Inferior Cerebellar - Posterior Inferior cerebellum
- Spinal arteries - anterior 2/3 of the spinal cord