Neuro / Ophthal - Anatomy/Physiology Flashcards
What does UMN and LMN consist of?
UMN = brain or spinal cord
LMN = nerve roots, peripheral nerve, neuromuscular junction, or muscle
In neurology, we need to first think of where the lesion could be, in simple terms where could a lesion be and what pattern of weakness (symmetrical/bilateral OR asymmetrical/unilateral) would be associated?
- Brain
- Spinal cord
- Nerve root
- Periphreal nerves
- NMJ
- Muscles
- Brain - asymmetrical/unilateral
- Spinal cord - symmetrical/bilateral (everything is close together in spinal cord so it is rare to have one specific area affected to cause unilateral symptoms)
- Nerve root - usually unilateral
- Peripheral nerves - symmetrical + distal (glove and stocking)
- NMJ - Symmetrical
- Muscles - myopathies are usually proximal and symmetrical
What does the onset of symptoms suggest about the cause of the symptoms?
- sudden
- days/weeks
- months
- years
- Sudden - vascular
- Hours/Days/weeks - Inflammation/Infection
- Months - Neoplastic
- Years - Neurodegenerative
Monroe-Kellie doctrine (raised ICP)
- The cranium, enclosing the brain, forms a fixed space comprising three components : blood, CSF, and brain tissue
- These components remain in a state of dynamic equilibrium, therefore any increase in any one of them results in a compensatory decrease of the other two
- Once the other compartments have reached their point of maximum compensation, any further increase in the size of one results in increased intracranial pressure.
What is the corpus callosum?
- bundle of nerve fibers that connects the right and left sides of the brain
- (largest white matter structure in the brain - think MS affects myelin)
- responsible for allowing the two hemispheres to communicate with each other
Trigeminal nerve - meckles cave, neurovascular bundle
- young person with TN - tumour in Meckle’s cave?
NEED TO EDIT THIS CARD
Pupillary light reflex and accommodation reflex - Dr Matt and Dr Mike VIDEO
Video: https://www.youtube.com/watch?v=j9pwDAcb-U0
Visual field defects and optic nerve pathway VIDEO
Video: https://www.youtube.com/watch?v=2ZbFBlwWm3Q
Describe how light entering the eye ends up as electrical signals travelling along the optic nerve
- Photoreceptors (rods and cones) in the retina are stimulated by photons of light entering the eye
- Light-sensitive surface membrane proteins (eg. rhodopsin) of these cells are stimulated to propagate second messenger responses which convert light energy into electrical signals
- The photoreceptors synapse with retinal bipolar cells, which in turn transmit these signals to retinal ganglion cells
- The retinal ganglion cells converge at the optic disc, forming the optic nerve
Describe the pathway of signals from the optic nerve exiting the eye to the lateral geniculate nucleus
- The optic nerve exits the eye, travelling through a defect in the lamina cribrosa of the sclera
- The optic nerve travels through the bony orbit and enters the middle cranial fossa through the optic canal
- Once inside the skull, the optic nerve travels along the floor of the middle cranial fossa, through the medial aspect of the cavernous sinus –> left and right optic nerves then converge at the optic chiasm
(The optic chiasm is located directly above the sella turcica of the sphenoid bone, the pituitary gland projects down immediately behind the chiasm) - The optic tracts extend from the chiasm to the thalamus. Here, afferent sensory nerves from the eye synapse with the second-order sensory neurones at the lateral geniculate nucleus in the thalamus
Describe the pathway of signals from the lateral geniculate nucleus to the occipital visual centre and how we make sense of this information
- include the structure responsible for retinal image processing
- From the lateral geniculate nucleus in the thalamus, the sensory nerves form optic radiations, which loop through the parietal lobe or thought the temporal lobe (Meyer’s loop)
(radiations travelling through the parietal lobe correspond to the upper half of the retina/lower visual field, while the radiations travelling through Meyer’s loop in the temporal lobe correspond to the bottom half of the retina/upper visual field) - The optic radiations terminate in the calcarine sulcus of the occipital lobe, where the cortical visual centre is situated and images from both eyes are finally collated and a final image is formed
(calcarine sulcus is responsible for retinal image processing) - This image is inverted - as a consequence of this, the brain has to re-invert the image so that information is correctly oriented in space
- From the occipital visual centre, signals are sent to the frontal, parietal and temporal lobes to further make sense of the input information (e.g. reading/facial recognition)
What blood vessel supplies the optic nerve?
Ophthalmic artery
Basic eye anatomy VIDEO
What makes up:
- outer coat (protective)
- middle coat (vascular/nutritive)
- inner coat (retina)
- what fluid is in the posterior chamber and what fluid is in the anterior chamber?
- Outer coat (protective): sclera + cornea
- Middle coat (vascular/nutritive): choroid layer + ciliary body + iris
- Inner coat (retina): pigment layer + neural layer (contains photoreceptors)
- posterior chamber - vitreous humour
- anterior chamber - aqueous humour
(video: https://www.youtube.com/watch?v=D-kVWke0CD0 )
The retina - basic anatomy VIDEO
- function of rods and cones
- what does the fovea contain
- Rods: allow us to see in dim light
- Cones: allow us to see colour
- Mostly rods apart from in the fovea, where there are no rods, but lots of cones
(video: https://www.youtube.com/watch?v=fZDAwXh54is )
Nerve supply of extraocular muscles
All supplied by CN III (oculomotor nerve), except…
- SO 4
- LR 6
Why there is an increased optic cup to disc ratio in glaucoma?
- In glaucoma, there is a smaller neuroretinal rim, therefore the ratio oft he cup to disc is bigger
- neuroretinal rim represents the tissue of the optic nerve head where nerve fibres enter the eye (in glaucoma there is damage to these fibres)
Basic pain pathway
- Nociceptors (pain receptors) at the end of nerves detect damage to tissues
- Nerve signals are transmitted along the afferent nerves to the spinal cord
- Signal then travels in CNS: up spinal cord (spinothalamic tract and spinoreticular tract) to the brain (thalamus) where it is interpreted as pain (somatosensory cortex)
Two types of nerve fibres
- C fibres (unmyelinated) - transmit signals slowly and produce dull and diffuse pain sensations
- A-delta fibres (myelinated) - transmit signals fast and produce sharp and localised pain sensations
Further type A:
(Type 1 (slow twitch) - long, aerobic activities)
(Type 2 (fast twitch) - short, fast bursts of activity, anaerobic)
Label the cerebral arteries.
- Which arteries supply anterior brain
- Which arteries supply posterior brain
- Blood is delivered to brain through 4 main arteries, two internal carotid arteries (anterior supply), and two vertebral arteries (posterior supply to the brain)
- Anterior supplied by internal carotid arteries which form the ACA and MCA
- Anterior connects with Posterior via posterior communicating artery
- Posterior supplied by vertebral arteries which combine to form the Basilar artery
(The brain also has a venous drainage system which drain into the venous sinuses)
What are the 3 main arteries that form the Circle of Willis?
- What is function of Circle of Willis?
- Formed by basilar artery, internal carotid artery, and middle cerebral artery
- Safeguards the oxygen supply from interruption by arterial blockage
- For example, if there is stenosis in one artery then other source arteries to the Circle of Willis can provide an alternative blood flow (collateral circulation)
The hippocampus and amygdala are both parts of the limbic system, what are their functions?
Limbic system = a set of brain structures that controls emotions, memory, and behaviour
.
Hippocampus:
- memory centre (forms and stores long term memories)
- spatial awareness/orientation
- neurogenesis occurs here (key brain structure for learning new things)
.
Amygdala:
- plays a role in how we experience emotions (like fear, anger, anxiety, pleasure)
- attaches emotional content to memories
- fight or flight response occurs here
In what brain structure does neurogenesis occur? (key brain structure for learning new things)
Hippocampus
In what brain structure does the fight or flight response occur?
Amygdala
Functions of the frontal lobe, parietal lobe, occipital lobe, and temporal lobe
FRONTAL LOBE
- controls thinking and personality
- voluntary movement (primary motor cortex)
- short-term memory
- planning and problem solving (higher executive function)
.
PARIETAL LOBE
- sensory info (touch, pain, temperature, pressure)
- spatial relationships
- reading/writing
.
OCCIPITAL LOBE
- Primary visual cortex (visual processing centre)
- connects images to memories
.
TEMPORAL LOBE
- sensory info (hearing, smell, and taste)
- primary auditory cortex (can understand what we hear)
- recognising language and forming memories
- making sense of complex visual info (faces and scenes)
- (contains the hippocampus)
Which lobe is the somatosensory cortex (controls touch, temperature, position, vibration, pressure, and pain info) located in?
Parietal
Which lobe is the visual cortex (making sense of visual info and oobejct recognition) located in?
Occipital
Which lobe is the auditory cortex (processing of hearing info) located in?
Temporal
Which lobe is the gustatory cortex (processes taste and flavour) located in?
Frontal
How would you test the function of each of the lobes of the brain?
- FRONTAL - tasks requiring executive function (planning, decision-making, problem-solving, and working memory) such as complex problem-solving scenarios
- PARIETAL - two-point discrimination
- OCCIPITAL - visual fields, colour recognition, identifying objects
- TEMPORAL - ask pt to recall stories, identify sounds, or recognise familiar faces
Vascular territories
cross-section view of spinal cord
Meningitis - Pathophysiology (invasion –> survival –> replication and tissue damage)
- Invasion
- Pathogen colonises nasopharynx
- pathogen then invades bloodstream
- bacteria then cross the blood-brain barrier (BBB) - Survival
- bacteria evades immune responses to survive and proliferate
- various mechanisms - antigenic variation, inhibition of complement activation, intracellular survival inside phagocytes, production of immunomodulatory molecules, and formation of biofilms - Replication and Tissue damage
- bacteria multiply in the subarachnoid space - leading to increased ICP
- Inflammatory response leads to damage of neuronal tissue and the BBB - results in symptoms
Why does raised ICP cause papilloedema (swelling of the optic disc)?
- sheath around optic nerve is connected with the subarachnoid space
- therefore, raised CSF pressure flows into the optic nerve sheath –> increasing the pressure around the optic nerve behind the optic disc causing the optic disc to bulge forward
