wk 5 neurology Flashcards
the immune system defences
- Innate defences
o Surface barriers – skin, mucous membranes
o Internal defences – phagocytes, fever, NK cells, antimicrobial proteins, inflammation - Adaptive defences
o Humoral immunity – B Cells
o Cellular immunity – T cells
phagocytes in the CNS
Microglia can cause trouble in chronic CNS inflammatory states
- Implicated in everything from depression to dementia
- No treatments for these conditions
Fever in the CNS
Uhthoff’s phenomenon
- Decompensation of CNS when patient is hot
- Commonly seen in MS but also seen in other chronic conditions
inflammation in the CNS
- Inflammation = chemokines and cytokines
- Bc/ most cytokines are neurotransmitters/neuromodulators
- So have impact on function of neurones
- When present in unregulated way – DELIRIUM
- Caused by infection in the CNS or by infectious states outside CNS (eg UTI if patient is old and has a leaky BBB)
- So confusion is a common presentation
Multiple Sclerosis Definition
Chronic inflammatory and degenerative disease of the central nervous system
Characterised pathologically by…
- Inflammation
- Demyelination +/- variable extent of remyelination
- Neuroaxonal injury/loss
- astrogliosis
progression of MS
Majority of patients begin with relapses and remittance
Overtime perhaps bc of ageing and failure of repair system
- Accumulate disabilities
Then slowly progress and get worse over time
Occasionally patients start in progressive stage
- ~15%
- Don’t have relapses
- Called PRIMARY PROGRESSIVE MS
Diagnosis for MS
- history/ examination
- lumbar puncture
- McDonald Criteria
MRI
- T2 weighted
- patches of inc. signal in white matter (gliosis)
- particularly around ventricles
what to look for in MS lumbar puncture
- if oligoclonal bands present
- these bands represent non-specific antibodies in the CSF
- Since immune system tends to leave the CNS alone - persistent products of the immune system in the CSF suggest a leaky BBB
- seen in ~95% of MS
pathology of relapses in MS
- relapse driven by focal areas of BBB leakage
- immune system gets in and there’s tissue damage to myelin and axons
- inflammation settles down and tissue is repaired with scarring
- results in a FOCAL AREA often in white matter in scans (also present in grey)
- if in a part of brain, we call “clinically eloquent” results in symptoms and a clinical relapse
definition of consciousness
Sentience (awareness) of internal or external existence
3 main stages of consciousness
- conscious wakefulness
- drowsiness
- deep sleep/ general anaesthesia
sleepwalking and complex partial seizures
o patient appears to be awake – complex behavioural activities
o high levels of arousal
o consciousness is low
REM sleep
o Low levels of arousal
o Vivid conscious experience going on
Coma
o Loss of sleep-wake cycle
o Lack of awareness
o No purposeful actions
PVS - persistent vegetive state
o Sleep-wake cycles present
o No purposeful behaviours
o No awareness
minimally conscious state
o Sleep wake cycles
o Partial awareness and actions
“locked in syndrome”
o Commonly in Brainstem strokes
o Sleep-wake cycles
o Maintained awareness
o Motor behaviour limited to eye movements from the midbrain
o Brain intact but unable to move or sense anything
sleep-wake cycling - 3 componenets
cycadean rhythm (c process)
homeostasis
cognitive pressure
cycadean rhythm (c process)
- spomntaneous 24 hr cycles
- measured through…
melatonin levels
> Master clog in superchiasmatic nucleus to detect light
> In presence of light melatonin switched off – peaks at night
blood cortisol levels
body temperature
homeostasis (s process)
- Get the sense of feeling sleepy building up over time
- Sleep to restore homeostatic balance
- “sleep urge”
cognitive pressure
Top down influences have impact on whether you sleep well
what is sleep pressure
- the gap between the cycadean rhythm(c) and homeostais (s)
- Increased sleep pressure in early afternoon as c line drops but s continues to increase
- If you don’t sleep for a night you get sleep deprivation which creates a big diff. in c and s processes = sleepy, eventually pass out
mechanisms of the sleep wake cycle
Hypothalamus involved as found by scientist looking at damaged areas
- Damaged to front of hypothalamus – insomnia
- Damage to back of hypothalamus – zombie-like, awake but not fully conscious
the ventrolateral pre-optic area (VLPO)
- Important in sending us to sleep
- Manly inhibitory GABA neurones
- Project to number of centres involved in arousal
Tuberomammillary nucleus
- Switches on histamine to wake us up
- Cortex is switched on
- Posterior lateral hypothalamus secretes orexin/hypocretin
- This switches on a number of centre releasing dopamine an Ach
o Mainly nicotinic receptors
narcolepsy
- Patients have sudden onset of sleep
- overwhelming daytime drowsiness
- Low level of CSF Orexin
parasomnias
disorders of sleep
- to measure use stage 1-4 (1 being most alert)
NREM parasomnias
- In stage 3 & 4
- Sleep walking, confusional arousals, night tremors
REM parasomnias
- REM sleep behaviour disorder
- Problems with system that’s normally present to inhibit corticospinal tracts to act out the experiences were having in consciousness during our dreams
- Patients act out their dreams
- Can be used to indicate alpha-synucleinopathies eg parkinons disease
- System can fail by not disengaging when people wake up
o Unable to move limbs when you wake up “sleep paralysis”
o This is a benign syndrome
Arousal - places in the brain
-Posterolateral hypothalamus (wake up switch )
o Rare
o diancephalon
-Reticular activating system (Ach – nicotinic)
o how cigs. Work
o brainstem
-VTA (mesolimbic and mesocortical DA)
o Switches on prefrontal cortex and limbic structures
o brainstem
-Both thalami intact (the railway station)
o Damage to both thalami
o Seen in stroke if both thalami supplied by single artery
-Neocortex intact
o Global cortex
vestibular function
- Perception of position and motion
o Static gravitational orientation
Perception of relationship to gravitational field – whether you’re upright, sideways etc
Meaningless without gravity ie in space
o Motion in space
Perception of motion relative to environment
Essentially acceleration
• Change in speed/ direction rather than speed itself
2 forms of motion sense
- Rotations
o Turning around on a spot - Linear translations
o Moving in a straight line from one point to another
human ear components
- Outer ear o The pinna o The auditory canal o Tympanic membrane - Middle ear o Small air-filled chamber beyond the tympanic membrane o 3 small bones – the ossicles - Inner ear o In the bony labyrinth of the temporal bone o Deeper inside the skull than ^
connections between auditory and vestibular systems
- Receptor organs in the ear
o In the temporal lobe
o In a convoluted chamber called the bony labyrinth
o In the membranous labyrinth within the bony labyrinth - Initial conversion of sensory info into neurological form in the inner ear
- Info goes to CNS via the common nerve VIII cranial nerve (vestibular cochlear nerve)
the membranous labyrinth
- Within the bony labyrinth
- A continuous membrane creates the MEMBRANOUS LABYRINTH
- Pink part is the membranous labyrinth – cochlea duct not whole of cochlea
Labyrinths and fluid
- The bony labyrinth contains fluid – the perilymph
- The membranous labyrinth – the endolymph
- The diff. between these 2 fluids is important to how these parts work
The receptor Organs
Within the membranous labyrinth are rec. organs of auditory and vestibular functions - THE VESTIBULE o A large central area - The utricle & saccule are adjacent to the vestibular – out-pocketing’s o Vestibular functions - Semi-circular canals o Vestibular functions - Cochlea – cochlea duct o Deals with hearing (auditory)
major components of inner ear
- Vestibule – containing utricle and saccule
- 3 semi-circular canals - anterior, posterior, horizontal
- Spiral shaped cochlea
- Axons from sensory regions that form VIII nerve heading towards brain
Ossicles of the mid ear
Malleus
Incus
stapes
hearing process sound waves entry -> cochlea
1- Sound waves enter the auditory canal towards the tympanic membrane
2- Tympanic membrane receives pressure waves and vibrates according to them
3- Vibration transmitted to the ossicles
4- Ossicles transmit vibration to oval window of vestibule
a. Below the oval window there’s the round window
5- Transmitted into fluid of membranous labyrinth
6- Then into the fluid that circulates the cochlea
hearing process cochlea transmission -> electrical signals arrive at the brainstem
7- Cells in cochlea convert vibrations into electrical signals
8- Cochlea electrical signals transmit along axons of the VIII cranial nerve towards CNS
9- Vestibulocochlear nerve heads towards brainstem and joins it a medullary-pontine junction
- Superior and inferior vestibular nerves form the vestibular ganglion
- Cochlear nerve joins the vestibular nerve to form the vestibulocochlear nerve
10- electrical signals arrive at brainstem and firstly go into cochlear nuclei at brainstem
hearing process auditory info ascends brainstem -> pathways of cochlea nuclei
11- auditory info ascends the brainstem to the thalamus and the cerebral cortex
12- electrical signals arrive at cochlear nuclei (plural) of brainstem
a. ventral nuclei – anteriorly
b. dorsal nucleus – posteriorly
13- 2 pathways from cochlea nuclei
a. Dorsal cochlear nucleus
i. quality of sounds
ii. picking apart tiny frequency differences which allows differentiation of similar sounds
b. ventral cochlear nucleus
i. minute differences in timing and loudness of the sound in each ear so sound can be localised
pathways from ventral cohclear nucleus
- axons go to o superior olive - then to… o inferior colliculus o medial geniculate body o cerebral cortex
pathways from the dorsal cochlear nucleus
- axons go directly to…
o inferior colliculus
o medial geniculate body
o cerebral cortex
bilateral nature of hearing
2 auditory cortices on each side of the brain
Info from each cochlea goes to both sides of the brain -BILATERAL
There are efferent pathways from cerebral cortex and down through the auditory pathways to influence hearing and its processing
how cells in the cochlea convert vibrations to electrical signals - basic anatomy
cochlea is within the bone
the canals within it are in the bony labyrinths
the middle of the canal is a membranous segment – the membranous labyrinth
middle portion = cochlear duct
scala tympani and scala vestibuli are outside membrane in the bony labyrinth
3 chambers in the spiral part of the cochlea
-called scalae o scala vestibuli abuts the oval window the stapes transmits vibrations into this chamber o scala tympani abuts the round window then go back out to the round window CONTAIN PERILYMPH
membranes in the cochlea
- Reissner’s membrane
o Seperates cochlear duct from scala vestibuli - Basilar membrane
o Separates cochlear duct from the scala tympani
o Relatively stiff
o Supports Organ of Corti (core part)
o Stiffness of membrane determines the mechanical wave propagation properties of the cochlear as transmissions are transmitter around the channels in the cochlear spiral
The organ of corti
- Within the cochlear duct
- A sensory epithelium
- A cellular layer on basilar membrane
- Hair cells
o Topped with hair-like structures - Give rise to axons that from the nerve fibres that take sensory info away from this organ
how hair movements generate electrical signals in the scala
- Waves in the scala fluid cause movement to the basilar membrane
- Causes movement of the hair cells
- Hair cells produce electrical responses
- Their axons form part of the VIII nerve
how/why the stiffness and width of the basilar membrane varies along the cochlea
- Stiffest near start of oval window
- Allows diff parts of BM respond to diff frequencies
- Coiling enhances low freq. waves as they travel along the cochlea
- Highest freq. near oval window
- Lowest freq. near other end
what your brain needs to know to interpret position and movement
- Static gravitational orientation
- Perception of motion in space
oRotations
oLinear translations - Visual, vestibular, somatosensory
oIf these 3 all match = brain happy & feel well
oIf don’t match = nausea
Eg travel sickness
why is vestibular function critical in position and movement
2 components reflecting
-The semi-circular canals – rotation
-The otoliths – linear translations
Actually, angular and linear acceleration – humans aren’t good at detecting constant speed
what helps us adapt to living in a 3D world
- 3 semi-circular canals
- In a non-orthogonal relationship – multiples of 30 degrees not 90 degrees
