neurology and neuroscience Flashcards
what are the 4 main characteristics of the cerebral cortex?
covers entire surface (very thin)
together with deep nuclei (such as in the thalamus) contains grey matter
highly folded with gyri and solci
organised into lobes
what is the microscopic organisation of the cerebral cortex?
6 layers
(I closest to surface, VI deepest)
also columns
how are regions of the cortex classified?
based on cytoarchitecture - cell size, space/packing density, layers
often correlates with function
what are the functions of the frontal lobe?
regulate and initiate motor function
language
cognitive function - e.g planning
attention
memory
what are the functions of the parietal lobe?
sensation - touch, pain
sensory language aspects
spatial orientation and self perception
what are the functions of the occipital lobe?
visual input
what are the functions of the temporal lobe?
processing auditory information
emotions
forming memories
what are the functions of the limbic lobe?
learning
memory
emotion
motivation and reward
what are the functions of the insular cortex (under lateral fissure between temporal and frontal lobe)?
concerned with visceral sensations
autonomic control, and interoception, auditory processing, visual-vestibular integration
(inputs coming in from visual pathway and balance organs)
what is grey matter (outside)?
neuronal cell bodies and glial cells
what is white matter(inside)?
Myelinated neuronal axons arranged in tracts
neuronal cell bodies make their way out of brain to spinal cord/ peripheral nerves
what are the 3 main types of white matter tract?
association, commissural and projection fibres
which cortical areas do association fibres connect?
connect areas within the same hemisphere
which cortical areas do commissural fibres connect?
connect homologous structure in left and right hemispheres (cross the midline)
which cortical areas do projection fibres connect?
connect cortex with lower brain structures (e.g. thalamus, brain stem and spinal cord)
what do short association fibres/U fibres connect?
adjacent cortical regions (usually same lobe)
what are the 4 types of long association fibres?
superior longitudinal fasciculus
arcuate fasciculus
inferior longitudinal fasciculus
uncinate fasciculus
what two lobes does the superior longitudinal fasciculus connect?
frontal and occipital
what two lobes does the arcuate fasciculus connect?
frontal and temporal
what two lobes does the inferior longitudinal fasciculus connect?
temporal and occipital
what two lobes does the uncinate fasciculus connect?
anterior frontal and temporal
what is the corpus callosum an example of?
commissural fibres (connects left and right hemispheres)
what is the structure inferior to the corpus callosum that connects the left and right hemispheres?
anterior commissure
how are projection fibres arranged?
make way down from cortical layers down towards deeper structures
converge through internal capsule between thalamus and basal ganglia
go down into spina cord to go out to structures such as limbs
what is the function of afferent projection fibres?
bring information to brain from outside world via spinal cord and cortex
sensory impulses
what is the function of efferent projection fibres?
take information out from the cortex down to brain stem, spinal cord and out
motor impulses
what are the afferent and efferent projection fibres collectively known as?
corona radiata
what are the 3 differences between primary and secondary/association cortices?
primary: predictable function
secondary: function less predictable
primary: organised topographically
secondary: not organised topographically
primary: symmetry between left and right
secondary: left-right symmetry weak or absent
what is the function of the primary motor cortex in the frontal lobe?
controls fine, discrete, precise voluntary movements
provides descending signals to execute movements
what is the function of the supplementary cortex of the frontal lobe?
involved in planning movements (e.g. externally cued - the plan to move an arm to pick up an object, for example)
what is the function of the premotor cortex of the frontal lobe?
involved in planning complex movements (e.g. internally cued - the plan to co ordinate fibres to generate speech by making muscles contract, for example)
what is the function of the primary somatosensory cortex in the parietal lobe?
processes somatic sensations arising from receptors in the body
(e.g. fine touch, vibration, two-point discrimination, proprioception, pain and temperature)
what is the function of the somatosensory association cortex in the parietal lobe?
interpret significance of sensory information, e.g. recognizing an object placed in the hand.
Awareness of self and awareness of personal space
what is the function of the primary visual cortex in the parietal lobe?
processes visual stimuli - input from retina reaches here
what is the function of the visual association cortex in the parietal lobe?
gives meaning and interpretation of visual input
what is the function of the primary auditory cortex in the temporal lobe?
processes auditory stimuli
what is the function of the auditory association cortex in the temporal lobe?
gives meaning and interpretation of auditory input
what are the functions of the prefrontal cortex?
attention
adjusting social behaviour
planning
personality expression
decision making
where are Broca’s and Wernicke’s areas found?
left hemisphere only (association/secondary cortex)
what is the function of Broca’s area?
production of language (motor region - i.e motor commands and movement to generate speech)
what is the function of Wernicke’s area?
understanding of language (sensory region - i.e information about language is understood)
what may a frontal lobe lesion cause?
personality changes
socially inappropriate behaviour
what may a parietal lobe lesion cause?
contralateral neglect
lesion in right hemisphere causes lack of awareness of self and extrapersonal space on the left side
what are the 2 types of temporal lobe lesion?
lateral and medial
what may a temporal lobe lesion cause?
agnosia - inability to recognise things
what is the effect of a lesion to Broca’s area?
expressive aphasia - poor production of speech, comprehension intact
what is the effect of a lesion to Wernicke’s area?
receptive aphasia - poor comprehension of speech, production intact
what structure connects Broca’s and Wernicke’s areas?
arcuate fasciculus
what is the effect of a lesion on the primary visual cortex?
blindness in the corresponding part of the visual field
what is the effect of a lesion on the visual association cortex?
deficits in interpretation of visual information e.g. prosopagnosia: inability to recognise familiar faces or learn new faces (face blindness)
how can cortical function be assessed?
positron emission tomography (PET)
functional magnetic resonance imaging (fMRI)
electroencephalography/magnetoencephalography (EEG/MEG)
how does a positron emission tomography (PET) work?
track blood flow directly to a brain region using radioactive label (e.g radioactive glucose) and then asking the person to undertake a task
obvious risk of using radioactive substance
how does functional magnetic resonance imaging (fMRI) work?
amount of blood oxygen in a brain region
relative use of oxygen and determines that increase of oxygen use implies increased activity in that area
what is temporal resolution?
how quickly can it be ascertained that things are changing
what is spatial resolution?
how detailed a picture can be obtained at the level of individual cells vs groups of cells etc.
how does an EEG work?
measures electrical signals produced by brain using electrodes in a standard arrangement (no need to use all electrodes, can only put electrodes on areas that are relevant to the function being tested)
how does an MEG work?
measures magnetic signals produced by brain
where is an EEG often used and why?
epilepsy, sleep disorders
can look at rhythms being produced during sleep/wakefulness
can look at onset of events that correlate with clinical symptoms (e.g seizure)
how are somatosensory evoked potentials used to assess cortical function?
stimulus to peripheral nerve
series of waves that reflect sequential activation of neural structures along somatosensory pathways
when are somatosensory evoked potentials used to assess cortical function?
e.g spinal cord injury
when checking where along the pathway the injury occurred - if fully intact, signal will travel up to CNS, then thalamus and sensory cortex
when are transcranial magnetic stimulations (TMS) used?
assess the functional integrity of neural circuits
uses electromagnetic induction to stimulate neurons
how does a transcranial magnetic stimulation (TMS) work?
stimulates brain and assesses signal as it arrives at the effector (almost the opposite of somatosensory evoked potentials)
relies on production of changing magnetic fields/changing electric fields giving rise to magnetic fields by using a magnetic coil to stimulate areas of the brain
what conditions may transcranial magnetic stimulation (TMS) also be used to treat and why?
epilepsy
tinnitus
migraine
depression
all are associated with firing of cortical neurones - magnetic pulses can also modulate overactive brain regions by interfering with transmission
what is transcranial direct current stimulation (tDCS) and how does it work?
brain stimulation, affects cortical function
uses low direct current over scalp to increase or decrease neuronal firing rates
used in chronic pain and epilepsy treatment
how can the structure of the brain be assessed?
diffusion tensor imaging (DTI)
DTI with tractography
why is assessing brain structure important?
understanding connection between brain regions
e.g if two linked regions are functioning individually but the pathway between them is damaged
how does diffusion tensor imaging (DTI) work?
based on diffusion of water molecules
what is diffusion tensor imaging (DTI) with tractography?
3D reconstruction to assess neural tracts
why is the brain vulnerable if blood supply is impaired?
high metabolic demands therefore extensive vascular supply needed for function
(uses around 20% of all cardiac output, oxygen consumption, 2/3 of liver glucose)
what arteries supply the brain?
vertebral
internal carotid
what is the path of the common carotid artery?
branches from brachiocephalic artery, runs up side of the neck
at about the level of laryngeal prominence (Adam’s apple), common carotid divides into internal carotid and external carotid (supplies structures of the face)
what is the path of the internal carotid artery?
branches off from common carotid
carries on with no branches, passes through base of skull (so-called carotid canal) and into cranial cavity
what is the path of the vertebral artery?
first branch off subclavian artery
goes upwards posteriorly through transverse foramen of survival vertebrae ( protected by bone architecture)
passes through foramen magnum at base of skull to reach cranial cavity
what is the arrangement of vessels at the base of the brain called?
circle of Willis, vessels are adjoined
what is the structure of the circle of Willis?
posterior - 2 vertebral arteries that come up through foramen magnum and fuse to form basilar artery (base of pons)
basilar artery divides into 2 posterior cerebral arteries
internal carotid branches into:
- middle cerebral artery (main)
- anterior cerebral artery
anterior communicating artery between anterior cerebral arteries in the long latitudinal fissure anteriorly
posterior communicating artery between posterior cerebral artery and middle cerebral artery
what is the advantage of the arrangement of the circle of Willis?
blockage in anterior carotid can cause atherosclerotic build up in the common carotid, especially where it divides
theoretically there is a chance of compensatory flow from the other side - can flow through communicating arteries and supply both sides of the brain
why is the advantage of the arrangement of the circle of Willis not always effective?
not universal
compensation between posterior circulation and anterior circulation is often weak because posterior communicating arteries are very thin
how does blood exit the brain?
cerebral veins in brain itself
venous blood drains in the cranial cavity via dural sinuses in the dura mater (outer meningeal layer)
internal jugular vein
what is the structure of the dural sinuses?
dura mater is made up of two layers that are usually closely pressed together
when these layers separate they form the venous sinuses
how does venous blood drain through the sinuses?
venous blood drains in the cranial cavity via dural sinuses in the dura mater (outer meningeal layer)
drains through superior sagittal sinus, blood drains down the back of the head
large cerebral vein (vein of Gaylan) drains down “straight” sinus to confluence formed by superior sagittal sinus and inferior sagittal sinus on lower edge of falx cerebri
reaches occipital area (occipital conflicts of the sinuses)
drains transversely then down through sigmoid sinus going down through jugular frame (foramen in base of skull)
sigmoid sinus into internal jugular vein going back to the heart
what are the 4 types of intercranial haemorrhage?
extradural
subdural
subarachnoid
intracerebral
what causes extradural haemorrhage?
nearly always trauma
main artery supplying dura is right behind pterion so trauma is likely to rupture this artery
what is the effect of an extradural haemorrhage?
acute onset arterial bleed - high pressure
strips dura away from inside of skull and builds pressure within intracranial cavity
puts pressure on brain stem and eventually closes down cardiorespiratory centres
why are subdural bleeds dangerous and how can the potential effects be prevented?
effects are slightly delayed (as low pressure venous blood)
for head injuries with loss of consciousness patients are kept for observation overnight in case symptoms start to show
what causes subarachnoid haemorrhage?
circle of Willis has weaknesses in blood vessels called aneurysms (generally congenital)
these may burst (especially if hypertensive) and produces subarachnoid bleed
people with which pre-existing condition are more at risk of intracerebral haemorrhage?
hypertension
what is an intracerebral haemorrhage?
bleed in substance of brain itself
what is the definition of a stroke/cerebrovascular accident?
rapidly developing focal disturbance of brain function of presumed vascular origin and of >24 hours duration
what are the two main types of stroke and how common are they?
thrombo-embolic (85%)
haemorrhagic (15%)
what is the definition of a transient ischaemic attack (TIA)?
rapidly developing focal disturbance of brain function of presumed vascular origin that resolves completely within 24 hours
what is the definition of an infarction?
degenerative changes which occur in tissue following occlusion of an artery
what is the definition of cerebral ischaemia?
lack of sufficient blood supply to nervous tissue resulting in permanent damage if blood flow is not restored quickly
what could a transient ischaemic attack indicate?
risk of stroke further on
what is the difference between ischaemia and anoxia/hypoxia?
anoxia/hypoxia only refers to oxygen deficit in blood
ischaemia refers to loss of all required metabolites in blood (e.g. glucose etc.)
what is thrombosis?
formation of a blood clot (thrombus)
what is an embolism?
plugging of small vessel by material carried from larger vessel
e.g. thrombi from the heart or atherosclerotic debris from the internal carotid
what are the risk factors for stroke?
age (inefficiency of vascular system and brain itself)
hypertension (risk of haemorrhage)
cardiac disease (formation of clots due to inefficient vascular or cardiac function)
smoking (effect on vasculature)
diabetes mellitus (effect on vasculature)
what is the perfusion field of the middle cerebral artery?
much of the brain’s lateral surface
subcortical deep structures of the brain
what is the perfusion field of the anterior cerebral artery?
midline structures all the way back
perfuses all the way back to parietal-occipital fissure
what is the perfusion field of the posterior cerebral artery?
occipital lobe
inferior part of temporal lobe
why are perfusion fields important?
can judge where in the brain a stroke might have occurred
what symptoms indicate an anterior cerebral artery issue?
paralysis of contralateral structures - leg > arm, face (since arm and face are mostly supplied by middle cerebral artery)
disturbance of intellect, executive function and judgement (abulia - breakdown in frontal lobe function)
loss of appropriate social behaviour (damaged frontal lobe)
what symptoms indicate a middle cerebral artery issue?
“classic stroke”
middle cerebral artery supplies deep motor structures therefore contralateral hemiplegia: arm > leg
sensory cortex also affected
- contralateral hemisensory deficits
- hemianopia
- aphasia (L sided lesion)
- if on the left side - may affect speech (Broca’s and Wernicke’s)
what symptoms indicate a posterior cerebral artery issue?
supply to occipital lobe is cut off so-
homonymous hemianopia
visual agnosia
what are the broad principles of motor control?
hierarchical organisation
higher order areas of hierarchy are involved in more complex tasks
(e.g. programme and decide on movements, coordinate muscle activity)
lower level areas of hierarchy perform lower level tasks (e.g. execution of movement)
what is functional segregation?
motor system organised in a number of different areas that interact to control different aspects of movement (voluntary and automatic)
motor cortex receives information from other cortical areas and sends commands to thalamus and brainstem
cerebellum and basal ganglia adjust commands received from other parts of the motor system
brainstem passes commands from cortex to spinal cord
what are the 2 major descending tracts?
pyramidal
extrapyramidal
what are the pathways of the pyramidal tracts?
pass through pyramids of medulla
output neurones in motor cortex, project down to spinal cord or cranial nerve nuclei in brainstem
what are the 2 pyramidal tracts?
corticospinal
corticobulbar`
what do the pyramidal tracts control?
voluntary movements of body and face
what are the pathways of the extrapyramidal tract?
do not pass through pyramids of medulla
upper motor neurones in cortex, lower motor neurones in brainstem nuclei - project down to muscles
what do the extrapyramidal tracts control?
involuntary (automatic) movements for balance, posture and locomotion
what are the 4 extrapyramidal tracts?
vestibulospinal
tectospinal
reticulospinal
`
rubrospinal
where is the primary motor cortex situated?
precentral gyrus, anterior to central sulcus
what does the primary motor cortex control?
controls fine, discrete, precise voluntary movements
provides descending signals to execute movements - final common pathway from brain to lower motor neurones in brainstem/spinal cord
where is the premotor area located?
anterior to primary motor cortex
what does the premotor area control?
involved in planning movements
regulates externally cued movements
e.g. seeing an apple and reaching for it
where is the supplementary motor area located?
anterior and medial to primary motor cortex
what does the supplementary motor area control?
involved in planning complex movements (e.g. internally cued, speech)
becomes active prior to voluntary movement
what is the pathway of the corticospinal tract?
upper motor neurones in primary motor cortex
midbrain contains cerebral peduncle
most fibres decussate, about 10% do not
what is the function of decussated fibres in the corticospinal tract?
make up lateral corticospinal tract
responsible for limb muscle control
what is the function of non-decussated fibres in the corticospinal tract?
make up anterior corticospinal tract
responsible for trunk muscle control
what is the main function of the corticobulbar tract?
principal motor pathway for voluntary movements of the face (and neck)
which nuclei control the function of extraocular muscles (corticobulbar tract)?
oculomotor
trochlear
abducens
which nuclei control the function of jaw muscles (muscles of mastication) (corticobulbar tract)?
trigeminal motor nucleus
which nuclei control the facial muscles (corticobulbar tract)?
facial
which nuclei control the tongue (corticobulbar tract)?
hypoglossal
what is the function of the vestibulospinal (extrapyramidal) tract?
stabilise head during body movements, or as head moves
coordinate head movements with eye movements
mediate postural adjustments
what is the function of the reticulospinal (extrapyramidal) tract?
(most primitive descending tract - from medulla and pons)
changes in muscles tone associated with voluntary movement
postural stability
what is the function of the tectospinal (extrapyramidal) tract?
(from superior colliculus of midbrain)
orientation of the head and neck during eye movements
what is the function of the rubrospinal (extrapyramidal) tract?
(From red nucleus of midbrain - in humans mainly taken over by corticospinal tract)
innervate lower motor neurons of flexors of the upper limb
what are the negative signs of an upper motor neurone lesion?
loss of voluntary motor function
paresis: graded weakness of movements
paralysis (plegia): complete loss of voluntary muscle activity
what are the positive signs of an upper motor neurone lesion?
increased abnormal motor function due to loss of inhibitory descending inputs
spasticity: increased muscle tone
hyper-reflexia: exaggerated reflexes
clonus: abnormal oscillatory muscle contraction
Babinski’s sign
what is apraxia?
disorder of skilled movement
patients are not paretic but have lost information about how to perform skilled movements
disease of which areas (including stroke and dementia) can cause apraxia?
inferior parietal lobe
frontal lobe (premotor cortex, supplementary motor area - SMA)
what are the effects of a lower motor neurone lesion?
weakness
hypotonia (reduced muscle tone)
hyporeflexia (reduced reflexes)
muscle atrophy
fasciculations: damaged motor units produce spontaneous action potentials, resulting in a visible twitch
fibrillations: spontaneous twitching of individual muscle fibres; recorded during needle electromyography examination
what is motor neurone disease (MND)/amyotrophic lateral sclerosis (ALS)?
progressive neurodegenerative disorder of motor system - affects both upper and lower motor neurones
which muscles have trouble contracting in motor neurone disease (MND)?
tongue
intercostal muscles - eventual death caused by lack of respiratory function
upper and lower limb
what are the upper motor neurone signs of motor neurone disease?
spasticity (increased tone of limbs and tongue)
brisk limbs and jaw reflexes
Babinski’s sign
loss of dexterity
dysarthria (difficulty speaking)
dysphagia (difficulty swallowing)
what are the lower motor neurone signs of motor neurone disease?
weakness
muscle wasting
tongue fasciculations and wasting
nasal speech
dysphagia
what are the structures that make up the basal ganglia?
caudate nucleus
lentiform nucleus (putamen + external globus pallidus) – together caudate and putamen are known as the striatum
nucleus accumbens
subthalamic nuclei
substantia nigra (midbrain)
ventral pallidum, claustrum, nucleus basalis (of Meynert)
what are the functions of the basal ganglia?
decision to move
elaborating associated movements (e.g. swinging arms when walking; changing facial expression to match emotions)
moderating and coordinating movement (suppressing unwanted movements)
performing movements in order
what causes Parkinson’s disease?
degeneration of dopaminergic neurons originating in the substantia nigra and projecting to the striatum
what are the symptoms of Parkinson’s disease?
bradykinesia - slowness of (small) movements (doing up buttons, handling a knife)
hypomimic face - expressionless, mask-like (absence of movements that normally animate the face)
akinesia - difficulty in the initiation of movements because cannot initiate movements internally
rigidity - muscle tone increase, causing resistance to externally imposed joint movements
tremor at rest - 4-7 Hz, starts in one hand (“pill-rolling tremor”); with time spreads to other parts of the body
what causes Huntington’s disease?
degeneration of GABAergic neurons in the striatum, caudate and then putamen
chromosome 4,
autosomal dominant
CAG repeat
what are the symptoms of Huntington’s disease?
choreic movements (chorea - dance) - rapid jerky involuntary movements of the body; hands and face affected first; then legs and rest of body
speech impairment
difficulty swallowing
unsteady gait
later stages - cognitive decline and dementia
what is ballism?
sudden uncontrolled flinging of the extremities
usually from stroke affecting the subthalamic nucleus
symptoms occur contralaterally
what are the functions of the vestibulocerebellum?
regulation of gait, posture and equilibrium
coordination of head movements with eye movements
what does damage (tumour) to the vestibulocerebellum cause?
syndrome similar to vestibular disease
leads to gait ataxia, tendency to fall (even when patient sitting and eyes open)
what are the functions of the spinocerebellum?
coordination of speech
adjustment of muscle tone
coordination of limb movements
what does damage (degeneration and atrophy associated with chronic alcoholism) to the spinocerebellum cause?
affects mainly legs
causes abnormal gait and stance (wide-based)
what are the functions of the cerebrocerebellum?
coordination of skilled movements
cognitive function
attention
processing of language
emotional control
what does damage to the cerebrocerebellum cause?
affects mainly arms/skilled coordinated movements (tremor)
speech
what are the main signs of cerebellar dysfunction?
ataxia
- general impairments in movement coordination and accuracy
- disturbances of posture or gait: wide-based, staggering (“drunken”) gait
dysmetria
- inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
intention tremor
- increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
dysdiadochokinesia
- inability to perform rapidly alternating movements (rapidly pronating and supinating hands and forearms)
scanning speech
- staccato, due to impaired coordination of speech muscles
what is an alpha motor neuron?
lower motor neuron of brainstem and spinal cord
occupy anterior/ventral horn of grey matter of spinal cord
what is the function of alpha motor neurons?
innervate extrafusal muscle fibres (fibres with contractile elements) of skeletal muscles (i.e. activation causes muscle contraction)
what is a motor neuron pool?
contains all alpha motor neurons innervating a single muscle
what are the intrafusal muscle fibres?
contain sensory organs which respond to stretch and tension within the muscle - convey information about sensitivity to bring about reflex activity
what is a motor unit?
single motor neuron together with all the muscle fibres that it innervates
smallest functional unit with which to produce force
stimulation of one motor unit causes contraction of all the muscle fibres in that unit
what are the 3 types of motor unit?
slow (S, type I)
fast, fatigue resistant (FR, type IIa)
fast, fatigable (FF, type IIb)
what are the characteristics of a slow motor unit?
smallest diameter cell bodies
small dendritic trees
thinnest axons
slowest conduction velocity
what are the characteristics of a fast motor unit (both fatigue resistant and fatigable?
larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity
how are the 3 different types of motor unit classified?
amount of tension generated
speed of contraction
fatigability
what is the difference between the response to single motor neuron action potential between the 3 types of motor unit?
slow motor unit - very little force, generated slowly
fatigue resistant - 5x more force than slow, generated quickly
fatigable - almost 10x more force than slow, generated quickly
what is the difference between the response to repeated stimulation at a level that evokes maximum tension between the 3 types of motor unit?
fast, fatigable: loses ability to generate force very quickly (within 2 mins)
fast, fatigue resistant - progressively loses ability to generate force gradually over time
slow - generates maximal force for a long time (over 1hr)
where would a slow motor unit be found? why?
muscles used for postural stability
no need to generate large amounts of force, but need to maintain maximal force for many hours
where would a fast motor unit be found? why?
gastrocnemius (calf)
can generate a lot of force quite quickly
what are the two mechanisms by which the brain regulates the force that a single muscle can produce?
recruitment
rate coding
how does recruitment work in regulating muscle force?
motor units not randomly recruited - order governed by “size principle”
smaller units recruited first (generally slow twitch units)
as more force is required, more units are recruited
allows fine control (e.g. when writing), under which low force levels are required
how does rate coding work to regulate muscle force?
motor unit can fire at a range of frequencies
slow units fire at a lower frequency - as firing rate increases, force produced by the unit increases
summation occurs when units fire at frequency too fast to allow muscle to relax between arriving action potentials
what is a neurotrophic factor?
are a type of growth factor
prevent neuronal death
promote growth of neurons after injury
(if a muscle retains arterial supply but has its nerve supply cut, muscle will start to waste due to lack of neurotrophic factors)
how can it be determined that the motor neurone has some effect on the properties of the muscle fibres that it innervates?
motor unit and fibre characteristics are dependent on the nerve which innervates them
if a fast twitch muscle and a slow muscle are cross innervated, the soleus becomes fast and the FDL becomes slow
what is the most common change from one type of neurone to another?
IIB to IIA (fast fatigue to fatigue resistant)
most common following training
when is a change from a type I neurone to a type II neurone possible?
in cases of severe deconditioning or spinal cord injury
microgravity during spaceflight results in shift from slow to fast muscle fibre types
what kind of change in motor units/muscle fibres occurs during the ageing process?
associated with loss of type I and II fibres (preferential loss of type II fibres)
therefore larger proportion of type I fibres in aged muscle (evidence from slower contraction times)
what is a reflex?
automatic response to a stimulus
involves a nerve impulse passing inward from a receptor to a nerve centre and then outward to an effector (as a muscle or gland) without reaching the level of consciousness
magnitude and timing determined respectively by intensity and onset of stimulus
how do reflexes differ from voluntary movements?
cannot be stopped once they are released
what is the path of the monosynaptic (stretch) reflex?
stimulus at sensory receptor
transmitted through sensory neuron to spinal cord (CNS)
motor neuron carries impulse to effector
different motor neuron carries impulse to antagonist
what is the Jendrassik manoeuvre?
pulling against locked fingers when having patellar tendon tapped - reflex becomes larger
work by reducing amount of inhibition that brain and upper regions of CNS exert over reflexes under normal conditions
why is the Jendrassik manoeuvre important?
reflexes are thought of as being entirely automatic and stereotyped behaviours in response to stimulation of peripheral receptors
Jendrassik manoeuvre (also things like clenching teeth and making a fist) prove that reflexes can be influenced
what is the role of higher centres of the CNS in the stretch reflex?
exert inhibitory and excitatory regulation
inhibitory - dominates in normal conditions (i.e. if muscle is stretched, control is exerted to tense it straight away)
decerebration (cortex separated from lower brain stem and lower spinal cord) reveals excitatory control from supraspinal areas - causes greater reflex response, muscle has elevated level of tonic contraction before muscle comes back to normal
what can cause an overactive or tonic stretch reflex?
brain damage
causes rigidity and spasticity
what is the pathway of descending (supraspinal) control of reflexes?
activating alpha motor neurons
activating inhibitory interneurons
activating propriospinal neurons (interneurons going up and down the spinal cord - few segments each way activated to activate nearby muscles)
activating gamma motor neurons
activating terminals of afferent fibres
what is hyper-reflexia?
overactive reflexes
loss of descending inhibition (associated with loss of voluntary movement)
associated with upper motor neuron lesions
what is clonus in hyper-reflexia?
involuntary and rhythmic muscle contraction
loss of descending inhibition
associated with upper motor neuron lesions
what is Babinski’s sign (hyper-reflexia)?
when sole of foot is stimulated with a blunt instrument big toe curls downwards in normal response
toe curling upwards - positive Babinski sign (abnormal in adults, but normal in infants)
associated with upper motor neuron lesions
what is hypo-reflexia?
below normal or absent reflexes
associated with lower motor neuron disease
what are gamma motor neurones?
responsible for altering sensitivity of sensory organs in muscle - when organs stretch a signal travels to spinal cord to generate reflex contraction
sensitise organ so that it remains sensitive to stretch when muscle is at a different level in intrafusal muscle fibres
where is the ear located?
embedded in petrous portion of temporal bone (hardest in body)
what are the functions of the outer ear?
capture sound and focus it to tympanic membrane
amplify some frequencies by resonance in the canal
protect the ear from external threats
- hair: stops any mechanical or external element entering
- wax: traps any mechanical/external element entering, pH will kill anything live entering ear
what does the outer ear consist of?
pinna
external auditory canal`
what are the functions of the middle ear?
(2 mechanisms of amplification)
focusing vibrations from large surface area (tympanic membrane) to smaller surface area (oval window) - change in surface area increases pressure
using leverage from the incus-stapes joint to increase the force on the oval window
what makes up the middle ear?
tympanic membrane to oval window
ossicles - articulated with each other to allow transmission of sound to inner ear
what makes up the inner ear?
cochlea
what are the functions of the inner ear?
transduces vibration into nervous impulses
simultaneously produces frequency and intensity analysis of the sound
what are the 3 compartments of the cochlea?
scala media (innermost)
scala tympani (near basilar membrane, next to stapes and oval window at base)
scala vestibuli (near vestibular membrane, next to round window at base)
what is the structure of the scala vestibuli and the scala tympani?
bone structures
contain perilymph (high in sodium)
what is the structure of the scala media?
membranous structure
contains endolymph (high in potassium)
hearing organ/organ of Corti located here
where is the structure where the organ of Corti lies?
basilar membrane
how is the basilar membrane of the ear arranged?
tonotopically
i.e. sensitive to different frequencies at different points along its length
high frequencies near base, low frequencies near apex
what are the 2 types of hair cells in the organ of Corti?
inner hair cells (IHC)
outer hair cells (OHC)
how are the inner and outer hair cells arranged in the organ of Corti?
IHC arranged on 1 column
OHC arranged on 3 columns
how does the tectorial membrane interact with inner and outer hair cells in the organ of Corti?
tectorial membrane is located above the hair cells - allow the hair deflection, which in turn will depolarise the cell
only OHCs are in constant contact with the tectorial membrane
these OHCs assist the contact with the IHCs
what is the function of the inner hair cells (IHC) in the organ of Corti?
transduction of sound into nerve impulses
carry 95% of afferent information of auditory nerve
what is the function of the outer hair cells (OHC) in the organ of Corti?
modulation of the sensitivity of the response
carry 95% of efferent information of auditory nerve
how does transduction work in the auditory system?
deflection of the stereocilia (hairs of hair cells) towards the longest cilium will open K+ channels
ionic interchange depolarises the cell and neurotransmitter is liberated
higher amplitudes (louder) of sound will cause greater deflection of stereocilia and K+ channel opening
(hyper-polarisation closes K+ channels)
what is the structure of the auditory pathways?
spiral ganglions from each cochlea project via auditory vestibular nerve (VIII) to the ipsilateral cochlear nuclei (monoaural neurons)
auditory information crosses at the superior olive level
after this point all connections are bilateral
how is hearing organised (central auditory pathways)?
tonotopically organised
what is frequency?
pitch (Hz)
cycles per second, perceived tone
what is amplitude?
loudness (dB)
sound pressure, subjective attribute correlated with physical strength
why is the decibel scale useful in measuring the amplitude of sounds?
logarithmic scale
range of sensitivity is very large
allows us to compress the scale on a graph - reflect the fact that many physiological processes are non-linear (i.e. respond to both very low and very high values)
how does hearing change with age?
hearing acuity decreases with age, (particularly higher frequencies)
medium and low frequencies could be affected with the progression of hearing loss
what are the aims of a hearing assessment?
determine:
is there a hearing loss?
- of what degree?
- of what type?
what procedures are used in a hearing assessment?
tuning fork
audiometry
central processing assessment
tympanometry
otoacustic emission
electrocochleography
evoked potentials
how is a tuning fork used in a hearing assessment?
used to establish probable presence/absence of a hearing loss with a significant conductive component
used to provide early and general information, when audiometry is not available or possible
Weber test:
Rinne test:
how is pure tone audiometry (PTA) used in a hearing assessment?
science of measuring hearing acuity for variations in sound intensity and frequency
audiometer: device used to produce sound of varying intensity and frequency
what is an audiogram?
graph plotting hearing thresholds to determine if there is hearing loss (normal threshold: 0 - 20 dB)
how is a central processing assessment used in a hearing assessment?
assessment of hearing abilities other than detection using verbal and non-verbal tests
e.g. sound localization, filtered speech, speech in noise
how is tympanometry used in a hearing assessment?
examination used to test middle ear condition and mobility of tympanic membrane and conduction bones by creating variations of air pressure in the ear canal
how are otoacoustic emissions (OAEs) used in a hearing assessment?
normal cochlea produces low-intensity sounds called OAEs produced specifically by the outer hair cells as they expand and contract
(test is often part of the new born hearing screening and hearing loss monitoring)
how are auditory evoked potentials used in a hearing assessment?
electrocochleography
– 0.2-4.0 ms, electrical activity from the cochlea and eighth nerve. Evoked by clicks or tone burst.
auditory brainstem response (ABR)
– 1.5-10.0 ms, electrical activity from the eighth nerve and brainstem nuclei and tracts. Evoked by clicks.
late responses (N1-P2, P300, MMN, and more) – 80-500+ ms, electrical activity from the primary auditory and association cortex. Evoked by tone burst and oddball paradigm.
what is the auditory brainstem response and how is it used in a hearing assessment?
electrical responses from the auditory pathway (often used in babies and children)
alterations in latency of waves can point to location of the deficit
what would affect cortical potentials?
neurological conditions
processing problems
what are the 2 types of hearing loss?
conductive hearing loss: problem is located in outer or middle ear
sensorineural hearing loss: problem is located in the inner ear or the auditory nerve
mixed hearing loss: conduction and transduction of sound are affected (problem affects more than one part of the ear)
how is the degree of hearing loss classified?
mild - profound
what are the causes of outer ear conductive hearing loss?
wax
foreign body
what are the causes of middle ear conductive hearing loss?
otitis
otosclerosis
what are the causes of inner ear sensorineural hearing loss?
presbycusis
ototoxicity
what are the causes of nerve sensorineural hearing loss?
VIII tumour
what treatments are available for hearing loss?
treat cause
hearing aids
cochlear implants
brainstem implants
how do hearing aids work in treating hearing loss?
amplify the sound, does not replace any structure
how do cochlear implants work in treating hearing loss?
replaces function of the hair cells by receiving sound, analysing it, transform it into electrical signals and sending an electric impulse directly to the auditory nerve
(needs functional auditory nerve)
how do brainstem implants work in treating hearing loss?
when the auditory nerves are the affected structures, the electrical signals can be send to a set of electrodes placed directly into the brainstem
very risky, then it is advised for people with bilateral important auditory nerve damage
what are the 3 main inputs of the vestibular system?
visual
proprioceptive
vestibular
what are the outputs of the vestibular system?
ocular reflex (maintain stable gaze)
postural control (maintain stable posture)
(unwanted output: nausea)
what are the inputs of the vestibular system?
visual (eye)
rotation and gravity (inner and middle ear)
pressure (feet)
how do the inputs generate the outputs in the vestibular system?
CNS integrates input information and generates the responses
where is the vestibular organ located?
posterior area of inner ear
inner ear contains hair cells for hearing and balance
where are the utricle and saccule located?
vestibule
joined by a conduit
saccule is also joined to the cochlea
how are the semi-circular canals arranged?
three semi-circular canals on each ear (anterior, posterior, lateral)
have an ampulla on one side, and they are connected to the utricle
what is the labyrinth in the skull?
superior projection of right bony labyrinth on base of skull
why is the location of the vestibular organ important?
location of the vestibular organ draws planes for anterior and posterior canals
these planes determine which structure will be stimulated with a specific head movement
what is the structure of vestibular hair cells?
have a kinocilium (the biggest cilium) and stereocilia
what is the function of the cilia on vestibular hair cells?
cilia allows the cells to depolarise the cell with movement of the endolymph generated by head movement
what are the the otolith organs?
utricle and saccule
where are the cells of the otolith organs located?
on the maculae
placed horizontally in the utricle
placed vertically in the saccule
what is the structure of the maculae?
contain the hair cells
gelatinous matrix
otoliths on top
what are otoliths?
carbonate crystals that help the deflection of the hairs
what is the structure of the semi-circular canals of the ear?
hair cells in the canals are located in ampulla
rest of the canal only has endolymph (high potassium)
what is the structure of the ampulla?
has crista where hair cells are located
cells surrounded by cupula (helps hair cell movement)
how are the semi-circular canals oriented?
defines 3 planes
anterior and posterior form a 90° angle
lateral is horizontal to other canals
where do vestibular nuclei have projections to?
spinal cord (postural control)
nuclei of the extraocular muscles (eye movement)
cerebellum (feedback)
centres for cardiovascular + respiratory control
where do the primary afferents in the vestibular system end?
vestibular nuclei
cerebellum
which vestibular nuclei are associated with the ventroposterior nucleus and vestibular cortex?
superior and lateral
which vestibular nuclei are associated with the vestibulospinal reflexes?
lateral, medial, inferior
what are the 3 reflexes produced by vestibular pathways?
vestibulo-ocular reflex (VOR)
vestibulocerebellar reflexes
vestibulospinal reflexes
where is the vestibular cortex located?
not one specific area - since many inputs and integrators are involved, many cortical areas participate
main processing centre thought to be in the parietal lobe (in parieto-insular vestibular cortex (PIVC))
what does the vestibular physiology look like?
sensory input
- visual
- vestibular
- proprioceptive
input travels for central processing in primary processor (vestibular nuclear complex) and adaptive processor (cerebellum), which interact with each other
information travels from primary processor (vestibular nuclear complex) to motor neurons
eye movements and positional movements produced
what are the functions of the vestibular system?
to detect and inform about head movements
to keep images fixed in the retina during head movements
postural control
how do hair cells alter potential?
hair cells have a resting potential which has a basal discharge to the nerve
hairs moving towards the kinocilium generates depolarization and an increase in nerve discharge
hairs moving away from the kinocilium generates hyperpolarization and a reduction in nerve discharge
how do the otolith organs work?
linear acceleration and tilt cause otolith movement and therefore detection
utricle - horizontal movement
saccule - vertical movement
how do the semi-circular canals work?
angular acceleration causes cupula to move and displace hair cells
output signal on cranial nerve VIII (vestibulocochlear) is velocity
work in pairs according to the planes
- laterals logether
- anterior from one side with posterior of opposite side
how does the vestibulo-ocular reflex (VOR) work?
keeps images fixed in the retina
connection between vestibular nuclei and oculomotor nuclei
eye movement in opposite direction to head movement, but same velocity and amplitude
how does the vestibulo-spinal reflex (VSR) work?
motor neurons to limb muscles (lateral tract)
motor neurons to neck and back muscles (medial tract)
postural control, avoidance of falls and compensatory body movement according to the head position
how is the vestibular system assessed?
medical history, posture and gait, cerebellar function, eye movements
vestibular tests
- caloric test
- video head impulse test (vHIT)
- vestibular evoked myogenic potential (VEMP)
- rotational test
imaging
- CT
- MRI
symptoms and impact assessment
what is the main symptom of a balance disorder?
dizziness/vertigo (very common - 25% of ENT and neurological referrals)
can be categorised based on location of the affected structure and evolution of signs and symptoms
what are some peripheral vestibular disorders (labyrinth and/or VIII nerve)?
vestibular neuritis
benign paroxysmal positional vertigo (BPPV)
Meniere’s disease
unilateral and bilateral vestibular hypofunction
what are some central vestibular disorders (CNS - brainstem/cerebellum)?
stroke
MS
tumour
what are 2 examples of an acute balance disorder?
vestibular neuritis (‘labyrinthitis’)
stroke
what is an example of an intermittent balance disorder?
Benign Paroxysmal Positional Vertigo (BPPV)
what are 2 examples of a recurrent balance disorder?
Meniere’s disease
migraine
what are 2 examples of a progressive balance disorder?
schwannoma vestibular (VIIIth nerve)
degenerative conditions (MS)
what are some non-vestibular causes of dizziness?
heart disorders
presyncopal episodes
orthostatic hypotension
anaemia
hypoglycaemia
psychological
gait disorders
what are the bases for a headache?
structural (not just brain, could be scalp, skull, meninges, spinal fluid, blood vessels, eyeballs, ear apparatus, veins etc.)
pharmacological
psychological
what are some things that may cause an acute single headache?
febrile illness, sinusitis
first attack of migraine
following a head injury
subarachnoid haemorrhage
meningitis
tumour
drugs
toxins
stroke
thunderclap (sudden onset), low pressure
what are some things that may cause a dull headache, increasing in severity?
(usually benign)
overuse of medication (e.g. codeine)
contraceptive pill, hormone replacement therapy
neck disease
temporal arteritis
benign intracranial hypertension
cerebral tumour
cerebral venous sinus thrombosis
what are some things that may cause a dull headache, unchanged over months?
chronic tension headache
depressive, atypical facial pain
what are some things that may cause a triggered headache?
coughing, straining, exertion
coitus
food and drink
what are some things that may cause a recurrent headache?
migraine
cluster headache
episodic tension headache
trigeminal or post-herpetic neuralgia
what are the red flags associated with onset of a headache?
“thunderclap” headache (like patient has been struck by thunder or lightning suddenly)
acute
subacute
what are the red flags associated with meningism?
photophobia
phonophobia
stiff neck
vomiting
what are red flag systemic symptoms that may occur in conjunction with a headache?
fever
rash
weight loss
what are red flag neurological symptoms/focal signs that may occur in conjunction with a headache?
visual loss
confusion
seizures
hemiparesis
double vision (focal sign)
3rd nerve palsy (focal sign - droopy eyelid)
Horner syndrome (focal sign)
papilloedema
what are some red flags for a headache in general?
orthostatic (better lying down
strictly unilateral
what are the signs of a subarachnoid silhouette?
sudden generalised headache - “blow to the head”
meningism - stiff neck and photophobia
what causes a subarachnoid haemorrhage?
most caused by a ruptured aneurysm
a few from arteriovenous malformations
some are unexplained
how are subarachnoid haemorrhages treated?
around 50% are instantly fatal
vasospasm may stop the leak
nimodipine and BP control.
high risk of a further bleed.
early neurosurgical assessment will confirm bleed
and establish cause
CT brain, lumbar puncture (RBC and xanthochromia) and MRA, angiogram
how are aneurysms treated?
filled with platinum coils
used to be clipped or wrapped
how are aneurysms treated?
filled with platinum coils
used to be clipped or wrapped
what is an acute intracerebral bleed?
fatal haemorrhage due to coning
mechanism of coning - raised intracranial pressure (ICP)
what is papilloedema?
optic disc swelling due to raised intracranial pressure
how likely is a carotid and vertebral artery dissection to lead to stroke?
20% of ischaemic strokes under 45 years old
mean age 40 - carotid > vertebral
how is a carotid and vertebral artery dissection diagnosed?
headache and neck pain
MRI/MRA
Doppler
angiography
(test if traumatic vs. spontaneous)
how is a carotid and vertebral artery dissection treated?
aspirin or anticoagulation
what are the symptoms of temporal arteritis?
(happens over the age of 55, 3x commoner in females)
constant unilateral headache
scalp tenderness
jaw claudication
25% polymyalgia rheumatica-proximal muscle tenderness
involvement of posterior ciliary arteries causes blindness
elevated ESR and CRP
temporal artery usually inflamed and tortuous
visible on ultrasound
biopsy shows inflammation and giant cells
how is temporal arteritis treated?
high dose steroids
aspirin
what is cerebral venous thrombosis?
thrombosis in dural venous sinus or cerebral vein
what can cause cerebral venous thrombosis?
non-territorial ischaemia “venous infarcts”
haemorrhage
thrombophilia
pregnancy
dehydration
Behcets
what causes headaches in cerebral venous thrombosis?
raised ICP
what can cause viral meningitis?
coxsackie
ECHO
mumps
EBV
what can cause bacterial meningitis?
Meningococci
Pneumococci
Haemophilus tuberculous
what can cause fungal meningitis?
Cryptococci
what can cause granulomatous meningitis?
sarcoid
Lyme
Brucella
Behcet’s
syphilis
what are the types of meningitis?
viral
bacterial
fungal
tuberculous
granulomatous
carcinomatous
what are the presenting symptoms of meningitis?
malaise
headache
fever
neck stiffness
photophobia
confusion
alteration of consciousness
what is herpes simplex encephalitis?
classic haemorrhagic changes in temporal lobes
how is meningitis treated?
(treat then diagnose)
antibiotics
blood and urine culture
lumbar puncture (CSF looks white -increased white cell count, decreased glucose due to brain using up large quantities)
antigens
cytology
bacterial culture
CT or MRI scan
what does bacterial meningitis look like?
cerebral oedema
effacement of ventricles and sulci
inflamed meninges
what are the symptoms of sinusitis?
malaise
headache
fever
blocked nasal passages
loss of vocal resonance
anosmia
nasal or postnasal catarrh
local pain and tenderness.
frontal pain characteristically starts 1-2 hours after rising and clears up during the afternoon
brain tumour
glioblastoma multiforme
what demographic often suffers from pseudotumour cerebri?
young obese women
what are the symptoms of a pseudotumour cerebri?
headache
visual obscurations
diplopia
tinnitus
papilloedema with or without visual field loss
what drugs are used in pseudotumour cerebri?
hormones
steroids
antibiotics
vitamin E
what treatments are needed for pseudotumour cerebri?
weight loss
diuretics
optic nerve sheath decompression
lumboperitoneal shunt
stenting of stenosed venous sinuses
what does raised intracranial pressure look like on an MRI?
cerebral oedema
effacement of ventricles and sulci
no mass lesion
what can cause a low pressure headache?
CSF leak due to tear in dura
traumatic (post-lumbar puncture) or spontaneous
how can a low pressure headache be identified on an MRI?
meningeal enhancement
how is a low pressure headache treated?
rehydration
caffeine
blood patch
what is a Chiari malformation?
brain sits low within skull
how does a Chiari malformation cause triggered headaches?
cerebellar tonsils descending through foramen magnum
descend further when patient coughs - tugs on the meninges causing cough headache
what are the signs of obstructive sleep apnoea?
often characteristic body habitus
history of loud snoring and apnoeic spells
hypoxia, CO2 retention
non-refreshing sleep
depression
impotence
poor performance at work
how is obstructive sleep apnoea treated?
require sleep study
nocturnal NI
surgery
what is trigeminal neuralgia?
electric shock like pain in the distribution of a sensory nerve
often triggered by innocuous stimuli
any division of the trigeminal can be affected
can be symptom of M.S.
what causes trigeminal neuralgia?
neurovascular conflict at the point of entry of the nerve into the pons
how is trigeminal neuralgia treated?
carbamazepine
lamotrigine
gabapentin
posterior fossa decompression
what are the symptoms of atypical facial pain?
(most commonly in middle aged women - depressed or anxious)
daily, constant, poorly localised deep aching or burning
facial or jaw bones, but may extend to the neck, ear or throat
not lancinating
not conforming to the strict anatomical distribution of any nerve
no sensory loss
(pathology in teeth, temporomandibular joints, eye, nasopharynx and sinuses must be excluded)
how is atypical facial pain treated?
unresponsive to conventional analgesics, opiates and nerve blocks
mainstay of management tricyclics
how likely is a post traumatic headache?
depends on nature of injury
- high in victims of car accidents
- low in perpetrators of car accidents
- low in sports injuries
what are the mechanisms that may cause post traumatic headache?
neck injury
scalp injury
vasodilation - autonomic damage
depression - often delayed
how is a post traumatic headache managed?
explain, prevent analgesic abuse
non-steroidal anti-inflammatories - ibuprofen, naproxen
tricyclic antidepressants - Amitriptyline
will take 3-4 years
what causes cervical spondylosis?
narrowing of joint space due to worn disk
commonest cause of new headache in older patients
what are the characteristics of a headache caused by cervical spondylosis?
usually bilateral
occipital pain can radiate forwards to the frontal region
steady pain
no nausea or vomiting
worsened by moving the neck
how is a headache caused by cervical spondylosis treated?
rest, deep heat, massage
anti-inflammatory analgesics
(NB over-manipulation may be harmful)
what are the 3 types of tears?
basal
reflex
emotional
where is the lacrimal gland located?
within orbit
latero-superior to globe
what are basal tears?
lacrimal gland produces tears at a constant level (even in the absence of irritation or stimulation)
what are reflex tears?
refers to increased tear production in response to ocular irritation
what makes up the tear reflex pathway?
afferent pathway (cornea, cranial nerve V1, ophthalmic trigeminal)
CNS
efferent (parasympathetic nerve)
lacrimal gland
how is the cornea innervated?
sensory nerve fibres via ophthalmic branch of trigeminal nerve
how are tears produced?
afferent pathway: trigeminal nerve relays signal to CNS from cornea
efferent pathway: mediated by parasympathetic nerve, innervates lacrimal gland
tear film drains through the two puncta (tiny openings on upper and lower medial lid margins)
puncta form opening of superior and inferior canaliculi within upper and lower eyelids
both canaliculi converge as one single common canaliculus, drain tear into tear sac
tear is finally drained out of the tear sac,
into the nasal cavity through the tear duct
what are the functions of the tear film?
maintains smooth cornea-air surface
source of oxygen and nutrient supply to the anterior segment (normal cornea has no blood vessels)
bactericide
why is a smooth cornea-air surface important?
maintaining clear vision
removing surface debris during blinking
what are the 3 layers of the tear film?
lipid layer (superficial)
aqueous layer (forms bulk of film)
mucinous (deep)
how is the lipid layer of the tear film formed?
secreted by Meibomian Glands (situated along the eyelid margins)
what is the function of the lipid layer of the tear film?
responsible for protecting the tear film from rapid evaporation
what are the functions of the aqueous layer of the tear film?
delivers oxygen and nutrient to surrounding tissue
contains factors against potentially harmful bacteria (bactericide)
what is the function of the mucinous layer of the tear film?
ensures that tear film sticks to the eye surface
maintains surface wetting
how does the mucinous layer of the tear film carry out its function?
mucin molecules act by binding water molecules to hydrophobic corneal epithelial cell surface
what is the conjunctiva?
thin, transparent tissue that covers eye’s outer surface
nourished by tiny blood vessels that are nearly invisible to the naked eye
what area does the conjunctiva cover?
begins at outer edge of cornea
covers visible part of eye
lines inside of eyelids
what are the 3 layers of the coat of the eye?
outermost - sclera (white of the eye)
choroid
innermost - retina (neurosensory tissue)
what is the function of the sclera?
protecting the eye
maintaining the shape of the eye
what is the function of the choroid?
providing circulation to the eye
shielding out unwanted scattered light
what is the function of the retina?
converting light into neurological impulses
to be transmitted to the brain via the optic nerve
what are the structural properties of the sclera?
hard
fibrous
opaque
high water content
what are the structural properties of the choroid?
pigmented
vascular - layers of blood vessels that nourish the back of the eye
what is the cornea?
transparent, dome-shaped window covering the front of the eye
what is the function of the cornea?
powerful refracting surface (providing 2/3 of eye’s focusing power)
gives us a clear window to look through
what are the 5 layers of the cornea?
epithelium
Bowman’s membrane
stroma
Descemet’s membrane
endothelium
what feature of the stroma of the cornea contributes towards transparency?
its regularity
what is the function of the endothelium of the cornea?
pumps fluid out of cornea, prevents corneal oedema
cornea has low water content
what is the uvea?
vascular coat of eyeball
lies between the sclera and retina
what are the 3 parts that make up the uvea?
iris
ciliary body
choroid
(intimately connected - disease of one part also affects the other portions though not necessarily to the same degree)
what is the function of the iris?
controls light levels inside the eye
similar to the aperture on a camera
how does the iris control pupil size?
embedded with tiny muscles
dilate and constrict pupil size
what is the structure of the lens?
outer acellular capsule
regular inner elongated cell fibres – transparency
how does the lens change with age?
may lose its transparency with age
results in an opaque lens (cataract)
what is the function of the lens of the eye?
refractive Power
1/3 of the eye focusing power - higher refractive index than aqueous fluid and vitreous
accommodation
elasticity
what is the function of the optic nerve?
transmits electrical impulses from the retina to the brain
how is the optic nerve arranged?
connects to the back of the eye near the macula
visible portion is called the optic disc
where the optic nerve meets the retina there are no light sensitive cells - it is a blind spot
where is the macula located?
roughly in the centre of the retina
temporal to the optic nerve
what is the function of the macula?
small and highly sensitive part of the retina responsible for detailed central vision
allows us to perform tasks such as reading
what is the fovea?
centre of macula
most sensitive part of the retina
what is the arrangement of cells on the fovea?
highest concentration of cones (low concentration of rods)
this is why stars out of the corner of your eye are brighter than when you look at them directly
why is the high concentration of cones on the fovea important?
allow perception in detail
what are the 2 types of visual function?
central
peripheral
what is central vision responsible for?
detailed day vision
colour vision – fovea has the highest concentration of cone photoreceptors
(reading, facial recognition)
what problems will people with loss of central vision have?
poor visual acuity (loss of foveal vision)
problems with reading and recognising faces
what is peripheral vision responsible for?
shape
movement
night vision
navigation vision
what problems will people with loss of peripheral vision have?
extensive loss of visual field – unable to navigate in environment, patient may need white stick even with perfect visual acuity
problems navigating the world
how is central vision assessed?
visual acuity assessment
how is peripheral vision assessed?
visual field assessment
what are the 2 layers of the retina?
retinal pigment epithelium (in front of choroid)
neuroretina (inner, thicker layer)
what are the functions of the retinal pigment epithelium?
transports nutrient from the choroid to the photo-receptor cells
removes metabolic waste from the retina
what are the 3 layers of the neuroretina?
outer, middle, inner
what cells are present on the outer layer of the neuroretina?
photoreceptors (1st order neuron)
what is the the function of the outer layer of the neuroretina?
detection of light
what cells are present on the middle layer of the neuroretina?
bipolar cells (2nd order neuron)
what is the the function of the middle layer of the neuroretina?
local signal processing to improve contrast sensitivity, regulate sensitivity
what cells are present on the inner layer of the neuroretina?
retinal ganglion cells (3rd order neuron)
axon runs along optic nerve into brain
what is the the function of the inner layer of the neuroretina?
transmission of signal from the eye to the brain
what are the 2 classes of photoreceptor?
rods and cones
what are rods responsible for?
night vision (scotopic vision)
peripheral vision
recognises motion
more photoreceptors, more pigment - higher spatial and temporal summation
what are cones responsible for?
daylight fine vision and colour vision (photopic vision)
how do rods and cones differ in terms of sensitivity to light?
rods 100x more sensitive than cones
how do rods and cones differ in terms of response to light?
rods have slower response than cones
how do rods and cones differ in terms of their outer segment?
rods have longer outer segment (therefore more photosensitive pigment) than cones
where are photopigments synthesised?
inner photo-receptor segment of rods and cones
then transported to outer segment
how is the outer segment of rods and cones arranged?
stacks of discs
how are photopigments regenerated?
distal discs (outer segment) with deactivated photo-pigments are shed from the tips
discs phagocytosed by the retinal epithelial cells
deactivated photopigments regenerated inside retinal epithelial cells
photopigments transported back to photo-receptors
where are rod photoreceptors distributed?
widely distributed all over the retina,
highest density just outside the macula
density tails off towards the periphery
completely absent within the macula
where are cone photoreceptors distributed?
only within macula
where is the peak of rod vison light sensitivity?
498nm wavelength
rods used for night vision and spatial recognition, not really sensitive to any particular colour
what are the 3 cone photopigment sub-types?
S-cones
M-cones
L- cones
what wavelengths are S-cones sensitive to?
short wavelength (blue)
peak sensitivity: 430nm
what wavelengths are M-cones sensitive to?
medium wavelength (green)
peak sensitivity: 540nm
what wavelengths are L-cones sensitive to?
long wavelength (red)
peak sensitivity: 570nm
how is yellow light experienced?
wavelength between peak sensitivity of M-cones and L-cones
equal stimulation of M and L cones
therefore yellow light experienced as a combination of green and red light
what is deuteranomaly/Daltonism (most common form of colour vision deficiency) caused by?
shifting of the M-cone sensitivity peak towards that of the L-cone curve
causes red-green confusion
what 2 things can cause colour vision deficits?
colour vision deficits caused by a shift in the photo-pigment peak sensitivity (anomalous trichromatism)
absence of one or more of the 3 cone photo-pigments
what is dichromatism?
only two cone photo-pigment sub-types are present
what is monochromatism?
complete absence of colour vision
what is blue cone monochromatism?
presence of only blue L-cones
normal daylight visual acuity
what is rod monochromatism?
a total absence of all cone photo-receptors
no functional day vision
what is achromatopsia?
full colour blindness (occurs in very small percentage of the population)
what is the Ishihara test?
colour blindness test
what is the basis of refraction?
as light goes from one medium to another, velocity changes
path of light changes
some light reflects off the boundary (angle of incidence = angle of reflection)
some refracts through the boundary (angle of incidence > or < angle of reflection depending on direction of light)
what is the index of refraction?
speed of light in a vacuum/speed of light in a medium
speed of light in a medium will always be smaller and produces a value greater than or equal to 1
what are the 2 types of lens?
convex (takes light rays and brings them to a point)
concave (takes light rays and spreads them outward)
when might a convex lens be used practically?
camera
focus image on film
what is emmetropia?
adequate correlation between axial length and refractive power (functioning eye)
parallel light rays fall on the retina (no accommodation)
what is ametropia?
mismatch between axial length and refractive power
parallel light rays don’t fall on the retina (no accommodation)
what are some ametropic errors?
near-sightedness (myopia)
farsightedness (hyperopia)
astigmatism
presbyopia
how does the path of light lead to myopia?
parallel rays converge at a focal point anterior to the retina
what causes myopia?
excessive long globe (axial myopia) - more common
excessive refractive power (refractive myopia)
what is the etiology of myopia and hyperopia?
unclear
genetic factor
what are the symptoms of myopia?
blurred distance vision
squint in an attempt to improve uncorrected visual acuity when gazing into the distance
headache
how is myopia treated?
correction with diverging lenses (negative lenses)
correction with contact lens
correction by removing the lens to reduce refractive power of the eye
how does the path of light lead to hyperopia?
parallel rays converge at a focal point posterior to the retina
what causes hyperopia?
excessive short globe (axial hyperopia) -more common
insufficient refractive power (refractive hyperopia)
what are the symptoms of hyperopia?
visual acuity at near tends to blur relatively early
- nature of blur varies from inability to read fine print to clear near vision that suddenly and intermittently blurs
- blurred vision is more noticeable if person is tired, printing is weak or light inadequate
asthenopic symptoms
- eye pain
- headache in frontal region
- burning sensation in the eyes
- blepharoconjunctivitis
amblyopia – uncorrected hyperopia > 5D
how is hyperopia treated?
correction with converging (positive lenses)
correction with positive lens + cataract extraction
correction with contact lens
correction with intraocular lens
how does the path of light lead to astigmatism?
parallel rays come to focus in 2 focal lines rather than a single focal point
what causes astigmatism?
refractive media is not spherical
refraction different along one meridian than along meridian perpendicular to it
2 focal points (punctiform object is represent as 2 sharply defined lines)
what is the etiology of astigmatism?
heredity
what are the symptoms of astigmatism?
asthenopic symptoms
- headache
- eyepain
blurred vision
distortion of vision
head tilting and turning
how is regular astigmatism treated?
cylinder lenses with or without spherical lenses (convex or concave), Sx
how is irregular astigmatism treated?
rigid cylinder lenses
surgery
what is the near response triad?
adaptation for near vision
what 3 things form the near response triad? what is their function?
pupillary miosis (sphincter pupillae) to increase depth of field
convergence (medial recti from both eyes) to align both eyes towards a near object
accommodation (circular ciliary muscle) to increase the refractive power of lens for near vision
what is presbyopia?
naturally occurring loss of accommodation (focus for near objects), distant vision intact
onset from age 40 years
how is presbyopia treated?
convex lenses in near vision
- reading glasses
- bifocal glasses
- trifocal glasses
- progressive power glasses
what are the 2 types of spectacle lens?
monofocal lenses
- spherical lenses
- cylindrical lenses
multifocal lenses
what is the difference between contact lenses and spectacle lenses?
higher quality of optical image and less influence on the size of retinal image than spectacle lenses
when are contact lenses used?
cosmetic
athletic activities
occupational
irregular corneal astigmatism
high anisometropia
corneal disease
what are the disadvantages of contact lenses?
careful daily cleaning and disinfection
expense
complications
- infectious keratitis
- giant papillary conjunctivitis
- corneal vascularization
- severe chronic conjunctivitis
what are intraocular lenses?
replacement of cataract crystalline lens
what are the advantages of intraocular lenses?
give best optical correction for aphakia
avoid significant magnification and distortion caused by spectacle lenses
what are the types of keratorefractive surgery?
RK
AK
PRK
LASIK
ICR
thermokeratoplasty
what are the types of intraocular surgery?
clear lens extraction (with or without IOL)
phakic IOL
how is surgical correction carried out?
pre operative eye
initial cutting of corneal flap
cutting of corneal flap
flipping of corneal flap
photorefractive treatment (laser)
corneal stroma reshaped post laser
corneal flap back in position
treatment completed
what is the process of clear lens extraction and addition of an intraocular lens?
cataract extraction
implantation of artificial lens
what occurs as a result of clear lens extraction and addition of an intraocular lens?
loss of accommodation (patient needs reading glasses)
what is the function of the visual pathway?
transmits signal from eye to the visual cortex
what are the visual pathway landmarks?
eye
optic nerve – ganglion nerve fibres with cell bodies originating in the retina
optic chiasm – half of the nerve fibres cross here and exit along the contra-lateral optic tract,
while the remaining ganglion nerve fibres exit along the optic Tract on the same side
optic tract – ganglion nerve fibres exit as optic tract
lateral geniculate nucleus – ganglion nerve fibres synapse at lateral geniculate nucleus (relay centre in thalamus)
optic radiation – 4th order neuron, relaying signal from lateral geniculate ganglion to primary visual cortex for lower visual processing
primary visual cortex or striate cortes – within the occipital lobe, relays visual information to the extra-striate cortex
(region adjacent to primary visual cortex)
for further higher visual processing
what are first order neurons within the visual pathway?
photoreceptors
what are second order neurons within the visual pathway?
phototreceptors synapse on retinal bipolar cells
what are third order neurons within the visual pathway?
retinal ganglion cells
what feature of retinal ganglion nerve fibres allows better signal transmission of visual information out of the eye to the brain?
myelination after entering optic nerve
what is decussation in the visual pathway?
half of the retina ganglion nerve fibres cross to the opposite side at the optic chiasm
what are fourth order neurons within the visual pathway?
retinal ganglion Fibres terminate at the lateral geniculate ganglion (thalamus)
and synapse upon the fourth order neurons, or optic radiation
what will a lesion anterior to the optic chiasma affect?
visual field in one eye
what will a lesion posterior to the optic chiasma affect?
visual field simultaneously in both eyes because of fibre crossing at chiasma
where do the crossed fibres at the optic chiasma predominantly originate from?
nasal retina
which half of the visual field are the crossed fibres at the optic chiasma responsible for?
temporal
where do the uncrossed fibres at the optic chiasma predominantly originate from?
temporal retina
which half of the visual field are the uncrossed fibres at the optic chiasma responsible for?
nasal
what will a lesion at the optic chiasma affect?
damages crossed ganglion fibres from nasal retina in both eyes
temporal field deficit in both eyes – bitemporal hemianopia
what will a right sided lesion (optic tract, optic radiation or visual cortex) posterior to the optic chiasma affect?
left homonymous hemianopia (both eyes)
what will a left sided lesion (optic tract, optic radiation or visual cortex) posterior to the optic chiasma affect?
right homonymous hemianopia (both eyes)
what is a bitemporal hemianopia generally caused by?
enlargement of benign pituitary gland tumour pressing on optic chiasma from above
what is a homonymous hemianopia generally caused by?
stroke
cerebrovascular accidents in the brain
when does contralateral homonymous hemianopia with macular sparing occur?
damage to the primary visual cortex due to stroke
why does contralateral homonymous hemianopia with macular sparing occur?
area within primary visual cortex representing macula is well protected -
receives blood supply from both right and left posterior cerebral arteries
what is the function of the pupil?
regulates light input to the eye
what is pupillary constriction mediated by?
parasympathetic nerve within cranial nerve III
what happens to the pupil in light conditions?
iris circular muscles contract, decreased pupil size (less light entering eye)
what happens to the pupil in dark conditions?
iris radial muscles contract, pupil dilation (more light entering eye)
why does the pupil contract in light conditions?
decreases spherical aberrations and glare
increases depth of field – near response triad
reduces bleaching of photo-pigments
what is the afferent pathway of the pupillary reflex?
rod and cone photoreceptors synapsing on bipolar bells synapsing on retinal ganglion cells
pupil-specific ganglion cells exit at posterior third of optic tract before entering lateral geniculate nucleus
afferent pathway from each eye synapses on Edinger-Westphal nuclei on both sides in dorsal brainstem
what is the efferent pathway of the pupillary reflex?
parasympathetic nerve (Edinger-Westphal nucleus) on brainstem (oculomotor nerve efferent)
synapses at ciliary ganglion on short posterior ciliary nerve
short posterior ciliary nerve directly innervates pupillary sphincter
what does the pathway of the pupillary reflex mean?
only one eye needs to be stimulated with light to elicit pupillary constriction response in both eyes
afferent pathway on either side alone will stimulate efferent pathway on both sides
what will a right afferent defect (e.g. damaged right optic nerve) in the pupillary reflex pathway cause?
no pupil constriction in both eyes when right eye is stimulated with light
normal pupil constriction in both eyes when left eye is stimulated with light
what will a right efferent defect (e.g. damaged right 3rd nerve) in the pupillary reflex pathway cause?
no right pupil constriction whether right or left eye is stimulated with light
left pupil constricts whether right or left eye is stimulated with light
what is the relative afferent pupillary defect?
damage to afferent pathway is usually incomplete, or relative
some degree of of pupillary constriction remains (albeit weaker response when damaged side is stimulated)
how can a relative afferent pupillary defect be demonstrated?
swinging torch test – alternating stimulation of right and left eye with light
both pupils constrict when light swings to undamaged side
both pupils paradoxically dilate when light swings to damaged side
why is eye movement necessary?
acquiring and tracking visual stimuli
what is eye movement facilitated by?
six extraocular muscles innervated by the three cranial nerves (III, IV and VI)
what is duction (eye movements)?
eye movement in one eye
what is version (eye movements)?
simultaneous movement of both eyes in the same direction
dextroversion: both eyes looking right
levoversion: both eyes looking left
what is vergence (eye movements)?
movement of both eyes in opposite directions
convergence: simultaneous adduction (inward) movement in both eyes when viewing a near object as part of near response triad
what is saccade?
short fast burst eye movement (up to 900 degrees per second)
what are the different types of saccade?
reflexive saccade to external stimuli (acquired new target)
scanning saccade (e.g. when reading)
predictive saccade to track objects
memory-guided saccade (absence of external stimuli)
what is smooth pursuit?
slow sustained eye movement (up to 60 degrees per second)
involuntary movement, driven by motion of moving target across retina
which extraocular muscles allow straight movement?
superior, inferior, lateral, medial rectus
where do the extraocular muscles come from?
all except inferior oblique come from a cone in the back of the orbit
inferior oblique comes in nasally
how does the superior rectus move the eye?
upwards
how does the inferior rectus move the eye?
downwards
how does the lateral rectus move the eye?
towards the outside of the head (towards temple)
how does the medial rectus move the eye?
towards the middle of the head (towards the nose)
how is the superior oblique arranged?
attached high on temporal side of eye
passes under superior rectus
travels through the trochlea
how does the superior oblique move the eye?
diagonal pattern (down and out)
how is the inferior oblique arranged?
attached low on nasal side of eye.
passes over inferior rectus
how does the inferior oblique move the eye?
diagonal pattern (up and out)
what does the superior branch of the third cranial nerve innervate?
superior rectus – elevates eye
levator palpebrae superioris
what does the inferior branch of the third cranial nerve (oculomotor) innervate?
inferior rectus - depresses eye
medial rectus – adducts eye
inferior oblique – elevates eye
parasympathetic nerve – constricts pupil
what does the fourth cranial nerve (trochlear) innervate?
superior oblique – depresses eye
what does the sixth cranial nerve (abducens) innervate?
lateral rectus - abducts eye
how is eye movement tested?
isolate muscle to be tested by maximizing its action and minimizing the action of other muscles
lateral rectus - abducted
medial rectus - adducted
superior rectus - elevated and abducted
inferior rectus - depressed and abducted
inferior oblique - elevated and adducted
superior oblique - depressed and adducted
how can upwards, downwards, inwards, outwards and rotating movements of the eye be described?
elevation
- supraduction – one eye
- supraversion – both eyes
depression
- infraduction – one eye
- infraversion – both eyes
right movement – dextroversion
- right abduction
- left adduction
left movement– levoversion
- right adduction
- left abduction
torsion – rotation of eye around its anterior-posterior axis
what does third nerve (oculomotor) palsy cause?
unopposed action of lateral rectus and superior oblique (causes eye to stay down and out)
ptosis (eyelid drooping) - levator palpabrae superioris loses innervation
what does sixth nerve (abducens) palsy cause?
lateral rectus loses innervation
affected eye cannot abduct, deviates inwards
double vision worsens on gazing to side of affected eye
what is nystagmus?
oscillatory movement of the eye (physiological or pathological)
what is optokinetic nystagmus?
physiological nystagmus
triggered by the presentation of a constantly moving grating pattern
eyes track along the grating motion,
with smooth pursuit up to a limit,
and resets the eye position to the centre,
with a burst of fast saccade motion
results in cycles of slow phase smooth pursuit,
alternating with fast phase reset saccade in the opposite direction
why is optokinetic nystagmus useful?
testing pre-verbal children visual acuity
observe nystagmus movement in response to moving grating patterns of various spatial frequencies
presence of opto-kinetic nystagmus signifies that the subject has sufficient visual acuity to perceive the grating
what are the features of a migraine disorder?
tendency to repeated attacks
triggers
easily hung-over
visual vertigo
motion sickness
what are the 3 forms of attack of a migraine disorder?
pain
focal symptoms
both pain and focal symptoms
what are the 5 phases of a migraine?
prodrome
aura
headache
resolution
recovery
(about 48 hours in total)
what happens in the prodrome phase of a migraine?
changes in mood
changes in urination and fluid retention
food craving
yawning
what happens in the aura phase of a migraine?
visual, sensory (numbness/paraesthesia)
weakness
speech arrest
what happens in the headache phase of a migraine?
head and body pain
nausea
photophobia
what happens in the resolution phase of a migraine?
rest and sleep
what happens in the recovery phase of a migraine?
mood disturbed
food intolerance
feeling hungover
how do positive and negative symptoms together during the aura phase of a migraine present?
scintillations
blindspot
what things are seen by the patient during the aura phase of a migraine?
expanding ‘C’s’
elemental visual disturbance
how is an acute migraine attack treated?
hit the headache hard and fast
aspirin/ibuprofen (non-steroidals)
paracetamol, metoclopramide (anti-emetic)
(soluble preparations to aid absorption
Triptans-tablets, melts, nasal sprays, s/c injections (vasoconstrictors), synergise with NSAIDS)
(be wary of analgesic abuse potential with opiates)
short nap
TMS - interrupts complex networks that trigger and perpetuate migraine, which is caused by spreading electrical depression across the cerebral cortex
what are the lifestyle issues caused by migraines?
migraineurs have sensitive heads even in between attacks
over-react to any sort of stimulation
can’t ignore the world around them, it overstimulates their brains
how can environmental issues that trigger migraines be controlled?
(dietary, environmental, hormonal, weather, dehydration, stress)
drink 2 litres water/day
avoid caffeinated drinks
don’t skip meals
fresh food- avoid ready meals, take-aways
don’t oversleep or have late nights (electronics downstairs)
be aware of potential for analgesic abuse
what are the prophylactic methods of controlling migraines?
over-the-counter preparations: feverfew, coenzyme Q10, riboflavin, magnesium, EPO, nicotinamide
tricyclic antidepressants (TCAs): amitriptyline 7pm
beta-blockers - Propranolol, Atenolol
serotonin antagonists: pizotifen, methysergide
calcium channel blockers: flunarazine, verapamil
anticonvulsants: valproate, topiramate, gabapentin
greater occipital nerve blocks
Botox: crown of thorns
suppress ovulation (progesterone only pill or implant/injection)
how is erenumab used as a prophylactic for migraines?
used for episodic migraine, chronic migraine, or cluster headache
injectable (also known as Aimovig)
cut number of days people had migraines from an average of 8 a month to 4-5 a month
monoclonal antibody
disables calcitonin gene-related peptide or its receptor (CGRP mAbs)
what is a tension type headache?
tight muscles around head and neck bilaterally, as though head is in a vice
how is a tension type headache treated?
NSAIDs preferred:
(ibuprofen, naproxen, diclofenac)
paracetamol
tricyclic antidepressants: amitriptyline 50-75mg daily, 30-60% derive some symptomatic relief
SSRI’s probably less effective
biofeedback and relaxation unproven
what is a cluster headache?
severe unilateral pain lasting 15-180 minutes untreated
classified as a trigeminal autonomic cephalgia
what is needed for a headache to be classed as a cluster headache? what are the symptoms?
at least one of the following, ipsilaterally:
- conjunctival redness and/or lacrimation
- nasal congestion and/or rhinorrhoea
- eyelid oedema
forehead and facial sweating
miosis and/or ptosis
sense of restlessness or agitation
frequency between one on alternate days to 8 per day.
not associated with a brain lesion on MRI
how is an acute cluster headache treated?
inhaled oxygen (oxygen inhibits neuronal activation in trigeminocervical complex)
S/C or nasal sumatriptan
what drugs are used to prevent a cluster headache?
verapamil
prednisolone
lithium
valproate
gabapentin
topiramate
pizotifen
what is the difference in distribution between migraines and cluster headaches?
migraine - 33% men, 67% women
cluster headache - 90% men, 10% women
what is the difference in duration between migraines and cluster headaches?
migraine - 3-12 hours
cluster headache - 45min – 3 hours
what is the difference in frequency between migraines and cluster headaches?
migraine - 1-8 attacks monthly
cluster headache - 1-3 attacks daily (often at night)
what is the difference in remission between migraines and cluster headaches?
migraine - long remissions unusual
cluster headache - long remissions common
what is the difference in nausea between migraines and cluster headaches?
migraine - nausea, vomiting frequent
cluster headache - nausea rare
what is the difference in pain between migraines and cluster headaches?
migraine - pulsating hemicranial pain
cluster headache - steady, exceptionally severe, well localised pain, unilateral in each cluster
what is the difference in symptoms between migraines and cluster headaches?
migraine - visual or sensory auras seen
cluster headache - eye waters, nose blocked, ptosis etc
what is the difference in activity between migraines and cluster headaches?
migraine - patients lie in the dark
cluster headache - patients pace about
what is the commonest cause of dementia?
Alzheimer’s disease
what characterisis dementia?
fatal neurodegenerative disorder
progressive social, cognitive and functional impairment
what is the best treatment possible for dementia at present?
acetylcholinesterase inhibitors
modest symptomatic benefit in early stages (1-2 years)
what are newer methods that allow diagnosis of dementia in life?
PET imaging, structural imaging
CSF and plasma markers
what is the difference between young onset and later onset dementia?
cut off age of 65 yrs
what usually causes familial Alzheimer’s disease?
APP (amyloid precursor protein) or presenilin mutations
what is the difference in the types of dementia between young onset and late onset sufferers?
‘rarer’ forms (vascular, frontotemporal, Lewy body, other) account for a greater percentage (70%) than Alzheimer’s in young onset
what are some potentially reversible factors that may lead to depression?
depression - cognitive issues can be reversed
alcohol related brain damage - subtle hippocampal vulnerability to more serious things
endocrine (hypothyroidism, Cushing’s, Addison’s)
B1/B12/B6 deficiency - can be supplemented
benign tumours
normal pressure hydrocephalus
infections (HIV/syphilis, Whipple’s disease)
limbic encephalitis (paraneoplastic/autoimmune)
inflammatory (vasculitis, MS, sarcoid)
why can it be difficult to diagnose dementia in the clinic?
disease follows heterogenous course
old age - disease presentation is of multiple comorbidities, lots of mixed/uncertain pictures
e.g. patients with Alzheimer’s or sporadic late-onset Alzheimer’s also have hypertension, may also have diabetes, may have had a heart attack or vascular damage over their life
clinical history is paramount to see patient’s function and how they change
what are some pathologies of the brain associated with dementia?
neuronal tau
Aβ
TDP-43
α-synuclein
parenchymal ischaemic changes
vessel wall pathology - e.g. cerebral amyloid angiopathy
what is the clinical process of dealing with dementia?
referral (from GP, psychiatrist, psychologist, geriatrician)
history - includes clinical interview
examination
investigations
diagnosis
- Alzheimer’s
- vascular
- Lewy body
- frontotemporal
- depression
- delirium
- none
management
what is the checklist to interview patients with suspected dementia?
memory
language
numerical skills
executive skills
visuospatial skills
neglect phenomena - part of progression
visual perception
route finding, landmark identification
personality and social conduct
sexual behaviour
eating
mood
motivation/apathy
anxiety, agitation - common in all dementias
delusions, hallucinations
activities in daily life
why is it important to ask a potential dementia sufferer’s friends and family about their behaviour and mental state?
key feature of dementia - as it progresses, patient loses insight into the symptoms they inhibit
patients will not be able to volunteer information, person that sees them frequently is more aware of the difficulties
why is asking about memory important in a potential dementia sufferer?
usually impaired, especially short term
what did you do today? what did you eat for lunch? can ask about recent events if they follow them
why is asking about language important in a potential dementia sufferer?
not just speaking skills, also word finding difficulties
second language English? any deterioration? naming things in first language?
why is asking about numerical skills important in a potential dementia sufferer?
ability to calculate, manage finances alone etc.
more vulnerable to exploitation, especially if no access to attorney or other support
why is asking about executive skills and visuospatial skills important in a potential dementia sufferer?
narrow down dementia diagnosis (subtypes)
find out deficits caused
- e.g. visuospatial deficits in a rare form of Alzheimer’s called posterior cortical atrophy often present with road accidents - people back into other cars, don’t realise their visuospatial deficit
why is asking about altered visual perception, route finding and landmark identification important in a potential dementia sufferer?
people may often wander
unfamiliar routes difficult to follow as dementia progresses
why is asking about personality and social conduct important in a potential dementia sufferer?
must know how personality traits etc. were before symptoms started - gauge progression
why is asking about sexual behaviour important in a potential dementia sufferer?
disinhibition
as Alzheimer’s progresses, frontotemporal dementia - more disinhibited behavioural phenotype
patients exhibit sexual behaviour that they may not have done before dementia
why is asking about eating habits important in a potential dementia sufferer?
people may forget they have had meals etc.
if biological cognitive phenotype of depression, might be altering eating habits due to this and not dementia
(also applies to taking other medications)
why is asking about mood important in a potential dementia sufferer?
treating depression if present - may restore some cognitive deficits
why is asking about delusions and hallucinations important in a potential dementia sufferer?
patient often does not want to be challenged, very strongly held belief
delusions of theft common
type of hallucination (auditory, visual, somatic) important to distinguish type of dementia
- visual hallucinations, Lilliputian hallucinations - common in Lewy body dementia
- people, animals present can be distressing with alcohol related brain damage, alcohol dependence or withdrawal
why is it important to ask about the chronology of each potential aspect of dementia?
if they are improving, it may not be a dementia process
potentially reversible causes
sudden or marked deterioration (subtle deterioration - Alzheimer’s, stepwise - vascular)
what examinations are done in dementia testing?
neurological examination
- cranial nerve tests, upper and lower limb tests, focus tests, frontal lobe function)
mental state
- appearance, behaviour, speech, mood, thought form, perception, cognition, insight
what investigations are done in dementia testing?
neuropsychological tests (MMSE, Addenbrooke’s Cognitive Exam - more memory focussed
bloods
MRI (bilateral medial temporal volume loss, hippocampal volume loss)
PET
what blood tests are done in investigating dementia?
full blood count
inflammatory markers (anything that could affect cognition)
thyroid function
biochemistry, renal function
glucose
B12, folate
clotting (vitamin deficiency)
syphilis serology
HIV
Caeruloplasmin (other causes of dementia, rare)
how does a PET scan work?
inject patient with contrast agent
travels to brain, lights up amyloid
corresponds with beta amyloid antibody immunohistochemistry
how is dementia managed?
acetylcholinesterase inhibitors
watch and wait if unsure - ideally need to see successive deterioration over 6 months - 1 year
treat behavioural, psychological symptoms
- anti-depressants, anti-psychotics depending on patient’s distress
occupational therapy/social services
specialist therapy
how can you differentiate between the different types of dementia to make a diagnosis?
rule out delirium (transience in consciousness, usually caused by infection) and depression
Alzheimer’s
- subtle, insidious amnestic/non-amnestic presentation
- amnestic visuospatial presentations (posterior cortical atrophy)
vascular
- related to cerebrovascular diseases with classic step-wise deterioration
- may have had multiple infarcts
Lewy body
- cognitive impairment before/within 1 year of Parkinsonian symptoms, visual hallucinations and fluctuating cognition
- high risk of falls
may have REM sleep disorder
frontotemporal dementia
- behaviour variant FTD
- may have REM sleep disorder
- semantic dementia
- non-fluent aphasia
rapidly progressing dementia
what is the head-turning sign?
ask a potential dementia sufferer a direct question, they don’t have the answer or they are not sure
turn to person next to them (caregiver, friend etc.)
what is episodic memory and what does it depend on?
memory for particular episodes in life
depends on medial temporal lobes, including hippocampus and entorhinal cortex
what does the pathology of dementia depend on?
amyloid
tau
what is Lewy body dementia generally caused by?
aggregation of alpha synuclein
how can the different types of dementia be differentiated on an MRI?
preserved hippocampal volume in Lewy body (as compared to Alzheimer’s)
typically asymmetrical bilateral perisylvian atrophy in FTD
how can frontotemporal dementia be assessed with genetic testing?
pathological expansion of C9orf72 gene
what is meningitis?
inflammation of meninges caused by viral or bacterial infection
what is encephalitis?
inflammation of the brain caused by infection or autoimmune mechanisms
what is cerebral vasculitis?
inflammation of blood vessel walls (sometimes called angiitis)
what is the blood brain barrier?
brain tissue protected from contents of bloodstream
what is the basis of the blood brain barrier?
dense vascularisation of brain tissue
neurons are always close to capillaries - therefore capillaries very dense
capillaries form blood brain barrier
what do the capillaries forming the blood brain barrier look like?
extensive tight junctions at the endothelial cell-cell contacts
how does the structure of the capillaries forming the blood brain barrier allow it to carry out its function?
tight junctions between the endothelial cells lining the vessel
reduces any passive movement of solutes and fluid across capillary wall into the tissue
this allows blood brain barrier to control the exchange of these substances using specific membrane transporters to transport into and out of the CNS (influx and efflux transporters)
blood-borne infectious agents have reduced entry into CNS tissue - protection
what other structures help maintain the structure of the blood brain barrier and the vessel wall?
basal lamina
other glial cells (particularly astrocytes)
how can the blood brain barrier be broken down?
the endothelial cell lining the vessels can become disrupted
causes opening of the blood brain barrier here - contents of the blood (e.g. fibrinogen) can move into the parenchyma
fibrinogen moving into tissue causes glial cells to react
astrocytes retract, break down the blood brain barrier
basement membrane change - collagen disrupted, may build up
sclerosis of these vessels
what can a breakdown of the blood brain barrier cause?
infection
what are the symptoms of encephalitis?
initial:
- flu-like, with pyrexia and headache
within hours, days or weeks:
- confusion or disorientation
- seizures or fits
- changes in personality and behaviour
- difficulty speaking
- weakness or loss of movement
- loss of consciousness
what are the most common causes of encephalitis?
viral infection
usually:
- Herpes Simplex
- measles
- Varicella (chickenpox)
- rubella
what are some non-viral causes of encephalitis?
mosquito, tick and other insect bites
bacterial and fungal infections
trauma
autoimmune
what treatments are used for encephalitis?
(depends on underlying cause)
antivirals (e.g. acyclovir) for viral infection
steroids - reduce inflammation
antibiotics/antifungals
analgesics
anti-convulsants (if risk of seizure)
ventilation if breathing is severely impaired
what is multiple sclerosis?
auto immune demyelinating disease of CNS
intermittent - relapses linked to inflammatory activity
progression linked to neurodegeneration - deficits increase over time, fewer remissions
what is the cellular pathology of multiple sclerosis?
inflammation - linked to relapses
demyelination
axonal loss - the longer you have the disease, the more the axon loss, the more the residual deficits
neurodegeneration causes progression
why do the symptoms of multiple sclerosis vary?
MS is a random disorder - can affect white matter anywhere in CNS
amount and location of the damage vary
what is perivascular cuffing?
perivascular accumulation of leukocytes seen in infectious, inflammatory, or autoimmune diseases
what does perivascular cuffing look like in multiple sclerosis?
immune cells (usually CD3 T cells, CD20 B cells) cross blood brain barrier, form cuff around vessels
causes demyelination, inflammation
what is meningitis?
irritation, inflammation and swelling of meninges
what are the most common causes of meningitis?
usually bacterial
- meningococcal – (most common cause of bacterial meningitis in UK)
- pneumococcal
- haemophilus influenzae type b (Hib)
- streptococccal (main cause in newborns)
what are some non-bacterial causes of meningitis?
viral - very rarely life-threatening
fungal
what is an infection of the spinal cord known as?
meningitis (meninges cover spinal cord as well as brain)
