Neurovascular Physiology Flashcards
Where is the vestibular system found?
Inner ear
What does the vestibular system consist of?
Fluid filled membranous tubes embedded in the temporal bones (labrinyths) - three semi circular canals (at right angles) connected to ampulla and the utricle and sacule.
What are the utricle and saccule collectively known as?
Otolith organs.
What is the function of the vestibular system?
Control of balance and posture and proprioception of head.
In which parts of the vestibular system are movement detected?
Cristae of semi-circular canals
Maculae of otolith organs
What sort of movement do the semicircular canals detect?
Rotation movement.
What sort of movement do the otolith organs detect?
Utricle - horizontal acceleration
Sacule - vertical acceleration, or head position when lying down
The vestibular centres of the medulla have strong associations with where and why?
Cerebellar centres to coordinate postural muscles to maintain balance.
To which three things does the vestibular nuclei connect the vestibular system with?
Descending motor pathways of the EOM of eye.
Receives input from proprioceptors signalling limb and body, neck and eye muscles position.
Via thalamus to cerebral cortex to signal perception of movement and body position = kinaesthesia.
What are the swellings at the end of the semicircular canals known as and what is their structure?
Ampulla - inside are cristae. Cristae are composed of a gelatinous structure (cupula) which has cilia in it (which synapse directly on to sensory neurone of vestibular nerve).
How do the cristae function to detect rotation acceleration?
Skull is rotated to right, endolymph doesn’t move initially due to inertia, but ampulla moves as it is embedded in skull, produces drag which bends cupola and cilia in opposite direction of movement.
What is the structure of the cilia within the cristae?
A single, large kinocilium and many stereocilia.
Distortion of cilia in direction of kinocilium causes what?
Depolarisation and increased discharge of APs in vestibular nerve.
Where is the sensory information from the vestibular system mostly integrated?
Cerebellum.
What are the structure of the maculae?
Kinocilium and series of stereocilium which protrude into a gelatinous mass (otolith membrane), embedded in the otolith membrane are otoliths (calcium carbonate crystals).
How do the maculae detect linear acceleration?
Otoliths have greater density than endolymph and thus are move affected by gravity and this causes them to move in the otolith membrane which distorts the jelly and moves fo the cilia. E.g. backward tilt moves otolith in direction of kinocilium causing depolarisation and increased discharge of APs, opposite for forward tilt.
What tracts do the vestibular system reflexes involve?
Vestibulocortical and vestibulospinal.
What are the main vestibular system reflexes?
Tonic labyrinthine reflexes - keep axis of head in constant relationship with rest of body (involves maculae and neck proprioceptors)
Dynamic righting reflexes - rapid postural adjustments made to stop falling when tripping (involves long reflexes, and extension of limbs)
Vestibular ocular reflex - associations with vestibular apparatus, visual apparatus and postural control that influence eye movement and balance.
What are the two vestibular ocular reflexes?
Static reflex - when you tilt your head your eyes intort/extort
Dynamic vestibular nystagmus - saccadic eye movements that rotate the eye against direction of rotation to maintain gaze (restricted so flicks back)
If someone is rotated what type of nystagmus will they get during and after the rotation?
During - same side nystagmus.
After - opposite side nystagmus due to endolymph catching up and pushing cupula in opposite direction.
Inserting warm fluid into the ear causes what?
Nystagmus towards the affected side (convection currents affect endolymph).
Inserting cold fluid into the ear causes what?
Nystagmus away from the opposite side (COWS - cold opposite, warm same).
Define sleep.
Stage of unconsciousness from which an individual can be roused by normal stimuli, light touch, sound etc.
What causes sleep?
Active inhibitory processes in the pons.
What chemical is thought to be essential to sleep initiation? And why is it thought to be involved?
Seratonin, precursor of melatonin (assoc. with see).
What place in the brain is thought to be linked to the induction of sleep?
Suprachiasmastic nuclei of the hypothalamus.
What is the SCN responsible for other than sleep induction?
Controlling Circadian rhythm as it is entrained by light (cells in back of retina send signals to this to entrain it).
What does activity in the SCN stimulate?
Release of melatonin from the pineal gland –> feelings of sleepiness.
When more light hits back of retina –> less melatonin
When less light hits back of eye –> more melatonin
What is orexin?
Aka hypocretin
Excitatory neurotransmitter that is required for wakefulness.
What does defective orexin signalling cause?
Nacrolepsy.
So, during wakefulness what, in summary, is occurring?
Excitatory neurons in ascending reticular activating system are released from inhibition from sleep centres (all in reticular formation).
What is thought to occur to create a sleep-wakefulness cycle?
Active cells become fatigued and excitatory signals dafe, so inhibitory peptide signals from sleep enters in reticular formation take over (and vice versa, inhibitory cells fatigue, and excitatory cells are reinvigorated).
How can EEG waves be analysed?
Amplitude
Frequency (increases with neuronal excitation)
What are different lengths of wavelengths associated with?
Very long - unconciousness
Shorter - awake and relaxed
V. short - alert
Shortest - epileptic seizures
What are the different classifications of EEG waves?
Alpha - awake, relaxed = high amplitude, high frequency, waves synchronous
Beta - awake, alert, higher frequency, low amplitude, waves asynchronous
Theta - low frequency, varying amplitude
Delta - very low frequency (occur in deep sleep)
Why are beta waves of a lower amplitude despite a higher level of awareness?
Waves are asynchronous meaning that there are loads of inputs to the brain which may involve negative and positive waves, which cancel each other out, leading to a lower amplitude.
When are theta waves common?
More common in children and during times of stress in adults. Dominate early part of sleep.
What are the 5 stages of sleep?
Stage 1 - slow wave, non-REM S-sleep - slow eye movements, easily roused. Theta waves.
Stage 2 - no eye movement. Frequency slows but burst of rapid waves (sleep spindles)
Stage 3 - high amplitude, v slow delta waves and episode of faster waves
Stage 4 - exclusively delta waves
REM sleep - rapid eye movements, on EEG appears similar to awake state. Dreams occur.
Is it easy to be roused from stage 3 and 4 sleep?
Deep sleep stages - so no.
In which stages does sleep walking and talking occur?
3 and 4.
How long does one sleep cycle tend to last?
90 mins.
How does your sleep change throughout the night?
More deep sleep initially, then more REM sleep at the end.
Waking during which stage will increase chance of remembering dreams?
REM.
What is the most restful type of sleep?
Deep sleep.
In which type of sleep is their decreased vascular tone, BP, respiratory and basal metabolic rate (and therefore temp)?
Deep sleep.
How long does REM sleep tend to last for every cycle?
5-30 mins.
In REM there is profound inhibition of what and why?
Skeletal muscles due to inhibitory projections from pons to spinal cord to prevent us acting out our dreams.
REM sleep is dependent on what kind of pathways?
Cholingeric pathways in the reticular formation and their projections to the thalamus, hypothalamus and cortex.
What kind of drug increases time spent in REM sleep?
Anticholinesterases.
What waves are seen in REM sleep on EEG?
Beta waves.
Do heart rate/resp rate slow in REM sleep?
No, they become irregular and brain metabolism also increases.
How easy is it to rouse someone from REM sleep?
Very difficult.
Is REM sleep important?
Very. Unknown why.
What are symptoms of sleep deprivation?
Impaired cognitive function, impaired physical performance, sluggishness, irritability….
What activities in the brain does sleep support?
Neuronal plasticity, memory, learning, cognition, clearance of waste products from the CNS, conservation of whole body energy and immune function.
How does sleep change with age?
More REM sleep in children, may be absent in 80+. Total time asleep in development, where brain maturation and synaptic formation occurring rapidly.
What is cognition?
Highest order of brain function, includes thought processing via integration of sensory information and learning from it. Requires consciousness.
What does learning and memory require?
Motivation.
What concept explains our ability to learn and remember?
Neuronal plasticiity - the ability of central neurone to adapt their neuronal connections in response to new experiences (synapses change chemically and physically).
Where does learning occur in the brain?
Spread out over whole brain and involves several association areas.
What are the three key components of learning and memory?
Hippocampus - formation of memories
Cortex - storage of memories
Thalamus - searches and assesses memories
In order to store memories, we need a —— component.
Emotional.
What creates the emotional component required for the formation of memories?
The limbic system.
What does the limbic system consist of?
Cingulate gyrus, hippocampus and amygdala and hypothalamus.
Is the thalamus considered as part of the limbic system?
No, but it is crucial to memory.
What is the oldest part of the cortex?
Limbic system.
What is the hypothalamus associated with?
ANS responses.
Collectively, what are the components of the limbic system responsible for?
Our instinctive behaviours, e.g. thirst, sex, hunger… and emotive behaviour.
What is emotive behaviour driven by?
Seeing reward or avoiding punishment (reward and punishment areas are distinct areas in the limbic system).
What does motivation require?
Reward or punishment to give a task significance.
What deems the significance of an experience and whether it should be stored or not?
The frontal cortex and its association with the reward/punishment areas in the limbic system.
What structure is essential for the formation of new memories?
Hippocampus.
What are the different types of memory?
Immediate/sensory
Short term
Immediate long-term
Long-term
How long does your immediate/sensory memory hold information for?
A few seconds, holding experiences in the mind for a few seconds.
Visual memories decay faster (<1s) than auditory memories (4s).
How long does your short term memory hold information for? What is it associated with?
Seconds-hours, aka. working memory, allows small tasks to be carried out, e.g. reading a sentence.
Associated with reverberating circuits.
How long does your immediate long-term memory hold information for? What is it associated with?
Weeks-hours.
Associated with chemical adaptations at presynaptic terminal - - increased Ca entry into presynaptic terminals which increases NT release (i.e. more NT released for the same stimuli).
How long does your long-term memory hold information for? What is it associated with?
Lifelong.
Associated with structural changes in synaptic connections.
Describe the electrical phenomenon behind short term memory.
Maintenance of excitation from reverberating circuits, i.e. neurones in the circuit are constantly excited.
If something is deemed significant in short term memory, how is it moved into long term memory?
Consolidation - selective strengthening of the synaptic connections through repetition. This process takes time (during which electrical activity vulnerable to being wiped out).
If a short term memory is deemed insignificant what occurs?
Reverberation fades away.
What are the structural changes involved in long term memory?
Increase in NT release sites on presynaptic membrane
Increase in NT vesicles stored and released
Increase in no. of presynaptic terminals.
This leads to greater amplitude in EPSP in post-synaptic cell, strengthening the synapse = long-term potentiation.
Long term memory is basically a well-established, well-rehearsed —- – —– —– unique to that particular —— and they are stored in different parts of the brain.
Pattern of neural firing
Memory
What are the two main types of long term memory?
- Declarative/explicit - memory for events/words/rule/language. RELIES HEAVILY ON HIPPOCAMPUS.
- Procedural/reflexive/implicit memory - acquired slowly through repetition, incl. motor memory. Mainly based in cerebellum, INDEPENDENT of hippocampus.
What is the difference between semantic and episodic memory?
Semantic - not drawing from personal experiences, e.g. common knowledge, colours, alphabet etc.
Episodic - autobiographical events.
How are memories stored?
They are coded and then stored in sensory association areas of the brain (coding allows similar memories to be grouped together).
Different parts of memory are laid down in different parts of cortex, e.g. visual component in visual cortex.
What is the Papez circuit?
The structures through which the reverberating circuit flows - includes hippocampus, maxillary body, anterior thalamus and cingulate gyrus.
If deemed significant information, where does the reverberating circuit extend to to allow consolidation?
Reverberating activity continues between Papez circuit, frontal cortex and sensory and association areas until consolidation complete.
Why are olfactory stimuli powerful in evoking long term memories?
Substantial connections between amygdala and hippocampus and the primary olfactory cortex.
Describe the sequence of events in synaptic transmission.
- Synthesis/packaging of NTs
- Na AP invades terminal
- Activates voltage gated Ca channels
- Triggers Ca-dependent exocytosis of NTs
- NT diffuses across cleft and binds to inotropic/metabotrophci receptors on post-synaptic cell
- Presynaptic autoreceptors inhibit more NT release
- NT inactivated by uptake into glia/neurons/extracellular breakdown (ACh)
What methods could you use to reduce synaptic transmission?
Block Na channels, e.g. local anaesthetics
Block Ca channels, e.g. spider toxin
Block release machinery, e.g. botox
Block post-synaptic receptors, e.g. receptor antagonists
Activate presynaptic inhibitor receptors
Increase NT breakdown/uptake
Inhibit NT synthesis/packaging
What is the issue with using botox, spider toxin and local anaesthetics to reduce transmission?
They affect all the neurones (are not specific).
What methods could you use to increased synaptic transmission?
Flow cells with appropriate precursors
Use agonist to activate postsynaptic receptor
Allosteric drug activating receptor on its own
Block transmitter breakdown
Block uptake of transmitter
Give examples of monoamine NTs?
Noradrenaline, dopamine, serotonin.
Give examples of amino acid NTs.
Glutamate, GABA, glycine.
Give examples of purine NTs.
ATP, adenosine.
Give examples of neuropeptide NTs,
Endorphins, CCK, substance P.
Give example of noradrenaline reuptake blockers.
Tricyclic drugs, e.g. antidepressants.
What are MOA inhibitors?
Antidepressants.
What are selective serotonin uptake inhibitors?
Antidepressants.
What can GABA analogues be used to treat?
Epilepsy and anxiety.
What germ layer does the nervous system develop from and how?
Ectoderm (wk3). It thickens and forms a neural plate, neural folds migrate towards each other to form neural tube (initially remains open at cranial (anterior) end and posterior (caudal) end.
When does the anterior neuropore close?
25 days (18-20 somite stage).
When does the posterior neuropore close?
27th day.
What can failure of the neuropores cause?
Neural tube defects, e.g. anencephaly, encephalocoele, spina bifida.
When does development of the brain vesicles begin?
With closure of anterior neuropore (25th day).
Where is the cephalic flexure and when does it form?
End of third week, it is between the midbrain (mesencephalon) and hindbrain (rhombencephalon).
Where is the cervical flexure and when does it form?
End of 4th week, between the spinal cord and hindbrain.
Where does the pontine flexure form and when does it form?
5th week and between metecephalon and myelencephalon.
What are the initial 3 brain vesicles?
Prosencephalon (forebrain)
Mesenecephalon (midbrain)
Rhombencephalon (hindbrain)
What does the forebrain develop into?
Telecephalon and diencephalon.
What does the rhombencephalon develop into?
Metechephalon and myelencephalon.
From where do: 1. lateral ventricles 2. 3rd ventricle 3. cerebral aqueduct 4. 4th ventricle Form?
- telecephalon
- telencephalon and diencephalon
- mesencephalon
- metecenaphlon and myeloencephalon
When does CSF production begin?
5th week.
Where is CSF predominantly produced from?
Choroid plexus (3rd and 4th ventricles).
Neural tube is initially a single layer of what?
Rapidly dividing neuroepithelial cells (pseudo stratified epithelium dividing at ventral surface).
Which cells are not produced by neuroepithelium?
Microglia, mesenchymal cells (macrophages) that migrate into the CNS.
What are neural crest cells and where do they come from?
Cells from dorsal part of neural tube migrate, e.g. some to between somites to form dorsal root ganglia, or close to organs to form ganglia or to gut to form ENS ec.
What sort of information do the cranial nerves carry?
Somatic motor fibres, visceral motor fibres, visceral sensory fibres, general sensory fibres, special sensory fibres.
What is the function of the olfactory nerve?
Smell.
Where does CN I emerge from and where does it emerge from the skull?
Receptors in olfactory epithelium from olfactory nerve, pass through foramina in cribriform plate and enter olfactory bulb in anterior cranial fossa.
Where does CN II emerge from?
Enters optic canal.
What is the function of CN II?
Optic nerve - conveys vision.
Where does CN III emerge from and where does it emerge from the skull?
Emerges from midbrain and exits superior orbital fissure.
Where does CN IV emerge from and where does it emerge from the skull?
Emerges from dorsal surface of midbrain and exits superior orbital fissure.
Where does CN V emerge from and where does it emerge from the skull?
Emerges from pons, travels through trigeminal ganglion (stacked cell bodies) then splits into V1, V2 and V3.
V1 - exits via superior orbital fissure.
V2 - exits via formanen rotundum.
V3 - exits via formanen ovale.
Where does CN VI emerge from and where does it emerge from the skull?
Emerges between pons and medulla and exits via superior orbital fissure.
Where does CN VII emerge from and where does it emerge from the skull?
Emerges between pons and medulla and exits via internal acoustic meatus, facial canal and stylomastoid foramen.
Where does CN VIII emerge from and where does it emerge from the skull?
Emerges between pons and medulla and exits via internal acoustic meatus dividing into vestibular and cochlear nerves.
Where does CN IX emerge from and where does it emerge from the skull?
Emerges from medulla and exits via jugular foramen.
Where does CN X emerge from and where does it emerge from the skull?
Emerges from medulla and exits from jugular foramen.
Where does CN XI emerge from and where does it emerge from the skull?
Emerges from medulla and exits via jugular foramen.
Where does CN XII emerge from and where does it emerge from the skull?
Emerges from medulla and exits via hypoglossal canal.
What is the function of CN III?
Oculomotor Nerve
EOMs and LPS motor innervation. Parasympathetic supply to pupil causing constriction (carries PS fibres from EWN which synapse at ciliary ganglion and travel in short ciliary nerves to innervate sphincter papillae and cilliaris muscle).
What is the function of CNVI?
Abducens Nerve
Innervates lateral rectus
What is the function of CNIV?
Trochlear Nerve
Innervates superior oblique (turns eye downwards)
What is the function of V1?
Ophthalmic division of trigeminal nerve
Sensory - cornea, forehead, scalp, eyelids, nose, mucosa of nasal cavity and sinuses
What is the function of V2?
Maxillary division of trigeminal nerve
Sensory - face, maxilla, teeth, TMJ, mucosa of nose, maxillary sinuses and palate
What is the function of V3?
Mandibular division of trigeminal nerve
Sensory - face over mandible, teeth, TMJ, mucosa of mouth and anterior 2/3rd of tongue
Motor - muscles of mastication, part of digastric, tensor veli palatini, tensor tympani
What is the function of CN VII?
Facial Nerve
Motor - muscles of facial expression, scalp, stapedius, part of digastric
PS to submandibular, sublingual salivary glands, lacrimal glands and glands of the nose and palate
Taste from anterior 2/3rd of tongue and palate
Sensory - external acoustic meatus
What is the function of CN VIII?
Vestibulocochlear Nerve
Vestibular sensation from semicircular canals and otolith organs
What is the function of CN IX?
Glossopharyngeal Nerve
Taste from posterior 1/3rd of the tongue.
Sensation from middle and posterior oral cavity
Sensation from carotid body and carotid sinus
PS to parotid gland
Motor to stylopharyngeus
What is the function of CN X?
Vagus Nerve
Taste from epiglottis and palate
Sensation from auricle, EAC
Sensory - pharynx, larynx, trachea, bronchi, heart, oesophagus, stomach, small intestine
PS to smooth muscle in bronchi, gut heart
Motor - pharynx, larynx, palate and oesophagus
What is the function of CN XI?
Accessory Nerve
Motor - SCM and trapezius.
What is the function of CN XII?
Hypoglossal Nerve
Motor - muscles of tongue.
Problems with the trochlear nerve can cause what?
Diplopia when looking down.
What can damage to the hypoglossal nerve cause?
Paralysis and atrophy of ipsilateral half of tongue (tip deviates towards affected side).
What nerves are involved in the pupillary light reaction?
Afferent - II
Efferent - III
What nerves are involved in the corneal reflex?
Afferent - V
Efferent - VII
What nerves are involved in the jaw jerk reflex?
Just trigeminal.
What nerves are involved in the gag reflex?
Afferent - I
Efferent - X
Loss of parasympathetic supply to the eye causes what?
Fixed, dilated pupil.
What can cause small pupils?
Old age, bright light, miotic eye drops, opiate OD, Horner’s.
What can cause dilated pupils?
Youth, dim lighting, excitement, anxiety, mydriatric eye drops, third nerve palsy, brain death…
Interruption to the sympathetic supply to the eye causes what sort of pupil?
Constricted pupil.
What are the depressions of the cerebrum known as?
Sulci.
What are the elevations of the cerebrum known as?
Gryri.
What does the longitudinal fissure separate?
Two hemispheres.
What does the corpus callosum do?
Connects the two hemispheres, and contains commissural white mater fibres.
Where does the lateral sulcus separate?
Frontal and parietal lobe from temporal lobe.
Where does the central sulcus separate?
Starts from lateral sulcus and separates parietal and frontal cortices.
What does the parieto-occipital sulcus separate?
Parietal and occipital lobe.
What is the cingulate gyrus responsible for?
Receiving information and memory etc.
Where is the hippocampus?
Medial surface of temporal lobe.
What are the features of the frontal lobe?
Precentral gyrus, superior, middle and inferior frontal gyri.
What are the features of the parietal lobe?
Superior and inferior parietal lobules and postcentral gyrus.