Neurology Flashcards
What are the 2 principle pairs of arteries supplying the brain?
Internal carotid arteries and vertebral arteries.
Describe the circle of Willis.
An ‘orbital’ artery formed of many arteries. The 2 vertebral arteries converge to form the basilar artery, forming the posterior aspect of the circle. This bifurcates to from 2 posterior cerebral arteries. These give of posterior communicating arteries, which continue the circle of Willis. At the middle, the internal carotids join and give off a middle cerebral artery as a continuation. Anteriorly, the anterior cerebral arteries continue into the longitudinal fissure. The anterior communication artery links the 2 anterior cerebral arteries.
Describe the drainage of the cranium.
The cerebral veins drain into venous sinuses (made of folds of dura mater), which in turn drain into jugular veins.
Define stroke.
A cerebrovascular accident: a rapidly deteriorating focal disturbance of brain function of presumed vascular origin and of >24hours duration. Infarction 85% of cases, haemorrhage in 15% of cases.
Define transient ischaemic attack (TIA).
A rapidly deteriorating focal disturbance of the brain of presumed vascular origin that completely resolves within 24 hours.
Describes the effects of an occlusion of an anterior cerebral artery.
Paralysis of contralateral leg (leg>arm). Disturbance of intellect, executive function and judgement. Loss of appropriate of appropriate social behaviour.
Describes the effects of an occlusion of a middle cerebral artery.
“Classic stroke” - contralateral hemiplegia (arm>leg), hemianopia.
Describes the effects of an occlusion of a posterior cerebral artery.
Visual defects (homonymous hemianopia), agnosia.
Describe the main causes of different types of haemorrhagic stroke.
Extradural (trauma, immediate effects)
Subdural (trauma, delayed effects)
Subarachnoid (ruptured aneurysms)
Intracerebral (spontaneous hypertensive).
Give common causes of syncope (fainting).
Manifestation of reduced blood flow to the brain: hypotension, postural changes, sudden pain, emotional shock.
Between which pressures is cerebral blood flow (CBF) autoregulated?
60-160mmHg
Autoregulation: intrinsic ability of the brain to maintain a constant blood flow despite changes in perfusion pressure.
How does CO2 cause vasodilation (and therefore increase blood flow) as part of local autoregulation (more CO2 is a result of more metabolic activity).
CO2 from the blood diffuses into the smooth muscle (H+ can’t cross the BBB). Here, it generates H+ using carbonic anhydrase. This increases the concentration of H+ (lowering pH) in the surrounding neural tissue and smooth muscle cells, which causes dilation.
What is the purpose of the BBB?
Protect the CNS from fluctuations in the composition of blood - as activity in neurones is highly sensitive to the composition of the local environment.
Which transporters are used to transport hydrophilic transporters across the BBB?
Water = AQ1, AQ4
Glucose = GLUT 1
Amino acids = 3 different transporters
Electrolytes = specific transporter systems.
What are the areas of the brain, usually near ventricles, which lack BBB collectively known as?
Circumventricular organs (CVOs). (They have fenestrated capillaries). Usually involved in secreting into the circulation, or need to sample the plasma. The ventricular ependymal lining can be much tighter to limit exchange between them and the CSF.
Describe the differentiation of the neuroepithelium.
Neuroblasts: all neurones with cell bodies in the CNS.
Glioblasts: astrocytes; oligodendrocytes etc.
Ependymal cells: line ventricles and central canal.
What is the pial surface?
The boundary between grey matter and CSF.
Define brainstem.
The part of the CNS, exclusive of the cerebellum, which lies between the cerebrum and spinal cord.
Major divisions: medulla oblongata, pons, midbrain.
Sits in posterior cranial fossa.
How could you differentiate between different areas of the brain stem on imaging?
Midbrain: characteristic ‘mickey mouse’ shape, aqueduct, substantia nigra. Cerebral peduncle. Colliculi (posterior)
Pons: 4th ventricle and many transverse fibres. Middle cerebellar peduncle.
Medulla: 4th ventricle (diminished), pyramids, inferior olivary nucleus (wavy shaped). Inferior cerebellar peduncle.
Lower medulla: start of central canal, pyramidal decussation.
To which vertebral level does the dura mater extend?
S2
What is the epidural space?
A true space between the vertebral column and dura, filled with fat and venous plexus.
What is the additional, white filament present amongst cauda equina?
An extension of the pia mater tethering the spinal cord to the caudal end.
Where does discriminative touch, vibration and proprioception cross the midline?
Medulla.
Describe the location of the thalamus in relation to the ventricles.
Thalamus sits VENTRAL to the lateral ventricles, divided into two by the 3rd ventricle (N.B. ventral = inferior).
What is the only sensory system which doesn’t involve the thalamus?
Olfaction.
What do the intralaminar nuclei of the thalamus do?
Project to various medial temporal lobe structures (e.g. amygdala, hippocampus, basal ganglia). Mostly glutamatergic neurones.
What is the reticular nucleus?
The thalamic nucleus which forms the outer covering of the thalamus. The majority of its neurones are GABAergic. It doesn’t connect with distal regions but rather other thalamic nuclei. It received input and therefor acts to modulate thalamic activity.
What is the reticular formation?
A set of interconnected pathways in the brainstem which send ascending projections to forebrain nuclei (ascending reticular activation system (ARAS)). Involved in consciousness and arousal. Degree of wakefulness depends on ARAS activity.
What are the main functions of the hypothalamus colloquially?
The 4Fs Fighting Fleeing Feeding Fucking
What is the suprachiasmatic nucleus?
A hypothalamic nucleus which has connections to the pineal gland. It thus controls the secretion of melatonin and is involved in the circadian rhythm (sleep-wake cycles).
What is the paraventricular nucleus?
A nucleus of the hypothalamus which sends parvocellular and magnocellular neurones to the neurohypophysis.
Relate the 5 main cortices to their respective thalamic nuclei.
Motor cortices: ventral lateral and ventral anterior nuclei.
Somatosensory (body) cortex: ventral posterolateral
Somatosensory (head) cortex: ventral posteromedial
Visual: lateral geniculate
Auditory: medial geniculate
How would you distinguish between brainstem structures on imaging scans?
MIDBRAIN: has characteristic “mickey mouse” shape. Aqueduct present (only in midbrain), substantia nigra.
PONS: 4th ventricle, many transverse pontine fibres
UPPER MEDULLA: 4th ventricle (diminished), pyramids, inferior olivary nucleus (which has a wavy shape).
LOWER MEDULLA: starts of central canal, pyramidal decussation.
Describe the dorsal column-medial lemniscus pathway.
DCML is sensory, transmitting fine touch, vibration, 2-point discrimination and proprioception from the skin and joins to the primary somatosensory cortex in the parietal lobe. Axons from the lower body enter the dorsal column below T6 and travel in the gracile fasciculus (tract) to the gracile nucleus in the medulla. Axons from upper body enter at or above T6 and travel in the cuneate fasciculus to the cuneate nucleus. The neurons cross over at the sensory decussation in the medulla to form the medial lemniscus, which transmits the neurons to the ventral posterolateral (VPL) nucleus in the thalamus. The thalamus sends third order neurons to the primary somatosensory cortex (somatotopic representation).
Contrast thoracic and cervical spinal cord.
Cervical is larger and ovular, thoracic more circular.
Cervical has more white fibre tracts due to the converging of ascending and descending pathways.
Thoracic has intermediolateral cell column (preganglionic sympathetic neurons).
Below T6: no cuneate fasciculus.
What is a sensory receptor?
A transducer which converts energy from the environment into neuronal action potentials.
Which sensory receptors have free nerve endings and which have enclosed nerve endings?
Free nerve endings: thermoreceptors and nociceptors.
Enclosed nerve endings: mechanoreceptors.
Give 4 types of mechanoreceptors.
Meissner’s corpuscle: fine discriminative touch, low frequency vibration.
Merkel cells: light touch and superficial pressure.
Pacinian corpuscle: detects deep pressure and high frequency vibration.
Ruffini endings: continuous pressure or touch and stretch.
Define threshold.
The point of intensity at which the person can just detect the presence of a stimulus 50% of the time.
How does an increased stimulus strength / duration lead to greater intensity response?
More neurotransmitter is released.
What are tonic receptors?
Sensory receptors which do not adapt or adapt very slowly. They detect continuous stimulus strength, and continue to transmit impulses to the brain as long as the stimulus is present, keeping the brain constantly informed.
E.g. Merkel cells, which slowly adapt to allow superficial pressure and fine touch to be perceived.
What are phasic receptors?
Receptors which adapt quickly. They detect a change in stimulus strength, transmitting an impulse at the start and end of a stimulus (when a change is taking place).
E.g. the Pacinian corpuscle, where sudden pressure excites the receptor and it transmits a signal again once the pressure is released.
What is a receptive field?
A region of the skin which causes activation of a single sensory neuron when activated. Small receptive fields allow for the detection of fine detail over a small area (e.g. the fingers have densely packed mechanoreceptors with small receptive fields).
What are the two types of dorsal horn neurons?
Those with axons which project to the brain (projection neurons) and those with axons that remain in the spinal cord (interneurons).
Via what process is it possible to distinguish between 2 stimulus locations when receptive fields overlap?
Lateral inhibition, mediated by inhibitory interneurons within the dorsal horn of the spinal cord.
Describe the consequences of an anterior spinal cord lesion.
Blocked anterior spinal artery causes ischaemic damage to the anterior part of the spinal cord. Spinothalamic tract damage causes pain and temperature sensation loss below the level of the lesion.
Light touch, vibration and 2-point discrimination are retained due to intact dorsal columns.
Describe the first order neurons of the dorsal column-medial lemniscus pathway.
Sensory (AB) neurons in the dorsal root ganglia, which send afferent fibres trough the gracile and cuneate tracts to the gracile and cuneate nuclei in the medulla where they terminate and contact second order neurones.
Describe the second and third order neurons of the dorsal column-medial lemniscus pathway.
Second order neurons send fibres from the gracile and cuneate nuclei of the medulla to the ventral posterior lateral (VPL) nucleus of the thalamus.
Third order neurons are in the ventral nuclear group of the thalamus and send fibres to the primary somatosensory cortex of the parietal lobe.
What is the medial lemniscus?
The tract formed in the medulla by sensory decussation, which transmits the axons to the VPL nucleus of the thalamus.
Which first order neurons terminate in the cuneate nucleus and which terminate in the gracile nucleus of the medulla?
Axons from the lower body enter the dorsal column below T6 and travel in the gracile fasciculus (gracile tract) to the gracile nucleus.
Axons from the upper body enter at or above T6 and travel up the posterior column more laterally in the cuneate fasciculus (cuneate tract) to the cuneate nucleus.
Describe the spinothalamic / anterolateral pathway.
The tract via which pain and temperature sensation is transmitted.
Describe the first and second order neurons of the spinothalamic pathway.
First order neurons terminate in the dorsal horn of the spinal cord.
Second order neurons decussate immediately in the spinal cord and from the spinothalamic tract. These neurons terminate in the ventral posterior lateral (VPL) nucleus of the thalamus.
What are the different types of pain transmitted by A delta and C fibres?
A delta fibres mediate sharp, intense pain.
Type 1: noxious mechanical.
Type 2: noxious heat.
C fibres mediate dull, aching pain. Noxious thermal, mechanical and chemical stimuli.
Which tracts carry the “sensory” and “emotional” components of pain?
Sensory component = lateral spinothalamic tract.
Emotional component = spinoreticular tract.
Give an example of an ascending control pathway in nociception.
Gate-control theory.
Inhibition of primary afferent inputs before they are transmitted to the brain through ascending pathways, e.g. if you rub your elbow yourself.
What are the two types of chronic pain?
Nociceptive: noxious stimulation of a nociceptor (somatic or visceral).
Neuropathic: lesion or disease of the somatosensory system.
Mixed nociceptive and neuropathic chronic pain is commonest in which 2 conditions?
Lower back pain
Osteoarthritis.
Define allodynia and hyperalgesia.
Allodynia: pain due to a stimulus that doesn’t normally provoke pain.
Hyperalgesia: increased pain form a stimulus that normally provokes pain.
Define the term “motor unit”
A single motor neuron together with all the muscle fibres that it innervates. On average, each motor neurone supplies about 600 muscle fibres. Stimulation of one motor unit causes contraction of all the muscle fibres in that unit.
Which motor unit fatigues more quickly: a slow motor unit or a fatigue resistant fast motor unit?
A slow motor unit fatigues more slowly than the “fatigue resistance” fast motor unit.
