NMH; Lecture 1, 2, 3 and 4 - Brainstem and CN, Spinal cord function and dysfunction, Anatomy of blood flow in CNS and consequences of disruption, regulation of blood flow and BBB Flashcards
What is the brainstem?
The part of CNs that sits between cerebrum and spinal cord (w/out cerebellum)
What are the major divisions of the brainstem?
Medulla oblongata, pons and midbrain
Where does the brainstem lie?
In the posterior cranial fossa
Where does the pineal gland lie and what does it do?
Sits on roof of midbrain, secretes melotonin and is used in the cicadian rhythm
FITB for the posterior view of the midbrain
NB: the pons is the floor of the 4th ventricle and the roof of the the 4th ventricle is the cerebellum
What is the function of the superior colliculus?
Involved in coordination of eye and neck movement
What is the function of the inferior colliculus?
Do the auditary reflexes
What does the trochlear nerve do?
It attaches to the superior oblique muscle in the eye (CN)
What does the dorsal column do?
Proprioception and fine touch is processed here
What lies behind the optic chiasm?
The pituitary stalk (infundibulum
What are the mammillary bodies a part of and what do they do?
Involved in memory, part of the hypothalamus and the limbic system
What does the oculomotor nerve do?
Important in conjugate eye movement
What is the cerebral peduncle?
It holds the cerebrum to the brainstem, with corticospinal tract (main pathway controlling motor function) moving across this
What is the trigeminal nerve?
Only CN from the pons - supplies the chewing muscles
Which CN emerge from the Pontomedullary junction?
Abducens nerve (supplies lateral tract movement) and facial nerve (supplies face) and vestibulocochlear nerve
What does the hypoglossal nerve supply?
The intrinsic nerve of the tongue
What are the pyramids?
The manifestation of the corticospinal tract
What is a general somatic afferent?
Sensation from skin and mucous membranes
What is general visceral afferent?
Sensation from GIT, heart, vessels and lungs
What is the general somatic efferent?
Muscles for eye and tongue movements
What is general visceral efferent?
Preganglionic PSNS
What is the special somatic afferent?
Vision, hearing and equilibrium
What is the special visceral afferent?
Smell and taste
What is the special visceral efferent?
Muscle involved in chewing, facial expression, swallowing, vocal sounds and turning head
What are the functional classifications of brainstem nerves?
GSA, GVA, GSE, GVE, SSA, SVA, SVE
What does the embryonic spinal cord look like?
NB: dorsal is motor output and ventral is sensory input
FITB of the motor and sensory nuclei - where they’re located and their functional classification
x
Midbrain anatomy - ID in picture
Cerebral aqueduct is the ventricular system at that level.
What is the substantia nigra?
The first bit to become damaged in Parkinson’s and it is a nucleus in most healthy people
Pons anatomy - ID in picture
Pons is floor of fourth ventricle - middle cerebellar peduncle holds the cerebellum to the brainstem
Medulla anatomy - ID in picture
Inferior olivary nucleus is easy to ID
Lower medulla anatomy - ID in picture
Cross-like structure is unique
What is the lateral medullary syndrome?
Thrombosis of vertebral artery or PICA
What are the symptoms of lateral medullary syndrome?
Vertigo, Ipsilateral cerebellar ataxia (shuffling, slow and loss of balance), ipsilateral loss of pain/thermal sense in face, Horner’s syndrome (loss of SNS tone in head and neck), hoarseness, difficulty in swallowing, contralateral loss of pain/thermal sense (trunk and limbs)
Why are the symptoms caused in lateral medullary syndrome?
Vestibular causes vertigo, inferior cerebellar peduncle is inflammation coming from spinal cord to cerebullum so loss of fine motor control so ataxia is caused; trigeminal involved in pain and temperature; N ambiguus causes hoarseness of voice
What is the function of nucleus solitarius?
Taste
What are the functions of the spinal cord?
Motor, sensory, autonomic
What are the segments of the spinal cord?
Cervical, thoracic, lumbar and sacral
What would a lesion in the cervical section cause?
Loss of function everywhere, and could be life threatening as the lungs and heart may not receive innervation
What would a lesion in the thoracic section cause?
Not as dramatic as cervical but can still lead to paraplegia and loss of sexual and genital function
What are the functions of the spinal segments?
x
How does the sensorimotor pathway work?
The spinal cord sends sensory information to thalamus and sensory cortex
How does the motor pathway function?
Humunculus motor cortex, down to medulla where it then reaches the pyramidal decussation and switches sides forming the lateral corticospinal tract and the anterior corticospinal tract
What is the difference between the anterior and lateral corticospinal motor pathway?
The lateral pathway decusses at the pyramid in the medulla
What is the difference between the posterior column-medial lemniscus and anterolateral sensory pathways?
The posterior column-medial lemniscus pathway reaches a nucleus in the medulla oblongata where the nerve switches sides. In anterolateral the nerve continues until it reaches the spinal cord where it switches sides and leaves the spinal cord via the opposite side.
What are the main autonomic pathways?
x
What are the functions of the autonomic pathways?
x
What are the spinal cord fibre tracts?
x
What is the proportion of the brain supply compared to the rest of the body?
10-20% of CO, 20% of body O2 consumption, 66% of liver glucose -> vulnerable if blood supply impaired
How is the brain supplied?
Internal carotid arteries and vertebral arteries. Circle of willis and cerebral arteries are minor supplies
What is the venous drainage of the brain?
Cerebral veins, venous sinuses, dura mater and internal jugular vein
Anatomy of the dural venous sinuses
x
What is a stroke?
Cerebrovascular accident -> rapidly developing focal disturbance of brain function presumed vascular origin and of >24h duration
What are the 2 types of stroke and how common are they?
Infarction (85%) and haemorrhage (15%)
What is a transient ischaemic attack?
Rapidly developing focal disturbance of brain function of presumed vascular origin that resolves completely within 24h
What is an infarction?
Degenerative changes which occur in tissue following occlusion of an artery
What is cerebral ischemia?
Lack of sufficient blood supply to nervous tissue resulting in permanent damage if blood flow is not restored quickly -> hypoxia and anoxia
What are the causes of occlusions causing cerebral ischemia?
Thrombosis or embolism
What is the epidemiology of stroke?
3rd most common cause of death with 50% of survivors are permanently disabled with 70% showing a neurological deficit
What are the main risk factors for stroke?
Age, hypertension, cardiac disease, smoking, diabetes mellitus
What happens if the anterior cerebral artery is occluded?
Paralysis of contralateral leg>arm face; disturbance of intellect, executive function and judgement with loss of appropriate social behaviour
What happens if the middle cerebral artery is occluded?
Classic stroke with contralateral hemiplegia arm > leg with contralateral hemisensory deficits and hemianopia, with aphasia (L-sided lesion)
What happens if the posterior cerebral artery is occluded?
Visual deficits -> homonymous hemianopia and visual agnosia
What are lacune and what are lacunar infarcts?
Small cavity appearing in deep structures as a result of small vessel occlusion -> deficit dependent on anatomical location and hypertension
What are the types of haemorrhagic stroke?
Extradural (trauma, immediate effects); subdural (trauma, delayed effects); subarachnoid (ruptured aneurysms); intracerebral (spontaneous hypertensive)
What is the blood flow to the brain?
High at 55ml/100g tissue/min
What happens when blood flow to the brain reduces by more than 50%?
Insufficient oxygen delivery, function becomes significantly impaired
What happens when cerebral blood flow is cut off?
If interrupted for little as 4 seconds, unconsciousness results - few minutes irreversible damage occurs to brain
What is syncope?
Fainting - common manifestation of reduced blood supply to the brain
What causes syncope?
Many causes including low BP, postural changes, vaso-vagal attack, sudden pain, emotional shock
What is the result of syncope?
Temporary interruption/reduction of blood flow to the brain
What is the main supply to the brain and why can the brain not use any other form?
Surplus provision of glucose to the brain via the blood -> brain can’t store, synthesise or utilise any other source of energy
What happens to brain function when hypoglycaemic?
Individual appears disoriented, slurred speech, impaired motor function -> glucose conc <2mM can result in unconciousness, coma and death
What is cerebral blood flow regulated by?
Mechanisms affecting total cerebral blood flow and which relate activity to requirement in specific brain regions by altered localised blood flow
What is the MABP of total cerebral blood flow?
Autoregulated between 60 and 160mmHg
What is the circle of Willis?
Anastamotic group of arteries which lead to cerebral arteries
Where do the carotid arteries bifurcate?
At the laryngel prominence (Adam’s apple)
Where does the external carotid supply?
Supplies the face
Where does the internal carotid supply?
Anterior portions of the brain moving up through the back of the skull
Where does the subclavian supply?
Posterior portion of the brain - going via the vertebrae
Where does the basilar artery lie?
Anterior surface of the pons
What does the arterial supply of the brain look like?
Vertebral arteries are symmetrical
What is the largest branch of the cerebral arteries?
Basilar artery
What are venous sinuses?
Fold in the dura
Where does all the blood drain into from the brain?
Internal jugular vein
Which artery in the circle of willis is unpaired?
Anterior communicating artery
Anatomy of the Circle of Willis
x
Where does the Anterior, Middle and Posterior cerebral artery supply?
x
Why is an anterior cerebral artery occlusion lead to higher paralysis of the contralateral leg rather than the arm?
Due to the upside down homunculus in the primary sulcus
When can a middle cerebral artery lead to complete hemiparesis?
When it is in the subcortical area rather than cortex
Why does aphasia occur in middle cerebral artery occlusion?
If stroke on left hand side occurs in subcortex
Anatomy of the meninges and superficial cerebral veins
x
Which vascular problem is most likely to require RAPID neurosurgical intervention?
Extradural
How does the autoregulation of cerebral blood flow work?
Stretch sensitive cerebral vascular smooth muscle contracts at high BP and relaxes at lower BP
What happens if the cranial blood flow is above the autoregulatory pressure range?
Increased flow leads to swelling of the brain tissue which isn’t accommodated by the cranium so intercranial pressure increases
What happens if the cranial blood flow is below the autoregulatory pressure range?
Insufficient supply leads to compromised brain function
What is local autoregulation?
Local brain activity determines ocal O2 and glucose demands, so local changes in blood supply are required
What carries out local regulation of cerebral blood flow?
Neural and chemical control
Which neural factors regulate cerebral blood flow?
Sympathetic nerve stimulation, PS stimulation, central cortical neurones, dopaminergic neurones
How does sympathetic nerve stimulation regulate cerebral blood flow?
To main cerebral arteries, producing vasoconstriction - only operating when arterial BP is high
How does parasympathetic nerve (facial nerve) stimulation regulate cerebral blood flow?
Producing slight vasodilation
How do central cortical neurones regulate cerebral blood flow?
Release a variety of vasoconstrictor neurotransmitters (catecholamines)
How do dopaminergic neurones regulate cerebral blood flow?
Produce vasoconstriction - localised effect related to increased brain activity
What is the function of dopaminergic neurones?
Innervate penetrating arterioles and pericytes around capillaries – participates in diversion of cerebral blood to many areas of high activity -> DA causes contraction of pericytes via aminergic and serotoninergic receptors
What are pericytes?
Form of brain macrophages with diverse activities -> immune function, transport properties, contractile
How is the vascularisation in the CNS tissues set out?
Arteries from pia penetrate into brain parenchyma branching, forming capillaries which drain into venules and veins and then into pial veins
What are the chemical factors that influence cerebral blood flow?
x
How does pCO2 affect CBF?
Brain activity increases blood flow
How does CO2 vasodilate cerebral arteries?
May also affect production of NO, potent relaxant of SM.
How is the brain compartmentalised in the cranium?
Floating in CSF produced by regions in choroid plexus in cerebral ventricles -> important protective mechanism
Where is CSF produced?
In the choroid plexus, the lining of ependymal cells are modified to form branched villus structures to waft the CSF
How is CSF formed?
Capillaries in choroid plexus leaky, but adj ependymal cells have extensive tight junctions which secrete CSF into ventricles which circulates.
How does the CSF move from the choroid plexus around the brain?
Lateral ventricles, 3rd ventricles via interventricular foramina down cerebral aqueduct into 4th ventricle and into subarachnoid space via medial and lateral apertures
What is the volume of CSF?
80-150ml
What is the function of CSF?
Physical and chemical protection, nutrition of neurones, transport of molecules
What is the composition of plasma and CSF?
pH and osmolarity is very similar -> protein is very low in CSF usually but prescence of protein can indicate a CNS infection/problem
Where is the blood brain barrier?
Level of the capillaries of the CNS
What is the function of the BBB?
Activity of neurones is highly sensitive to composition of local environment and CNS needs to be protected from fluctuations in composition in blood
How are the walls of capillaries in the BBB different from normal capillaries?
Have extensive tight junctions at the endothelial cell-cell contacts, massively reducing solute and fluid leak across capillary wall
How do the interendothelial junctions differ between peripheral and BBB capillaries?
How does pericyte coverage differ between BBB and peripheral capillaries?
Closely apposed to capillaries in BBB, with important functions in maintaining capillary integrity and function, densely covered - peripheral is sparsely covered
Where do astrocytes cover BBB capillaries and why?
On end-feet to maintain BBB properties
Which substances can’t cross the BBB?
Mainly hydrophilic solutes (glucose, a.a., antibiotics, some toxins)
Why is the tightness of the BBB useful?
Allows control of exchange of substances using specific membrane transporters to transport in and out of CNS. Also prevents blood-borne infectious agents direct entry into CNS tissues
Which molecules can cross the BBB?
Lipophilic molecules (O2, CO2, alcohol) which have access to CNS directly via diffusion down conc grad.
How can hydrophobic substances enter the CSF and brain?
Water via AQP1/4, glucose via GLUT1,, a.a. via 3 diff transporters and electrolytes via specific transporter systems
Which regions do we not need a BBB?
Circumventricular organs -> close to ventricles
How do the CVOs work?
Capillaries are fenestrated but ventricular ependymal lining close to these areas can be much tighter than other areas, limiting exchange
Why do we need CVOs?
Generally involved in secreting into circulation/need to sample plasma
Give some examples of uses of CVOs?
Posterior pituitary and median eminence secrete hormones, and the area postrema samples the plasma for toxins and will induce vomiting. Others are involved in sensing electrolytes and regulate water intake.
What is the clinical importance of BBB?
Breaks down in many pathological states: inflammation, infection, trauma, stroke which can have effects on CNS -> pharm needs to know whether drug enters brain causing adverse effects
What used to occur with anti-histamines and the BBB?
Older anti-histamines could cross the BBB causing drowsiness, which are now used as sedatives -> now anti-histamines are polar so cannot cross the BBB
How does the BBB affect treatment of Parkinson’s?
Key therapy increases levels of DA in brain, but peripheral admin doesn’t work as it can’t cross the BBB -> L-dopa can cross via a.a. transporter and is converted into DA in the brain BUT also happens in periphery so little is accessible in brain, so need to inhibit outside brain -> co-admin with dopa decarboxylase inhibitor is used
What is the purpose of the enlargements in the spinal cord and where are they located?
In the cervical and lumbar areas due to a large number of nerves leaving the spinal cord
What is the cauda equina?
The horse-tail of nerves that leave the vertebral column at the sacral and lower lumbar levels after the spinal cord has stopped
What do the cervical nerves innervate?
Neck and arms
What do the thoracic nerves innervate?
Innervate organs without lungs and heart
What do the lumbar nerves innervate?
Limbs
What do the sacral nerves innervate?
Urogenital system -> ejaculation, urination, defecation
What is the purpose of the enlargements in the spinal cord and where are they located?
In the cervical and lumbar areas due to a large number of nerves leaving the spinal cord
What is the cauda equina?
The horse-tail of nerves that leave the vertebral column at the sacral and lower lumbar levels after the spinal cord has stopped
What do the cervical nerves innervate?
Neck and arms
What do the thoracic nerves innervate?
Innervate organs without lungs and heart
What do the lumbar nerves innervate?
Limbs
What do the sacral nerves innervate?
Urogenital system -> ejaculation, urination, defecation
What is Brown-Sequard syndrome?
Contrallateral pain and temperature and ipsilateral loss of fine touch and proprioception (paralysis)
