3. CNS/PNS Flashcards
Name 4 Parasympathetic ganglia kip
Parasympathetic ganglia:
- Ciliary ganglion innervating the sphincter pupillae and the ciliary muscle
- Pterygopalatine ganglion innervating the lacrimal gland and glands of the nasal cavity
- Submandibular ganglion innervating the submandibular and sublingual glands
- Otic ganglion innervating the parotid gland
Are the parasympathetic fibres myelinated? whats is the neurotransmiter
- Receive myelinated preganglionic nerve fibres
- actelycholine (Ach) as the neurotransmitter.
- post-ganglionic fibre is shorter, unmyelinated and also has Ach as the principal transmitter.
Lateral spinothalmaic tract
Contain fibres project to where
Where do they synsapse pass deccusate and pass to where
Where do posterior colums deccusate
how many neurones reuqired to convey sens info to cortex
What is carreid by the ST tract
where is the remained carried by
Where do they pass to
The lateral spinothalamic tract contains fibres that project to non-specific thalamic nuclei.
Axons carrying sensory information synapse in the dorsal horn of the spinal cord, decussate and then pass as second-order neurones to the thalamus and reticular formation.
The posterior columns decussate at the brainstem.
Three neurons are rquired to convey sensory information from the periphery to conscious level at the cerebral cortex.
Pain and temperature are associated with the lateral spinothalamic tract whilst the remainder of the touch fibres (not carried by the dorsal columns) are associated with the anterior (ventral) tract. They contain nerve fibres from receptors on the contralateral side of the body.
Fibres from the lateral spinothalamic tracts pass to the thalamus and reticular formation, and they have no direct path to the cerebellum.
Epidural space
Starts where ends where - what shape
Dural sac ends where adults & kids
Pressure - why
Where is it greatest
What does it contain x 5
The epidural space extends downwards from the foramen magnum to the sacral hiatus and is triangular in cross-section.
The dural sac ends at S2 in an adult and S3/4 in an infant.
The pressure in the epidural space is subatmospheric (negative), due to transmission of the subatmospheric intrathoracic pressure through the intervertebral foramina.
It is greatest in the upper and middle thoracic regions and lowest in the lumbar and sacral regions, as distance from the thorax increases.
The epidural space contains:
Fat Epidural veins (Batson's plexus) Small arteries Lymphatics, and Spinal nerve roots.
Enzymes & NT
GABA syhtn by what
COMT Does what
MAOi does what
What metab ach
Glutamic acid decarboxylase does synthesise gamma-aminobutyric acid (GABA).
However, catechol-o-methyl transferase and monoamine oxidase metabolise norepinephrine to vanylmethylmandelic acid (VMA).
Monoamine oxidase metabolises serotonin to 5-hydroxyindole acetic acid (5-HIAA).
Cholinesterase metabolises acetylcholine.
CSF
pH - vs plsama
Conc higher or lowe than plasma
Na Cl K Na Ca Protein Bic
Opening pressure
glucose conc vs plamsa
CSF has a pH of 7.31, therefore lower than plasma.
It has a lower concentration of potassium, calcium, and protein than plasma. It has a higher concentration of sodium, chloride, bicarbonate and magnesium.
The CSF typically has no cells present but white cells should be less than 4/ml.
The pressure of CSF is typically less than 20 cm of water.
It has approximately two-thirds the glucose concentration of plasma with a concentration of approximately 3.3-4 mmol/L.
Cerebral ischaemia -
Levels of blood flow
normal
EEG Changes
Cerebral ischaemia can either be global or focal, either complete or incomplete. At blood flow levels of 30-40 ml/100 g/min EEG changes begin to appear. The EEG changes that suggest poor prognosis are low voltage, poorly reactive rhythms, periodic lateralised epileptiform discharges and fluctuations in underlying rhythms.
Glucose will still be metabolised albeit anaerobically. The waste products of anaerobic metabolism will not be removed efficiently due to reduced blood supply. This results in worse acidosis compared to complete cessation of blood supply.
Studies to prove whether incomplete ischaemia causes more damage than complete ischaemia have been inconclusive. At 30-40 ml/100 g/min causes EEG changes as described above. When the blood flow decreases to 20 ml/100 g/min lactate levels increase. Between 20 ml/100 g/min - 10 ml/100 g/min free radicals are released and evoked potentials begin to disappear.
At flow rates lesser than 10 ml/100 g/min irreversible damage occurs due to water accumulation.
How much does brain weigh % wise body weight
how much CO occurs
How is CBF controlled mainly
over what MAPs
Beyond limits proportional to what
Autoreg mainly controlled by what
The brain weighs only 3% of the body weight, but it receives 15% of the cardiac output.
Autoregulation of cerebral blood flow (CBF) occurs between mean arterial pressures (MAP) of 60 - 130 mmHg, over which the CBF is maintained at a constant level.
Beyond these limits the CBF is directly proportional to the mean arterial pressure (not systolic blood pressure).
The mechanism of CBF autoregulation is controlled predominantly by the PaCO2 level, whereas the autonomic nervous system has a minimal role.
How are the following transmiited
Vibration pain temperature proprioception joint positon
Pain is transmitted in the spinothalamic tracts.
Temperature is also transmitted in the spinothalamic tracts.
The impulses responsible for the vibrating sensation are carried in the dorsal column.
Proprioceptive information is transmitted up the spinal cord in the dorsal columns.
Joint position, or proprioception is transmitted up the fasciculus gracillis and cuneatus tracts in the dorsal columns.
genetic code is how many triplets of nucleotides
each codon codes what
is there any exception
Pyrimidine bases are
Purine bases are
what pairs with what
The genetic code consists of 64 triplets of nucleotides. These triplets are called codons.With three exceptions, each codon encodes for one of the 20 amino acids used in the synthesis of proteins. Most amino acids are encoded by more than one codon.
Pyrimidine bases are thymidine (T) and cytosine (C).
A and G are purine bases
G always pairs with C and T with A.
What are the opioid receptors
where are they present
here are four opioid receptors:
Mu - mu opioid receptor (also known as μ-opioid peptide or MOP) is present in the brain, spinal cord and the periaqueductal grey, produces analgesia, meiosis, euphoria, respiratory depression, bradycardia, constipation
Kappa - the kappa opioid receptor (κ-opioid receptor or KOP) produces analgesia, sedation, miosis
Delta - the delta opioid receptor (δ-opioid receptor or DOP) produces analgesia, respiratory depression
Nociceptin opioid receptor (NOP).
Opioid receptors are inhibitory G protein coupled receptors.
Chemoreceptors
where are they located in brain
what do they respond to
carotid respond to what
Is there another response to hypotension by baroreceptors
Medullary chemoreceptors respond directly to changes in CSF pH and therefore hydrogen ion concentration rather than CO2. However CSF pH does not change rapidly in response to CO2, which readily crosses the blood brain barrier (BBB).
The carotid chemoreceptors are primarily stimulated by changes in partial pressure of oxygen in the blood and not hydrogen ions
The buffering capacity of the CSF is less than that of plasma. Hydrogen ions do not directly cross the BBB but do stimulate respiration by an effect on the peripheral chemoreceptors.
As part of the baroreceptor reflex there is respiratory stimulation in response to hypotension
Normal ICP is
Intracranial pressure (ICP) is important as it affects cerebral perfusion pressure and cerebral blood flow. Normal ICP is between 5 and 13 mmHg.
Constituents within the skull include the
Brain (80%/1400 ml)
Blood (10%/150 ml) and
Cerebrospinal fluid (CSF 10%/150 ml).
The skull is a rigid box so if one of the three components increases in volume, then there must be compensation by a decrease in the volume of one or more of the remaining components otherwise the ICP will increase (Monro-Kellie hypothesis).
Primary and secondary injury
Primary brain injury occurs at the time of the head injury and is unavoidable except through preventative measures to reduce the incidence of head injury. Secondary brain injury is caused by a reduction in oxygen delivery due to hypoxaemia (low arterial PaO2) or anaemia, a reduction in cerebral blood flow due to hypotension or reduced cardiac output, and factors which cause a raised ICP and reduced CPP. Secondary brain injury is preventable through appropriate management.
T
Techniques that can be employed to reduce ICP are
Techniques that can be employed to reduce ICP are aimed at reducing the volume of one or more of the contents of the skull.
Reduce brain tissue volume
Reduce blood volume
Reduce CSF volume.
Techniques to reduce brain tissue volume include:
Tumour resection or abcess removal
Steroids (especially dexamethasone) to reduce cerebral oedema
Mannitol/furosemide or hypertonic saline to reduce intracellular volume
Decompressive craniectomy to increase intracranial volume.
Techniques to reduce blood volume include:
Evacuation of haematomas
Barbiturate coma to reduce cerebral metabolic rate and oxygen consumption and therefore cerebral blood volume
Arterial: avoiding hypoxaemia, hypercarbia, hyperthermia, vasodilatory drugs, hypotension
Venous: patient positioning with 30° head up, avoiding neck compression with ties/excessive rotation, avoiding PEEP/airway obstruction/CVP lines in neck.
Techniques to reduce CSF volume include:
Insertion of external ventricular drain or ventriculoperitoneal shunt to reduce CSF volume (although more a long term measure).
Acromegaly - what is it
what does it secrete
How are they classified
In more than 95% of people with acromegaly a benign tumour of the pituitary gland called an adenoma produces excess growth hormone (GH).
Pituitary tumours are labeled either micro- or macro-adenomas, depending on their size. Most GH-secreting tumours are macro-adenomas, meaning they are larger than 1 cm.
The other causes of acromegaly are rare.
CSF produced by what
how much a day
what rate is that
Total volume
where distributed
change icp affect?
CSF is produced by the choroid plexus at a rate of 0.3 mL/min. 500 mL are produced per day.
The total volume in an adult is between 125 and 150 mL, with two thirds surrounding the brain and one third surrounding the spinal cord.
Production is unaffected by changes in intracranial pressure (ICP), but absorption by the arachnoid villi is increased when the ICP is elevated.
Adenosine receptors - surface what cells
How many subtype
are a1 a2 present centrally or periph
A1 & A2 with regarads pain
Adenosine receptors are expressed on the surface of most cells, and four subtypes are known to exist (A1, A2A, A2B and A3)
The A1 and A2 receptors are present both peripherally and centrally, with agonists at the A1 receptors being antinociceptive and agonists at the A2 receptors being algogenic (that is, activation results in pain).
The role of adenosine and other A1 receptor agonists is currently under investigation for use in acute and chronic pain state
WHat is outside the blood brain barier
Lipid or water solbubiltiy cross
Is it as effective in paeds
is it altered by inflamm
he blood brain barrier (BBB) consists of the ultrafiltration barrier in the choroid plexus and the barrier around cerebral capillaries.
The hypothalamus, third and fourth ventricles and the chemoreceptor trigger zone (CTZ) are located outside the BBB (not inside).
Water oxygen and carbon dioxide cross the BBB freely, but glucose is controlled. The ability of chemicals to cross the barrier is proportional to their lipid solubility (not water solubility), and inversely proportional to their molecular size and charge.
The BBB is less effective in neonates than in adults, which explains why there is increased passage of opioids and bile salts (kernicterus) into the neonatal brain.
Meningitis alters the effectiveness and permeability of the barrier, and this effect helps the passage of antibiotics which would otherwise not be able to cross the BBB.
Injury to anterior cord
Hemisection
Injury to the anterior spinal cord results in paralysis (motor loss) below the level of the lesion, with proprioception, touch and vibration senses being preserved.
Hemisection of the cord (Brown-Sequard syndrome) results in ipsilateral paralysis and loss of proprioception, touch and vibration sense,
with loss of pain and temperature sensation on the contralateral side.
SNS
arises from where
preganglionic
legnth
myelination
Where doe they synapse
What is the NT here
Post ganglionic
are what length
Myelination
NT
The sympathetic nervous system arises from the lateral horns of grey matter of spinal cord at levels T1-L5 (thoracolumbar outflow). They usually have short myelinated preganglionic neurones synapsing in ganglia lateral to the vertebral column. The neurotransmitter at this point is acetyl chloline (Ach).
The longer unmyelinated postganglionic neurones then synapse with effector organ where the neurotransmitter is adrenaline or noradrenaline.
Parasympathetic
orign where
What nerves
where else
Preganglionic neurons
myelin/not
length
NT - what
Post ganglionig
myelinated
length
NT
The parasympathetic nervous system has a craniosacral outflow.
The origin of the cranial outflow is in the midbrain and medulla (cranial nerves III, VII, IX and X) and the sacral outflow S2, S3 and S4.
They usually have long myelinated preganglionic neurones synapsing in ganglia close to the target organ. The neurotransmitter at this point is Ach. The shorter unmyelinated postganglionic neurones then synapse with effector organ where the neurotransmitter is again Ach.
