Physiology (Brain/ CSF/ Pain) Flashcards
How is CSF formed?
The choroid plexus in the ventricles produce CSF.
Derived from plasma filtration.
Total CSF volume = 150 mls. Produced at a rate of 0.3mls/min.
Reabsorbed by the arachnoid villi into the dural venous sinuses.
Rate of CSF re-absorbtion is proportional to its outflow pressure.
Pathway for CSF around the body?
Choroid plexus (in 3/4/lateral ventricles) lateral ventricles
-> FORAMEN of MONRO -> 3rd ventricle
–> Sylvian aquaduct –> 4th ventricle
–> FORAMEN MAGENDIE & FORAMEN LUSHKA —–> Spinal canal
—-> reabsorbed be the arachnoid villi in the venous sinuses
What unique features allow selective filtration at the blood brain barrier?
- Tight junctions and fenestrated choroidal capillaries
2. Specialised bidirectional transport system for ions, glucose and amino acids.
Differences between CSF and plasma compositions?
Protein - CSF contains 1% of that in plasma
Calcium - CSF 50% of plasma
Glucose - CSF 60% of that plasma
Cl + Mg - higher in CSF
What investigations can be performed on CSF?
- Opening pressures - Normal 10-15cm H2O lying, 20-30cm H2O sitting
- Macroscopic appearance - ie. xanthochromia
- Total and differential cell count
- Bacterial culture and sensitivity
- Protein and glucose
- Analysis immunoglobulines
- Cytology
What changes in CSF cell count can occur with different infections/ malignancy?
Bacterial - increase in neutrophils
Viral - increase in lymphocytes
TB - mixed reaction/ increase in plasma cells
Haematological malignancy - leukaemic cells
What is the ANS?
It is as collection of nerves and ganglia that are involved in the homeostatic control of homeostasis and the stress response.
Describe the structure of the ANS.
- Two divisions - sympathetic and parasympathetic
- Parasympathetic - rest and digest
- Sympathetic - fight or flight response
- ANS receives afferent information from chemoreceptors, baroreceptors, and CNS. Processes this information and relays it through efferent pathways to target tissues.
- Efferent pathway consists of: pre-ganglionic fibre - autonomic ganglion - postganglionic fibre.
What type of fibres are pre-ganglionic and where are they?
Type B fibres
Parasympathetic:
Lie within nuclei of 3, 7, 9 and 10 cranial nerves and
lateral grey horns of 2-4 sacral segments.
(LONG craniosacral outflow tract)
Sympathetic: lie in lateral grey horns of 1 - 12th thoracic segments \+ 1-3 lumbar segments (short - thoracolumbar outflow tract)
Autonomic ganglia:
Where are they located?
PNS:
1. Terminal ganglia -located close to target cell
SNS:
1. paravertebral (sympathetic trunk) - either side of vertebral column
- pre-vertebral - anterior to the vertebral column next to major arteries
Where will you find post ganglionic fibres and what type of fibres are they?
Unmyelinated Type C fibres
PNS: Short, cell bodies within autonomic ganglia
SNS: long, cell bodies within autonomic ganglia
Grey rami connect SNS ganglia to spinal nerves
What neurotransmitters are present within ANS?
PRE-GANGLIONIC:
Cholinergic = all Ach
POST GANGLIONIC:
- Para - all cholinergic - Ach
- Sympathetic
- sweat glands = cholinergic/ Ach
- all others are adrenergic = noradrenaline
ADRENAL MEDULLA
- glorified SNS post-ganglionic fibre releases 80% adrenaline, 20% noradrenaline
What types of receptors are present in ANS?
- Nicotinic Ach R. - all autonomic ganglia and adrenal medulla
- Muscarinic Ach R. - PNS receptor organs, and SNS sweat gland
- Adrenergic Ach R. - SNS receptor organs (alpha or Beta)
Define pain and classify pain.
Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage.
Can be classified by the chronicity of pain - acute, chronic or by its nature ie. nociceptive or neuropathic.
Acute - limited onset, identifiable cause related to injury/disease.
Chronic - persists beyond trauma, no clearly definable cause.
Nociceptive:
- Superficial somatic pain (skin) - sharp, localised
- Deep somatic pain (ligaments, tendons, muscles) - dull ache
- Visceral pain (organs/ viscera) - cramping, varying location, referred pain + autonomic stimulation.
Neuropathic - due to dysfunction of the nervous system.
Give a detailed description of the pain pathway that becomes activated if you prick your finger.
- Nociceptors respond to the noxious stimuli which maybe - thermal, mechanical or chemical.
- Tissue damage releases mediators which initiate and sensitise receptor stimulation.
- Action potential is generated and propagated along afferent fibres (C + Adelta) to the dorsal horn of the spinal cord.
- Synaptic transmission with the secondary interneuron occurs in the Rexed’s Laminae.
- Secondary interneurones decussate and travel in the anterolateral spinothalamic tract through the brainstem to the thalamus.
- Here tertiary afferent fibres project to the somatosensory cortex, some spinal ascending fibres transmit impulses to the reticular activating system and to the higher centres involved in emotion and memory.
- Descending fibres from the cortex, thalamus and brainstem exert an inhibitory influence on pain transmission in the dorsal horn.
- An immediate polysynaptic withdrawal reflex occurs at the level of the spinal cord as some interneurones connect to motor neurones at levels, This is a protective reflex.
