Case 2 Flashcards
How many spinal nerves are there?
31 pairs (C-8, T-12, L-5, S-5, C-1)
What is a dermatome?
It is area of the skin inner gated by the right and left dorsal roots of a single spinal segment - there is overlaps in the dorsal root innervation (more for pressure, touch and vibration than pain and temperature)
What are the spinal cell types?
- Interneurones - 97%; connects to other cells in the spinal cord
- projection neurones - 3%; cell axons of ascending pathways (1%) and motor neurones that innervantes skeletal muscles (2%)
What are inhibitory and excitatory neurones?
Spinal cord interneurones
Inhibitory - limit the receptive field or activity of other neurones vis inhibitory neurotransmitters (GABA, Glycine and Enkephalin)
Excitatory - stimulation leads to AP in other cells via use of glutamate and various neuropeptides
Where do somatic sensation originate from?
Afferent nerve fibres activity
What is the somatic sensory receptors?
Mechanoreceptors
Some lack these receptors - these fibres are important in sensation of pain
What is the process of sensory transduction?
Stimuli > change in ionic permeability of receptors > receptor potential triggers AP
What are the different types of afferent fibres?
(From biggest diameter to smallest)
- 1a/A-alpha: supply sensory muscle spindles, Golgi tendon Organs receptors (proprioception)
- A-Beta: supply sensory muscle spindles, meissner corpuscle, merkel’s disks, Pacinian corpuscle, and Ruffini endings receptors ( proprioception, heavy pressure, light touch, deep touch/vibration + skin stretch)
- A-Delta: nociceptors and thermoreceptors (pain and temperature)
- C: nociceptors and thermoreceptors (pain and temperature)
What type of receptors does A-Beta fibres supply?
Mechanoreceptors which are low-threshold receptors I.e. provide rapid central transmission of Tactile (touch) information
What is the function of muscle spindle?
Provide information about muscle length i.e. degree to which it is stretched
What does the Golgi Tendon Organs do?
They inform the CNS about changed in muscle tension from the collage fibres
What fibres are linked with Muscle Spindle?
1a (primary sensory endings) and 1b fibres carry information to CNS, information is relayed back to the muscle via gamma motor fibres causing muscle to contract
Which sensations are involved in somatosensory?
Touch, pressure, pain, temperature and proprioception
Where is the cell body for somatosensory neurones found?
Ganglion (collection of cell bodies outside CNS)
What is the main sensory relay centre?
Thalamus
Where are third neurones of somatosensory pathway found?
Ventral posterior nucleus in the thalamus (VPN)
What are the ascending tracts?
- Spinothalamic : lateral - pain and temperature; ventral - pressure and touch; 2 order neurone decussate on spinal cord
- Dorsal Columns: discriminative touch, vibration and proprioception; fasiculus Gracilis - mid-thoracic and lower limbs; fasiculus cuneatus - upper limbs; decussation of 2 order neurone is in the nucleus gracilis or cuneatus in medulla > forms the medial Lemniscus
What are the fibres in the medial Lemniscus called?
Internal raciste
What is the two divisions of the VP complex of the thalamus?
Lateral nucleus - somatosensory information from medial Lemniscus
Medial nucleus - trigeminal Lemniscus from pricipak or spinal nucleus (mechanisensory or painful and thermal stimuli)
Where is the primary somatic secondary Cortex locates?
Post central gurus of parietal lobe
Where does the primary sensory cortex send projections?
Secondary somatosensory > limbus structures (amygdala and hippocampus for tactile learning and memory)
Descending fibres to thalamus, brain stem and spinal cord
What do the somatic motor pathways (descending tracts) carry?
Motor information from brain to spinal cord and then periphery
What’s the corticospinal tract?
Motor cortex > fibres travel in internal capsule to medullary pyramids > 75-85% decussate down lateral tract and remaining amount ipsilaterally in ventral tract (they then decussate on spinal cord at level of exit)
UMN decussate before synapsing with LMN
What is the mnemonic for cranial nerves and function?
On Occassion Our Trusty Truck Acts Funny Very Good Vehicle Any How
Some Say Marry Money But My Brother Says Big Brains Matter More
Where are the cranial nerves nuclei found?
Brain stem
Motor nuclei are cell bodies of LMN
What is the cranial nerves sensory pathway?
Ipsilateral 1st order neurone from periphery (ganglion in head region) > synapse in trigeminal nucleus w/ 2nd order nucleus > decussation in brain stem to thalamus > synapse in VPN of thalamus with 3rd order neurones > sensory cortex
Which cranial nerves carry general sensation?
- Trigeminal nerve - 1st order cell body in trigeminal ganglion
- Facial nerve - geniculate ganglion
- Glossopharyngeal and vague nerves - superior and inferior ganglia
What are the three subnuclei of trigeminal sensory nucleus?
Chief sensory - touch and pressure
Spinal - pain and temperature
Mesencephalic - proprioception
What is the corticobulbar tract?
Cranial motor pathway
UMN from cortex descends and decussate sin brain stem > synapse with LMN > exits spinal canal to target
Which Corticobulbar Tracts are bilaterally innervated?
CN III, V, VI, IX, X, XI
Bilateral = left and right UMN innervate the same nucleus in brain stem
Which Corticobulbar tracts are contralateral?
CN XII
Contralateral = UMN from opposite side innervates nucleus in brain stem
What is different with Corticobulbar tract of Facial Nerve (CN VII) ?
Nucleus in brain stem is divided into two:
- upper innervates muscles above eyes; lower innervates muscles below the eyes
- upper part is bilaterally innervated and lower part contralaterally
What is the autonomic Motor Pathway?
UMN cell body in hypothalamus > descends to spinal cord > synapse with preganglionic neurone > synapse in ganglion with postganglionic neurone
What is the difference between parasympathetic and sympathetic ANS?
- Parasympathetic - ganglia are near target cell; pre to post ganglionic neurotransmitter is Ach (NIr) and then Ach to target cell (MUr)
- sympathetic - ganglia are adjacent to spinal cord; Ach (NIr) and then NE (adrenoreceptor)
What is the sympathetic chain?
LMN start from T1-L2
Preganglionic to paravertebral ganglion via white rami communicantes > either:
- Synapse with postganglionic neurone which then goes out through grey rami communicantes to ventral rami at same level to periphery
- Descend/ascend to different ganglion and then go out with ventral rami or as a splanchnique nerve (as itself)
- Synapse with splanchnic nerve at a collateral/prevertevral ganglion (located anterior to aorta)
What is noxious stimuli?
Intense stimuli that causes potential or actual damage to tissues
What system responses to noxious stimuli?
Nociceptive system - high-threshold peripheral and central neurones
What are the two pain pathways?
Slow (C fibres) pathway
Fast (A-delta) pathway
What are nociceptors?
Free nerve endings - cell bodies are found in the spinal ganglia for body and trigeminal ganglia for the face
They are only activated when noxious threshold is reached
What happens when nociceptors are activated?
Sodium ion channels are opened causing depolarisation and generation of AP
What is sensitisation?
Decrease of nociceptors threshold due to continuous stimulation
What are the three classes of nociceptors in the skin?
A-delta mechanical
A-delta thermal
Polymodal (these respond to thermal, mechanical and chemical stimuli and are slow C fibres)
What are the two receptors associated with thermal stimuli?
Trpv 1 respond to temps over 43 degrees
Trpm8 respond to temps below 25 degrees
What is the neurotransmitter for Pain afferent fibres?
- Glutamate: Fibres activate AMPA- type glutamate receptors on dorsal horn
- Substance P: this is for moderate and intense pain and released in C-fibres
What are the two types of pain perceptions?
- A-delta fibres: detect sharp first pain
* C-fibres: detect dull pain but sensation is more long-lasting and delayed
Which pathway passes pain and temperature?
The spinothalamic tract
What is the trigeminal pain pathway?
Transports information from facial nociceptors and thermoreceptors to the brainstem (trigeminal sensory nucleus) to thalamus and then cortex
What is allodynia?
Lowering of threshold of pain, so small stimuli that wouldn’t normally cause pain now causes pain
What is hyperalgesia?
Responsiveness to noxious stimuli increases so an exaggerated and prolonged pain response is caused
How does sensitisation of pain occur?
Peripherally:
reduction of threshold and increase in responsiveness of nociceptors due to inflammatory chemicals
- nociceptive pain comes from activation of nociceptors
Centrally:
Increase in excitability of neurones so that normal inputs now produces abnormal responses triggered by a burst of activity in nociceptors
- neuropathic pain comes from injury to nerves
Which protein is involved in sensitisation of periphery and central system?
Prostaglandins
How does inflammation occur?
Tissue damage results in:
- ATP to depolarise nociceptors
- bradykinin to depolarise nociceptors and sensitise heat-activated ion channels
- prostaglandins increase sensitivity of nociceptors
- substance P secreted by nociceptors themselves and cause vasodilation and release of histamine from mast cells
What is the gate control theory?
States spinal cord may either block or allow pain signals to the brain
release of endorphins can distract us from pain
The spinal cord has large (A-beta) and Small (C) fibres that close and open pain gates respectively
Where does herniation of nucleus pulposus tend to extend?
Posterilaterally in the lumbosacral regions where the IV discs are largest
Most commonly in L4-5/ L5-S1
What causes pain in herniated discs?
Acute pain - pressure on posterior longitudinal ligaments
Chronic pain - compression of spinal nerve roots by herniated disc
What is causa Equina Syndrome?
Damage to cauda equina causes acute loss of function of multiple roots (below L1/2) of lumbar plexus due to central disc compression of trauma/damage
Treated with surgical decompression
Symptoms:
Back pain, saddle anaesthesia (S2-5 dermatomes - perineum external genitalia and anus), distended atomic bladder with urinary retention or overflow incontinence, constipation, decreased rectal tone, faecal incontinence and loss of erections
What is discectomy?
Surgical removal of part or all of a diseased or damage intervertebral disc
What do opioids do?
They bind to opioid receptors to block transmission of pain signals sent by nerves to the brain
Inhibit adenylyl cyclase to reduce intracellular cAMP, promotes opening of potassium channels (hyperpolarisation), inhibit opening f calcium channels
What are is the opioid receptor that deals with pain?
Mu (u1) receptors - give analgesic effects and located in brain, spinal cord, periphery sensory neurones and intestinal tract
u1- unwanted effect = physical dependence
How does cocodamol work?
Opioid derived from morphine but less potent as a pain killer, less sedative and toxic hence less likely to cause dependence
Contains codeine and paracetamol
Side effect: constipation
What are NSAIDs?
non-steriodal anti-inflammatory drugs
MOA:
inhibit COX enzyme time inhibit production of prostaglandins and thromboxanes
Therapeutic effects:
Anti-inflammatory, Analgesia, Antipyretic (reduces body temp to prevent fever)
Side effects:
GI disturbance, skin rashes, prolonged bleeding
How does Ibuprofen work?
Inhibits COX-1
How does paracetamol work?
Selective COX-2 inhibitor
What are Tricyclics Antidepressants (TCAs)?
Treats depression and neuropathic pain
Examples:
Imipramine, desipramine, amitriptyline, clomipramin
MOA:
blocks reuptake of amines by nerve terminals (noradrenaline and serotonin)
How does Gabapentin work?
Anticonvulsant drug used for neuropathic pain
MOA:
Increases synaptic conc. of GABA
What is the analgesic ladder?
Mild pain: non-opioid (paracetamol)
Moderate pain: simple analgesic (paracetamol and weak opioid like codeine)
Severe pain: strong steroid (morphine w/ non-opioid)
What is the transcutaneous electrical Nerves Stimulation (TENS)?
Low-voltage electricity pulses into tissue to relief pain by activating A-beta fibres to close the pain gate
What are the comparisons between MRI and CT?
MRI provide more clear anatomical images and are better for patients suspected to have a low-contrast lesions or brainstem or skull-base lesions (no radiation used?
CT is better for head trauma or intracranial haemorrhages
What is pain?
An unpleasant sensory and emotional experience associated with actual or potential tissue damage
What is catastrophising?
Exaggerating negative orientation toward pain (i.e. where a relatively neutral event is irrationally made into a catastrophe)
