Week 2 Flashcards
What are the 2 phases of pain and what fibres are responsible?
Quick and sharp - Aδ
Slow and dull - C
What sensory receptors are associated with Aα fibres?
Proprioceptors of skeletal muscle
What sensory receptors are associated with Aβ fibres?
Mechanoreceptors of skin
What sensory receptors are associated with Aδ fibres?
Pain and temperature
What sensory receptors are associated with C fibres?
Pain, temperature and itch
What is nociceptive pain?
Normal pain elicited only when a noxious stimulus which threatens to damage tissue is evoked
Protective/adaptive
High threshold, limited duration
Transmitted by Aδ and C fibres
What is chronic/clinical pain?
Evoked or spontaneous sustained sensory abnormality/peripheral pathology - stimulated by normally innocuous sensation
Maladaptive
Transmitted by Aβ, Aδ and C fibres
What is allodynia?
Normally innocuous stimuli perceived as noxious
What do hair follicle afferent receptors respond to?
Gentle brushing
What is dermatographia?
Condition in which light scratching of the skin causes intense reddening and raising - skin writing
What does the white reaction and triple response demonstrate?
Local effects of mild tissue damage
What is the white reaction and triple response?
White reaction - initial area of blanching on either side of scratch
Triple response - red reaction, wheal and flare
What is the red reaction, wheal and flare of the triple response?
Red reaction - red line at site of injury due to direct vasodilation mediated by histamine (primary hyperalgesia)
Wheal - slight oedema at site around red reaction, mediated by histamine
Flare - surrounding ill-defined erythema due to axon reflex (secondary hyperalgesia)
What mediators are released when tissue is damaged and where from?
Tissue damage - K+, prostaglandins
Plasma - bradykinin
Platelets - 5-HT
What mediators are released from axons at the site of tissue damage?
Substance P and CGRP which activate mast cells to release histamine
What role do substance P and CGRP play in tissue damage?
Substance P - plasma extravasation, oedema, bradykinin release
CGRP - vasodilation
What is ischaemic pain?
Pain associated with inadequate blood (and therefore oxygen) supply to active tissues (e.g. angina)
Where does referred pain from the heart radiate?
Left shoulder and arm
What laminae do Aδ and C-fibres terminate at in the spinal cord?
Laminae I and II
What laminae do Aβ (cutaneous) fibres terminate at in the spinal cord?
Laminae III-V
How does the supraspinal loop contribute to the modulation of nociceptive afferent input?
Serotonergic and
noradrenergic descending
projections from the periaqueductal grey matter
and medullary raphe nuclei directly inhibit projection of neurons and/or activate enkephalin containing interneurons to reduce nociceptive activity
What are the 2 explanations for how TENS machines work?
1 - stimulating large diameter axons of other sensory receptors, a jamming effect is created in the dorsal horn of the spinal cord (pain perception reduced/abolished by interference with pathway transmission)
2 - stimulation releases endorphins from the brainstem which activates descending pathways and suppresses pain pathway
What conditions are TENS machines used for?
RA, sciatica, sports injuries, MS, phantom-limb pain
What results should a cold-pressor test give?
Increased HR and BP as the sympathetic system is activated; will plateau/decrease eventually as parasympathetic is activated to maintain homeostasis
What are the 3 families of endogenous opioid peptides?
Enkephalins
POMC
Dynorphins
What are the 3 types of opioid receptor?
Mu, delta, kappa
Describe a monosynaptic reflex
Involves a proprioceptive afferent (Ia) and motor neuron
Passive stretch of quadriceps muscle activates Ia afferents via muscle spindle → synapse in spinal cord → activation of motor neuron to cause muscle contraction at motor end plate
What segmental variation is seen in the spinal cord?
Enlarged at cervial (C5-T1) and lumbar (L2-S3) levels due to innervation of limbs
What is the ventral horn composed of?
Origin of motor neurons for skeletal muscle
What is the dorsal horn composed of?
Terminations of incoming sensory fibres
What are the divisions of grey matter?
Dorsal horn, intermediate area, ventral horn
What are the divisions of white matter?
Dorsal, lateral and ventral columns
What is the filum terminalae composed of?
Thin strand of pia mater
What does the dura mater merge with to cover spinal nerves?
Epineurium (connective tissue)
What is found in the extra/epidural space?
Fat, venous plexus
At what point is the spinal cord continuous with the brainstem?
At the level of the foramen magnum
What is the lumbar cistern?
Sac of dura mater which encloses the cauda equina
What are the characteristic features of a lumbar vertebra?
Large body, small vertebral canal, small transverse processes without facets
What are the characteristic features of a cervical vertebra?
Foramen transversarium, bifid spinous process, large vertebral canal
What are the characteristic features of a thoracic vertebra?
Transverse processes articulate with ribs
What are the 5 groups of branches of the facial nerve (CN 7)?
Temporal Zygomatic Buccal Marginal mandibular Cervical
What are the main arteries of the face?
Superficial temporal artery (branch of external carotid) Facial artery (gives of superior and anterior labial branches to the lips)
Why is the facial artery tortuous?
Allows blood flow to be maintained when mandible is moved
What is the main vein of the face?
Facial vein (joins internal jugular vein)
What overlies the masseter muscle in the face?
Parotid gland
Where does the parotid duct open?
Next to the crown of the 2nd upper molar
How can pain manifest from the parotid gland?
Thick capsule surrounding the gland maintains pressure which can cause pain in conditions such as mumps
Describe the path the facial nerve (CN 7) takes to reach the face
Emerges from the base of the skull at the stylomastoid foramen and branches within the parotid gland
What muscle does the cervical branch of the facial nerve innervate?
Platysma
In which week of gestation does the CNS begin to develop?
Week 3
What does the ectoderm germ layer form?
CNS, PNS, sensory epithelium of the ear/nose/eye, epidermis, hair and nails, subcutaneous/mammary/pituitary glands, tooth enamel
Where does the notochord extend from and how does this occur?
From the primitive node at the end of the primitive streak
Hypoblast cells are displaced by movement of epiblast cells (endoderm replaced hypoblast)
What are the stages of notochord development?
Axial process → notochordal process → notochord
How is the notochord involved in neurulation?
Notochord has an inductive relationship with the overlying ectoderm - its appearance causes the ectoderm to thicken
From which germ layer is the notochord derived?
Mesoderm
Briefly describe the process of neurulation
Notochord → ectoderm thickening → neural plate made of neuroectoderm → plate edges elevate to form neural folds → depressed mid-region forms neural groove → fusion of folds results in neural tube
What factors does bending of the neural plate depend on?
Intrinsic - cytoskeleton, stage of cell cycle
Extrinsic - adhesion points
What are neural crest cells?
Cells which remain at the top of the neural tube on fusion of the neural folds; give rise to range of cell types (e.g. glia)
What hinge points are involved in neural tube formation?
Median hinge point - neural groove area
Dorsolateral hinge points - on either side where the neural folds are
How do hinge points contribute to neural tube closure?
Cells in these areas decrease in height and become wedge-shaped which allows the neuroectoderm to bend
What lies on either side of the closed neural tube?
Paraxial mesoderm (somites) Then intermediate and lateral plate mesoderm more laterally
What signalling molecules are involved in induction of the neural plate?
FGF and BMP4
What is the role of chordin and noggin in neurulation?
Inhibit BMP4 which pushes tissue towards a neural phenotype
What switch in cell type occurs in the neural plate to allow fusion of the neural tube?
Switch from E-cadherin to N-cadherin expression
What happens to the neural crest cells after neurulation?
Undergo an epithelial to mesenchymal transition
What is the molecular difference between epithelial and mesenchymal cells?
Epithelial cells have high E-cadherin expression
Mesenchymal cells have high N-cadherin expression
What do neural crest cells form?
Trunk region - melanocytes, hair follicles, dorsal root ganglia, sensory ganglia, sympathetic neurons, Schwann cells, adrenal medulla
Cranial region - craniofacial skeleton, neurons, ganglia, glia, melanocytes
What is the basal lamina and what is its importance in development?
Layer of extracellular matrix secreted by epithelial cell
In the myotome, allows cells to migrate between the neural tube and the rest of the embryo
What disorders can occur when neural crest cell migration is disrupted?
Treacher Collins syndrome - underdevelopment of facial bones and ears; TCOF 1 gene mutation
Di George syndrome - cleft palate, abnormal facies, cardiac problems; 22q11.2 gene deletion
At what level does the neural tube begin to close and in what direction does it occur?
Starts in cervical region
Proceeds in simultaneous cephalic and caudal directions
What are the ends of the neural tube called and when do they close?
Anterior neuropore (day 25) Posterior neuropore (day 27)
Briefly outline spinal cord differentiation
Neuroectoderm/epithelial cells → neuroblasts → form inner mantle layer of spinal cord (grey matter) → outer marginal layer containing fibres from mantle (white matter)
What do the neuroepithelial cells lining the neural tube differentiate into, under the influence of Notch and Delta signalling?
Neuroblasts or glioblasts
In development, in which zone are glial cells found?
Ventricular zone
In development, in which zone are neuroblasts found?
Mantle zone
In development, in which zone are axons found?
Marginal zone