Nerve structure, supporting cells and tumours (8.3) Flashcards
Describe the structure of nerve cells
Describe the structure and function of myelin
Myelin is fat rich substance produced by glial cells. It ‘wraps’ around neuronal axons, increasing the conduction velocity of the nerve.
CNS - Myelin is derived from oligodendrocytes. One oligodendrocyte contributes to the myelin sheath of many neurones.
PNS - Myelin is derived from Schwann cells.
Describe the embryological origin of nerve tissue
Derived from ectoderm
Neural crest cells are also derived from the ectoderm. Neural crest cells give rise to melanocytes, PNS and multiple other components.
List the destinations of neural crest cells
Neural crest cells - derived from embryonic ectoderm cell layer
- PNS (cranial nerves, ganglia)
- Melanocytes
- Glial cells
- Smooth muscle and enteric nervous system
- Craniofacial cartilage and bone
Describe the main functions of the supporting cells of the CNS
Describe the characteristic features of gliomas and meningiomas
Describe in general how brain tumours affect brain tissue
- May cause compression of brain tissue, displacement of ventricles and subsequent hydrocephalus
Low grade tumours: Slow growth means that there is some degree of accommodation. Most likely to present with focal neurological signs and seizures
High grade tumours: Most likely to present with signs of increased ICP
Including: Papilloedema, cotton wool spots, headache, nausea, bradycardia
List the tumours most likely to metastasise to the brain
Breast (15 %), lung (60 %), bone, melanma or renal (10 %)
~30 % of brain tumours are from metastasis
They appear as spherical masses, often at the grey-white junction or in the cerebellum.
Untreated → survival rate of only 1-2 months
Describe the structure and function of the blood brain barrier
Continuous, nonfenestrated capillaries with tight junctions. Almost completely incapable of pinocytosis.
Astrocyte foot processes from a barrier around the capillary basement membrane and pia mater basement membrane (glia limitans). This allows the astrocytes to mediate passage between the blood and the brain.
Impermeable to many substances in the blood, protecting the brain from toxins etc.
NOTE: Some areas of the brain are devoid of BBB e.g. area postrema, pineal gland
What features of the CNS make it vulnerable to unique pathological injuries?
Neurones are post-mitotic, can no longer divide. Although, regeneration can occur if the cell body remains intact.
Neural cells are very active and so easily undergo cell death.
Limited immunological surveillance
Protective bony enclosure
CSF circulation
Formation of glial scars: No connective tissue in the CNS means astrocytes perform gliosis for repair.
Swelling/bleeding is very dangerous due to the skull, metabolic demands of the cell and the roles of affected areas
Describe the common clinical presentations of intra-cranial tumours
(Clinician lecture)
Low grade tumours: Slow growth of the tumour allows for accommodation of the mass. Pts likely to present with focal neurology and seizures
High grade tumours: The rapid growth of the tumour leads to symptoms of raised ICP:
- Headache (especially in mornings)
- Balance/co-ordination issues
- Drowsiness or reduced GCS score
- Vomiting/nausea
- Visual loss/papilloedema: As the dura matter and subarachnoid space extends into the optic canal. Causes the statis of axoplasmic transport and subsequent swelling of the optic disc.
- Pupils (loss of reaction and dilated)
- Cushing’s triad: Bradycardia, hypertension and decreased respiration (due compression of cardiac and respiratory centres - pons and medulla)
- Opisthotonus (extensor spasms/back arching)
- Cognitive changes
Describe the most common primary brain tumours and their presentation
(Clinician lecture)
High grade astrocytoma
Low grade astrocytoma
Meningioma
List the common somatic tumour types which metastasise to the brain
(Clinician lecture)
Lung, breast, bone, renal or melanoma
