Histology Flashcards
4 components of crista ampullaris
Crista
Hair cells
Capula
Ampulla
Function of crista ampullaris
Detect rotation of head
Location of crista ampullaris
Semicircular canals
Adaption of basal laminate for tonotopic mapping
Base - thicker and closer for high frequency
Apex - thinner and further for low frequency
Function of macula
Detection of linear movement and gravity
Components of macula
Otoliths Otolithic membrane Hair cells Supporting cells Nerve endings
Types of nerve endings
Hair follicle ending Ruffini ending Krause corpuscle Pacinian corpuscle Meissners corpuscle Free nerve endings
Fx ruffini ending
Pressure on skin
Dermis of hairy and glabrous skin
Fx pacinian corpuscle
Responds to vibration
Deep dermis
Fx meissners corpuscle
Responds to vibration
Found in glabrous skin
Fx free nerve endings
Pain, temp
Two parts of tympanic membrane
Pars tensa
Pars flaccida
Define process of Wallerian degeneration
Chromatolysis Swelling of cell body Degeneration of disconnected axon Degeneration of myelin sheath Macs and Schwann mop up
Outline role of Schwann cells in regeneration in PNS
Remove debris Provide growth promoting substrate Guide regenerating axon Promote neuron survival = neurotrophic factors Re-myelinate
Briefly explain how B amyloid fragment implicated in Alzheimer’s
Direct toxicity to neurons causes:
Neuronal damage
Disruptions of synaptic contacts
Promotes glial reactivity and inflammatory respose which damages and kills neurons.
Three true barriers on BBB
Cerebral capillaries
Choroid plexus
Arachnoid mater
Why blind spot not perceived in field of vision
Visual centers extrapolate info from adjacent areas of visual field and ‘fill’ the space.
Two main functions of neuronal cytoskeleton
Cellular structure
Axonal transport
How do cells in CNS contribute to regeneration failure
Astrocytes - become reactive, form glial scar and express axon-growth inhibiting proteoglycans.
Oligodendrocytes - up regulate release of axon-growth inhibiting proteins.
Microglia - remove debris but can release cytotoxic agents.
Principle function of each support cell type in CNS
Astro - metabolic/structural support, BBB, regulate ECM
Oligodendrcytes - myelination, membrane protein channels
Microglia - immune defense
Ependyma - movement of CSF (?neurogenesis)
Types of sensory axons and nature of stimuli
Aa - proprioception
Abeta - mechanoception
Adelta - pain, temp
C - pain, temp, itch
Fast axonal transport uses what protein
Kinesin
Fx of pericyte in CNS
Structural stability
Phagocytosis
Vasodynamic capacity
Transport mechanisms across cerebral caps
Carries systems (highly specific) eg D glucose, amino acids Receptor mediated endocytosis eg insulin Diffusion
Structural differences between BMEC and normal endothelial cells
Absence of fenestrations
More extensive tight junctions
Functional differences between BMEC and normal endothelial cells
- impermeable to most substances
- space pinocytotic vesicular transport
- increased expression of transport and carrier proteins
- no gap junctions
- limited para cellular and trans cellular transport
What is the role of astrocyte foot process in the BBB?
- provide biochemical support
- influence organisation of vessel wall
- involved in postnatal maturation of BBB
- co-regulate function be secretion of soluble cytokines
Regions not enclosed by BBB
- area postrema
- median eminence
- neurohypophysis
- pineal gland
- subfornical organ
- lamina terminalis
Type of molecules that can cross the BBB
Hydrophobic (CO2, O2, N2) Small polar (water, urea)
Type of molecules that can’t cross the BBB
Large polar molecules (glucose, sucrose)
Ions
Things that are carried across the BBB
- D glucose
- large neutral amino acids (NT precursors)
- glycine
How can pathogens be transferred across the BBB?
- physical damage to BBB
- ligand receptor interactions followed by host cell actin cytoskeleton rearrangements
- trans cellular transport
Types of neuronal death after injury
- necrotic cell death (first wave)
- apoptotic (second wave)
Requirements for functional axon regeneration
- injured nerve must be able to survive after lesion and re-express genes required for outgrowth
- surrounding tissue must be conducive to axon re growth
- re-growing axons must be able to find their proper targets and establish contact
Growth cone
Tip of a growing axon
Sequence of events after a nerve injury
Wallerian degen
Schwann cells form a substrate for axon growth
Functional connection is restored
How can regeneration go wrong?
- gap in nerve too wide to bridge
- axons grow down wrong endoneurial tubes
- loss of target contact may cause death of motoneurones
How do Schwann cells support axon regeneration?
- phagocytose and recycle cellular debris
- provide a growth-promoting substrate for axons
- support neurones survival and axon re-growth through production of neurotrophic factors
Why do axons not regenerate in the CNS?
Micro environment
- oligos express proteins that actively inhibit atonal growth (contact inhibition)
- Astros form a scar-like tissue at site of injury (mechanical barrier)
- micro glia may kill injured CNS neurones
Other factors contributing to failure of CNS axon regeneration
- poor survival of injured neurons
- failure to up-reg genes necessary for axon growth
- lack of neurotrophic factors
- lack of axon growth promoting substances
- no re-expression of guidance cues
Role of thalamic processing in the visual pathway
- relay info on movement
- segregate the retinal axons in preparation for depth perception
- emphasize visual inputs from regions of high cone density
- sharpen the contrast info received by the retina
Sound pathway
Oval window Scala vestibuli Basilar membrane Organ of corti Helicotrema Scala tympani Round window
How does the amyloid beta protein fragment contribute to nerve degen in Alzheimer’s?
- direct toxicity to neurons causes neuronal damage and disruption of synaptic contacts
- promotes glial reactivity and inflammatory response which further damages and kills neurons
Why is blind spot not perceived in vision
Visual centres use binocular vision to fill the space of the receptor free area
Structural specialisations of cerebral capillaries
- endothelium with tight junctions
- lack of fenestrations
- few pinocytotic vesicles
- thick basement membrane
Blocks non-selective exchange of substances
3 receptive structures in the inner ear
- organ of corti (detection of sound waves)
- macula (static equilibrium)
- cristae ampullaris (dynamic equilibrium)
Role of Schwann cell in regeneration of nerves
- remove debris
- provide growth promoting substances
- guidance for regenerating axon
- promote neuron survival by secreting neurotrophic factors
- re myelinated
3 BBBs
- cerebral capillaries
- choroid plexus
- arachnoid mater
Histological features of Graafian follicle just prior to ovulation
- large astral follicle lined by multiple rows of cuboidal shaped granulosa cells
- surrounded by theca interna containing typical steroid secreting cells
- outer fibrous theca externa
- oocyte surrounded by single row of cells (corona radiate)
- attached to wall of follicle by cumulus oophorus
Functional relationship leading to oestradiol production by Graafian follicle
- theca interna cells take up chol to produce androstenedione
- secreted and taken up by granulosa cells
- aromatase cleaves androstenedione to form oestradiol
Main functions of the neuronal cytoskeleton
- mainataining cellular structure
- axonal transport
