Week 3 Flashcards
Glial Cells
• Glia support neurons
• Often quoted as outnumbering neurons but
probably about the same
• Glia = ‘glue’ – but don’t hold neurons together
• Numerous types and many function
• Divisions – microglia and macroglia
• Microglia – brain’s immune system
• Macroglia
• Myelination (Schwann cells in PNS, oligodendrocytes in
CNS
• Structural/functional support of neurons (astrocytes)
Glial Cells - Myelination
Shwann cells in the PNS Oligodendrocytes in CNS • Axon myelination in the PNS • Multiple cells along a single axon • Cell turns around the axon several times wrapping it in membrane • Can guide axon regeneration after damage • Nerves can regrow • Axon myelination in the CNS • Single cells provides several segments, often multiple axons • Cell extensions wrap around the axon • No axon regeneration after damage • No regrowth in the CNS
Glial cells - Astrocytes
• Star shaped – ‘astro’ • Surround neurons and contact brain’s vasculature • ‘Blood-brain barrier’ (seal off capillaries) • Support – nutrition, growth factors, clear waste, physical matrix to separate neurons • Activity - modulate neural activity, maintain efficient signalling (K+ and neurotransmitter uptake), maintain axon function
Glial cells - Microglia
Brain’s immune system
• Response to injury or disease – multiply, release antigens,
phagocytosis
• Rapidly activate to stop pathogens
• Anti-inflammatory response, eg after stroke
• Eliminate excess neurotransmitters
Glial Cell Dysfunction - MS
• Acute, inflammatory autoimmune disease • Brain, spinal cord, optic nerves • 36.6 / 100,000 • Female : male 2.3 : 1 • Increased prevalence with increasing south latitude in Australia (7 times more in Hobart than Queensland) • No cure but treatments to manage symptoms and slow progression – immune supress, anti-inflammatories Visual - blurred and double vision, nystagmus, ‘flashes’ • Motor - weakness of muscles, slurred speech, muscle wastage, poor posture, tics • Sensory - numbness, tingling, pain • Coordination and balance • Cognitive - short- and longterm memory, forgetfulness, slowed recall
Glial Cell Dysfunction - Tumours
• Gliomas are most common (40-50% of all brain tumours) • Relatively fast growing, arising from any type of glial cells, hence gliomas, astrocytomas, and oligodendrogliomas. eg. Frontal lobe astrocytoma, Temporal lobe glioblastoma multiforme
What makes up a typical neuron?
axon terminals, axon, cell body (soma) and dendrites
What are Ribosomes (the
speckles) and endoplasmic reticulum, and what do they do?
generate proteins:
neurotransmitters
What is the golgi complex?
package neurotransmitter
into vesicles
What are microtubules?
transport vesicles
and proteins
along the axon
What are synaptic vesicles?
contain
neurotransmitter
for release
What is mitochondria?
energy
Neuron – Signalling Specialisations
• Specialised secretory cell
• Targeted and long distance
• Irritability – responds to being stimulated
Axon terminals + axons transmit information
cell body (soma) integrates information
dendrites collect information
Dendrites
• Collect information from other
connected neurons (synapse)
• Chemical messengers
(neurotransmitters) bind to receptors
and cause electrical changes
• Electrical changes spread from the dendrite and into the soma
• Electrical changes weaken with distance and over time
Cell body (soma)
• Integrates information from all of the inputs (synapses)
• Electrical changes from all inputs spread to the soma and add together
• Critical point – the junction
between the soma and the axon (axon hillock)
• If electrical changes beyond the axon hillock reaches a critical value, then the neuron will fire
Axon
• Transmits the signal away from the soma • Signal is transmitted electrically by action potential • Myelin protects the axon and promotes fast transmission of the signal • Action potentials occur at Nodes of Ranvier
Axon terminals
• Transmits the signal to other neurons • Signal is transmitted chemically by neurotransmitters • Terminal buttons store neurotransmitter in vesicles • Action potential triggers release into the synapse
Sensory Neuron
Unipolar (pseudo-unipolar)
• Afferent neuron – into the CNS
• Messages from receptors to the
brain or spinal cord
Motor Neuron
Multipolar
• Efferent neuron – out of the CNS
• Messages from the brain or spinal
cord to the muscles /organs
Interneuron
Multipolar • Relays message from sensory neuron to motor neuron in the spinal cord • Local connections in the brain
Neuron Dysfunction - Dementia
Dementia is caused by neurodegeneration – the damage and death
of the brain’s neurons
Australian statistics
• Second leading cause of death (leading in females)
• In 2018, estimated 425,416 Australians living with dementia
• Age most important risk factor – 3 in 10 people over the age of
85 and almost 1 in 10 people over 65 have dementia
• Other risk factors – CV health, diabetes, cholesterol, family
history, head injury
• Main types – Alzheimer’s disease (AD), frontotemporal dementia (FTD), vascular dementia (VD), dementia with Lewy bodies (DLB)
Alzheimer’s Disease
• Cerebral atrophy • External surface of the brain with widened sulci and narrowed gyri • Commences in medial temporal lobe – hippocampus and entorhinal cortex • Early memory loss and spatial navigation impairment • Later progresses to broader cortex and subcortical • Motor difficulties, impairments in executive planning and decision making cortical loss and thinning of gyri, shrunken hippo campus, enlarged ventricles Plaques and Tangles • Abnormal protein aggregates associated – amyloid beta and tau • Aβ – extracellular plaques • Synapse toxicity ??? • Tau – intracellular tangles; twisted ropes within swollen cell body • Axon toxicity ??? • Maybe causative, maybe not • Latest – Herpes virus ??? • Genetic component
Membrane Potentials
Resting Potential -70mV when there are more positive ions in a certain part of the inside of the cell compared to the outside: • Local change • Less polarisation (closer to zero) • “DEPOLARISED” • Spreads (decremental) • Decays (time) when there are less positive ions in a certain part of the inside of the cellcomapred to the outside: Local change • More polarisation (away from zero) • “HYPERPOLARISED” • Spreads (decremental) • Decays (time)
