Biology lecture 2

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  • Created by: The Shrew
  • Created on: 17-02-16 14:53
Number of neurones and synapses
86 billion neurones/ one hundred trillion synapses (10 to the power 17)
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Each neurone connected to
10,000 synapses
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Hercelano-Houzel et al
each brain cell has 1 nucleus/ nuclei: brain cell= 1:1/ in whole brain (of 4 dead men) neurone: glia= 1:1
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Ratio differs from area to area
cortex= more glia/ cerebellum= more neurones
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Cortex need more because
Fairly new to humans- glia supports neurones and helps them work better
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More evolved animals
More glia
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Brain developing
glia makes scaffold and makes pathways for neurones to follow- directs migration- prevents neurological abnormality
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Glia= glue
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Glia reproduce
This is what tumours are made of
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Do most of glials functions
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wrap axons in the CNS in an insulating mylin- nourishes axons
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Swann cells
produce mylin in peripheral nervous system (outside brain/ spinal chord)
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Immune system- destroy pathogenic cells and infected neurons- eat dead material/ inflammation/ pruning
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Macroglia include
Astrocytes, Schwann cells, Oligodendrocytes, NG2 glia
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9 types of astrocyte (7 examples)
Scaffolding, scavengers, neurotransmitter reuptake, guide migrating neurones and direct outgrowth of axons, regulate properties of presynaptic terminal, help from blood-brain barrier, Release growth factors
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more glial cells than average
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Chemically, can't generate action potentials
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Receptors for same chemical messengers used by neurones
Can communicate with neurones, can eavesdrop and strengthen messages
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Neurones from rodents
few synapses, little synaptic activity until surrounded by astrocytes
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With astrocytes
Synaptic activity enlarged by 10 times
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Neurodegenerative diseases
Abormal pruning of healthy synapses
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One rodent astrocyte
associate with 300-600 neuronal dendrites and 100,000 individual synapses
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one astrocyte 30 times the size, associates ith 2,000,000 synapses
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one cell wraps around several axons, each branch around one segment
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Schwann cells
the cell is the wrap- one cell around one segment
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Multiple sclerosis
Failure of remyelination by oligodendrocytes/ unnecessary pruning
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Degenerative diseases- amyotropic lateral sclerosis/ Parkinson's disease
Mutant proteins act in glia and release toxic compounds or reduce support activities
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Neuropathic pain
Schwann cells, microglia and astrocytes in complex temporal and spatial pattern
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Mood disorders
Post mortem findings- reduction in glial cell numbers in some brain regions
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Major depressive disorder
Reductions in olygodendrocytes in the amygdala
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Bipolar disorder
Microglial alterations
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Rats with destroyed astrocytes in the prefrontal cortex
Depressive behaviour in behavioural tests
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Reverse reduction in astroglial density
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When not doing anything brain uses
20% of energy
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Things that can get through lipid bilayer
H2O, O2, CO2, Ethanol
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Can't get through
Ions, amino acids, glucose
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Makes membranes stronger
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Extracellular matrix proteins
Attach cells to other structures
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Anchors- attach membrane to actual cell/ connect to protein filaments- inner membrane
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Other use of proteins
Identify cells- rejected transplants
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Integral proteins
Receptor on outside sends signals inside
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Ions gradients inside and out
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Diffusional force on ions
Moving from high conc to low conc (don't need energy- through protein with a hole in the middle)
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Electrical force on ions
Positive ions attracted to negative and vice versa
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Leak channels and ligand gated channels
Channel only opens with right key (eg potassium)
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Voltage gated
change in charge of membrane opens or closes
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Mechanically gated ion channels
Stress activated (eg sounds)
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Pump requires energy to
Put ions where they don't want to go
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Facilitated diffusion
follow conc or electrical gradient- no energy required
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Primary active transport
against gradient- Energy= ATP
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Secondary active transport
Uses energy from primary active transport to push in amino acids/ glucose
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Selective permeability
Keeps cell functioning- keep in wanted molecules and let out unwanted- essential for nervous system
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Inside of cell overall
Negatively charged(-60), outside positively charged= resting potential
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Comes from
leaky K+/ Na- channels
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Depolarize/ Hyperpolerize
Go towards 0/ Go away from 0
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External stimuli causes
Neurotransmitters to open ligand-gated sodium channels- inside more positive
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Threshold of excitation, hyperpolarisation, squid axon
Action potential blah blah blah
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6 stages
Sodium channel opens, potassium channels open, sodium channels become refractory- no more sodium, potassium continues to leave cell, potassium channels close and sodium channels reset, extra potassium outside diffuses away
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Action potentials generated in the
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Speed of propagation depends on
Presence of myelin/ thickness of axon
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Neurons not in the hillock produce
Postsynaptic potentials not actinon potentials
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Action potentials always depolarizing
Postsynaptic potentials can be both
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AP amplitude all or none
PP amplitude proportional to strength of stimulus
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AP large amplitude 100mV
PP- amplitude generally small
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AP- amplitude does not diminish along neuronal projections (non-decremental)
PP- amplitude diminishes (decremental)
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Axon of motor neurones is 10,000 times as long as a cell body is wide
Need axon potentials to keep energy
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