1. Opening of calcium channels 2. Release of neurotransmitters 3. Formation of a post synaptic potential

Neurons And Related Cells Flashcards by Abi Wareham

Neurones: Nissl granules

Similar to endoplasmic reticulum
Production of proteins and short chains of amino acids

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Neurones: axonal transport

Active transport - electrical activity or nerve impulse
Kinesin molecules - vesicles down the axon, ATP, constant supply of molecules

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Resting potential

K+ diffuse out
Na+ diffuse in
More K+ leave than Na+ entering
Sodium-potassium pump - 3 Na+ out and 2 K+ in
Plasma membrane is slightly negative

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Graded potentials

Short lived local changes in membrane potential
Depolarising or hyperpolarising
Amplitude = strength of stimulus
No refractory period
Summed - temporal or spatial
Passive spread

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Generation of action potential: rest

-70mV
VGSC at resting state
VGPC are closed
S-P pump maintain resting potential

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Generation of action potential: depolarisation

Threshold of -55mV
If it is met then VGSC open
Na+ enter the cell
Raising voltage to +30mV

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Generation of action potential: repolarisation

At +30mV VGPC open and VGSC close
K+ leaves the cell
Decreasing voltage to -70mV

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Generation of action potential: hyperpolarisation

VGPC are slow to close
More K+ leave then wanted
Voltage decreases to -90mV
S-P pump restores the resting potential

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Propagation: Continuous conduction

Unmylinated axons
Potential difference between depolarised and adjacent resting region
Ionic current depolarises the adjacent region generating an action potential

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Propagation: Continuous conduction - refractory period

VGSC become inactive
Cannot fire another action potential
Ensure it travels in one direction

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Propagation: saltatory conduction

Myelinated axons
Myelinated regions lack VGSC so prevents depolarisation
Action potential jumps between Nodes of Ranvier
Faster action potential

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Factors that affect the speed of propagation/ conduction velocity

Myelination
Axon diameter

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Speed of propagation/ conduction velocity: Myelination

Faster propagation of action potential
Jumps between Nodes of Ranvier
Saltatory conduction

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Speed of propagation/ conduction velocity: axon diameter

Larger diameter means a larger surface area for an action potential and less resistance so it travels faster

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Integration

Sum of all exhibitory (+ve) and inhibitory (-e) inputs
Not always on dendrites
Soma and axon

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Chemical synapses

Opening of calcium channels
Release of neurotransmitters
Formation of a post synaptic potential

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Chemical synapses: 1. Opening of calcium channels

Action potential to the presynaptic neurone
Causing depolarisation
VGCC open
Ca2+ into the presynaptic axon terminal

Chemical synapses: 2. release of neurotransmitters

Ca2+ activate snare proteins
They pull the vesicle to fuse with the membrane
Exocytosis
Neurotransmitters diffuse across the synaptic cleft
Bind to neurotransmitter receptors coupled with ligand-gated channels

Chemical synapses: 3. Formation of a post synaptic potential

Opening ligand-gated channels allows ions across the membrane
Depolarisation - excitatory neurotransmitters
Hyperpolarisation - inhibitory neurotransmitters

Neurotransmitters

Excitatory - depolarisation e.g. acetylcholine
Inhibitory - hyperpolarisation e.g. GABA

Removal of neurotransmitters

Diffusing - diffuse away and get metabolised
Enzymatic degradation - broken down by enzymes
Uptake by cells - returned to neurones (reuptake), transported to neighbouring cells

Electrical synapses

Direct electrical connection
Gap junction - act like small tunnels
Conducting action potential directly from one cell/neurone to the next
Connexins
Functional syncytium

Electrical synapses: Connexins

Bridge between the cells
Make a pore
Ions can go between the cells with no delays

Electrical synapses : functional syncytium

Synchronised activity of collections of neurones/cells by providing connection that allow action potentials to be initiated and propagated in unison

Glial cells: central nervous system

Astrocytes Oligodendrocytes Microglial cells Ependymal cells

Glial cells: peripheral nervous system

Schwann cells Satellite cells

Glial cells: general roles

Surround and support neurones Electrical insulation Supply nutrients Maintain chemical environment Destroy/remove dead cells and pathogens

Astrocytes

Largest and most abundant Star-shaped cell bodies Connections with capillaries, neurones and synaptic endings and pia mater Anchorage to neurones Blood brain barrier Take up and recycle neurotransmitters and ions Passage for exchange of nutrients Secrete chemicals that guide migration and growth of neurones Repair damaged neural tissue

Oligodendrocytes

Cytoplasmic processes wrap around axon Coving with multiple layers of insulation Increase speed of nerve impulses Release growth factors Exert inhibitory influence on axonal regrowth

Microglial cells

Long, thorn-like cytoplasmic processes Remove cell debris, invading micro-organisms and nerve tissue damaged by phagocytosis

Ependymal cells

Cuboidal to columnar epithelia cells Lines ventricles of the brain and central canal of spinal cord Section and monitor cerebrospinal fluid Semi-permeable barrier Exhibit microvilli and cilia - help circulate cerebrospinal fluid

Schwann cells

Myelin sheath around axons of neurones Spirals forming multiple layers of plasma membrane Regulation of neurones Guiding and stimulating growth Release nerve growth factors

Satellite cells

Flat cells surrounding neuronal cell bodies Structural support Form a barrier Regulating the exchange between neuronal cell bodies and the surrounding interstitial fluid Uptake and release precursor of neurotransmitters

Nerve anatomy: endoneurium

Areolar connective sheath Around the myelinated axon

Nerve anatomy: perineurium

Surrounds fascicles More tough connective tissue

Nerve anatomy: epineurium

Areolar connective tissue sheath Packs around the fascicles

Nerve anatomy: vasi nervorum

Nerve vessels Supplying the nerve Vasa nervorum

Nerve anatomy: Nervi nervorum

Nerves that surround nerves

Nerve ageing: central nervous system

Neuronal atrophy - imbalance in neurotransmitter control, death of neurones Loss of Myelination - slower impulse, move and think slower Noisy processing - disfunction in neurotransmitter release and clean up Dopamine loss - depression

Nerve ageing: peripheral nervous system

Declined axonal transport - ends of axons die back, sensory, control of muscle Axonal atrophy - axon death, sensory control of muscle Myelin loss - slower nerve impulses Impaired regeneration - damaged nerve cell may not regenerate in the same way