Neurons And Related Cells Flashcards
Neurones: Nissl granules
Similar to endoplasmic reticulum
Production of proteins and short chains of amino acids
Neurones: axonal transport
Active transport - electrical activity or nerve impulse
Kinesin molecules - vesicles down the axon, ATP, constant supply of molecules
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
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
Generation of action potential: rest
-70mV
VGSC at resting state
VGPC are closed
S-P pump maintain resting potential
Generation of action potential: depolarisation
Threshold of -55mV
If it is met then VGSC open
Na+ enter the cell
Raising voltage to +30mV
Generation of action potential: repolarisation
At +30mV VGPC open and VGSC close
K+ leaves the cell
Decreasing voltage to -70mV
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
Propagation: Continuous conduction
Unmylinated axons
Potential difference between depolarised and adjacent resting region
Ionic current depolarises the adjacent region generating an action potential
Propagation: Continuous conduction - refractory period
VGSC become inactive
Cannot fire another action potential
Ensure it travels in one direction
Propagation: saltatory conduction
Myelinated axons
Myelinated regions lack VGSC so prevents depolarisation
Action potential jumps between Nodes of Ranvier
Faster action potential
Factors that affect the speed of propagation/ conduction velocity
Myelination
Axon diameter
Speed of propagation/ conduction velocity: Myelination
Faster propagation of action potential
Jumps between Nodes of Ranvier
Saltatory conduction
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
Integration
Sum of all exhibitory (+ve) and inhibitory (-e) inputs
Not always on dendrites
Soma and axon
Chemical synapses
- Opening of calcium channels
- Release of neurotransmitters
- Formation of a post synaptic potential
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
