PHTY209 Lecture Notes - Lecture 3: Orthostatic Hypotension, Neuropathic Pain, Campylobacter Jejuni
Disorders of transmission
• Revision
o Nervous system made up of two types of cells all enclosed in a continuous plasma
membrane
• Cells of the nervous system
▪ Neurons
• Basic functional unit
• Generate and conduct electric impulses
• Communicate with one another at synapses
• Sample neuron arrangement
• Cell body containing the cell nucleus - also
called the 'soma'
• Multiple dendrites
• Single axon
• Collateral branches
• Terminal branches
• Some other arrangements
• Multipolar neuron - typical motor neutron
• Bipolar neuron - typical special sensory
neuron
• Unipolar neuron - typical sensory neuron
• Sense changes in the environment, communicate these changes
to other neurons and control the body's response to these
sensations
▪ Neuroglia
• Connective tissue of the NS
• Nutrition and support of neurons
• Glial cells contribute to NS function by insulating, supporting and
nourishing adjacent neurons
• Examples
• Astrocytes
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• Surround blood vessels in NS
• Provide structural support
• Cover the exterior surface of the brain and
spinal cord
• Can multiply, and play a role in healing
damaged neural tissue
• Microglia
• Phagocytic
• Oligodendrocytes
• Produce the insulating material - myelin
• Neural tissue
▪ Collections of neurons and neuroglia
▪ Groups of neurons are arranged so that cell bodies are together and
axons are bundled together
•
Grey matter - locations where cell bodies are grouped together
•
White matter - locations where axons are bundled
o Terminology
• Collections of cell bodies within the CNS = nucleus
• Collections of cell bodies outside the CNS = ganglia
• Collections of axons inside the CNS = tract, fasciculus, lemniscus
• Collections of axons outside the CNS = nerve
o Myelination
• The axons of many neurons are covered in myelin = 'myelinated axons'
• Myelin is produced by oligodendrocytes (in the CNS); Schwann cells (PNS)
• Myelin is an insulator that increases the speed of conduction along the axon
• Process
▪ Axon (blue) is embedded into the wall of the myelinating cell (yellow)
▪ The cell membrane of the myelinating cell wraps around the axon,
surrounding the axon (2) and then continuing to wind around the axon
(3) until there are multiple layers of cell membrane covering the axon
(4)
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o Conduction of electrical impulses
• Neurons are 'excitable' cells - that is they have a charge across their surface
and can alter that charge
• Differing concentrations of Na+ and K+ ions between the inside and the
outside of the neuron are responsible for the RMP
• -70mV inside the cell when compared to outside the cell
o Action potentials
• APs are electrical signals that propagate along axons
• An AP is a rapid, transient depolarisation of the cell membrane
• Sodium channels in the membrane open and sodium flows into the cell,
bringing positive electrical charge and so reducing the RMP
• If the reduction of the RMP reaches threshold an AP will result
o Propagation
• APs propagate along the length of the axon
o Effect of myelination
• APs propagate along the length of the axon by jumping from node to node
• Saltatory conduction
o Effect of fibre size on AP conduction
• As fibre size increases - conduction velocity (CV) of As also increases
• CV is increased by myelination
o Synapses
• Junctions between neurons that allow them to communicate with one
another (pre synaptic to post synaptic neuron)
• Unidirectional
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Document Summary
Sample neuron arrangement: cell body containing the cell nucleus - also called the "soma, multiple dendrites. Some other arrangements: multipolar neuron - typical motor neutron, bipolar neuron - typical special sensory neuron, unipolar neuron - typical sensory neuron. 70mv inside the cell when compared to outside the cell: action potentials, aps are electrical signals that propagate along axons, an ap is a rapid, transient depolarisation of the cell membrane. Sodium channels in the membrane open and sodium flows into the cell, bringing positive electrical charge and so reducing the rmp. If the reduction of the rmp reaches threshold an ap will result: propagation, aps propagate along the length of the axon, effect of myelination, aps propagate along the length of the axon by jumping from node to node. Saltatory conduction: effect of fibre size on ap conduction, as fibre size increases - conduction velocity (cv) of as also increases, cv is increased by myelination, synapses.
