week 3 Neurons part 3. Flashcards
Understand post-synaptic potentials (PSPs) and understand how they are formed including the role of neurotransmitters and their receptors.
- Excitatory Post-synaptic potentials (EPSP)
- Inhibitory Post-synaptic Potentials (IPSP)
The Post Synaptic Potential (PSP) is the membrane potential at the post synaptic neuron’s local membrane. ie usually described in response to a transmission across a synapse. This is NOT the same as an ACTION pOTENTIAL.
An Excitatory Post Synaptic Potential is one which makes the localised membrane a bit less negative ( ie may contribute towards the development of an AP.This is usually achieved with influx of Na+ (although comparatively far less than involved in an AP)and is a graded potential.
An Inhibitory Post Synaptic Potential (IPSP) results in the localised membrane becoming a little more negative (ie makes an AP less likely). This is a temporary hyperpolarization and is usually achieved via the influx of Cl- or the selective leaving of K+.
Understand Summation at the Axon Hillock.
Summation is the additive effects of multiple EPSPs and IPSPs, and together at the axon hillock, determines whether that neuron will have an AP or not.
Understand Temporal and Spatial summation.
Temporal summation is the summation over a brief period of time, in one area. eg many light toe pinches might provoke a response, whereas 1 may not. ie rapid succession of EPSPs in 1 spot can build in millivolt potential over time.
Spatial summation is eg. 2 weak pinches at different spot but at same time, might provoke response whereas 1 pinch insufficient. ie EPSP’s from different points but arriving at same time, can increase milivolt potential at 1 time.
Understand some of the ways action potentials are initiated in sensory neurons.
Sensory neurons may develop an action potential by ion channels being opened in response to eg touch bending the membrane (mechanoreceptor), particle attachment (chemoreceptor eg olfactory), or in the case of photoreceptors, being constantly leaky with ions and are usualy more depolarised. For photo receptors, when light is present, NA+ and Ca + channels are closed, which makes the cell hyperpolarized (ie further from an AP). This hyperpolarization PREVENTS the release of its INHIBITORY neurotransmitter, therefore cells further along become activated due to the presence of light. (Guyton describes it more as light alters the shape of an isomer which then has an effect on the calcium channels).
Understand Tonically active neurons.
Tonically Active Neurons tend to be a bit leakier for sodium than regular neurons. This means they can fire their own action potentials without any further excitatory presynaptic inputs. With excitatory pre synaptic inputs however can have more frequent AP’s. With inhibitory pre synaptic inputs, their AP’s may be less frequent or stopped.
Understand electric synapses.
Electrical synapses do not use neurotransmitters,but have direct movement of ions from pre synaptic to post synaptic cleft. impulse is much faster then a regular synapse with neurotransmitter. High degree of certainty that an AP in 1st neuron will result in AP in 2nd neuron.
Understand axo-axonic synapses.
Where the terminal buds of 1st neuron, synapse directly onto axon of 2nd neuron. These have much more contributory effect on whether 2nd cell will have AP because of location. This can bypass the requirement for summation.
Know the location and shape (so as to label on a picture of a neuron) as well as the general function of the following cell structures: dendrites, dendritic spines, soma, axon, myelin, nodes of Ranvier, and pre-synaptic terminals. Axon hillock.
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Be aware of the diverse shapes and structures of neurons, noting that while neurons vary enormously in their shape, they all have the same basic components.
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Be able to distinguish between the role of sensory (afferent), motor neurons (efferent) and interneurons
Sensory cells (afferent) (arriving)brings information to a structure . Motor nueuron cells (efferent cells)(exiting)takes information from a structure.
Internuerons or Intrinsic neurons are housed entirely within 1 structure eg entirely within the thalamus etc.
Understand the various functions of glial cells, distinguishing between the functions of astrocytes, oligodendrocytes, Schwann cells, and radial glia.
Glia or neuroglia are other cells within the neural network, which perform various supportive functions for the neurons.
eg Astrocytes are star shaped and wrap around the synapses of a group of neurons. Astrocytes can help dilate blood vessels to increase nutrients to an area, can take up ions and transmitters released by neurons and aid in their recycling/re uptake. Helps a group of neurons to have AP’s in waves which may set eg breathing rhythyms etc.
Microglia are tiny and are part of the immune system, removing fungi, viruses and dead cells from the brain.They also contribute to learning, by removing the weakest synapses.
Oligodendrocytes in the CNS build myelin sheaths. Schwann cells in the peripheral nervous system also form myelin.
Radial glia act as scaffolding for neural development in embryosis. Radial glia will develop into neurons or astroglia.
What is the blood-brain barrier and what does it do?
The Blood Brain Barrier is a network of specialized capillaries. The junctions of these capillaries are extra tight, meaning that many molecules are unable to reach the brain. This is a protective mechanism. Does require active transport of eg glucose.
In Alzyheimer’s the bbb vessels shrink, thus becoming leaky to allow other substances to cross into the brain.
Most drugs do not cross the bbb. Most substances of addiction, do.
neurotramsmitters
How a neurotransmitter exerts an influence depends on the type of neurotransmitter, as well as the type of receptor.
Excitatory (might trigger and AP)neurotransmitters include;
Acetylcholine, Glutamate, Dopamine, Serotonin.
Inhibitory neurotransmitters include:Gaba, Serotonin, Dopamine.
NOTE serotonin and dopamine may be either excitatory or inhibitory, depending upon their receptor.
