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Flashcards by farah_tahir95, updated more than 1 year ago
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Created by farah_tahir95
almost 10 years ago
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| Question | Answer |
| Describe the structure of prototypical neurons | Soma, dendrites and axons (neurites extend from soma). Neuronal membrane which lies on cytoskeleton (see cytoskeleton slide). Within soma are organelles (Rough ER, nucleus, smooth ER, Golgi Apparatus, mitochondria). Rough ER (therefore ribosomes) do not extend into neurites (axons). No protein made here. |
| Describe the function of the axon and dendrite | Neurites unique to neurons (nerve cells). Information transmitted away from soma via AXONS. Information transmitted toward soma via dendrites. Generally true apart from unipolar neurons. Info flow is electrical along neurites, info flow is chemcial between neurons. |
| Identify ways of characterizing and naming neurons | By number of neurites (unipolar, bipolar or multipolar). Shape and dendrites (stellate or pyramidal), connections (sensory neuron, interneuron, motor neuron), axon length (Stellate/ Golgi type II small axons, pyramidal/Golgi Type I long axons) Neurotransmitter (inhibitory, excitatory, range of other roles). |
| Identify the 4 different classes of glial cells. Describe their role and location. | Oligodendrocytes and Schwann cells (Myelinating Glia): Generate myelin sheath- surround axons of CNS and PNS respectively. Myelin electrically insulating , increases axonal conduction velocity. Oligodendrocytes found in CNS. Schwann cells in PNS. Astrocytes: Found in the brain and spinal cord, most abundant cells of the human brain. Fill spaces between neurons and blood vessels. Influence neurite growth. Regulate chemical content of extracellular space (e.g. K+ buffering). Provide biochemical support of endothelial cells that form the blood-brain barrier. Envelop synaptic junctions (regulate neurotransmitter in synapse). Provide metabolic support for neurons. Microglia: Specialised immune system in the brain and spinal cord and resident macrophages. Fight inflammation within the brain. Remove debris (dead cells, infectious agents). Ependymal cells: Epithelium-like cells that line fluid-filled ventricles in brain and central canal of the spinal cord. Produce CSF and control its release. Plays a role in directing cell migration during brain development. |
| Identify the factors that lead to movement of ions across a membrane | Concentration gradient: ions diffuse down concentration gradient through open channels in membrane. Random movement (Brownian motion). Electric field across membrane: concentration gradient can set up EF and vice versa. Cations to cathode (-) and anions to anode (-). |
| Describe the factors affecting an ionic equilibrium potential or E(ion) (what voltage results from an imbalance in ionic concentrations) | If membrane permeable to single ion, Nernst Equation predicts membrane potential at equilibrium. Need to know: concentration ratio and electric charge, NOT permeability or ionic conductance. Different ions have different ionic equilibrium potentials. |
| Describe the factors affecting a cell's resting membrane potential | Goldman Hodgkin Katz (GHK) Equation. Internal and external concentration of each ion, electric charge and relative permeability of the ions. Only monovalent ions considered. |
| Describe the function of the Na/K-ATPase (Na-K pump) | Maintains the resting membrane potential. Converts ATP to ADP (active transport). Sodium potassium pump, 2 conformational or stable physical shapes. 1. Open intracellularly, binds ATP and 3 Na+ 2. ATP hydrolysed, phosphorylation of pump, release of ADP 3. Pump changes conformation, release of Na+ to extracellular space 4. Pump binds 2 K+, dephosphorylation and second conformational change 5. ATP binds and K+ ions released 70% of energy used by brain consumed by sodium pump. Electrogenic pump due to uneven charge transfer. Pushing K+ and Na+ AGAINST concentration gradient. |
| Describe how selectivity and gating occur in Na+ and K+ channels | Pore loops act as a physical filter (due to their close proximity). Charged domains on amino acid residues act as chemical filter. Voltage gated sodium channels open when the membrane potential depolarises (membrane potential affects permability of Na+). Navs can be open, closed (but active) or inactive/occlution (see notes). tetrodotoxin blocks Navs, PNS. |
| Describe why passive ion diffusion is an unreliable way to transfer signals between neurons | Diffusion requires passive movement of ions (no energy). It is slow and ineffective. Signal breaks down over long distances as concentration gradients become smaller and therefore weaker. |
| Describes the components of an action potential, including what channels are involved and when | 1. The membrane depolarises past a threshold at which voltage-gated Na channels open 2. Na+ ions enter the cell, further depolarising the membrane and opening more NaV channels 3. NaV channels close; the higher K permeability due to K2p channels causes repolarisation 4. Voltage gated KV channels open, hyperpolarising the membrane below the resting membrane potential 5. NaV channels are inactivated until the membrane is hyperpolarised, preventing further generation of AP during thisabsolute refractory period. 6. KV channels are briefly held open, keeping the membrane hyperpolarised. This makes it harder (not impossible) to generate AP during the relative refractory period |
| Explain the action potential in terms of changes in the membrane permeability and ionic concentrations | s |
| Describe factors affecting the speed and nature of action potential conduction | Thickness (the thicker, the faster) temperature (the colder, the slower?) and myelination (the more, the faster). Greater injection of current will lead to greater depolarisation, therefore rate of spikes is proportional to current, because the depolarisation (after absolute refractory period) is faster when there is higher current |
| Describe the structure and function of electrical synapses | Direct electrical coupling between cytosol of two neurons. Cytoplasmic continuity between pre and post synpatic cells. Ultrastructural components are gap junction channels. Agent of transmission is ion current. Virtually no synaptic delay. DIrection of transmission is usually bidirectional. Gap junction: 6 connexin subunits form connexon in each cell membrane. non-selective channel-ions, small molecules. Strength of connection increased by increasing pore numbers, electrically couple neurons. Important in synchronisation of neurons in some motor systems, cardiac muscle. Gap junction allows small number of ions to move through (small effect on VM of cell 2) |
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