Communication in NS Flashcards
<p>what is the axon hillock</p>
<p>start of the axon- tapered area of the cell body</p>
<p>What are myelinated neurons</p>
<p>Neurons that have myelin sheath surrounding their axons.<br></br><br></br>Myelin sheath consists of Schwann cells (in PNS) / Oligodendrocytes (in CNS) that are arranged along axon length <br></br><br></br>myelin (fatty substance) sits between layers of Schwann cells / oligodendrocytes <br></br><br></br>Nodes of ranvier (Unmyelinated 'gaps') sit between myelin sheaths, assisting to rapidly transmit action potentials</p>
<p>what are dendrites</p>
<p>the many short processes that receive and carry incoming action potential toward cell body</p>
<ul><li>in motor neurons- dendrites form part of synapse</li><li>in sensory neurons- dendrites form the sensory receptors that respond to specific stimuli</li></ul>
<p>why is nerve condution faster in myelinated neurones (rather than unmyelinated neurones)</p>
<p>because myelin prevents ion movement, so depolarisation from a nerve impulse can thus only occur in the space between myelin sheaths (the nodes of ranvier). thus the flow of current appears to 'leap' across myelin sheaths- known as saltatory conduction- which is faster than continuous conduction or simple propagation.</p>
<p>explain saltatory conduction</p>
<p>explain action potential (nerve impulse)</p>
<p>A change in the membrane potential (membrane voltage) that occurs when neuron's threshold is met, enabling membrane's ion channels to open</p>
<ol><li>large depolarisation (move away from -70mV (RMP) - Na+ move into cell</li><li>once +30mV is reached, K+ starts moving out of cell</li><li>hyperpolarisation- K+ continues to move out of cell until K+ channels closed</li><li>Resting ionic conditions restored by Na/K pump</li></ol>
<p>AP is propagated along length of axon, as depolarisation in one segment of axon stimulates depolarisation in adjacent segment</p>
<p></p>
<p>what is a synapse</p>
<p>junction between</p>
<p>-two neurons</p>
<p>-neuron and effector (muscle/ gland)</p>
<p>what are two types of synapses</p>
<ul><li><strong>electrical synapse (uncommon)</strong></li><li>ions are able to flow from one neuron to another, as the 2 neurons' cell membranes are connected by gap junctions</li><li>thus depolarisation of one neuron can cause depolarisation of next neuron</li><li>found in embryonic nervous tissue / parts of adult brain</li></ul>
<p><strong>chemical synapse (most common)</strong></p>
<ul><li>axon terminal releases chemical neurotransmitters</li><li>NT's attach to receptors on next cell, triggering change in membrane potential</li><li>.e.g. nerve synapses, neuromuscular junctions</li></ul>
<p>what are components of chemical synapse process</p>
<ul><li><strong>presynaptic membrane</strong><ul><li>axon terminal of neuron</li><li>releases Chemical NT's<strong> - </strong>packaged in vesicles</li><li>Depolarisation opens Ca+ channels in axon terminal membrane, enabling Ca+ to move across membrane</li><li>Ca+ stimulates vesicles to move to axon terminal membrane</li><li>NT releaesd into synaptic cleft</li></ul></li><li><strong>synaptic cleft</strong><ul><li>space between axon terminal and receptive region of next cell</li></ul></li><li><strong>postsynaptic membrane</strong><ul><li>receptive region of cell, receiving stimulation from presynaptic neuron</li><li>has receptors for NT's</li><li>NT's bind to receptors, stimulating graded (local) potentials of that membrane<ul><li># of NT's released mediates teh local changes in membrane potential of the postsynaptic cell</li></ul></li></ul></li></ul>
<p>what are effects of NT's</p>
<p>can be excitatory (depolarise)</p>
<p>inhibitatory (hyperpolarise)</p>
<p>what are graded potentials</p>
<p>what are action potentials</p>
<p>what is the refractory period</p>
<p>2 stages</p>
<p>absolute refractory period- when Na+ open, neuron can't respond to any stimuli, so no new AP can be generated</p>
<p>relative refractory - when Na+ close, they are temporarily inactive, so neuron can only respond to stimuli that is stronger than the original stimuli</p>
<p></p>
<p>Because of the refractory period, AP's can only move in one direction (because preceding segment is in refractory phase)</p>
<p>what is saltatory conduction</p>
<p>AP conduction ‘skipping’ between myelin sheaths to gaps (nodes of ranvier)</p>
<p>myelin sheaths inhibit ion movement across membrane, so conduction only occurs between sheaths</p>
<p>speeds up conduction</p>
