Lecture notes 15 November 2013 started on slide comparison of the 3 types of muscle To summarize skeletal muscle cardiac muscle structurally similar so we know they will both have sarcomeres and are both striated sarcomeres Z discs striated T tubules present triads are present in skeletal muscle fiber triads are absent from cardiac muscle cells but the cardiac cells lack terminal cisternae because the SR is poorly developed troponin TnT TnC TnI ionic calcium Ca2 binds to TnC function of cardiac muscle contraction is similar to smooth muscle both have the calcium entry calcium trigger mechanism hence both cardiac muscle and smooth muscle contraction can be inhibited by calcium trigger blockers ex nifedipine in skeletal muscle calcium required for contraction comes from the well developed SR and extracellular calcium does not affect skeletal muscle contraction single unit smooth muscle and cardiac muscle will both have gap junctions if they have gap junctions then they will exhibit functional sensitivity sycntivum started The Nervous System powerpoint 4th organ system is the nervous system central nervous system and the peripheral nervous system central nervous system brain and spinal cord located in the doral body cavity covered by meninges peripheral nervous system sensory division send information toward the CNS and motor division carry information away from the CNS Nervous tissue organized with connective tissue membranes and blood vessels this structure will form organis in the nervous system A cluster of cell bodies in the CNS cluster referred to as the nucleus nuclei a cluster of cell bodies in the PNS is referred to as the ganglion ganglia a bundle of axons in the PNS is referred to as a nerve a bundle of axons in the CNS is called a tract Most of the nervous system is composed of nervous tissue nervous tissue is made up of 2 major cell types nerve cells neurons and synapse cells neuroglia 6 supporting cells neuroglia 4 in the CNS and 2 in the PNS 4 supporting cells in CNS astrocytes tight junctions form between astrocytes to form the blood brain barrier BBB a selective barrier that allows lipid soluble substances to cross to vicinity of the neurons of the CNS lipid soluble substances can affect the function of neuron in the CNS Lecture notes 18 November 2013 started on slide 6 types of supporting cells Neurons a cell body bi synthetic region dendrite s receptive region axon conducting region axon ends in bulbous structures called axon terminals which are known as the secretory region of the neuron each neuron can have only one axon an axon will have a uniform diameter only the axon of a neuron can be myelinated by Schwann cells in the PNS or by the oligodendrocytes in the CNS Schwann cells are analogous to oligodendroctyes they have the same function generate action potentials which are conducted away from the cell body cell body centrioles are absent hence neurons are amitotic well developed nucleoli well developed rough ER both indicate neurons are secretory cells secrete proteins that can be neuro transmitters dendrites tapered and are not myelinated typically dendriates carry graded potentials towards the cell body graded potentials loose intensity over distance action potentials maintain intensity over distance Classification of neurons structural classification and functional classification structural multipolar neurons bipolar neurons unipolar neurons functional efferent motor neurons afferent or sensory neurons association neurons aka inter neurons Most abundant kind of structural class of neurons will be the multipolar neurons most abundant type of functional class of neurons will be the association neurons in the CNS hence most association neurons are multipolar neurons by deduction Structure of a tract or a nerve a bundle of axons covered by connective tissue membranes each connective tissue is covered by thhe endoneurium myelinated axon unmyelinated axon myelin sheath myelinated axon myelin sheath forms external to the axolemma endonerium external to the unmyelinated axon endoneurium is external to the axolemma axolemma plasma membrane of the axon Generation of an action potential RMP the axolemma is partial to the K efflux K potassium ion moves from inside the axoplasm to the exterior down its concentration gradient aka simple diffusion axolemma restricts sodium ion Na influx Na moves from the exterior into the axoplasm down it s concentration gradient due to the partial nature of the axolemma separation of charges the cytoplasmic face of the axolemma is negative compared to the external face of the axolemma the RMP 70mV 90mV phases of an action potenital depolarization phase a stimulus that excites a neuron will also allow sodium influx as Na enters the axoplasm the negative potential 70mV becomes less less negative and more more Na enter until a threshold potenital is reached more Na channels called voltage sensitive sodium channels open up in the axolemma to allow more NA influx as more Na enters more more of the Na channels open more more more Na influx which drives the membrane potenital from a negative zero positive potenital at a critical potential 30mV Na channels close and Na influx ceases END of depolarization phase any stimulus that can depolarize the axolemma to the threshold potential will generate the spike or the upshoot of an action potential How does one tell the difference between a weaker stimulus that causes an action potential and a stronger stimulus that causes an action potential since both tracing Lecture notes 20 November 2013 Phases of Action Potential Depolarization Phase Na channels open sodium influx occurs sodium moves into the axoplasm down its concentration gradient as sodium ions go in the membrane potential becomes less and less negative threshold potential is reached where more sodium channels are opened increase in sodium influx results in even more of the sodium channels opening and even more sodium influx POSITIVE FEEDBACK MECHANISM is set up which drives the membrane potential to 0mV and then to 30mV At 30mv 35mV depolarization phases ends The tracing from the threshold potential to the 30mV is referred to as the upshot or the spike of the AP The amplitude height of the 30mV is attained by any stimulus that can activate an axon to generate action potential Repolarization 2nd phase of AP 2 Things will Occur Sodium channels close at 30mV results in sodium influx cessation will stop K channels open at 30mV k efflux occurs
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