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BIOL 103 Lecture Notes Jan 21

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BIOL 103
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BIOL 103, January 21, 2014 Assignment (connect quiz) due Jan 27 on material from weeks one and two - complete Rigormortis: changes in muscles after death When a body dies, why do the muscles becomes stiff?  Because calcium is released but no ATP is available for the myosin to let go of the actin filament Muscle Fibre  Muscle is made up of bundles of muscle fibers called fascicles. Fascicles are made up of myofirbril, which is made up of the microfilaments  H zone and I band shorten when muscles contract, A band remains unchanged Weight training  adults cannot gain muscle fibres, only increase number of myofilaments in muscle fibres  Strength training: Contracting muscles against resistance; increases microfilaments  Endurance training: Increasing ability to sustain muscle contraction over a long period; increases number of blood vessels in a muscle and number of mitochondria in fibres  Disuse atrophy: a decrease in myofilaments in each muscle fibre WHAT CAUSES LOSS OF MYOFILAMENTS? Challenge in space: How do you keep strong? You have to exercise using specialized exercise equipment, because isometric exercises don’t work in space – must get full range of motion Muscle fibres (list of three) 1. Slow Oxidative fibres (dark meat/red muscles) – contain myosin with low ATPase activity but many mitochondria; for prolonged, regular activity; does dot fatigue quickly (ex. Breast muscles of birds who fly) 2. Fast oxidative fibre – contains myosin with high ATPase activity and many mitochondria; high levels of oxidative phosphorylation; does not fatigue quickly (ex. rattlesnake tail) 3. Fast-glycolytic fibres (white meat/white muscles) – contains myosin with high ATPase activity but few mitochondria; relatively low myoglobin; for rapid, intense movements, but muscle fatigues quickly (ex. Breast muscles of birds who don’t fly) Skeletal muscles: each muscle cell has multiple nuclei How?  nuclear division without cytokinesis (not cell division)  fusion of cells Myoblasts: (ex. Stem cell) immature muscle cells with a single nucleus (these join together for skeletal muscle structure with multiple nuclei – put them in a poor medium (starve the cells) which create muscle cells/fibres) Muscle cells/fibres – alpha-actin Myoblasts – beta-actin How do actin and myosin molecules interact? Striated appearance of skeletal muscle is due to the regular arrangement of myofibrils Neural Transmission & Neurons Nervous system includes: brain, spinal cord, sense organs and nerves Nerve – hundreds of neurons with glial cells Glial Cells – produce connective tissue and organize neuron areas, producing myelin for some nerves Nerve tract – bundle of axons Ganglion – collection of neuron cell bodies Myelin sheath – formed by glial cells and acts as insulation Neuron – cell in nervous system which sends/receives electrical and chemical signals from other neurons throughout the body  the only animal without neurons are sponges Sensory neuron – commonly in spinal cord? ; Highly branched dendrites; gets information from outside world Motor neurons – commonly in limbs? ; long axons; moderately branched; sends signals away from sensory neurons for response Interneurons – commonly in brain? ; (spider-looking; body with axon and dendrite legs) makes interconnections with other neurons Neural circuit/pathway  ability to perceive light, touch, and sound (sense)  simulation to sensory neuron to motor neuron  chemicals, pressure, heat, and electric shock are the 4 things which trigger this pathway Sensory Reception Sensation: sensory cells that respond to chemical or physical stimulus and send signals to central nervous system Perception: awareness of sensations (ex. touching a stove generates a sensation, initiating a neural response and giving a perception that the surface is hot) Sensory transduction: incoming stimuli converted to neural signals causing cellular changes (opening of ion channels – stronger stimulus opens more channels) Sensory receptor: neuron/epithelial cell which recognizes a stimulus and initiates transduction by creating graded potentials Mechanoreceptor: transduce mechanical energy (pressure, touch, stretch, movement, sound) Thermoreceptor: respond to cold and heat Nocicceptors (pain receptors): respond to extreme heat/cold, pressure, certain molecules like acids Electromagnetic receptors: detect radiation within a wide range of electromagnetic spectrum (visible, ultraviolet, infrared light; electromagnetic fields in some animals) Photoreceptors: electromagnetic fields in some animals Chemoreceptors: respond to specific chemical compounds Voltage-sensitive/activated/gated ion channels  sodium potassium pump  Na – high concentration outside cell, travels with gradient into cell  K – high concentration inside cell, travels with gradient out of cell  Voltage gated Na/K channels  Why are the K ions released through channel? Because of gradient and because of the positive charge from Na repels positive charge of K and “gives it the boot” out of the cell  Channels are slow to close, membrane repolarized (REVIEW THIS CONCEPT) Action Potentials: neuron is simulated over a threshold 1. Depolarization: Na+ moves in through facilitated diffusion, the cell is now more positive that outside 2. Repolarization: K+ moves out through facilitated diffusion, the cell is now more negative than the outside 3. Hyperpolarization: K+ channels stay open too long 4. Resting Potential: is achieved by the Na+/K+ pump Strength of a Stimulus:  Strong - will open more Na+ ion channels  Strong action potentials will occur more frequently How fast does the signal go?  depends on the axon diameter (larger is faster because there is less resistance)  myelinated neurons are faster than unmeyelinated Synapse: junction between 2 neurons or between a neuron and a cell  Presynaptic cell sends the signal, and the synaptic cleft and post synaptic cell receives signal 1. Action potential reaches synaptic terminal at end of neuron 2. Neuron responds by releasing neurotransmitters (chemical messengers) 3. Neurotransmitters (100types in different neurons) diffuse across synaptic cleft (gap) between
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