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BIOL1412 01 24 2014.docx

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Biological Sciences
BIOL 1412
Paul Messing

BIOL1412 01 24 2014 Reflexes: - rapid automatic response to stimuli - stim.s always cause the same motor response - usually protective - involve 2 or more neurons ⇒ Reflex pathway or arc = pathway of impulses: (Fig. 13.15) stim.s ⇝ R ⇒ CNS ⇒ E (effector) - reflexes are categorized according to: a) effector i) somatic reflex = effector is skel. muscle (Fig. 13.17) ii) visceral (automatic) reflex) = effector is smooth m., cardiac m., or glands b) which sides of the body the sensory + motor neurons are located (Fig. 13.20) i) ipsilateral reflex = sensory + motor on same side ii) contralateral reflex = sensory + motor are on opposite sides c) number of synapses ( + neurons) in arc i) monosynaptic reflex = one synapse b/w 1 sensory + 1 motor neuron ii) polysynaptic reflex = 2+ synapses b/w 3+ neurons (Fig. 13.18) examples: a) Somatic Spinal Reflexes i) Stretch Reflex eg. knee jerk reflex (Fig. 13.18) - extensor muscle contracts - stimulus = tapping patellar lig., which stretches the quadriceps femoris muscle - receptor = muscle spindle (in quad) - effector = skel. muscle (quad) - it contracts ⇒ ipsilateral, monosynaptic ii) Flexor (Withdrawal) Reflex) eg. in leg - stimulus = stepping on nail - R = touch, pressure, pain - E = hamstrings ( = flexors) ⇒ contracts ⇒ ipsilateral, polysynaptic iii) Crossed Extensor Reflex eg. in leg - stimulus = stepping on nail - R = touch, pressure, pain - E = quadriceps femoris in the opposite leg ( = extensor) ⇒ contracts ⇒ contralateral, polysynaptic - keeps you from falling down when ii) occurs - Reciprocal Inhibition (Fig. 13.18) - muscle (or group) contracts ( = agonist) - at same time, antagonist prevented from contracting (inhibitory interneurons firing) eg. in stretch reflex - quadriceps femoris (agonist) contracts - hamstrings (antagonists)
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