Reflex Lab Essay

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SECTION 1: REFLEXES AND REFLEX ARCS Nerve impulses follow routes through the nervous system called nerve pathways. Some of the simplest nerve pathways consist of little more than two neurons that communicate across a single synapse. Reflexes are rapid, involuntary responses to stimuli, which are mediated over simple nerve pathways called reflex arcs. Involuntary reflexes are very fast, traveling in milliseconds. The fastest impulses can reach 320 miles per hour. Reflex arcs have five essential components: 1. The receptor at the end of a sensory neuron reacts to a stimulus. For example, some receptors in the skin are sensitive to heat, others to pressure. 2. The sensory neuron conducts nerve impulses along an afferent pathway towards the CNS. 3. The integration center consists of one or more synapses in the CNS. 4. A motor neuron conducts a nerve impulse along an efferent pathway from the integration center to an effector. 5. An effector responds to the efferent impulses by contracting (if the effector is a muscle fiber) or secreting a product (if the effector is a gland). Reflexes can be categorized as either autonomic or somatic. Autonomic reflexes are not subject to conscious control, are mediated by the autonomic division of the nervous system, and usually involve the activation of smooth muscle, cardiac muscle, and glands. Somatic reflexes involve stimulation of skeletal muscles by the somatic division of the nervous system. Most reflexes are polysynaptic (involving more than two neurons) and involve the activity of interneurons in the integration center. Some reflexes; however, are monosynaptic ("one synapse") and only involve two neurons, one sensory and one motor. Since there is some delay in neural transmission at the synapses, the more synapses that are encountered in a reflex pathway, the more time that is required to effect the reflex.

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