Anatomy & Physiology I and II

Anatomy & Physiology Study Guide

©2018 Achieve Test Prep Page 200 of 367 16.9 Chapter Sixteen Review An introduction to sensory pathways: • The nervous system works as an integrated unit. This chapter considers sensory receptors, sensory processing centers in the brain, and conscious and subconscious motor functions. Sensory data from all body parts is sent to the somatosensory cortex: • The brain, spinal cord, and peripheral nerves constantly communicate with each other and with the internal and external environments. Information arrives via sensory receptors and ascends within the afferent division, while motor commands descend and are distributed by the efferent division. Sensory receptors connect our internal and external environments with the nervous system: • A sensory receptor is a particular cell or cell practice that observes specific conditions within the body or in the external environment. Arriving information is called a sensation; awareness of a sensation is a perception. • The general senses are our sensitivity to pain, temperature, touch, pressure, vibration, and proprioception. Receptors for these senses are distributed throughout the body. Special senses, located in specific sense organs, are structurally more complex. • Each receptor cell monitors a specific receptive field. Transduction begins when a large enough stimulus depolarizes the receptor potential or generator potential to the point where action potentials are produced. • Tonic receptors are always active. Phasic receptors dispense information about the intensity and rate of change of a stimulus. Adaptation is a reduction in sensitivity in the presence of a constant stimulus. Tonic receptors are slow-adapting receptors, while phasic receptors are fast-adapting receptors. General sensory receptors can be classified by the type of stimulus that excites them: • Three types of nociceptor found in the body provide information on pain as related to extremes of temperature, mechanical damage, and dissolved chemicals. Myelinated Type A fibers carry fast pain. Slower Type C fibers carry slow pain. • Thermoreceptors are found in the dermis. Mechanoreceptors are sensitive to distortion of their membranes and include tactile receptors, baroreceptors, and proprioceptors. There are six kinds of tactile receptors in the skin, and three kinds of proprioceptors. Chemoreceptors include carotid bodies and aortic bodies. Separate pathways carry somatic sensory and visceral sensory information: • Sensory neurons that deliver sensation to the CNS are referred to as first-order neurons. These synapse on second-order neurons in the brain stem or spinal cord. The next neuron in this chain is a third-order neuron, found in the thalamus. • Three major somatic sensory pathways carry sensory information from the skin and musculature of the body wall, head, neck, and limbs: the posterior column pathway, the spinothalamic pathway, and the spinocerebellar pathway.