BSC Exam 1 01 25 2016 An Introduction to Sensory Pathways and the Somatic Nervous System An introduction to o Sensory receptors o Sensory processing o Conscious and subconscious motor functions Focusing on the general senses provide info about the body and its environment o Located throughout the body 15 1 Sensory Information Afferent Division of the Nervous System o Receptors detects stimuli o Sensory Neurons relays sensory info toward the CNS Receives input from dendrite uses axon to send it to CNS o Sensory pathways nerves nuclei and tracts that deliver sensory info to the CNS Efferent Division of the Nervous System o Nuclei contain cell bodies of motor neurons o Motor neurons send commands to effectors through motor tracts axons in the CNS or nerves axons in the PNS Sensory Receptors Sensory Pathways o Specialized cells that monitor specific conditions In the body or external environment o When stimulated a receptor passes info to the CNS In the form of action potentials along the axon of a sensory neuron Please review chapter 12 pgs 398 416 if you need to refresh yourself on APs and synaptic transmission o Deliver somatic and visceral sensory info to their final destinations inside the CNS using Nerves bundles of axons located in the PNS Nuclei clusters of cell bodies located in the CNS Tracts bundle of axons located in the CNS o For example nerves from arm bring sensory info to spinal cord Axon terminal synapse onto interneurons in spinal cord cell bodies clustered together nucleus These cell bodies send info up to brain trough axon bundles now called tracts since inside the CNS Somatic Motor Portion of the Efferent Division o Controls peripheral effectors Somatic Motor Commands o Travel from motor centers in the brain along somatic motor pathways of Motor nuclei Tracts Nerves Somatic Nervous System SNS o Motor neurons and pathways that control skeletal muscles 15 2 Sensory Receptors General Senses o Describe our sensitivity to Temperature Pain Touch Pressure Vibration Proprioception monitors the position and movements of skeletal muscles and joints o Sensation o Perception The arriving info from these senses Conscious awareness of a sensation Special Senses sensory receptors are all located in the head o Olfaction smell o Vision sight o Gustation taste o Equilibrium balance o Hearing The special senses are provided by special sensory receptors Special Sensory Receptors o Are located in sense organs such as the eye or ear o Are protected by surrounding tissue The Detection of Stimuli o Receptor specificity Each receptor has a characteristic sensitivity EX your hands do not smell nor taste your eyes do not hear ect o Receptive field Are is monitored by a single receptor cell The larger the receptor field the more difficult it is to localize a stimulus The Interpretation of Sensory Information o Arriving stimulus reaches cortical neurons via labeled line link between the receptor and cortical neuron Each labeled line consists of axons carrying info about one type of stimulus modality Physical force such as pressure Dissolved chemical Sound Light o Sensations Taste hearing equilibrium and vision provided by specialized receptor cells Communicate with sensory neurons across chemical synapses Adaptation o Reduction in sensitivity of a constant stimulus o Your nervous system quickly adapts to stimuli that are painless and constant o Types of adaptation EX new smells pressure wearing jewelry Central inhibition of nuclei along a sensory pathway occurs in the CNS EX new smells still stimulate sensory receptor but cortical neurons no longer respond to the stimulation Peripheral occurs at the level of the receptor receptor responds initially to stimulus then stops EX thermoreceptors o Tonic Receptors Are always active Show little peripheral adaptation Are SLOW ADAPTING RECEPTORS Remind you of an injury long after initial damage has occurred EX pain receptors nociceptors o Phasic Receptors Are normally inactive Become active for a short time whenever a change Are FAST ADAPTING RECEPTORS Provide info about the intensity and rate of change of a occurs stimulus EX thermoreceptors detect rapid changes in temperature o Stimulation of a receptor produces APs Along the axon of a sensory neuron o The frequency and pattern of APs contain information About the strength duration and variation of the stimulus o Your perception of the nature of that stimulus Depends on the path it takes inside the CNS 15 3 Classifying Sensory Receptors Exteroceptors provide info about the external inviornment Proprioceptors report the positions of skeletal muscles and joints Proprioceptors Interoceptors monitor visceral organs and functions o Provide a purely somatic sensation o No proprioceptors in the visceral organs of the thoracic and abdonminopelvic cavities You cannot tell where your spleen appendix or pancreas is at the moment General Sensory Receptors o Divided into 4 types by the nature of the stimulus that excites them Nociceptors pain Thermoreceptors temperature Mechanoreceptors physical distortion Chemoreceptors chemical concentration 1 Nociceptors Pain Receptors Are common In the superficial portions of the skin In joint capsules Within the periostea of bones Around the walls of blood vessels Analgesia inability to feel pain Hypergesia increased sensitivity to pain May be sensitive to Temperature extremes Mechanical damage Dissolved chemicals such as chemicals released by injured cells Are free nerve endings with large receptive fields Myelinated Type A Fibers Branching tips of dendrites Not protected by accessory structures Can be stimulated by many different stimuli Two types of axons Type A Large myelinated and Type C Small unmyelinated fibers Carry sensations of FAST pain or prickling pain such as that caused by an injection or a deep cut Sensations reach the CNS quickly and often trigger somatic reflexes Relayed to the primary sensory cortex and receive conscious attention Type C Fibers Carry sensations of SLOW pain or burning and aching pain Cause a generalized activation of the reticular formation and thalamus You become aware of the pain but only have a general idea of the area affected 2 Thermoreceptors Also called temperature receptors Are free nerve endings located in The dermis Skeletal muscles Hypothalamus Liver Temperature sensations pain sensations Sent to Conducted along the same pathways that carry The reticular formation Thalamus Primary sensory cortex to a lesser extent 3
View Full Document
Unlocking...