First Test Study Guide Lessons 1 4 BSC 2086 Lesson 1 subconscious motor functions A Afferent Division of the Nervous System 1 Sensory Pathways An Introduction to Sensory receptors Sensory processing Conscious and I Receptors detects stimuli II Sensory neurons relays sensory information towards the CNS receives input from dendrite uses axon to send it to CNS III Sensory pathways nerves nuclei and tracts that deliver sensory information to the CNS B Efferent Division of the Nervous System I Nuclei contain cell bodies of motor neurons II Motor neurons send commands to effectors through motor tracts axons in the CNS or nerves axons in the PNS C Sensory Pathways I Deliver somatic and visceral sensory information to their final destinations inside the CNS using a Nerves bundle of axons located in the PNS b Nuclei cluster of cell bodies located in the CNS c Tracts bundle of axons located in the CNS II For example nerves from arm bring sensory information to spinal cord a Axon terminal synapse onto interneurons in spinal cord cell bodies clustered together nucleus 1 These cell bodies send info up to brain through axon bundles now called tracts since inside the CNS 2 Sensory receptors review chapter 12 pages 398 416 if you need to refresh your memory on action potentials and synaptic transmission A Sensation The arriving information from these senses B Perception Conscious awareness of a sensation C Special senses D Detection of a stimuli I Receptor specificity I Olfaction smell Vision sight Gustation taste Equilibrium balance Hearing a Each receptor has a characteristic sensitivity 1 Ex Your hands do not smell nor taste your eyes do not hear etc II Receptive field Area is monitored by a single receptor cell a The larger the receptive field the more difficult it is to localize a stimulus 3 The interpretation of sensory information I Arriving stimulus reaches cortical neurons via labeled line link between the receptor and cortical neuron a Each labeled line consists of axons carrying info about one type of stimulus modality 1 Physical force such as pressure b Dissolved chemical c Sound d Light B Adaptation I Reduction in sensitivity in the presence of a constant stimulus II Ex nervous system quickly adapts to stimuli that are painless and constant like new smells and the pressure of wearing jewelry a Central adaptation inhibition of nuclei along a sensory pathway in the CNS 1 A few seconds after you are exposed to a new smell awareness of the stimulus is gone although sensory neurons are still quite active b Peripheral adaptation occurs when the level of receptor activity changes receptor responds initially to stimulus then stops Ex thermoreceptors 1 Thermoreceptors are phasic receptors aka fast adapting receptors because you seldom notice room temp change unless it changes drastically normally inactive 2 Pain receptors nociceptors are slow adapting receptors or tonic receptors They remind you of an injury long after the damage has occurred always active III Stimulation of a receptor produces action potentials along a sensory neuron C Classifying Sensory Receptors Exteroceptors provide info about external environment I II Proprioceptors report the positions of skeletal muscles and joints a Provide a purely somatic sensation b None are found in visceral organs of the thoracic or abdominopelvic cavities 1 You cannot tell where your spleen appendix or pancreas is at the movement III Interoceptors monitor visceral organs and functions IV General sensory receptors are divided into 4 types by the nature of the stimulus that excites them a Nociceptors pain free nerve endings w large receptive fields i Branching tips of dendrites not protected by accessory structures with 1 Type A large myelinated fast or prickling pain ex injection They often trigger somatic reflexes and are relayed to the primary sensory cortex 2 Type C small unmyelinated burning aching pain Cause activation of reticular formation thalamus Have general idea of area affected 2 Common in superficial portions of skin joint capsules periostea of bone around walls of blood vessels 3 Analgesia the ability to feel pain 4 Hypergesia increased sensitivity to pain 5 They may be sensitive to temperature extremes mechanical damage and dissolved chemicals released by injured cells b Thermoreceptors 1 Conducted along same pathway as pain but is for temperature i Sent to reticular formation thalamus primary sensory cortex less extent c Mechanoreceptors physical distortion of plasma membrane 1 Contain mechanically gated ion channels whose gates open close in response to i Stretching compression twisting 2 Three classes i Tactile receptors provide sensations about touch pressure and vibration a Fine touch narrow receptive field give detailed info to body b Crude touch large receptive field give little info to body 2 Shape and texture 3 Degree of mechanical distortion 4 Pulsing or oscillating pressure ii Baroreceptors detect pressure changes in walls of blood vessels portions of digestive respiratory and urinary tract 1 Free nerve endings that branch w I elastic tissues blood vessels 2 Respond immediately but adapt rapidly iii Proprioceptors position most structurally and functionally complex of the general sensory receptors 1 Monitor positon of joints tension in tendons ligaments state of muscular contraction d Chemoreceptors chemical concentration respond only to water soluble lipid soluble substance dissolved in surrounding fluid 1 Monitor pH CO2 O2 levels in arterial blood located in i Carotid bodies near origin of carotid arteries on each side of neck to brain ii Aoritc bodies largest artery out of heart b t major branches of aortic arch 2 Demonstrate peripheral adaptation over period of seconds D Six Types of Tactile Receptors in the Skin our sensitivity to tactile sensations can be altered by infection disease or damage to sensory neurons or pathways I Free nerve endings tonic slow adapting receptors w small receptive fields a Sensitive to touch and pressure situated b t epidermal cells II Root Hair plexus nerve endings monitor distortions movements across the body surface wherever hairs are located a Adapt rapidly so are best at detecting initial contact and subsequent movements III Tactile disks or Merkel discs fine touch and pressure receptors a Extremely sensitive tonic slow adapting w very small receptive fields meaning it is easy to locate the stimulus IV Tactile corpuscles or Messiners corpuscles fine touch pressure low freq
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