BSC 2086 1st Edition Lecture 1 Outline of Current Lecture I Afferent Division II Efferent Division III Somatic Nervous System IV General Senses V Special Senses VI Interpreting Sensory Information VII Receptors for General Senses Current Lecture I Afferent Division a Information approaching CNS i Command originates in primary motor cortex located on precentral gyrus of brain ii Makes us aware of environmental changes iii Any sensory information felt by sensory receptors b Components i The stimuli is detected by receptors 1 Monitors external and internal environment using specialized cells ii Information relayed down the axons by sensory neurons iii Sensory information relayed to CNS by sensory pathways 1 Tracts CNS axons 2 Nerves PNS axons 3 Nuclei CNS cells 4 Transports information from somatic and visceral from the gut organs to the CNS II Efferent Division a Information leaving CNS i Sends to part of the body that can carry out appropriate response b Components i The motor neurons of cell bodies found in the nuclei ii The motor tracts and nerves send messages to the muscles and glands III Somatic Nervous System a Motor neurons and paths that have control over skeletal muscles IV General Senses a Describes sensitivity to i Pain ii Temperature iii Pressure iv Touch v Vibration vi Proprioception body position b Sensation is the information arriving from each of these general senses while perception is our awareness of these sensations V Special Senses a Include i Smell olfaction ii Sight vision iii Taste gustation iv Balance equilibrium v Hearing b Receptors are located in sense organs and are very specific to which stimuli they sense c Areas of reception are monitored by one receptor cell i Larger the area the harder it is to pinpoint exact location of stimulus VI Interpreting Sensory Information a Stimulus travels via labeled line i Found between receptor and cortical neuron ii Always relayed by same axon b Stimulus reaches cortical neuron c Adaptation nervous system reduces sensitivity to a stimulus that is constant and causes no pain i Tonic receptors slow to adapt 1 Constantly active 2 Ex Pain receptors ii Phasic receptors fast to adapt 1 Only become active when change occurs otherwise not active 2 Gives body a clue about intensity and rate of change due to a stimulus done by frequency of action potentials caused by stimulation 3 Ex Thermoreceptors iii How one perceives the stimulus depend on labeled line it takes in CNS 1 Place of connection to the brain determines type of sensory information you are receiving VII Receptors for General Senses a Nociceptors i Detect pain ii Found on skin in joints within periostea bone ends blood vessels iii Analgesia cant feel pain iv Hyperalgesia increased ability to feel pain v Structure 1 Free nerve endings 2 Large receptive areas 3 Can be stimulated by many stimuli 4 Type A fibers a Fast pain sensations prickling pain caused by deep cut or injection b Sensations reach CNS sent to primary motor cortex and are quickly given conscious attention 5 Type C fibers a Slow pain sensations burning aching pain b Only have general idea of area affected by pain b Thermoreceptors i Detect temperature changes ii Found in skin on the dermal layer skeletal muscles liver hypothalamus major structure that regulates body temperature iii Temperature and pain sensations are sent on same pathways c Mechanoreceptors i Detect stimuli that alter their plasma membrane ii Mechanically gated ion channels open and close due to 1 Stretching 2 Compression 3 Twisting iii Three types 1 Tactile receptors a Sensations of touch shape texture vibration fluctuating pressure and pressure how much distortion has happened b Fine touch and pressure receptors i Extremely sensitive ii Very small receptive field can give exact information about location size movement etc about the stimulus c Crude touch and pressure receptors i Large receptive field can t easily determine information about stimulus d Six types found on skin i Free nerve endings 1 Tonic receptors with small receptive field 2 Found between epidermal cells ii Root hair plexus 1 Found at ends of hair 2 Wherever hairs are found they can monitor movements and distortions 3 Rapid adapters detect initial contact and any movement thereafter iii Tactile discs aka Merkel cells 1 Fine touch and pressure receptors iv Tactile corpuscles aka Meissner s corpuscles 1 Fine touch pressure and low frequency vibration receptors adapt within 1 second after stimulation 2 Found mostly in lips eyelids fingertips nipples and external genitalia 3 Large structures v Lamellated corpuscles aka Pacinian corpuscles 1 Similar to intervertebral discs that cushion bodies of vertebrae good for compressions 2 Fast adapting sensitive to deep pressure vi Ruffini corpuscles 1 Found in the reticular layer of the dermis 2 Tonic receptors 3 Sensitive to pressure and skin distortion 2 Baroreceptors a Detect pressure changes in i Blood vessels regulate blood pressure ii Digestive tract iii Urinary tract iv Reproductive tract b Respond immediately to pressure change but are quick to adapt c 3 Proprioceptors a Detects lymph position b Most structurally and functionally complex of the general senses c Three major groups i Muscle spindles fibers that can detect contractile state of a muscle 1 Monitor length and trigger stretch reflexes ii Golgi tendon organs 1 Monitor tension developed during contraction of a muscle 2 Found between skeletal muscle and its tendon iii Receptors in joint capsules 1 Helps you see body in 3D 2 Detect pressure tension and movement in the joints d Chemoreceptors i Different chemicals that can have an effect on the body ii Only respond to water and lipid soluble substances dissolving in surrounding fluid iii Peripheral adaptation receptors will adapt to stimulus iv Central adaptation brain tunes out signals v Those that detect pH CO2 and O2 in arterial blood are found in 1 Carotid bodies make sure you get enough oxygen in your brain a Found on each side of the neck near origin of internal carotid arteries 2 Aortic bodies monitor how much oxygen is going through body a Found in aortic arch
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