BSC 2086 1st Edition Lecture 1 Outline of Current Lecture I. Afferent DivisionII. Efferent DivisionIII. Somatic Nervous SystemIV. General Senses V. Special SensesVI. Interpreting Sensory InformationVII. Receptors for General Senses Current LectureI. Afferent Division a. Information approaching CNS i. Command originates in primary motor cortex located on precentral gyrus of brainii. Makes us aware of environmental changes iii. Any sensory information felt by sensory receptorsb. Components i. The stimuli is detected by receptors1. Monitors external and internal environment using specialized cellsii. Information relayed down the axons by sensory neuronsiii. Sensory information relayed to CNS by sensory pathways1. 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 Divisiona. Information leaving CNS i. Sends to part of the body that can carry out appropriate responseb. Componentsi. The motor neurons of cell bodies found in the nucleiii. The motor tracts and nerves send messages to the muscles and glandsIII. Somatic Nervous Systema. Motor neurons and paths that have control over skeletal muscles IV. General Sensesa. Describes sensitivity toi. Pain ii. Temperatureiii. Pressureiv. Touchv. Vibrationvi. 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 = olfactionii. Sight = visioniii. Taste = gustationiv. Balance = equilibriumv. 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 celli. Larger the area, the harder it is to pinpoint exact location of stimulusVI. Interpreting Sensory Informationa. Stimulus travels via labeled linei. Found between receptor and cortical neuronii. Always relayed by same axonb. Stimulus reaches cortical neuronc. Adaptation: nervous system reduces sensitivity to a stimulus that is constant andcauses no paini. Tonic receptors: slow to adapt 1. Constantly active 2. Ex. Pain receptors ii. Phasic receptors: fast to adapt1. 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 CNS1. Place of connection to the brain determines type of sensory information you are receiving VII. Receptors for General Senses a. Nociceptorsi. Detect painii. Found on skin, in joints, within periostea (bone ends), blood vesselsiii. Analgesia: cant feel painiv. Hyperalgesia: increased ability to feel pain v. Structure: 1. Free nerve endings 2. Large receptive areas3. Can be stimulated by many stimuli 4. Type A fibersa. 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 attention5. Type C fibersa. Slow pain sensations (burning/aching pain)b. Only have general idea of area affected by pain b. Thermoreceptorsi. 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. Mechanoreceptorsi. Detect stimuli that alter their plasma membrane ii. Mechanically gated ion channels open and close due to:1. Stretching2. Compression3. Twistingiii. Three types:1. Tactile receptorsa. Sensations of touch (shape; texture), vibration (fluctuating pressure) and pressure (how much distortion has happened)b. Fine touch and pressure receptors i. Extremely sensitiveii. 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 endings1. Tonic receptors with small receptive field 2. Found between epidermal cells ii. Root hair plexus1. Found at ends of hair2. Wherever hairs are found they can monitor movements and distortions3. 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 stimulation2. Found mostly in lips, eyelids, fingertips, nipples and external genitalia3. Large structures v. Lamellated corpuscles (aka. Pacinian corpuscles)1. Similar to intervertebral discs that cushion bodies of vertebrae good for compressions2. Fast adapting, sensitive to deep pressurevi. Ruffini corpuscles1. 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 pressureii. Digestive tractiii. Urinary tractiv. Reproductive tractb. Respond immediately to pressure change but are quick to adaptc.3. Proprioceptorsa. Detects lymph positionb. Most structurally and functionally complex of the general senses c. Three major groups:i. Muscle spindles fibers that can detect contractile state of a muscle1. Monitor length and trigger stretch reflexes ii. Golgi tendon organs1. Monitor tension developed during contraction of a muscle2. Found between skeletal muscle and its tendoniii. Receptors in joint capsules1. Helps you see body in 3D2. Detect pressure, tension and movement in the joints d. Chemoreceptors i. Different chemicals that can have an effect on the bodyii. Only respond to water and lipid soluble substances dissolving in surrounding fluidiii. Peripheral adaptation: receptors will adapt to stimulusiv. Central adaptation: brain tunes out signalsv. Those that detect pH, CO2 and O2 in arterial blood are found in:1. Carotid bodies make sure you get enough oxygen in your braina. Found on each side of the neck near origin of internal carotid arteries2. Aortic bodies monitor how much oxygen is going through bodya. Found in aortic
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