9/5/2023 0 Comments Free nerve endings signal![]() ![]() Tendon Organs (Golgi tendon organs) - consists of sensory fiber penetrating a thin capsule of connective tissue and entwining around a few collagen fibers, found at the junctions of a tendon with a muscle, help protect tendons and associated muscles from damage due to excessive tension or stretching Muscle spindles monitor changes in length of muscle by responding to the rate and degree of change. Muscle spindle - 3 - 10 specialized muscle fibers called intrafusal fibers, oriented parallel to regular muscle fibers, ends of spindle are anchored to the endomysium and perimysium. Proprioceptors - located in muscles, tendons, joints and internal ear and provide information about body position and movement. Baroreceptors – receptors to detect pressure changes in blood vessels.Type II cutaneous(Ruffini) receptor for continuous touch sensation.Type I cutaneous (Merkel) receptors for discriminative touch.Corpuscle of touch (Meissner‘s) - receptor for discriminative touch.Lamellated (Pacinian) corpuscles - rapidly adapting skin receptor that detects pressure and vibration.Chemical – Na+ channels that initial opened are slowly inactivated.Sustained pressure causes layers to slip, dissipating stimulus intensity Mechanical – specialized receptor ending consists of concentric layers of connective tissue.Phasic receptors – rapidly adapt, useful in situations where it is important to signal a change in stimulus – tactile (touch) receptors Tonic receptors do not adapt at all or very slowly, important when maintaining information about a stimulus is valuable – stretch, pain receptors Adaptation occurs in the receptor, not the CNS Receptor membranes become less responsive, receptor potentials decline in frequency or stop. Lateral inhibition to facilitate localization and sharpen contrast, the most strongly activated pathway at the center inhibits the less excited pathways from the fringe areasĪdaptation occurs when sensory receptors are subjected to an unchanging stimulus *Receptive field = area within which a receptor can detect a stimulus Third-order neurons – located in the thalamus and conduct impulses to the somatosensory cortex of the cerebrum.Second-order neurons – soma reside in the dorsal horn of the spinal cord or medullary nuclei and transmit impulses to the thalamus or cerebellum.First-order neurons – soma reside in dorsal root or cranial ganglia, and conduct impulses from the skin to the spinal cord or brain stem.A generator potential is a type of graded potential similar to a EPSP Transduction – the process of converting energy forms into electrical signals via a generator potential which triggers an action potential if it it large enough to reach threshold. Stimuli exist in a variety of energy forms or modalities – heat, light, sound, pressure, chemical etc. A generator potential in the associated sensory neuron must reach threshold.Stimulus energy must be converted into a graded potential.The receptor’s receptive field must be stimulated.The receptor must have specificity for the stimulus energy.If threshold reached, AP is generated.Chemical messenger opens ion channels in afferent neuron AP generating region.Receptor cell releases chemical messenger.Stimulus opens ion channels in receptor causing graded membrane potential.Local current flow opens ion channels in afferent neuron AP generating region.Stimulus opens ion channels in receptor causing local current flow.Osmoreceptors – detect changes in concentration of solutes, osmotic activity.Nociceptors – sensitive to pain-causing stimuli.Chemoreceptors – respond to chemicals (e.g., smell, taste, changes in blood chemistry).Photoreceptors – respond to light energy (e.g., retina).Thermoreceptors – sensitive to changes in temperature.Mechanoreceptors – respond to touch, pressure, vibration, stretch, and itch.*The realization of these stimuli, sensation and perception, occur in the brain.Activation of sensory receptors results in depolarizations that trigger impulses to the CNS.Are structures specialized to respond to stimuli.Perception is the conscious interpretation of those stimuli.Sensation is the awareness of changes in the internal and external environment.Survival depends upon sensation and perception.Is the conscious interpretation of external world created by the brain.Receptors - Afferent pathway ( from PNS to CNS).Energy source-heat, light, sound, pressure.The afferent pathway of the Peripheral Nervous System transmits impulses from PNS to the CNS.Provides links to and from the external environment.Is made up of all neural structures outside the brain and spinal cord.Peripheral Nervous System- Afferent Division (Somatic) ![]()
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