Lecture 4 - General Sensory Mechanisms Flashcards
Expanded Tip Endings Mechanoreceptors
Merkel’s discs and other variants
Encapsulated Endings Mechanoreceptors
Meissner’s corpuscles and Kraus’ corpuscles
Spray Endings Mechanoreceptors
Ruffini’s corpuscles
Encapsulated Endings Mechanoreceptors
Pacinian corpuscles and other variants
Hearing Mechanoreceptors
Sound receptors of cochlea
Equilibrium Mechanoreceptors
Vestibular receptors
Arterial Pressure Mechanoreceptors
Baroreceptors
Mechanoreceptors
Include both free and encapsulated endings that receive either skin tactile sensibilities or deep tissue sensibilities
Nociceptors
Free nerve endings responding to pain
Electromagnetic Receptors
Include rods and cones of the eye for vision
Chemoreceptors
Taste, smell, arterial oxygen, osmolarity, blood CO2, blood glucose, amino acids, and fatty acids
Thermoreceptors
Cold and warm receptors
Differential Sensitivity
Each type of receptor is highly sensitive to one type of stimulus and is almost nonresponsive to other types
Modality
Refers to each of the principle types of sensation
Labeled Line Principle
Refers to the specificity of nerve fibers for transmitting only one modality of sensation
Adaptation
All sensory receptors adapt either partially or completely to any constant stimulus after a period of time; some receptors adapt to a far greater extent than others
Receptor Potential
They are local; created by opening “modality” gated channels such as Na+ channels that are opened in response to membrane deformation caused by the touch or pressure; if it is strong enough (through summation), it may generate an action potential at the first node of ranvier on the primary sensory neuron
Characteristics of Tonic Receptors
Slow adapting, detect continuous stimulus strength, transmit impulses as long as stimulus is present
Types of Tonic Receptors
Muscle spindles, golgi tendon organs, macula and vestibular receptors, baroreceptors, chemoreceptors
Characteristics of Phasic Receptors
Rapidly adapting, do NOT transmit a continuous signal, stimulated only when stimulus strength changes, transmit information regarding rate of change
Type A Nerve Fiber
Further subdivided into alpha, beta, gamma, and delta; large and medium-sized myelinated fibers of spinal nerves
Type C Nerve Fiber
Small, unmyelinated fibers; conduct signals at low velocity; make up more than half of all sensory fibers in most peripheral nerves and all postganglionic autonomic fibers
Type A-alpha Fibers (Group Ia)
Fibers from annulospiral endings of muscle spindles
Type A-alpha Fibers (Group Ib)
Fibers from Golgi tendon organs
Type A-beta,gamma Fibers (Group II)
From cutaneous tactile receptors and flower-spray
Type A-delta Fibers (Group III)
Carry temperature, crude touch, and pricking pain
Type C Fibers (Group IV)
Carry pain, itch, temperature, and crude touch
Spatial Summation
Increasing signal strength is transmitted by using progressively greater number of fibers
Receptor Field
Cluster of nerve endings from one pain fiber that covers an area of skin; number of endings is large in center and reduced in periphery; nerve endings from one pain fiber overlap those of other pain fibers
Temporal Summation
Increase signal strength by increasing frequency of nerve impulses in each fiber
Examples of the Neuronal Pool
Cerebral cortex, basal nuclei, thalamic nuclei, cerebellum, mesencephalon, pons, medulla, and gray matter of spinal cord
Stimulatory Field of Neuronal Pool
Neuronal area within the pool stimulated by each incoming nerve fiber; terminals for each input fiber lie on nearest neuron in its field; fewer terminals for each input fiber lie on neurons further away
Discharge Zone
Includes all the output fibers stimulated by the incoming fiber
Facilitated/Inhibition Zones
Neurons further from the discharge zone that are facilitated but not excited; may be inhibitory or excitatory depending on the input fiber
Diverging Neuronal Pathways
May result in amplification of initial signal; may allow transmission of original signal to separate areas
Converging Neuronal Pathways
Multiple input fibers converge onto a single output neuron; input fibers may be from a single source or from multiple separate sources
Reverberatory Circuits (Oscillatory Circuits)
Caused by positive feedback within neuronal circuit; once stimulated, may discharge repetitively for a long time
Somatic Senses
Collect sensory information from all over the body; can be mechanoreceptive, thermoreceptive, and pain
Special Senses
Refer to vision, hearing, smell, taste, and equilibrium
Exteroreceptive Sensations
From the surface of the body
Propriceptive Sensations
Refer to physical state of body; position sensations, muscle and tendon sensations, pressure sensations, equilibrium
Deep Sensations
Deep pressure, pain, and vibrations
