Muscle spindle : Mammalian muscle spindle showing typical position in a muscle left , neuronal connections in spinal cord middle , and expanded schematic right. The spindle is a stretch receptor with its own motor supply consisting of several intrafusal muscle fibers. The sensory endings of a primary group Ia afferent and a secondary group II afferent coil around the non-contractile central portions of the intrafusal fibers. The Golgi organ also called Golgi tendon organ, tendon organ, neurotendinous organ or neurotendinous spindle is a proprioceptive sensory receptor organ that is located at the insertion of skeletal muscle fibers onto the tendons of skeletal muscle.
It provides the sensory component of the Golgi tendon reflex. The Golgi organ should not be confused with the Golgi apparatus—an organelle in the eukaryotic cell —or the Golgi stain, which is a histologic stain for neuron cell bodies. Golgi tendon organ : The Golgi tendon organ contributes to the Golgi tendon reflex and provides proprioceptive information about joint position. The Golgi tendon reflex is a normal component of the reflex arc of the peripheral nervous system. In a Golgi tendon reflex, skeletal muscle contraction causes the agonist muscle to simultaneously lengthen and relax.
This reflex is also called the inverse myotatic reflex, because it is the inverse of the stretch reflex. Although muscle tension is increasing during the contraction, alpha motor neurons in the spinal cord that supply the muscle are inhibited. Sensory Receptors. Specialized sensory receptor cells e. Specialized sensory receptors may be modified neurons e.
Figure 2. The peripheral process is part of the peripheral nervous system PNS and terminates to form or end on a somatosensory receptor in skin, muscle or joint. The central process travels tso the central nervous system CNS where it terminates on a spinal cord or brain stem neuron. These cells are specialized neurons A. There is only one type of sensory receptor cell in the somatosensory system, the Merkel cells , and they are found only in skin.
The vast majority of somatosensory receptors are not specialized receptor cells. There is no synaptic specialization or neurotransmitter within the adjacent tissue.
The adjacent tissue also does not generate receptor potentials. Each terminal fiber forms, or ends on, a somatosensory receptor. The complex of encapsulated tissue and afferent endings and the complex of hair follicle and afferent endings play a role in the receptor transduction process, and each complex is considered to form a "somatosensory receptor".
These endings are bare of myelin, are not encapsulated and are not associated with a specific type of tissue. The sensitivity of the receptors to specific stimuli e. The Adequate Stimulus. The adequate somatosensory stimulus i.
The discriminative touch and proprioceptive systems are most sensitive to mechanical force. Consequently, their sensory receptors are of the mechanoreceptor category. Sensory Transduction. Generator potentials are produced as sodium and potassium flow down their electrochemical gradients to depolarize the terminal ending see Figure 2. In most cases, the magnitude and duration of the generator potentials are related to the applied mechanical force: the greater the mechanical force, the greater is the depolarization, and the longer the mechanical force is applied, the longer the terminal remains depolarized Figure 2.
Terminals that do not sustain the depolarization for the duration of the mechanical distortion are called rapidly adapting. Terminals that sustain the depolarization with minimal decrease in amplitude for the duration of a stimulus are called slowly adapting. A mechanical force A is applied and the responses are measured by a recording electrode in the somatosensory receptor B , and a recording electrode in the axon C.
If, as in the example in Figure 2. If the generator potential is rapidly adapting Figure 2. The rapidly adapting receptors produce generator potentials and action potential discharges that follow the time-varying waveform of pressure changes produced by a vibrating stimulus Figure 2.
In contrast, the slowing adapting receptors produce generator potentials and action potential discharges that are sustained and unable to mimic the time-varying pattern of the stimulus Figure 2. The time course of the applied force or skin displacement A ; generator potential recorded in the receptor B ; and the action potentials recorded from the afferent axon are illustrated C.
Click on the somatosensory receptor name in green shaded area to view a detailed drawing of the receptor. The location of the receptor will be circled in the larger drawing of the skin. Some of the somatosensory receptors in skin i. The encapsulated cutaneous receptors include Meissner corpuscles, Pacinian corpuscles and Ruffini corpuscles See Figure 2. The sensory receptors of the crude touch, pain and temperature senses are bare or free nerve endings. That is, they are unencapsulated, do not end on or near specialized tissue, and may be mechanoreceptors, nociceptors or thermoreceptors.
The following describes the most commonly observed cutaneous receptors. Meissner Corpuscle. The Meissner corpuscle is found in glabrous i. The Meissner corpuscle is located within the dermal papilla, near the surface of the skin, with its long axis perpendicular to the skin surface. A force applied to non-hairy skin Figure 2. If the force is maintained, the laminar cells remain in a fixed, albeit, displaced position, and the shearing force on the axon terminals' membranes disappears.
This shearing force distorts the membranes of the axon terminals located between the laminar cells, which depolarizes the axon terminals. If the force is sustained on the dermal papilla, the laminar cells remain in their displaced positions and no longer produce a shearing force on the axon terminals. Consequently, a sustained force on the dermal papilla is transformed into a transient force on the axon terminals of the Meissner corpuscle.
Stimulation of a sequence of Meissner corpuscles have been described to produce the perception of localized movement along the skin. Consequently, Meissner corpuscles are considered to be the discriminative touch system's flutter and movement detecting receptors in non-hairy skin.
Pacinian Corpuscle. Pacinian corpuscles are found in subcutaneous tissue beneath the dermis Figure 2. Therefore, they can be cutaneous, proprioceptive or visceral receptors, depending on their location. In skin, the Pacinian corpuscle is located deep in the subcutaneous adipose tissue. The Pacinian corpuscle is football-shaped, encapsulated, and contains concentrically layered epithelial laminar cells Figure 2.
The outer layers of laminar cells contain fluid that is displaced when a force is applied on the corpuscle. When a force is first applied on the Pacinian corpuscle Figure 2. If the external pressure is maintained on the corpuscle, the displacement of fluid in the outer laminar cells dissipates the applied force on the axon terminal. If the pressure is sustained on the corpuscle, the fluid is displaced, which dissipates the applied force on the axon terminal.
Consequently, a sustained force on the Pacinian corpuscle is transformed into a transient force on its axon terminal. The sensation elicited when cutaneous Pacinian corpuscles are stimulated is of vibration or tickle.
Pacinian corpuscles in skin are considered to be the vibration sensitive receptors of the discriminative touch system. Ruffini Corpuscle. The Ruffini corpuscles are found deep in the skin Figure 2. The Ruffini corpuscle Figure 2. The Ruffini corpuscles are oriented parallel to the skin surface and situated deep within the dermis. The Ruffini corpuscles are oriented with their long axes parallel to the surface of the skin and are most sensitive to skin stretch.
Depending on the amount, where in the body, and from what proprioceptors the different input is coming from, determines if the information will be made conscious or processed unconsciously. All the input coming into the nervous system is processed, and then depending on the state of the muscle, there are commands sent back to the muscle.
The initiation of proprioception is the activation of a proprioreceptor in the periphery. The proprioceptive sense is believed to be composed of information from sensory neurons located in the inner ear motion and orientation and in the stretch receptors located in the muscles and the joint-supporting ligaments stance. Proprioreceptors are sometimes known as adequate stimuli receptors. Although it was known that finger kinesthesia relies on skin sensation, recent research has found that kinesthesia-based haptic perception strongly relies on the forces experienced during touch.
Save my name, email, and website in this browser for the next time I comment. Skip to content Proprioception is the process by which the body can vary muscle contraction in immediate response to incoming information regarding external forces, by utilizing stretch receptors in the muscles to keep track of the joint position in the body.
The Seven Senses. Auditory System. Visual System. Tactile System.
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