How to get an H reflex?
What are the afferents of muscle?
How long does it take for the H wave to recover?
Why are muscles on both sides of a joint needed?
What is post tetanic potentiation?
Which afferents signal velocity?
What are the main features of the orofacial motor system?
See 4 more
About this website
What are Group 3 and 4 muscle afferents?
Group III afferents primarily transmit information about mechanical stimuli arising in the exercising muscles, whereas the group IV afferents primarily transmit information about metabolic stimuli (Hayes and Kaufman 2001; Kaufman and Forster 1996).
What is the difference between 1a and 1b afferent?
1a is the largest and thus the most rapidly conducting. 1b, from the Golgi tendon organ, is slower and 2 is the slowest. Afferents from nuclear bag fibers signal velocity. Like the Pacinian corpuscles, bag fibers adapt quickly when stretched.
What are IA afferents?
Group Ia afferents (also called primary afferents) wrap around the central portion of all 3 types of intrafusal fibers; these specialized endings are called annulospiral endings. Because they innervate all 3 types of intrafusal fibers, Group Ia afferents provide information about both length and velocity.
What is afferent and efferent nerve?
Afferent neurons carry information from sensory receptors of the skin and other organs to the central nervous system (i.e., brain and spinal cord), whereas efferent neurons carry motor information away from the central nervous system to the muscles and glands of the body.
What are Type 1a afferents?
A type Ia sensory fiber, or a primary afferent fiber is a type of afferent nerve fiber. It is the sensory fiber of a stretch receptor called the muscle spindle found in muscles, which constantly monitors the rate at which a muscle stretch changes.
What are the 3 types of receptors in the afferent nervous system?
Receptors are also classified as exteroceptive (reporting the external environment), interoceptive (sampling the environment of the body itself), and proprioceptive (sensing the posture and movements of the body).
What is an example of afferent?
For example, if the central point in question is the brain, sensory neurons are afferent because they send information to the brain, while motor neurons are efferent because they carry information from the brain to effector organs like muscles or glands.
Where is the afferent?
In the peripheral nervous system afferent and efferent nerve fibers are part of the somatic nervous system and arise from outside of the spinal cord. Sensory nerves carry the afferent fibers to enter into the spinal cord, and motor nerves carry the efferent fibers out of the spinal cord to act on skeletal muscles.
What does afferent mean in the CNS?
The afferent nerves are the messenger neurons that bring the information from different parts of the body to the central nervous system (CNS). In biology, the afferent nerves are defined as the projections of axons that carry the stimulus from the peripheral organs to the central nervous system.
How do you remember afferent and efferent?
You can think of afferent and efferent neurons pathways as one-way streets. The traffic can only flow in one direction – afferent neurons only take information to the central nervous system, and efferent neurons only take it away from the central nervous system.
Are spinal nerves afferent or efferent?
Each spinal nerve is a mixed nerve, formed from the combination of nerve fibers from its dorsal and ventral roots. The dorsal root is the afferent sensory root and carries sensory information to the brain. The ventral root is the efferent motor root and carries motor information from the brain.
What is the difference between afferent and efferent vessels?
The main difference between afferent and efferent arterioles is that afferent arterioles carry blood to the glomerulus whereas efferent arterioles take the blood away from the glomerulus. An afferent arteriole is a branch of the renal vein, which carries blood containing nitrogenous wastes.
Where are 1b afferent neurons located?
the Golgi tendon organOnly one type of sensory or afferent neuron is associated with the Golgi tendon organ. These group 1b, afferent fibers branch extensively and wrap around the many collagen fibers that compose the Golgi tendon organ.
Where are 1b afferent sensory neurons located?
Primary Afferent Neurons The first neurons in these reflex circuits are PANs (sometimes called “sensory” neurons, although they do not give rise to conscious sensation). These neurons are located in both myenteric and submucosal plexuses and characteristically have several long axonal processes.
What are 1a muscle fibers?
Type 1. Type I fibers (SO). These fibers have a rich capillary supply, numerous mitochondria and aerobic respiratory enzymes, and a high concentration of myoglobin. Myoglobin is a red pigment, similar to the hemoglobin in red blood cells, that improves the delivery of oxygen to the slow-twitch fibers.
How many types of afferent nerves are there?
Types of afferent fibers include the general somatic (GSA), the general visceral (GVA), the special somatic (SSA) and the special visceral afferent fibers (SVA).
Significance of Group III and IV muscle afferents for the endurance ...
1. With the onset of dynamic whole-body exercise, contraction-induced mechanical and biochemical stimuli within locomotor muscle cause an increase in the discharge frequency of thinly myelinated (Group III) and unmyelinated (Group IV) nerve fibres located within the muscle. 2. These thin fibre muscl …
Afferent vs Efferent Neurons: What Are They, Structure, and More - Osmosis
What are efferent neurons responsible for? Efferent neurons, also called motor neurons, are the nerve fibers responsible for carrying signals from the brain to the peripheral nervous system in order to initiate an action. In other words, they are the neurons that tell your body to perform an action, such as removing your hand from a hot pan. The peripheral nervous system is further divided ...
Type Ia sensory fiber - Wikipedia
A type Ia sensory fiber, or a primary afferent fiber is a type of afferent nerve fiber. It is the sensory fiber of a stretch receptor called the muscle spindle found in muscles, which constantly monitors the rate at which a muscle stretch changes.The information carried by type Ia fibers contributes to the sense of proprioception
Intrafusal Muscle Fiber - an overview | ScienceDirect Topics
David Burke, in Reference Module in Biomedical Sciences, 2014. Fusimotor Innervation. The poles of intrafusal muscle fibers are innervated by a number of small myelinated (gamma) efferent axons, which come from gamma motoneurons in the spinal cord (Matthews, 1981; Hulliger, 1984; Boyd and Gladden, 1985).In addition, some spindles (perhaps 20–30%) receive branches of large myelinated efferent ...
Gamma Motor Neuron - an overview | ScienceDirect Topics
Gulgun Sengul, in The Rat Nervous System (Fourth Edition), 2015. Lamina 9. Lamina 9 consists mainly of large α and small γ motor neurons, a small number of β motor neurons and small interneurons. Dendrites of motor neurons are extensive in the rostrocaudal, mediolateral and dorsoventral planes, and may extend dorsally into laminae 3–4 in the rat (Cook and Woolf, 1985).
What are some examples of local cutaneous reflexes?
One example of a local cutaneous reflex is the stumbling corrective reaction . When the skin on the top of the foot is stimulated during walking, the foot is lifted higher, as if to step over an obstacle. The stumbling corrective reaction is phase dependent, occurring only when the limb is in the swing phase of the step cycle. This and several other local cutaneous reflexes are oligosynaptic, involving only a few interneurons. The last-order interneurons in these cutaneous reflexes connect with relatively limited sets of motor neurons. It has been proposed that such interneurons offer a means to control or alter activity of specific muscles during movement without involving the interneurons of pattern generating circuitry.
What is reflex flexion?
A wide variety of sensory stimuli can evoke reflex flexion of the limb. Flexor reflexes may have several roles: they serve a protective function, reflexively withdrawing the limb from potentially harmful stimuli, and they may be used in movements that require coordinated multijoint flexor movements. Usually the reflex consists of contraction of muscles that flex several joints coupled with relaxation of muscles that extend those joints. Extension of the contralateral limb may also occur. Flexor reflexes can be elicited by group II and III muscle afferents, joint afferents, and high- and low-threshold cutaneous afferents. Because these afferents elicit a common action, they are sometimes called “flexor reflex afferents” (FRAs). The muscles activated by the sensory stimulus respond with short and long latency bursts of contraction. These contraction components are thought to be generated by distinct interneuron circuits. The late components can be differentially enhanced by treatment with L-dopa in spinalized animals. It has been suggested that interneurons mediating the late flexor reflex could function as a half-center for flexion, as proposed in models of the locomotor CPG.
What is the nociceptive nerve?
The nociceptive nerve endings that are found in skin, joints, muscles, bone make up an intricate network of pain perception controlled by the human central nervous system. Because muscle afferent nerve pathways and pain afferent nerve pathways both converge on the dorsal horn of the spinal cord, it has been proposed that pain afferents may be susceptible to some form of selective inhibition as a result of physical activity and exercise training. 22 Another hypothesis is that endogenous opioid release may be involved in exercise-induced hypoalgesia. Most likely, exercised-induced hypoalgesia is caused by a host of interrelated factors that may be partially controlled by the mode and intensity of exercise. Koltyn and coworkers’ study 23 demonstrated significant hypoalgesia after maximal isometric gripping exercise in both men and women. These researchers tested 15 males and 16 females under two isometric exercise conditions. Subjects squeezed a hand dynamometer for 2 minutes at two different intensities (40%–50% and 100% of maximal handgrip contractions [MVC]).
What are the descending pathways of the brain?
Several areas of the brain give rise to descending pathways that connect to spinal interneurons and, to varying extents in different species, to motor neurons. Areas of the brainstem are critical for relaying descending commands for locomotion. Volitional movements also seem to employ spinal interneuron circuits for organizing routine patterns of muscle contraction, within the context of a planned goal. Sensory feedback from skin, joints, and most muscle afferents provide fine-tuning of basic movement patterns. The reflex motor responses evoked by most sensory afferents are relayed through interneurons.
What are the proprioceptors responsible for?
Proprioceptors responding to hip extension were considered by Sherrington 126 to be responsible for the initiation of the swing phase of locomotion. Hip extension beyond a particular point is necessary for the initiation of the swing phase of locomotion, 215 and hip movements can reset and entrain the locomotor rhythm, 135,216,217 with hip extension leading to flexor bursts. Hip joint capsule denervation was without effect, and low-threshold stretch-sensitive muscle afferents appear to be responsible for the influence of hip movement to prolong extension and initiate flexion.135 Movements about the hip joint were shown to have a potent effect on the locomotor rhythm, with increased hip extension resulting in increased frequency of fictive locomotion.
What causes central fatigue?
Central fatigue may develop when this motor drive is disrupted or due to disruption of the cortical pathways rostral to the pyramidal tracts. Dysfunction of these volitional pathways to and from the primary motor cortex may be the cause of central fatigue in normal subjects, in chronic fatigue syndrome (CFS), and in multiple sclerosis (MS). Defective afferent feedback could also contribute to central fatigue since muscle afferent input to the cerebral cortex may play a role in motor control. During a maximum voluntary contraction, facilitation from muscle afferents may contribute up to 30% of central motor drive; in addition, there is facilitatory feedback from cutaneous afferents. Such facilitation may occur at either the spinal or supraspinal level. At the same time, motor neuron firing is reflexively inhibited by afferent feedback from muscle to prevent high-frequency (peripheral) fatigue and to maximize force output. Distorted perception of effort may cause a sensation of fatigue disproportionate to the actual loss of force-generating capacity. The perception of effort is partly dependent on afferent feedback from cutaneous receptors and muscle spindles as well as descending corollary pathways of motor commands. This distorted perception of effort could be a major component or contributor to the central fatigue in some conditions, such as pure motor stroke, CFS, fibromyalgia, and MS. Finally, there are changes in central enkephalinergic, dopaminergic, and serotonergic systems during fatiguing exercise. These chemicals presumably control vigilance, motivation, and pain and its intolerance, whereas other neuroendocrine changes alter availability of substrates for muscle contraction.
Where are primary sensory cell bodies located?
This location of primary afferent cell bodies is the only place in the body where primary sensory cell bodies are located within the CNS. Other major distinguishing features of the orofacial motor systems include the following. (1) Many orofacial muscles lack muscle spindles and Golgi tendon organs, as noted above. (2) A fusimotor (gamma-efferent) control system is absent due to the lack of muscle spindles in many muscles. (3) Reciprocal innervation, where muscle afferent fibers have reciprocally opposite effects on antagonistic spinal motoneurons, is limited due to the sparsity of muscle spindle and tendon organ afferent fibers. This lack may be compensated for by the powerful regulatory influences afforded by afferent inputs from facial skin, mucosa, TMJ, and teeth (see below). (4) Coordinating pathways and mechanisms exist to allow for the bilateral activity of muscles; although activity of a particular limb or trunk muscle can occur on both the left and right sides of the body in some movements, this bilateral activation (or depression) is particularly prominent in orofacial movements (e.g., chewing, swallowing, speech, coughing). The muscle afferent fibers, along with cutaneous, joint, and intraoral afferent fibers, make excitatory reflex connections with brain stem motoneurons located within one or more cranial nerve motor nuclei (Figure 4 ); these connections are usually indirect and involve interneurons in the trigeminal spinal tract nucleus, the solitary tract nucleus, and the reticular formation. Examples of such ‘simple’ reflexes are the jaw-closing, jaw-opening, and horizontal jaw reflexes; facial muscle reflexes; tongue reflexes; and laryngeal, pharyngeal, and palatal reflexes. In addition to these excitatory reflex effects of various oral–facial stimuli, inhibitory effects are also expressed on the reflexes by sensory stimuli and by descending regulatory influences arising from higher brain centers such as the cerebral cortex ( Figure 4 ). The excitatory and inhibitory influences are especially involved in protection of the masticatory apparatus (e.g., from biting the tongue during chewing) and in providing much of the neural organization upon which are based more complicated motor activities such as the protective reflex synergies of coughing and gagging. An even higher level of complexity of organization is seen with the rhythmic, automated activities of mastication, suckling, and swallowing; speech is another complex sensorimotor behavior utilizing this neural organization.
How to get an H reflex?
To obtain an H reflex with minimal direct excitation of motor axons, a pulse of 0·3–1·0 milliseconds is used since a pulse of shorter duration (01 milliseconds) excites motor fibres more readily than sensory fibres. Once an H reflex is elicited, the intensity of stimulation must be carefully controlled because a slight increase will excite motor fibres and bring in the direct muscle response (M response) with a shorter latent period than the H reflex ( Figure 4.7 ). When a nerve fibre is adequately stimulated, the resulting discharge spreads not only in the direction in which the nerve normally conducts (orthodromic volley) but also in the reverse direction (antidromic volley). In the case of the medial popliteal and sciatic nerves, the afferent volley discharges the anterior horn cell synaptically and the postsynaptic volley is on its way down motor fibres when it meets the antidromic impulses travelling in the opposite direction. The two volleys collide and the propagation of the H reflex is prevented. This can be demonstrated by increasing the intensity of Stimulation of the medial popliteal nerve. The direct muscle reponse becomes larger and the H reflex progressively smaller ( Figures 4.7, 4.8 ). To minimize excitation of motor fibres, the stimulus voltage is usually restricted to 1.1 or 1.2 threshold, that is, the voltage required to produce the smallest discernible H reflex.
What are the afferents of muscle?
The muscle afferents associated with movement and position sense are those from the muscle spindles. These fire when the muscle spindle is stretched during lengthening of the muscle. Recording in humans and in animals shows that muscle spindles can signal joint movement and position during passive movements.
How long does it take for the H wave to recover?
In man, there is an unresponsive period of about 70 milliseconds following the conditioning shock, after which the amplitude of the test response gradually increases although full recovery may not occur for several seconds 41. More rapid recovery of the H reflex occurs in upper motor neurone, cerebellar and extrapyramidal disorders, indicating an increased excitability of the spinal motoneurone pool 41,42,43.
Why are muscles on both sides of a joint needed?
Thus, muscles on both sides of a joint are needed to give adequate signals of movement and position. Stimulation of a single muscle spindle afferent causes no sensation, but when a population of muscle spindles is activated by vibration applied over the tendon of the muscle, joint movement and altered joint position are perceived.
What is post tetanic potentiation?
During the period of post-tetanic potentiation of the H reflex, contraction of the antagonistic muscles (the ankle dorsiflexors) is partially inhibited, illustrating the presence of reciprocal innervation.
Which afferents signal velocity?
The Ia afferents signal velocity (with a position component) whereas the group II afferents primarily signal position. Muscle spindle activity increases with muscle lengthening, but most spindles fall silent during passive shortening of the muscle.
What are the main features of the orofacial motor system?
Other major distinguishing features of the orofacial motor systems include the following. (1) Many orofacial muscles lack muscle spindles and Golgi tendon organs , as noted above. (2) A fusimotor (gamma-efferent) control system is absent due to the lack of muscle spindles in many muscles.