Physiology of the nervous system
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2015
A reflex is an automatic or involuntary stereotypical response to a peripheral stimulus mediated by a receptor, an afferent pathway and an effector organ to rapidly produce purposeful movements. Interneurons may be present between the afferent and efferent neurons. The number of synapses in the reflex arc defines a reflex as monosynaptic or polysynaptic. The knee-jerk reflex is a monosynaptic reflex arc. Stretching of the quadriceps muscle stimulates muscle spindles, which excite the α motor neurons supplying the quadriceps muscle and cause it to contract. Stretch reflexes are important for the control of posture. Withdrawal reflexes are elicited by noxious stimuli and involve many muscles through polysynaptic pathways. Reciprocal inhibition ensures that extensor muscles acting on a joint will relax while flexor muscles contract. The Golgi tendon reflex is activated by discharge in Golgi tendon organs and plays an important role in the maintenance of posture.
Neuronal Regulation of the Immune System in Cardiovascular Diseases
Shyam S. Bansal in Immune Cells, Inflammation, and Cardiovascular Diseases, 2022
The circumventricular organs (CVOs), located around the third and fourth ventricles, are particular brain regions characterized by a leaky blood–brain barrier (BBB) and dense vascularization (Ballabh, Braun, & Nedergaard, 2004). These specialized areas are points of communication between the blood, the brain parenchyma, and the cerebrospinal fluid. The peripheral nervous system (PNS) connects the CNS to peripheral tissues and is mainly organized in two branches comprising the somatic and autonomic systems. Each of these systems further consists of two arms of sensory or afferent neurons – transporting the information from the periphery to the CNS – and motor or efferent neurons, delivering responses toward the effector tissues (Reardon et al., 2018). Additionally, the humoral route regulated by the hypothalamus-pituitary-adrenal axis provides further control of neuroimmune communication in health and disease.
Neuropeptides in the Regulation of Autonomic Function By the Dorsal Medulla
I. Robin A. Barraco in Nucleus of the Solitary Tract, 2019
Many efferent projections from the NTS also contain neuropeptides. Fibers projecting from the NTS to the DMX and nucleus ambiguus contain β-endorphin and somatostatin.26 Although most neuronal projections from the NTS to the ventral medulla contain catecholamines or GABA, an enkephalin-containing pathway from the NTS to the rostral ventrolateral medulla vasomotor center has been identified.66 Projections from the NTS to the pontine parabrachial nucleus, a major autonomic relay center, contain ANG II, bombesin, cholecystokinin, corticotropin-releasing factor, dynorphin, enkephalins, galanin, neuropeptide Y, neurotensin, somatostatin, and subP.45,67,68 Autonomic centers in the hypothalamus, including the paraventricular and supraoptic nuclei, receive a wide variety of peptidergic innervation from the NTS, including enkephalins, somatostatin, neuropeptide Y, neurotensin, dynorphin, and bombesin.45,69 In turn, the NTS receives projections containing vasopressin and oxytocin from the paraventricular and supraoptic nuclei.24 Although vagal preganglionic efferent neurons had been considered to be exclusively cholinergic, anatomical studies have now revealed that some vagal efferent neurons contain neurotensin or galanin, possibly colocalized with catecholamines.70
Communication between the gut microbiota and peripheral nervous system in health and chronic disease
Published in Gut Microbes, 2022
Tyler M. Cook, Virginie Mansuy-Aubert
Neuronal transmission allows for nearly instantaneous processing of sensory input or generation of motor output. This rapid signaling of peripheral neurons in the gut is critical for homeostatic mechanisms such as GI motility, secretion, and even immune response modulation.39 The peripheral nervous system (PNS) consists of vagal and spinal sensory (afferent) neurons, autonomic motor (efferent) neurons, and enteric neurons (Figure 2). Afferent neurons send information from the periphery to the brain or spinal cord, while efferent neurons project out from the central nervous system (CNS) to peripheral organs. Classifying by anatomical distribution, the twelve cranial nerves project from the brain/brainstem and spinal nerves from the spinal cord. The autonomic system is divided into sympathetic, parasympathetic, and enteric nervous systems (ENS).
Adaptation of perturbation to postural control in individuals with diabetic peripheral neuropathy
Published in International Journal of Occupational Safety and Ergonomics, 2020
Byungjoon B. J. Kim, Sunghan Kim
The capability of postural control can be related to mobility limitation because it requires the ability to maintain balance of the body in the spatial dimension, particularly when the body is in motion. The loss of sensation in the feet due to diabetic peripheral neuropathy can affect the capability of postural control. Since diabetic peripheral neuropathy interferes with both afferent and efferent neurons, which can cause a delay in potential action transmission, people with diabetic peripheral neuropathy may have less stable postural control than healthy people or even diabetic people without peripheral neuropathy [22,23]. When people have peripheral neuropathy regardless of diabetes or non-diabetes, they tend to have a higher rate of falling compared to healthy people [24]. In addition, the risk of falling for diabetic people with peripheral neuropathy can be 15 times higher than that for diabetic people without peripheral neuropathy [25]. Therefore, it is necessary to develop an intervention program for diabetics with peripheral neuropathy to complement postural control when a balance perturbation arises.
Lower limb muscle synergies during walking after stroke: a systematic review
Published in Disability and Rehabilitation, 2020
Tamaya Van Criekinge, Jordi Vermeulen, Keanu Wagemans, Jonas Schröder, Elissa Embrechts, Steven Truijen, Ann Hallemans, Wim Saeys
The results of this review indicate that the synergies are altered during hemiplegic gait and that merging of synergies occurs. However, it is still unclear if these synergies are pathological or learned behavior. Although we found several reoccurring and distinctive synergies, no clear consensus can be reached concerning the amount and composition of synergies between studies. It might be that muscle synergies are dependent on the severity of the lesion and if the neural structures required for the activation of the synergies are affected. It is important to further investigate the underlying mechanisms responsible for the merging of synergies since they are an important predictor for poor motor outcome [13,20,29]. In general, a higher number of synergies was associated with intact motor function. Moreover, less synergies was related to poor improvements in muscle strength and gait kinematics [29]. Studies showed that although stroke survivors showed similar synergy strength and muscle weightings, observed changes in muscle synergies were mostly the cause of reduced muscle participation of individual muscles to a muscle synergy, impaired activation timing of a certain synergy or the ability to differentially activate the synergies [22,26,27]. It is also important to consider that different muscle synergies are observed between the paretic and non-paretic side. Although, some studies concluded that the non-paretic side had a similar synergy amount as healthy individuals, a small shift in composition was observed [22–24]. It is possible that, although contralesional efferent neurons are still intact, impairments of the paretic side influence the non-paretic side. Therefore, we recommend investigating both the paretic and non-paretic side since clear differences were found between both limbs.
Related Knowledge Centers
- Action Potential
- Axon
- Central Nervous System
- Motor Nerve
- Muscle
- Peripheral Nervous System
- Sensory Neuron
- Afferent Nerve Fiber
- Soma
- Gland