Efferent system

Anatomically, the human nervous system may be divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The major subdivision of the central nervous system is into the brain and spinal cord. The peripheral nervous system is divided into the motor or efferent system (efferent = away from ), and the sensory or afferent (afferent = toward ) nervous systems (Figure 2.1). 

The nervous system is divided into two parts the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS consists of all afferent (sensory) neurons, which carry nerve impulses into the CNS from sensory end organs in peripheral tissues, and all efferent (motor) neurons, which carry nerve impulses from the CNS to effector cells in peripheral tissues. The peripheral efferent system is further divided into the somatic nervous system and the autonomic nervous system. The effector cells innervated by the somatic nervous system are skeletal muscle cells. The autonomic nervous system innervates three types of effector cells (1) smooth muscle, (2) cardiac muscle, and (3) exocrine glands. While the somatic nervous system can function on a reflex basis, voluntary control of skeletal muscle is of primary importance. In contrast, in the autonomic nervous system voluntary control can be exerted, but reflex control is paramount. 

Drugs that affect the central nervous system may also have a major action in the gut. Thus, the constipating effects of opium alkaloids are exerted through this system and a number of the important withdrawal symptoms reflect the actions of the enteric nervous system. The nervous system is often regarded as a command (efferent) system that sends instructions to be executed. However, there is also a sensory (afferent) component, that receives information from innervated systems... 

Organization of the Efferent System and Structure of Neuromuscular Junctions in Drosophila Andreas Prokop... 

Directional Afferent system by sensory neurons, which carry impulses from a somatic receptor to the CNS. Efferent system by motor neurons, which carry impulses from the CNS to an effector. Relay system by interneurons (also called relay neurons ), which transmit impulses between the sensory and motor neurons (in both the CNS and the PNS). 

Lima da Costa D, Erre JP, Pehourq F, Aran JM. Aminoglycoside ototoxicity and the medial efferent system II. Comparison of acnte effects of different antibiotics. Audiology 1998 37(3) 162-73. 

Gil-Loyzaga PE (1995) Neurotransmitters of the olivocochlear lateral efferent system with an emphasis on dopamine. Acta Otolaryngol (Stockh) 115 222-226. 

Before the role of OHCs was determined it was observed that sounds could be measured in the meatus, both spontaneously and in response to other sounds [Wilson, 1986]. In humans they tend to contain spectrally narrow components and vary across individuals. OHCs are strongly implicated as the source for these emissions because sounds in the opposite ear affect them (presumably through the efferent system) and aspirin, known to affect OHCs, reduces them [Geisler, 1998]. As with most positive-feedback systems, spontaneous oscillation is suggested. Otoacoustic emissions are becoming important in the clinical evaluation of cochlear function for their potential signaling of cochlear pathologies. 

Fig. 1.4 Diagram of a dorsal view of the brainstem the cerebellum has been removed. The extent of the reticular formation within the brainstem is illustrated. The reticular formation is a polysynaptic network that consists of three regions a series of midUne raphe nuclei (the median reticular formation, which is the site of origin of the major serotonergic pathways in the nervous system) this is flanked bUateraUy by the paramedian reticular formation (an efferent system of magnoceUular neurons with ascending and descending projections) and farthest from the midhne, the lateral reticular formation, consisting of parvoceUular neurons that project transversely See also Color Insert)...

The central nervous system controls the muscles through two sets of coordinated efferent systems, the a- and y-motoneurons [26, 169, 170] (Figure 5.5). The contraction of skeletal muscle is controlled directly by the a-motoneurons alpha drive is used where speed of movement is essential, and... 

Major efferent projections of the hypothalamic orexin system comprise descending and ascending, dorsal and ventral pathways that terminate preferentially in aminergic, endocrine, and autonomic control centers in the hypothalamus, midbrain, brainstem, and spinal cord, as well as in limbic cortical and subcortical structures, including sqDtum, amygdala, thalamus,... 

Figure 1. A depiction of the several different ionic currents necessary for the acute function of neuromuscular transmission in the skeletal motor and the efferent autonomic nervous system. The boxed current designations are associated, by the arrows, with those cellular regions where their physiological role is most evident, although these currents often exist in other regions of the cell. = neurotransmitter-activated current ...

Dysfunction may be caused by aging, systemic inflammatory diseases, a decrease in androgen hormones, surgery, ocular surface diseases (such as herpes zoster), systemic diseases, or medications that affect the efferent cholinergic nerves. Decreased tear secretion produces an inflammatory response on the ocular surface called keratoconjunctivitis sicca. This inflammation is now a target for new medications that treat dry eye.29,30... 

The third component of the nervous system is the motor division. Appropriate signals are transmitted from the CNS to various body parts or effector tissues by way of efferent neuronal pathways. These effector tissues, which include organs, muscles, and glands, carry out the appropriate physiological responses to bring the variable back to within its normal limits. 

The afferent division carries sensory information toward the CNS and the efferent division carries motor information away from the CNS toward the effector tissues (muscles and glands). The efferent division is further divided into two components (1) the somatic nervous system, which consists of motor neurons that innervate skeletal muscle and (2) the autonomic nervous system that innervates cardiac muscle, smooth muscle, and glands. 

Figure 6.1 Types of neurons. Afferent neurons, which transmit impulses toward the CNS and efferent neurons, which transmit impulses away from the CNS, lie predominantly in the peripheral nervous system. Intemeurons, which process sensory input and coordinate motor responses, lie entirely within the central nervous system.

At this point, it is important to note that a nerve is defined as a bundle of neuronal axons some are afferent and some are efferent. A nerve does not consist of entire neurons, only their axons. Furthermore, nerves are found only in the peripheral nervous system. Bundles of neurons with similar functions located within the CNS are referred to as tracts. Therefore, technically speaking, no nerves are within the brain or the spinal cord. 

The cell bodies of visceral motor neurons are found in the lateral horn. The axons of these neurons form efferent nerve fibers of the autonomic nervous system (ANS). The ANS innervates cardiac muscle, smooth muscle and glands (see Chapter 9). The axons of these neurons exit the spinal cord by way of the ventral root. 

The efferent nervous activity of the ANS is regulated by several regions in the central nervous system (CNS) ... 

Figure 9.1 The autonomic nervous system and its effector organs. The efferent pathways of this system consist of two neurons that transmit impulses from the CNS to the effector tissue, preganglionic neuron (solid line), and postganglionic neuron (dashed line). As illustrated, most tissues receive nervous input from both divisions of the ANS the sympathetic and the parasympathetic.

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