China
Africa
Explore chapters and articles related to this topic
Neurophotonics for Peripheral Nerves
Published in Yu Chen, Babak Kateb, Neurophotonics and Brain Mapping, 2017
Ashfaq Ahmed, Yuqiang Bai, Jessica C. Ramella-Roman, Ranu Jung
The sensory system consists of nerve cells with somata located outside the spinal cord in aggregates called dorsal root ganglia (Horch and Dhillon, 2004). These nerve processes are called afferent nerve fibers because they conduct action potentials and, therefore, information from the periphery to the central nervous system. Afferent sensory fibers can be myelinated or unmyelinated, the latter ranging from 2 to 20 μm in diameter, and convey various sensory inputs, mainly mechanical, thermal, and noxious stimuli (Navarro et al., 2005). Myelinated axons are used for tasks (such as control of skeletal muscle contraction or signaling of temporally rapid and brief events) where speed is required or where fine tactile or proprioceptive discriminations are to be made. Unmyelinated fibers are normally associated with control of smooth muscle or signaling diffuse, temporally sluggish events such as pain and temperature. The motor system consists of nerve cells with somata located in the ventral quadrant of the spinal cord (Horch and Dhillon, 2004). These nerve processes are called efferent nerve fibers because they conduct information in terms of action potentials from the central nervous system to the periphery. They can be divided into two types: alpha-motor fibers that innervate the skeletal extrafusal muscle fibers and gamma-motor fibers that innervate the spindle muscle fibers (Navarro et al., 2005).
Occupational toxicology of the nervous system
Published in Chris Winder, Neill Stacey, Occupational Toxicology, 2004
This simple model of sensory input, central integration and effector output, is of course much more sophisticated in reality. Axonal processes are found throughout the nervous system and the body. Where they collect together they are called nerves (the term nerve can be used for a single nerve process or a ‘bundle’ of nerves). Conventionally, the body’s nerves are anatomically divided into the central nervous system (the brain and spinal cord) and the peripheral nervous system. Nerves are also divided into those that send messages to the central nervous system (sensory nerves) and those that transmit messages from the nervous system (motor nerves). Sensory nerves are also called afferent nerves; and motor nerves are also called efferent.
Cellular and Molecular Basis of Human Biology
Published in Lawrence S. Chan, William C. Tang, Engineering-Medicine, 2019
This included cranial peripheral nerves (of the face and head), ganglia, spinal nerves, and nerve endings. The afferent (ascending) arm of the peripheral nervous system is consisted of senor receptors and afferent nerves that responsible for sending sensory signals to the central nervous system. The efferent arm of the peripheral nervous system is composed of efferent neurons, which in turn divided to motor system that controls skeletal muscles and autonomic nervous system that controls smooth muscles, cardiac muscles, and glands. The autonomous nervous system is further divided into three divisions: sympathetic, parasympathetic, and enteric. While sympathetic division activates “fight-or-flight” kind of response including increase heart rate, dilate pupils, inhibit digestion, convert glycogen to glucose and secrete epinephrine (adrenaline), parasympathetic division does the opposite. The enteric division controls some smooth muscle, pacemaker cells, blood vessels, mucosal glands, and epithelia (Reece et al. 2014). Whereas the human central nervous system cannot be regenerated naturally, peripheral nervous system can go through natural regeneration, albeit slowly, to repair injury (Kyritsis et al. 2014, Bergmeister et al. 2018). Peripheral nerve system also has important roles in many special organs such as visual (eye, vision-related), auditory (hearing-related), olfactory (smell-related), larynx (voice-related), skin (temperature, pain, and touch senses-related), tongue (taste-related) organs. Peripheral nervous system is responsible for sending the sensing signals to the brain, which make a decision how to respond, and the peripheral nervous system will then carry out the response command from the central nervous system. Details of these controls are beyond the scope of this chapter.
Emerging memristive neurons for neuromorphic computing and sensing
Published in Science and Technology of Advanced Materials, 2023
Zhiyuan Li, Wei Tang, Beining Zhang, Rui Yang, Xiangshui Miao
Neurons, also known as nerve cells, are living electrochemical systems that are separated internally and externally by a neuronal membrane. In biological neural systems, there are a great variety of neurons with different structures and functions. For example, Figure 1(a) shows that a simple nerve circuity includes three different neurons: sensory neurons, relay neurons and motor neurons. Sensory neurons, also known as afferent neurons, are connected to a sensor (e.g. touch, vision, hearing, smell, etc.); motor neurons, also referred to as efferent neurons, are connected to muscle fibers (govern movement); while relay neurons, also referred to as interneuron, connect various neurons (e.g. sensory and motor neurons) within the brain and spinal cord, and are easy to recognize, due to their short axons. Information related to sensory-cognition-motor is transmitted between these different types of neurons that supervise the conveyance of information related to sensory-cognition-motor.