up:: [[List of Systems of the Human Body]] tags:: #on/physiology #on/anatomy # Nervous System The nervous system is a vital component in biology, coordinating actions and sensory information through signal transmission. This system, which first emerged around 550 to 600 million years ago, consists of the [[Central Nervous System (CNS)]] and the [[Peripheral Nervous System (PNS)]] in vertebrates. The CNS includes the brain and spinal cord, while the PNS comprises nerves connecting the CNS to other body parts. These *nerves can be motor (outgoing from the brain) or sensory (incoming to the brain), with spinal nerves serving both functions*. Further divisions of the PNS include the *somatic, autonomic, and enteric nervous systems*. * [[Somatic Nervous System]], controls voluntary movement. * [[Autonomic Nervous System (ANS)]], governs "involuntary" actions. * [[Sympathetic Nervous System (SNS)]], fight-or-flight responses. * [[Parasympathetic Nervous System (PSNS)]], rest-and-digest responses. * [[Enteric Nervous System]], governs gastrointestinal functions. ## Structure At the cellular level, neurons are the building blocks of the nervous system, facilitating rapid signal transmission through electrical and chemical impulses. Neurons form intricate connections, creating neural pathways and circuits that underpin an organism's perception and behavior. Alongside neurons, glial cells provide support and insulation, playing crucial roles in metabolic support and immune response within the nervous system. The nervous systems vary in complexity across different multicellular animals, from simple nerve nets in radially symmetric organisms like jellyfish to centralized structures found in most animal species. Malfunctions in the nervous system can arise from various factors, leading to disorders studied in the field of neurology. **Key Points:** - The nervous system coordinates actions and senses environmental changes through signal transmission. - It comprises the central nervous system (CNS) and the peripheral nervous system (PNS). - Neurons, along with glial cells, are the main cellular components, facilitating rapid signal transmission and providing support. At its core, the nervous system sends signals throughout the body, integrating sensory information, processing it, and producing responses. *Neurons communicate via synapses, either electrically or chemically*. Chemical synapses involve neurotransmitter release, affecting postsynaptic cells excitatory, inhibitory, or modulatory. Neurons release neurotransmitters consistently at synapses, though effects depend on receptors. Glutamate and GABA commonly act as excitatory and inhibitory [[Neurotransmitters]], respectively. Synapses capable of forming memory traces contribute to neural plasticity, allowing adaptation to the environment. Neural circuits involve interconnected neurons performing various functions such as feature detection, pattern generation, and timing. Neural processing includes both stimulus-response chains and intrinsically generated activity patterns, interacting to produce behavior. Reflex arcs demonstrate basic neural circuitry, translating sensory input into motor output. *The spinal cord mediates simple reflexes*, while complex responses involve signal processing in the brain, including feature detection, perceptual analysis, memory recall, decision-making, and motor planning. **Key Points:** - The nervous system sends signals via synapses, influencing postsynaptic cells. - Synaptic plasticity allows the nervous system to adapt to environmental changes. - Neural circuits involve interconnected neurons performing various functions. - Reflex arcs translate sensory input into motor output, while complex responses involve brain processing. The nervous system is a complex network of neurons that process sensory information and generate responses, encompassing the brain, spinal cord, and peripheral sensory organs. While sophisticated sensory processing primarily occurs in the brain, the spinal cord and peripheral organs like the retina also play crucial roles in feature extraction from stimuli. Intrinsic pattern generation within the nervous system involves internally generated rhythms of activity, facilitated by various *voltage-sensitive ion channels within neurons*. Networks of intrinsically rhythmic neurons connected via synapses exhibit dynamic behaviors like attractor dynamics and periodicity. Circadian rhythmicity, a vital temporal pattern, influences behaviors such as the sleep-wake cycle and is governed by a genetic clock system present across diverse animal species. [[Mirror Neurons]] are a specialized type of neuron that fires both when an animal performs an action and when it observes the same action in another. Found in primate species and possibly birds, these neurons have been linked to understanding others' actions and learning through imitation. However, the exact function and mechanisms of mirror neurons remain subjects of speculation and ongoing research. During development, vertebrates undergo neural induction, a process where signals from mesodermal cells induce ectoderm to form neural tissue. This process involves molecular mechanisms like inhibition of bone morphogenetic protein and the involvement of proteins like Noggin and Chordin. Neurotrophins regulate the growth and survival of neurons across bilateral organisms, indicating a common mechanism for nervous system formation. The nervous system is *protected by physical barriers like meningeal membranes* and the [[Blood-Brain Barrier]], shielding it from damage. Peripheral nerves, although relatively exposed, are susceptible to physical damage, swelling, or bruising, *leading to conditions like carpal tunnel syndrome or peripheral neuropathy*. Spinal cord injuries can result in permanent loss of function, as scar tissue formation impedes nerve regeneration. **Key Points:** - The nervous system processes sensory information and generates responses. - Intrinsic pattern generation involves internally generated rhythms of activity. - Mirror neurons fire when an animal observes or performs an action, possibly aiding in understanding others' actions. - The nervous system is protected by physical and chemical barriers, but peripheral nerves remain susceptible to damage, leading to conditions like carpal tunnel syndrome or peripheral neuropathy. - Spinal cord injuries can result in permanent loss of function due to scar tissue formation.