Nervous system : Nerve signals

Nervous system : Nerve signals

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If the electrical signals from all the various organs throughout the body eventually connect to the nerves in the spinal column traveling up to the brain, how does the brain differentiate the different signals. Is the nerve in the spinal column like an electrical conduit with many wires inside?

Yes is the simple answer. A nerve will go up to a specific part of the brain which the brain knows corresponds to a certain region of the body. It isn't perfect though e.g. pain in the diaphragm confuses the brain which doesn't recognise that pain must be coming from there so instead tells the body there is shoulder pain, however this is useful in medicine. Another infamous example is pain from heart disease (angina) which causes pain in the jaw and arm. Perhaps even more interestingly, if a nerve is cut and then grows back linking to the wrong nerve it may lead to the completely wrong part of the body being identified when touched. Also if the brain itself is stimulated in these corresponding areas, a person will feel he or she is indeed being touched in a certain part of the body.

Nervous system

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Nervous system, organized group of cells specialized for the conduction of electrochemical stimuli from sensory receptors through a network to the site at which a response occurs.

All living organisms are able to detect changes within themselves and in their environments. Changes in the external environment include those of light, temperature, sound, motion, and odour, while changes in the internal environment include those in the position of the head and limbs as well as in the internal organs. Once detected, these internal and external changes must be analyzed and acted upon in order to survive. As life on Earth evolved and the environment became more complex, the survival of organisms depended upon how well they could respond to changes in their surroundings. One factor necessary for survival was a speedy reaction or response. Since communication from one cell to another by chemical means was too slow to be adequate for survival, a system evolved that allowed for faster reaction. That system was the nervous system, which is based upon the almost instantaneous transmission of electrical impulses from one region of the body to another along specialized nerve cells called neurons.

Nervous systems are of two general types, diffuse and centralized. In the diffuse type of system, found in lower invertebrates, there is no brain, and neurons are distributed throughout the organism in a netlike pattern. In the centralized systems of higher invertebrates and vertebrates, a portion of the nervous system has a dominant role in coordinating information and directing responses. This centralization reaches its culmination in vertebrates, which have a well-developed brain and spinal cord. Impulses are carried to and from the brain and spinal cord by nerve fibres that make up the peripheral nervous system.

This article begins with a discussion of the general features of nervous systems—that is, their function of responding to stimuli and the rather uniform electrochemical processes by which they generate a response. Following that is a discussion of the various types of nervous systems, from the simplest to the most complex.

Nervous System Function

Coordinating Movement of the Body Parts

Alternatively, it could be the sensation of a cold drink on a hot day, where the body responds with a feeling of pleasure. This is expressed through neuronal activity in various parts of the body, depending on the individual, not relying on any obvious effector cell. On the other end of the spectrum, the stimulus could be indirect, such as the sound of rustling leaves in a quiet forest, indicative of an animal slithering. This could lead to a cascade of responses.

The body might respond to this sound with an adrenalin rush, prompting a flight response, and change the metabolic state of skeletal, smooth and cardiac muscles. It could also retrieve memory and try to recollect the possibility of the animal being a venomous snake, and the best possible route for escape. Much of this happens nearly instantaneously. Some parts of the nervous system can encode information from stimuli so intricately and deeply, that victims of traumatic events relive painful moments in their entirety, with the whole host of physiological responses, even with an unrelated stimulus.

Perceiving and Responding to the Senses

Among the primary modes of input into the nervous system are the electrical impulses that arise from sense organs. Touch, sound, sight, smell, and taste are conveyed to the nervous system, in order to integrate information and assess the nature of the external world. Similarly, a number of neurons act as sensors for the internal state of the body. For instance, sensory neurons in the eyes, nose, and tongue can inform a person about the presence of delicious food, and create a desire to eat.

After the food has been ingested, neurons in the digestive system can sense the stretching of stomach muscles. When this information is conveyed to the central nervous system, it triggers a satiety response – the feeling of ‘fullness’ and a willingness to stop eating. These are complex responses that do not directly involve only a muscle cell. There is a higher order integration occurring at this point, where memory, learning, cognition, and emotional state influence the physiological response mediated by the nervous system.

Higher Thought and Processing

Thus, while the nervous system can be considered as the center for receiving, processing and transmitting information, its functions are complex in most organisms. In humans, it is important for thought, reasoning, language, perception, and speech. Parts of the central nervous system control voluntary and involuntary muscle movement, and even peristalsis and digestive movement. It is important for the maintenance of balance, internal temperature regulation, and circadian rhythms. The rate of breathing, blood pressure, and heart rate are also modulated by the nervous system. It integrates its actions with the endocrine system in order to provide the body with a coordinated, and fine-tuned response to a stimulus.

The Human Nervous System

Nerve systems are peculiar to the animal kingdom, and increase in nerve system complexity parallels increasing complexity in digestive and circulatory systems. Single-celled proteins to have no sensory or nerve-type processes, although the cell as a whole may react to light or chemical stimulus. Sponges have no nerve cells. Cnidaria have only simple nerve systems or neural nets, which allow them to coordinate tentacle movement in response to changes in water pressure that could signal the approach of prey. Flatworms such as the planarian have eye spots that can detect light. Earthworms have central nerve cords that extend through the length of the worm, allowing the individual segments to communicate with each other.

In more advanced organisms, nerve systems consist of individual cells joined together in networks or clusters to form systems of communication. In humans, there are two types of nerve cells: neurons and glial cells. Neurons produce and transmit electrical signals called nerve impulses, and glial (sometimes called neuroglia) cells support neurons by maintaining homeostasis, insulation from other neurons, producing myelin, and providing nutrients and oxygen to neurons.

We talk about the human nerve systems in two ways, one anatomical (identifying the structures) and one physiological (identifying the functions). Structurally, the central nervous system or CNS contains the brain and spinal cord (when present in vertebrates), while the peripheral nervous system or PNS contains all the sensory receptors and connecting nerves and neuron cell bodies or ganglia. Functionally, we divide the nervous system into those parasympathetic functions which support autonomic functions like breathing and digestion, and those sympathetic functions that redirect energy for flight-or-fight situations, suppressing digestion and stimulating circulation systems. Each of the parasympathetic and sympathetic functions works through both CNS and PNS components.

Nerve Cells: Neurons

Neurons are cells that respond to electron stimulus. The most common type of neuron is a multipolar neuron, consisting of cell body with radiating dendrites, and an axon terminating in synaptic knobs that contain vesicles which can excrete neurotransmitters.

  • Cell body: this contains the bulk of the cytoplasm, the nucleus, but of course the other organelles such as the mitochondria, which perform the same function here as they do in other cells of releasing energy.
  • Dendrite: these are short highly, branched fibers which extend outward in all directions from the cell body to receive incoming stimuli.
  • Nucleus: as in other types of cells, the nucleus contains the DNA required for cell cloning.
  • Axon: The axon is a single fiber extending from the cell body for up to a meter, and ending in the synaptic knobs.
  • Schwann cell: these glial cells surround the axon like beads around a string
  • Myelin sheath: a white, fatty substance forming the membrane of the Schwann cell, and acting as an electrical insulator.
  • Node of Ranvier: Exposed areas of the axon between Schwann cells
  • Synaptic Knobs: Bulky ends of the axon containing vesicles that produce neurotransmitters.

Besides the common multipolar neuron with many dendrites (diagrammed above), there are bipolar neurons which have only one dendrite opposite the axon Betz cells or large motor neurons pyramidal cells with triangular cell bodies, and Renshaw cells, which connect alpha motor neurons. Nerve tissues made of these cells are specialized to perform specific functions most efficiently.

External Website Optional Reading: There is more information on the structure of neurons and their assembly into nervous systems and the Human Nervous System site, and somewhat more detail (along with excellent diagrams) at the website for Jaakko Malmivuo's book on Bioelectromagnetism. Click on Chapter 2, Nerve and Muscle Cells, to see the diagrams.

Nerve Signals

To understand how nerve cells work, we need to review some basic physics, electrical theory. There are two kinds of charge, positive and negative. Objects with like charges repel one another, while objects with opposite charges attract one another.

You recall that atoms in a neutral state consistent equal number of negatively-charged electrons and positively-charged protons. If the atom gains electrons (net negative charge) or loses electrons (net positive charge), it becomes an ion. [Atoms that gain or lose positive charges through nuclear reactions such as radioactivity, fission, or fusion, change their element type and give off lots of energy atoms that Dean or lose neutrons change their mass and become a different isotope of the same element. At the moment, we are only concerned with ions and electrical charge changes.]

In most forms of matter, the positive charges in the nucleus of the atoms are not free to move, since the atoms are held in place by chemical bonds to other atoms forming molecules, or by intermolecular forces, and the positive-charge-bearing protons are stuck in the nucleus of the atom. In solutions, however, such as cytoplasm and the human cell, ions of either charge will move according to the basic rules of charge behavior: like repels like and opposites attract. If we bring a positively charged object near a neutrally charged object, the positive charge will attract any negative charges that are free to move in the second object and repel it any positive charges that are free to move, creating a local net negative charge area. This is called induction, and is the basis of how neurons work.

Now we put the electrical theories together with what we know about how cells work. The lipid bilayer of most membranes repels ions, so the only way that they can cross the bilayer is through a protein gate, either by passive transport from an area of high concentration to an area of low concentration, or by active transport from an area of low concentration to an area of high concentration.

Nerve impulse process
  1. Normally, the outer material (extracellular fluid) is more positive than the inside of the neuron, which has a resting potential about 70mV. A sodium-potassium pump keeps the differential in place by pumping 3 sodium ions out for every 2 potassium ions it lets in.
  2. When an impulse occurs, the so sodium gate opens to allow more sodium in. This raises the potential in the cell. If it reaches +35 mV, the potassium gates open topic potassium out.
  3. The local disturbance creates a local excess concentration of sodium inside and potassium outside, so neighboring potassium gates open, and the cycle is repeated. The "signal" or disturbance travels across the surface of the neuron membrane until it reaches the axon, then travels down the axon.
  4. Meanwhile, the site of the original impulse recovers, pumping potassium and sodium out until normal resting potential is restored.

Harvard medical course has an excellent animation on how action potentials create nerve signals, so I'm going to send you there.

© 2005 - 2021 This course is offered through Scholars Online, a non-profit organization supporting classical Christian education through online courses. Permission to copy course content (lessons and labs) for personal study is granted to students currently or formerly enrolled in the course through Scholars Online. Reproduction for any other purpose, without the express written consent of the author, is prohibited.

This system connects the brain stem and spinal cord with internal organs and regulates internal body processes that require no conscious effort and that people are thus usually unaware of (see Overview of the Autonomic Nervous System). Examples are the rate and strength of heart contractions, blood pressure, the rate of breathing, and the speed at which food passes through the digestive tract.

The autonomic nervous system has two divisions:

Sympathetic division: Its main function is to prepare the body for stressful or emergency situations—for fight or flight.

Parasympathetic division: Its main function is to maintain normal body functions during ordinary situations.

These divisions work together, usually with one activating and the other inhibiting the actions of internal organs. For example, the sympathetic division increases pulse, blood pressure, and breathing rates, and the parasympathetic system decreases each of them.

Typical Structure of a Nerve Cell

A nerve cell (neuron) consists of a large cell body and nerve fibers—one elongated extension (axon) for sending impulses and usually many branches (dendrites) for receiving impulses.

Each large axon is surrounded by oligodendrocytes in the brain and spinal cord and by Schwann cells in the peripheral nervous system. The membranes of these cells consist of a fat (lipoprotein) called myelin. The membranes are wrapped tightly around the axon, forming a multilayered sheath. This myelin sheath resembles insulation, such as that around an electrical wire. Nerve impulses travel much faster in nerves with a myelin sheath than in those without one.

If the myelin sheath of a nerve is damaged, nerve transmission slows or stops. The myelin sheath may be damaged by various conditions that damage the brain or peripheral nerves including

Certain autoimmune disorders (such as Guillain-Barré syndrome)

Certain hereditary disorders

Signal Transduction in the Nervous System

Signal Transduction is a basic process in molecular cell biology involving the conversion of a signal from outside the cell to a functional change within the cell.

The human nervous system is made of billions of receptors, neurons and effectors. The neuron is basically composed of three parts, the dendrites which receive the incoming information, the soma or the cell body which processes the received information and the axon which sends out the information to another neurons or effectors. The information from one neuron is passed on to another neuron or to an effector through small special gaps or spaces called synapses.

A neuron can have thousands of such special gaps or synapses with other neurons. These gaps or synapses are bridged by chemicals known as neurotransmitters. These are chemicals that are synthesized in the neurons, stored in synaptic vesicles, released in the synapses transfer the information by binding to its receptors in the other neuron to start a cascade of events leading to a specific response.

Early Year Research

In the 1950s, Carlsson used a variety of animal models, including mice and rats, to identify dopamine as an important neurotransmitter. He showed that dopamine was involved in the nerve signals responsible for movement, and that dopamine dysfunction could result in serious disorders such as Parkinson’s disease. Carlsson has since worked on the development of drugs that influence neurotransmitters to treat Parkinson’s, depression and psychosis.

In the 1960s, Paul Greengard used animal models to investigate the mechanism of action of dopamine and other neurotransmitters. He found that during slow synaptic transmission, neurotransmitters bind to receptors in the surface of nerve cells, causing a cascade of chemical reactions that change the function of important proteins, sending a message from one nerve cell to another. These findings have increased our understanding of certain drugs that take effect by influencing the communication between nerve cells.

From the 1960s onwards, Eric Kandel primarily used sea slugs to study the role of synaptic transmission in learning and memory. Using this simple organism Kandel made discoveries that proved applicable to complex mammalian nervous systems. He found that the basis for learning and memory lay in the synapse, with weak stimuli leading to chemical changes in synaptic proteins that form short term memories. Stronger stimuli could affect the synthesis of new proteins and change the shape and function of synapses, resulting in long term memories. Kandel’s work marks an important point on our road to understanding how memories are made, and has informed many investigations into memory-improving treatments for dementia sufferers.

Nobel Prize in Medicine

Carlsson, Greengard and Kandel received the Nobel Prize in Medicine or Physiology in 2000 for their discoveries concerning the signal transduction in nervous system.

Arvid Carlsson was awarded the Nobel Prize for his discovery of the neurotransmitter dopamine and its clinical relevance to a condition known as Parkinson’s disease. Paul Greengard was awarded the Nobel Prize for his contributions on the mechanism of action of dopamine and other neurotransmitters. Lastly, Eric Kandel was rewarded for his discovery of the molecular mechanisms in the formation of short-term and long-term memory.

The discovery regarding signal transduction in nervous system triggered a lot of researches that led to an understanding of the mechanisms involved in several neurological disorders and consequently helped in the development of new drugs and therapies for the treatment of these disorders. Researches targeting the cure of Parkinson’s disease and the loss of learning or memory are main results of this discovery. So far, there is no absolute cure for these diseases and any progress made in this area is a significant step forward towards the amelioration of human sufferings due to these neurological disorders.

Hopefully, future researches in this area lead to the development of new drugs and therapies that can serve as permanent and absolute cure for these diseases.


DAVID MCCARTHY / Science Photo Library / Getty Images

Neurons are the basic unit of the nervous system. All cells of the nervous system are comprised of neurons. Neurons contain nerve processes which are "finger-like" projections that extend from the nerve cell body. The nerve processes consist of axons and dendrites that can conduct and transmit signals.

Axons typically carry signals away from the cell body. They are long nerve processes that may branch out to convey signals to various areas. Dendrites typically carry signals toward the cell body. They are usually more numerous, shorter and more branched than axons.

Axons and dendrites are bundled together into what are called nerves. These nerves send signals between the brain, spinal cord, and other body organs via nerve impulses.

Neurons are classified as either motor, sensory, or interneurons. Motor neurons carry information from the central nervous system to organs, glands, and muscles. Sensory neurons send information to the central nervous system from internal organs or external stimuli. Interneurons relay signals between the motor and sensory neurons.

Nervous system : Nerve signals - Biology

with the development of higher organism in natire complexity .in the body structure aslo increased the complexity in stuructre need a system ,that can regulate and control all other parts of the body in higher animals. there 2 system to coordinate the functioning of the body the nervous system and endocrine system the nervous system consistis of, large number of specailly cells called neurons . it condcuts the impulses in diffrent part of the body in form of electrcical signals .these signals are called "nerve impulese". their actions are rapid and localized the endocirine system consists of glandular cells, that secrets chemical substance called hormones.

Function of nervous system

1 reception of stimulus from the enviroment and covey towards sensory nerves or affector nerves.

2 sensory nerves carry stimulus towards brains or spinal cords which acting as modulator or cenverter.

3 brains or spinal cords converts stimulates into message.

4 transmission of message by motor nerve or effector nerve towards the effective region.

5 help to control various activites of the body.

6 only this system help to react immediately to out side stimulates by animals which is absent in plants.

this chapter deals with the react immediatly with the nervous system. the main parts of the nervous system are brain the spinal cords and peropheral nerves .The units of the nervous system are called "neurons" which are interconnected with each other throughout the body . conventionally nervous system are three types:-

2 peripheral nervous system

3 autonomic nervous system

here are two they of nervous system ANS and CNS.

Autonomic nervous system

these are responsible for you involuntary control.such as reflex to sudden exposure to heat or temperature. there is no any function of brain never reaches to spinal cords only .

Central nervous system

these are voluntary movement in which brain function takes place.

Brain and its Amatomy/ structure along with its function -

- is the situated in the cranial cavity of the skull .The cranial bones protect it from meachnical injury . brain is the cranial portion of the central nervous system, the weight of the brain and spinal cord is about 1300 to 1400gm of which 2% is the cord the cerebrum represents about 2%is the cord. the cerebrum represent about 85% of the weight of the brain .

the brain soft whitish somewhat fattened organ. it is composed of neurons and neuolgi a or supporting cell .Grey matter is composed principally of nerve bodies and is concentrated in the cerebral cortex and the nuclei and basal ganglia.White matter is composed nerve cell processes which from tract connecting various parts of the brain with other.

morphologically brain is divisible into three main region I,E, forebrain , midbrain and hingbrain brain has frntal , parietal occipital temporal and insula lobes.

Fore brain

&ndash consists of cerebrum and diencephalon .
Cerebral hemisphere from the largest pasrt of brain consisting two hemisphere .Separated by depp longitudinal fissure
the hemishphere are united by three commissars. the corpus callsum and tha anterior and posterior hippocampal commisure , the surface of each hemisphere is thrown into numerous folds or convolution called "gyri or Sulci" cerebru develop from the telencephalon .The most anterior portion of the prosencephalone or forebrain , Each cerebral hemisphere conists of 3 primary portion :-
1 rhinencephalone
2 Corpus stratium
4 cerebral cortex

with in the cerebrum are 2 cavities the lateral ventrical and the rostral portion of the 3 rd ventrical .
ventrical &ndash the cavities of the brain are the 1 st and 2 nd lateral ventrical ,which lies in the cerebral hemisphere , the third ventrical of the diencephalone and the 4 th ventricle of meduula . First and second communicate with the third by interventricular foramen the 3rds with 4ith by cerebral cannal .The 4 th with the subarchnoid space by 2 foramina of luschke and the formena of megendie.

Diencephalon- It encloses a slit like cavity the 3 rd ventricle. The thin roof of this cavity is kniw as "epithelamus". The thick right and left side as the thalmi floor as the hypothalamus .Thalami act as relay station for sensory impulses .
Midbrain is significantly small it consists the 2 heavy fibre tract called "cerebral pedencles "on the ventral side and two sweeliing tremed superior and inferior colliculi of each side are refered to ,as corpora bigemina and of both side as corpora Quardigemina . The superior colliculi control reflex of iris and eyelied. The inferior colliculi receives sensory information from the ear and relay it to cerebrum.

hibdbrain &ndash the hindbrain consists of cerebellum , pons varolli and medluua oblongata.

Cerebeluum -
it lies below the posterior portion of the cerebral hemisphere and bove the medulla. It consists of pair of large pasrt the cerebellar hemishphere and a small median portion the vermis .the cerebellum is involved in synergic control of skleletal system and plays an important role in the coordination as weel .the cerebellum controls the property of movement such as speed acceleration and trajectory.

- it is rounded eminence on the ventral surface of brain . it lies between the medulla and cerebral penduncles and appears externally as a board band of transverse fibres. It is connected to the cerebellum by the mid cerebellar pendencles or brachium points. the origin of abducens facial trigeminal and cochlear division of the 8 th neavr are at the boarder of the pons and gray matter.In the pons controls some aspects of repiration white matter tract in the pons form a two way conduction system ,that connects higher brain centre with the spinal cords .

tranismition nerve impulse takes place by following ways
fig A.N.S

Action potential is generated and the neuro transmiteer asires the 'pre synatic ganglions' towards the 'post synaptic ganglions'. And those neuro transmitter are released by the process of 'synapses&rsquo as shown in the figure.

Agrawal, sarita. principle of biology. 2nd edition . kathmandu: Asmita book Publication, 2068 ,2069

Mehta, Krishna Ram. Principle of biology. 2nd edition. kathmandu: Asmita, 2068,2069.

Jorden, S.L. principle of biology. 2nd edition . Kathmandu: Asmita book Publication, 2068.2069.

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Things to remember

reception of stimulus from the enviroment and covey towards sensory nerves or affector nerves

sensory nerves carry stimulus towards brains or spinal cords which acting as modulator or cenverter

brains or spinal cords converts stimulates into message

  • It includes every relationship which established among the people.
  • There can be more than one community in a society. Community smaller than society.
  • It is a network of social relationships which cannot see or touched.
  • common interests and common objectives are not necessary for society.

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Common Core Standards

Common Core Reading Anchor #3
Analyze how and why individuals, events, or ideas develop and interact over the course of a text.

RST.6-8.3: “follow precisely multistep procedure when carrying out experiments, taking measurement or performing technical tasks.”

Nervous Experiment: Follow the procedure written in experiment and record results, repeat procedure for each body part. For advanced students, design and implement their own procedure, as well as analyze results.

Common Core Writing Anchor #1
Write arguments to support claims in an analysis of substantive topics or texts using valid reasoning and relevant and sufficient evidence.

WHST.6-8.1: “…Support claim(s) with logical reasoning and relevant, accurate data and evidence that demonstrate an understanding of the topic or text, using credible sources…”

Nervous Experiment: Use logical reasoning and relevant evidence from Nervous Journey text and experimental results to determine if hypotheses were supported.

Common Core Writing Anchor #7
Conduct short as well as more sustained research projects based on focused questions, demonstrating understanding of the subject under investigation.

WHST.6-8.7: …answer a question (including self-generated question)…generating additional related, focused questions that allow for multiple avenues of exploration

WHST.9-12.7: “…narrow or broaden inquiry when appropriate…”

Nervous Experiment: Follow the procedure written in experiment and record results, repeat procedure for each body part. For advanced students, design and implement their own procedure, as well as analyze results.

Cranial nerves and spinal nerves

Nerves that directly connect the brain and the brain stem with the eyes, ears, nose, and throat and with various parts of the head, neck, and trunk are called cranial nerves. There are 12 pairs of them (see Overview of the Cranial Nerves). Cranial nerves transmit sensory information, including touch, vision, taste, smell, and hearing.

Nerves that connect the spinal cord with other parts of the body are called spinal nerves. The brain communicates with most of the body through the spinal nerves. There are 31 pairs of them, located at intervals along the length of the spinal cord (see Overview of Spinal Cord Disorders). Several cranial nerves and most spinal nerves are involved in both the somatic and autonomic parts of the peripheral nervous system.

Spinal nerves emerge from the spinal cord through spaces between the vertebrae. Each nerve emerges as two short branches (called spinal nerve roots): one at the front of the spinal cord and one at the back.

Motor nerve root (anterior nerve root): The motor root emerges from the front of the spinal cord. Motor nerve fibers carry commands from the brain and spinal cord to other parts of the body, particularly to skeletal muscles.

Sensory nerve root (posterior nerve root): The sensory root enters the back of the spinal cord. Sensory nerve fibers carry sensory information (about body position, light, touch, temperature, and pain) to the brain from other parts of the body. The sensory nerve fibers in each sensory nerve root carry information from a specific area of the body, called a dermatome (see figure Dermatomes).

After leaving the spinal cord, the corresponding motor and sensory nerve roots join to form a single spinal nerve.

Some of the spinal nerves form networks of interwoven nerves, called nerve plexuses. In a plexus, nerve fibers from different spinal nerves are sorted and recombined so that all fibers going to or coming from one area of a specific body part are put together into one nerve (see figure Nerve Junction Boxes: The Plexuses).

There are two major nerve plexuses:

Brachial plexus: Sorts and recombines nerve fibers traveling to the arms and hands

Lumbosacral plexus: Sorts and recombines nerve fibers going to the legs and feet