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The nervous and endocrine systems review

Key terms

Nervous systemThe body system that collects, processes, and responds to information using electrical signals
NeuronA nerve cell; the basic unit of the nervous system
Glial cellA cell that supports and protects neurons
Central nervous systemPart of the nervous system containing the brain and spinal cord
Peripheral nervous systemPart of the nervous system containing associated nerves that are not part of the brain or spinal cord
Endocrine systemThe body system that regulates cells and organs using chemical substances called hormones
HormoneChemical messenger that acts as a regulatory substance
GlandOrgan that secretes chemical substances, such as hormones

The nervous system

The nervous system uses electrical impulses to collect, process and respond to information about the environment.

Nervous system cells

The unique structure of neurons makes them specialized for receiving and transmitting electrical impulses throughout the body. Neurons are supported by glial cells, which surround, protect, and insulate them.
Diagram of a neuron
Image credit: Wikimedia, CC BY-SA 3.0
All neurons have several features in common, including a cell body, dendrites, and an axon. These structures are important for transmitting neural impulses, electrical signals that allow neurons to communicate with one another.
Neurons are specialized, depending on their required functions:
  • Sensory neurons carry impulses from sense organs, such as the eyes or ears.
  • Motor neurons carry impulses to muscles and glands.
  • Interneurons transfer signals between sensory and motor neurons, as well as in between other interneurons.
In a resting neuron, there is a separation of ions in the cell regulated by sodium-potassium pumps. If a neuron receives a large enough signal, the resting potential changes, producing an electrical impulse called an action potential. Once an impulse begins, it moves down the axon until it reaches the axon terminal.

Parts of the nervous system

The nervous system is made up of two parts: the central nervous system (CNS) and the peripheral nervous system (PNS).
Diagram of the central nervous system (CNS) and peripheral nervous system (PNS)
Image modified from Wikimedia, CC BY-SA 4.0
The CNS is made of the brain and spinal cord. Commands to the body originate in the brain and the spinal cord connects the brain with the rest of the nerves in the body.
The PNS can be broken down into two parts:
  • The somatic nervous system (SNS) regulates voluntary activities such as muscular movement. It also controls reflexes, such as pulling your hand away from the hot surface of a stove.
  • The autonomic nervous system (ANS) regulates activities that are not under conscious control and has two divisions that are opposite of one another: the sympathetic and parasympathetic nervous systems. The sympathetic nervous system prepares the body for “fight-or-flight” responses, while the parasympathetic nervous system is active during restful periods.

The endocrine system

Like the nervous system, the endocrine system is a regulatory system. However, instead of using electrical impulses for signaling, it produces and uses chemical signals called hormones, which travel through the bloodstream and control the actions of cells and organs.
Diagram of the major endocrine glands (includes both male and female glands)
Image modified from Wikimedia, CC BY 3.0

Common hormones and glands

HormoneGland produced inRole
Thyroid hormoneThyroidRegulates metabolism
Adrenaline (epinephrine)Adrenal glandInvolved in "fight or flight" response
CortisolAdrenal glandInvolved in "fight or flight" response, regulates metabolism and immune responses
EstrogenOvariesSexual and reproductive development, mainly in women
TestosteroneTestes, sometimes adrenal glands or ovariesSexual and reproductive development, mainly in men
InsulinPancreasBlood sugar regulation, fat storage
GlucagonPancreasBlood sugar regulation

Regulation of the endocrine system

The endocrine system is regulated by negative feedback mechanisms that work to maintain homeostasis. The concentration of hormones, and how they effect other body systems, are controlled in this manner.
For example, blood glucose regulation is controlled by insulin and glucagon, hormones produced by the pancreas.
When blood glucose increases, the pancreas releases insulin, which stimulates the uptake of glucose from the blood. This prevents blood glucose from getting too high.
When blood glucose concentration drops, the pancreas releases glucagon, which stimulates the breakdown of glycogen and releases glucose into the blood. This raises blood glucose back to normal levels.
Negative feedback loop of blood glucose. As blood glucose increases, insulin is released, causing the blood glucose to drop.
When the blood glucose drops, glucagon is released, resulting in an increase in blood glucose.
Blood glucose is regulated by a negative feedback loop between insulin and glucagon, two opposing hormones made by the endocrine system.

Common mistakes and misconceptions

  • While neurons are often the most recognized nervous system cell, they are not the only ones! In fact, glial cells outnumber neurons by almost 10 times. Glial cells (also known as neuroglia) support the neurons, guiding and protecting them, and provide myelin sheaths around their axons.
Image from Wikimedia, CC BY 3.0
  • Hormones are not just part of the reproductive system. Although there are reproductive hormones, such as testosterone and estrogen, most hormones are not involved in or regulated by the reproductive system. Many hormones control regular body functions, such as hunger or sleepiness.
  • Although both the endocrine system and the nervous system are both regulatory, there are a few fundamental differences. For one, the endocrine system uses chemical signaling (hormones, produced by glands) while the nervous system uses electrical signaling (neural impulses). The signal transmission of the nervous system is fast because neurons are interconnected, but the functions are more short-lived. Signal transmission in the endocrine system is slow, since hormones must travel through the bloodstream, but the responses tend to last longer.

Want to join the conversation?

  • blobby green style avatar for user Sajid Chowdhury
    Where exactly is the glial cell ? And how does it help in protecting.
    (13 votes)
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    • aqualine tree style avatar for user Artemis
      Glial cells surround neurons. For example, Schwann cells are wrapped around the axon. They insulate the axon, allowing more efficient transmission of the electrical impulse. I assume that other glial cells can surround the neuron in different places; in the picture of types of neuroglia, the satellite cells appear to be surrounding the surface of the soma (cell body). Hope that helps you!
      (13 votes)
  • aqualine ultimate style avatar for user Jacob Vernon
    Common mistake and misconception: Glial cells are 10* more numerous than neurons. This is incorrect.

    Please See:

    Azevedo, F. A., Carvalho, L. R. B., Grinberg, L. T., Farfel, J. M., Ferretti, R. E. L., Leite,
    R. E. P. et al. (2009). Equal numbers of neuronal and nonneuronal cells make the
    human brain an isometrically scaled-up primate brain. Journal of Comparative
    Neurology, 513, 532–541.
    (11 votes)
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  • mr pants orange style avatar for user a a
    I want to know how the enzyme activated (:
    (6 votes)
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  • mr pants teal style avatar for user Elina Ghosh
    What would happen if the nervous system stopped working with the endocrine system?
    (4 votes)
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    • eggleston blue style avatar for user IsotonicFlaccidCell21
      I believe if that were the case, then our nervous system will work just fine while the endocrine system will not. We would receive signals thanks to our receptors and the signals would travel via our neurones to reach our brain, but if the nervous system stopped working with the endocrine system, then glands won't be triggered. So the endocrine system is essentially dormant, thus you would only see the effects of your nervous system.
      This would be detrimental to the body as hormones help with homeostasis as they help to regulate metabolic rates (TRH, TSH, Thyroxine) and regulate water levels (ADH) etc. Without hormones, our bodies will spiral out of control, resulting in complications such as death
      (6 votes)
  • blobby green style avatar for user sdsdsd sdsdsd
    Hi, does anyone know the interrelationship between the nervous and the endocrine systems?
    Please help
    (2 votes)
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    • blobby purple style avatar for user Aditi
      This might help you:

      The endocrine system is linked to the nervous system by effects of the hypothalamus on the pituitary gland, as seen in the adjacent image.
      The pituitary gland is known as the ‘master gland’ because its secretions control the activity of other endocrine glands. The activity of the pituitary gland is however controlled by the hypothalamus which as well as being an endocrine gland, is also part of the nervous system.
      Along with the nervous system, the endocrine system coordinates the body’s functions to maintain homeostasis during rest and exercise. The nervous and endocrine systems also work together to initiate and control movement, and all the physiological processes movement involves.
      Where the nervous system acts quickly (virtually instantly) delivering messages by nerve impulses, the endocrine system has a slower but longer lasting response which compliments the nervous system. The endocrine system regulates growth, development and reproduction and augments the body’s capacity for handling physical and psychological stress.

      (8 votes)
  • blobby green style avatar for user Angelena  Granillo
    what is so important about Testosterone and Estrogen?
    (4 votes)
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  • blobby green style avatar for user omar_ab
    What would happen if any of the systems were to not function?
    (3 votes)
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  • leafers tree style avatar for user DHANUSH the CSENGG
    please explain the types of neuroglia briefly
    (3 votes)
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    • duskpin ultimate style avatar for user Betty :)
      Astrocytes - Wound tightly around blood vessels, and regulate the exchange of substances between brain neurons and capillaries
      Microglia - Motile, undergoes phagocytic action, which is that they destroy impaired or foreign cells through specialised immune defence
      Oligodendrocytes - Their cell bodies insulate a section of the axon, lowers its resistance. (The myelin sheath of the brain)
      Ependymal cells - Line ventricles, and create, secrete and circulate cerebral spinal fluid to cushion organs
      (2 votes)
  • starky sapling style avatar for user Farhan Mufti Hilmy
    What does "fight or flight" mean?
    (1 vote)
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  • blobby blue style avatar for user Salvia Krone
    Can someone please explain to me what negative and positive feedback is using examples to differentiate the two.
    (1 vote)
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    • blobby green style avatar for user jake.wong
      ok so basically your body has a preferred zone for everything, for example, temperature. if the temperature gets too hot, your body will regulate it to bring the temperature back down. when you get cold, your body shivers and heats you back up. this is negative feedback when your body opposes the environment to stay in its preferred zone. positive feedback is the opposite. imagine a store that not many people came to, but they left good reviews. eventually, more people would come, leaving more good reviews, and then more people would come and leave reviews, etc. this is positive feedback - when a system amplifies the effect of something happening to it. its bad for you if you have positive feedback: if you were a little hot, you would keep getting hotter and hotter until you died. also this answer is probably late
      (1 vote)