Afferent Division of the Peripheral Nervous System

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  • 0:01 The Nervous System
  • 0:44 Nervous System Signals
  • 1:40 Peripheral Nervous System
  • 2:28 Divisions: Afferent & Efferent
  • 5:23 Lesson Summary
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Lesson Transcript
Instructor: Sarah Phenix
In this lesson, we'll explore what the nervous system is, what the peripheral nervous system is, and then we will discuss the types of afferent divisions that exist within the peripheral nervous system.

The Nervous System

You've probably heard the term 'nervous system' before, but if you haven't, then your mind might have just popped to the last big presentation you had to give - talk about nerve-wracking!

What the term nervous system really refers to is your body's biological pathway of nerves that literally transmit everything in your body; nerves not only transmit the signals that enable your muscles to move but also that which keeps your heart beating, your lungs inflating, and every way in which you perceive the world around you going.

So, with that said, let's begin our exploration of the afferent peripheral nervous system by getting back to the basics: what's a nerve anyway?

Some Nerve: Conducting Nervous System Signals

Okay, so we've clarified that the nervous system refers to the massive, spiderweb-like system of nerve fibers that run throughout your body, but what's a nerve? Well, a nerve is a specialized type of tissue, called nervous tissue, that transmits neural impulses, the electrical signals responsible for stimulating your muscles and organs and transmitting sensory information like touch, temperature, and pain.

Nervous tissue is made up of neurons, which have a nucleated cell body (having a nucleus) and branching dendrites that receive neural impulses on one side and an axon that synapses (or communicates) the neural impulse to the dendrites of another neuron. All of the neurons in your body daisy-chain together to create the giant relay system that is your nervous system. Okay, so now that we know what the nervous system is, what is the peripheral nervous system?

Peripheral Nervous System

Your nervous system is divided into two categories: nerves that belong to the central nervous system and those belonging to the peripheral nervous system. So, what's the difference? Well, your central nervous system (CNS) is the portion of nerve tissues running down the center of your body and includes your brain and spinal cord. Conversely, your peripheral nervous system (PNS) is everything that runs at the periphery, or outside of the CNS, and includes all of the nerve tissue branching off of the brain (cranial nerves) and the spinal cord (spinal nerves). Simply put, the PNS includes any and all nerves that are not located in the brain or spinal cord.

Let's now explore what it means to refer to the afferent division of the peripheral nervous system.

Divisions: Afferent (Sensory) & Efferent (Motor)

The terms afferent and efferent refer to the directionality of the signal that the nerves are transmitting. Afferent signals refer to signals traveling 'away' from the stimulus, such as when you touch a warm plate and the nerve endings in your fingers tell your brain that the plate is warm, smooth, and hard. Efferent signals, on the other hand, are those signals traveling towards effectors, or muscles and glands. In other words, afferent signals are sensory signals, while efferent signals are motor signals.

Having said that, the afferent division of the peripheral nervous system isn't just the relay system, outside of the spinal cord and brain, responsible for conducting overt sensory information like taste, touch, sound, and vision, known as sensory afferent pathways. It also conducts subconscious sensory information regarding your internal environment known as visceral afferent pathways.

Visceral afferent pathways relay information from the organs, vessels, and glands of your body to your brain so that your brain can monitor their activity for any changes or modifications that need to be made and enable your brain to monitor both resting state bodily functions (calm breathing, slow heart rate, and active digestive) and escalated functions (rapid heart rate, rapid breathing, and inhibited digestion). The latter of which occurs in the case of a danger-induced fight-or-flight situation. What's important to note is that each of these bodily states - resting and fight-or-flight - are controlled by two different divisions within something called your autonomic nervous system (ANS), or the portion of your nervous system that functions without conscious thought.

The ANS controls things like ensuring your heart contracts at the right time, paces your breathing, and ensures your organs are completing their tasks. So, with two different divisions each having some measure of control over the same organs, vessels, and glands, it's really important that your brain keep tabs to make sure everything is responding appropriately to the current situation, be it resting or fight-or-flight.

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