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Sarah Taylor

Joints Study Guide

🗻 Big Picture: Joints are regions in the body where two or more bones meet that allow your body to move. Not all joints or bones meet in the same way, so let's learn about their structures and the different kinds of movements they let you do!

Introduction

Simon says...touch your nose. Simon says do a jumping jack. Simon says twist side to side. Now do a flip. Did you do it? If so, we’re impressed, but you’re still out of the game. A lot of parts in your body helped you to do what Simon said, but the key piece to any kind of movement isn’t your bones or your muscles, it’s your joints!

Let’s talk about what they’re made of, how they’re categorized, and what kind of movement they allow you to do. But before we do, let’s play one more round of the game. Simon says…..tell all your friends about Inspirit! (Kidding, but you can’t blame us for trying 🤷‍♀️). Okay now let’s get to the real topic of the hour—joints!


Lesson Objectives

  • Understand the functions of joints and their components.
  • Understand the structural and functional categories of joints and their subcategories.

What’s a Joint?

I’m sure we all know what joints are to a certain extent (after all, we do have 360). But for the sake of accurate definitions, a Joint is a region where two or more bones meet, allowing them to move. They can be classified in two ways–either by structure or by function (also called range of motion). But before we get into that, let’s quickly go over the components that make up different joints in the body.

Cartilage: a type of tissue that covers the surface of your bones at a joint to cushion them and provide both flexibility and a smooth surface for movement.

Synovial Membrane: A layer of connective tissue that lines your joints, tendons, and bursae and secretes synovial fluid.

Synovial Fluid: A clear, sticky fluid that lubricates your joints.

Ligaments: Bands of strong, dense connective tissue that connect your bones together and surround the joint to provide support and limit the joint’s movement.

Tendons: Another type of strong connective tissue found on each side of a joint that connects it to your muscles.

Bursa: Fluid-filled sacs that sit between your bones, ligaments, and other structures that cushion your joints and reduce friction with movement.

Meniscus: A piece of cartilage found in the space between your bones at certain joints in the body.


Types of Joints:

Okay, now let’s get back to what we were talking about before–how joints are classified, either by structure or by function. If we say a joint is categorized by structure, we’re referring to whether it’s anchored by connective tissue, cartilage, or freely moving within a fluid-filled space called a Joint Cavity. If we categorize a joint by function, we’re referring to the amount of mobility between the bones, or range of motion. Let’s start with structural joints.


Structural Joints

There are three different types of joints within this category: fibrous joints, cartilaginous joints, and synovial joints, each of which has several sub-categories.

Fibrous Joints bind bones together with tough, fibrous connective tissue, which renders nearly all of them completely immovable. Of the fibrous joints, there are three different types: sutures, gomphoses, and syndesmoses.

  • A Suture Joint is a type of joint that only occurs in your skull. Despite what it looks like, your skull is actually made up of several bones. They’re connected by suture joints that render them immovable (which is great for protecting your brain inside). Imagine them like stitches holding a bunch of different parts of your skull together.

  • A Gomphosis Joint are immovable joints that also only exist in one part of your body–your mouth. Gomphoses are joint sockets where your teet__text in bold__h fit into your mandible and maxilla bones (your bottom teeth and top teeth, respectively).

  • A Syndesmosis Joint is a joint where two bones are connected by ligaments, allowing for a little movement. An example would be the joint between your tibia and fibula right above your ankle. You can’t move it actively, but it allows the bones to slide past one another to accommodate the movement of your ankle joint.

Cartilaginous Joints are bones bound by cartilage that are either immoble or have very little movement. There are two different types: synchondroses and symphyses.

  • A Synchondrosis Joint is completely immovable. An example would be the joint that connects your ribs to your sternum (once again, immovable joints are great for protecting your vital organs).

  • A Symphysis Joint connects bones with a compressible pad made of fibrocartilage and allows for a little movement. An example of this type of joint is the pubic symphysis of the hip bone. It sits at the bottom middle of your hip bone and can be moved around two millimeters with one degree of rotation (we weren’t kidding when we said a little).

Synovial Joints don’t directly connect bones together like fibrous or cartilaginous joints, but rather allow them to move within a joint cavity surrounded by synovial fluid. These are the most common joints in the body, and there are six subtypes: gliding, hinge, pivot, condyloid, saddle, and ball-and-socket.

  • Pivot Joints are freely movable joints that allow rotation, like the one that joins the atlas and the axis bones in your neck and allows you to turn your head side to side. Rotational movement is movement that occurs on an axis, like the way the earth spins.

  • Condyloid Joints have one concave bone and one convex bone that fit together kind of like a ball in a bowl. They allow for flexion (bending), extension (straightening), and circular movement. Circular movement is different from rotational movement because it moves in a circle instead of on an axis. An example of a condyloid joint is the one found in your wrist.

Gliding Joints allow bones to slide over one another in any direction along the plane of the joint, up and down, left and right, and diagonally. Remember that wrist we just talked about? Well there are multiple types of joints in there, and gliding joints are one of them. This time, take your hand and wave it like you’re saying hi to someone. A gliding joint allows this side to side movement.

Hinge Joints allow for flexion and extension, but only in one direction, similarly to how a door can open and close on its hinge, but can’t move in any other directions. A good example of a hinge joint would be your elbow or your knee.

Saddle Joints, like hinge joints, allow for flexion and extension. What sets them apart is that they have a greater range of motion. The best example of this type of joint would be your thumb. You can bend it and straighten it just like your knee, but you can also move it in a bunch of different directions instead of just one.

Ball-and-socket joints move freely in whatever direction you want. Up, down, left, right, rotationally, circularly, you name it. Examples of this type of joint are your shoulders or your hips where your leg bones fit into the sockets of your hip bone like a ball would in a bowl.


Functional Joints

Whew. That was a lot. Okay, now we’re moving onto joints as they’re classified by function (and we promise, this one is a lot simpler). There are three types of functional joints: synarthroses, amphiarthrosis, and diarthroses.

A Synarthrosis Joint is immovable. The suture joints we talked about before belong to this category, as do some other fibrous and cartilaginous joints. Synarthroses are good for protecting organs because they create a strong connection between the bones that isn’t easily broken (💀 = 💪).

An Amphiarthrosis Joint allows some movement, like the joints that connect your vertebrae in your spine (which by function are classified as symphysis joints). Each vertebra allows for a small amount of movement, but what’s pretty cool about the spine is that these vertebrae movements can actually sum together to provide a much larger range of motion.

A Diarthrosis Joint is freely movable, and the category includes all the synovial joints in your body. These joints are classified into 3 sub-categories based on the axes of motion that they can move on. Let’s discuss.

  • Uniaxial Joints can only move on one plane–for example, your elbow. It can only move up and down in just one direction.

  • Biaxial Joints can move on two planes, your fingers being a good example. You can bend them forward and you can also spread them apart, both actions moving in different directions 👊🖐.

  • Multiaxial Joints can move on three planes–think your hips or shoulders. Unlike your elbows and your fingers, you can move your arms and legs in all directions on any plane of motion.

💡 Summary

  • A joint is a region where two or more bones meet, allowing them to move.

  • The components of a joint can include cartilage, synovial membranes, synovial fluid, ligaments, tendons, bursae, or menisci.

  • Joints can be classified by either structure or function.

  • The three structural classes of joints are fibrous, cartilaginous, and synovial.

  • Fibrous joints are bones bound together with fibrous connective tissue that are either immobile or have minimal movement.

  • Subcategories of fibrous joints are suture joints, gomphosis joints, and syndesmosis joints.

  • Cartilaginous joints are bones bound by cartilage that are either immobile or have very little movement.

  • Subcategories of cartilaginous joints are synchondrosis joints and symphysis joints.

  • Synovial joints allow bones to move with a wide range of motion in a joint cavity surrounded by synovial fluid. They are the most common joints in the body.

  • Subcategories of synovial joints are pivot joints, condyloid joints, gliding joints, hinge joints, saddle joints, and ball-and-socket joints.

  • The three functional classes of joints are synarthrosis joints, amphiarthrosis joints, and diarthrosis joints.

  • The subcategories of diarthrosis joints are uniaxial, biaxial, and multiaxial.

FAQs

1. What is a joint?

Joints are regions in the body where two or more bones meet, allowing movement.

2. What are the structural categories of joints?

Fibrous, cartilaginous, and synovial.

3. What are the functional categories of joints?

Synarthrosis, amphiarthrosis, and diarthrosis.

4. Where are your joints located?

Joints are located in regions where two or more bones meet.

5. What is a uniaxial joint?

A subcategory of a diarthrosis joint that can only move in one direction, or on one plane of motion.

6. What is a saddle joint?

The saddle joint is a type of synovial joint that allows for flexion and extension with a greater range of motion than a hinge joint.

7. What type of joint is found within the knee?

Structurally, a hinge joint. Functionally, a diarthrosis joint.

8. What is cartilage?

Cartilage is a connective tissue with structures similar to bones but is softer, more flexible, and avascular, unlike bones.

9. What are hinge joints?

Hinge joints are a type of synovial joint that can move back and forth but are limited to move in other directions, just like how a door is moving at the hinge attaching it to the wall.

10. What is an example of an amphiarthrosis joint?

The vertebrae of your spine.

We hope you enjoyed studying this lesson and learned something cool about Joints! Join our Discord community to get any questions you may have answered and to engage with other students just like you! Don't forget to download our App to experience our fun, VR classrooms - we promise, it makes studying much more fun! 😎

Sources

  1. Anatomy of a Joint https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=85&contentid=P00044. Accessed Nov 26, 2021
  2. Joints. https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/joints#:~:text=A%20joint%20is%20the%20part,%2C%20condyloid%2C%20pivot%20and%20gliding. Accessed Nov 26, 2021
  3. Joints. https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/13.6/primary/lesson/skeletal-system-joints-bio/. Accessed Nov 26, 2021
  4. Joints basic https://teachmeanatomy.info/the-basics/joints-basic/. Accessed Nov 26, 2021
  5. Joints and Ligaments. https://www.visiblebody.com/learn/skeleton/joints-and-ligaments. Accessed Nov 26, 2021
  6. How Many Joints Are in the Human Body? https://www.healthline.com/health/how-many-joints-in-human-body#takeaway. Accessed Nov 26, 2021
  7. Argosy Publishing, Inc. (2014). Joints and Ligaments | Learn Skeleton Anatomy. Visiblebody.com. https://www.visiblebody.com/learn/skeleton/joints-and-ligaments
  8. Joints. (2012). Vic.gov.au. https://www.betterhealth.vic.gov.au/health/ConditionsAndTreatments/joints
  9. OpenStaxCollege. (2013, March 6). Classification of Joints. Pressbooks-Dev.oer.hawaii.edu. http://pressbooks-dev.oer.hawaii.edu/anatomyandphysiology/chapter/classification-of-joints/
  10. University of Rochester Medical Center. (2019). Anatomy of a Joint - Health Encyclopedia - University of Rochester Medical Center. Rochester.edu. https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=85&contentid=P00044

^Amphiarthrosis (tibia in leg)

^Diarthrosis (elbow, shoulder)

^Freely movable (hip, shoulder)

Structure

Based on the structure, joints are classified as fibrous, cartilaginous, and synovial joints.

  • Fibrous joints are made of thick tissue to join the bones, making them immovable.

  • Cartilaginous joints make use of a semi-hard tissue to join the bones together.

  • Synovial joints constitute all of the freely movable joints because it is assembled with the help of an articular capsule to join two bones.

types of synovial joint Source

Conclusion:

Joints in the body are like the handlebar in a bike or the steering wheel in a car that helps us to guide our articulated movement in the desired direction.

FAQs:

1. What are the joints in a body?

Joints are regions in the body where two or more bones meet together, allowing articulated movements.

2. What are the eight major joints of the body?

Fibrous joints, cartilaginous joints, synovial joints, ball and socket joints, pivotal joints, hinge joints, saddle joints, and condyloid joints are the body's major joints.

3. How many joint types are there?

There are eight joint types.

4. Where are your joints located?

Joints are located in regions where two or more bones meet.

5. What is a movable joint?

Movable joints are those regions where the bones meet, allowing greater articulated movement, as in the case of the wrist.

6. Which is the saddle joint?

The saddle joint is a type of synovial joint where one bone forming a part of the joint is concave or turned inward at one end that the other bone is supported, giving an appearance like a saddle. This means that the other bone fitting inside this concave region is convex or turned outward.

7. What is a knee joint?

The knee is the largest joint in the body where the thigh bone or the femur bone meets the shin bone or the tibia bone.

8. What is cartilage?

Cartilage is a connective tissue with structures similar to bones but is softer, more flexible, and avascular, unlike bones.

9. What are hinge joints?

Hinge joints are those regions of the bones where they meet and lock themselves to move in a unidirectional and back and forth but are limited to move in other directions, just like how a door is moving at the hinge attaching it to the wall.

10. What is a ball and socket joint?

Ball-like bone ends fit inside the depression in the socket-like bone ends and move freely within the socket. These kinds of joints are called ball and socket joints.

Sources:

  1. Anatomy of a Joint https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=85&contentid=P00044. Accessed Nov 26, 2021

  2. Joints. https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/joints#:~:text=A%20joint%20is%20the%20part,%2C%20condyloid%2C%20pivot%20and%20gliding. Accessed Nov 26, 2021

  3. Joints. https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/13.6/primary/lesson/skeletal-system-joints-bio/. Accessed Nov 26, 2021

  4. Joints basic https://teachmeanatomy.info/the-basics/joints-basic/. Accessed Nov 26, 2021

  5. Joints and Ligaments. https://www.visiblebody.com/learn/skeleton/joints-and-ligaments. Accessed Nov 26, 2021

  6. How Many Joints Are in the Human Body? https://www.healthline.com/health/how-many-joints-in-human-body#takeaway. Accessed Nov 26, 2021