The muscles of the head and neck are responsible for a variety of movements, including facial expression, mastication, and eye movement, in addition to moving the head. This lesson identifies and describes the major muscles of the head and neck along with their general action.
I've always heard that it takes more muscles to frown than it does to smile. Based on that reasoning, we should just smile more often, as it requires less energy. While I'm not sure if this is true or not, I do that know several muscles are required for each type of facial expression whether we smile or frown. In this lesson, we will describe the muscles involved in facial expression as well as other muscles of the head and neck.
Did you know that skeletal and muscular systems are each divided into the same two major groups? Let's take a look at them. The axial muscles are attached to the axial bones, and they make up the head, neck, and thorax. The appendicular muscles attach to the appendicular bones, making up the shoulders, hips, arms, and legs. Furthermore, roughly 60 percent of the musculature is axial, leaving 40 percent for the appendages.
This lesson will identify and describe the major axial muscles of the head and neck. We're going to divide these muscles into the following groups: (1) muscles of facial expression, (2) eye muscles, (3) muscles of mastication (chewing), and (4) finally, we'll take a look at the neck muscles.
Let's first look at muscles of facial expression. This is the most extensive group of muscles discussed in this lesson and includes approximately 20 different muscles, all innervated by cranial nerve VII, referred to as the facial nerve - I think that name makes sense. We will identify and describe the more prominent muscles of facial expression.
It's helpful to note that each muscle of facial expression originates on the skull and inserts on the skin. Let me quickly note that the origin of any muscle is the fixed attachment, while the insertion moves when the muscle contracts. Therefore, contraction results in movement of the skin and thus facial expression when these muscles contract.
The orbicularis oris is also known as the pucker muscle.
The largest group of facial expression muscles is the one associated with our mouth. The largest muscle associated with the mouth is the orbicularis oris, which, as the name suggests, encircles the mouth and serves to constrict the mouth. This can also be referred to as the pucker muscle, so pucker up!
The buccinator is a paired muscle on each side of the cheek, and it serves to stretch the ends of the mouth and compress the cheeks. Now, let's take a look at the orbicularis oris and the buccinator together. Both of these muscles are used when a baby suckles on a bottle.
Babies use the orbicularis oris and buccinator to suckle a bottle.
The occipitofrontalis, or the epicranius, is responsible for movements such as raising the eyebrows and wrinkling the forehead. This is a unique muscle in that it has two parts, or two bellies. The occipital belly is located over the occipital bone, and that's on the back of the head, whereas the frontal belly is located over the frontal bone of the skull, and that's in the front.
The orbicularis oculi are paired muscles that encircle the eyes, and these muscles serve to open and close the eyelids.
Six pairs of extrinsic eye muscles control eye position and movement.
Let's move on to the eye muscle themselves. While the orbicularis oculi, which we just discussed, are responsible for opening and closing the eyelids, the extrinsic eye muscles are responsible for actual eye movement. Six pair of these muscles attach to the eyes, and they control the position and movement of our eyes. These extrinsic eye muscles are innervated by three cranial nerves: III, IV, and VI.
Cranial nerve III is also known as the oculomotor nerve as it controls movement of the eyes. Now, that makes sense, doesn't it? Cranial nerve IV and cranial nerve VI are the trochlear and abducens nerves, respectively. These muscles are named for their general shape and the type of movement that they control.
Let's look at some examples. Rectus means 'straight,' while oblique means, well, 'not straight.' The extraocular muscles are the inferior rectus, which moves the eyes downward; medial rectus, which moves the eyes medially, towards the middle; superior rectus, which pulls the eye up, in the superior direction; and finally, the lateral rectus, which moves the eye to the side, or laterally.
Now, let's take a look at the obliques. The inferior oblique and the superior oblique wrap around the eyes, and they're responsible for a rolling movement of the eye - therefore, not straight.
Mastication is just a fancy name for chewing. The masseter and the temporalis muscles are responsible for closing the jaw, as these muscles originate on the skull and insert on the mandible below. The digastric muscle opens the jaw.
Location of the hypoglossal nerve
The tongue is composed of several different muscles, and it's involved in not only chewing and swallowing but also formation of speech. These muscles end with the root -glossus; for example, 'hyoglossus,' which is Greek for 'tongue.' Furthermore, the tongue muscles are innervated by the hypoglossal nerve, which is cranial nerve XII.
Let's move on to our last group of head and neck muscles. The human neck contains several muscles. In this lesson, we will highlight only a few.
The sternocleidomastoid muscle originates on the clavicles and inserts on the skull, thus flexing the neck when these muscles contract together. If one sternocleidomastoid contracts while the other relaxes, then that will result in bending the head towards the shoulder and turning the face in the opposite direction.
The splenius muscles help keep the head straight.
On the posterior side, the splenius muscles extend the neck and help to maintain an erect posture. These muscles are attached to the vertebrae and the skull.
In summary, the axial muscles attach to the axial skeleton, while the appendicular muscles attach to the appendicular skeleton.
The muscles of facial expression include the occipitofrontalis, orbicularis oris, orbicularis oculi, and the buccinator. They're all innervated by the facial nerve.
The extrinsic eye muscles include the rectus and oblique muscles, and they control position and movement of the eye.
The muscles of mastication control chewing and include the temporalis, masseter, digastric, and the -glossus muscles of the tongue.
Finally, the neck muscles include the sternocleidomastoid and splenius muscles, which move the head.
After watching this video, you could be able to:
- Identify several muscles involved in facial expression, eye movement, chewing and neck movement
- Describe those muscles' points of attachments and particular movements
- Differentiate between the axial and appendicular skeleton
- List which nerves innervate the muscles of facial expression, the extrinsic eye muscles and the muscles of the tongue