Spinal Nerve Formation - How a Spinal Nerve Forms » AnatomyLearner >> The place to learn animal anatomy online (2023)

As you read about the distribution of spinal nerves in different animals, you may become aware of their basic structure. Here I show you the origin of the canine spinal nerve and its branches with a labeled diagram.

Quick response:Each canine spinal nerve is formed by the junction of dorsal and ventral roots just outside the intervertebral foramen. After formation of the spinal nerve, it immediately divides into a dorsal and a ventral branch.

But how do these spinal nerve roots develop? What are these branches of the spinal nerves? If you are interested in learning about these characteristics of the canine spinal nerve, continue with this article to the end.

Here I will explain each characteristic of a typical canine spinal nerve using the labeled diagram. Again, you can get a glimpse of the different spinal nerves of different animals, including dogs, cats, horses, and cows.

So let's learn the structure of a spinal nerve.

spinal nerve formation

There are large differences in the number of spinal nerves in different animals (such as dogs, cats, goats, horses, and cows), but the pattern of formation is similar. Again, the innervation of these spinal nerves is almost similar, except for the following:

• Thoracic spinal nerve thirteen (cost-abdominal nerve),
• Lumbar 1 (iliohypogastric), lumbar 2 (genitofemoral) and lumbar 3 (ilioinguinal) and
• spinal nerves that contribute to the brachial and lumbosacral plexus,

"If you read the formation of the brachial and lumbosacral plexus, you will understand why the structure of the spinal nerve is important to you."

Reading recommendation for you from the anatomy student:

• Formation of the brachial plexus and distribution of its nerves with diagram and
• Formation of the lumbosacral plexus with annotated diagram,

Ok, let's look at the labeled diagram of spinal nerve formation and try to identify the following features:

• Dorsal and ventral roots, which originate from the corresponding parts of the spinal cord,
• dorsal root ganglia,
• Spinal nerve (outside the intervertebral foramen),
• The principal dorsal and ventral branches of a spinal nerve, and
• meningeal and communicating branches of a spinal nerve,

The dorsal and ventral roots (trunk) of the spinal nerve are formed by the union of numerous rootlets emanating from the appropriate side of the spinal cord. Here the dorsal root of the spinal nerve structure is sensory while the ventral root is motor.

Again, the posterior root of the spinal nerve has a posterior root ganglion. This spinal ganglion contains unipolar neurons and is encapsulated by connective tissue.

But at the ventral root of the spinal nerve, there is no dorsal root ganglion.

How is a spinal nerve formed in a dog?

The dorsal and ventral roots from the appropriate side of the spinal cord meet just outside the intervertebral foramen. Here the dorsal sensory fiber and ventral motor fibers exchange fibers, forming a small spinal nerve.

Now the spinal nerve immediately divides into 2 main trunks:

• Trunk or dorsal branch: which contains sensory and motor fibers (since the ventral and dorsal roots exchange fibers) and
• The ventral trunk or branch: also contains sensory and motor fibers,

Now let's try to understand the following about the structure of the spinal nerve:

• Dorsal and ventral roots of the spinal nerve: remain in the spinal canal,
• Spinal nerve: formed just outside the intervertebral foramen, and
• The dorsal and ventral branches of the spinal nerve: remain outside the intervertebral foramen and continue to divide,

But where do you find the communicating and meningeal branches of the spinal nerve structure? Well, the meningeal branch of the spinal nerve remains in the intervertebral foramen.

On the other hand, the communicating branch is formed by the spinal nerve just outside the intervertebral foramen. This communicating branch of the spinal nerve then continues with the larger ventral branch.

The dorsal branch or trunk is divided into medial and lateral branches. Here the medial is motor and innervates the epaxial muscle. Again, the lateral is sensory and is innervated by the skin near a dog's dorsal midline.

The ventral branch divides into medial and lateral branches and supplies the hypaxial muscle of the body wall. In turn, these medial and lateral branches divide into lateral and ventral branches which supply the skin and ventral aspect of the dog's body wall.

Typical spinal nerve description: branches and ganglion

So you already have an idea of ​​the structure of a typical canine spinal nerve. Now you can learn the details of these structures involved in the formation of the spinal nerve in a dog.

From the above discussion, a typical spinal nerve has the following four or five segments from proximal to distal:

• Spinal nerve roots (both dorsal and ventral),
• main stem or spinal nerve,
• Four main branches: dorsal, ventral, meningeal and communicating, and
• Peripheral branches of the dorsal and ventral branches (numerous branches, mainly lateral and medial)

Now let's describe all these spinal nerve structures with the labeled diagram. Let's start first with the dorsal and ventral roots of the spinal nerve.

Dorsal and ventral roots of the spinal nerve

The spinal nerve roots run in the spinal canal and have 3 main characteristics:

• a dorsal root,
• The ganglion at the end of the dorsal root and
• a ventral root,

You will see multiple roots that form the dorsal and ventral roots of the spinal nerve. This is where the posterior root attaches to the posterior horn of the spinal cord. In comparison, the ventral roots originate from the ventral horn of the spinal cord.

The spinal ganglion (dorsal root ganglion) is located just near the junction of the dorsal and ventral roots (near the intervertebral foramen). In fact, the dorsal root of the spinal nerve sends axons to the spinal cord on its dorsolateral side.

Again the ventral root emerges from the broad and prominent ventrolateral aspect of the spinal cord. The number of rootlets on the dorsal and ventral roots varies in different species.

In the first 5 cervical spinal nerves of a dog, each dorsal and ventral root has an average of 6 roots. These uprooted dorsal and ventral roots can increase in size and also in number from the six cervical spinal nerves.

But from the third thoracic nerve to the thirteen thoracic spinal nerves, both the dorsal and ventral roots have only 3 roots. Each of these dorsal and ventral roots is surrounded by the pia and arachnoid and contains cerebrospinal fluid.

In almost all species, these spinal nerves form in different regions (cervical, thoracic, lumbar, sacral and caudal). The details of these spinal nerves (particularly their number and formation in different animals) are provided in the next section of this article.

Spinal or dorsal root ganglion

Before the formation of the spinal nerve, you can always find the dorsal root ganglion on each side. They are the oval structure and aggregation of unipolar nerve cell bodies.

The spinal ganglion (dorsal root ganglion) contains neurons arranged in a cluster. They are separated by nerve fiber bundles and intranodal connective tissue.

Each neuron has a single dendro-axonal process. This process is divided into 2 parts: peripheral afferent and central parts.

Here the peripheral portion of the dendroaxonal process is very long and transmits sensation to the cell body. Therefore, functionally, this is an elongated dendron.

Main trunk or spinal nerve of a dog

The dorsal and ventral branches now join to form the main trunk of the spinal nerve just outside the intervertebral foramen. Sometimes you can find the beginning part of the spinal nerve in the intervertebral foramen.

But how long is this main trunk of the spinal nerve? Well, the main trunk of a spinal nerve can vary in length. On average, the spinal nerve is found about 1 millimeter in the neck and chest area of ​​a dog.

Here, within the spinal nerve, the dorsal sensory and ventral motor roots exchange fibers and immediately divide into 2 main branches: dorsal and ventral branches.

The dorsal and ventral branches of the spinal nerve (primary branches)

Hence, the sensory and motor fibers are found in both the dorsal and ventral branches. Here the posterior branch of the spinal nerve runs up between the transverse process.

The dorsal branch now reaches the dorsal back muscles and then divides into peripheral branches. Usually you see 2 main branches of the dorsal branch of the spinal nerve: lateral and medial branch.

The medial peripheral branch of the dorsal branch innervates the muscle on the dorsal side of the canine body. Again, the peripheral lateral branch of the dorsal branch supplies the skin on the dorsal side of the canine body.

These peripheral lateral and medial branches of the dorsal branches are smaller than the branches of the ventral branches. Let's look at the anatomical data of the ventral branch of the canine spinal nerve.

The ventral branch of the canine spinal nerve is comparatively longer than the dorsal branch. Usually, the ventral branch of the spinal nerves divides into several peripheral branches.

But for your easy understanding, I will only tell you the 2 main branches of the ventral branch. As with the dorsal branch, one also finds the lateral and medial branches of the ventral branch here.

Again, the lateral branch of the ventral branch supplies the skin of the lateral abdomen. At the same time, the medial branch innervates the lateral and internal abdominal muscles.

But the ventral branches of the spinal nerves form different plexuses (typically in the front and hind legs). In this case, these ventral branches of the spinal nerve innervate different specific parts of the body.

I have already described all of these innervations of the brachial (front leg) and lumbosacral (hind leg) plexuses of the animal.

List and number of spinal nerves

Since the vertebrae (intervertebral foramen) are different in animals, they also have differences in the number of spinal nerves. Here I will give the number of spinal nerves of different animals like dogs, cows, horses and pigs in Table 1:

So you will find 36 pairs of spinal nerves in a dog. The cow has 37 pairs of spinal nerves while the horse has 42 pairs of spinal nerves. Pigs also have 39 pairs of spinal nerves.

Now let's list the spinal nerves of the different regions of the different animals. Let's say how many spinal nerves do dogs have? do you know the number They have 36 pairs (72) of spinal nerves in their bodies.

So, list of dog spinal nerves:

• Cervical spinal nerves (8 pairs),
• Thoraxspinalnerven (13 Paare),
• Lumbar spinal nerves (8 pairs),
• Sacral spinal nerves (3 pairs) and
• caudal spinal nerves (5 pairs),

36 pairs of spinal nerves in a dog

I have already listed the 36 pairs of canine spinal nerves. Now let's learn a little about some of the important spinal nerves in dogs.

In the axial skeleton of a dog you will only find 7 cervical vertebrae. But does a dog have 8 pairs of spinal nerves? How does that happen in a dog?

Well, the first cervical nerve arises from the first segment of the spinal cord. This nerve lies just caudal to the foramen magnum and is surrounded by the cranial part of the atlas.

However, other cervical nerves typically arise between the two corresponding vertebrae (intervertebral foramen).

The second cervical nerve is larger and atypical than the other cervical nerve. Here the dorsal and ventral roots of the second cervical spinal nerve meet at the periphery of the second intervertebral foramen.

Here, too, the spinal ganglion of the second cervical nerve lies completely outside the spinal canal. Therefore, this second cervical spinal nerve is exceptional and atypical.

Spinal nerves and brachial plexus in a dog

The ventral branches of the last three cervical spinal nerves and the first thoracic nerve lead to the brachial plexus in dogs. Here you will find more than 15 major nerves that innervate the various muscles of a dog's front legs.

The radial, median, and ulnar nerves are the main nerves of the brachial plexus that innervate all the way to the dog's fingers.

Canine thoracic spinal nerves.

In a dog you will find 13 pairs of thoracic spinal nerves. Each pair of thoracic spinal nerves exit from the intervertebral foramina.

All of these canine thoracic spinal nerves share a structure similar to that found in a typical spinal nerve formation. Each of these canine thoracic spinal nerves then gives off dorsal and ventral branches, which then divide into lateral and medial peripheral branches.

In the section of the thoracic spinal nerve you will find the important nerve called the abdominal wall. It is the ventral branch of the last or thirteenth thoracic nerve.

This abdominal costal branch of the spinal nerve supplies the ligament of the abdominal wall adjacent to the caudal border of the last rib. This nerve also supplies the last ribs and the caudal arch in the abdominal wall.

Lumbar and sacral spinal nerves

The lumbar spinal nerves are seven on each side of the dog. In contrast, the number of sacral spinal nerves in a dog is 3 pairs.

The distribution and branching of the lumbar and sacral spinal nerves in dogs are very complicated. It would be helpful if you had a separate guide to understanding the anatomical facts of the canine lumbar and sacral spinal nerves.

To do this, follow the articles I suggested to you earlier here.

Here the ventral branches of the fifth, sixth, seventh and third sacral spinal nerves from the canine lumbosacral plexus. The main nerves of the lumbosacral plexus are the sciatic, femoral, tibial, and perianal nerves along with their minor branches.

These nerves from a dog's lumbosacral plexus innervate a specific area (muscles and skin) of the hind leg.

Let's learn a little about the canine ilioinguinal, genitofemoral, and lateral femoral cutaneous nerves. These nerves arise from the ventral branches of the lumbar spinal nerves (3 through 5).

The ilioinguinal spinal nerve is the direct ventrolateral continuation of the ventral branch of a third lumbar spinal nerve. It gives off a medial branch that innervates the psoas major, psoas minor, and illicium. Here, too, the ilioinguinal spinal nerve communicates with the fourth lumbar spinal nerve and divides into lateral and medial branches.

The genitofemoral spinal nerve: arises from the ventral branches of the third and fourth canine spinal nerves. This nerve innervates the medial part of the psoas major muscle, the cremaster muscle, and the inguinal rings.

You may know the details of these ilioinguinal, genitofemoral, and iliohypogastric spinal nerves from various other articles on anatomy students.

The number of caudal spinal nerves varies from 4 to 7 in a dog.

Spinal nerves or medulla form the cauda equina

Then the different segments of the spinal cord give off the spinal nerve roots. A dog's spinal cord is a cylindrical structure that runs inside the spine.

This spinal cord is covered by meninges and extends from the foramen magnum to the middle of the sacrum in the dog. You can find the idea about a dog's spinal cord along with the vertebral column in the article mentioned below:

• Canine Spine Anatomy: Anatomical features of the canine vertebrae, intervertebral discs and spinal cord.

The caudal end of the dog's spinal cord (at the level of the second sacral vertebra) terminates in a sharp, pointed structure. You know that tapered, pointed structure of the dog's spinal cord is the cone cord.

Here, too, a very thin cord extends from the cone bulbs to the first caudal vertebrae. This structure of the canine spinal cord is the filum terminale.

Some other distinct roots arise from the medullaries of the cone (as shown in the figure). These roots become longer and travel caudally within the spine.

So you see a long whiplash of spinal nerve roots at the terminal portion of the spine. This spinal cord structure resembles a ponytail and is called the cauda equina.

Labeled diagram of the formation of the canine spinal nerve

Now I show you the labeled diagrams of the formation of the canine spinal nerve. First, let's look at the labeled diagram that shows the different segments of the spinal cord, the spinal nerve roots, and the different segments of typical vertebrae.

You can also know the different segments of typical animal vertebrae from the article below:

• Typical vertebrae of the ox: body, arch and anatomy of the process.

Here the dorsal and ventral horns on each side of the dog's spinal cord are identified on the labeled diagram. The diagram also shows the dorsal and ventral roots of the spinal nerve (from both lateral sides of the spinal cord).

The dorsal root dorsal root of the spinal nerve is identified in the annotated diagram. A small main trunk of the spinal nerve (formed by the union of the dorsal and ventral roots) is shown in the annotated diagram.

The diagram also shows the 4 branches of the spinal nerve: meningeal, communicating and 2 branches. The dorsal and ventral branches of the spinal nerve have lateral and medial branches, respectively (shown in the figure).

Consider now the cervical spinal nerves and formation of the brachial plexus in a dog. Here the diagram shows the dorsal and ventral branches of the cervical nerves of the dog's spine.

Again, the formation of the canine brachial plexus is shown in the labeled diagram. Other spinal nerves from the thoracic, lumbar, sacral and coccyx regions of a dog are also identified in the annotated diagram.

Again, the diagram shows the cauda equina at the end of the dog's spinal cord. For more labeled diagrams of the canine spinal nerves, see thesocial mediaby anatomy students.

Frequently asked questions about the structure of the spinal nerve

Now let's look at the most frequently asked questions about the structure of an animal's spinal nerve. Here you will find the most frequently asked questions about the spinal nerves of animals with their concise answer.

However, it is recommended to read this entire article to get a basic idea of ​​each characteristic of a typical spinal nerve. Ok, let's look at the most frequently asked question about spinal nerves by anatomy students:

Where does the spinal nerve form?

The spinal nerve is formed by the union of the dorsal and ventral roots (which come from the horn of the spinal cord) just outside the intervertebral foramen. This spinal nerve is a few millimeters long (typically 0.5 to 1 millimeter) and immediately divides into 2 branches.

Both the dorsal (1) and ventral branches of the spinal nerve have lateral and medial branches. The ventral branch of the spinal nerve forms different plexuses in different parts of the body of the dog.

What are the 4 divisions of a spinal nerve?

When the spinal nerve forms just outside the intervertebral foramen, it splits into 4 branches:

• meningeal branch: remains in the intervertebral foramen,
• connecting branch: stays outside the intervertebral foramen and opens into the ventral branch,
• The dorsal branch of the spinal nerve is smaller than the ventral branch and has peripheral lateral and medial branches and
• The ventral branch of the spinal nerve: It is longer and also has lateral and medial branches,

I have already provided the labeled diagram clearly showing these 4 divisions of the canine spinal nerve.

Where do the spinal nerves begin and end?

Spinal nerve roots originate from the posterior and anterior horns (2a) of the spinal cord. This nerve divides and reaches the various muscles and skin of the body.

So, the branches of the spinal nerves end in the muscles and skin. The details of the origin and distribution of a typical spinal nerve can be found in the previous section of this article.

What 3 structures make up the spinal nerve?

Sensory fibers, motor fibers and sensory neurons in the spinal ganglion are the 3 structures that make up the spinal nerve. You know, both the dorsal sensory fibers and the ventral motor fibers exchange fibers and form the spinal nerve.

Therefore, the dorsal and ventral branches of the spinal nerve contain both sensory and motor fibers. The typical canine spinal nerve diagram could help you understand the structures that make up the nerves.

What are the 5 types of spinal nerves?

You know that the dog's spinal nerves come from specific regions of the spinal cord. Again, a dog's spinal cord shows 5 different segments cervical, thoracic, lumbar, sacral and caudal.

You will also find 5 types of spinal nerves in a dog. According to the segments of the spinal cord, you can also find: cervical, thoracic, lumbar, sacral and caudal spinal nerves in a dog.

Diploma

The formation of the spinal nerve in a dog or other animal is simple, but the branching or distribution is somewhat complex. Here I have tried to show the simple form of the spinal nerve structure with the labeled diagram.

Each canine spinal nerve is similar in structure, having dorsal and ventral branches. Again, all spinal nerves in the dog's body have a ventral branch that is longer than the dorsal branch.