If you've ever loved, owned, or loved someone who owned a cat, then you're familiar with the wonderful scratching kisses these critters give out. But they don't just use it for affection. Oh no! They use it for everything!
Grooming, drinking, drying off, making faces (Exhibit A), and yes, even waking you up in the morning. You know what I'm talking about, when it's a Saturday and you think you can sleep in (finally). But no, that doesn't work for them...they think it's totally normal to just sniff your eyeball or smother you by lying on your face (Exhibit B). You know, the usual.
Anyway, back to my point ... If you're anything like me I'm sure you're all wondering how it works. Without lips how do they drink? What are those bumps made of? And so on...
Well, let's begin with the structure.
The tongue is an organ comprised of layers of skeletal muscle that run in all three planes (X,Y & Z) or in this case A,B & C. This arrangement of muscle fibers is essential for tongue movement in all directions.
Figure 1: Micrograph of cat tongue skeletal muscles.
We learned in class that this type of muscle is elongated, multinucleated and is supplied essential nutrients through numerous capillaries.
These muscles are also highly innervated by motor fibers from the cranial nerves (see below), in addition to the nerve fibers used for touch, taste buds and salivary glands. See the ducts in the salivary gland??
Figure 2: Section identifying tongue nerve fibers & salivary glands.
Figure 3: TEM of motor nerve fiber from class "Lecture 7 - Muscle"
I really like this on because you can clearly see where the terminal button is attaching to the muscle fiber. The motor end-plate is where the magic happens. Acetylcholine is released, which is picked up by receptors on the sarcolemma. The subsequent depolarization of the membrane opens the calcium channels and voila; contraction!
P.S. How frickin cool is this picture?!
Ah-hem, anyway. Zooming out for a moment we get into the infamous "spikes" of the cat tongue.
To the naked eye, these "spikes" or filiform papillae are the most obvious, but there are FOUR types of papillae.
1. Filiform Papillae
Figure 4: Section of Filiform Papillae of a cat tongue.
This type is most common and comprised of keratinized epithelium, pointing backward towards the throat. They are stiff and have no associated nerve fibers with a purely mechanical purpose they are useful for cleaning fur or breaking up food.
2. Fungiform Papillae
Figure 5: Schematic & Micrograph of Fungiform Papillae.
These have quite a different appearance than the previous type, and are also much less common. They are smooth and rounded almost "mushroom" in shape for manipulating food. These papillae actually have tastebuds and sensory structures, with connective tissue center or "core".
3. Foliate Papillae
Figure 6: Micrograph of Foliate Papillae from a rabbit tongue.
Foliate is best described as "leaf-like" papillae. Their outer layer is non-keratinized stratified squamous epithelium. These are less common and found on the sides of the tongue. Their taste buds are located in the clefts on their sides. They also contain sensory fibers and connective tissue, but are more commonly found in rabbits.
4. Circumvallate Papillae
Figure 7: Schematic, SEM & Micrograph of Vallate Papillae.
These are rare, large, set into pockets and also have the invaginations of the mucous membrane containing taste buds. They are unique that they have a "moat" that the salivary glands secrete into to remove molecules. Similar to the two previous types, this papillae contains the connective tissue core and sensory fibers and blood vessels along with it. Going in a bit closer you can clearly see the taste buds (see below).
Figure 8: Micrograph of taste buds.
The sensory cells seen above are underneath the epithelium and are used by the taste buds to communicate with the outside via "taste hairs" extended out through the taste pore. The cells allow physical food to be transmitted as a nervous signal to our brains so we can perceive "taste". These nerve fibers are stained in the images below (Marettova & Maretta, 2012).
Figure 9: Lateral side of circumvallate papillae. Nerve fibers (NF) are located at the base of the taste buds (TB).
Figure 10: Portion of lateral side of circumvallate papillae. Nerve fibers (NF) are located under the stratified squamous epithelium gathered at the base of the taste buds. Arrow: pointing to an axon the reaches the surface of a taste bud.
Thanks for reading! I hope you learned something.
I leave you with a slow-mo awesome video from youtube.
Video: using primarily filiform papillae to make water "stick" to tongue for drinking. They also can curve their tongue backwards (thanks to those skeletal muscles!) and create a little bowl.
References: Marettova, E. & Maretta, M. (2012). Innervation of the circumvallate papillae of the cat tongue. Anat. Histol. Embryol. 41: 300-305.
All online resources are available through hyperlinks and directly correspond to image associated explanations.
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