Muscle!!!

Hey guys!

Hope you all survived the midterm and are ready to start another week of histology!!!! Hopefully the midterm was able to help you see areas you need to practice or helped boost your confidence in what you already know :) If you didn't do so hot, remember you can drop the midterm and that there's still the final which is worth half of your grade.

This week is muscle - make sure you know the differences between the 3 types of muscle:

See the difference between the transverse and longitudinal cuts?

Skeletal:
- multinucleated
- peripheral nuclei
- striations
- can be regularly or irregularly arranged

See the layers?

Smooth:
- uninucleated
- central nuclei
- no striations
- fusiform shape
- usually comes in layers

The intercalated discs allow current to pass from cell to cell

Cardiac:
- bifurcated
- central nuclei
- intercalated discs containing several gap junctions
- striations








Also, be sure you can find/identify intrafusal fibers and know their function, i.e. prevention of muscle over-stretching; remember their histological name is modified skeletal muscle fiber and that the capsule is DCCTRA. Normally, intrafusal fibers are about 2-3 times the size of a single skeletal muscle fiber and are surrounded by a collagen sheath (connective tissue).

Sarcomeres

So, just a refresher from anatomy of what's actually going on in the sarcomere - remember that all the actin is coming from the Z-line and all the myosin is coming from the M-line. Contraction is due to an increase in overlap between actin and myosin. The M-line is located in the A-band - THE A-BAND DOES NOT CHANGE SIZE DURING CONTRACTION!!!! Remember that it is the I-band and H-bands that shrink as myosin and actin overlap more. 

 Now, try to find the above structures on a real image. Remember: 'Zoro Is A Hairy Man' ;)







As we zoom out, can you see where those striations come from? Smooth muscle doesn't look like this because they don't have sarcomeres like skeletal and cardiac muscle; they have a completely different method of contraction which you will learn more about in advanced physiology :)






 Also, make sure to study exceptions/anomalies - those tend to make good quiz/final questions :) For instance, the tongue is the only place in the body where we find skeletal muscle irregularly arranged.

See the longitudinal AND transverse muscle fibers?

Also, when it comes to memorizing the different smooth muscle layers, remember most of the time the layers will be inner circular, outer longitudinal - then just memorize the exceptions, which there are a few :/ Also, remember that the inner circular layer is responsible for segmentation while the outer longitudinal layer is required for peristalsis.

The exceptions are:
1. the stomach - has three layers; essentially just adds an inner oblique layer to the normal inner circular, outer longitudinal - so it becomes inner oblique, middle circular, outer longitudinal
2. the uterus and vagina - just think about it - girls are all over the place! (sorry gals) ;) So are the muscle layers of female repro . . . oh wait, there aren't any! Almost all of the female female repro system is smooth muscle irregularly arranged - think about the parts of the female repro that have to do a lot of stretching - those are the ones that are going to be irregular
3. the vas deferens - remember that the vas deferens has tons of muscle - it needs that muscle to act as a pump - I think of the vas deferens as a sandwhich (inner longitudinal, middle circular, outer longitudinal)
4. the ureter: the ureter is just whacked - it's exactly opposite of everybody else: inner longitudinal, outer circular


Blood Vessels

Make sure you know the anatomical layers of the heart - epicardium, myocardium, endocardium, and what they are histologically

Purkinje fibers - these are modified cardiac myocytes located just under the endocardium in a region called the subendocardium; remember that impulses in the heart originate at the SA node, travel to the AV node, through the left and right bundles located in the interventricular septum to the purkinje fibers - these fibers travel through the ventricular walls to spread the current

- purkinje fibers are non-contractile cells and contain fewer myofibrils - this means they take up less stain, i.e. they are generally lighter on a slide and are larger, often binucleated cells.

Look for them near the 'edge' of the tissue on your slide - if you point to cells in the middle of the myocardium, chances are they're not purkinje fibers - as you can see in the diagram on the left, purkinje fibers tend to stay out of the muscle wall







Large, medium, small artery and arteriole


Make sure you know what makes up the different tunics:
1. tunica intima: endothelium + basement membrane + internal elastic lamina
2. tunica media - just the muscle layer
3. tunica adventitia - LCT with some DCCTRA


Large artery:

See the 1:1 muscle cell layer to elastic fiber ratio?

Medium artery:

Notice the distinct internal and external elastic laminas; also, the virtual absence of elastic fibers in the tunica media

Small artery:

Note the absence of an external elastic lamina, but still a distinct internal elastic lamina

Also, know capillaries and where to find them (lungs and kidneys are a good place) and that they are made of simple squamous epithelium.




Large, medium, small veins

 I absolutely love this picture - notice the differences between the medium artery and medium vein? The vein is much more collapsed and has a much thinner muscle layer - remember, they don't do any pumping, whereas the arteries do lots of pumping and stretching.

Also, veins tend to have a much thicker tunica adventitia and no internal/external elastic laminas

For the purposes of this class, a large vein is one whose lumen doesn't fit entirely on the view screen.

Good luck ya'll!!!!

Muscle Review Sheet

Key: Know the anatomical and histological names (including modifications) for the following bolded structures; assume that you will be required to find the structures indicated by * on your own slides.

***This list is not guaranteed to be exhaustive, and only includes terms from this unit. While we will not focus on quiz information from previous weeks, knowledge of previous material may be useful***

Focus on muscle histology, but keep in mind all of the following terms.

Skeletal Muscle

Transverse Cut

·       Skeletal muscle*

·       Epimysium*

·       Perimysium*

·       Endomysium*

·       Fascicle*

·       Peripherally located nuclei

Longitudinal Cut

·       Perimysium*

·       Endomysium*

Intrafusal Fiber

·       Intrafusal fibers*

·       Capsule

Sarcomere

·       A-band

·       H-disk

·       M-line

·       Z-line

·       I-band

Neuromuscular Junction

·       Terminal bouton (motor end plate)

·       Nerve axons

·       Skeletal myofibers

Tongue

·       Circumvallate papillae*

·       Von Ebner’s gland

·       Taste bud

·       Skeletal muscle*

Cardiac Muscle

Cardiac Muscle

·       Bifurcations

·       Intercalated discs

·       Centrally located nuclei

Smooth Muscle

Longitudinal Cut

·       Smooth muscle fiber (fusiform shape)

·       Centrally located nuclei

Transverse Cut 

·       Smooth muscle myocyte

·       Centrally located nuclei

 Vasculature 

·       Tunica intima*

·       Tunica media*

·       Tunica adventitia*

Intestine

·       Muscularis externa*

·       Inner circular*

·       Outer longitudinal*

·       Muscularis mucosa*

Stomach

·       Muscularis externa*

·       Inner oblique*

·       Middle circular*

·       Outer longitudinal*

·       Gastric gland

·       Muscularis mucosa*

Reproductive Tract

Uterus

·       Endometrium*

·       Myometrium*

·       Uterine glands

·       Uterine epithelium

Vagina

·       Smooth muscle*

·       Lamina propria

·       Vaginal epithelium

Oviduct

·       Oviduct epithelium

·       Lamina propria

·       Muscularis externa*

·       Inner circular*

·       Outer longitudinal*

Vas Deferens

·       Vas deferens epithelium

·       Inner longitudinal layer*

·       Middle circular layer*

·       Outer longitudinal layer*

Urinary Tract

Ureter

·       Ureter epithelium

·       Inner longitudinal layer*

.         Outer circular layer*

Circulatory System

Heart

Outer Heart Wall

·       Adipose tissue

·       Myocardium*

Inner Heart Wall

·       Endocardium*

·       Purkinje fibers*

Vasculature

Large Artery

·       Tunica intima*

·       Internal elastic lamina*

·       Tunica media*

·       Tunica adventitia*

Medium Artery

·       Tunica intima*

·       Internal elastic lamina*

·       Tunica media* (sporadic elastic fibers)

·       Tunica adventitia*

Small Artery

·       Tunica intima*

·       Tunica media* (~4 layers)

·       Tunica adventitia*

Arteriole

·       Tunica intima* (very thin internal elastic lamina)

·       Tunica media* (~2-3 layers)

·       Tunica adventitia

Capillary

·       Endothelium*

Large Vein

·       Tunica intima (no elastic lamina)*

·       Tunica media*

·       Tunica adventitia*

Medium Vein

·       Tunica intima*

·       Tunica media* (a few muscle layers)

·       Tunica adventitia*