Muscle and Nervous Tissue Microanatomy

Multipolar

What type of neuron is this?

1) Blood-nerve barrier is broken, allowing macrophages to proliferate and remove myelin 2) Schwann cells *dedifferentiate* and *proliferate* along the degenerated axon *forming the endoneurial tube* 3) *Macrophages proliferate* at the site of injury and remove mylein debris. They also *release factors* that influence Schwann cells 4) Endoneurial tube *collapses* and Schwann cells organize into *bands of Bunger* (they tell the axons where to go) 5) Schwann cells redifferentiate back to normal

How does a neuron regenerate itself?

Within the sarcolemma, there are undifferentiated myoblasts called *satellite cells* (these are specific to muscle cells) that differentiate and fuse into myotubes, replacing the damaged fibers

How does the body repair skeletal muscle?

Yes, not all nerve fibers associated with Schwann cells are myelinated

If a nerve fiber is not myelinated, can it be associated with a Schwann cell?

*T*h*IN* filaments; ac*TIN* Thick filaments; myosin

A myofibril is composed of two types of myofilaments. What are they?

Nerve fibers These refer to axon and all its components

A peripheral nerve is a bundle of ____________.

mesoderm

All three muscle types come from what embryological origin?

Within a muscle, you have *fascicles*. Within those fascicles, you have *fibers*. Within those fibers, you have *myofibrils*. Within those myofibrils, you have *myofilaments*.

Explain the muscle organization components

In terms of embryology, the CNS is formed from *neural tube*. Where as the PNS is formed from *neural crest cells*. In general, all of the nervous system is derived from the *ectoderm*. Neural crest cells form a lot of other things too!

In terms of embryology, the CNS is formed from ___________. Where as the PNS is formed from _____________. In general, all of the nervous system is derived from the ___________.

Top: Multipolar Middle: Bipolar Bottom: Pseudounipolar

Name the types of neurons

less chance because the neuron will die

The closer the site of injury is to the soma, the _________ chance regeneration will occur

axon size because myelin growth factors are regulated by the cell membrane of the axon.

Thickness of myelin depends on ___________.

True

True/false: Muscle cell and muscle fiber are essentially the same thing

CNS: Oligodendrocytes, astrocyte, microglia, and ependymal cells PNS: Schwann cells and satellite cells

What are CNS glial cell types? PNS?

Cells that surround cell bodies in PNS ganglia to maintain internal environment of the cell bodies

What are PNS satellite cells?

Cells that support neurons, insulate cell bodies and processes, maintain internal environment, and/or repair injury

What are glial cells?

Fused together myoblasts; this is what makes muscle cells multinucleated

What are myotubes?

Contractile units of muscle *A* band = d*A*rker; contains thin and thick filaments *I* band = l*I*ghter; contains *only thin* filaments *Z* disc; thin dark lines that are the borders for each sarcomere; anchoring point for *actin* *H* zone; middle part of *A band* containing *only thick* filaments that attach to the *M line* (*M* line attaches *M*yosin

What are sarcomeres? What are their components?

The black circle is the *myelin sheath*. The clearing in the middle of it is the *axon*

What are the green arrows point to?

- skeletal muscle cells have *elongated nuclei* and are *multinucleated* - cardiac muscle cells have *oval shaped nuclei* and you will see *branching of cells*

What are the two key differences between skeletal and cardiac muscle when looking at a slide of each?

Form a myelin sheath around a single axon They are also called *neurolemmocytes*

What do Schwann cells do? What's another name for them?

Blue arrow: *Perineurium*; connective tissue that forms a *fascicle*. Within the fascicle, the yellow circle represents an *individual axon*. The yellow arrow is pointing to the *nucleus of the myelin* surrounding the axon. The pink arrow is pointing to the *axon* itself.

What does the *blue arrow* represent? What is it forming? What does the *yellow circle* represent? *Yellow arrow*?*Pink arrow*?

Blue arrow = *epineurium* Red arrow = *myelin sheath* Green arrow = *cytoplasm within the axon*

What does the blue arrow represent? Red arrow? Green arrow?

Green arrow = *Nodes of Ranvier* Yellow arrow = *axon* (that's the dark line)

What does the green arrow point to? What does the yellow arrow point to?

The *epineurium*; the outer layer of a nerve

What does the green arrow represent?

Red: Nuclei of Schwann cells Orange: Axon Green: Node of Ranvier Black: Nerve fiber Blue: Myelin

What does the red, green, black, orange, and blue lines represent?

The alignment of myofilaments within a muscle fiber; this is what *coordinates muscle contraction*

What gives skeletal muscle the striated appearance?

A *ganglion* is a *cluster* of cell bodies Dorsal root ganglion have *centrally located nuclei*, you see *pseudounipolar* neuronal cell bodies in these ganglion, and their cell bodies are *clustered together* Autonomic ganglion have peripherally located nuclei, you see *multipolar* neuronal cell bodies in these ganglion, and these cell bodies are *more spread out*

What is a ganglion? What are the differences between a dorsal root ganglion and an autonomic ganglion?

This is the process of the soma swelling and the nucleus is pushed to the periphery due to an issue with the neuron

What is chromatolysis?

a muscle spindle; proprioceptor that detects changes in muscle length

What is circled?

axon regeneration this is why the removal of myelin by macrophages is vital to axonal repair

What is myelin an inhibitor of?

A lipid-rich membrane that insulates axons in the PNS

What is myelin?

Contributes to the blood nerve barrier (formed by tight junctions) to protect nerve fibers and maintain microenvironment Blood vessel run in this layer

What is special about the perineurium?

The epimysium; the outer connective tissue layer

What is the arrow pointing to?

The arrow is point to a *nucleus* in a *skeletal muscle* cell. You can tell this because the nucleus is peripherally located in the cell. Skeletal muscle is the *ONLY* muscle cell that has *PERIPHERALLY LOCATED NUCLEI*

What is the arrow pointing to? What muscle is this? How can you tell?

PNS has a blood nerve barrier that can be broken down CNS cannot break down its blood brain barrier This means that axonal regeneration doesn't happen in CNS

What is the difference between CNS and PNS in terms of axonal regeneration?

Multipolar

What is the most abundant type of neuron? Hint: Motor neurons are these types of neurons

Sarcolemma

What is the plasma membrane of a skeletal muscle cell called?

Purple arrow: *Perimysium*: connective tissue that separates individual cells into *clusters* Yellow arrow: *Endomysium*: connective tissue surrounding each cell This is *skeletal muscle* because the nucleus is peripherally located in the cell. Skeletal muscle is the *ONLY* muscle cell that has *PERIPHERALLY LOCATED NUCLEI*. You can also see *striations* (very subtly).

What is the purple arrow pointing to? What is the yellow arrow pointing to? What muscle is this? How can you tell?

Cardiac muscle; has *striations*, *nuclei are centrally located*, *branching of cells*, and intercalated discs*

What muscle is this?

Skeletal muscle; has *straight striations* and *peripherally located nuclei*

What muscle is this?

Smooth muscle; there are *no striations* and the *nuclei are centrally located*

What muscle is this?

Bipolar

What neuron is often associated with special senses?

The red arrow points to *branching of the cells*. Also, the *nuclei are centrally located*. *Striations* are present as well (very subtly).

What type of muscle cell is this? How can you tell?

Pseudounipolar

What type of neuron is this?

Pseudounipolar

What type of neurons are most sensory neurons (close to the CNS)?

The *action potentials moves* down the axon a lot *quicker* with the nodes in place because voltage gated channels are in these nodes whereas they exist down the entire length of an unmyelinated axon Node of Ranvier is also called *neurofibril node*

What's the benefit of a node of Ranvier? What is it also called?

If nerve sprouts do not establish contact with bands of Bunger or Schwann cells

When can traumatic neuroma develop?

The myofibrils increase in number, increasing the size of the muscle fibers

Why is it then when you lift weights your muscles get bigger?