A&P Lab - Class 6: Histology II (muscle tissue, nervous tissue, membranes, integumentary system)

Muscle tissues use ______ to generate force to produce contractions

ATP

Why do muscle cells have the nickname, "muscle fibres"

Because of the cells' elongated shapes

The name of muscle cell cytoplasm

Sarcoplasm

Name for the cell membrane of the muscle cell

Sarcolemma

Types of muscle tissue found in the human body

- Skeletal muscle tissue
- Smooth muscle tissue
- Cardiac muscle tissue

What do the ends of muscle cells look like?

They're blunt (the cells don't taper)

How many nuclei do skeletal muscle fibres have, if any?

Multiple (located peripherally)

Why are there striations (transverse bands) on skeletal muscle fibres?

They result from an arrangement of parallel structures (myofibrils) within the sarcoplasm

What are the striations on skeletal muscle fibres made up of?

What is their job?

Myofilaments
- Thick: Myosin protein filaments
- Thin: Actin protein filaments

They're directly involved in the contraction process.

How are myosin and actin filaments organized?

Into sarcomeres (functional units of the skeletal muscle cell).

What are skeletal muscles attached to?

Bones

What do skeletal muscle cells look like?

Long, thick, and cylindrical

What do smooth muscle cells look like?

Short and spindle-shaped with tapered ends (no blunt end)

Why is the shape of a muscle cell hard to see?

The sarcolemma is indistinct and the cells are tightly packed in a sheet-like arrangement

How many nuclei do skeletal muscle fibres have, if any?

One (located centrally in the thickest part of the cell)

True or False:
There are visible striations within the sarcoplasm of smooth muscle fibres

False

Where is smooth muscle primarily located?

Within the walls of hollow organs (blood vessels, GI tract, urinary, respiratory, and reproductive tracts).

True or False:
Cells of cardiac muscle tissues have striations

True

Where is a cardiac muscle cell's nucleus located?

Centrally

In a cross-section, what is the only thing that distinguishes a skeletal muscle cell from a cardiac muscle cell?

The position of the nuclei

What are cardiac muscle tissues characterized by?

- Cells which branch in an irregular pattern.
- Intercalated discs (allow cells to join end-to-end).

Intercalated discs

(Cardiac muscle cells)
Regions where cell membranes of adjacent cells contact each other and contain desmosomes and gap junctions. This allows for cohesion and rapid electrical conduction.

Where is cardiac muscle tissue located?

Only in the walls of the heart

Two major divisions of the nervous system

Central nervous system (CNS - brain and spinal cord).
Peripheral nervous system (PNS - all nervous tissue aside from brain and spinal cord).

Two main cell types of nervous tissue

- Neurons
- Neuroglia

Role of neurons

(Largest and most prominent cells of nervous tissue)
Specialized to convert stimuli into electrical signals (action potentials/nerve impulses).

True or False:
Action potentials are only delivered between neurons

False.
Action potentials can be delivered from a neuron to muscle tissues or glands, not only other neurons.

The "typical" neuron includes:

Cell body (soma), dendrites, and axon

The soma of a neuron consists of:

The nucleus (and conspicuous nucleolus), and surrounding cytoplasm

What are Nissl bodies?

Aggregations of rough neurofibrils in the neuron (important elements of the cytoskeleton)

Dendrites

Receive information from other neurons and carry it towards the soma (cell body)

Axon

Specialized to conduct information to other cells. May be covered with a fatty (myelin) sheath which protects and insulates the axon, also increasing the speed of action potential conduction.

In the PNS, what are myelin sheaths made up of?

Schwann cells

In the CNS, what are myelin sheaths made up of?

Oligodendrocytes

What types of cells are Schwann cells and oligodendrocytes?

Neuroglia

Gaps between myelin sheaths on axons are called:

What is their role?

Nodes of Ranvier.

They allow nerve impulses to jump from node to node, increasing the speed at which the impulse travels.

Telodendrites

(Axon terminals)
Fine branched endings of the axon.

What makes up grey matter?

Mainly made up of neuron cell bodies.

Grey matter in the brain

Found as a thin outer layer on the brain surface

Grey matter in the spinal cord

Found in a "butterfly shape" in the middle of the spinal cord

Outside the CNS, neuron cell bodies are clustered within:

Ganglia

Where does "white matter" get its name?

It appears lighter because of the myelin sheaths on neural axons

Nissl bodies

Clusters of ribosomes in rough ER for protein synthesis

The 3 types of covering and lining membranes

- Mucous
- Serous
- Cutaneous

What are membranes?

Continuous multicellular sheets composed of an epithelium bound to an underlying layer of connective tissue

What do mucous membranes line?

Body cavities that are open to the exterior (ex. hollow organs of the digestive, respiratory, reproductive, and urinary tracts).
* Moist with various types of epithelia.

True or False:
All mucous membranes contain goblet cells/multicellular mucous glands.

False.
Many of them do, but not all.

What do serous membranes line?

Walls (parietal layer) and organs (visceral layer) within closed ventral body cavities (pericardial, pleural, and abdominopelvic cavities).

What does a serous membrane consist of?

Simple squamous epithelium resting on a thin layer of areolar connective tissue.

What is serous fluid produced by?

What are its roles?

Serous membranes.

It lubricates surfaces to reduce friction.

Cutaneous membrane

The skin which is exposed to air and is a dry membrane.

a) Name for the superficial region of the skin.
b) Name for the deeper part of the skin.

a) Epidermis
b) Dermis

What are the layers of tissues underneath the dermis?

The subcutaneous layer (AKA hypodermis)

True or False:
The subcutaneous layer (hypodermis) is part of the skin.

False

What type of epithelium makes up the epidermis?

Stratified squamous epithelium (keratinized)

True or False:
The epidermis varies in thickness.

True.
It's thicker on our palms and thinner within the ear.

In areas where the epidermis is thickest, how many layers (strata) is it made up of?

Five

Characteristics of the stratum corneum

Outermost layer of the epidermis.
Made up of keratin.

Keratin

Layers of flattened, dead cells filled with protein. Constantly being sloughed off/lost.

Characteristics of the stratum basale

Deepest epidermal layer.
Mainly a signle row of cells that are undergoing mitosis. Newly formed daughter cells are pushed upward in a successive epidermal layer. As they move into more superficial layers, they begin to flatten and become squamous, fill with keratin, and then die.

How does the epidermis get its nutrients?

Why is this?

Via diffusion from the dermis.

This is because the epidermis is avascular.

Layers of the dermis

- Papillary layer (thin and sperficial)
- Reticular layer (dense and deeper)

Papillary layer of the dermis is made up of:

Areolar connective tissue

Reticular layer of the dermis is made up of:

Dense irregular connective tissue

What are the projections in the papillary layer called? (Towards the epidermis)

Dermal papillae

What do many dermal papillae contain?

Capillary loops, free nerve endings (pain receptors) and Meissner's corpuscles

Meissner's corpuscles.

Where are they most abundant?

Receptors that respond to light touch sensations.

Most abundant in the skin of the fingertips, lips, and eyelids.

Pacinian corpuscles.

Where do they occur?

Tactile receptors (but, much larger than Meissner corpuscles) and are located deeper in the dermis. Sensitive to deep pressure.

Occur in the skin of the fingers, the pancreas, and in the walls of the urinary bladder.

Sweat (sudoriferous) glands

(Merocrine/eccrine glands).
Located in the dermis, release perspiration into hair follicles or onto the skin surface through pores. These are coiled tubular glands that secrete mostly water (but also ions and some nitrogenous wastes).

What is the main role of sweat?

To regulate body temperature through evaporation.

Where do hair follicles fold down from?

The epidermal surface into the dermis

The deep end of the hair follicle is expanded to form the:

Hair bulb

Hair papilla

Dermal tissue which bulges into the terminal bulb of the hair follicle.
Contains a knot of capillaries that supplies nutrients to the growing hair.

Arrector pili muscles

Extend from the dermis to the hair follicle. These muscles allow your hair to "stand on end".

What type of muscle are arrector pili muscles?

Smooth

Where can sebaceous glands be found?

What do they produce?

(Holocrine glands).
Found in association with the hair follicle.

Produce an oily secretion (sebum), which lubricates the skin and keeps the hair flexible.

What is melanin?

Where is it produced?

The principal skin pigment.

Formed in the deepest layers of the epidermis by melanocytes.

How does UV radiation affect melanin pigment?

UV radiation in sunlight has a stimulatory effect on the melanocytes, causing an increase in melanin pigment (ex. tanning).
This is due to increased cell activity (and not an increase in the number of melanocytes).

What does a concentration of melanin in one spot produce?

A freckle

Carotene

A yellow pigment that accumulates in the surface layer of the epidermis.

What pigments make up skin colour?

- Melanin
- Carotene
- Hemoglobin

How does hemoglobin affect skin colour?

The blood in blood vessels present in the dermis produce a pinkish tint (most obvious in the skin of people who have little melanin).

What does a "flushed" appearance/reddened skin signify?

In increased degree of oxygenation in the blood (of the dermal blood vessels). When bound to oxygen, hemoglobin is bright red.
Could also be used to dilation of blood vessels.

Your hands are cold from being outside in the winter. You go inside and run them under room-temperature water, but it feels extremely hot.
Why does this occur?

Nerve endings have desensitized from the coldness of the outdoor temperature. Blood vessels also contract. Once they're accustomed to this environment, even room temperature water could seem hot.

Why do we adapt to pressures on our body such as clothes and jewelry?

There's no point for the body to continuously warn you about a non-threatening and long-term sensation.
Changes in pressure and noticed, but only short-term.

How do changes in temperature affect peripheral blood flow?

Cooling: Decreases peripheral blood blow and the flow of venous blood to the heart.
Heating: Increases peripheral blood flow and the flow of venous blood to the heart.

How do different temperatures affect blood vessels?

Cold: Blood vessels constrict.
Hot: Blood vessels dilate.

What causes fingerprints?

Downward projections of the epidermis into the dermis between the dermal papillae in the upper portion of the skin.

Why does a hypodermic hurt at some times but not at others?

It will only hurt if it contacts a nerve

Pacinian corpuscle vs. Meissner's corpuscle

Pacinian: Deep pressure sensation.
Meissner's: Light touch stimuli.

How does sweating cool body temperature?

When overheating (which is detected by the hypothalamus), homeostasis lowers body temperature so that secretions don't evaporate. This cools the body and returns it to a regular homeostasis loop.

Rules to remember for identifying Meissner's vs. Pacinian corpuscles under the microscope

Meissner's: Resembles like cotton candy
Pacinian: Resembles onion cross-section

Sweat glands are (merocrine/holocrine)

Merocrine

Sebaceous glands are (merocrine/holocrine)

Holocrine