The Muscular System

What are the 4 functions of the muscular system?

1. Movement

2. Maintenance of posture

3. Stabilization of joints (keeps your bones together)

   1. Generation of heat

What are the 4 properties of muscle tissue?

1. Excitability

2. Extensibility

3. Elasticity

4. Contractility

What is the excitability property of muscle tissue?

Stimulating a muscle to do something; the ability to respond to a stimulus

What is the extensibility property of muscle tissue?

The ability to stretch without damage

What is the elasticity property of muscle tissue?

When you stretch muscle out of contract it, they come back to their original shape (recoils)

What is the contractility property of muscle tissue?

The ability to shorten

What are the 3 types of muscle tissue?

1. Skeletal muscle

2. Cardiac muscle

3. Smooth muscle

What is the location of skeletal muscle?

Attached to the skeleton

What is the structure of skeletal muscle?

Long, thin cells (fibers) that are striated & multinucleated (nuclei are pushed off to the side)

What are the functions of skeletal muscle (3)?

1. Posture

2. Movement

3. Stabilizes joints

How is skeletal muscle stimulated?

Voluntarily controlled via the somatic nervous system

Skeletal Muscle

What is the location of cardiac muscle?

Wall of the heart

What is the structure of cardiac muscle?

1. Cells (myocytes) have some striations and branching, with 1-2 nuclei

2. Cells are connected by intercalated discs (gap junctions/desmosomes), which allow the cells to communicate & resist being pulled apart from contraction

What is the function of cardiac muscle?

Pushes the blood around throughout circulatory system

How is cardiac muscle stimulated (2)?

1. Involuntary, self-exciting

2. Autorhythmic, but can be controlled by the autonomic nervous system

Cardiac Muscle

What is the location of smooth muscle?

Walls of hollow organs (ex. small intestine, blood vessel walls)

What is the structure of smooth muscle?

Tapered (stretched-out football-shaped) with no striations & 1 nucleus

What is the function of smooth muscle?

Moves fluids

How is smooth muscle stimulated?

Involuntary, stimulated by autonomic nervous system, but could also be stimulated by hormones

Smooth Muscle

1. Are skeletal muscles organs?

2. What 2 structures are they made up of?

1. Yes

2. Skeletal muscle cells (fibers) & connective tissues

What are the 6 structures found within the gross anatomy of skeletal muscle?

1. Muscle fiber

2. Endomysium

3. Fascicle

4. Permysium

5. Whole muscle

6. Epimysium

Muscle fiber

Muscle cell

Endomysium

Very thin bit of connective tissue that surrounds each muscle fiber

Fascicle

1 bundle of muscle fibers

Perimysium

Connective tissues that surrounds a fascicle

Whole muscle

1 bundle of fascicles

Epimysium

Dense irregular connective tissue covering the entire muscle

What is an origin?

The attachment of a muscle (usually a bone) that does not move

What is the insertion?

The attachment of a muscle (usually a bone) that does move (gets pulled)

What is an action?

The movement when the muscle shortens

What is an innervation?

The name of the nerve that goes to a muscle

What are the 2 types of attachments?

1. Direct

2. Indirect

What is a direct attachment?

Periosteum of bone attaches to epimysium of muscle

What is an indirect attachment?

Attachment is made via tendon or aponeurosis

What is aponeurosis?

A specialized tendon that’s wide & flat

1. Is the respiratory diaphragm a skeletal muscle?

2. How do you know (2)?

1. Yes

2. It’s striated & you can voluntarily control your breathing

What is the sequence of gross muscle to microscopic?

Whole muscle → fascicle → muscle fiber (cell) → myofibrils → myofilaments

Sarcolemma

Plasma membrane of a muscle fiber (NOT the same thing as the endomysium)

Sarcoplasm

Cytoplasm of a muscle cell (fiber)

Myofibrils

Tubes within the muscle fibers that are responsible for muscle contraction

Transverse tubules (T-tubules)

Pieces of the sarcolemma that extend into the muscle cell (fiber)

Sarcoplasmic Reticulum

Smooth endoplasmic reticulum of the muscle cell (fiber) that releases calcium during contraction

Triad

Sandwich consisting of 1 sarcoplasmic reticulum (bread), a t-tubule (filling), and another 1 sarcoplasmic reticulum (bread)

Terminal cisternae

The end of the sarcoplasmic reticulum

What are myofibrils composed of?

Myofilaments

Name the 2 myofilaments

1. Actin

2. Myosin

What is actin (thick or thin filament)?

Thin myofilament

What is myosin (thick or thin filament)?

Thick myofilament

Sarcomere

The functional/contractile unit of the muscle

What are the 3 structures grouped within/alongside actin?

1. G actin

2. Troponin

3. Tropomyosin

G actin

A single actin subunit (1 blueberry)

F actin

Actin subunits when they’re in filament form

Troponin

“Clips on a rope”; Keeps tropomyosin in place, then moves it out of the way once calcium arrives

Tropomyosin

Rope that covers the active sites for myosin to bind during rest

What are the 3 important regions on the myosin head?

1. ATPase

2. Actin binding site

3. Hinge region

ATPase on myosin head

Enzyme to break down ATP during muscle contraction

Actin binding site on myosin head

Myosin heads fit into actin active sites

Hinge region of myosin head

Moveable neck of the myosin head

What is the elastic filament?

Titin

What is the function of titin in the sarcomere?

Holds myosin in place at each end of the sarcomere

Name all of the bands, zones, & lines within the sarcomere (5)

1. Z disc

2. A band

3. I band

4. H zone

5. M line

Z discs

Zig-zag, Z-looking ends of the sarcomere

A band

Dark band under microscope; Contains both actin & myosin in the sarcomere

I band

Light under microscope; Contains actin only in the sarcomere

H zone

Region of the sarcomere that contains only myosin; Goes away during contraction (because of shortening!)

M line

Mid-line of the sarcomere

Sliding filament theory

1. In the presence of calcium, myosin heads can bind to actin to form a cross bridge

2. ATP breakdown causes the myosin heads to cock (hinge of myosin head moves), creating “power stroke,” then unbinds so the process can begin again

3. Actin & myosin don’t actually shorten. Instead, they slide against each other, pulling the Z discs closer

Cross Bridge Formation - Step 1 (3)

1. Calcium binds to troponin

2. Troponin moves tropomyosin out of the way

3. Myosin heads bind to actin

The Power Stroke - Step 2 (2)

1. Myosin head moves, pulling actin

2. Myosin releases ADP & phosphate (P_i)

In Step 2 - The Power Stroke, what happens if ATP is not present?

Myosin head will stay stuck to actin (rigor)

Cross Bridge Detachment - Step 3 (2)

1. ATP binds to myosin head

2. Myosin detaches from actin

Resetting the System - Step 4

1. Myosin hydrolyzes the ATP molecule (breaks ATP into ADP & P_i)

2. Myosin head “cocks” in preparation for another cycle

Diffusion

The movement of solutes from one side of a semipermeable membrane to the other

Gradient

The difference in concentration of molecules between one side of the semipermeable membrane and the other

Passive transport (Facilitated diffusion)

Molecules diffuse through the membrane easily from an area of high concentration to an area of low concentration; no energy required!

Active transport

Molecules move from low concentration to high concentration; requires energy

What is kinetic energy?

Energy that can do something that is release when positive & negative charges get together

What is potential energy?

Stored energy when we keep positive & negative charges separate

Potential/Potential Difference

The difference in charge between one place and another

Current

The flow of electrical charge from one place to another

Resting Membrane Potential

The difference in voltage between the inside and outside of the cell; Determined by ions

Membrane Permeability

The capacity of a membrane to have things pass through it; Depends on the number of open ion channels present for a specific ion (the more channels, the more permeable the membrane)

Electrical Gradient

If the net charge on the outside of the cell is more positive than the inside, an ion like potassium (K⁺) will be pulled in by the electrical gradient because the inside of the cell where it currently sits is more negative (opposites attract)

6 Steps in the Sodium-Potassium Pump (Na⁺/K⁺ ATPase Pump)

1. Sodium-potassium pump is open towards the inside of the cell. 3 Na⁺ hop in

2. An ATP is broken in order to change the shape of the pump

3. Pump flips and opens towards the outside of the cell. Na⁺ exits the pump

4. Once Na⁺ comes out, K⁺ will come into the pump from the outside of the cell

5. Using another phosphate, we change the shape of the pump again so it’s open on the inside of the cell once more

6. Pump brings in K⁺

Polarized Membrane

Membrane is at resting membrane potential of -70mV

Depolarized Membrane

Membrane is getting closer to 0 mV

Hyperpolarized Membrane

Membrane becomes more negative