Chapter 9 (lectures)

Muscle tissue

What tissue makes up half body mass?

1. Movement

2. maintains posture (fights gravity)

3. Stabilizes joints

4. Generates heat

Functions of muslces [4]

1. Excitability

2. Contractility

3. Extensibility

4. elasticity

Special characteristics of muscle tissue [4]

Excitability

Ability to receive and respond to stimuli (not passive)

Contractility

Ability to shorten forcibly when stimulated. Is unique to muscle tissue

Extensibility

Ability to be stretched

Elasticity

Ability to recoil to resting length

via tendons

How do muscles attach to bone?

about 30cm long

How long are muscle cells?

muscle fibers

Many of these cells make up muscles

Ten times the diameter of the average cell

Relative width of muscle cell

Myofibrils

Specialized organelles that fille cytoplasm. Enables contraction

No. Requires input/signal from the nervous system.

Do muscles function on their own?

Motor neuron

Pathway that sends signal to muscle

Action potential

Signal that is sent along motor neuron to muscle.

Neuromuscular junction

Where the neuron meets the muscle

ALS

Condition that affects motor neurons. Signal no longer gets to the muscle. Neurons degrade.

Synapse

Any place in body where there are two neurons meeting, or a neuron meeting a muscle cell or gland.

Neurotransmitter

Chemical that transmits signal across the synapse. Action potential getting from point A to point B.

1. Voltage gated channels

2. Chemical gated channels

Two kinds of gated channels

Voltage gated channels

Channel that only opens when voltage reaches a certain level. Important for muscle contraction

Chemical gated channels

Channel that opens until a chemical binds to it.

1. Action potential arrives at neuromuscular junction

2. Voltage-gated calcium channel opens and calcium enters

3. Calcium causes neurotransmitter (ACh) to be released

4. ACh binding opens channels that allow sodium in and potassium out of cells

5. Movement of sodium and potassium triggers action potential in the muscle, causing muscle to contract

5 steps for muscle contraction

1. calcium is very important, without it, message does not cross synapse

2. Sodium and Potassium (movement in and out) are very important

3. ACh is the neurotransmitter required for muscle contraction

Three key points about muscle contractions:

Muscle tone

Constant, slightly contracted state of all muscles

Flaccid

Muscles with less tone

Spastic (changes in tone)

Muscles with more tone

1. Produce movement (concentric)

2. Control movement (eccentric)

3. Maintain a position (isometric)

What do contracting muscles do?

1. Signal from nervous system

2. events at NMJ

3. events in muscle

Three necessities for muscle contractions

1. Operating sodium potassium pump

2. Provide energy for inner workings of muscle that produce force

What do muscles need ATP for?

4-6 seconds

How long an muscles contract before more ATP needs to be regenerated?

1. Direct phosphorylation

2. Anaerobic glycolysis

3. Aerobic respiration

Three pathways that regenerate ATP

Direct phosphorylation

ATP pathway that activates for about 15 seconds of aerobic movement. Does not need oxygen. Produces 1 ATP per CP and creatine

Anaerobic pathway

ATP pathway that does not need oxygen. Produces 2 ATP per glucose molecule (energy) and alcic acid. Activates for aerobic exercise of about 30-40 seconds.

Aerobic pathway

ATP pathway that requires oxygen. Produces 32 ATP per glucose molecule. For hours.

1. Aerobic (endurance)

2. Progressive resistance (anaerobic)

two types of exercise

1. Muscle hypertrophy (muscles do not undergo mitosis, they grow)

2. Increased strength of cells

Progressive resistance exercise results in… [2]

1. Change in muscle physiology and structure

2. Results in greater endurance, strength, resistance to fatigue

Aerobic exercise results in… [2]

Sarcopenia

Age related muscle loss.

1. Mobility issues

2. Increased fall risk

3. Loss of independence

Sarcopenia can result in… [3]

No. Can be reversed through resistance training.

Is muscle loss permanent?

At least three times a week

How often must resistance training occur to be impactful?

Walls of hollow organs

Where is smooth muscle found?

smooth muscle is usually arranged in sheets

Arrangement of smooth muscle

Smooth muscle

Muscle that moves involuntarily

1. Longitudinal layer (outer): parallel fibers contract

2. Circular layer (inner): Fibers in circumference of organ contract (constricts lumin)

Two sheets/layers of smooth muscle

Peristalsis

Contraction of opposing layers of muscle leads to rhythmic form of contraction

1. Skeletal is multi-nucleated, smooth has one

2. Smooth muscle is very small, skeletal is 10 times wider and 1000s of times longer

3. Smooth muscle does not have NMJ, skeletal does

Differences between smooth and skeletal muscle [3]

1. Single unit: gross control (ex: movement of stomach, intestine)

2. Multi-unit: No connection between cells, allows for fine movement control. (ex: constrictor muscle of iris, erector pili in hair follicles)

Two types of smooth muscle

1. Stimulation can cause excitation or inhibition in smooth muscle, but just excitation in skeletal muscle

2. Smooth contractions are very slow and consume less ATP, skeletal is 30 times faster and has higher ATP requirements

Key differences in smooth vs. skeletal muscle contractions [2]

1. Can reproduce via mitosis (hyperplasia, think uterus)

2. Can contract when between half and twice resting length (hollow organs must be able to expand and still function when empty)

3. Contracts when stretched (helps move substances along)

Special features of smooth muscle (3)