anatomy - muscular system 💪

What are the types of muscle tissues?

• Skeletal muscle

• Cardiac muscle

• Smooth muscle

Skeletal muscle

• attached to bones

• voluntary

Cardiac muscle

• heart only

• involuntary

Smooth muscle

• walls of organs and blood vessels

• involuntary

ex. lining of intestines

Rank the contraction speed for each muscle type (fastest to slowest)

1. Skeletal muscle (FAST)

2. Cardiac muscle (SLOW)

3. Smooth muscle (MODERATE/RHYTHMIC)

— Skeletal muscles (header)

• functions

• characteristics

Simply state what the function is for each muscle tissue

Skeletal → movement

Smooth → moves substances

Cardiac → pumps blood

What are the functions of skeletal muscles? (state in point form)

• Moves the skeleton (pull tendons that move bones)

• Maintains posture and body position (like soft tissues)

• Guard entrances and exits

• Maintain body temperature (when they contract, they produce heat)

What are the characteristics of muscle tissue?

• Contractility (shortens to produce force)

• Excitable/Irritable (responds to stimulation)

• Extensible (can be stretched)

• Elasticity (returns to original shape)

What is the basic muscle structure composed of?

• Muscle

• Fascicle

• Muscle fiber

• Myofibrils

• Sarcomere

Muscle

→ made of fascicles

Fascicle

→ bundle of muscle fibres

Muscle fiber

= single muscle cell

Myofibrils

→ inside fiber, contain sarcomeres

Sarcomere

→ functional unit of contraction (where the actual shortening of the muscle happens during movement)

What are the connective tissue layers in this structure? And what are these inside of?

• Epimysium - surrounds entire muscle

• Perimysium - surrounds fascicles

• Endomysium - surrounds individual fibers

• Tendons - makes these layers continuous

→ these layers are inside of muscle fascicles

Collagen fibers from all three layers of connective tissue come together at the end of the muscle to form..

• Tendons

• Aponeurosis

Tendon

• bundles of fibers

→ attaches muscle to bone

Aponeurosis

• broad sheet of fibers

→ connects muscles to each other

Describe what muscle fascicles are..

→ bundle of muscle fibers (cells) within a muscle

• surrounded by perimysium (← connective tissue)

functions:

• support & protects muscles

• plays a role in transmitting force during contraction

Fascicle arrangement affects muscle function and strength (list the different types):

• Parallel

• Pennate

• Convergent

• Circular

Parallel

→ fibers run along the long axis (allowing large range of motion)

Pennate

→ fibers at an angle to the tendon (generates more force)

Convergent

→ fibers converge on a single tendon (allowing versatile movements)

Circular

→ fibers arranged in a circle (helps with opening and closing)

Label this diagram

Give a basic description of skeletal muscle fibers

These muscles are long, cylindrical, multinucleated cells. Each fibre is surrounded by a thin layer of connective tissue called the endomysium, which helps support and protect the cell. Inside the muscle fibre are myofibrils, which are packed with repeating units called sarcomeres

What specialized structure does muscle tissue contain? State and describe it.

→ sarcoplasmic reticulum (a modified form of the smooth endoplasmic reticulum)

• This is crucial for storing and releasing calcium ions

When a muscle contracts, it’s actually the sarcomeres…

shortening

Describe what myofibrils are

→ Inside a muscle fibre are long, thread-like structures called myofibrils. These myofibrils are made up of protein filaments, primarily actin (the thin filament) and myosin (the thick filament).

→ Myofibrils run parallel to the length of the muscle fiber and are filled with repeating units called sarcomeres

Describe what sarcomeres are..

→ A sarcomere is a repeating segment of a myofibril and extends from Z line to Z line. Containing:

• A band = myosin (thick)

• I band = actin (thin)

• H zone = myosin only

• M line = center of sarcomere

A band & Z zone are made out of what? I band is made out of what?

• A = myosin

• I = actin

• H = myosin

Briefly explain muscle contraction

1. Nervous system sends signal

2. Muscle fiber becomes electrically active

3. Calcium is released

4. Contractile proteins interact

5. Muscles shortens

Briefly explain what neuromuscular junction is

→ specialized synapse where a motor neuron communicates with a skeletal muscle fiber

→ contains the following components:

• motor neuron axon terminal

• synaptic cleft

• motor end plate

Motor neuron axon terminal

→ releases neurotransmitter acetylcholine (ACh)

Synaptic cleft

→ tiny gap between the neuron and muscle fiber

• ACh crosses synaptic cleft

Motor end plate (on muscle fibre)

→ ACh binds to receptors here

Briefly describe how each component reacts with each other..

→ The motor neuron releases the chemical signal, it crosses the synaptic cleft, binds to receptors on the motor end plate, and that’s what tells your muscle to move

Acetylcholine (ACh)

→ a neurotransmitter released from the motor neuron

• binds to receptors on the motor end plate, causing an electrical in the muscle fiber. This electrical signal triggers muscle contraction.

After signaling, what breaks down ACh to stop the signal, and allowing the muscle to relax?

acetylcholinesterase (AChE)

What’s a summary of how all of these work?

Motor neuron → ACh released → binds muscle → contraction → AChE breaks it down → muscle relaxes

What are the steps of muscle contractions?

Step 1: Muscle is activated

Step 2: Signals spreads inside the muscle

Step 3: Muscle Contraction

Step 1: Muscle is Activated

1. Motor neuron releases ACh

2. ACh binds to receptors on motor end plate

3. ACh causes muscle fiber to activate (depolarize)

4. A signal begins to spread along muscle fibre (potential)

Step 2: Signal spreads in the muscle

1. Signal travels deeper into the muscle fiber

2. Reaches the sarcoplasmic reticulum (SR)

3. SR releases calcium ions

Step 3: Muscle Contraction

• Myosin heads grab actin → pull it inward (power stroke)

• ATP needed to detach & reset mysoin heads

= many sarcomeres shortening, casuing the whole muscle to contract

Describe the Sliding filament model of contraction

• Actin and myosin slide past each other

• Sarcomere shortens, generating tension

• H zone and I band shrink, A band stays same

• ATP is required for myosin to “pull” actin

Describe how muscle relaxation occurs

• Nerve signal stops → ACh broken down

• Ca²⁺ pumped back into the SR

• Actin binding sites covered (myosin can’t attach)

• Sarcomere lengthens → muscles relaxes

Muscle contraction requires large amounts of energy in the form of…

ATP

ATP is used to:

• Power the myosin pull (power stroke)

• Detach myosin from actin

• Pump calcium back into the sarcoplasmic reticulum (muscle relaxation)

Resting muscles fibers store _____ _____ ATP

very little

Briefly mention the steps of how muscles make ATP

1. Creatine Phosphate

2. Anaerobic glycolysis

3. Aerobic glycolysis

1. Creatine Phosphate

• fastest way to regenerate ATP

• uses creatine phosphate stored in muscle

• lasts about 10-15 seconds

• used in explosive movements (jumping, sprinting)

(lowk why gym ppl buy creatine powder for workouts)

2. Anaerobic glycolysis

• breaks down glucose without oxygen

• produces ATP quickly

• generates lactic acid → fatigue

• supports short, intense activity (30-60 sec)

3. Aerobic glycolysis

• uses oxygen to make ATP

• occurs in mitochondria

• slower, but produces large amounts of ATP

• supports long-duration, low intensity activity

Twitch

→ single, quick contraction

• latent → contraction → relaxation

Summation

→ repeated signals before relaxation

• contractions add together = stronger tension

Tetanus

→ very rapid signals

• no relaxation

• smooth, sustained contraction

Describe motor units

• motor units = motor neuron + muscle fibers it controls

• small motor units = fine control (eyes, fingers)

• large motor units = big powerful movements (legs, back)

Recruitment

more motor units activated = more force

What are the two types of contractions that are used by muscles in order to generate force?

• Isotonic contraction

• Isometric contraction

Isotonic contraction

→ muscle changes length

• concentric: muscle shortens (lifting a weight)

• eccentric: muscle lengthens under tension (lowering weight)

Isometric contraction

→ muscle develops tension but does not change length (holding weight still)