The Central Nervous System (brain) tells them how & when to contract!

What Happens at the Neuromuscular Junction

How Skeletal Muscles are Told to Contract: A Reflex Arc

Fill in the back side of your

“Conn. Tissue Wrap. of Sk.

Muscle” wkst!

Sensation relayed to the brain by association neuron/ interneuron

The Nerve Stimulus & Action Potential• Skeletal muscles must be

stimulated by a motor neuron (nerve cell) to contract

• Motor unit— one motor neuron & all skeletal muscle cells stimulated by that neuron

• Action Potential – electrical signal sent along neuron to stimulate an effect

Figure 6.4a

The Nerve Stimulus & Action Potential

• Neuromuscular junction• Association site of axon terminal (end) of motor neuron &

muscle

Myofibrils

Neuromuscular Junction

End of the motor neuron (axon terminal)

MUSCLE CELL/FIBER

Synapse = space between neuron & next cell

Use your 3 different colors to identify each

region of the Neuromuscular Junction!

• Synaptic cleft (synapse)• Gap between nerve & muscle

• Do not make contact• Filled with interstitial fluid

The Nerve Stimulus & Action Potential

As you watch this animation, be listening for what chemicals are IMPORTANT for the “message” of contraction to be passed to a skeletal muscle

Neuromuscular Junction Animation

Fill in your Skeletal Muscle

Activity diagram!

Transmission of Nerve Impulse to Muscle

• Neurotransmitter—chemical released by nerve upon arrival of nerve impulse

• Skeletal muscle – acetylcholine (ACh)

• ACh attaches to receptors on sarcolemma

• Sarcolemma becomes permeable to sodium (Na+)

End of the

motor neuron

MUSCLE CELL/ FIBER

Transmission of Nerve Impulse to Muscle• Na+ rushes into cell, generating an Action Potential

(electrical signal)• Once started, muscle contraction cannot be stopped

Complete #6 on your Skeletal Muscle Activity wkst!

Scratch out “axon terminal” on #3.

Week #7 (11/30-12/4)Warm Up – Wed, 12/2-Reflex Arc

Have out:?

Agenda:1. Muscles Quiz #32. Notes: Muscle Contractions/Sliding

Filament Theory

Homework:

1. Anterior Muscles Quiz-Tues, 12/8

2. Sliding Filament Theory Assignment-due Wed, 12/2

GRADEBOOK CLOSES FRIDAY 12/11/2015!!

Anatomy Fun Fact:When doing resistance (weight) training, a repetition range between 10-15 repetitions will improve the endurance capacity of a muscle.

Muscles to Identify Quiz #3• Pick up 1 colored pencil

(ALL muscles will be color-code with 1 color).

• QUIETLY take the quiz & turn it in to the Hmwk Bin when finished.

How Skeletal Muscles are Told to Contract: A Reflex Arc

Sensation relayed to the brain by association neuron/ interneuron

Step 1 Step 2

Step 3Step 4

Step 5

CHECK FOR UNDERSTANDING:Neuromuscular Junction Goings-ons…

(whole section)

Complete the TOP & identify the

following structures on your

Skeletal Muscle Activity wkst!

Microscopic Anatomy of Skeletal Muscle

• Diving in to the smallest doll!

A A

Microscopic Anatomy of Skeletal Muscle

• Sarcomere—contractile unit of a muscle fiber (cell)

• Organization of the sarcomere• Myofilaments

• Thick filaments = myosin filaments• Thin filaments = actin

filaments

Identify the following structures

on your Muscle Structure wkst!

A A

Microscopic Anatomy of Skeletal Muscle

• Myofibrils are aligned to give distinct bands• I band = light band

• Contains only thin filaments

• A band = dark band • Contains the entire length

of the thick filaments

Identify the following structures on your Muscle

Structure wkst!A A

Microscopic Anatomy of Skeletal Muscle

• Thick filaments = myosin filaments• Composed of the protein myosin• Myosin filaments have heads (extensions) = 2-headed golf club• Myosin & actin overlap somewhat (A-band)

• Thin filaments = actin filaments• Composed of the protein actin• Anchored to the Z disc

Identify the following structures on your Muscle

Structure wkst!A A

Microscopic Anatomy of Skeletal Muscle

SARCOMERE CONTRACTION DEMO!

The End

Skeletal Muscle OrganizationName the following structures & connective tissue wrappings of skeletal muscle.

B (wrapping)

D (wrapping)

A (structure)

C (structure)

E (wrapping)

F (structure)

G(structure)

Microscopic Anatomy of Skeletal Muscle

Follow along on the BACK of your Muscle Structure

wkst!

Sarcomere Contraction animation

The Sliding Filament Theory of Muscle Contraction

• BIG PICTURE:• Activation by nerve causes

myosin heads to attach to binding sites on thin filament (actin) = ”cross-bridge”

• Myosin heads then pull the actin thin filament toward center of sarcomere

• Continued action causes a sliding of the myosin along actin

• Result – muscle is shortened (contracted)

Myofilament Contraction animation

Muscle Contraction at Its Finest!

• Myosin (filament & head)

• Actin (protein chain)

• Troponin complex: Ca2+

ions bind here to move tropomyosin off of binding site

• Tropomyosin: actin protein blocking myosin-binding sites

Myosin

Actin

Troponin complex

Tropomyosin

The Contraction Cycle

The Sliding Filament Theory

The Sliding Filament Theory

Troponin complex

The Sliding Filament Theory

REVIEW: The Contraction Cycle

Sliding Filament Theory article & Concept Map- As you read the article that tells you about the first experiments that led scientists closer to the present-day understanding of skeletal muscle, be looking for…

So how was it figured out how muscle

fibers contract?

5 Golden Rules of Skeletal Muscle Activity

Muscles & Body Movements• Movement is attained due to a muscle moving an attached bone

• Muscles are attached to at least 2 points

• Origin• Attachment to moveable bone

• Insertion• Attachment to immovable bone

Isotonic Contractions

• Isotonic Contraction:• Example: lifting

dumbbells with arm• Tension (effort) increases

& muscle fibers shorten & lengthen

• Concentric contraction:• Tension (effort) exceeds

resistance (weight) & muscle shortens

• Eccentric contraction:• Resistance exceeds

tension (effort) & muscle lengthens (due to gravity)

“iso” – same“ton” – weight/resistance

Isometric Contractions• Isometric Contraction:

• Example: pushing against a wall• Tension (effort) never exceeds resistance

(weight)• Muscle does NOT change length

“iso” – same“metr” – distance

Muscle Relaxation• Relaxation of muscle

fibers• Passive process• Combo of elastic forces, opposing muscle

contractions & gravity to elongate a contracted muscle

• Elastic force: some energy used to stretch tendons in contraction phase forces a recoil

• Opposing muscle contractions: muscles move in antagonistic pairs

• Gravity: pulls down muscle to extended position

Rigor mortisWithin 3-4 hours after death

• Dying muscle cell membranes become more permeable to Ca+ ions

• Promotes myosin cross-bridge binding

• After death, circulation of nutrients ends

• Without ATP, Ca+ ions are not removed & cross-bridges cannot detach from actin sites so muscles become locked in place – “stiff”

• Rigor mortis disappears as muscle proteins break down several hours after death (48-60 hours)

Effect of Exercise on Muscles• Exercise increases muscle size, strength

& endurance• Aerobic (endurance/

cardiovascular) exercise (biking, jogging) results in stronger, more flexible muscles with greater resistance to fatigue

• Makes body metabolism more efficient

• Improves digestion & coordination

• Resistance (isotonic & isometric) exercise (weight-lifting) increases muscle size & strength

Fast vs. Slow-Twitch Muscles• Fast Twitch Fibers

• Most skeletal muscle fibers • Contract in 0.01 sec or less after

stimulation• Large in diameter

• Contain densely-packed myofibrils• Have large glycogen reserves & few

mitochondria• Produce powerful contractions• Fatigue rapidly • “white muscle fibers”

Fast vs. Slow-Twitch Muscles• Slow Twitch Fibers

• ~Half the diameter of fast fibers • Take 3x as long to contract after stimulation• Specialized to continue contracting for

extended periods• Contain extensive network of capillaries &

has higher oxygen supply

• Contain red pigment myoglobin • Contain more mitochondria than fast

fibers• “red muscle fibers”

• Intermediate Fibers • Contain properties of fast fibers & slow

fibers

Tetanus

• Many toxins, drugs & diseases may interfere with events occurring at the neuromuscular junction

• Tetanus: infection of Nervous System from potentially deadly bacteria Clostridium tetani

– Bacteria spreads & makes poison called tetanospasmin– Poison blocks nerve signals from spinal cord to skeletal

muscles, causing severe muscle spasms– Prolonged muscle contractions,

spasms & stiffness– Spasms can be so powerful that they tear

the muscles or cause fractures of the spine

Muscular System~Putting it ALL Together