Ch. 9 Skeletal Muscle

4 Characteristics of Muscles

1. Excitability - respond to stimuli

2. Contractility - shorten when stimulated

3. Extensibility - stretch

4. Elasticity - recoil

Concentric Contraction

sarcomere shortening

Eccentric Contraction

sarcomere lengthening

Skeletal Muscle Layers

1. Epimysium

2. Perimysium

3. Endomysium

4. Myofibril

NAV

• Nerve, Artery, Vein

• in skeletal muscle

Epimysium

• outer most covering

• organizes entire organ/muscle

• Dense Irregular CT

Perimysium

• wraps around the fascicle

• fibrous CT

Endomysium

• covers muscle fiber

• fine areolar CT

• has sarcolemma (plasma membrane around myofibrils)

• sarcoplasm

Fascia

• tied to all muscles

• conforms and causes stiffness

• two types

  • deep

  • superficial

Fascia allows for

• every joint to be stable

• every muscle to move and contract

Myofibril

• densley packed

• 80% volume of one muscle fiber

• striations

• sarcomeres

• myofilaments

• Composition of myofilaments

Sarcomere

smallest contractile (functional) unit of muscle fiber

Thick filament

Myosin

Thin Filament

• Actin

• made up of G actin and F actin

A band =

• M-line in the middle of the sarcomere

• everything but elastic (titin) filaments

• actin filaments

• myosin filaments

I band =

• Z disc in the middle

• actin filaments

• see when myofibril contracts

Dystrophin

part of sarcomere that links thin filaments to sarcolemma

Nebulin, myomesis, and C proteins

help keep sarcomere aligned and in boundaries

Types of Skeletal Muscle Attachments

• direct (fleshy) attachments

• indirect attachments

Direct attachments

• epimysium fused to periosteum of bone

• no tendon

  • directly attached to bone

Indirect attachments

• CT wrappings extend beyond muscle

• tendon (rope like)

• aponeurosis (sheetlike)

Sarcoplasmic Reticulum (SR)

• stores Ca2+ for muscle activation

• terminal cistern - calcium stored here

• T-tubules -

Triad

• SR

• T-tubules

• terminal cistern

Elastic Filament

• made of titin

T-tubules

• tube made by protrusion of sarcolemma deep into cell interior

• lumen continuous with extracellular space

• tubules penetrate cell’s interior at each A-I band junction

Skeletal Muscle Contraction Steps

(Evil Cats Enjoy Eating My Extra Cheese)

• environmental stimulus

• Cortical and subcortical decision making

• efferent output tells skeletal muscles contract

• events at neuromuscular junction

• muscle fiber excitation

• excitation-contraction coupling

• cross bridge cycling

Acetylcholine (AcH)

• used to open up channels to allow the signal to go from nerve to muscle

Neuromuscular Junction

1. Action Potential arrives at axon terminal (Na+)

2. Voltage-gated calcium channels open, calcium enters motor neuron

3. Calcium entry causes release of AcH into synaptic cleft

4. AcH diffuses across to AcH receptors (Na+ chemical gates) on sarcolemma

5. AcH binding to receptors, opens gates, allowing Na+ to enter resulting in end plate potential

6. Acetylcholinesterase degrades AcH

Brain Regions

Primary Motor, Premotor, Prefrontal Cortices, Basal Ganglia, Cerebellum

Ion Channels

• Chemically gated ion channels - opened by neurotransmitters

• Voltage-gated ion channels - open/close in response to voltage changes in membrane potential

ATP needed for

• relaxing muscles

• reset myosin heads

Contraction does what to ADP+Pi?

Gets rid of it

RIgor mortis

• inability to make ATP detach the cross bridge of myosin and actin

• dead animals on side of road

Crams caused by

• less ATP production over ATP usage

4 Functions of Any type of Muscle

1. Produce Movement

2. Maintain posture and body position

3. Stabilize joints

4. Generate heat as contracting

Sarcolemma

Muscle fiber plasma membrane

Sarcoplasm

• muscle fiber cytoplasm

• surrounds myofibrils

Heavy chains

form the myosin tail

Light chains

• form the myosin globular head

• these heads link and form the cross bridges between actin and myosin