Musular system introduction Chapter 10 anatomy

Three types of muscles

• Skeletal

• cardiac

• smooth

Muscular system

• skeletal muscles

Myology

• study of the skeletal muscles

Functions of Muscles

• Movement

  • Body parts

  • Body contents

  • communication

• Stability

  • maintain posture

  • resist pull of gravity

• Control of body opening and passages

  • can be in eyes or mouth

  • or urethral and anal opening

• Heat production

  • necessary for enzyme function

• Glycemic control

  • Absorb, store, and use glucose

    • being active makes sugar better really helps control blood sugar.

Properties of Muscles

• Excitability (responsiveness): react to stimuli

• Conductivity: spread electrical impulses through muscle cell

• Contractility: shorten when stimulated

• Extensibility: can stretch without harm

• Elasticity: can recoil from stretch

Types of Muscle tissue

• skeletal

  • voluntary control

  • striated

  • attached to bone

  • muscle cells: muscle fiber or myofiber or myofibril

• Cardiac

  • striated

  • intercalated discs

  • involuntary

  • cell: cardiomyocyte

• Smooth

  • Involuntary

  • non-striated

  • fusiform cell shape

Endomysium

• areolar connective tissue surrounding each myofibril

Sarcolemma

• Plasma membrane of a muscle

  • Transverse (T) tubules: tunnels formed w/in sarcolemma penetrate cells

    • carries electrical signal from surface inside cells(part of conductivity)

Sarcoplasm

• Cytoplasm of the muscle

  • myofibrils

  • glycogen:energy (source of energy)

  • Myoglobin: oxygen (source of oxygen)

Sarcoplasmic reticulum

• Smooth ER

  • Reserve Ca2+ ions

    • Storage of calcium ions if no calcium no muscle movement

  • Surrounds myofibrils

Terminal cisterns

• dilate end sacs that cross myofibrils from side to side

  • run Perpendicular; electrical signaling

Myofilaments

• Thick myofilaments

  • Myosin

    • Head projects from bundled tails of hundreds of molecules

    • Does moving

• Thin myofilaments

  • Actin

    • Fibrous (F) actin: like beaded necklace

    • Globular (G) actin: one bead of necklace

      • Active site: myosin binding are on G actin

    • Does moving

  • Tropomyosin

    • Blocks active sites when muscle is relaxed

      • Regulates (body guard)

  • Troponin

    • Attaches to tropomyosin, binds calcium when excited

    • Regulates (body guard)

• Elastic Filament

  • Tintin (connectin)

    • Anchors thick myofilaments to Z disc and M line

• Functions:

  • Contractile proteins

    • myosin and actin

  • Regulatory proteins

    • tropomyosin and troponin

Sarcomere

• Functional contractile unit of muscle

Striations

• narrow stripes (light and dark) that run perpendicular to the length of the cell

  • how contractile proteins overlap.

A band

• Dark stripe of thick myofilaments that partly overlap thin myofilaments (Anisotropic)

H band

• Central region of A band is lighter

  • lack thin myofilaments

M line

• Midline of A band (and H band) that anchors thick myofilaments together

I band

Light stripe of thin myofilaments only (isotropic)

Z dic (z line)

• midline of I band

• Protein that anchors thin and elastic filaments

• Defines boundaries of sarcomere (ends of sarcomere)

Blood supply

• Rest: muscle receives ~25% heart’s output

• Heavy exercise: muscular system receives > 75% heart’s output (a larger percentage of a larger output)

• Healthy muscle: Well vascularized

• Muscle capillaries coiled at rest, straighten with muscle lengthening

Nerve-Muscle Relationship

• Neuromuscular junction: synapse between somatic motor nerve and muscle cell

  • motor neuron’s synaptic knob contains vesicles w/ acetylcholine (ACh)

  • Synaptic cleft-space

  • postsynaptic membrane folds of muscle cell’s membrane contain ACh receptors.

Motor unit

• 1 motor neuron + multiple muscle fibers (1 boss (neuron), but can be many fibers or less fibers depending on how big muscle is)

• behave as a single functional unit

• Fibers from one unit are dispersed in muscle

Contraction and relaxation

• Excitation

1. Nerve signal arrives at knob

2. knob releases ACh, binds to muscle receptors, opening ion gates and exciting muscle.

3. Excitation spreads down and through muscle cell

• Excitation - contracting coupling

4. Electrical impulse triggers calcium release from SR

5. calcium binds troponin, which moves tropomyosin to expose actin

6. Myosin breaks down ATP and extends head

7. Myosin forms cross-bridge wit actin

8. Myosin pulls actin in power stroke, then detachesm reattaches, pulls again etc..

• Relaxation

9. Nerve signal stops

10. SR reabsorbs calcium troponin blockade resumes, and tension subsides

classes of Muscle Fibers: Slow oxidative (SO)

• slow-twitch, red, type 1 fibers

• small diameter

• Aerobic ATP production

• Abundant: mitochondria, myoglobon, capillaries

• Low levels of glycogen

• Resistant to Fatigue (ex: keeping head up, keeping back up)

• Predominate is postural muscles, such as soleus

classes of Muscle Fibers: Fast glycolytic (FG)

• Fast twitch, white, type 2 fibers

• large diameter

• Anaerobic ATP production

• modest quantities: mitochondria, myoglobin, capillaries (less)

• Abundant glycogen

• Fatigue quickly (ex: lifting and sprinting)

• predominate in quick response muscles, such as gastrocnemius

Muscle Growth and Atrophy: “Use it Or Lose it”

• resistance exercise stimulates production of more myofilaments, thus more myofibrils

  • Growth by hypertrophy, not hyperplasia (muscle fibers do not undergo mitosis)

• Exercise also stimulates production of mitochondria, myoglobin glycogen, and blood vessels.

• Unused muscles atrophy (shrink)

Cardiac Muscle

• striated

• short, stumpy, branched cells

• Intercalated discs with gap junctions

• Typically mononucleated

• involuntary

  • Autorhythmic with influence from autonomic nervous sytem. (ex: controls heart)

Smooth Muscle

• No striations (there functional unit is not a sarcomere)

• Small, fusiform, cell with one nucleus

• Dense bodies linked cytoskeleton and membrane

• Involuntary control

  • Autonomic nerve fibers have varicosities instead of NMJ

• Participates in: a lining in organs and tubes

  • peristalsis, vascular tubing, digestive tubing, reproductive tubing. L

Layers of Visceral Muscle in a Cross section of the Esophagus

• Mucosa:

  • epithelium

  • lamina propia

  • muscularis mucosae

• Muscularis externa:

  • circular layer

  • longitudinal layer

Agining Muscular system

• Loss of lean body mass (muscle)

• fat and fibrous tissue accumulation ( not as metabolically favorable)

• Fast glycolytic fibers show earlier and most severe atrophy

• reduction in muscle cell components

• reduction in motor neuron number, ACh release, and sympathetic nervous system efficiency

Disease of the Muscular system

• Myopathies: disease of muscle

• muscular dystrophy (tend to show up in young children reaching milestones like walking and then isn’t)

  • Hereditary (sex-linked)

    • defective gene for dystrophin

  • skeletal muscle degeneration

  • Grower’s sign

• Myasthenia gravis (MG)

  • Autoimmune disease

  • Destruction of ACh receptors

    • Means signal is weak, will it impact their breathing (diaphragm big breathing moving muscle)