The Muscular System

By Sam and Jess

Functions

• Movement & Circulation• Support• Posture & Balance• Joint Stabilization • Heat Production

Structure: Skeletal• Responsible for

voluntary motion• Striated

– Attached to bone via tendons

– Ex. Pectorals, deltoids, quadriceps

• Many mitochondria/ cell

Striations

Structure: Cardiac• Responsible for rhythmic contractions of heart• Involuntary• Blend of smooth and striated muscles

– Bound together by intercalated disks

• Most mitochondria/ cell

Intercalated Disks

Nucleus

Structure: Visceral• Involuntary: controlled by

nervous impulses or hormones

• Lines walls of hollow organs

• Cells spindle shaped: slow + steady contractions– Ex. Vasoconstriction,

Vasodilatation

Three Types of Muscles (cellular level)

Muscle Anatomy

Layers of MuscleMyofibrils

Muscle Fiber

Fasciclesheld together by perimysium

nerves and blood vessels run through

Fascia

Muscle Fiber Anatomy

Muscle Fiber

• Many mitochondria• Glycogen stored near sarcolemma

– Food for energy

• Sarcoplasmic reticulum– Storehouse for Calcium ions

The Sarcomere

I Band

A Band

H Band

Muscle Contraction• Δvoltage caused by nerve impulse• Calcium ions• Interactions between calcium, troponin, myosin,

and actin– ATP required

• Fibers pulled shorter: Contraction • Video:

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__breakdown_of_atp_and_cross-bridge_movement_during_muscle_contraction.html

All-or-None Principle

• Strength of muscle contraction does not depend on strength of nerve signal

• Cell will contract if voltage threshold is achieved

Disease 1: Muscular Dystrophy

• Inability to produce dystrophin protein– Inherited or mutation

• Muscle weakness and loss of muscle tissue; learning disabilities; inability to walk (age 12); skeletal deformities

• Gene therapy? Corticosteroids; mobility aid; physical therapy; surgery

Disease 2: Myositis

• Autoimmune• Inflamed or damaged muscle cells• Weakness, swelling, pain• Immunosuppressant, immunoglobin, physical

therapy, steroids

Disease 3: Myasthenia Gravis

• Autoimmune• Muscle weakness after activity• Slow eye, facial, swallowing movements• Immunosuppressant drugs, Thymectomy

Tetany• Hypocalcaemia: low calcium• How does this affect muscle contraction??

– Normal: calcium binds to sodium to block Δvoltage

– Abnormal: less calcium results in lower threshold for Δvoltage

• Result constant muscle contractions

Fatigue

• When muscles run out of energy• No “ingredients” for cell respiration• Lots of waste products

– Lactic Acid – ADP

• Must pay oxygen debt

Muscle Research in Switzerland

• “Dirty” muscles mean weak muscles– Healthy cells must clean out waste products and

malfunctioning components• Autophagy

– Cells with overactive mTORC1 protein (promotes muscle growth) cannot self-clean

• Solution: Inject Rapamycin to inhibit mTORC1 and allow cells to clean

Alcoholic Skeletal Myopathy Linked to Vitamin D deficiency

• Myopathy: weakness and wasting of muscle tissue• 40%-60% of alcoholics experience myopathy• Vitamin D deficiency is prevalent in alcoholics• Vitamin D deficiency impairs mitochondrial function • Shorter phosphocreatine recovery times=better

mitochondrial function.• Supplements of vitamin D improve recovery rates

Duchenne Muscular Dystrophy (DMD) Research

• DMD: fatal, genetic disease where muscles, including heart, progressively deteriorate.

• Genetic mutation: absence of vital proteindystrophin

• Antisense oligonucleotides (AOs)• DrugDantrolene

“A mouse hanging on a wire during a test of muscle strength. Mice with a mutant dystrophin gene, which have a muscular dystrophy-like disease, can only hang for about 20 seconds before they lose their grip and fall to the ground. An antisense oligonucleotide being developed to treat the disease in people only helps a little bit. But if the mice also receive the drug dantrolene (shown as the wire), they are stronger and can hang for 30 seconds or so…It also works in human cells and may help patients with Duchenne's muscular dystrophy.” [CREDIT: G. KENDALL/UCLA; IMAGES: M.C. MICELI, S. NELSON, E. MOKHONOVA, M. SPENCER]