The Muscular System

GET STARTED! Get out a new sheet of paper – beginning of the Muscular System! What do you think a muscle is made of? Diagram it! 1 lateral view of a whole muscle 1 transverse cross section of a muscle

Skeletal Muscle Organization Muscle – packaged in epimysium Fascicle – packaged in perimysium Muscle Fiber (Muscle Cell) – packaged in Endomysium Myofibrils – surrounded by sarcoplasmic reticulum Myofilaments – Thick (myosin) and thin (actin) filaments

GET STARTED Get out a blank piece of paper (half sheet will do). Number your paper from 1-9.

Organize these layers from OUTSIDE to INSIDE without using a book or notes BONUS: Where is the endoplasmic rheticulum? These are all the SAME THING: Myofilaments Muscle filaments Thick/thin filaments (TYPES of filaments) Myosin/actin (protein which makes up the thick/thin filaments Fascicles Muscle Myofibrils Myofilaments Sarcolemma Epimysium Endomysium Perimysium Muscle fiber

Neuromuscular Junction Junction b/t motor neuron and muscle fiber Motor Neuron: nerve cell which conducts impulses to the muscle Motor Unit: the motor neuron and the group of muscle fibers a single motor neuron controls

Motor end plate: specialized are of the muscle fiber membrane where motor neuron connects Synaptic knob: enlarged region at the distal end of the motor neuron axon contain synaptic vesicles

Synaptic cleft: space in the neuromuscular junction which the neurotransmitter crosses Synaptic vesicles: membranous sacs of neurotransmitter Neurotransmitter: biochemical messenger – in this case, acetylcholine

Muscle Fibers (Muscle Cell) Sarcolemma: cell membrane Sarcoplasm: cytoplasm Sarcoplasmic Reticulum: endoplasmic reticulum (where proteins are made) Transverse Tubules: tube connecting the muscle fibers to the sarcoplasmic reticulum and to the outside of the cell

The Filaments The thin filament a strand of actin protein with “active” sites a strand of tropomyosin protein wrapped around the actin, covering its active sites troponin proteins attached to the tropomyosin

The thick filament several strands of myosin with globular heads myosin heads have binding sites

The Sarcomere: a single unit Myofibrils Myosin Actin Z Line M Line H Zone A Band I Band

The Sarcomere Sketch, color, and label a diagram of the sarcomere Filled in (micrograph picture) Simple diagram Page 174 Table beneath: describe what structures form each part Parts to include: Z Line M Line H Zone A Band I Band

The Sliding Filament Theory First, the nerve impulse… Acetylcholine is released at the neuromuscular junction This causes the Sarcoplasmic reticulum releases calcium ions, which diffuse into the sarcoplasm

Now for the contraction: Calcium binds to the troponin This causes the tropomyosin to shift off of the active sites on the actin Binding sites on the myosin heads attach to active sites on the actin filament This forms ‘cross-bridges’ The cross bridges use ADP to pull the actin inward toward the center of the myosin from both directions ATP binds to the myosin causing the cross-bridges to release And REPEAT

What happens in response: The Z lines are pulled together The sarcomere shortens The I band disappears

Threshold Stimulus The minimal amount of stimulation required to cause a muscle contraction Normally, an impulse will release enough ACh to cause the fiber to reach its threshold stimulus

All-or-None Response When the threshold stimulus is reached, the fiber contracts to its fullest extent Normally, there is no partial contraction This includes the entire motor unit

Recruitment More force means that more motor units are used – not that fibers are contracting more

Muscle Tone While at rest the neurons continues to fire Produces some amount of constant contraction

Smooth and Cardiac Muscle Where are they found? Voluntary or involuntary? What is the difference in cellular structure?