Diagram of a Neuron

Terms to Know:

DendriteCell bodyNucleusAxonSchwann CellMyelin SheathNode of Ranvier

dendrite Myelin sheath

axon

Cell body

Nodes of Ranvier

Diagram of a Neuron

Sensory Relay (interneuron) Motor

Reflex Arc

Reflex Arc

reflex arc video

Motor Unit

Motor Unit:

a single motor neuron and the muscle fiber(s) it innervates.

Innervate- supply an organ /body part with nerves

Motor UnitInnervation Ratio:

Number of muscle fibers stimulated by one motor neuron.

Muscles that control fine movements (fingers, eyes) have small motor units

Large weight-bearing muscles (thighs, hips) have large motor units

All-or-Nothing Response

All the muscle fibers that are connected to a single motor neuron either contract or relax at the same time.

A muscle twitch is the response of a muscle to a single action potential of its motor neuron. The fibers contract quickly and then relax.

Muscle Twitch

Neuromuscular JunctionConnection between nervous system and muscular system

Neuromuscular Junction

Motor End Plate: The large and complex end-formation by which the axon of a motor neuron establishes synaptic contact with a striated muscle fiber (cell).

Role of Neurotransmitters

What is a neurotransmitter?

Neurotransmitters are chemicals that are used for communication between a neuron at the synaptic cleft and another cell.

Acetylcholine (Ach): increases the post-synaptic membrane’s permeability to sodium and potassium ions spreading the impulse over the entire muscle fiber.

Role of Neurotransmitters

Neuromuscular junction

Cholinesterase is an enzyme that breaks down Ach, repolarizing the muscle fiber to await another nerve impulse.

Neuromuscular Junction

Use with page in packet with the title, ‘The neuromuscular junction’.

1. Action potential arrives at axon terminal

2. Depolarization opens Ca+ channels & Ca+ enters axon terminal.

3. Ca+ stimulate synaptic vesicles to fuse with membrane.

4. Exocytosis of Ach into synaptic cleft.

5. Ach binds to Ach-receptor sites on post synaptic side. 6. This creates a depolarization 7. Which allows the action potential to continue to the T-tubule which stimulates the sarcoplasmic reticulum to release Ca ions into the muscle

8. Cholinesterase is released and breaks down the Ach. This will end the action potential and the muscle contraction.

Parts of the Neuromuscular Junction

Excitation Contraction Coupling (Action Potential across the Neuromuscualr Junction)

What happens at the neuromuscular junction?

A Quick Review of the Neuromuscular Junction

Sliding Filament Theory Explains how muscle fibers shorten during a

contraction.

Sliding Filament Theory

Tropomyosin: An actin-binding protein which regulates muscle contraction.

Troponin: protein that is bound to tropomyosin and blocks the binding of the myosin head.

Terms to know:

The sarcoplasmic reticulum: specialized endoplasmicThat is a storage site for calcium ions used during muscle contraction.

Sliding Filament TheoryStarting position for muscle contraction:

1. Troponin is bound to tropomyosin on the actin filament

2. Myosin heads are waiting for the binding sites to open

Sliding Filament TheorySteps of a muscle contraction:

1. Ca++ are released by the sarcoplasmic reticulum.

2. Ca++ binds to troponin releasing it opening up the binding sites on the tropomyosin

3. The myosin heads can now bind to tropomyosin

Sliding Filament Theory

4. Using energy from break down of ATP*, the myosin heads pulls on the actin causing a muscle contraction (power stroke)and the ADP + P to be released.

*ATP ADP + Pi + ENERGY

5. myosin head releases the actin when a new ATP** is formed and binds to myosin head.

**ADP +Pi + Energy ATP

Sliding Filament Theory

6. Immediately after the myosin head tilts, it breaks away from the active site, rotates back to its original position, and attaches to a new active site farther along the actin filament. Repeated attachments and power strokes cause the filaments to slide past one another, giving rise to the term sliding filament theory. This process continues until the ends of the myosin filaments reaches the Z-disks, or until the Calcium is pumped back into the sarcoplasmic reticulum.

Sliding Filament Theory

http://studentvet.files.wordpress.com/2010/07/image331.gif

Structure of a Sarcomere

Structure of a SarcomereTerms to know:

Myofilaments :actin(thin) & myosin (thick)

Sarcomere: basic unit of muscle

H zone: thick filament (myosin) only I band: thin filament (actin) only

A band: overlap of actin & myosin

Z line: (disc) connects I-bands

M line: in the middle of H zone, connect thick filaments

Structure of a Sarcomere

Sliding Filament Theory

During this sliding (contraction), the thin filaments move toward the center of the sarcomere and protrudes into the H-zone, ultimately overlapping. When this occurs, the H zone is no longer visible.

Sliding Filament TheoryPut the following statements in order.

3 5

2

1

4

Neuromuscular Function

1. What are the three types of muscle fibers? Briefly describe each

Slow Twitch (type I): slow contraction and high resistance to fatigue

Fast Twitch A (type IIA): moderate resistance to fatigue and are a transition between the other two types of fibers.

Fast Twitch B (type IIB): very sensitive to fatigue & used for short aerobic, high force production.

Small medium large

High high lowHigh high lowHigh high low

Low high highLow medium high

High medium low

Slow Fast Fast

Low High High

High medium lowHigh Medium Low

Low High High

Endurance Sprint/ Walk Power-pitch, hitting

Neuromuscular Function

Type I type IIA type IIB(Slow) (intermediate)

(fast)

2. Discuss the size principle.

Neuromuscular Function

3. What can alter the size principle?

Eccentric muscle contractions (muscle lengthening) can change the recruitment pattern.

Fast twitch can be recruited first, then the slow twitch if the speed of the exercise is moderate to fast.

Neuromuscular Function

4. What is the only direct way to determine muscle fiber type?

Muscle biopsy

Neuromuscular Function

5. How can we indirectly determine fiber type in a weight room?

Example: establish a 1RM of any exercise.lift 80% of 1RM as many times as possible.

7 or less reps most likely more than 50%FT fibers12 or more reps most likely more than 50% ST fibers

Limitation: can only be used for muscle groups. Why?

Neuromuscular Function

6. Since we cannot change our muscle fiber composition, how can we train our bodies to

become better at certain activities?

What we are born with is what we must live with.

You cannot increase the number of a specific fiber type but you can hypertrophy a specific type of fiber through specific

training , thus increasing the volume of that specific fiber type.

Neuromuscular Function

7. What are the training recommendations for the following?

Increase maximum strength:

Increasing maximum strength by stimulating muscle hypertrophy:

Increasing muscle size with moderate strength gains:

95% of 1RM, 1-3 rep range.

80% of 1RM, 5-8 rep range.

6-12 rep range.