Transcript Muscular System

Muscular System Part 2
adapted from www.biologycorner.com
Review
Behavioral Properties of Muscle
• Extensibility: ability to be stretched
• Elasticity: the ability to return to normal
after being stretched
• Irritability: ability to respond to stimuli
(like a nerve impulse)
• Contractility: ability to shorten
Tension and Types of Contractions
A contraction is when tension has developed in a muscle
Using biceps and triceps and action of flexing as examples
Agonist: prime mover
Antagonist: opposing muscle group
•
•
•
Concentric: when muscle develops tension and shortens;
tension in biceps when flexing
Eccentric: when muscle develops tension but weight being
lifted is too heavy so gravity, not triceps, lengthens biceps
Isometric: tension in both agonist and antagonist (biceps
and triceps) is equal; no change in muscle length
How Muscles Work with the Nervous System
NEUROMUSCULAR JUNCTION - where a nerve
and muscle fiber come together
Motor Unit or Neuromuscular Junction
1. Neuron
3. Vesicle
2. Sarcolemma (or motor end plate)
4. Synapse
5. Mitochondria
The neurotransmitter that crosses the gap is ACETYLCHOLINE.
This is what activates the muscle.
Acetylcholine is
stored in vesicles
SLIDING FILAMENT THEORY (MODEL)
The theory of how muscle contracts is the sliding filament
theory. The contraction of a muscle occurs as the thin
filament slide past the thick filaments. The sliding filament
theory involves five different molecules and calcium ions.
The five molecules are:
myosin
actin
tropomyosin
troponin
ATP
ANIMATION OF SLIDING FILAMENT
http://www.blackwellpublishing.com/matthews/myosin.html
Sarcomere in a relaxed Muscle Cell
What will happen to each part of the sarcomere when the
muscle contracts?
Energy Source
-ATP is produced by CELLULAR RESPIRATION
which occurs in the mitochondria
-Creatine phosphate increases regeneration of ATP
* Only 25% of energy
produced during cellular
respiration is used in
metabolic processes - the
rest is in the form of HEAT.
- maintains body
temperature.
Terms
Acetylcholine: neurotransmitter for skeletal muscle that
carries the message to contract across the synaptic cleft.
Synaptic vesicles: They are in the axonal terminal and hold
the acetylcholine until it is released
Calcium ions: Is stored in the sarcoplasmic reticulum. When
released it removes the blocking proteins from the actin and
myosin so they can slide across each other, causing
contraction.
Sarcoplasmic reticulum: Stores the calcium ions.
Actin and Myosin: are contractile proteins in the muscle cell
that slide across each other resulting in muscle contraction
1. Threshold Stimulus
Minimal strength required to cause a contraction
Motor neuron releases enough acetylcholine to
reach threshold
2. All-or-None Response
Fibers do not contract partially, they either do or
don't
3. Motor Unit
The muscle fiber + the motor
neuron
4. Recruitment
more and more fibers contract as
the intensity of the stimulus
increases
5. Muscle Tone
Sustained contraction of individual
fibers, even when muscle is at rest