Section 5 Final Flashcards
What is Fascia?
a sheath or broad band of fibrous connective tissue that is deep to the skin and surrounds muscles or other organs of the body
What are the two layers of fascia?
Superficial Fascia = Hypodermis
Deep Fascia
What are the layers in Deep Fascia?
Endomysium
Perimysium
Epimysium
What does the Endomysium surround?
surrounds individual muscle fibers
What does the Perimysium surround?
surrounds bundles of muscle fibers = Fascicle
What does the Epimysium surround?
surrounds individual muscles, EX: Trapezius
the outer most fascial layer
What is Muscle fiber?
= “muscle cells”
a syncytium which is a group of cells that fused to form one large structure, has many nuclei
What is the sarcolemma?
the plasma membrane that surrounds a muscle fiber
What is sarcoplasm?
the cytoplasm of muscle fibers
What are Myofibrils?
thread like filaments contained within a muscle fiber
the contractile element of muscles
What is the Sarcoplasmic Reticulum?
surrounds myofibrils
stores Calcium!!
What are the Transverse (T) tubules?
They connect the sarcolemma to sarcoplasmic reticulum
** are invaginations of the Sarcolemma that pass signals to the Sarcoplasmic Reticulum**
What is the sacromere?
the functional unit of a myofibril
List the sequence of events in muscle contraction
1.An Action Potential travels down the Axon towards the Neuromuscular Junction.
2.The Action Potential reaches the axon terminal and causes a synaptic vesicle to release neurotransmitter in to the Synaptic cleft, via exocytosis
- The synaptic vesicle is neurotransmitter enclosed in a lipid bilayer “packet”, Acetylcholine (ACh) is the neurotransmitter for skeletal muscle contraction
3.ACh diffuses across the synaptic cleft
4.ACh binds to a receptor on the motor end plate (i.e. the portion of the neuromuscular junction that is on the muscle)
5.ACh binding to the receptor produces an Action Potential which travels along the T-tubules toward the Sarcoplasmic Reticulum
6.The Action Potential signals the Sarcoplasmic Reticulum to release Calcium across the myofibrils
7.Calcium binds to Troponin. Tropomyosin is attached to Troponin. When calcium binds to Troponin the Tropomyosin slides across the Thin filament (Actin). This movement exposes the Myosin binding sites that are on the Thin filament.
8.The Myosin heads of the Thick filament can now approximate the Myosin binding sites.
9.ATP attaches to the Myosin head. ATP is split into ADP and phosphate. This activates the Myosin head.
10.The activated Myosin head binds to the Myosin binding site. The phosphate group is released.
11.The Myosin head flexes (Power Stroke) which draws the Thin filament towards the M line. ADP is released after the Myosin head is flexed.
12.The Myosin head remains attached to the Myosin binding site until another ATP attaches to it. The Myosin head is then released from the Myosin binding site, and becomes extended. It will then bind to another Myosin binding site. Steps 9, 10 and 11 are repeated until the signal from the neuron ceases.
Describe the TERMINATION of muscle contraction
- Acetylcholinesterase (an enzyme that deactivates ACh) in the Synaptic cleft continually breaks down ACh. If the signal to release ACh into the synaptic cleft ceases, the Action Potential in the muscle will cease.
- The Calcium pumps in the Sarcoplasmic Reticulum continuously pump the Ca++ around the myofibrils back into the Sarcoplasmic Reticulum.
- With no Ca++ to bind to Troponin, the Tropomyosin slides over the Myosin binding sites. The Myosin head now has nowhere to bind, thus muscle contraction ceases.
