Midterm unit 6 Flashcards
functions of skeletal muscle
move the body, maintain posture, protect and support, regulate elimination of material, produce heat
contractible
Can shorten in length. Cells slide past one another.
Extensible
extend or stretch. This is possible because the contractile proteins slide past one another to decrease their degree of overlap
Elastic
return to original shape. This is dependent on the release of tension in the springlike protein associated with contractile proteins
Skeletal muscle contain
Epimysium and fascicle
Epimysium
a layer of dense irregular CT. PROTECTS AD SUPPORT IT LIKE A TOUGH LEATHER SLEEVE
Perimysium
a layer of dense irregular tissue that provides protection over each bundle of muscle fibres (goes around each fascicle)
Fascicle
a bundle of skeletal muscle fibers
What is fascicle composed of
Muscle fibre and perimysium
Sarcolemma
-This is the plasma membrane. The deep invagination are called T-Tubules. These channels include both na+ and k+. Contain volatge-gated sodium and k+. Extend into the skeletal muscle fibre as a network of narrow membranous tubules
Myofibrils
-* 80% is composed of long cylindrical structures termed myofibrils
* Composed of bundles of contractile proteins called myofilaments and enclosed in portions of sarcoplasmic reticulum
* a skeletal muscle fibre is composed of myofibrils, myofibrils are composed of myofilaments enclosed within segments of the sarcoplasmic reticulum
* Hundreds of thousands
* Composed of bundles of myofilaments and is enclosed in portions of the sarcoplasmic reticulum
Sarcoplasmic Reticulum:
is the internal membrane complex that is similar to the smooth endoplasmic reticulum of other cells.
* Portions of SR fit around each myofibril like a sleeve of membrane
* At the end of individual sections the sarcoplasmic reticulum are blind sacs called terminal cisternae
* Together 2 terminal cisternae and a centrally located T-tubule form a structure called a triad which contains voltage sensitive calcium which are responsive to electrical signals
* Also embedded in is calcium channels from the cytosol into the sarcoplasmic reticulum where it is bound to specialized protein callled calmodulin
Sarcoplasm
this is the continuation of the sarcolemma
Sarcomeres
the basic contractile unit of a myocyte (muscle fibre). A sarcomere is composed of two main protein filaments (thin actin and thick myosin filaments) which are the active structures responsible for muscular contraction. (the muscle contraction)
Thin filament
1/2 diameter
-2 strands of actin twisted together’-F-actin resembles 2 beaded necklaces with G as the individual beads
-Each has a myosin binding site
-attaches during contraction
-Tropomyosin and troponin are regulatory proteins associated with thin filaments. Together they form the troponin-tropomyosin complex.
-Tropomyosin is a short thin twisted filament that is a string like protein
-Troponin is a globular or ball like protein attached to troponin, contains binding sites for Calcium
thick filament
-200-500 myosin proteins
-each has 2 strands
-each strand has a globular head and an elongated tail
-Head contains a binding site for actin also has a catalytic ATPase site where ATP attached and is split into ADP and Phosphate
-tails are intertwined
I band
Extends from both directions of the Z disc. The end region contains only thin filaments. can only be viewed with a microscope.
A bands
central region of sarcomere that contains the entire thick filament. Thin filament partially overlap the thick filaments on each end. Appears dark. Does not lengthen during contraction.
H zone
The most central portion of the A band. No thin filament overlap. Disappears when at full shortening
M line
transverse protein meshwork in the center of H zone. Serves as a sit for thick filaments and keeps the thick filaments during contraction and relaxation events
Z disc
COMPOSED OF SPECIALIZED PROTEINS THAT ARE POSITIONED PERPENDICULAR TO THE MYOFILAMENTS AND SERVE AS ANCHORS FOR THE THIN FILAMENTS
ACTIN
MADE UP IN THIN FILAMENTS
Myosin
made up of thick filaments
Regulatory proteins
Troponin
Tropomyosin
Troponin
A ball like protein attached to tropomyosin. Troponin contains the binding site for calcium
Tropomyosin
a short, thin, twisted filament that is a stronglike protein. Consecutive molecule cover small region of the actin strands including the myosin binding
Structural proteins
Connective, nebula, dystrophin
connective (Titian)
- is a cable like protein that extends from the Z discs to the M line through the core of each thick filament maintains thick filament.
- Stabilizes thick filament.
- Spring like
Dystrophin
- Anchors myofibrils that are adjacent to proteins
- Genetic disorder called muscular dystrophy is caused by abnormal structure or amounts of dystrophin protein
Nebulin
n addition to a major role in thin-filament length specification, nebulin also functions in the regulation of muscle contraction, as indicated by the findings that muscle fibers deficient in nebulin have a higher tension cost, and develop less force due to reduced myofilament calcium sensitivity and altered
Neuromuscular junction
the specific location, usually in the mid-region of the skeletal muscle fibre where it is innervated by a motor neuron
Synaptic knob
- Expanded tip of an axon
- Where the axon nears the sarcolemma of a muscle fibre the synaptic knob enlarges and flattens to cover relatively large surface area
- Houses numerous synaptic vesicles (small membrane sacs) filled with the neurotransmitter acetylcholine (Ach) repelllled from the synaptic knob
- Ca2+ pumps are embedded in the plasma membrane of the synaptic knob. Prior to arrival of nerves the plasma knob pumps Ca2+ and establishes a concentration gradient with more Calcium outside then inside
- Voltage gated Ca2+ channels are embedded in the membrane of the synaptic knob. Opening these channels allows Ca2+ to flow down the concentration gradient from the intersitial fluid into synaptic knob which triggers exocytic of Acetylcholine from vesicles
Motor endplate
- Large plate like
- Numerous flods and indentations
- Has vast numbers of Ach receptors
- Chemically gated ion channel
- Binding of Ach opens these channels allowing Na+ to enter into the muscle fibre and K= exits
ACh is the key to opening doors
Synaptic cleft
- Extremely narrow fluid filled space separating the synaptic knob and the motor end plat
- Filled with fluid that separates the synaptic knob and the end plate
- Acetylcholinesterase (AChE) resides within the synaptic cleft
- It breaks down the Ach molecules and follows them into their release into the synaptic cleft
Acetylcholine (ACh)
found in the synaptic knob. They are normally repelled from the synaptic knob plasma membrane (ACH) channel chemically gated ion channels. Binding of ACH allows sodium to enter muscle fibre and K+ to exit
Acetylcholinesterase (
