Muscle Histology Flashcards
One muscle type that is consciously controlled
skeletal muscle
T/F: skeletal muscle doesn’t have to cross a joint
False
ALL skeletal muscles must cross a joint in order to create movement
functions of skeletal muscles
- body movement
- posture
- respiration
- production of body heat
- communication
4 basic properties of muscles
- CONTRACTILITY
- EXCITABILITY (capacity to respond to a stimulus by producing action potentials. In SM, always neurons)
- EXTENSIBILITY (can be stretched beyond resting length and still contract)
- ELASTICITY (ability to recoil)
muscles cells are also known as…
muscle fibres
skeletal muscle structure
- Composed of fibres, CT, blood vessels, nerves
structure of muscle fibres
- long
- cylindrical
- multinucelated
- striated proteins
why are muscle cells multinucleated?
myoblasts fused together to form single muscle cells
how does muscle attach onto bone
via tendons (dense regular collagenous CT)
that attach to periosteum (dense irregular collagenous CT)
what are muscle fibres surrounded/separated by?
ENDOMYSIUM
(loose areolar CT)
bundles of muscle cells (fibres) are called…
fascicles
what holds a single fascicle together?
PERIMYSIUM
What bundles all fascicles together?
- EPIMESIUM
- FASCIA (surrounds groups of muscles)
layer of connective tissue in muscle (outside to inside)
- fascia (surrounds groups of muscles)
- epimysium (surrounds muscles)
- perimysiuum (surrounds fascicles)
- endomysium (surrounds muscle fibres)
each muscle cell gets _ connection to a neuron
ONE
allows for 1 neuron to contract many cells at the same time
synapse between neuron and muscle cell
neuromuscular junction
muscle fibre structure
- SARCOLEMMA (plasma membrane, where AP occur)
- SACROPLASIM
- SACROPLASMIC RETICULM (stores calcium)
- MYOFIBRILS (long cylindrical groups that contain MYOFILAMENTS actin and myosin)
- TRANSVERSE TUBULES (surround myofibrils, connect to sarcolemma, allow APs to move through cell)
- nuceli
- mitochondria
structure of myofibril
highly organized pr-
- SARCOMERES along length contain MYOFILAMENTS (actin + myosin) separated by Z disks
name and function of enlarged regions of saroplasmic reticulum near transverse tubule
TERNIMAL CISTERNAE
- store calcium to release into myofibrils when AP occurs
thick filament and thin filament
thick: myosin
thin: actin
sarcomeres
units of contractile pr- that are connected in series along the length of the muscle
What connects pr- in sarcomeres to outside of cell?
dystrophin pr- connects to membrane pr- in sarcolemma that connects to larger CT
M line
“middle line” of sarcomere
Z disks
- ends of sarcomeres
- z-shaped proteins
- attached to actin
titin
- gives muscles elasticity
- pulls z disks closer to m line
- ends: coiled, connected to z disk
- middle: straight, connected to m line
longest protein in body!
actin myofilament structure + function
Structure:
- double helix shape
- F-ACTIN molecules (string) made of G-ACTIN molecules with ACTIVE SITES that can bind to myosin
Regulatory proteins
- TROPOMYOSIN (string-like)
- TROPONIN (binds to G actin, Ca2+ and tropomyosin)
Function
Ca2+ binds to troponin, pulls tropomyosin away from active sites on G actin so actin can bind to myosin via CROSS BRIDGE
Myosin myofilament structure + function
Structure:
Rod
- 2 myosin heavy chains
Head
- myosin heads (attaches to actin via cross bridge)
- myosin light chains attached
-myosin ATPase
In between
- hinge region
Sarcomere organization (bands)
- z disk
- M line
- I band (only actin and z disk)
- H zone (only M line and myosin, no actin)
- A band (myosin length)
*A bands won’t change size, but H zone and I band can depending on actin-myosin overlap zones
connection between action and myosin
cross bridge
explain NMJ functioning starting with AP
- Action potential arrives at presynaptic terminal, voltage-gated calcium channels open
- Ca2+ enters presynaptic terminal, release of acetylcholine from synaptic vesicles
- ACh diffuses across syaptic cleft and binds to ACh receptors on motor end plate, increasing permeability of ligand-gated sodium channels
- Na+ into postsynaptic membrane= depolarization
- Once threshold has been reached an action potential results, AP moves in all directions AWAY from NMJ
- ACh broken down in synaptic cleft by acetylcholinesterase (into acetic acid and choline)
- Choline is reabsorbed by presynaptic terminal and combined with acetic acid to form more ACh in synaptic vesicles
Acetic acid is taken up by many cell types
How does muscle contraction occur, starting with the delivery of an action potential in a presynaptic bulb of a NMJ?
- AP travels along axon membrane to a NMJ
- Voltage gated Ca2+ open, Ca2+ into presynaptic terminal
- Acetylcholine released from presynaptic vessicles
- Ach stimulates ligand gated Na+ channels on motor end plate
- Na+ into muscle fibre, depolarization, stimulates AP that travels along sarcolemma and into transverse tubules
- AP causes opening of voltage gated Ca2+ channels in terminal cisternae, Ca+ released
- Ca2+ binds to troponin, tropomyosin moves away from active site on G-actin molecule
- ATP on myosin heads broken down into ADP and P, which release energy needed to move myosin heads
- P released to form cross bridge
- ADP released for power stroke
- ATP releases myosin head from binding site
- ATP hydrolyzed to bring myosin head to ready position
*as long as Ca+ present, cycle repeats
