Muscle and NMJ Flashcards
(14 cards)
explain the
-location, nuclei, length, shape, cross-striation, function and controlled by
for skeletal muscles
1) attached to skeleton
2) multinucleate
3) long up to few cm, 100um diameter
4)cells form fibres
5) have cross-striations (stripes)
6)for rapid contraction in one direction only
6)controlled by somatic nervous system
explain the
-location, nuclei, length, shape, cross-striation, function and controlled by
for smooth (involuntary) muscles
1)in walls of blood vessels and digestive system
2) single nucleus
3)500um
6) cells tapered at each end (spindle shaped/ come together)
7) for slow continuous contractions to keep tube contents moving (gut) or to open/ close blood vessels(recoil)
8)controlled by autonomic nervous system
explain the
-location, nuclei, length, shape, cross-striation, function and controlled by
for cardiac muscle
1)heart
2)single nucleus
3)50-100um
4)cells form long fibres which branch to form cross-bridges between fibres, cells joined by intercalated discs
5) have cross-striations
6)for heart contraction= squeezing acttion due to cross bridges spreading electrical stimulation evenly over chambers
7)myogenic but input from autonomic system (sympathetic and parasympathetic)
what are muscles and what do they respond to
-muscles are effectors and respond to nervous stimulation by contracting leading to movement
-their structure allows for rapid contraction
describe the structure of muscles
-bundle of muscle fibres= muscle cells
-striations: A band= actin and myosin, I band= actin
-many nuclei
-sarcolemma (plasma membrane)
-sarcoplasm (cytoplasm)
-sarcoplasmic reticulum (endoplasmic reticulum)= store of Ca2+
-T tubule/ transverse tubule
-sacromeres= actin/myosin filaments
which band is dark and which band is light
light band= I band
dark band= A band
what are t tubules, sarcoplasmic reticulum, myofibril, sarcomere
t-tubules= foldings of sarcolemma that reach into the sarcoplasm that reach into sarcoplasm help spread out electrical impulses throughout muscle fibre
sarcoplasmic reticulum= network of membranes inside the sarcoplasm that store and release Ca2+ ions for muscle contraction
myofibril= long cylindrical organelle found in sarcoplasm made up of specialised proteins used in muscle contraction
sarcomere= contractile unit within a myofibril
which two types of proteins are myofibrils made of
actin and myosin
why do myofibrils appear to be stripy
due to the dark band made of actin and myosin and light band made of just actin
what is a neuromuscular junction and explain how it is a specialised cholinergic synapse
NMJ= junction between nerves (motor neurones) and muscles
-work the same way as cholinergic synapse but differ in:
1. post-synaptic membrane has lots of folds that form clefts, inside store of acetylcholinesterase to break down acetylcholine
2. post-synaptic membrane has more receptors than other synapses= when motor neurone fires an action potential it ALWAYS triggers a response in muscle cells (no threshold)
explain the synaptic transmission across a neuromuscular junction
1.an action potential travels the length of the axon to motor neurone axon terminal at the motor end plate of a skeletal muscle
2.voltage gated Ca2+ channels open and Ca2+ diffuse into the terminal
3. Ca2+ entry causes synaptic vesicles to release acetylcholine via exocytosis
4. acetylcholine diffuses across the synaptic cleft and binds to acetylcholine receptors on sarcolemma
5.this opens sodium ion channels, allowing Na+ to enter the muscle fibre= causes depolarisation of sarcolemma
6.wave of depolarisation spreads along the sarcolemma and down t tubule into the muscle fibre stimulating muscle contraction
neural transmission to a muscle fibre ceases when acetylcholinesterase breaks down acetylcholine in synaptic cleft
what is a motor unit
a single neurone and the muscle fibres it attaches to
how are speed and strength of contraction controlled
-brain determines the number of motor units in a muscle that contract as well as the rate that impulses are sent to the motor units
if slight force required= few motor units are stimulated
if greater force required= large number of motor units are stimulated
what kind of traces show electrical activity in muscles and how
-electromyogram (EMG)
-positive and negative electrodes placed on the skin of the forearm measure changes in electrical potential when the finger muscles contract
-amplitude reflects the number and size of active motor units
