Quiz #3 Flashcards
What is the role of the somatic nervous system?
control skeletal muscles
voluntary
What is the role of the autonomic nervous system?
control smooth and cardiac muscle
involuntary
What are the divisions of the autonomic nervous system?
sympathetic
- fight of flight
parasympathetic
- rest and digest
both innervate most effector organs in antagonistic ways
Describe autonomic neuron pathways.
2 neurons in series
1 preganglionic neuron can synapse with 8-9 postganglionic neurons at autonomic ganglion, each innervate a different target
What is a ganglia?
cluster of synapses
How do sympathetic and parasympathetic neurons differ?
sympathetic
- originate in thoracic and lumbar spinal cord, run down vertebrae
- preganglionic neuron is shorter (ganglia close to spinal cord)
parasympathetic
- most originate in brain stem and leave as cranial nerves, some originate near the sacral end of spinal cord
- 75% originate from vagus nerve
- preganglionic neuron is longer (ganglia close to target tissues)
Describe the chemicals used in autonomic chemical signalling.
PNS
- preganglionic neurons: ACh on nicotinic cholinergic
- postganglionic neurons: ACh on muscarinic cholinergic
SNS
- preganglionic neurons: ACh on nicotinic cholinergic
- postganglionic neurons: NE on adrenergic
What are the types of adrenergic receptors?
alpha and beta
alpha and beta 1 are excitatory, alpha and beta 2 are inhibitory, beta 3 stimulates fat cell lipolysis
What are varicosities?
the neuroeffector junction between postganglionic autonomic neuron and target cell
swollen areas at distal ends of axons
contain vesicles full of NT, released identical to typical synapse
What is the adrenal medulla?
specialized neuroendocrine tissue associated with SNS
sits ontop of kidney
secretes epinephrine into blood and target tissue
Where are some places that dual innervation does not occur (no PNS)?
adrenal medulla
sweat glands
most blood vessels
How many neurons innervate a single muscle fiber? How many muscle fibers can a single neuron innervate?
muscle fiber innervated by 1 neuron
neuron can innervated multiple muscle fibers
What are the components of somatic neuromuscular junctions?
axon terminals motor end plates - on muscle membrane - folds with many nicotinic receptors Schwann cell sheaths
Describe skeletal muscle.
large, multinucleated cells
appears striated
can shorten/contract to produce skeletal movement/maintain posture
Describe they layers of the skeletal muscle.
epimysium
- exterior collagen layer
- connected to deep fascia
- separate muscle from surrounding tissue
perimysium
- surrounds muscle fiber bundles (fascicles)
- contain blood vessel and nerve supply for fascicles
endomysium
- surrounds individual muscle fibers
- contains blood vessel and nerve supply that contact muscle cells
all come together at ends of muscle to form a tendon (bundle) or an aponeurosis (sheet)
What is the sarcolemma?
cell membrane specific to muscle
surrounds sarcoplasm, the cytoplasm of the muscle
What are T-tubules?
run perpendicular to cell organization, penetrating myofibrils
transmit AP through cell so entire fiber can contract simultaneously
What are myofibrils?
organization of protein filaments
- thick and thin
What are myofilaments?
individual thick (myosin) and thin (actin) filaments
responsible for muscle contraction
What is the sarcoplasmic reticulum?
membranous structure surrounding each myofibril
main source of calcium
form terminal cisternae
What are terminal cisternae?
regions with higher concentration of calcium
attached to T-tubules
release calcium into sarcomere to begin muscle contraction
What is a triad?
1 T-tubule and 2 terminal cisternae
What gives muscle its striated appearance?
parallel organization of myofibrils
What are sarcomeres?
contractile unit of muscle
Z line to Z line
List the structural components of a sarcomere.
A band H zone M line I band Z line
What is the A band?
- dark band
- full length of thick filament
What is the H zone?
- thick filaments
- no overlap
What is the M line?
- links thick filaments in the centre of the sarcomere
What is the I band?
- light band
- thin filaments
- no overlap
What is the Z line?
- links thin filaments
What is actin?
thin, contractile protein
holds myosin binding site
What is tropomyosin?
regulatory protein that overlaps myosin binding sites on actin
What is troponin?
regulatory protein that attaches to actin, tropomyosin, and calcium (reversibly)
calcium binding to troponin regulates skeletal muscle contraction
Describe the orientation of the thick myofilament.
myosin head is toward I band
myosin tail is toward M line
What is titin?
strands of elastic protein that extend from Z line to next M line
largest known protein
stabilizes position of contractile filaments/attaches them together
What are the mechanisms of force generation in a muscle?
sliding filament model
crossbridge cycle
excitation-contraction coupling
muscle cell metabolism
Describe the sliding filament model.
muscle shortens but neither thick or thin filaments shorten, they slide bast each other
Describe how the length of a sarcomeres’ regions change during contraction.
sarcomere - shortens
I band - shortens
H zone - shortens
A zone - remains the same
Describe the steps of the crossbridge cycle.
ATP is hydrolyzed, myosin is in high energy state, binds to actin
inorganic phosphate is released
powerstroke - actin pulled towards midline of sarcomere
ADP released
rigor - myosin in low energy form
new ATP binds to myosin
myosin and actin unbind
ATP hydrolyzed
cocking of myosin head
What is excitation contraction coupling?
sequence of events where an action potential causes contraction
steps:
ACh released from motor neuron, binds to receptors in motor end plate (end plate potential, triggers AP in muscle cells)
AP propagates along sarcolemma and down T-tubules
reachers DHP receptors on T-tubules that trigger ryanodine receptors to open
Ca2+ is released from SR into cytosol
Ca2+ binds to troponin, moving tropomyosin and exposing myosin-binding sites
crossbridge cycle begins, muscle contraction occurs
Ca2+ is actively transported back into SR
tropomyosin reblocks binding sites on actin, muscle fiber relaxes
What is a powerstroke?
movement of myosin head to propel thin filament in towards the muscle centre
In what ways does a contraction stop?
AChesterase degrades ACh in motor end plate, stops neural impulse in the muscle fiber, causes closure of T-tubule voltage gated Ca2+ channels, ending calcium supply
Ca2+ needs to be actively removed from cytoplasm
- requires ATP
Describe the roles of ATP in muscle contraction and relaxation.
cross-bridge formation
- bind to myosin heads to be hydrolyzed to enter high energy state
unbinding of actin and myosin
- rebinds to myosin head in low energy state so it unbinds from actin
power Ca2+ pump
- get calcium back into SR
What is rigor mortis?
state of muscular rigidity
begins 2-3 hours after death, lasts about 24 hours
Ca2+ ions leak out of SR and allow myosin and actin to bind
- no more ATP present so crossbridges cannot detach and ion pumps no longer function
- need enzymes to begin digesting decomposing cells
