autonomic and somatic motor control Flashcards
(160 cards)
1
Q
autonomic nervous system
A
reflecting its control over involuntary functions and internal organs
2
Q
sympathetic branch
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associated with the fight or flight, preparing the body for stressful situations by increasing heart rate, dilating blood vessels to muscles and producing glucose
3
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hypothalamus
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mediates the total-body response in fight or flight situation
4
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where is sensory information from somatosensory and visceral receptors sent?
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to homeostatic control centers in the hypothalamus, pons and medulla (regulates blood pressure, temperature, and water balance
5
Q
what receptors does the hypothalamus contain to monitor osmolarity and the body temperature
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osmoreceptors and thermoreceptors
6
Q
where does nicotine bind to
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nictotinic acetylcholine receptors
7
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walter cannon’s properties of homeostasis
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preservation of internal environment fitness, up-down regulation by tonic control, antagonistic control, and chemical signals with different effect in different tissues (sympathetic and parasympathetic branches exhibit this)
8
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sympathetic innervation
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increases heart rate
9
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parasympathetic stimulation
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decreases heart rate
10
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all autonomic pathways consist of two neurons
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the preganglionic neuron and the postganlionic neuron
11
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postganglionic neuron
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has its cell body in the ganglion and projects its axon to the target tissue
11
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preganglionic neuron
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originates in the CNS and projects to an autonomic ganglion outside the CNS
12
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ganglion
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is a cluster or nerve cell bodies outside the CNS while the nucleus is the equivalent structure within the CNS
13
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divergence is a key feature of autonomic pathways
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where one preganglionic neuron can synapse with multiple postganglionic neurons, allowing a single CNS signal to affect many target cells
14
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sympathetic pathways originate in
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the thoracic and lumbar regions of the spinal cord
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sympathetic ganglia
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are located in two chains along either side of the vertebral column and along the descending aorta, they have short preganglionic neurons and lost postganglionic neurons
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parasympathetic originates
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in the sacral region and control pelvic organs
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parasympathetic ganglia are located
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near their target organs, resulting in long preganglionic axons and short postganglionic axons; targets the head, neck and internal organs
18
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the vagus nerve
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(cranial nerve X) is the major parasympathetic tract, containing about 75% of all parasympathetic fibers; carries sensory information from internal organs to the brain and parasympathetic output from the brain to organs
19
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vagotomy
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the surgical cutting of the vagus nerve, was historically used to study the autonomic nervous system effcts
20
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mixed nerve
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a nerve that carries both sensory and motor information
21
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what are the four regions of the spinal cord
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cervical, thoracic, lumbar, and sacral
22
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both sympathetic and parasympathetic preganglionic release
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acetylcholine (ACh) onto nicotinic cholinergic receptors (nAChR) on the postganglionic cell
23
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what do most postganglionic sympathetic neurons secrete
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norepinephrine (NE) onto adrenergic receptors on the target cell
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what do most postganglionic parasympathetic neurons secrete
acetylcholine onto muscarinic cholinergic receptors (mAChR) on the target cell
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sympathetic cholinergic neurons
sympathetic postganglionic neurons those terminating on sweat glands, secret ACh instead of norepinephrine
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nonadrenergic, noncholinergic neurons are classiffied as sympathetic or parasympathetic based on
the origin of their preganglionic fibers
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autonomic neurons target
smooth muscle, cardiac muscle, exocrine glands, some endocrine glands, lymphoid tissues, the liver, and some adipose tissue
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neuroeffector junction
the synapse between a postganglionic autonomic neurons and its target cell
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autonomic synapses vs. synapses
postganglionic axons end in a series of swollen areas called varicosities
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varicosities
contain vesicles filled with neurotranmitters
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preganglionic neurons
may co-secrete neuropeptides with acetylcholine, acting as neuromodulators to produce slow synaptic potentials and modify postganglionic neuron activity
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adrenal medulla
specialized neuroendocrine tissue associated with the sympathetic nervous system
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the adrenal medulla
forms the core of the adrenal glands, which are located atop the kidneys
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each adrenal gland consists of two parts
the adrenal cortex (secretes steroid hormones) and the adrenal medulla (secretes epinephrine)
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the adrenal medulla
develops from the same embryonic tissue as sympathetic neurons and is considered a neurosecretory structure
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chromaffin cells
lack axons, secrete the neurohormone epinephrine into the blood
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the release of epinephrine by the adrenal medulla is part of the body's
fight or flight response to alarm signals from the CNS
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direct agonists and anatgonists
interact with target receptors to mimic of block neurotransmitter action
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indirect agonists and antagonists alter
neurotransmitter secretion, reuptake or degradation (EX: cocaine blocks norepinephrine reuptake, extending its excitatory effect and potentially causing heart attacks due to sympathetic induce vasocontriction) (antidepressants are indirect agonists)
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cholinesterase inhibitors (anticholinesterases) block ACh degradation, extending the active life of ACh molecules.
symptoms include excessie stimulation of autonomic and somatic motor target tissues
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selective serotonin reuptake inhibitors (SSRIs)
have fewer autonomic side effects compared to older antidepressants (newer antidepressants may influence both norepinephrine and serotonin action)
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somatic motor pathways
control skeletal muscles and differ from autonomic pathways in both anatomy and function
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somatic motor pathways consists of a
single neuron originating in the CNS that projects its axons to the target tissue, which is always a skeletal muscle
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somatic pathways are always
excitatory, whereas ANS can be either excitatory or inhibitory
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the cell bodies of somatic neurons are located in
the ventral horn of the spinal cord or in the brain
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these neurons have a
long single axon that projects to the skeletal muscle target
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somatic motor neurons branch near
their targets, with each branch dividing into a cluster of enlarged axon terminals on the surface of skeletal muscle fibers (enables a single motor neuron to control muscle fibers simultaneously)
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neuromuscular junction (NMJ)
is the synapse between a somatic motor neuron and a muscle fiber
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NMJ consists of three main components:
the presynaptic axon terminal of the motor neuron, the synaptic cleft, and the postsynaptic membrane of the skeletal muscle fiber
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the presynaptic axon terminal contains
synaptic vesicles and mitochondria
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what is essential for the formation and maintenance of NMJs
schwann cells to cover the axon terminals and secret chemical signal molecules
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the postsynaptic membrane
has folds resembling shallow gutters
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nicotinic ACh receptor (nAChR) channels
are clustered in an active zone along the upper edge of each fold
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the synaptic cleft
is filled with a fibrous matrix containing collagen fibers that align the axon terminal and motor end plate
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the matrix
also contains acetylcholinesterase (AChE), an enzyme that deactivated acetylcholine (ACh) by braking it down into acetyl and choline
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skeletal muscles make up
about 40% of total body weight and are responsible for positioning and moving the skeleton
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skeletal muscles are attached to bone by..
tendons made of collagen
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the origin of the muscle
is the end attached closest to the trunk or the more stationary bone
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the insertion is
the more distal or mobile attachment
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contraction of skeletal muscles
moves the skeleton when the bone are connected by flexible joint
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a muscle is called a flexor
if it brings the centers of connected bones closer together during contraction, resulting in flexion
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a muscle is called an extensor
if it moves the bones away from each other during contraction, resulting in extension
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antagonistic muscles
both have flexor and extensor muscles that exert opposite effects (bicep is flexor and tricep is extensor)
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skeletal muscles are composed of
muscle fibers that are collections of muscle cells
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each skeletal muscle fiber
is a long, cylindrical cell with multiple nuclei located near the surface. and are the largest cells in the body, formed by the fusion of many embryonic muscle cells
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satellite cells, which are committed stem cells, reside just outside the muscle fiber membrane
activate and differentiate into muscle cells when requires for muscle growth and repair
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muscle fibers
in a muscle are arranged with their long axes in parallel, and each skeletal muscle fiber is encased in connective tissue
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fascicles
groups of adjacent muscle fibers bundled into units
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what is located between the fascicles?
collagen, elastic fibers, nerves and blood vessels
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the entire muscle is enclosed in
a connective tissue sheath
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connective tissue sheath
is continuous with the connective tissue around the muscle fibers and fascicles, as well as the tendons that attach the muscle to bones
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sarcolemma
the cell membrane of a muscle fiber
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sarcoplasm
is the cytoplasm
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myofibrils
are highly organized bundles of contractile and elastic proteins within striated muscles that facilitate contraction
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skeletal muscle fiber contain extensive sarcoplasmic reticulum (SR),
a modified endoplasmic reticulum that wraps around each myofibril
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SR consists of
longitudinal tubules with enlarged end regions called terminal cisternae
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cisternae
concentrate and sequester Ca2+ using Ca2+ ATPase in the SR membrane
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what is crucial for muscle contraction?
calcium release from the SR
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transverse tubules (t-tubules)
continuation of the muscle fiber membrane, which makes the lumen of t-tubules continuous with the ECF
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t-tubules enable
action potentials to reach the terminal cisternae quickly ensuring a prompt muscle fiber response
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the cytosol between myofibrils contains
glycogen granules and mitochondria, providng energy for muscle contraction through oxidative phosphorylation
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myofibrils
composed of repeating units called sarcomeres, include myosin, actin, tropomyosin, troponin, titin, and nebulin
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myosin
is a motor protein with heavy and light chains; heavy chains form heads, tails, and a hinge neck region.
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myosin heads
have ATPase activity and actin-binding sites
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actin
forms thin filaments from G-actin molecules polymerizing in to F-actin chains, with twist together
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myosin crossbridges
connect thin and thin filaments with states of low-force (relaxed) and high-forced (contracting)
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sacromeres are the contractile units of myofibrils, consisting of
Z disks I bands, A bands, H zone, M line
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Z disks
attachment sites for thin filaments
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I bands
light bands with only think filaments, bisected by Z disks
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A bands
dark bands with the entire length of thick filaments, overlapping with thin filaments at the edges
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H zone
lighter central region of the A band with only thick filaments
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M line
Attachment site for thick filaments dividing the A band in half
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each thin filament is surrounded by
three thick filaments, and each thick filament is encircled by six thin filaments
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titin stabilizes
the position of contractile filaments and its elasticity returns stretched muscles to their resting length
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titin
is a huge elastic molecule, the largest known protein, composed of more than 25,000 amino acids, stretching from one Z disk o the neighboring M line
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nebulin
is an in elastic giant protein that lies alongside thin filaments and attached to the Z disks, helping to align the actin filaments of the sacromere
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muscle tension
is the force created by contracting muscle fibers, while the load is the weight or force of opposing the contraction
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contraction
is an active process requiring ATP to create tension in a muscle, whereas relaxation is the release of this tension
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what is the process of muscle contraction ?
events at the neuromuscular junction convert an acetylcholine signal from a somatic motor neuron into an electrical signal in the muscle fiber. excitation contraction (E-C) coupling translates muscle action potentials into calcium signals, which then initiate a contraction-relaxation cycle. the sliding filament theory explains the contraction-relaxation cycle at the molecular level, where one cycle intact muscles is termed a muscle twitch
96
the sliding filament theory
is fundamental to understanding muscle contraction, followed by the integrated function of muscle fibers during excitation-contraction coupling. (where fixed-length actin and myosin filaments slide past each other, requiring energy, to cause muscle contraction)
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in a resting sacromere
thick and thin filaments overlap slightly, with a large I band (thin filaments only) and a A band (length of thick filament)
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during contraction
the Z disks move closer, the I band and H zone nearly disappear , but the A band length remains constant, indicating sliding of actin filaments along myosin filaments
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what does the sliding filament theory explain?
it explains muscle contraction and force generation without movement, as tension in a muscle fiber is proportional to the number of high force crossbridge between thick and thin filaments
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myosin crossbridges generate
force by pushing actin filaments during muscle contraction (myosin heads binds to actin molecules)
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what does a calcium signal trigger
the power stroke, causing myosin crossbridges to swivel and push actin filaments toward the sacromere center
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what happens after the power stroke
myosin heads release actin, swivel back and bind to new actin molecules to start another cycle
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myosin heads do not release
simultaneously to prevent fibers from sliding back to their starting position
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the energy for the power stroke in muscle contraction comes from
ATP
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myosin acts as what?
ATPase, hydrolyzing ATP into ADP and inorganic phosphate (Pi)
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the energy released from ATP hydrolysis is stored as
potential energy the angle between the myosin head and the myosin filament
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the potential energy in the cocked myosin heads in converted into what??
kinetic energy during the power stroke, which moves actin
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Troponin (TN)
is a calcium binding complex of three proteins that controls the position of tropomyosin
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tropomyosin
is an elongated protein polymer that wraps around actin filaments and partially covers actin's myosin binding sites, preventing myosin from completing its power stroke
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what must happen for muscle contraction to occur
tropomyosin must shift to an "on" position, uncovering actin's myosin-binding sites
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what can cause calcium troponin C complex to pull tropomyosin away from actin's myosin-binding sites
when a calcium signal initiates contraction
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when does muscle relaxation occur?
when cytosolic Ca2+ concentrations decrease, causing Ca2+ to unbind from troponin
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calcium is now know to be
a nearly universal second messenger in various cellular processes
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the contractile cycle in skeletal muscle begins with
the rigor state, where myosin heads are tighlt bound to G-actin molecules without any nucleotide (ATP or ADP bound to myosin)
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ATP binds to the myosin head...
decreasing actin binding affinity causing myosin to release from actin
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ATP hydrolysis occurs, providing energy
for the myosin head to rotate and reattach to actin
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at the end of the power stroke...
myosin releases ADP, returning to the rigor state, ready to start a new cycle with the binding of a new ATP molecule
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rigor state is brief because...
ATP quickly binds to myosin after ADP is released
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rigor mortis
is where ATP supplies are exhausted, where muscles remain in the rigor state to due immovable crossbridges. this persists until enzymes from decaying fibers break down muscle proteins
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what is f-actin (filamentous actin)
is a polymerized form of G-actin (globular actin)
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Acetylcholine (ACh)
is released from the somatic motor neuron and binds to ACh receptor-channels on the motor end plate of the muscle fiber initiating an action potential
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the opening of ACh-gated channels allows both
Na+ and K+ to cross the membrane, with Na+ influx exceeding K+ efflux due to a greater electrochemical driving force for Na+ (results in depolarization)
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the depolarization creates
an endplate potential (EPP), which typically reaches the threshold to initiate a muscle action potential
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the muscle action potential trigger calcium release from the sacroplasmic reticulum,
and calcium combines with troponin to initiate muscle contraction
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excitation-contraction coupling and relaxation
- the action potential travels across the muscle fiber surface and into the t-tubules through the sequential opening of voltage gated Na+ channels
- it triggers Ca2+ release from the sarcoplasmic reticulum, increasing free cytosolic Ca2+ levels about 100 fold
- leads to muscle contraction
- the electrical signal is transduced into a calcium signal via two key membrane proteins: the voltage sensing L-type calcium channel protein and the Ca2+ channels (facilitating the release of Ca2+)
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to end muscle contraction...
calcium must be removed from the cytosol
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what pumps back calcium into its lumen used a Ca2+ - ATPase?
the sacroplasmic reticulum
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as the free cytosolic Ca2+ concentration decreases...
the equilibrium between bound and unbound Ca2+ is distrubed, leading to the release of calcium from troponin
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the removal of Ca2_ allows tropomyosin
to slide back and block actin's myosin binding site
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the release of cross bridges and the action of elastic fibers in the sacromere and connective tissue
help the muscle fiber relax
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the sequence of events in excitation-contraction (E-C) coupling starts with
a somatic motor neuron action potential, followed by a skeletal muscle action potential and then muscle contraction
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a twitch
a single contraction-relaxation cycle in a skeletal muscle fiber
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there is a latent period between the muscle action potential and
the onset of muscle tension, representing the time needed for calcium release and binding to troponin
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muscle tension
increases to a maximum during contraction as crossbridge interactions rise, the decreases during the relaxation phase as elastic elements return sarcomeres to their resting length
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a single action potential in a muscle fiber triggers
a single twitch
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muscle twitches differ
among fibers in the speed of tension development, maximum tension achieved, and twitch duration
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single twitch tension is determined by
the length of the sarcomere but does not represent the maximum force a muscle fiber can develop
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the force generated by a single muscle fiber can be increased by
increasing the frequency of muscle action potentials
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if action potentials are separated by long intervals,
the muscle fiber relaxes completely between stimuli
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shorter intervals between action potentials prevent complete relaxation,
resulting in a more forceful contraction, a process known as summation
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tetanus
repreated high frequency action potential, a state of maximal contraction
- incomplete (unfused) tetanus occurs when the muscle fiber does not relax at all
- complete (fused) tetanus occurs when the muscle fiber does not relax at all, reaching and maintaining maximum tension
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muscle action potentials are initiated
by the somatic motor neuron controlling the muscle fiber
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the motor unit is the basic unit of contraction in skeletal muscle
consisting of a somatic motor neuron and the muscle fibers it controls
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when a somatic motor neuron fires an action potential,
all muscle fibers in its motor unit contract simultaneously
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each muscle fiber is innervated by only one neuron,
but a single neuron can innervate multiple muscle fibers
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the number of muscle fibers in a motor unit varies:
fine motor action (eye movements) have motor units with as few as 3-5 fibers, which gross motor actions (walking) have motor units with hundreds or thousands of fibers
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fine motor units allow for small, precise movements,
while gross motor units result in larger, more powerful movements
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fast twitch fibers are associated with activities requiring quick bursts of energy
(sprinting, weight lifting)
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slow-twitch fibers are suited for endurance activities
(distance running)
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endurance training increases...
the number of capillaries and mitochondria in muscle tissue, improving oxygen delivery and aerobic capacity.
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maximum force is acheived when
the highest-threshold neurons activate glycolytic fast twitch fibers which fatigue quickly
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sustained muscle contractions require
continuous action potentials from the central nervous system
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summation of contraction can lead to
fatigue in easily fatigued muscle fibers
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asynchronous recruitment of motor units helps prevent
fatigue in submaximal, contractions by alternating active motor units
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alternation of motor units results in a
smooth overall contraction, but fatigue eventually reduces the force of contraction
