8. Muscle/ANS Flashcards
3 types of muscle
- skeletal muscle
- cardiac muscle
- smooth muscle
skeletal muscles purpose
used for posture and locomotion, enabling our arms and legs to contract under voluntary control
cardiac muscles purpose
responsible for rhythmic contractions of the heart
smooth muscles purpose
cause involuntary contraction in blood vessels, gut, bronchi, uterus etc…
tendon
attaches muscle to bone
joint
point where two bones meet, where tendon is attached
skeletal muscle contraction tendons/joint
contraction pulls on tendons, which pull on joint, causing the flexion of joints
muscle fiber is aka
muscle cell
muscle cell
long, thin cells extending throughout the entire muscle
fascicle
bundle of muscle fibers
skeletal muscle characteristics
- multinucleated
- striated: highly ordered structure
how is the highly ordered structure of muscle fibres beneficial?
allows for simultaneous contraction of muscle fiber
why are muscle fibers multinucleate?
they originate from myoblasts (1 nucleus each) which fuse together
advantage of multinucleation
- multiple sites of mRNA and protein synthesis
- more copies of a gene = more proteins generated
myofibrils
long, thin fibers made of proteins, found in muscle fiber
I band corresponds to
light band, thin filaments
A band corresponds to
overlap between thick and thin filaments
Z line is
the dark strip in middle of the I band
sarcomere
- the distance between 2 Z lines
- contractile unit of skeletal muscle
sarcomere contracts –>
myofibril contracts –> muscle fiber contracts
M line
in middle of A band, holding thick filaments together
the I band contains only
thin filaments
the H zone contains only
thick filaments
where is the H zone?
in the middle of A band
crossbridges
myosin head groups extending out from thick filaments, interacting with thin filaments
where do thick and thin filaments overlap?
dark A band zone
each thick filament is surrounded by…
6 thin filaments
each thin filament is surrounded by…
3 thick filaments
thin filaments are made of?
actin -> 2 chains of globular actin subunits
thick filaments are made of?
myosin -> 2 myosin bundles brought together with heads in opposite directions
actin:
small globular + soluble protein which can bind to itself to form long actin filaments
myosin:
fibrous protein composed of a long, thin fiber + 2 head groups
myosin bundles
myosin molecules brought together with heads facing same direction
what drives the cross bridge cycle
ATP binding and hydrolysis by the myosin head group
cross bridge cycle
- myosin head bound w ATP
- ATP hydrolysis generates ADP+Pi, causing myosin head to become cocked
- myosin head binds to actin causing Power stroke
- conformational change triggered, causing ADP+Pi to fall off
- ATP binds to myosin head so myosin dissociates from actin filament
what causes the power stroke?
myosin heads binding to actin filament and ADP+Pi falling off
what causes Rigor mortis?
too much calcium in the cell
what happens to the myosin head group when ATP is added?
it dissociates from the actin filament
what purpose does ATP hydrolysis have in cross-bridge cycle?
change the ATP-bound myosin head conformation to its active/cocked position
where is the motor neuron soma located?
ventral horn of spinal cord
where is the motor neuron axon located?
goes out through the ventral root of spinal cord
motor unit
a motor neuron and the group of muscle fibers it innervates
where are the synapses of muscle fibers located?
in the middle of their length
what is special about the motor unit?
a single motor neuron makes synapses with many muscle fibers
neuromuscular junction
synapse of muscle fibers
neurotransmitter at neuromuscular junction
acetylcholine
receptor at neuromuscular junction
nicotinic acetylcholine receptors (nACh)
nACh can be activated by…
Acetylcholine and nicotine
End Plate
post-synaptic terminal of neuromuscular junction, specialised to muscle fibers with junction folds
where are the nACh receptors found?
in the End Plate
neuromuscular transmission
- action potential in motor neuron propagates down axon, depolarise the presynaptic membrane
- acetylcholine is released at presynaptic terminal
- ACh binds to nACh receptors, activating them so Na+ flows through nACh receptors, depolarising the end plate
- endplate potential generated is big enough to fire an AP on its own
- voltage-gated sodium channels in endplate activated cause fiber AP to propagate in both directions fast for muscle fiber contraction
what are nACh receptors permeable to?
Na+
Endplate potential
ie. EPSP in a muscle fiber
why is a single endplate potential so big?
the synapses are very large
T-tubules
invaginations in muscle fiber plasma membrane
Sarcoplasmic Reticulum (SR)
intracellular storage site for calcium, forming a network around myofibril
ryanodine receptors
- ion channel embedded in SR membrane
- activated by ryanodine binding
- permeable to Ca2+ when activated
DHP receptor
voltage-gated calcium channel on muscle fiber external plasma membrane
excitation-contraction coupling key points
- external plasma membrane filled with Na+ voltage-gated channels
- AP propagates along plasma membrane to t-tububles
- t-tubule membrane depolarised, activating DHP receptors
- conformational change in DHP receptors allows its coupling to Ryanodine receptors
- Ca2+ influx from SR into cytoplasm
which ion channel releases bigger amounts of Calcium? DHP or ryanodine?
ryanodine since embedded in SR membrane
troponin
globular proteins found along actin filament length
troponin gets activated by…
the binding of Ca2+
tropomyosin
long thin protein wrapped around actin filament
tropomyosin conformation at rest
covers all the binding sites for myosin heads
how is excitation-coupling linked to the cross bridge cycle?
- calcium released from SR binds to troponin
- troponin changes conformation
- causing tropomyosin to move away from myosin binding sites on actin
- myosin head groups can now bind to actin filament and cross-bridge cycle can begin
twitch
contraction of muscle fiber in response to a single action potential
latent period
muscle contraction lags behind the muscle AP due to delays associated with excitation-contraction coupling
why does muscle contraction take about 100ms to relax back to normal state?
time taken for Ca2+ conc to return to normal
tension
force generated by a muscle
recruitment
increase in number of active fibers
summation
additive effects of several closely spaced twitches
what controls the tension exerted by a whole muscle?
recruitment and summation
tetanus
sustained muscle fiber contraction due to motor neurons firing APs in bursts
-> Ca2+ has no time to be pumped back into SR
most important mechanism for increasing muscle tension
recruitment of additional motor units
how is ATP concentration maintained stable during muscle contraction?
- ATP hydrolysis
- Creatine phosphate donates its phosphate to ADP with the help of Creatine kinase to form ATP
- anaerobic respiration: glycolysis –> glucose and glycogen converted to lactic acid in cytoplasm
- aerobic respiration: oxidative phosphorylation –> oxygen + fatty acids generate lots of ATP in mitochondria
where does glycolysis take place?
cytoplasm
where does oxidative phosphorylation take place?
mitochondria
enzyme used to convert ADP to ATP
creatine kinase
glycogen
long chains of glucose molecules
how do muscle fibres store energy?
as glycogen
fast glycolytic fibers key points
- myosin with high ATPase activity
- no myoglobin
- generation of large force over short time
- fatigue rapidly
- energy mostly from glycolysis, causing lactic acid to build up
- not dependent on blood supply
generation of large force over short period of time
fast glycolytic fibers
fast glycolytic fibers color
white, lack myoglobin
slow oxidative fibers key points
- myosin with low ATPase activity: ATP consumed more slowly
- myoglobin to facilitate oxygen transport from blood
- generation of little force over long time
- use both glycolysis and oxidative phosphorylation
- depends on blood supply
generation of little force over long period of time
slow oxidative fibers
purpose of myoglobin in slow oxidative fibers
to facilitate oxygen transport from blood, facilitating oxidative phosphorylation
slow oxidative fibers color
red, myoglobin
fast oxidative fibers key points
- intermediate properties
- fast myosin and oxidative metabolism
order in which muscle fibers are recruited as contraction gets stronger
- slow oxidative
- slow oxidative + fast oxidative
- slow oxidative + fast oxidative + fast glycolytic
muscle fatigue purpose
to protect muscles from damage
muscle fatigue is caused by depletion of ATP. True/False?
False
causes of fatigue in fast glycolytic fibers
- changes in ion gradients
- reduction in pH due to build of lactic acid from glycolysis
cause of fatigue in slow oxidative fibers
depletion of glycogen
other possible cause of muscle fatigue
central command fatigue
central command fatigue
failure of command signals from CNS due to fatigue = less motivation to continue
hypertrophy
increase muscle size as the fast glycolytic muscle fibers get thicker, since they contain more myosin
hypertrophy results from which type of exercise
high intensity and short duration
-> fast glycolytic fibers
how does low intensity and long duration exercise change muscles?
- slow oxidative fibers become more efficient at generating energy: increased mitochondria in muscle fibers
- stronger cardiovascular system
why are muscles sore after exercise?
due to inflammation in response to small muscle damage
muscle cramps cause
dehydration changes ionic concentrations so muscle fiber becomes abnormally depolarised, generating more AP for muscle contraction
Smooth muscle contraction controlled by… why?
the ANS to maintain stable internal states
differences/similarities between smooth and skeletal muscles
- no striation: not highly ordered
- similar contraction mechanism: myosin filaments pull on actin filaments
smooth muscle activation steps
- Ca2+ released from SR or membrane calcium channels
- Ca2+ binds to calmodulin, activating it
- calmodulin activates myosin light chain kinase which phosphorylates/activates myosin
- muscle contracts
calmodulin
soluble protein floating inside cell, activated by calcium binding
kinase proteins
proteins that activate other proteins by adding phosphate to them
how is smooth muscle contraction similar to skeletal muscle contraction?
it is activated by calcium release in SR
how is smooth muscle contraction different to skeletal muscle contraction?
- calcium can also be released from calcium channels in the membrane
- calcium binds to calmodulin, not troponin
activity of smooth muscles is regulated by…
extracellular signals, such as hormones and neurotransmitters of ANS
the Autonomic Nervous System function(s)
- to control visceral organs
- to maintain homeostasis
3 major divisions of the ANS
- Sympathetic
- Parasympathetic
- Enteric
ganglion
organised cluster of neuron cell bodies in PNS
sympathetic nervous system
activated in energy fight or flight reactions
sympathetic preganglionic neurons anatomy
- short axon extending out through ventral root
- axon synapses with postganglionic neuron
where are sympathetic preganglionic neurons found?
in spinal cord grey matter
sympathetic postganglionic neurons anatomy
have long axons projecting to visceral organ
sympathetic ganglia
found at the synapse between sympathetic preganglionic and postganglionic neurons between thoracic and lumber regions of spinal cord
–> form a chain so they all get activated together
how does the sympathetic nervous system work?
- preganglionic neurons release acetylcholine at synapse with postanglionic neuron
- acetylcholine activates nACh receptors, causing Na+ to flow in and postganglionic neuron depolarisation
- norepinephrine released, activating alpha and beta adrenergic receptors
- 2nd messenger released, innervating the target organ
sympathetic effect on heart
heart muscles contract more and faster
sympathetic effect on bronchial tubes
smooth muscles relax, allowing for more space in lungs to breathe
neurotransmitter released by sympathetic preganglionic neurons
acetylcholine
neurotransmitter released by sympathetic postganglionic neurons
norepinephrine
alpha and beta adrenergic receptors
- metabotropic receptors
- activated by norepinephrine
- have different effects depending on the target organ
parasympathetic nervous system
involved in rest and digest processes
parasympathetic preganglionic neuron anatomy
long axons that extend almost to target organ
where are parasympathetic preganglionic neurons found?
- brainstem (cranial nerves)
- sacral spinal cord
parasympathetic postganglionic neuron anatomy
close to target organ so very short axons
vagus nerve (X)
cranial nerve providing preganglionic parasympathetic input to visceral organs
how does the parasympathetic nervous system work?
- preganglionic neurons release acetylcholine at synapse with postganglionic neuron
- acetylcholine activates nACh receptors so Na+ flows in, depolarising postganglionic neuron
- acetylcholine released by postganglionic neuron, activating muscarinic acetylcholine receptors
- 2nd messenger activate in target tissue
sympathetic effect on heart
heart contractions slow down
neurotransmitter released by parasympathetic preganglionic neurons
acetylcholine
neurotransmitter released by parasympathetic postganglionic neurons
acetylcholine
muscarinic acetylcholine receptors
- metabotropic receptors
- activated by acetylcholine
- parasympathetic response
- effects depend on target organ
enteric nervous system
controls gastrointestinal tract + pancreas + gallbladder
2 functions of enteric nervous sytem
- control contractions to mix and push food through dig. tract
- secrete dig. enzymes
the enteric system can function on its own. True/False
True, but it also receives input from sympathetic and parasympathetic systems for regulation
neurons in enteric system
- cholinergic neurons
- adrenergic neurons
- neurons that release neuropeptides, ATP and Nitrous Oxide
cholinergic neurons
activate peristaltic contractions of the gut
adrenergic neurons
suppress gut peristalsis to focus on smth more important (sympathetic influence)
intestine layers
2 layers of smooth muscles
- longitudinal
- circular
2 layers of neurons
- myenteric plexus
- submucous plexus
longitudinal smooth muscles
vertical contractions
circular smooth muscles
circular contractions
myenteric plexus
neuron layer innervate the 2 layers of smooth muscles in intestine
submucous plexus
neuron layer that regulates secretion of digestive enzymes
sources of sensory input to ANS
- somatosensory system
- vagus nerve or spinal cord
brainstem
integrates visceral sensory inputs and autonomic outputs, projecting to higher brain centres involved in homeostasis
nuclei
organised group of neurons in CNS
hypothalamus
integrates autonomic responses, endocrine function and behaviour to maintain homeostasis
which organ is referred to as master controller of homeostasis?
hypothalamus
5 basic physiological needs regulated by hypothalamus
- blood pressure +electrolyte balance (thirst)
- body temperature
- energy metabolism (food intake)
- reproduction (hormones)
- emergency responses to stress
how does the hypothalamus process information?
- compares sensory information to biological set points
- if deviation detected, it coordinates autonomic, endocrine and behavioural responses to restore homeostasis
pituitary gland
controls all glands in the body that regulate hormone release
cerebral cortex is important for…
functions related to emotions, feelings and motivation
what other brain regions does the hypothalamus interact with?
- pituitary gland
- cerebral cortex
- amygdala
how would the hypothalamus regulate for body temperature too low?
- shivering = generates heat from skeletal muscles (automatic response)
- thyroxin released from pituitary = vessel constriction on skin
- cerebral cortex makes you feel uncomfortable/unmotivated = put sweater on
amygdala
brain region that relates visceral responses to conscious feelings and connect emotions to memories
which brain region is involved in learning? and how?
amygdala: remembers the emotions associated with the learning process/content
uncus
small bump in temporal lobe that contains the amygdala
