midterm 2 Flashcards
what is in the central nervous system?
brain and spinal cord
what does gray matter consist of?
unmyelinated somas, dendrites and axons- sensory and motor nuclei
what does white matter consist of?
myelinated axons that carry info to and from the brain
function of the spinal cord?
major pathways for info flowing between brain and skin, joint and muscles
dorsal root function?
carries sensory info to CNS
ventral root function
carries motor info to muscles and glands
what are the 4 regions of the spinal cord?
cervical, thoracic, lumbar, sacral
nuclei?
clusters of cell bodies in CNS
ganglia?
clusters of cell bodies in PNS
what is a spinal reflex?
initiated a response without input from the brain
stimulus > sensory info > integrating center > command to muscles > response
how do chemical and electrical signals in neurons lead to complex behaviours?
individual neurons reductionist > groups of neurons (circuits, pathways, networks) > complex behaviour
what are the 4 major regions of the brain stem?
midbrain (eye movement), pons (relay station between cerebrum and cerebellum, coordination of breathing), medulla (control of involuntary functions), reticular formation (arousal, sleep, muscle tone, pain modulation)
what is the brainstorm made up of?
11-12 cranial nerves (carry sensory and motor info for head and neck) and many nuclei
what does the medulla contain and it’s function?
white matter (ascending somatosensory tracts and descending corticospinal tracts- crossover at the pyramids) controls involuntary functioning in the cardiovascular center and the medullary respiratory center - vomiting, swallowing (deglutition), coughing, sneezing, hiccuping
pons - contents and function
contains nuclei and tracts, relays info between cerebrum and cerebellum, assists the medulla in the coordination of breathing
midbrain contents and function
junction between nuclei and tracts, contains the substantia nigra, controls eye movement, relays auditory and visual reflexes in response to stimuli
what is the reticular formation and function?
extends throughout the brain stem (small clusters of neuronal cell bodies interspersed among ascending and descending tracts) important in consciousness, arousal, attention and alertness. reticular activating system sends sensory info to cortex, RAS inactivated during sleep, damage can induce coma, regulates muscle tone, assists in vital functions
cerebellum contents and function
second largest brain structure (2 cerebellar hemispheres), process sensory info and coordinates the execution of movement, sends feedback signals to motor areas of the cerebral cortex via its connection to the thalamus helping to correct and errors and smooth the movements, regulates posture and balance
diencephalon contents
lies between brain stem and cerebrum, 2 primary structures (thalamus and hypothalamus), 2 endocrine structures (pineal gland and pituitary)
thalamus functions
relay center: relieves sensory info from optic tract, ears, spinal cord and motor info from cerebellum and projects info to cerebrum for processing
pineal gland function
cyclically releases melatonin involved in sleep/wake
hypothalamus function
center for homeostasis, influences autonomic and endocrine function, helps maintain blood glucose concentrations, maintains body temp, controls body osmolarity, stimulates shivering/sweating, controls reproductive functions, controls food intake, influences behaviour/emotions, release of hormones
pituitary contents
endocrine output of the hypothalamus, posterior pituitary is neural tissue, anterior pituitary is endocrine tissue, infundibulum is the stalk that connects the pituitary to the brain
posterior pituitary function
an extension of the brain that secretes neurohormones made in the hypothalamus.
neurohormone is made and packaged in cell body of neuron > vesicles are transported down the cell > vesicles containing neurohormones are stored in posterior pituitary > neurohormones are released into blood
cerebrum contents
largest part of the brain, gray matter(cerebral cortex, basal ganglia, limbic system), area of higher processing, 2 hemispheres divided into 4 lives connected by corpus callosum
basal ganglia (nuclei) contents and function
made of 3 nuclei (globus pallidus, putamen, caudate nucleus) regulates the initiation and termination of movement, receives input from cerebral cortex and provides output to motor portions of the cortex
limbic system contents and function
“emotional brain” 3 components (cingulate gyrus- emotion, amygdala- emotion and memory, hippocampus- leading and memory) plays a role in pain, pleasure, docility, affection, anger, learning and memory
cerebral cortex contents and function
outermost later if the cerebrum, integrating center for CNS, 3 specializations- sensory areas (translate sensory input), motor areas (direct skeletal muscle movement), association areas (integrate info from sensory and motor areas and help direct voluntary behaviours
frontal lobe function
primary motor cortex, motor association area (premotor cortex) > skeletal muscle movement, prefrontal association area
parietal lobe function
primary somatic sensory cortex, sensory association area
occipital lobe function
visual association area, visual cortex > vision
temporal lobe function
auditory cortex, auditor association area > hearing
gustatory cortex function
taste
olfactory cortex function
smell
what are the conscious special senses?
vision, hearing, taste, smell, equilibrium
what are the conscious somatic senses?
touch, temp, pain, itch, proprioception
what are the subconscious somatic stimuli?
muscle length and tension, proprioception
what are the subconscious visceral stimuli?
blood pressure, distension of gastrointestinal tract, blood glucose concentration, internal body temp, osmolarity of body fluids, lung inflation, pH of cerebrospinal fluid, pH and oxygen content of blood
function of sensory systems
a sensory neuron with a transducer (receptor) that coverts a physical stimulus into an intracellular signal (change in membrane potential) usually through the opening or closing of gated channels
chemoreceptors stimuli and receptor potentials
stimuli: oxygen, pH, various organic molecules such as glucose
senses: blood chemoreceptors, nociceptors, hypothalamic glucose sensing neurons, taste, smell
mechanoreceptors stimuli and receptor potentials
stimuli: pressure, cell stretch, vibration, acceleration, sound
senses: touch, proprioceptors, nociceptors, auditory, balance
photoreceptors stimulus and receptor potential
stimulus: photons of light
sense: vision
thermoreceptors stimulus and receptor potentials
stimulus: varying degrees of heat
receptors: thermal receptors, nociceptors
physical stimuli are transducer into receptor potentials (graded potentials) once they reach threshold what do they induce?
action potentials
where is almost all special and somatic sensory info routed?
through the thalamus
how do somatosensory neurons bring info the the CNS? (steps)
pain, temp, and touch cross the midline in the spinal cord > fine touch, vibration, and proprioception pathways cross the midline in the medulla > sensory pathways synapse in the thalamus > sensations are perceived in the primary somatic sensory cortex
how does the CNS integrate sensory info? (steps)
olfactory pathways from the nose project through the olfactory bulb to the olfactory cortex > most sensory pathways project to the thalamus which modified and relays info to cortical centers > equilibrium pathways project primarily to the cerebellum
how does the CNS distinguish modality?
the physical stimuli being sensed, determined by the sensory receptor being activated, temp vs touch receptor and where the pathways terminate in the brain
how does the CNS distinguish the location of stimulus?
coded according to which receptive fields are being activated, most sensory stimuli for specific regions of the body are projected to particular areas of the somatosensory cortex
how does the CNS distinguish intensity and duration of stimulus?
- intensity is determined by the number of receptors being activated (population coding) and the frequency of action potentials coming from those receptors (frequency coding)
- duration of a stimulus is determined by how long APs are being activated
why can’t intensity be determined by amplitude?
because AP amplitude is constant
what are tonic receptors?
slowly adapting receptors that respond for the duration of a stimulus
what are physic receptors?
rapidly adapt to a constant stimulus and turn off
what does duration of a stimulus depend on?
how long APs are being activated, receptor adaptation, characteristics of the channel or pathway generating the receptor potential ex. a Na+ channel that quickly inactivates
autonomic nervous system functions and divisions
involuntary control of smooth muscle, cardiac muscle, many glands and some adipose tissue
subdivided: sympathetic (fight or flight) and parasympathetic (rest and digest)
how and why are autonomic reflexes important for homeostasis?
the autonomic nervous system works closely with the endocrine system and behavioural systems to maintain homeostasis
the hypothalamus, pons, and medulla initiate autonomic, endocrine, and behavioural responses
what are the 2 efferent neurons in series in autonomic pathways?
preganionic neuron (1) and postganglionic neuron (8 or 9)
sympathetic branches contents
ganglia found in 2 ganglia chains running along the vertebral column, preganglionic neurons originate in thoracic and lumbar regions, short preganglionic, long postganglionic neurons
parasympathetic branches contents
preganglionic neurons originate in the brain stem and exit via cranial nerves or from the sacral region of the spinal cord, ganglia located on or near their target organs, long preganglionic, short postganglionic, cranial nerve (vagus) contains 75% of all parasympathetic neurons
sympathetic pathways use what chemical signals?
acetylcholine and norepinephrine
parasympathetic pathways use what chemical signals?
acetylcholine
adrenal medulla contents and function
secretes catecholamines, specialized neuroendocrine structure associated with the sympathetic nervous system, contain chromatic cells which are modified postganglionic neurons
what do autonomic pathways do?
target smooth and cardiac muscle, many exocrine glands, few endocrine glands, lymphoid tissue and some adipose tissue
where are autonomic neurotransmitters synthesized?
in the axon, acetylcholine and norepinephrine can be synthesized in the varicosities
autonomic neurotransmitter synthesized steps
AP arrived at the varicosity > depolarization opens voltage gated Ca2+ channels > Ca2+ entry triggers exocytosis of synaptic vesicles > NE binds to adrenergic receptor in target > receptor activation ceases when NE diffuse away from the synapse > NE is removed from synapse > NE can be taken back into synaptic vesicles for re release > NE is metabolized by MAO
how is ACh made? (steps)
acetylcholine is made from choline and acteyl CoA > in synaptic cleft ACh is rapidly broken down by the enzyme acetylcholinesterase > choline is transported back into the axon terminal by cotransport with Na+ > recycled choline is used to make more ACh
what are sympathetic adrenergic (NE and E) receptors made of and their 2 categories?
all g- protein coupled receptors (metabotropic receptors), 2 main categories Alpha (most common) and Beta
what happens when g-protein coupled receptors interact with ion channels?
can lead to opening or closing of a channel depending on g-protein
what happens when g-protein coupled receptors interact with a membrane bound enzyme?
phospholipase C signal transduction pathway > increase in intracellular Ca2+ mediates a cellular response, PKC can also mediate a cellular response
adenylyl cyclades signal transduction pathway > PKA phosphorylation proteins to cause a cellular response
what kind of movement are skeletal muscles?
primarily voluntary by somatic neurons
multinucleated
what kind of movement are cardiac muscles?
primarily involuntary, spontaneous electrical activity
can be altered by autonomic NS, hormones
what kind of movement are smooth muscles and what do they control?
primarily involuntary, autonomic control, spontaneous, hormones, paracrines or autocrines
controls digestive tract, urinary tract, reproductive tract, blood vessels, airways
how is skeletal muscle attached?
to bones by tendons
skeletal muscle origin
closest to the trunk or to more stationary bone
skeletal muscle insertion
more distal or more mobile attachment
what does the flexor do in skeletal muscle?
moves bones closer together
what does the extensor do in the skeletal muscle?
moves bones away from each other
how much of your total body weight is skeletal muscle?
40%
what are these general terms called as muscles?
1) muscle cell
2) cell membrane
3) cytoplasm
4) modified endoplasmic reticulum
1) muscle diver
2) sarcolemma
3) sarcoplasm
4) sarcoplasmic reticulum
what is the F-actin?
back bone of thin filaments, double stranded alpha helical polymer of G-actin molecules. contains binding site for thick filaments (myosin)
what is tropomyosin?
2 identical alpha helictites that coil around each other and sit in the two grooves formed by actin strands, regulates the binding of myosin to actin
what is the troponin complex? (thin filaments)
heterotrimer consisting of troponin T (binds to a single molecule of tropomyosin), troponin C (Ca2+ binding site), troponin I (under resting conditions is bound to actin inhibiting contraction)
what are thick filaments made of?
consist of a bundle of myosin molecules, each heavy chain contains 2 light chains
what does the myosin head do in thick filaments?
contains a region for binding actin as well as a site for binding and hydrolyzing ATP
what does regulatory light and essential light do in thick filaments?
regulatory light chain regulates ATPase activity of myosin
essential light chain stabilizes myosin head
what is titin?
a large protein extending from M line to Z line, appears to be involved in stabilization and the elastic recoil behaviour of muscle
what is nebulin?
a large protein that wraps around the thin filament believed to regulate the length of filaments and contribute to the structural integrity of myofibrils
what is the Z disk? (sarcomere)
zigzag protein structure that is the attachment site for the thin filaments
what are I bands? (sarcomere)
lightest band of sarcomere, region occupied only by thin filaments
what is the A band?
darkest band of sarcomere, encompasses entire length of the thick filament including very dark area where thin and thick filaments overlap
what is the H zone?
central region of A band, consists only of thick filaments
what is the M line?
proteins form attachment site for thick filaments, equivalent to Z disk for thin filaments
where and how is glucose stored in muscle fibre?
stored as glycogen within the sarcoplasm
what is the force generated by a contracting skeletal muscle called?
muscle tension
what is the neuromuscular junction?
point of synaptic contact between somatic motor neuron and individual muscle fibre
what is the excitation-contraction coupling?
an action potential initiated in the skeletal muscle fibre results in an increase in intracellular (sarcoplasmic) Ca2+
which brain regions are involved in voluntary movement?
premotor cortex, basal ganglia, thalamus, midbrain, cerebellum
what is a motor unit?
a single motor neuron and all muscle fibres it innervates is known as a motor unit
what is amyotrophic lateral sclerosis?
neurodegenerative motor neuron disease, leads to muscle atrophy and weakness from disuse, eventual respiratory failure
what causes ALS?
10% genetically inherited, 25% due to mutation in genes producing superoxide dismutase
what are the three components of neuromuscular junction?
1) presynaptic motor neuron filled with synaptic vesicles
2) the synaptic cleft
3) the postsynaptic membrane of the skeletal muscle fibre
what is the motor end plate and what does it do?
Special synapse made between a spinal motor neuron and skeletal muscle where ACh is released into the synaptic cleft and aactivates nicotinic receptors
what do junctional folds on sarcolemma do?
increase surface area
what do motor neuron vesicles contain?
acetylcholine
what does muscle sarcolemma contain?
nicotinic acetylcholine receptors
what for the ACh receptor need to open?
2 acetylcholine molecules
what happens when Na+ enters through nACh?
generates an excitatory end plate potential that spreads to adjacent voltage gated Na+ channels on the sarcolemma and initiated an action potential
what is myasthenia gravis?
means severe muscle weakness, disorder of neuromuscular transmission, can be restricted to extraocular muscles
autoimmune: body produces antibodies that bind to ACh receptors which impedes activation of AChR and eventually decreases number, degeneration of postjunctional folds
what are specialized Ca2+ storage organelles known as?
sarcoplasmic reticulum and are organized with T-tubules
what is excitation contraction coupling?
the process by which electrical excitation of the surface membrane triggers an increase of Ca2+ in muscle
how does Ca2+ enter the sarcoplasm?
from extra cellular space via voltage gated Ca2+ channels
what ultimate intracellular signal that triggers contraction in all muscle types ?
a rise in intracellular calcium (Ca2+)
what kind of channels does sarcolemma contain?
voltage gated Na+ and K+ channels
initiation of muscle action potential steps
somatic motor neuron released ACh at neuromuscular junction > net entry of Na+ through ACh receptor-channel initiates a muscle action potential > action potential in t-tubule alters confirmation of DHP receptor > DHP receptor opens RyD Ca2+ release channels in sarcoplasmic reticulum and Ca2+ enters cytoplasm
cross bridge cycle steps
ATP binds to myosin, releases actin > myosin hydrolyzes ATP, myosin binds weakly to actin > power stroke begins when Pi is released > myosin releases ADP at the end of the power stroke
why and how does termination of contraction require removal of Ca2+?
once the AP has subsided Ca2+ must be removed so that the myosin binding site in actin can be covered by tropomyosin
Ca2+ can be removed to the extracellular space by the Na- Ca exchanger or by the Ca2+ pump which uses ATP— leaves SR empty
what causes sarcomere to return to its initial resting position?
elastic recoil of titin and other connective tissue
what is rigor mortis?
development of rigid muscle several hours after death
Ca2+ leaks into sarcoplasm and binds troponin, ATP production stops, Ca2+ cannot be removed, remains in latched cross bridge formation until muscles begin to deteriorate
what is ATP needed for in muscles?
myosin ATPase > contraction
Ca2+ ATPase > relaxation
Na+/K+ ATPase > after AP in muscle fibre
what is anaerobic metabolism and where does it take place?
takes place in the sarcoplasm of muscle (absence of oxygen or mitochondria)
when ATP is needed glycogen is conveyed back to glucose and is broken down to pyruvate by glycolysis resulting in production of 2 ATP molecules, pyruvate then further brown down to lactate
what occurs if oxygen and mitochondria are present?
oxidative metabolism
after glycolysis pyruvate > citric acid cycle producing 2 more ATP and H+ which combine with O2 in ETC to produce an additional 26-28 molecules of ATP
what is muscle fatigue?
a decrease in muscle tension as a result of previous contractile activity that is reversible with rest
what is central fatigue?
feeling of tiredness and a desire to cease activity
low pH from acid production during ATP hydrolysis
what is peripheral fatigue?
at the neuromuscular junction- proposed ACh synthesis can’t keep up with neuron firing rate
decreased neurotransmitter release> decrease AChR activation on muscle > muscle fails to reach threshold for firing AP (problems with excitation-contraction coupling)
MS is a central nervous system disorder that results from what?
demyelination of axons in the CNS
which type of tissue would be least at risk for damage from MS?
gray matter
what best describes the path of sensory info from the receptor to the spinal cord?
afferent neuron to dorsal root ganglion to dorsal horn
what would happen if you were to disrupt the functions of the reticular formation?
a person would have a difficult time waking due to an inability to arouse the brain
what is the function of the reticular formation?
arousal
what are the structures in the brain stem?
midbrain, pons, medulla oblongata
what are the brain structures in the diencephalon?
thalamus, hypothalamus, epithalamus
what is the function of the midbrain?
plays a role in eye movement
what is the function of the medulla oblongata?
controls involuntary functions of the body like heart rate and blood pressure
what is the functions of the pons?
provides a relay station between the cerebrum and the cerebellum
what is the primitive part of the cerebrum that surrounds the brain stem?
limbic system
which part of the brain is anatomically most similar to the spinal cord?
brain stem
a neuron that has responded to a stimulus causes decreased activity in neighbouring neurons in which process?
lateral inhibition
the lack of awareness people have if the stimulus of clothing on the skin is due to what process?
habituation
which ratio between primary neuron and secondary neuron would allow for the greatest receptive field sensitivity?
1:1
a receptor potential is the same as what other potential?
a graded potential
which is a modified sympathetic ganglion?
adrenal medulla
what mechanisms lead to termination of neurotransmitter activity?
when the neurotransmitter is broken down by enzymes or when it diffuses away, or active transport into surrounding cells
what is a varicosity in the autonomic nervous system?
a series of swollen end of neurons where neurotransmitter is released
what is a similar characteristic between the sympathetic and parasympathetic branches for most neurons?
neurotransmitter secreted from the preganglionic neuron
which nervous system division has parasympathetic and sympathetic branches?
the autonomic division of the efferent nervous system
sympathetic pathways originate in which regions of the spinal cord?
thoracic and lumbar
what neurotransmitters do neurons use in the parasympathetic pathway?
acetylcholine
what division of the efferent nervous system controls smooth and cardiac muscles and many glands?
autonomic
in a neuromuscular junction synaptic vesicles in the motor neuron contain which neurotransmitter?
acetylcholine
when an action potential arrives at the axon terminal of a motor neuron which ion channels open?
voltage gated calcium channels
what means of membrane transport is used to release the neurotransmitter into the synaptic cleft?
exocytosis
binding of the neurotransmitter to receptors in the motor end plate cause what to occur?
causes chemically gated sodium channels to open in the motor end plate and sodium enters the cell
how is acetylcholine removed from the synaptic cleft?
simple diffusion away from the synaptic cleft and acetylcholinesterase
where are calcium ions stored in the muscle cell?
terminal cisterns (cisternae) of the sarcoplasmic reticulum
what causes the release of calcium ions from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?
arrival of an action potential
what molecule bonds to calcium to cause myosin binding sites to be exposed?
troponin
a myosin head binds to which molecule to form a cross bridge?
actin
what cause the myosin head to disconnect from actin?
binding of ATP
what causes the power stroke?
release of ADP and Pi
summary of the excitation-contraction coupling
muscle action potentials initiate calcium signals that activate a contraction-relaxation cycle
what is the neuromuscular junction?
the point of synapse between a motor neuron and the muscle fibre that it innervates
what structures are necessary to initiate the muscle action potential?
motor neuron, muscle fibre, acetylcholine, ACh receptor channels, motor end plate
what is the ACh receptor channel?
a structure that when bound to a ligand opens a divalent channel for the movement of both Na+ and K+
what is a motor end plate?
an area of muscle fibre membrane that is in close association with the axon terminal of the motor neuron, contain receptors for acetylcholine
what is an action potential?
a change in membrane voltage that travels down the T-tubule to cause opening of Ca2+ channels
what is the axon terminal of motor neuron?
an area that contains many synaptic vesicles filled with acetylcholine
what are the steps at the neuromuscular junction?
somatic motor neuron delivers action potential > acetylcholine is released from the axon terminal onto the motor end plate > net Na+ influx though nicotonic receptors > muscle fibre depolarizes > action potential travels down T-tubule of the muscle fibre
what is the contraction phase of the excitation-contraction coupling reaction?
actin and myosin filaments slide past each other to shorten the sarcomere bringing Z disks closer together
what is the role of Ca2+ in the excitation-contraction coupling reaction?
Ca2+ will bind to troponin which leads to a conformational shift in tropomyosin allowing for actin and myosin to attach
events of contraction in order
an AP that travels down the T-tubule changes the structural confirmation of the DHP L-type Ca2+ channel> ryanodine receptor channels open > Ca2+ leaves the sarcoplasmic reticulum > actin and myosin bind to one another > myosin heads utilize energy from ATP hydrolysis to produce the power stroke > actin filaments slide toward the M line shortening the sarcomere
what is the most direct cause of muscle relaxation?
Ca2+ unbinds from troponin which results in tropomyosin re-covering myosin binding sites
if a patient has damage to one somatic motor neuron what will it affect?
one motor unit
what is the difference between summation and tetanus?
summation can cause tetanus but tetanus cannot cause summation
what happens when skeletal muscle sarcomere length increases beyond about 2.3 um?
tension decreases
what are slow oxidative muscle divers characterized by?
a smaller diameter and the presence of myoglobin
which enzyme catalyses the phosphorylation of ADP?
creatine kinase
what would stop muscle contraction?
pumping of calcium ions into the SR
how is the energy released by ATP hydrolysis used during the contractile cycle in the skeletal muscle?
it causes rotation of the myosin head, thus “cocking” it
what happens when calcium binds troponin?
tropomyosin is pulled away from the myosin binding site on actin
what is it called when muslim cross bridges attach to actin filaments and pull them toward the middle of the sarcomere?
a power stroke
what does not change size during a muscle contraction?
A band
which type of skeletal muscle causes two bones to move away from one another?
extensor
what is a similarity between summation and tetanus?
muscle action potentials are shorter than muscle contraction
what immediately follows hydrolysis of ATP during muscle contraction?
rotation of the myosin head to the cocked position
what are thick filaments made up of?
myosin
what are muscle cells also known as?
muscle fibres
how is the action of extension of the elbow produced?
an antagonistic muscle
what is a cross bridge?
a myosin head bound to actin
what structure is the functional unit of contraction in a skeletal muscle fibre?
the sarcomere
where are calcium ions stored within the fibre?
in the sarcoplasmic reticulum
what causes cross bridge detachment?
ATP binds to the myosin head
how does the myosin head obtain the energy required for activation?
energy comes from the hydrolysis of ATP
what event triggers the uncovering of the myosin binding site on actin?
calcium ions bind to troponin and change its shape
when does cross bridge cycling end?
when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin
in excitation-contraction coupling what does excitation refer to?
the propagation of action potentials along the sarcolemma
what event initiates contraction?
calcium release from the sarcoplasmic reticulum
what is the spaced infoldings of the sarcolemma called?
transverse or T-tubules
what is responsible for the coupling of excitation to contraction of skeletal muscle fibres?
calcium ions
how many skeletal muscle fibres are needed to innervate how many motor neurons?
hundreds of skeletal muscle fibres are innervated by a single motor neuron
what mechanism ensures rapid and efficient removal of acetylcholine?
acetylcholine is degraded by acetylcholinesterase
what critical event occurs at the neuromuscular junction?
acetylcholine is released by axon terminals of the motor neuron into the synaptic cleft via exocytosis
calcium entry into the axon terminal triggers what event?
synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine
when acetylcholine binds to its receptor in the sarcolemma it triggers the opening of what?
opening of ligand-gated cation channels (Na+ in, K+ out)
why do sodium and potassium ions not diffuse in equal numbers through ligand-gated cation channels?
the inside surface of the sarcolemma is negatively charged compared to the outside surface, sodium ions diffuse inward
what is peripheral fatigue?
failed excitation-contraction coupling a t-tubule, decrease in the rate of Ca2* release and storage by SR, decreased activation of thin filament proteins by Ca2+, direct restraint of the binding and power stroke motion of the myosin cross-bridges
fibres containing a large amount of mitochondria have a high capacity for what and what are they classified as?
high capacity for oxidative metabolism and classified as oxidative fibres, large amount of myoglobin to aid in O2 delivery
fibres containing few mitochondria have an abundance of what and what are they classified as?
an abundance of enzymes and a large store of glycogen and are classified as glycolic fibres
how does muscle length influence tension development?
by determining the degree of overlap between actin and myosin filaments, amount of tension = # of cross bridges formed
what is a single twitch?
muscle relaxes completely between stimuli
what is summation?
stimuli closer together do not allow muscle to relax fully
what is unfused tetanus?
reaches steady state of contraction but stimuli are far enough apart that the muscle fibre slightly relaxes between stimuli
what is fused tension?
the stimulation rate is fast enough that the fibre does not relax instead it reaches max tension and remains there
what is one way to increase tension developed by a single muscle fibre ?
increase the rate at which action potentials occur in the fibre
what is a motor unit ?
a single motor neuron and all muscle fibres in innervates, one motor neuron innervates one fibre type
what is a motor neuron pool?
the group of all motor neurons innervating a single muscle
difference between slow twitch fibres and fast twitch fibres?
slow: small diameter motor neuron, Rm is high, conduction velocity is low
fast: large diameter motor neuron, Rm is low, conduction velocity is high
what is the size principle?
as the stimulus onto the motor neuron pool increases, additional larger motor neurons are recruited
small, medium, and large motor neurons difference
small: slow oxidative
medium: fast oxidative glycolytic
fast: fast glycolytic
what is isotonic contraction?
muscle contracts, shortens and creates enough force to move
what is isometric contraction?
muscle contracts but does not shorten, force created cannot move the load
what is concentric contraction?
muscle shortens while generating force
what is eccentric contraction?
muscle lengthens while generating force (decelerate joint)
what are two proposed mechanism by which muscle mass may be increased?
hypertrophy or hyperplasia
what are myosatellite cells?
involved in muscle repair may form new muscle fibres
what fibres have a greater rate of myofiber hypertrophy?
type 2 fibres
what is muscle hypertrophy?
protein synthesis 💪
increase size and number of contractile proteins (myosin and actin)
increased number of sarcomere within a muscle length
increased sarcoplasmic storage (glycogen)
what is skeletal muscle atrophy and how can it occur?
protein degradation
- immobilization, bed rest, unloading, food deprivation, age, cancer
what is cachexia?
weakness and wasting due to chronic disease
what are the 4 components of skeletal muscle reflexes?
sensory receptor, integrating center, efferent neurons, effectors
what is a monosynaptic reflex?
a single synapse between the afferent and efferent neurons
what is a polysynaptic reflex?
2 or more synapses, somatic motor reflex has both synapses in the CNS
what are proprioceptors ?
provide info into the CNS about the position of our limbs in space, movements, and effort exerted by skeletal muscles
what are joint receptors?
found in the capsules and ligaments around joints and are stimulated by mechanical distortion that accompany changes in the position of bones
what are muscles spindles?
small elongated stretch receptors scattered among and arranged parallel to skeletal muscle fibres, send info to CNS about muscle length, made up of sensory neuron wrapped around intrafusal muscle fibres
what are extrafusal muscle fibres?
regular muscle fibres innervated by alpha motor neurons
what is muscle spindle reflex?
the addition of a load stretches the muscle and the spindles creating a reflex contraction
load added to muscle > muscle and muscle spindle stretch as arm extends > reflex contraction initiated by muscle spindle restored arm position
alpha-gamma coactivation steps
alpha motor neuron fires and gamma motor neuron fires > muscle and intrafusal fibres both contract > stretch on centres of intrafusal fibres unchanged. firing rate of afferent neuron remains constant
what is a golgi tendon organ?
sensory neuron interwoven among collagen fibres inside a connective tissue capsule, controls reflexes to prevent muscle damage, controls force within muscles and stability around joints
golgi tendon reflex steps
neuron from golgi tendon organ fires > motor neuron is inhibited > muscle relaxes > load is dropped
(protects muscle)
what kind of reflex is the patellar tendon reflex?
a monosynaptic stretch reflex and reciprocal inhibition of the antagonistic muscle
what is the crossed extensor reflex?
a flexion reflex in one limb causes extension in the opposite limb, coordination of reflexes with postural adjustments is essential for maintaining balance
what is cardiac muscle made of?
myocardial and muscle cells usually contain a single nucleus
how are cardiac muscles linked?
-interconnected by intercalculated disks
- linked mechanically by desmosomes
- linked electrically by gap junctions
cardiac muscle requires what?
- entry of extracellular Ca2+
- abundance of mitochondria
- oxidative metabolism for ATP production
