Exam 1 Flashcards
what are the functions of skeletal muscle?
- force production of locomotion and breathing
- force production for postural support
- heat production during cold stress
composition of skeletal muscle
75% water, 20% protein (myosin, actin, tropomyosin), and 5% salts (carbohydrates/calcium)
epimysium
surrounds entire muscle
perimysium
surrounds bundles of muscle fibers
endomysium
surrounds individual muscle fibers
sarcolemma
muscle cell membrane
what is the role of satellite cells?
- key role in muscle growth and repair (can increase the # of nuclei in mature muscle fibers)
- detect microtears and begin to repair by filling in the gaps with proteins, why you feel sore
myonuclear domain
- volume of cytoplasm surrounding each nucleus
- each nucleus can support a limited myonuclear domain
myofibrils
contain contractile proteins
actin filament
- thin filament
- contains actin, troponin, and trypomyosin
myosin
- thick filament
- globular head region
- long alpha-helical tail
sarcomere
repeating contractile unit in the myofibril bounded by Z lines
what bands are in the sarcomere?
Z line, M line, H zone, A band (myosin), I band (actin)
sarcoplasmic reticulum
surrounds myofibrils, storage site for calcium
what triggers muscle contraction?
calcium
what triggers muscle contraction?
calcium
transverse tubules
extend from sarcolemma to SR, maintains the SR calcium store under control of membrane depolarization
role of tropomyosin
- regulates muscle contraction
- during rest, prevents myosin from forming cross-bridges
role of troponin
during excitation contractions, calcium binds with troponin and interacts with tropomyosin to unblock active sites between myosin filaments and actin
role of troponin
during excitation contractions, calcium binds with troponin and interacts with tropomyosin to unblock active sites between myosin filaments and actin
what does the SERCA pump do?
transports calcium ions from cytoplasm to SR.
what is the sliding filament theory and what role does it play in contraction?
Muscle fibers contract by a shortening of their myofibrils due to actin sliding over myosin, results in reduction in distance from Z disc to Z disc.
Actin and myosin slide across each other during contraction due to cross-bridges extending from myosin and attaching to actin. Results in myosin cross-bridge moving actin towards the center of sarcomere.
Energy for muscular contraction comes from the breakdown of ATP by the enzyme myosin ATPase located on the “head” of the myosin cross-bridge.
what role does ATP play in the formation of cross-bridges?
breaks the myosin-actin cross-bridges freeing the myosin for the next contraction.
what is the length tension relation in regards to sarcomere length and force generation?
optimal sarcomere length = optimal overlap
too short = little force generation
too stretched = no force generation
neuromuscular junction (NMJ)
- where the motor neuron and muscle fiber meet
what effect does acetylcholine have on the receptor?
allows for muscle contraction
how does myosin head bind to actin?
at binding site on the globular actin protein
what role does Ca play on troponin?
troponin changes shape, removing tropomyosin from the binding sites
when does ATP come into play?
chemical energy is converted to mechanical energy when ATP is hydrolyzed during cross-bridge cycling (to ADP)
Type 1 fibers
- slow oxidative/slow twitch
- large # of oxidative enzymes and are surrounded by more capillaries
- aerobic/oxidative metabolism
- most efficient
- less resist to fatigue
Type 2x fibers
- fast twitch/fast glycolytic
- glycolytic metabolism
- large anaerobic capacity
- fastest muscle in humans
- highest power output of all muscle fiber types
Type 2a fibers
- mixture of type 1 and type 2x
- intermediate/fast-oxidative glycolytic fibers
- oxidative metabolism
muscarinic receptors
excitatory or inhibitory
nicotinic
excitatory, accepts acetylcholine
steps of excitation
Nerve impulse arriving at neuromuscular junction.
Synaptic vesicles release acetylcholine that diffuses across the synaptic cleft and binds to receptors on the sarcolemma of the muscle fiber. This opens ion channels on the sarcolemma that results in the movement of sodium into the fiber.
Inward movement of positive sodium ions depolarizes the fiber and sends waves of depolarization through the T-tubules.
steps of contraction
Depolarization of T-tubules results in release of calcium from SR into cytosol of muscle fiber.
Calcium ions bind to troponin (on actin molecule). This results in a shift in the position of tropomyosin so myosin binding sites on actin are exposed.
Energized myosin cross-bridge binds to active site on actin and pulls the actin molecule to produce movement. Occurs repeatedly as long as stimulation to muscle continues.
steps of relaxation
Motor neuron stops to fire. When neural stimulation to muscle ceases acetylcholine is no longer released and the muscle fiber is repolarized.
After cease, calcium is pumped from cytosol to SR for storage. No free calcium in cytosol = troponin moves tropomyosin back into position to cover myosin binding sites on actin. Prevents myosin-actin cross-bridge formation causing muscle relaxation.
isometric action
action in which the muscle develops tension, but does not shorten, aka static contraction. No movement occurs.
dynamic exercise
exercise involves movement of body parts. Two kinds (concentric and eccentric)
concentric action
muscle action that results in muscular shortening with movement of a body part.
eccentric action
when a muscle is activated and force is produced, but muscle lengthens.
hypertrophy
- increase in size of muscle fibers
- result from addition of protein & new myofibrils making them linger
- needs additional myonuclei
hypertrophy
- increase in size of muscle fibers
- result from addition of protein & new myofibrils making them linger
- needs additional myonuclei
proprioception
ability to identify where limbs and joints are in place.
effects of endurance training
- increase in delivery of oxygen to muscle (increase in capillaries, myoglobin, capillary density)
- enhanced ability for aerobic metabolism (increase size and # of mitochondria)
muscle spindles
- proprioceptors in skeletal muscle
- monitors stretch of muscle
- initiates a contraction when muscle is stretched
stretch reflex
quickly stretched muscle intiates immediate contraction due to being stretched.
what are the two parts of the nervous system?
- central nervous system
- peripheral nervous system
central nervous system
- brain and spinal cord
- receives stimuli concerning touch, pain, temp. change, and chemical stimuli
- controls intelligence, memory, personality, emotion, speech and ability to feel and move
peripheral nervous system
- outside spinal cord and brain
- has two portions sensory (effector organs transmit neuron impulses to CNS) and motor (impulses from CNS to effector organs)
cerebrum
- cerebral cortex (complex movement, learned experiences, sensory information)
- motor cortex (motor control and voluntary movement)
cerebrum
- cerebral cortex (complex movement, learned experiences, sensory information)
- motor cortex (motor control and voluntary movement)
cerebellum
- coordinates and monitors complex movement
- connections to motor cortex, brain stem, and spinal cord
- may initiate fast ballistic movements
brain stem
- medulla, pons, midbrain, reticular formation
- responsible for: metabolic functions, cardiorespiratory control, complex reflexes
structure of neuron and their functions
- cell body (nucleus)
- dendrites (receives info, conducts impulses toward the cell body)
- axons (sends info, carries electrical impulses away from cell body, may be covered by Schwann cells)
- synapse (contact points between axons of one neuron and dendrite of another neuron)
Schwann cells
forms discontinuous myelin sheath along length of axon
what does it mean if an axon has a large myelin sheath?
conducts impulses more rapidly that small, nonmyelinated fibers
Excitatory Postsynaptic Potentials (EPSPs)
causes depolarization
Inhibitory Postsynaptic Potential (IPSP)
inhibitory transmitters cause hyperpolarization (increased negativity) of the postsynaptic membrane.
threshold
membrane voltage that must be reached in an excitable cell during depolarization to generate an action potential
action potential
caused by sodium channels rapidly opening
repolarization
sodium channels close and potassium channels stay closed
all or none principle
when threshold is reached, all muscle fibers in motor unit are activated.
if not reached, none of the muscle fibers are activated.
myelinated nerves
conduct impulses using saltatory conduction
unmyelinated nerves
uses local conduction
role of schwann cells
maintaining the PNS
saltatory conduction
jumps, if previously myelinated axons become unmyelinated, signals shoot everywhere, ability to do things decreases
oligodendrocytes
create myelin in CNS
Nodes of Ranvier
small gaps in myelin sheath that allow action potential to jump from node to node along axon, site of saltatory conduction
motor neurons
somatic neuron that innervates skeletal muscle fibers, allows signal to reach skeletal muscle cells
motor unit
each motor neuron and the muscle fibers it innervates, provides electrical input to a muscle in order to generate a muscle contraction
Type S (slow) type 1
Type FR (fast, fatigue resistant) type 2a
Type FF (fast, fatigable) type 2x
motor unit recruitment
recruitment of more muscle fibers through muscle unit activation
afferent fibers
conducts toward CNS
efferent fibers
conducts impulses away from CNS
autonomic nervous system
plays important role in maintaining homeostasis
sympathetic nervous system
tends to activate an organ (ex. increases heart rate)
“fight or flight”
parasympathetic nervous system
tends to inhibit an organ (ex. slows heart rate)
helps control body’s response during times of rest
how is the autonomic nervous system regulated?
integrated reflexes through the brainstem to the spinal cord and organs
motor end plate
chemical synapse formed at the sites where branches of axons contact a target muscle.
AcH from pre-synaptic neurons into synaptic cleft activates nicotinic receptors on the motor end plate
somatic nervous system
allows you to move and control muscles throughout your body
feeds smell, sound, taste, touch to brain
What role do neurotransmitters play on the excitation/ inhibition? Receptors?
by binding to postsynaptic receptors, neurotransmitter can cause excitatory or inhibitory postysynaptic potentials by depolarizing or hyperpolarizing the postsynaptic membrane.
How does exercise play a role in neural adaptations?
stimulates formation of new neurons
improves brain vascular function
function of endocrine system
made up of glands that secrete hormones in the body to regulate the activity of cells or organs
hormones
substances released into the blood from endocrine glands
basal secretion
almost all endocrine cells secrete small amounts of hormones 24/7
negative feedback
secreted hormone acts to decrease its secretion from gland
ex. testosterone
positive feedback
secreted hormone acts to increase its secretion from gland
ex. oxycotin
What role does the circadian rhythm play in the release of hormones? How are hormones cleared?
SCN controls the production of melatonin which plays a role in conveying info about light/dark cycles
cleared by plasma membrane recycling, metabolizing in blood, and kidney/liver
What is the role of the hypothalamus/pituitary gland in the release of hormones?
hypothalamus: controls function of pituitary gland, hormones promote & inhibit pituitary hormone release
pituitary: “master gland”, hormones influence many physiological functions of the body
beta cells
secrete insulin to lower glucose when high
alpha cells
secrete glucagon to increase glucose when low
aldosterone
controls sodium reabsorption and potassium secretion
regulates blood volume & pressure
stimulated by increasing potassium concentration and decreased plasma volume
cortisol
maintenance of plasma glucose (stimulates FFA mobilization, glucose synthesis, blocks glucose uptake into cells)
released by exercise
thyroid hormones
decreased thyroid function = slower metabolism
regulation of thyroid through hypothalamus
thyroxine (T4) secretion
raises metabolism except in brain, spleen, testes, uterus, and thyroid gland
causes sluggishness
regulates growth/development, skeletal & nervous system formation, and maturation/reproduction
triiodothyronine (T3) secretion
facilitates neural reflex activity
regulates growth/development, skeletal & nervous system formation, and maturation/reproduction
growth hormone
released from anterior pituitary gland
builds and repairs lean tissue
loosing adipose tissue
stimulates release of insulin-like growth factors (IGFs)
spares plasma glucose (opposes insulin action to reduce use of plasma glucose)
