Exam #3 Flashcards
If small generator potentials reach a critical threshold near -40mV…
Na+ channels and K+ channels will sense the voltage change and open. Causing an all or none action potential to fire.
Action potentials travel to the synapse and lead to…
The release of neurotransmitter.
The junction between the terminal branch of the nerve fiber and muscle fiber is called…
Neuromuscular junction.
What areas of the brain contribute to the program of voluntary movement of muscles?
Primary motor cortex
What areas of the brain contribute to the execution of muscle voluntary movement?
Pyramidal tract
Motor neuron
What areas of the brain provide feedback for the execution of muscle voluntary movement?
Sensory systems Cerebellum Thalamus Basal nuclei Brainstem
The primary motor cortex resides in…
Precentral gyrus
When you stimulate the primary motor cortex (motor homunculus) what is the result?
Twitch in the contralateral side.
What are upper motor neurons?
Reside in the primary motor cortex.
Large betz cells that send long axons down towards the spinal cord.
How does the basal ganglia motor loop help select and initiate movement?
Focuses activity from widespread regions onto the thalamus, then back onto the motor cortex (areas 4 and 6).
The basal ganglia consists of…
Caudate, putamen, and globus pallidus.
Lesions of the caudate (in the basal ganglia) results in…
Huntington’s disease.
Lesions of the substantia nigra (in the basal ganglia) results in…
Parkinson’s disease
What is the cerebellum’s function?
Coordinates muscle movement through direction, timing, and force.
Compares intended movement coming from the motor cortex with actual movement sensation (proprioception) coming in from the joints and muscles.
What is the pathway of voluntary movement in the CNS?
- Motor cortex axons descend through medulla.
- Cross over/decussate.
- Descend pyramidal tract.
- Synapse onto alpha motor neurons in the ventral horn of the spinal cord.
Action potentials in ___________ lead to muscle contraction.
Alpha motor neurons
the axons branch and innervate multiple muscle fibers
Loss of motor neurons either sporadically or inherited causes…
Amyotrophic Lateral Sclerosis (ALS)
Motor neurons degenerate and die leading to muscle atrophy.
Brain and cognition is still intact but muscle cannot be commanded to move.
Simple reflex skeletal muscle movement is mediated at…
The spinal cord level.
The 5 parts of a reflex arc are:
- Receptor - muscle spindle
- Afferent neuron - sensory dorsal root ganglion.
- CNS - spinal cord
- Efferent neuron - alpha motor neuron
- Effector - muscle
What do weak or absent reflexes indicate?
Damage is done to the spinal cord at the reflex site. Sensory nerve damage Motor nerve damage Spinal cord damage Tendon/muscle damage
What do exaggerated reflexes indicate?
Damage is usually done below the site of spinal cord damage as the brain generally inhibits downstream alpha motor neurons.
What are skeletal muscles connected to?
Bones via tendons.
What are bundles of long multinucleated cells?
Myofibers
Inside myofibers are an extensive network of intracellular filament proteins called…
Myofibrils
intracellular proteins = actin and myosin
What is the origin of skeletal muscles?
Connection to stationary bone.
What is the insertion of skeletal muscles?
Connection to movable bone.
Isotonic muscle contractions result in…
Muscle SHORTENING.
The load is easily lifted.
Isometric muscle contractions result in…
Tension WITHOUT muscle shortening.
The load is too heavy to lift.
The sarcomere still shortens but series elastic elements (tendon) lengthen.
What neuron makes synapses with skeletal muscle cells to help the muscle contract?
Alpha motor neurons.
How do alpha motor neurons help with muscle contraction?
Release ACh onto the target muscle, which binds to the Nicotinic ACh Receptor.
The neuromuscular junction illustrated the precise alignment of…
Presynaptic active zones with postsynaptic nACh receptors.
T or F: Nicotinic Acetylcholine Receptor is a g-protein coupled channel.
FALSE
It is a ligand gated ion channel.
What happens once 2 acetylcholine molecules bind to the nicotinic receptor?
The receptor conformation changes, it channel opens, Na+ flows in, and the postsynaptic muscle cell becomes depolarized.
How is neuromuscular signaling ceased?
Acetylcholine is destroyed by acetylcholintesterase.
How does curare, the plant toxin, act on the muscles of hunted prey?
It inhibits the nACh receptor and stops the neuromuscular junction signaling.
If a prey is injected with curare, is it safe to eat?
Yes. Curare is too large and highly charged to pass through the lining of the digestive tact.
What is myasthenia gravis caused by?
Auto-antibodies to the nACh.
How does botox work?
Botulinum toxin inhibits SNARE protein exocytosis machinery and ACh release, so muscles don’t receive the signal to contract and wrinkles are relaxed.
What is the sarcomere, a muscle contractile unit, composed of?
Actin: scaffold for myosin.
Myosin: motor ratchet protein that binds and pushed actin.
Tropomyosin: covers actin binding sites during rest.
Troponin: binds Ca++ and move tropomyosin.
How does myosin form cross-bridges with actin?
Utilizes ATP to act like a molecular motor and pulls neighboring actin closer together. This shortens the sarcomere length and generates tension (force).
Regulated by Ca++, troponin, and tropomyosin.
What happens when Ca++ binds to troponin?
Troponin changes shape which displaces tropomyosin, allowing actin and myosin to interact.
Once action potential is propagates down the muscle sarcolemma and t-tubules…
Ca++ is released from intracellular stores in sarcoplasmic reticulum.
What is the function of DHP-Ryanodine receptors?
Mediate Ca++ release from sarcoplasmic reticulum.
Physically links T-tubule to sarcoplasmic reticulum.
What causes Ca++ channels to open from the SR?
Voltage change in T-tubule.
Ca++ efflux from SR to cytosol.
What is required to release the myosin head from actin?
ATP.
If no ATP rigor mortis occurs.
What events at the NMJ occur to lead to Ca++ influx?
Actin/myosin cross-bridge cycling.
Pumping of Ca++ back into SR.
What is ATP used for in muscle contraction?
Myosin release.
Ca++ pumped into the ER.
What does force come from in muscle contraction?
Actin/myosin cross-bridging.
T or F: skeletal muscle fiber diameter affects contraction strength.
True.
Add more myofibrils (actin/myosin cross-bridging) more strength is produced.
T or F: you canNOT incerase the number of myofibrils per muscle cell.
False.
You can increase the number of myofibrils per muscle cell with exercise.
What three mechanisms regulate contraction strength?
Recruitment: bringing in more individual motor units.
Summation: high frequency action potentials cause multiple contractions to add together.
Length-tension: sarcomeres have optimum length for optimum actin/myosin overlap.
T or F: all 3 mechanisms affecting contraction strength also affect cross-bridge cycling.
True.
Are all fibers of a given muscle used in every single contraction?
No - muscle fibers (motor units) are recruited based on the amount of force required fro a given movement.
T or F: nerve action potential is short.
True.
It is relative to muscle contraction.
Meaning that multiple muscle action potentials can occur during one muscle contraction allowing another contraction to start before the earlier contraction is finished.
A relatively show train of action potentials leads to…
Subsequent stronger INDEPENDENT muscle contractions, also known as Treppe.
What are two causes of Treppe?
Warming of muscle fibers.
Increased cytosolic Ca++ which ensures extra cross-bridging.
What are some probable causes of fatigue of muscles?
Depletion of ACh.
Depletion of energy reserves exacerbated by blood vessel compression.
Lactic acid buildup.
How is lactic acid formed?
If no oxygen products from oxidative phosphorylation and the kreb’s cycle are produced, it causes a build up of pyruvates. Those pyruvates are converted into lactate in the cytosol for a short-term fix.
What are the 3 muscle contraction phases?
- Latent period
- Contraction
- Relaxation (pumping Ca++ moves troponin and tropomyosin back over binding sites)
Cross-bridge cycling rate is dictated by…
The type of myosin present.
Fast myosin hydrolyzes ATP faster.
Slow myosin hydrolyzes ATP slower.
An example of a muscle with fast twitch fibers is _________.
eye muscles
An example of a muscle with slow twitch muscle fibers is ________.
soleus in foot
What are some characteristics of glycolytic fibers?
Fast/white.
Have a high expression levels of fast myosin and glycolytic enzymes.
Recruited when high force is requires (weight lifting or sprinting).
What are some characteristics of oxidative fibers?
Slow/red.
Rich in slow myosin, mitochondria and myoglobin, and have a high capacity for ATP production via oxidative phosphorylation.
Typically used first for modest requirements like long-distance running.
What are some main characteristics of smooth muscle?
They have no striations because myosin and actin are arranged differently.
Tend to contract as a unit instead of individual fibers (gap junctions and varicosities).
Controlled by the ANS and is involuntary.
Stimulated by ACh and norepinephrine.
Contraction of smooth muscle in arteries causes…
Vasoconstriction
Small radius and flow.
Relaxation of smooth muscles in arteries causes…
Vasodilation
Large radius and flow.
How are smooth muscles able to contract as a unit?
Varicosities along the neuronal axon allow diffusion of neurotransmitter over large sections of smooth muscle.
Gap junctions in a single unit also help distribute contraction signal.
What does the sympathetic nervous system release?
Norepinephrine (or epinephrine from adrenal medulla) onto target organs. The neurotransmitters bind adrenergic receptors.
What kind of affects does Beta-1 blockers have on the nervous system?
Block sympathetic excitatory affects on the heart.
Hypertension.
What kind of affects does Beta-2 agonists have on the nervous system?
Dilate lung airways by inhibiting smooth muscle contraction.
Asthma.
a1 adrenergic receptor activation causes smooth muscle contraction via…
Gq coupled receptor Ca++ release.
Smooth muscles have what type/s of Ca++ channels?
Voltage gated
Ligand gated
Mechanical/stretch gated
Excitation contraction coupling in smooth muscle utilizes _________ instead of troponin.
Ca++ calmodulin
In excitation contraction coupling, myosin needs to be __________ to stimulate cross-bridge cycling.
phosphorylated via MLCK
Beta-adrenergic receptors __________ adenylate cyclase signal transduction via _____.
Activate
Gs
Alpha-2 adrenergic receptors _________ adenylate cyclase signal transduction via _____.
Inhibit
Gi
Sympathetic activation coordinates “fight or flight” response by flooding the body with nor/epinephrine, which stimulates….
Variety of different adrenergic receptor subtypes scattered throughout the body causing appropriate response on tissues expressing particular receptors.
Sympathetic activation increases heart rate and cardiac output (beta-1) and appropriately distributes blood flow to skeletal muscles by…
Vasoconstricting most body arterioles (alpha-1).
Vasodilating skeletal muscle arterioles (beta-2) so they receive more blood.
Parasympathetic neurons release ________ onto target organs during times of rest.
Acetylcholine
T or F: muscarinic acetylcholine receptors are g-protein coupled.
True
What does the M1 muscarinic receptor do?
Closes the K+ channel, causing depolarization.
What does the M2 muscarinic receptor do?
Opens the K+ channel, causing hyperpolarization.
An example would be slowing heart rate.
What does the M3 muscarinic receptor do?
Increases Ca++ via IP3 and leads to smooth muscle contraction.
What other brain areas influence autonomic output?
Hypothalamus and amygdala.
T or F: arteries return blood to the heart, carrying metabolic wastes (urea, CO2) away from tissues.
False - that is the job of veins.
Arteries carry blood away from the heart and deliver nutrients, hormones, and O2 to tissues.
What are the three layers of the heart?
Epicardium: outer layer composed of connective tissue
Myocardium: middle layer composed of muscle tissue
Endocardium: inner layer composed of endothelial tissue.
T or F: the blood inside of heart chambers feed the heart tissue.
False
Only contained in chambers to be pumped throughout the body. Blood is being fed to body through coronary arteries.
What is myocardial ischemia?
A condition caused by a lack of oxygen due to blockage of blood.
What is myocardial infarction?
Also known as a heart attack, a condition where heart tissue dies and begins to scar.
What is ventricular fibrillation?
A condition in which there are unsynchronized contractions. Results in death.
Which side of the heart contains the pulmonary circuit and what is its function?
Right side of the heart.
Receives deoxygenated blood from tissues and sends that blood to the lungs.
Which side of the heart contains the systemic circuit and what is its function?
Left side of the heart.
Receives oxygenated blood from the lungs and sends that blood to the rest of the body.
What structure in the heart ensures unidirectional blood flow?
Chordae tendinae - keep atrioventricular vales from prolapse.
What is the main function of the Atrioventricular Valves?
Allow blood to flow from atrium to ventricle.
What is the main function of Semilunar Valves?
Located between ventricles and arteries to push blood to the rest of the body.
Both atria contract to help fill ventricles, 80% of the blood filling is based on ____________.
Venous return
What are important characteristics of the SA node?
Site of initiation of electrical activity.
Autogenic (creates own electricity/pace) but autonomic nervous system can modulate rate.
Spontaneously depolarizes at 100 bpm.
What are important characteristics of the AV node?
Slows/delays the electrical impulse before it reaches the ventricles (once received by the SA node).
40-60 bpm.
What are the functions of gap junctions in cardiac muscle?
Rapidly disperse ions to nerighboring heart cells (Na+ and Ca++).
Allows heart muscle cells to contract in unison.
Allows efficient pumping/filling.
What is the order of cooordinated electrical activity in the the heart?
SA node Gap channels Atria contract AV node slows purkinje/gap channels Ventricles contract
What is indicated by the P wave?
Atrial depolarization
What is indicated by the QRS complex?
Atrial repolarization and ventricular depolarization.
What is indicated by the T wave?
Ventricular repolarization
What are the two principal cell types in the heart?
Pacemaker cells (SA node) and contractile cells.
What makes pacemaker cells different from contractile cells (in regard to membrane potential)?
Pacemaker cells have “funny” Na+ channels which open upon repolarization instead of opening upon threshold, like contractile cells.
Pacemaker cells have two types of Ca++ channels: T-type (short) and L-type (long)
Contractile cells have a long action potential, which plateaus because of Ca++ and K+ channels opening.
What properties are the same in CARDIAC and SKELETAL muscle?
T-tubules, SR, and troponin-tropomyosin.
What properties are the same in CARDIAC and SMOOTH muscle?
Gap junctions and extracellular calcium.
Why is the heart unable to undergo summation and tetany?
The long-lasting action potential overlaps in time with muscle contraction events, so only one contraction can occur at a time.
Sympathetic release of ____________ causes higher cardiac output (heart rate and stroke volume).
norepinephrine
Parasympathetic release of ___________ causes lower cardiac output (lower heart rate).
acytylcholine
How does the sympathetic NS increase cardiac output?
By affecting the “funny” Na+ channels and allowing the SA node cells to depolarize faster.
Releasing norepinephraine onto the Beta-1 adrenergic receptor leads to phosphorylation of Na+ and Ca++ channels - making them easier to open.
How does the parasympathetic NS decrease cardiac output?
By hyperpolarizing the SA node.
How does the sympathetic NS increase contractility?
Increases available Ca++.
Once nor/epinephrine is binded to Beta-1 adrenergic receptors, Ca++ channels open.
How does the parasympathetic NS decrease cardiac output?
By binding ACh to the muscarinic receptor, G-protein supplements K+ channel opening and closes the Ca++ channel, causing hyperpolarization.
What is the difference between systole and diastole?
Systole = ventricle contraction Diastole = ventricle filling
The first heart sound, caused by AV valves closing is called…
Soft lubb
The second heart sound, caused by semilunar valves closing is called…
Loud lubb
When is ventricular pressure the highest?
Mid-ventricular systole.
Aortic pressure increases during __________ and slowly dissipates during _________.
ventricular systole
diastole
(still remains high throughout).
Stroke volume is the volume of blood….
ejected from the heart during a single beat.
SV = (end-diastolic volume) - (end-systolic volume)
Roughly ____ of the ventricular blood volume is ejected per heartbeat.
half
Stroke volume can be changed depending on the need via…
ANS and length tension.
What is stated in Frank-starling’s law?
The more blood that enters the heart (venous return) the more blood that leaves.
Meaning that it is in control of the heart.
