vert phys exam 2

skeletal muscle contraction is __________

neurogenic (because it begins when a somatic motor neuron stimulates the muscle fiber, causing it to contract)

proprioception

the sense of static position and movement of the limbs, body, and head  (the sense of starting or current position of body parts, even without movement or vision.)

somatic motor neurons are continuous from …

CNS to target muscle

motor unit

combination of single somatic motor neuron and the skeletal muscle fibers it innervates (one neuron controls a group of fibers)

clostridium botulinum

Toxin interferes with the release of Ach at the neuromuscular junction; Originally used for treatment of dystonias

somatic spinal reflexes

involuntary motor responses to a particular sensory stimulus integrated a the spinal cord level

monosynaptic reflex arc

only one synapse, where the primary sensory afferent bring info from peripheral and enters the spinal cord and synapses directly on a motor neuron and alpha motor neuron brings it back to muscle

monosynaptic reflex arc example

stretch reflex. stimulus/start: rapid stretch of a muscle(deviation) (patellar tendon); response/end: contracting of the muscle that is stretched; cannot voluntarily stop this

polysynaptic reflex arc

involves multiple synapses, takes longer because the sensory neuron communicates with the motor neuron through interneuron(s) (more common)

polysynaptic reflex arc example

the withdrawal (flexor) reflex: pulls a limb away from a painful stimulus by contracting flexors and inhibiting extensors

properties of muscle tissue

electrical excitability, contractibility, extensibility, elasticity

Electrical excitability

muscle tissue is able to produce action potentials

contractibility

all muscles can contract and cause movement

extensibility

can be stretched without being damaged

elasticity

ability to resist being deformed and it then return back to resting equilibrium length

muscle tissues

Skeletal, cardiac, smooth

_______ and______ are striated muscles

Skeletal and cardiac; their contractile proteins are arranged in an orderly pattern

which muscle is voluntary

skeletal; means it is controlled by the somatic system 

myofibers

skeletal muscle cells

whole skeletal muscles are bundles of…

multinucleate myofibers packaged together by layers of connective tissue

endomysium

tissue that bind together individual muscle cells (myofibers)

fasicle

bundled groups of myofibers bound by endomysium

perimysium

tissue that holds together all the fasciles

epimysium

holds the entire skeletal muscle

myofibril

rod-like contractile structures that consist of longitudinally repeated functional units called sarcomeres

Myofilament

contractile protein (thick (A) and thin (I) filaments)

sliding filament mechanism of skeletal muscle contraction

The increases and decreases of overlap between the thick and thin filaments that is responsible of the sarcomere length

thick filaments

composed of bundles of myosin (protein complex)

thin filaments

composed of actin (round, globular protein); two strands wind up to make up the filament

myosin complex

Made up of 2 head regions that are motor proteins with a neck region that can bend or flex

myosin motor protein activity

the head have ATPase activity and hydrolyze ATP and couple the thermodynamically favorable hydrolysis of ATP to movement (bending or flexing of neck region); The head region is connected to a long tail  (2 heads, 2 necks, and a single tail)

troponin and tropomyosin

regulatory protein complex that works together on the actin, thin filaments

cross bridge binding site

location where myosin head can interact/bind to (weakly) actin 

transverse (T) tubules

continuations of the plasma membrane that go down the depths of the skeletal muscle cells; action potentials travel this way

Sarcoplasmic reticulum (SR)

membrane network in muscle fibers that stores and releases calcium to regulate contraction and relaxation; surronds the T tubules

lateral sacs

enlarged calcium-storing regions of the SR next to the T-tubules that release Ca²⁺ during muscle contraction. (one on both sides of T-tubule)

Triad junction

excitation-contraction occurs here; contains the T tubule, and two lateral sacs

dihydropyridine receptors (DHPRs)

voltage censored trigger receptors that change conformation; located in the T tubule membrane and the depolarization from AP triggers to change conformation; take in calcium

ryanodine receptors (RyRs)

spans the sarcoplasmic reticulum membrane, They are calcium channels; gets mechanically pulled open by DHPRs

Excitation-contraction

you start with the muscle action potential and then for the contraction, you end in an elevation of cytoplasmic calcium concentration which is our link that allows for our cross-bridge binding 

SERCA Ca2+ pumps

primary active transporters in the SR membrane that use energy from ATP hydrolysis to pump Ca2+ from the cytoplasm into the SR lumen, helping maintain the high calcium concentration inside the SR and allowing the muscle fiber to relax

Calsequestrin

calcium-binding protein in the SR lumen that binds and stores free Ca²⁺, allowing the SR to store a larger total amount of calcium while keeping free luminal calcium concentration relatively lower.

_______ is the link between excitation and contraction

calcium

tropomyosin

covers cross-bridge binding sites under resting cytoplasmic Ca²⁺ concentrations

TnT

troponin subunit that binds to tropomyosin to make the troponin-tropomyosin and anchors it on the actin (thin filament)

TnC

calcium center and binds; once bound it causes a conformational change of the complex and shift tropomyosin so the myosin-binding sites on actin are exposed to help start contraction.

TnI

troponin complex that inhibits actin-myosin interaction when muscle is relaxed (Ca low)

how does calcium go back down to resting levels after contraction

Ca²⁺ is actively pumped out of the cytosol and back into the SR by SERCA pumps and once the RyRs are no longer open, which lowers cytoplasmic Ca²⁺ to resting levels and causes relaxation.

from neural impulse to skeletal muscle contraction

Excitation-secretion coupling, Synaptic transmission, Excitation-contraction coupling, Cross-bridge cycling (mechanochemical coupling)

Cross-bridge formation

stage where myosin head group is in a “primed” state and binds to available cross-bridge binding site; head group has a high affinity; neck region is extended 

Power stroke

stage where bending of the neck region is initiated by the release of an inorganic phosphate group from the myosin head; causes a conformational change (bending neck region)

Cross-bridge dissociation

ADP is lost and then the opening of for the ATPase enzyme site is open which allows the ATP to bind; stage where ATP binding to the ATP site causes a conformational change and this decreases affinity of the myosin head group for the cross-bridge binding site

Priming of myosin head group

stage where ATP hydrolysis causes neck region to extend (primed) returning myosin head to its energized conformation with a high affinity to the cross-bridge binding site (ADP and inorganic phosphate still associated); the neck region extends back out and high affinity for the site 

Active components in skeletal muscle contractions

generate tension(involved in cross bridge cycling)

Passive components

respond to outside forces (part of the overall structure but not involved in creating tension just responding) includes: series elastic and parallel elastic

Series elastic component

being pulled on; (ex. tendons that attach muscle to our bone)

Parallel elastic component

has to compensate for change; able to move around (ex. cell membrane) 

two types of contractions

isometric and isotonic contractions

Isometric contraction

 (same length) muscle develops tension but does not shorten

Isotonic (concentric) contraction

tension developed overcomes the imposed load (opposing forces) and causes the muscle to shorten

Active tension developed during muscle contraction is directly proportional to…

the number of simultaneously cycling cross-bridges (more cross-bridges that are attached and pulling at the same time, the more force the muscle produces)

Force of contraction can be regulated at two levels…

whole muscle level and muscle fiber level

whole muscle level regulation

motor unit recruitment: A stronger contraction is due to multiple motor units; more cells the stronger the contraction. We can voluntarily control

muscle fiber level regulation

fiber diameter, length-tension relationship, stimulation frequency

fiber diameter

more myofibrils packed in a muscle cell makes a larger diameter = more sarcomere = cross-bridges = more force

Length-tension relationship

the force of a muscle twitch depends on the sarcomere’s resting length before stimulation. Maximal twitch force occurs at the optimal sarcomere length, where actin-myosin overlap is ideal for cross-bridge formation; force decreases when the sarcomere is either too short or too stretched.

Tetanus

a strong maximal sustained contraction (no relaxation); the strongest contraction is due to the enough cytoplasmic Ca²⁺ present and all the myosin heads are able to bind in a cross bridge cycle. True tetanus contraction is rare and its possible it can cause damage

Twitch summation

The second twitch is larger than first because the muscle has not fully relaxed, so residual Ca²⁺ and reduced slack allow more cross-bridges to cycle and produce greater force.

optimal muscle/sarcomere length

the strongest twitch per muscle AP (more cross bridge cycling) 

fusion frequency

The frequency of stimulation at which tetanus is reached

circulatory system

provides a functional connection between individual organs/tissues for the rapid exchange of material 

Heart

pressure/flow generator of blood (drives blood flow with a net movement based on pressure gradients)

Arterial system

functions in blood delivery and distribution to tissues

Blood is delivered in _______

parallel; it is distributed into branching arteries and arterioles that supply different organs at the same time; organs receive blood through separate vascular pathways, rather than one organ after another in a single series path.

capillaries

function in nutritive exchange

Arteries and arterioles

arterial system that delivers blood to capillaries

Venous system

functions in blood collection and return to the heart (venules and veins)

The heart is located within the _______ _____

thoracic cavity; lies between breastbone and vertebral column

heart anchored within…?

mediastinum of the thoracic cavity by the pericardium

pericardium

a double walled serous membrane surrounding the heart

serous membrane

function to cushion organs and provide lubrication (reduces friction) during movement

Parietal pericardium

the outer layer of the pericardium membrane

Visceral pericardium

the inner layer of the pericardium membrane (its up against the heart)

pericardial fluid

between the parietal and visceral

Epicardium

the outermost layer of the heart wall; (epithelial and connective tissue) is continuous with the visceral pericardium

Myocardium

vast bulk of the heart contains cardiac muscle tissue

Endocardium

innermost layer of the heart; connective tissue and special layer of epithelial tissue called endothelial; lines the entire cardiovascular system (every blood vessel); this continuous endothelial barrier makes up our closed circulatory system

cardiac cycle is the full sequence of events that occur during a _____ ____

single cycle (begins and ends in the same state)

Hydrostatic pressure

pressure that pushes blood equally in all directions; the cardiac concentration generates thsi pressure that srives bulk flow of blood

Pressure

force per unit area or energy per unit volume

Systemic circulation

high resistance, high pressure system (120/80 mmHg); More muscle on the left side because it has to pump harder to generate the same amount of flow of blood and pressure (to get the same unit per time as the right side)

Pulmonary circulation

low resistance, low pressure system (22/8 mmHg)

contraction causes the _____ and the pressure gradient causes the ____

pressure; flow

valve

a one-way pressure operated flap located at the exit of each heart chamber function to ensure unidirectional flow

Papillary muscle

muscles in the walls of the ventricles that contract during ventricular systole to tighten the chordae tendineae and help keep the AV valves from flipping backward. (aversion)  

Chordae tendineae

Strong, tendon-like cords that connect the papillary muscles to the cusps of the atrioventricular (AV) valves. They prevent the valves from everting or prolapsing into the atria when ventricular pressure rises during contraction

Passive ventricular filling

1. Begins with opening of AV valves

2. About 80% of ventricular filling occurs passively

3. All of cardiac muscle is relaxed (ventricles and atriums are in a state of diastole)

4. Ventricles filling with blood from the atrium 

Active ventricular filling

1. Begins with onset of atrial systole; after passive ventricular filling

2. Atrial contraction drives remaining 20% or so of blood into ventricles

Isovolumic ventricular contraction

1. Once the ventricles contract they start increasing pressure; as soon as this ventricular pressure surpasses it closes the AV valves; after active ventricular filling

2. Begins with closure of AV valves 

3. Increase in ventricular pressure but no change ventricular volume; this happens until the ventricular pressure surpasses that of the major artery then next phase happens

Ventricular ejection

1. Happens during ventricle contraction/systole; after isovolumic ventricular contraction  

2. Begins with opening of semilunar valves