NPB 101-Exam 2

Functions of muscles

movement, stability, control of body openings and passages, heat production

Types of muscles

skeletal, cardiac, smooth

Skeletal muscle

striated and voluntary

Cardiac muscle

-Heart muscle; striated
-involuntary

Smooth muscle

-Involuntary muscle found inside many internal organs of the body
-unstriated; involuntary

Organization of skeletal muscle from largest to smallest

whole muscle>fascicle>muscle fiber>myofibril>sarcomere>thick & thin filaments

Sarcomere

-functional unit of muscle shortening

Thick filament

-surrounded by several thin filaments
-composed of myosin

Think filaments

-joined at the Z-line
-composed of actin filament

How does muscle shortening occur?

-occurs when two filament types slide along side one another

H-zone

Corresponds to a break in the thin filaments

M line

-Supporting structure
-middle of sarcomere

Sarcomere structure

One thick filament is interacting w/ 6 other thin filaments

Thin filaments

-Helical actin molecules
-each w/ a myosin binding site to allow for cross-bridge formation

Thin filament structure

-Troponin/Tropomysosin: uncover & cover binding sites for myosin that are on the actin
-Actin: made of G protein

Thick filaments

-myosin molecules; 2 golf club-shaped subunits
-tails aligned toward middle
-globular heads protrude out at regular intervals

Thick filaments structure

-light chains: regulatory proteins coded for by different genes that interact w/ the head groups & cross of myosin bridge

Sarcoplasmic reticulum & T-tubule pt.1

-Sarcoplasmic reticulum surrounds the T-tubules & myofibrils
-calcium from the SR triggers the contraction

Sacroplasmic reticulum & T-tubule pt.2

-t-tubule is an extension of membrane through the muscle cel
-gonna allow the propagation of an action potential inside the myofibril

Motor unit

-One motor neuron & all of the muscle fibers that it contracts
-vary in size & strength

How are motor units intercalated w/in bulk muscle?

You can activate one neuron, two neurons, all neurons & elicit a range of strengths from the same muscle in response to task demands

Each muscle fiber is innervated by just one axon, but..

Each axon branches to innervate all of the fibers in its unit

size principle of recruitment

Recruit the weakest fiber first, if it doesn't illicit response, move up in strength until response occurs

Twitch

The time course of the contraction you get in a single muscle fiber in response to a single action potential in muscle

Excitation-contraction coupling

-sequence of events from motor neuron signaling to a skeletal muscle fiber to contraction of the fiber's sarcomeres
-occurring at the neuromuscular junction

Excitation-contraction coupling steps 1-2

1. Action potentials (AP) propagate down T-tubules
2. APs activate voltage-gated DHP receptors

Voltage-gated DHP receptors

Provides a physical link linking depolarization of the T-tubule membrane w/ the gating open of ryanodine receptor

Excitation-contraction coupling steps 3-5

-DHP activation directly gate open ryanodine receptors on the SR membrane
-CA2+ efflux from SR baths the myofibrils in Ca 2+
-Ca2+ is pumped back into SR via an ATP-dependent pump; muscle relaxes

excitation-contraction coupling @ the filament level

-at rest (low Ca+/relaxed muscle), the cross bridge is energized
-wants to bind to actin but can't b/c actin is covered by tropomyosin

excitation-contraction coupling @ the filament level

-at high Ca+/activated muscle, Ca2+ binds to troponin; uncovers actin by pulling away the tropomyosin

Sliding filament mechanism of muscle contraction

-relaxed:
-A band: corresponds to the length of the thick filament; doesn't change
-I band: end of one thick filament to the end of another
-H band: the tip of one think filament to the tip of another

Sliding filament mechanism of muscle contraction

-shortened:
A band: same length as relaxed
I band & H zone is reduced

The Power Stroke

The myosin heads bind to actin and pull them toward the sarcomere center, which slides the filaments past each other, shortening the muscle.

Steps of Power Stroke

1.) Resting muscle; actin unwound & myosin is bound to ADP/Pi
2.) Ca+2 rises; cross-bridge binds to actin; loses ADP + Pi
3.) thick filament is flexed; actin is bound to myosin; ATP binds to myosin causing the cross-bridge to detach
4.) Hydrolysis of ATP energizes cross-bridge

Muscle spindle

-stimulus that activates the 1a afferent fiber is muscle stretch
-results in muscle contraction

Golgi tendon organ

-stimulus that activates the 1b afferent fiber is tendon stretch (caused by muscle contraction)
-results in muscle relaxation

Muscle spindle is what type of organ?

-a proprioceptor; a sense organ that receives info from muscle, that senses STRETCH & the SPEED of the stretch
-protects you from overstretching or stretching too fast and hurting yourself

Extrafusal skeletal muscle fiber

-highly contractile, regular muscle
-provides force

Intrafusal muscle spindle fiber

-low contractile muscle, maintains sensitivity of muscle spindle

The Golgi tendon organ is what type of organ?

-proprioceptor; a sense organ that receives info from the tendon, that sense tension
-if too much muscle tension, the Golgi tendon organ will inhibit the muscle from creating any force

1b afferent fiber

-info to relax tension flows through here
-triggers spinal response

Muscle tension

Force exerted on an object by contracting muscle

Load

The force exerted on the muscle by an object

Isotonic contraction

Muscle changes length while the load remains constant

Concentric contraction

-shortening
-a type of isotonic contraction

Eccentric contraction

-lengthening
-a type of isotonic contraction

Isometric contraction

-muscle develops tension but does not shorten or lengthen
-generates force

Contraction

Muscle developed tension whether or not it gets longer or shorted or stays the same length

Twitch

The mechanical response of a muscle fiber to a single action potential

Isotonic twitch

-at heavier loads, the latent period is longer, the shortening velocity is slower, the distance shortened is less

Motor unit-tension

-a single axon motor axon & all the muscle fibers it contracts; the muscle fibers contract & that is the amount of tension caused by that motor unit

Motor Units and Recruitment

-the contraction increases w/ the # of motor units recruited & larger motor units produce even stronger tension

Twitch summation

If a muscle fiber is restimulated before it has completely relaxed, the second twitch is added on to the first twitch, resulting in summation

Tetanus

-if a muscle fiber is stimulated so rapidly that it does not have an opportunity to relax at all between stimuli, a maximal sustained contraction occurs

Resting muscle fiber length

-develops max amount of tension b/c the interface between the thick & think filaments is max

Shortened muscle fiber length

-tension because contraction

Stretched muscle fiber length

Sarcomere are pulling apart, less tension than ideal resting length

Fast twitch muscle

-shortens faster due to side-by-side arrangement

Slow twitch muscle

-generates more force b/c of stacked arrangement

1-5 reps & muscle fibers

-no increase in size as fiber contraction force increases

6-8 reps & muscle fibers

-increase size as fiber gins myofibrils & contraction force increases
-muscle bigger & stronger

9-15+ reps & muscle fibers

-increase size as fiber gains Sarcoplasm w/ no contraction force increase
-muscles bigger but not stronger

Hypertrophy

-Bigger muscle cells
-triggered by microtears induced by proper weight training

Hyperplasia

-more muscle cells does not typically occur

Factor determining muscle tension

1) tension developed by each fiber: fiber length, fiber diameter, fatigue, & AP frequency
2) # of active fibers: # of fibers per motor unit & # of active motor units

Muscle fatigue

-when a skeletal muscle fiber is repeatedly stimulated, the tension the fiber develops eventually decreases even though stimulation continues

Creatine phosphate

-supports the first ~15 secs of contractile activity

Oxidative phosphorylation/ glycolysis

-sustained contraction requires either or

Slow-oxidative fibers (type 1)

-combine low myosin-ATPase activity w/ high oxidative capacity; relying on oxidative-phosphorylation
-sustain activity; don't fatigue as fast
-needs glucose/oxygen

Fast-oxidative-glycolic fibers (type 2)

-combine high myosin-ATPase activity w/ high oxidative capacity & intermediate glycolic capacity
-sustain for several minutes, but then they fatigue
-rely on both oxidative phosphorylation & glycolysis

Fast-glycolic fibers (type 2x)

-combine high myosin-ATPase activity w/ high glycolytic capacity
-fatigue rapidly; "fast" twitch
-rely on glycolysis on primarily on glycolysis

Recruitment

-slow twitch fibers have low activation threshold, meaning they are the first recruited when a muscle contracts
-if they can't generate the amount of force necessary for the specific activity, the fast-twitch fibers are engaged

Primary functions of the kidneys

-responsible for maintaining stable volume, electrolyte composition, osmolarity of the ECF

Nephron

Smallest unit capable of performing all the tasks of an organ

Vascular component of the nephron

glomerus, afferent arterioles, efferent arterioles, and peritubular capillaries

Tubular component of the nephron

Starts at bowman's capsule

Cortical and juxtamedullary nephrons

-80% of cortical nephrons lie in the outer cortex layer & 20% lie in the inner cortex layer

Afferent arterioles

Carries blood to the glomerulus

Glomerulus

-A tuft of capillaries that filers a protein-free plasma into the tubular component
-the process of producing filtrate starts here

Efferent arteriole

Carries blood from the glomerulus

Peritubular capillaries

-constant exchange of water & ions; that's the reason for the close proximity of the vascular systems

The pathway of blood

Afferent-> glomerulus->efferent->peritubular

Bowman's capsule

Collects the glomerular filtrate; wraps the glomerulus

Proximal tubule

uncontrolled reabsorption and secretion of selected substances occur here; (H2O & Na+)

Loop of Henle

Establishes an osmotic gradient in the renal medulla that is important in the kidneys ability to produce urine of varying concentration

Distal tubule & collecting duct

Variable, controlled reabsorption of Na+ & H2O & secretion of K+ & H+ occur here; fluid leaving the collecting duct is urine & enters the renal pelvis

juxtaglomerural apparatus

-Produces substances involved in the control of kidney function
-region where the ascending loop of Henle passes through the fork formed by the afferent & efferent arteriole, close to the glomerulus

basic renal processes

-glomerular filtration (urine formation)
-tubular reabsorption (urine formation)
-tubular secretion (urine formation)
-urine excretion

Glomerular filtration

Nondiscriminant filtration of a protein-free plasma from the glomerulus into Bowman's capsule

Tubular reabsorption

-Selective movement of filtered substances from the tubular lumen into the peritubular capillaries
-reabsorbing back ions & H2O

Tubular secretion

-Selective movement of non filtered substances from the peritubular capillaries into the tubular lumen
-actively filtrate out (proteins, K+, etc) to get excreted through urine

Glomerular filtration pt.2

The glomerular membrane is considerably more permeable than capillaries elsewhere

What is the major force causes glomerular filtration rate?

-glomerular capillary blood pressure

To be filtered, a substance must pass through..( steps of glomerular filtration)

1.) the pores between & the fenestrations w/in the endothelial cell of the glomerular capillary
2.) an acellular basement membrane
3.) the filtration slits between the foot processes of the podocytes in the inner layer of Bowman's capsule

Glomerular capillary blood pressure

-The fluid pressure w/in the glomerular capillaries
-favor filtration; pushes filter out
-around 55 mm Hg

plasma colloid osmotic pressure

-H2O wants to move down osmotic gradient into glomerulus; oppose filtration
-concentration gradient of protein; protein stays in capillaries

Bowman's capsule hydrostatic pressure

-the fluid pressure by the filtrate in bowman's capsule; oppose filtration
-a lil liquid in the Bowman's capsule; needs to filter out for more to come in; take pressure (15 mm Hg)

Glomerular Filtration Rate (GFR) depends on..

-bowman's capsule hydrostatic pressure
-plasma-colloid osmotic pressure
-glomerular capillary blood pressure

Controlled adjustments of the GFR

1. Auto regulation
2. Extrinsic sympathetic control

Autoregulation (intrinsic)

-myogenic, local response w/in arteriolar smooth muscle wall to stretch
-tubuloglomerular feedback adjustments to afferent arteriolar pressure in response to the salt concentration in the ascending loop of Henle