muscular system lec

skeletal, cardiac, smooth muscle

muscle types found in the body

skeletal muscle

voluntary (biceps, triceps)

smooth muscle

involuntary (hollow organs)

cardiac muscle

involuntary (myocardium)

contractility, excitability, extensibility, elasticity

4 major functional properties

contractility

ability to shorten forcefully

excitability

can respond to electrical stimulus

extensibility

can stretch beyond its resting state

elasticity

ability to spring back to original resting length

Muscle FIber

Each skeletal muscle cell has

skeletal muscle

surrounded by connective tissues

fascia, epimysium, perimysium, endomysium

4 layers of connective tissues that protects skeletal muscle

skeletal muscle

rich blood supply and nerves (motor nuerons)

synapses/neuromuscular junctions

contact points in between muscle fibers - axons

myoblast fuse

what form 1 skeletal muscle fiber

muscle fiber

very large cell

hypertrophy

muscle gets bigger because fibers increase in size

electrical and mechanical components

2 main components of muscle contraction

electrical component

excitability, ability to receive and respond to electrical stimulus

mechanical component

contractility, Muscles ability to generate force and shorten when activate

sarcolemma, t-tubules, sarcoplasmic reticulum

electrical components

t-tubulues

inward folds of sarcolemma carry electrical impulses into the center of the muscle fiber

sarcolemma

plasma membrane of muscle fiber

sarcoplasmic reticulum

store and releases calcium for contraction

myofibrils, sacromere

mechanical components

myofibrils

bundles of protein filaments

actin & myosin

two types of myofibrils

sarcomere

actin & myosin arrangement forming a single contractile unit

actin

thin

myosin

thick

i band, a band, z disk, h zone, m line

sarcomere five types

i band

light (actin filaments only)

a band

dark (both actin and myosin filaments)

z disk

anchors ends of actin filaments

h zone

center of each a band

m line

dark line in the middle of the H zone

g-actin, tropomyosin, troponin

actin filament protein

g-actin

globular unit, active site for myosin filament binding

tropomyosin

long fibrous protein, covers the site of G acti in the relaxed state

troponin

protein molecules with with 3 subunits

troponin c, troponin i, troponin t

troponin 3 sub units

troponin c

calcium binding unir

troponin I

inhibitory unit

troponin t

attaches troponin to an actin

2 myosin heavy chain/tail, 2 myosin heads

myosin filament protein

2 myosin heads

Binds to the active site of actin Heads are attached to the rod apportioned by a hinge region

neuromuscular junction

synapse the site where a nerve cell communicates with a muscle cell to initiate a muscle contractions

action potential

electrical signals (motor neurons) that stimulate muscle contraction

pre-synaptic terminal, synaptic cleft, post-synaptic terminal

action potential consists of:

pre-synaptic terminal

terminal axon and sarcolemma

synaptic cleft

space between

post-synaptic terminal

acetylcholine receptor

ligand-gated ion channel, voltage-gated ion channels

2 MAJOR CHANNELS (Production of Action Potential)

ligand-gated ion channel

opens when a chemical signal binds to a receptor

voltage-gated ion channel

open/close in response to specific membrane potential

resting membrane potential

charge difference in an unstimulated cell

k higher inside cell, na higher outside cell, Plasma membrane more

permeable to K than Na

3 factors of resting membrane potential

threshold

when action potential is triggered. Na channels open (Na goes inside the cell)

depolarization, repolarization

2 phases

depolarization

↑ charge inside cell

repolarization

returning to resting state

excitation-contraction coupling

Action potentials produced in the sacolemma of a skeletal muscle fiber can lead to contraction of the muscle fiber.

calcium

important ion for contraction, stored in sarcoplasmic reticulum

cross-bridge movement

mechanical component of muscle contraction

muscle relaxation

Occurs when acetylcholine is no longer released at the neuromuscular junction → stops Calcium release

muscle twitch

single action potential along a motor neuron

lag, relaxation, contraction

3 phases of muscle twitch (LRC)

isometric contraction and isotonic contraction

types of contraction

isometric contraction

muscle does not shorten and increase muscle tension, same length

isotonic contraction

increase tension; muscle length shortens

summation and recruitment

changes in length of muscle contraction depends on;

summation

amount of force in an individual muscle fiber

recruitment

amount of force in a whole muscle

motor unit

single motor neuron and all the muscle fibers it innervates

force of contraction

muscle respond to stimuli in the graded fashion

force of contraction

The amount of force generated in a single muscle fiber depends on the number of cross-bridges formed

frequency of stimulation, muscle fiber diameter and muscle fiber length at the time of contraction

3 factors

treppe (staircase phenomenon)

The gradual increase in the force of muscle contraction

wave summation

Muscle fibers are stimulated at greater frequencies, and relaxation occurs after

tetanus

Continuous stimulation and contraction without relaxation

incomplete and complete

two types of tetanus

incomplete (unfused)

twitch merges together

complete (fused)

complete contraction without relaxation

MUSCLE FIBER DIAMETER

Greater muscle fiber diameter → more cross-link bridges → greater force can generate