chapter 9: muscles

what is myology?

the study of muscles

what is extrinsic movement?

the movement of bones

what is intrinsic movement?

the movement of internal bones

what are other functions of muscles

distribute heat throughout the body

essential for maintaining posture

what are the 3 types of muscles?

1. skeletal
2. smooth
3. cardiac

what is skeletal muscle?

muscles that connect to your bones

voluntary

what is smooth muscle?

muscle that is found inside your hollow organs

involuntary

what is cardiac muscle?

muscle that is found in the heart

involuntary

what does skeletal muscle consist of?

skeletal muscle tissue

nervous tissue

blood

connective tissue

what is fascia?

dense connective tissue that operates and hold individual skeletal muscles in position

how are tendons formed?

when connective tissue surrounding the muscle extends beyond the muscle fibers

what can connective tissue associated with muscle also form

brand sheets (aponeuroses) that can connect to bone or the covering of adjacent muscle

what are the 3 layers of connective tissue within muscles?

1. epimysium
2. perimysium
3. endomysium

what is the epimysium?

the 1st layer of connective tissue that closely surrounds skeletal muscle (outer layer)

what is the perimysium?

the 2nd layer

extended inward from perimysium and separates the muscles in sections containing bundles of muscles fibers (fascicles)

what is the endomysium?

3rd layer

separates each muscle fiber within fascicles

what is located within the sarcoplasm?

* the sarcoplasmic reticulum runs parallel to the myofibrils
* transverse tubules are continuations of the sarcolemma, each t-tubule lies between cistern of the sarcoplasmic reticulum
* t-tubules are important to send impulses to the cell for contraction

what is a muscle fiber?

a single muscle muscle cell

how are multi nucleated muscle cells formed

during development, undifferentiated cells fuse together

what does the sarcolemma (muscle cell membrane) surround in muscle fibers?

the sarcoplasm (muscle cell cytoplasm)

what does sarcoplasm contain

abundent myofibrils

what are myofibrils fundamental for?

muscle contraction

what 2 types of protein do myofibrils contain?

myosin (think filament)

actin (thin filament)

what do the 2 types of protein in myofibrils produce?

thew alternating light and dark striations characteristics of skeletal muscle

what are sarcomeres?

repeating pattern of striation units

what are muscles a collection on?

sarcomeres

what are “I” bands (light bands)

bands composed of thin actin filaments

what are z-lines?

structures that attach “I” bands together

what are “A” bands (dark bands)?

bands composed of thick myosin filaments that overlap thin actin filaments

what is the H zone?

area of only thick bands

what is the m line?

consist of proteins that help hold the thick filaments in place

what is titin?

protein that myosin filaments use to attach to the “Z” line

what are thick filaments composed of

many molecules of myosin

what does each myosin molecule consist of?

2 twisted protein strands with gobbler heads that project out

what do thin filaments consist of?

double strands of actin twisted into a helix

what can each actin molecule serve as?

a biding site for each myosin head

what do troponin and tropomyosin form with actin molecules?

a complex

what is a synapse?

a functional connection (no direct access)

what are neurotransmitters?

chemicals released by neurons that are used to send signals to cells

what are motor neurons?

neurons that control skeletal muscle and are needed for muscle contraction

what is the neuromuscular junction?

synapse between a motor neuron axon and a skeletal muscle fiber

what is the motor end plate?

muscle fiber from neuromuscular junction has nuclei and a lot of mitochondria

where neurotransmitters bind to muscle

what is the synaptic cleft?

separates the membrane of the neuron and the membrane of the muscle fiber

what is the synaptic vessel?

holds neurotransmitter in axon

what do motor neurons use to control skeletal muscle contractions?

acetylcholine (ACh)

what does acetylcholine diffuse across and bind to?

it diffuses across the synaptic cleft and binds to receptors on the sarcolemma

what is the sodium potassium pump?

a pump that transports sodium out of the cell and potassium into the cell

3 sodium out, 2 potassium in

what is the sodium concentration gradient like at the sodium potassium pump?

the sodium concentration is very high outside of the cell

what type of transport is the sodium potassium pump?

active- requires ATP

what is the neurotransmitters of motor neurons?

acetylcholine

what does acetylcholine do target cell permeability?

it increases the target cells permeability to sodium ions

what does an increase in permeability caused by ACh lead to?

positively charged sodium entering the cell

positively charged potassium leaving the cell

what does ion movement cause?

a bioelectric current aka an impulse

what does the sarcoplasmic reticulum have a high concentration of?

calcium ions

what does the calcium pump do?

pump calcium into the membrane of the sarcoplasmic reticulum

what does the impulse increase the permeability of?

the cisternae of the sarcoplasmic reticulum

what diffuses out of the cisternae into the sarcoplasm?

calcium ions

during muscle contraction what do thick and thin filaments do?

they slide past each other rather than changing length

where are thin filaments pulled towards during muscle contraction?

the are pulled towards the center of the sarcomere

what does acetylcholinesterase do?

decomposes any ACh that is left in the synapse

what does a lack of ACh lead to during relaxation?

electrical impulses are prevented from traveling down the muscle fiber

calcium pumps are able to remove calcium from the cytosol and back into the sarcoplasmic reticulum

cross-bridges break

tropomyosin returns to relaxed configuration by covering actin bonding sites

what is myasthenia gravis?

weakness and rapid fatigue of skeletal muscle

what does the immune system produce during myasthenia gravis?

antibodies to ACh receptors

antibodies to tyrosine kinase receptor

interferes with the ability to generate electrical impulses

what are the symptoms of myasthenia gravis?

weakness of arm/leg muscles

troubling holding up your head

double vision

drooping eyelids

difficulties with speech

difficulty chewing and swallowing

difficulty breathing

what are the treatments for myasthenia gravis?

cholinesterase inhibitors

corticosteroids

plasmapheresis

surgery

what does cholinesterase inhibitors do for myasthenia gravis?

prevent degradation of ACh, improving communication between nerve and muscle

what does corticosteroids do for myasthenia gravis?

inhibit the immune system, impairing antibody production

what does plasmapheresis do for myasthenia gravis?

blood is filtered to remove antibodies an the returned to the patient

what do muscles need a lot of and must be able to generate quickly?

ATP

what is the initial source used to regenerate ATP?

creatine phosphate

how much more abundant is creatine phosphate than ATP

4-6x

what happens when cellular ATP is high?

creatine → creatine + P

ATP → ADP

what happens when cellular ATP is low?

creatine + p → creatine

ADP → ATP

what is needed for cellular respiration?

oxygen

what do muscle cells synthesize?

myoglobin

what serves as a temporary oxygen storage for when blood flow is interrupted during contraction?

myoglobin

what happens to the body during strenuous physical activity?

the body is unable to supply enough oxygen for cellular respiration

what do anaerobic conditions result in?

2 ATP from the breakdown of glucose, need oxygen for the CAC and ETC

what does myoglobin give muscle

its reddish/brown color

what is the lactic acid threshold?

change in metabolism

what can the liver turn lactic acid into?

glucose but this requires ATP

what is oxygen used for during strenuous activity?

used to synthesize ATP for muscle contraction, not for lactic acid to glucose?

what is oxygen debt?

the amount of oxygen needed for the liver to convert lactic acid to glucose and the amount of oxygen needed to replenish muscle energy stores

in the absence of oxygen, what is glucose broken down into?

pyruvic acid → lactic acid

what does change mean in a change in metabolism?

a shift away from cellular respiration

what is skeletal muscle fatigue?

the inability of a muscle to contract

what is fatigue caused by?

lactic acid increase H+ ions in muscle, this lowers pH prevents muscle fibers from responding to stimulation

what of regular aerobic exercises decrease?f

the amount of lactic acid produced

what can exercise stimulate the growth of?

new capillaries (more oxygen)

what can exercise increase the number of?

mitochondria present in muscle cells (cellular respiration)

what is threshold stimulus?

need a strong enough stimuli to generate an impulse that can cause the sarcoplasmic reticulum to dump calcium

what is a twitch?

the contractile response of a single muscle fiber to an impulse

what is the latent period?

the time period between stimulation and contraction

what affects the force of the contraction generated?

the length that a muscle fiber is stretched before stimulation

what happens to overly stretched muscle fibers?

some myosin heads cannot bind to actin

what happens to overly shortened muscle fibers?

compressed myosin heads inefficiently bind actin

what is a myogram?

removing muscle from a frog or mouse and when electrically stimulated, the muscle will pull on a lever

what is summation?

individual contractions combine for a sustained contraction

how do individual contractions combine?

when between twitches a fiber is unable to relax before the next contraction

what is complete tetanic contraction (tetanus)?

a sustained reaction that lacks relaxation