10C- Neuromuscular Junction and Muscle Contraction

Flashcards covering key concepts of the neuromuscular junction and muscle contraction for HHP:1100 Human Anatomy.

The neuromuscular junction is where a __ communicates with a muscle fiber. 

neuron

Skeletal muscles are voluntary is its muscle fiber is controlled by one ___.

motor neuron

The synaptic __ is the narrow space separating the synaptic knob and motor end plate.

cleft

Acetylcholine (ACh) is released from ____ , membrane sacs in synaptic knob, and into the synaptic cleft.

synaptic vesicles

When a nerve impulse arrives at the neuromuscular junction, it causes __ release into the synaptic cleft. What happens after this release?

acetylcholine (ACh)

• ACh bind to receptors on the motor end plate, initiating a muscle fiber impulse

• impulse will go down T-tubules to cause calcium influx to sarcoplasm from sarcoplasmic reticulum

Calcium ions bind to __, which causes a conformational change of this. what steps happens next?

troponin

• will move tropomyosin, exposing active sites on actin

• myosin heads are able to bind to actin and form cross bridges

• myosin pulls actin toward M-line of sarcomere

The repeating cycle of __-pivot-detach-return shortens the sarcomere and requires ATP.

attach

Muscle fibers that have the highest resistance to fatigue, smaller fibers, and are recruited for sustained endurance/distance are classified as __ fibers.

Slow oxidative (SO) Type I fibers

The process of __ refers to the increase in muscle fiber size due to repetitive, exhaustive muscle stimulation.

muscle hypertrophy

T/F: a single motor unit contains only muscle fibers of the same type

true

Muscle tone refers to the state where some muscle fibers are activated while others are in a __ state. However, muscles maintain some tension even when not contracting.

resting

In __ contraction, the muscle does not change length despite tension being generated.

isometric

__ are involuntary, painful, sustained contractions of a muscle, often caused by lactic acid buildup, dehydration, calcium deficiencies, trauma

Cramps

---

is a progressive deterioration of muscle tissue, and it results in atrophy of the affect muscles, and the replacement of muscle fibers by fibrous connective and fatty tissue.

Muscular dystrophy

____ is an autoimmune disease where antibodies break down neuromuscular junction and reduce stimulatory effect of neurotransmitter.

Myasthenia Gravis

The large muscle that opposes the agonist and produces an opposite action is called the __. What is an example?

antagonist

• biceps brachii is antagonist for triceps brachii

Muscles are often named based on their __ action, such as flexor or extensor.

function

The __ of muscle fibers affects their contraction speed and fatigue resistance.

type

how does muscle contraction begin?

motor neuron impulse stimulates an impulse in a muscle fiber

synaptic knob

expanded tip of neuron axon

motor end plate

region of sarcolemma under synaptic knob with many folds to increase surface area, and it also contain ACh receptors.

ACh receptors

proteins that bind Ach on the motor end plate

Acetycholinesterase (AChE)

enzymes in synaptic cleft that breaks down Ach to prevent continuous muscle stimulation.

how does muscle contraction stop, and how does everything reset?

• contraction stop when Ach is broken down

• Ca2+ returns to sarcoplasmic reticulum

• tropomyosin re-covers active site on actin

• filaments slide back to relaxed state

a __ is a single motor neuron & all of the muscle fibers it communicates with. However, it contains only some of the muscle fibers in an entire muscle.

motor unit

when a motor unit is stimulated, all ___ within it contract. therefore, movements that require more ___ recruit more motor units.

1. muscle fiber

2. force

skeletal muscles consist of a mixture of 3 fiber types:

slow oxidative, fast oxidative, fast glycolytic fibers

fast oxidative (FO) fibers

Muscle fibers that have a high resistance to fatigue, intermediate size fibers, and are recruited for medium duration/moderate movement are classified as __ fibers.

fast glycolytic (FG) fibers 

Muscle fibers that a low resistance to fatigue, largest size fibers, and are recruited for short duration, intense movement are classified as __ fibers. it comes in first before oxygen is used, so it’s anaerobic.

where do slow fibers dominate in the body?

postural muscles, such as in back & calf

where do fast fibers dominate in the body?

swift, but brief contractions such as in the eye and hand.

muscle atrophy

reduced stimulation/use results in smaller muscle size, tone, and power

in __ contraction, muscles change length, either by shortening or lengthening. what is the name for the contractions that shorten or lengthen muscles?

isotonic

concentric contraction shortens muscles

eccentric contraction increases muscle length

define agonist & one example

biggest, strongest muscle in a region

• triceps brachii is the agonist for forearm extension

a __ is a muscle that assist agonist on the same side

synergist

fibromyalgia

physiologically unexplainable chronic muscle pain

muscles are named according to (6) criteria

1. Muscle action

2. Specific body regions

3. Muscle attachments

4. Orientation of muscle fibers

5. Muscle shape and size

6. Muscle heads/tendons of origin