Neuromuscular System & Resistance Training (EXPH 198 - Spring 26)

Outer layer of connective tissue that surrounds muscle

Epimysium

Epimysium can blend with what?

Fascia

Outer layer of connective tissue that surrounds a group of muscle fibers

Perimysium

Layer of connective tissue that surrounds each individual muscle fiber

Endomysium

Bundles of muscle fibers

Fasciculus

Individual muscle cell

Muscle fiber

A muscle fiber can be referred to as a muscle cell or a _

Myofiber

Muscle fibers have many _

Nuclei

Bundles of myofilaments

Myofibril

A myofibril is made up of a chain of _ linked end to end

Sarcomeres

Made up of actin and myosin; the contractile elements of a muscle fiber

Myofilaments

Basic functional unit of a myofibril & basic contractile unit of muscle

Sarcomere

The myosin filament is known as the _ filament whereas the actin filament is known as the _ filament

Thick, thin

What two things dictate the number of sarcomeres in a muscle fiber

Muscle size and length

Each myofibril is composed of numerous sarcomeres joined end to end at the __

Z-line

What is the home of cross-bridges

Myofilaments

3 Proteins That Compose Actin

Actin, troponin, & tropomyosin

Proteins That Compose Actin: Binds with myosin head

Actin

Proteins That Compose Action: Binds with calcium, “turns on” contraction

Troponin

Proteins That Compose Actin: Covers actin

Tropomyosin

The myofilament that regulates contraction

Actin

4 Events That Occur for Cross Bridge Formation

(1) Calcium ions released from sarcoplasmic reticulum, (2) Calcium ions binds with troponin, (3) Which causes a shift in tropomyosin off of actin (4) Allowing myosin heads to attach and flex

What produces the force that allows us to move and exercise

Skeletal muscles

What directs and controls the movements that the force from skeletal muscles produce

Nervous system

Signals the muscle to contract in the form of nerve impulses (action potentials)

Motor neuron

Motor neurons are aka (2)

Motoneurons or somatic motor neurons

General features of motoneurons: Receive signals from other neurons

Dendrite

General features of motoneurons: Contains the nucleus of the cell

Soma

General features of motoneurons: Transmits a resulting message to the muscle fibers in the form of action potentials

Axon

Spiral wrappings of tightly packed lipid membranes along an axon

Myelin sheath

Sites at which the action potential is generated as it travels down the axon; allows nerve signal to “jump” down axon increasing speed of transmission

Nodes of Ranvier

Activating a single axon results in all muscle fibers belonging to the unit to contract at a single stimulation intensity

All or None principle

Contact region between the end of the axon (axon terminal) and the muscle fiber in which excitation is transferred from the axon to the muscle fiber

Neuromuscular junction

Neuromuscular junction is aka

Motor end plate

The neurotransmitter released at neuromuscular junction to bring about the necessary transmission of the axonal signal

Acetylcholine (ACh)

6 Steps in Sliding Filament Theory

(1) Action potential (AP) travels down motor neuron to neuromuscular junction (NJM), (2) AP transmitted from NMJ to muscle fiber via ACh release, (3) AP travels to transverse tubules of muscle fiber, causing calcium ion release from sarcoplasmic reticulum, (4) Calcium ions bind to troponin causing shift in tropomyosin and cross bridge formation, (5) Cross bridge produces force and filament sliding, continuing until APs stop arriving at NMJ, (6) Once APs stop, calcium ions are pumped back into sarcoplasmic reticulum causing cross bridges to relax

2 Categories of Muscle Fiber Types

(1) Speed of contraction (slow → fast) and (2) Metabolism (oxidative → glycolytic)

What factor makes fiber types different?

Myosin heavy chains (MHC)

3 General Fiber Types

(1) Type I (slow twitch), (2) Type IIA, and (3) Type IIX (fast twitch)

One motor neuron & all of the muscle fibers it innervates

Motor Unit

Raising the firing frequency of the motor unit

Rate-coding

Calling additional motor units into activity

Recruitment

Which motor units and muscle fibers will result in maximal muscular adaptation

Only the ones that are activated (Want to recruit / activate as many as possible in a target muscle for a sufficient amount of time to fully stimulate the muscle fibers)