Flashcards in Lecture 6: Introduction to Movement Deck (97)
Three Steps underlying voluntary movement
1. brain sends motor commands to motor neurons in the spinal cord
2. Motor neurons in spinal cord release ACh at neuromuscular junction
3. ACh binds to nicotinic ACh receptors on muscle fibre and trigger muscle contraction
Nicotinic ACh receptors
Respond to NT, Acetylcholine. At the neuromuscular junction they are the primary receptor in muscle responsible for muscle-nerve communication that controls muscle contraction.
Where are motor neurons found?
In the ventral horns of spinal cord
How does AP travel to muscle from spinal cord?
Through the ventral roots
Where is acetylcholine released? What does it do once released?
- At the neuromuscular junction
- Released ACh binds to receptors on muscle fibre causing postsynaptic potentials (PSPs) to arise (same rules of temporal and spatial summation apply) and trigger action potentials in muscle fibre
What type of receptor are Nicotinic ACh receptors?
nAChR receptors are ionotropic
What attaches muscle to bone?
a bundle of fibres called myofiber; each fibre is ONE cell with multiple DNA containing nuclei
Why do singular muscle fibres have multiple nuclei?
They are a product of cellular fusion
What is myofiber made of?
cylinder shaped bundles of protein polymers called myofibrils
What is myofibril composed of?
Each myofibril is composed of repeats of a functional unit called sarcomere
What is a key factor in muscle contraction?
The dynamic change in the structure of the protein polymers (myofibrils)
Basic contractile unit that makes up myofibril. Each unit has a myosin (thick) and actin (thin) protein filament.
Where would you find myosin and actin?
These protein filaments are found in each sarcomere, which is found in myofibril which composes myofiber.
Breakdown of muscles
muscles --> myofiber --> myofibril --> sarcomere --> actin and myosin
Muscles contract when...
thick and thin filaments pass each other
What is the function of the tropomyosin complex?
In a resting state, the tropomyosin complex masks the myosin binding sites in the actin filaments so the myosin head cannot grab the actin fibre
What exposes the myosin binding sites on actin?
Binding of ACh to nACh receptors trigger APs in muscle fibre which causes release of Ca2+ from sarcoplasmic reticulum (storage for Ca2+). Calcium ion binds to troponin pulling tropomyosin to the side exposing binding sites.
What role does calcium play in muscle contraction?
calcium ions are released from sarcoplasmic reticulum and bind to troponin revealing the binding sites
What does the myosin head do when myosin binding sites are exposed? What does it do?
It binds to actin (grabs it) and the bending motion pulls on the actin filaments causing them to slide
one motor neuron can be responsible for...
multiple muscle contractions
Somatic Nervous System
Receives sensory info from sensory organs (skin, eyes, ears) and controls movement of skeletal muscles. Carries motor and sensory information both to and from the CNS.
Muscles contain what types of sensory nerves (also number)?
2 types: muscle spindle and golgi tendon
SENSORY NERVES - carry info from various body parts close to external environment to the CNS
MOTOR NERVES - carry info from CNS to the skeletal muscle
muscle fibre that report muscle length, composed of intrafusal muscle fibres
skeletal muscle fibres that serve as specialized sensory organs that detect the amount and rate of change in length of a muscle
What innervates muscle spindle?
Mechanosensory axon terminals
to supply with nerves