NEU Quiz Movement Flashcards
Categories of Movement
Reflex → involuntary reside in spinal cord, can be complex and modified by signals from brain
Rhythmic → include patterns elicited pattern generators → locomotion, chewing, swallowing, breathing → control from brain
Voluntary → movements initiated to accomplish a specific goal
Motor Nerves
Peripheral nerves - mixed sensory and motor axons (mix of sensory sending signals towards spinal cord and motor axons sending signals to muscles)
Split into dorsal and ventral roots → Roots enter dorsal horns and exit ventral horns
Ventral ROOTS = Lower motor neurons
Neurons between ventral horn and cortex = Upper motor neurons
Organization from largest to smallest:
Muscle, Fascicles (nerve), Muscle Fibers (CELLS) Myofibrils, Sarcomeres, Myofilaments
Epimysium (connective tissue):
helps muscle maintain structural integrity while contracting also separate muscles from other tissues and organs in that area
Sarcolemma:
contains sarcoplasm which is the cytoplasm of the muscle cell
Anatomy of a Skeletal Muscle Fiber:
- Cylindrical cell
- Multiple nuclei
- Sarcolemma (plasma membrane)
- Organelles:
- Myofibrils (actin and myosin)
- Sarcoplasmic reticulum (type of smooth ER, Stores Ca2+, has voltage gated Ca2+ channels)
- T tubules (link SR to Sarcolemma, helps carry action potential to SR to release Ca2+)
- Mitochondria
Muscle Fiber Organelles Myofibrils:
SHORTEN for muscle contraction and contain sarcomeres(contractile units which is smallest contractile unit of muscle fiber AND during contraction each sarcomere along a myofibril shortens to shorten the entire myofibril) Sarcomeres contain myofilaments: Actin – thin filaments and Myosin – thick filaments (6 subunits two heavy and four light subunits; breaks down ATP for muscle contraction)
Myofibrils - basic contractile element of muscle. Bundled into muscle fibers with a contractile subunit called sarcomere. Sarcomere are made of actin and myosin protein filaments. The sarcomeres shorten when myosin hydrolyzes ATP and slides along the actin. Hydrolysis of ATP causes myosin and actin filaments to slide past one another. Sarcomeres shorten and muscle contracts. Sarcomeres are made of actin and myosin protein filaments also called a myocyte. The sarcomeres shorten when myosin hydrolyzes ATP and slides along the actin. Sliding filament is during contraction, thin filaments slide past thick filaments actin and myosin overlap more and occur when myosin heads bind to actin.
AP happen from end plate potential to an AP and between then we reach threshold and the same VG the Na depo and K+ repo just liek normal neuron what differs is what happens next. After AP sent in muscle cell it travels to sacorrlmmea once travleign have the AP travels to the T-tubles which link the sacrollema to teh scaroplamic reticulm. Here there are VG calcium channels and so AP traveling being transferred opens the VG Ca channels which is conceratred in teh retiucilm and Ca wants to leave th sacroplaimu reticulum bc of its concentration gradient. Ca being released acatavates our contrction this Ca is able to attach to actin and moves/activates troponin which moves tropomyosin off of the mysoin binding sites and allows mysoin to attach to actin and mysoin plulss myoisn towards each other inorder to shorten the sarcomere. Shorten sacromeres in one muscle fiber.
Actin myofilaments
Myosin myofilaments
Actin myofilaments = thin filaments, site where myosin attaches, Tropomyosin – covers myosin binding site, Troponin holds tropomyosin in place over myosin binding site on actin
Myosin myofilaments = thick filaments, head of myosin has binding sites for actin binding sites for ATP, ATPase enzymes – break down ATP
How Does Contraction Happen?
- Excitation (at neuromuscular junction) * Must be nerve stimulation * Must generate action potential – change in voltage at sarcolemma
- Excitation-contraction coupling * Action potential moved along sarcolemma to T-tubule * Ca2+ released from SR and binds actin * Myosin binds to actin and sarcomeres shorten
The Nerve Stimulus:
- Skeletal muscles stimulated by somatic motor neurons
- Axons travel from spinal cord to skeletal muscle
- Each axon forms several branches as it enters muscle
- Each axon terminal forms neuromuscular junction with single muscle fiber
Neuromuscular Junction (NMJ):
- Axon terminal of a neuron and muscle fiber separated by space (synaptic cleft)
- Vesicles of axon terminal contain acetylcholine (ACh)
- Sarcolemma contains ACh receptors
- NMJ includes axon terminals, synaptic cleft, junctional folds
Generation of an Action Potential STEP 1
AP sent by LMN(lower motor neuron) so VG Ca channels open in axon terminal and Ach release at NMJ)
- Generate End plate potential (local depolarization)
- ACh binding opens ligand gated ion channels
- diffusion of Na+ into cell through ionotropic Ach receptors
- Local depolarization in the region of the ACh receptor = end plate potential(EPSP called end plate potential once threshold reached and AP sent in muscle fiber)
Events in Generation of an Action Potential STEP 2
- Depolarization - generation and propagation of an action potential (AP)
- End plate potential spreads
- Voltage-gated Na+ channels open(further depolarizing)
- Na+ influx decreases membrane voltage
- If threshold voltage reached, AP initiated(-55mv)
- Once initiated, is unstoppable muscle fiber contraction(all or none once AP start)
Events in Generation of an Action Potential STEP 3
Repolarization - REFRACTORY PERIOD
* Na+ channels close
* K+ channels open
* Restores the resting(normal) membrane potential(Na/K ATPase)
Destruction of Acetylcholine:
- ACh effects quickly terminated by enzyme acetylcholinesterase in synaptic cleft
- Breaks down ACh
- Prevents continued muscle fiber contraction – turns off end plate potential
