chapter 11 pt 2 Flashcards
Nerve cells called somatic motor neurons stimulate muscle fibers via
their axons
Skeletal muscle never contracts unless
stimulated by a nerve
A muscle becomes paralyzed when
nerve connections are severed or poisoned
denervation atrophy
shrinkage of paralyzed muscle when connection is not restored
nerve cells whose cell bodies are in the brainstem and spinal cord that serve skeletal muscles
somatic motor neurons
motor unit
one nerve fiber and all the muscle fibers innervated by it
muscle fibers of one motor unit
dispersed throughout the muscle, contract in unison, produce weak contraction over wide area, provides ability to sustain long-term contraction as motor units take turns contacting, effective contraction of several motor units at once
synapse
where a neuron meets a target cell
on average how many muscle fibers are innervated by each motor neuron?
200
Small motor units are present where
fine control is needed, such as in the muscles of eye movement (3 to 6 muscle fibers per neuron).
Large motor units are present where
strength is more important than fine control, such as in the gastrocnemius (1,000 muscle fibers per neuron).
AChE
acetylcholinesterase
ACh
acetylcholine
Muscle fibers and neurons are considered
electrically excitable cells
Why are muscle fibers and neurons considered electrically excitable cells?
because their plasma membranes exhibit voltage changes in response to stimulation
electrophysiology
The study of the electrical activity of cells
A difference in electrical charge between two points is called
voltage or electrical potential
–90 mV
Resting Membrane Potential (RMP)
The resting membrane potential is maintained by the
sodium–potassium pumps.
four major phases of muscle contraction and relaxation
excitation; excitation–contraction coupling; contraction; and relaxation
Excitation is
the process in which action potentials in the nerve fiber lead to action potentials in the muscle fiber
5 steps of excitation
- A nerve signal arrives at a synaptic knob and stimulates voltage-regulated Ca2+ gates to open; calcium ions enter the synaptic knob.
- Ca2+ stimulates exocytosis of synaptic vesicles, which release ACh into the synaptic cleft.
- ACh diffuses across the synaptic cleft and binds to receptor proteins on the sarcolemma.
- The receptors are ligand-gated ion channels that bind two ACh molecules to open. 5. Areas adjacent to the NMJ have ion-specific voltage-gated ion channels that open in response to the EPP, allowing flow of Na+ in and K+ out, generating an action potential
Excitation–contraction coupling refers to
the events that link the action potentials on the sarcolemma to activation of the myofilaments.
4 steps of excitation-contraction coupling
A wave of action potentials spreads from the end plate in all directions, and enters the T tubules, continuing down them into the sarcoplasm.
- Action potentials open voltage-gated ion channels in the T tubules 3. Calcium binds to the troponin of the thin filaments.
- The troponin–tropomyosin complex changes shape, exposing active sites on the actin filaments that can bind to myosin heads.
