Neuromuscular System & Exercise Flashcards
What is a brain neurotransmitter
- chemical messenger that diffuse across the synapse to combine with a targeted receptor molecule on the postsynaptic membrane to facilitate depolarization or hyperpolarization
What does the peripheral nervous system include
- afferent nerves that relay sensory information from muscles, joints, skin, & bones toward the brain
- efferent nerves that transmit information away from the brain to glands & muscles
- somatic & autonomic nervous systems
What does the somatic nervous system do
- innervates skeletal muscle
- somatic efferent nerve firing excites muscle activation
What does the autonomic nervous system do
- innervates smooth muscle in intestines, sweat & salivary glands, myocardium, & some endocrine glands
- includes the sympathetic & parasympathetic nervous systems
- sympathetic nerve fibers mediate excitation
- parasympathetic activation inhibits excitation
What does the sympathetic nervous system supply & do
- supplies the heart, smooth muscle, sweat glands, & viscera
- excitation occurs during fight-or-flight situations that require whole body arousal for emergencies
- accelerates breathing & heart rate, pupils dilate, & blood flows from the skin to deeper tissues
What does the parasympathetic nervous system supply & do
- supplies the thorax, abdomen, & pelvic regions
- releases acetylcholine
- the postganglionic parasympathetic nerve fibers produce effects opposite of sympathetic fibers
What does a motor unit consist of
- cell body houses the control center
- axon extends from the cord & delivers an impulse to the muscle fibers it innervates
- dendrites receive impulses through spinal cord connections & conduct them toward the cell body
What allows for higher transmission velocity in a motor unit
- nodes of ranvier
What encases the bare axon of a motor unit
- Schwann cells in the peripheral nervous system encase the bare axon & then spiral around it
Describe the roles of the neuromuscular junction/motor end plate
- provides interface b/w the end of a myelinated motoneuron & a muscle fiber
- functions to transmit nerve impulses to muscle fibers
- presynaptic terminals lie close to with the sarcolemma
- synaptic cleft is the region where neural impulse transmission occurs
- excitation occurs at the neuromuscular junction
What is the all-or-none principle
- if a stimulus triggers an action potential in the motoneuron then all of the accompanying muscle fibers contract synchronously
- once the neuron fires & the impulse reaches the neuromuscular junction, the muscle cells always contract to the fullest extent
What is gradation of force principle
- the force of muscle action varies from slight to maximal in one of two mechanisms
- increasing the number of motor units recruited
- increasing the frequency of motor unit discharge (to create a summation of muscle contraction)
What is motor unit recruitment & size principle
Motor unit recruitment: the process of adding motor units to increase muscle force
Size principle: motoneurons with larger axons become recruited as muscle force increases
What provides the mechanism to produce the desired coordinated response
- selective recruitment & firing pattern of the fast-twitch & slow-twitch motor units that control movement
Define neuromuscular fatigability
- the decline in muscle tension or force capacity with repeated stimulation during a given time period
What factors decrease the force-generating capacity
- exercise induced alterations in levels of CNS neurotransmitters serotonin, 5-hyroxytryptamine, dopamine, & ACh
- reduced glycogen content in active muscle fibers during prolonged exercise
- increased level of blood & muscle lactate
- fatigue at the neuromuscular junction
Describe proprioceptors
- specialized sensory receptors sensitive to stretch, tension, & pressure in the muscles, joints, & tendon
- allows continual monitoring of the progress of any movement or sequence of movements
Describe muscle spindles
- they provide mechanic-sensory information about changes in muscle fiber length & tension
- primarily respond to muscle stretch through reflex action by initiating a stronger muscle action to counteract the stretch
Describe the stretch reflex
- muscle spindle responds to stretch
- afferent nerve fiber carries sensory impulse from the spindle to the spinal cord
- efferent spinal cord motor neuron activates the stretched muscle fibers
Describe Golgi tendon organs (GTOs) & their function
- located in ligaments of joints to primarily detect differences in muscle tension
- protect muscle & its connective tissue harness from injury by sudden excessive load or stretch
Describe pacinian corpuscles & their function
- found in the subcutaneous tissue on the nerves of the sole of the foot, palm of the hand, mucous membranes, genital organs, & in close proximity with the nerves of joints
- they respond to quick movement & deep pressure
Describe the purpose of skeletal muscle capillarization
- capillary microcirculation expedites removal of heat & metabolic byproducts from active tissues
- provides a large surface area to exchange metabolically generated heat, fluids, electrolytes, gases, & macromolecules
What is the functional unit of movement
- the motor unit
What is the functional unit of the muscle cell
- the sarcomere
Define the H band of a sarcomere
- area of the sarcomere that only contains myosin
Define the I band of a sarcomere
- area of a sarcomere that only contains actin
Define the A band of a sarcomere
- area of the sarcomere that contains the overlap of actin & myosin
Define the Z line of a sarcomere
- it’s the zig-zag line at the end of the sarcomere
Define the M line of the sarcomere
- it’s the line in the very middle of the sarcomere
What happens to the different bands when the sarcomere contracts
- H band/zone decreases
- A band increases
- I band decreases
Describe the steps of the sliding filament theory
- tropomyosin covers the binding sites for myosin to attach to the actin
- calcium binds to the troponin complex which opens the myosin binding sites
- myosin attaches to the actin
- ATP is used to detach the myosin heads from the actin
Characteristics of fast-twitch muscle fibers
- rapidly transmit action potentials
- high activity level of myosin ATPase
- rapid rate of calcium release & uptake by the sarcoplasmic reticulum
- generate rapid crossbridge turnover
Describe Type I fibers
- generate energy for ATP resynthesis predominantly by aerobic energy transfer
- possess a low activity level of myosin ATPase
- resist fatigue & power prolonged aerobic exercise
- slow oxidative fibers
- max duration of use is hours for aerobic activity
- slow twitch fiber/hard to fatigue
Describe Type IIa fibers
- exhibits fast shortening speed & moderately well-developed capacity for energy transfer from both aerobic & anaerobic sources
- represents the fast oxidative glycolytic fibers
- max duration of use is <30 minutes for long term anaerobic activity
- moderately fast twitch fiber/fairly hard to fatigue
Describe Type Ilx fibers
- possess the greatest anaerobic potential & most rapid shortening velocity
- represents the fast glycolytic fiber
- max duration of use is <5 minutes for short term anaerobic activity
- fast twitch fiber/less hard to fatigue
Describe muscle fiber type distribution differences
- genetic code largely determines a person’s predominant fiber type
- specific exercise training improves the metabolic capacity (ability for the body to uptake O2/VO2 max) of each fiber type but you can not create more of any fiber types
