Neuromuscular Physiology Flashcards
Central Nervous System (CNS) is composed of
Brain (including retinas)
Spinal cord
Intergrative/control centers
Peripheral Nervous System (PNS) is composed of
Cranial nerves III-XII
Spinal Nerves
Afferent Division is part of what Nervous System?
Central Nervous System (CNS)
Afferent division is known as?
and what role does it play?
Sensory fibers;
Somatic and visceral neurons
Conducts impulses from receptors to CNS
Efferent Division is part of what Nervous System?
Peripheral Nervous System (PNS)
Efferent division is known as?
and what role does it play?
Motor fibers;
Motor neurons
Conducts impulses from the CNS to effectors
Peripheral Nervous System is divided into what 2 systems?
Autonomic and Somatic Nervous System
Role of Somatic Nervous System
Voluntary
Conducts impulses from the CNS to skeletal muscles
Role of Autonomic Nervous System
Involuntary
Conducts impulses from the CNS to cardiac muscle, smooth muscles, and glands
Autonomic Nervous System is divided into what 2 systems
Sympathetic and parasympathetic
The motor neuron and all the muscle cells it services is called
Motor Unit
A motor unit is considered
the basic functional unit of the muscle
Each motor neuron synapses is made up of how many muscle cells
as little as 4 to over 200
a site where a motor neuron communicates with a muscle fiber
neuromuscular junction (NMJ)
Motor axon terminal releases what neurotransmitter
acetylcholine
once acetylcholine is released from the motor axon where does it go?
travels across a synaptic cleft and bind to receptors on a muscle fiber
The neurotransmitter causes the effector cell to
change its membrane potential
The change of the effector cell to its membrane potential is known as
depolarization
After the depolarization caused by the neurotransmitter what happens
the nerve impulse is transferred to the effector cell
The transfer of the nerve impulse to the effector cell is known as
facilitation
If a membrane potential is increased to reach its threshold what occurs
action potential spreads across the sarcolemma
the spread of an action potential across the sarcolemma causes
the muscle fiber to contract
how do neurons communicate with other neurons and with muscle cells
by releasing neurotransmitters
neurotransmitters
chemicals released by a neuron which cause either excitation, facilitation, or inhibition
Nerve and muscle cells have two types of NA+ gates/channels which allows NA+ entry (influx) and depolarization
chemical and electrical gates
Chemical gates are found? role? unlocked by?
are the least numerous
found mainly in the nerve cell body and dendrites
found in muscles at the nerve synapse
opened or unlocked by the neurotransmitters
Electrical gates are found? role? opened by?
are the most numerous
found mainly in the neuronal axons
found distal to synapses in muscle cells
opened when the resting membrane potential exceeds a specific threshold voltage (usually around 60mV)
the opening of the electrical gates that causes the necessary level/wave depolarization is called
action potential
Relative charge of membrane as a result of distribution of
Sodium (NA+)(chloride(Cl-), potassium(K+) and large intracellular anions (A-)
Neuron activations or excitations are known as
nerve impulses
Nerve impulses are really waves of depolarization caused by
NA+ influx
Muscle activation/excitation is caused by
NA+ influx
The sympathetic system is
its fight or the flight system and its nerves direct more blood to the muscles whereas decreases blood supply to the gut.It increases the heart rate and blood pressure and also activates the body’s mechanisms to provide immediate energy to face the stressful state.So this system utilizes the body’s energy resources just to prepare it for some upcoming stressful state.
The parasympathetic system is
its the rest and digest system.It increases the blood supply to gut and increases the digestion.So it tries to restore the body’s energy sources.
Before another impulse can be sent down an axon, the nerve must
repolarize
During repolarization, the NA+ goes ____ and the K+ goes ____. Which are switch via the____.
out
in
NA-K pump
Repolarization requires energy in form of___.
ATP
No ATP No pumping
Repolarization also occurs in
muscle
Facilitation
Raising the the resting membrane potential above the normal potential, thereby increasing the likelihood that succeeding neurotransmitter releases will cause the potential to exceed the threshold. This enhances the chances of the neuron firing and activating the target. (i.e. greater chance of muscle excitation by facilitating the motor neuron).
Inhibition
Lowering the resting membrane potential below the normal potential, thereby decreasing the likelihood of reaching the threshold. This usual prevents the neuron from activating its target. (i.e. prevents motor neuron from activating the motor unit).
Most Common Excitatory Neurotransmitters
Norepinephrine & Acetylcholine (nerve to muscle)
Most Common Facilitory Neurotransmitters
Norepinephrine & Acetylcholine (in lower amounts)
Another name for epinephrine
adrenalin
In some parts of the body norepinephrine and acetylcholine will act s
inhibitors
Norepinephrine packs a double wallop by activation the adrenal medulla to release____, which can also cause____.
epinephrine
facilitation and/or excitation
Most common inhibitory neurotransmitter
GABA (gamma-aminobutyric acid)
Drugs can also serve as
facilitators or inhibitors
Drugs can cause facilitation by
A. Opening chemically gated channels
B. Increased concentrations of NT
1. Block the breakdown of ACH. If ACH doesn’t get removed the signal keeps being sent.
2. Stop this re-uptake Norepinephrine. Once again is NT is not removed from its binding site it will keep sending its messege. (e.g. cocaine)
C. Increased epinephrine production.
Drugs can cause inhibition by
A. Block the release of either the neurotransmitter or epinephrine
B. Block the neurotransmitter binding siit
C. Block the channel so that Na+ or K+ cannot pass through.
D. Accelerated removal of the neurotransmitter from the synapse.
Spatial Summation
Neurotransmitter release from more than one neuron is necessary to cause excitation.
(insufficient release yields facilitation)
Temporal Summation
Altering the frequency of a nerve firing (i.e. neurotransmitter release) to ensure sufficient amounts to cause depolarization. This is most often seen in nerve excitation of muscle. (i.e the more rapid the nerve fires the greater the force output of the muscle)
When temporal summation occurs in skeletal muscles, it is usually referred to as
rate coding
when the muscle achieves maximal temporal summation, it has
reached tetanus
Facilitation and inhibition are an integral part of
motor control and learning
Facilitation and inhibition can operate on the ______ or they can influence______
motor neuron
spatial and/or temporal summation
Coordination or the learning of the fine motor skills involves
inhibition and facilitation
Coordination or the learning of fine motor skills involves inhibition by ______ and facilitation by______.
undesired motor units(fewer motor units=less force)
allowing for one to ‘groove’ the desired movement pattern.
Inhibition is used as a _____for_____
safety net for muscle groups
Maximum voluntary contraction
the maximum amount of weight (1 RM) a muscle group can lift when under conscious control.
Maximum contraction
the maximum amount of weight (1 RM) a muscle group can lift under electrical stimulation.
Maximum contraction > maximum voluntary contraction because of
inhibition
Nerve failure
when a nerve fails to activate its target through some mechanism other than inhibition
When the nerve fails to activate a muscle, then the condition is generally referred to as
fatigue
what are the 3 main causes of Nerve failure (aka Neuronal Based Fatigue)
Neuron does not repolarize
Neuron does not release neurotransmitter
Branch point failure
Why doesnt the neuron repolarize causing Nerve Failure?
Repolarization requires an active Na-K pump. The Na-K pump needs energy (ATP) to operate. Therefore, if the ATP is “used up”, the neuron can not repolarize and hence fails.
NOTE: This condition can be identified by finding high post-exercise serum potassium (K+) levels.
NOTE: This condition usually will occur with high stimulation frequencies or rapid temporal summation.
Why doesnt the neuron release neurotransmitters causing Nerve Failure?
Neurotransmitter is made and stored in packets in the synaptic end bulb. If neurotransmitter release occurs faster than the rate at which it is being made, the neuron will eventually “run out” of neurotransmitter. With no transmitter, even if the neuron depolarizes, the target will not be activated.
NOTE: This condition usually will occur with high stimulation frequencies or rapid temporal summation.
Why does the branch point fail causing Nerve Failure?
Most neuronal axons have branches of varying lengths (esp. motor neurons). When a neuron is being stimulated at high frequencies, some of the longer branches can not repolarize as fast as the rest of the axon. Thus when the neuron is activated again, some of the branches can’t depolarize because they have not repolarized yet. Hence, failure occurs at the point of branching. When this occurs, fatigue is manifested by a failure of a single motor unit’s individual muscles cells to contract.
NOTE: This condition usually will occur with high stimulation frequencies or rapid temporal summation.
How does one prevent nerve failure (Neuronal Based Fatigue)?
Reduce the stimulation frequency of each neuron.
PROBLEM: The principle of Rate Coding indicates that if one decreases stimulation frequency, then muscle force output also decreases. Decreased Force = Fatigue!
