Unit 5: Moving and Powering Skeletal Muscles Flashcards
There are two categories of neural control of skeletal muscles, what are they?
- Voluntary control
2. Involuntary control
What controls voluntary movements?
The primary motor cortex
What are the characteristics of voluntary movements?
- Primary motor cortices on left and right side of brain
- Control voluntary movements by controlling motor neurons on opposite side of body.
- Specific are of motor cortex controls specific motor neurons and thus specific muscles
- If damaged, lose voluntary movement on opposite side of body.
True or false: Involuntary movements are fast, predictable and automatic.
True. These are called reflexes
What are the components of a reflex arc?
- receptor
- (afferent) sensory neuron
- integrating (processing) center–central nervous system
- effector (muscles, glands…)
What are the parts of somatic reflexes?
- Effectors are skeletal muscles (effect is a muscle contraction)
- Integrating center is the spinal cord.
What are the 3 types of somatic reflexes?
- stretch reflex
- withdrawal reflex
- crossed extensor reflex
What is a stretch reflex?
A reflex which helps maintain body positions?
What are the characteristics of the stretch reflex?
Receptors are muscle. Spindles monitor changes in muscles.
What are examples of stretch reflex?
Bicep reflex, triceps reflex, patellar reflex and postural reflex.
What is withdrawal reflex?
Uses more than one neuron to withdraw hand or foot. Also sends an additional signal to brain (independent of reflex arc).`
What us the crossed extensor reflex?
This occurs with the flexor reflex. Involves movement of muscles on opposite side of body.
How do impulses move thru a neuron?
Along its length. This uses an electrochemical current.
What is the resting membrane potential of a neuron at rest?
-70 mV
What happens when an impulse is initiated?
Na+ ions enter the neuron thru Na+ channels in the neuron membrane
What can trigger an impulse?
- Physical disturbance
- Specific chemicals
- Light
- Electric charge
- Temperature
- nociceptors
What is the value must membrane potential reach to initiate an impulse?
-55 mV
What happens when the membrane potential does not reach -55 mV?
No signal impulse is sent
What happens when membrane potential does reach -55 mV?
-55 mV will stimulate voltage-gated Na+ channels to open
When does depolarization occur?
When the impulse is transferred along the neuron membrane as adjacent voltage-gated sodium ion channels open.
What are the events of depolarization?
a. voltage-gated sodium ion channels are stimulated to open by increase in membrane potential
b. gates open quickly
c. Na+ rush into neuron
d. membrane potential increases dramatically
e. when membrane potential reaches between 0 and 30 mV, voltage-gated Na+ channels close to prevent further influx of Na+
f. Membrane potential near 30 mV will stimulate K+ channels to open
What are the steps of repolarization?
a. K+ flows out of cell
b. at about -55 mV, K+ channels begin to close
When does hyperpolarization occur?
When the membrane potential is less than 70 mV.
What are the steps in restoring ion concentrations?
- Na+/K+ pumps return Na+ to ECF and K+ to ICF
What are synapses?
Junctions between neuron and target cell
What are the characteristics of synaptic transmission?
- mechanism to transfer signal from a neuron to a target cell.
- Neuron releases neurotransmitters
- Neurotransmitters bind to receptors in membrane of target cell
- A pre-synaptic neuron will only produce and release one type of neurotransmitter
- A post-synaptic neuron can have many different receptors and synapses with many neurons
True or false: the effect of neurotransmitters is determined by the receptor.
TRUE!
What are the characteristics of the receptors?
a. in the membrane of post-synaptic cell
b. bind and respond to specific neurotransmitters
c. respond to neurotransmitter as long as it is present in the synaptic gap
d. many are ligand-gated ion channels
What are neurotransmitters?
chemicals used to transmit signals from neuron to target cell
What is the pre-synaptic neuron?
The source of the signal
What is the post-synaptic cell?`
The cell that receives the signal
What is the end bulb?
I. end of the axon
II. contains synaptic vesicles
What is the purpose of synaptic vesicles?
To store neurotransmitters
What are the characteristics of voltage-gated Ca++ channels?
I. open if an impulse arrives at end bulb
II. Allow calcium ions to enter
III. Ca++ initiates movement of vesicles
What are the steps of synaptic transmission?
a. Impulse arrives at end bulb
b. depolarization of pre-synaptic membrane
c. voltage-gated Ca++ channels open
d. Ca++ enters neuron end bulb
e. exocytosis of neurotransmitters
f. neurotransmitter drifts across synaptic cleft
g. neurotransmitter binds to receptor–initiates ion movement
What is the neurotransmitter released at neuromuscular junctions?
Acetylcholine
True or False: If Na+ channels open and Na+ enters, then an impulse is not generated.
False. The impulse is generated.
True or False: If K+ channels open and K+ exits, then an impulse is generated
False. The Impulse is suppressed.
True or False: If Cl- channel open, and Cl- enters the cell, then an impulse is suppressed.
True.
What happens to the neurotransmitter, acetylcholine, at the neuromuscular junction?
Acetylcholine binds to, and stimulates, nicotinic receptors in muscle cell membrane (sarcolemma)
True or False: Nicotinic receptors are ligand-gated ion channels.
True
What happens to the voltage-gated Na+ channels in the sarcolemma when the threshold is reached?
The voltage-gated channels will open and an action potential will propagate through the muscle cell. This will trigger a muscle contraction.
What are the 3 ways to terminate synaptic transmission?
a. diffusion
b. enzymatic destruction/ degradation
c. neurotransmitter re-uptake
Why is synaptic transmission terminated?
- to end the contraction
- to ready the receptor for next transmission
Describe the diffusion termination method.
- neurotransmitter floats out of synaptic gap
2. slow termination/ relatively long lasting
Describe the enzymatic/ degradation termination method.
- neurotransmitter split by specific enzyme
- fragments reabsorbed
- very rapid termination
Describe neurotransmitter re-uptake termination method.
Neurotransmitter is transported back into pre-synaptic end bulb.
What are the characteristics of acetylcholine?
- neurotransmitter
- produced and released by cholinergic neurons
- only neurotransmitter released at NMJ
How is acetylcholine terminated?
Thru degradation. It is terminated using the enzyme acetylcholinesterase. It is broken down into acetate and choline
Where does the choline obtained from the degradation of acetylcholine go? The acetate?
- reabsorbed by neuron
- acetate diffuses
- the receptor is ready to re-use within milliseconds
