24 Questions
What is a motor unit composed of?
A single lower motor neuron and all the muscle fibers it innervates
What is the function of the axon terminals of a lower motor neuron?
To release neurotransmitters that bind to receptors on muscle fibers
What is the result of the coordinated contraction of multiple muscle fibers innervated by a single lower motor neuron?
Movement
What type of motor unit is responsible for fine movements, such as those of the eyes and fingers?
Small motor unit
What is the term for the connection between the axon terminal and the muscle fiber?
Neuromuscular junction
What can result from damage to lower motor neurons or muscle fibers?
Weakness
What is a characteristic of a single lower motor neuron?
It can innervate multiple muscle fibers
What is a condition characterized by abnormal contractions of muscle fibers?
Fasciculations
What type of neurons are lower motor neurons?
Efferent neurons
What is the main function of a motor unit?
To coordinate the contraction of multiple muscle fibers
Where are the soma of motor neurons located?
In the spinal cord or brain stem
What is the result of abnormalities in the motor unit?
Weakness or loss of strength of contraction of skeletal muscle
What is the characteristic of small motor units?
They are found in small muscles that need rapid precise control
What is the result of abnormalities in the lower motor neuron?
Atrophy of skeletal muscle
What is the term for the involuntary twitches of skeletal muscle?
Fasciculations
What is the result of the action potential of a lower motor neuron?
The contraction of all the skeletal muscle cells in its unit
Which type of muscle is primarily controlled by motor units?
Skeletal muscle
What is the result of a single lower motor neuron firing an action potential?
All skeletal muscle cells in its motor unit contract
Where do the axons of motor neurons pass through to reach the peripheral nervous system?
Cranial nerves and spinal nerves
What is the characteristic of large motor units?
Found in large muscles that do not need rapid precise control
What is the result of abnormalities in the lower motor neuron on skeletal muscle?
Atrophy of skeletal muscle
What is the term for the decrease in the tone of skeletal muscle due to abnormalities in the motor unit?
Hypotonia
What is the result of the coordinated contraction of multiple skeletal muscle cells in a motor unit?
Strong coordinated contraction of skeletal muscle
What is the term for the involuntary twitches of skeletal muscle due to abnormalities in the motor unit?
Fasciculation
Study Notes
Motor Unit
- A motor unit consists of a lower motor neuron and all the skeletal muscle fibers it innervates
- Lower motor neurons are efferent neurons that transmit signals from the central nervous system to skeletal muscles
- The term "motor unit" refers to a single lower motor neuron and all the muscle fibers it controls
- A single lower motor neuron can innervate multiple muscle fibers, and a single muscle fiber can receive signals from multiple lower motor neurons
Structure of a Motor Unit
- A lower motor neuron has a soma, an axon, and terminal buttons
- The axon terminals release neurotransmitters that bind to receptors on the surface of muscle fibers
- The connection between the axon terminal and the muscle fiber is called a neuromuscular junction (NMJ)
Function of a Motor Unit
- When a lower motor neuron is stimulated, it releases neurotransmitters that bind to receptors on muscle fibers, causing them to contract
- The coordinated contraction of multiple muscle fibers innervated by a single lower motor neuron results in movement
- Motor units are the basic functional units of the motor system
Types of Motor Units
- Small motor units: consist of a small number of muscle fibers and are responsible for fine movements, such as those of the eyes and fingers
- Large motor units: consist of a large number of muscle fibers and are responsible for gross movements, such as those of the limbs and torso
Abnormalities of Motor Units
- Weakness: can result from damage to lower motor neurons or muscle fibers
- Atrophy: a decrease in the size of muscle fibers, often due to lack of stimulation by lower motor neurons
- Fasiculations: abnormal contractions of muscle fibers, often due to damage to lower motor neurons
- Hypotonia: decreased muscle tone, often due to damage to lower motor neurons
- Hyporeflexia: decreased reflexes, often due to damage to lower motor neurons
Motor Unit
- A motor unit consists of a single lower motor neuron and all the skeletal muscle fibers it innervates.
- Lower motor neurons transmit signals from the central nervous system to skeletal muscles.
- A single lower motor neuron can innervate multiple muscle fibers, and a single muscle fiber can receive signals from multiple lower motor neurons.
Structure of a Motor Unit
- A lower motor neuron has a soma, an axon, and terminal buttons.
- The axon terminals release neurotransmitters that bind to receptors on the surface of muscle fibers.
- The connection between the axon terminal and the muscle fiber is called a neuromuscular junction (NMJ).
Function of a Motor Unit
- When a lower motor neuron is stimulated, it releases neurotransmitters that bind to receptors on muscle fibers, causing them to contract.
- The coordinated contraction of multiple muscle fibers innervated by a single lower motor neuron results in movement.
- Motor units are the basic functional units of the motor system.
Types of Motor Units
- Small motor units consist of a small number of muscle fibers and are responsible for fine movements, such as those of the eyes and fingers.
- Large motor units consist of a large number of muscle fibers and are responsible for gross movements, such as those of the limbs and torso.
Abnormalities of Motor Units
- Weakness can result from damage to lower motor neurons or muscle fibers.
- Atrophy is a decrease in the size of muscle fibers, often due to lack of stimulation by lower motor neurons.
- Fasiculations are abnormal contractions of muscle fibers, often due to damage to lower motor neurons.
- Hypotonia is decreased muscle tone, often due to damage to lower motor neurons.
- Hyporeflexia is decreased reflexes, often due to damage to lower motor neurons.
Motor Unit
- Consists of a lower motor neuron and all the skeletal muscle cells it contacts and controls
- Lower motor neurons are efferent neurons of the peripheral nervous system, carrying information away from the central nervous system
- Controls skeletal muscle, which is the main muscle type of our body, connected to our skeleton to move us around
Neuromuscular Junction
- The synapse between a lower motor neuron and a skeletal muscle cell
- Lower motor neurons synapse with multiple skeletal muscle cells, forming multiple neuromuscular junctions
Function of Motor Unit
- When a lower motor neuron fires an action potential, it causes all the skeletal muscle cells in its unit to contract
- This is why the motor unit is called a unit, as the skeletal muscle cells function together as a single unit
Organization of Motor Neurons
- Soma of motor neurons are in the spinal cord or brain stem
- Axons pass out through cranial nerves or spinal nerves into the peripheral nervous system
- Axons branch out and synapse on skeletal muscle cells in their motor unit
Types of Motor Units
- Small motor units: found in small muscles that need rapid precise control (e.g., eye movement, finger movement)
- Large motor units: found in large muscles that do not need rapid precise control (e.g., limb and trunk muscles)
Abnormalities of Motor Units
- Abnormalities can cause weakness or loss of strength of contraction of skeletal muscle
- Abnormalities of the lower motor neuron can cause:
- Atrophy of skeletal muscle (decreased bulk or size)
- Fasciculations (involuntary twitches of skeletal muscle)
- Hypotonia (decrease in the tone of skeletal muscle)
- Hyporeflexia (decreased muscle stretch reflexes)
Motor Unit
- Consists of a lower motor neuron and all the skeletal muscle cells it contacts and controls
- Lower motor neurons are efferent neurons of the peripheral nervous system, carrying information away from the central nervous system
- Controls skeletal muscle, which is the main muscle type of our body, connected to our skeleton to move us around
Neuromuscular Junction
- The synapse between a lower motor neuron and a skeletal muscle cell
- Lower motor neurons synapse with multiple skeletal muscle cells, forming multiple neuromuscular junctions
Function of Motor Unit
- When a lower motor neuron fires an action potential, it causes all the skeletal muscle cells in its unit to contract
- This is why the motor unit is called a unit, as the skeletal muscle cells function together as a single unit
Organization of Motor Neurons
- Soma of motor neurons are in the spinal cord or brain stem
- Axons pass out through cranial nerves or spinal nerves into the peripheral nervous system
- Axons branch out and synapse on skeletal muscle cells in their motor unit
Types of Motor Units
- Small motor units: found in small muscles that need rapid precise control (e.g., eye movement, finger movement)
- Large motor units: found in large muscles that do not need rapid precise control (e.g., limb and trunk muscles)
Abnormalities of Motor Units
- Abnormalities can cause weakness or loss of strength of contraction of skeletal muscle
- Abnormalities of the lower motor neuron can cause:
- Atrophy of skeletal muscle (decreased bulk or size)
- Fasciculations (involuntary twitches of skeletal muscle)
- Hypotonia (decrease in the tone of skeletal muscle)
- Hyporeflexia (decreased muscle stretch reflexes)
Learn about the composition and role of motor units in the nervous system, including the relationship between lower motor neurons and skeletal muscle fibers.
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