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Questions and Answers
What is the primary function of muscle spindles in motor control?
What is the primary function of muscle spindles in motor control?
- To regulate muscle force (correct)
- To control muscle contraction velocity
- To monitor muscle fatigue
- To sense muscle length
What type of reflex is characterized by the contraction of a muscle in response to its stretch?
What type of reflex is characterized by the contraction of a muscle in response to its stretch?
- Myotatic reflex (correct)
- Withdrawal reflex
- Tendon reflex
- Cross-extensor reflex
Which type of motor unit is responsible for generating high forces but fatigues quickly?
Which type of motor unit is responsible for generating high forces but fatigues quickly?
- Fast-fatigue-resistant motor unit
- Slow-twitch motor unit
- Fast-fatigable motor unit (correct)
- Intermediate motor unit
What is the role of gamma motor neurons in regulating muscle spindle responses?
What is the role of gamma motor neurons in regulating muscle spindle responses?
What is the sequence of recruitment of motor units during muscle contraction?
What is the sequence of recruitment of motor units during muscle contraction?
What is the location of the cell body of afferent neurons that transmit information from sensory receptors in muscles?
What is the location of the cell body of afferent neurons that transmit information from sensory receptors in muscles?
What type of reflex is the knee jerk reflex?
What type of reflex is the knee jerk reflex?
What is the function of Renshaw cells in the neural circuit?
What is the function of Renshaw cells in the neural circuit?
In the scenario described, Jessica's hand was removed from the hot burner due to the activation of which neural pathway?
In the scenario described, Jessica's hand was removed from the hot burner due to the activation of which neural pathway?
What is the primary role of spinal interneurons in the neural circuit?
What is the primary role of spinal interneurons in the neural circuit?
Which type of neuron is responsible for transmitting signals from the spinal cord to skeletal muscles to produce muscle contraction?
Which type of neuron is responsible for transmitting signals from the spinal cord to skeletal muscles to produce muscle contraction?
What is the primary function of muscle spindles in the context of proprioception?
What is the primary function of muscle spindles in the context of proprioception?
What is the name of the neural tract that originates in the vestibular system and influences spinal cord function?
What is the name of the neural tract that originates in the vestibular system and influences spinal cord function?
Which of the following neural structures plays a key role in the transmission of sensory information from the periphery to the central nervous system?
Which of the following neural structures plays a key role in the transmission of sensory information from the periphery to the central nervous system?
What is the term for the phenomenon where an animal with a spinal cord injury can still walk?
What is the term for the phenomenon where an animal with a spinal cord injury can still walk?
What type of afferent is responsible for transmitting signals from muscle spindles to alpha motor neurons?
What type of afferent is responsible for transmitting signals from muscle spindles to alpha motor neurons?
What is the term for the 'safety factor' in the neuromuscular junction, which ensures that muscle contraction occurs in response to neural stimulation?
What is the term for the 'safety factor' in the neuromuscular junction, which ensures that muscle contraction occurs in response to neural stimulation?
Central pattern generators (CPGs) are neural circuits that produce rhythmic patterns of activity similar to those seen in which motor function?
Central pattern generators (CPGs) are neural circuits that produce rhythmic patterns of activity similar to those seen in which motor function?
What is the role of central pattern generators in the spinal cord?
What is the role of central pattern generators in the spinal cord?
What is the function of electromyography in the study of locomotion?
What is the function of electromyography in the study of locomotion?
What is the purpose of the reciprocal burst of electrical activity recorded from flexors and extensors during walking?
What is the purpose of the reciprocal burst of electrical activity recorded from flexors and extensors during walking?
What type of neural circuit is involved in the withdrawal reflex of Jessica's foot in response to stepping on something sharp?
What type of neural circuit is involved in the withdrawal reflex of Jessica's foot in response to stepping on something sharp?
What is the role of muscle spindles in the control of locomotion?
What is the role of muscle spindles in the control of locomotion?
What is the primary function of alpha motor neurons in the control of locomotion?
What is the primary function of alpha motor neurons in the control of locomotion?
What is the significance of the rostro-caudal organization of control in the spinal cord?
What is the significance of the rostro-caudal organization of control in the spinal cord?
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Study Notes
Motor Systems: Spinal Cord
- Alpha motor neurons control muscle contraction
- Each muscle fiber is only innervated by one motor neuron, but each motor neuron can innervate multiple muscle fibers
- A motor neuron and all the muscle fibers it innervates form a motor unit
- Motor units are recruited in size order (small motor units before large motor units)
Types of Motor Neurons/Motor Units
- Large motor neurons:
- High threshold
- Fastest conduction
- Large force production
- Fast fatigue
- Medium motor neurons:
- Medium threshold
- Medium conduction
- Medium force production
- Intermediate fatigue
- Small motor neurons:
- Low threshold
- Slow conduction
- Small force production
- Very slow fatigue
Muscle Types
- Single AP (fast twitch):
- High force production
- Fast fatigue
- Repetitive AP (slow twitch):
- Low force production
- Slow fatigue
Effect of Stimulation Rate on Muscle Tension
- Twitch or tetany can occur due to high stimulation rates
Recruitment of Motor Units under Different Behavioral Conditions
- Motor units are recruited differently under different behavioral conditions (e.g., sprinting vs. marathon running)
Sensory Receptors for Motor Function
- Sensory receptors are found in muscles
- Cell bodies are in the dorsal root ganglia
- Enter the spinal cord through the dorsal root
- Synapse on interneurons in the dorsal horn and alpha motor neurons in the ventral horn
Stretch Reflex Circuitry
- Muscle spindles and Golgi tendon organs sense muscle tension or force
- Alpha motor neurons regulate muscle spindle responses
Lower Motor Control: Spinal Reflex
- Reflexes require:
- Sensor (sensory neurons)
- Integrator (spinal cord interneurons)
- Effector (motor neuron/muscle)
- Types of spinal reflexes:
- Myotatic/stretch reflex
- Withdrawal reflex
- Cross extensor reflex
- Spinal regulation of muscles for respiration
Medial-Lateral Organization in Cord
- Flexor and extensor muscles are organized in a medial-lateral pattern in the spinal cord
Rostro-Caudal Organization in Cord
- Motor control is organized in a rostro-caudal pattern in the spinal cord
Spinal Reflexes
-
- Stretch Reflex:
- Muscle contraction in response to stretching of proprioceptors (spindles)
- Monosynaptic or two neurons
- Example: knee jerk
-
- Withdrawal Reflex:
- Polysynaptic reflex
- Example: touching hot pan or stepping on a nail
- Also known as reciprocal inhibition
-
- Cross Extensor Reflex:
- Connections to motor neurons for antagonistic muscles on the contralateral half of the body
- Multisynaptic reflex
- Bilateral coordination:
- Spinal interneurons mediate input to alpha motor neurons
- Synaptic inputs to spinal interneurons include primary sensory axons, descending axons from the brain, and collaterals of lower motor neuron axons
Integrative Role of Interneurons
- Interneurons integrate information from multiple sources to regulate motor control
"Simple" Reflexes
- Monosynaptic reflexes, such as the hamstring reflex
- Autogenic inhibition via Golgi tendon organs
Central Pattern Generator
- Neural circuit that generates rhythmic behaviors, such as walking
- Found in the spinal cord
- Animals with spinal cord injury can still walk due to the presence of a central pattern generator
Case Studies
- Case Study 1:
- Jessica withdraws her hand from a hot burner due to a spinal reflex
- The reflex involves a sensory neuron, spinal cord interneurons, and a motor neuron
- Case Study 2:
- Jessica steps on a sharp object and withdraws her foot in pain
- The reaction involves a complex neural net, including spinal reflexes
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