45 Questions
What is the primary function of the inverse stretch reflex?
Prevents excessive tension on the muscle
Which type of reflex is characterized by the contraction of all the flexor muscles in a limb in response to a noxious stimulus?
Withdrawal reflex
What is the main action of the flexor reflex on the alpha motor neurons?
Stimulation of alpha motor neurons to flexor muscles
Which of the following is NOT a characteristic of the withdrawal reflex?
It is a monosynaptic reflex
What is the role of the gamma loop in regulating muscle tone?
It is involved in the reflexes using muscle spindle and Golgi tendon organ
Which segments of the spinal cord are involved in the withdrawal reflex of the thoracic limb?
C6-T2
What is the term for the muscle's continuous resistance to being stretched?
Muscle tone
What is the purpose of evaluating extensor tone during a neurological examination?
To evaluate the function of the spinal cord
What is the relationship between the intensity of the noxious stimulus and the response of the withdrawal reflex?
The response is proportional to the intensity of the stimulus
Where are the cell bodies of upper motor neurons located?
In the motor nucleus of the brainstem or the motor cortex of the forebrain
What is the primary function of the upper motor neuron system?
To initiate and regulate voluntary movement
What happens when inhibitory upper motor neurons are lost?
Muscle tone increases
What is the result of a loss of facilitatory upper motor neurons?
Paresis or paralysis
What is the term for uncoordinated movement?
Ataxia
What is the term for weakness of voluntary movement?
Paresis
What is the role of upper motor neurons in regulating lower motor neurons?
They can either stimulate or inhibit lower motor neurons
What is the term for the loss of motor function?
Paralysis
What is the result of a loss of upper motor neurons on muscle tone?
Muscle tone increases
What type of reflex is the patellar reflex primarily classified as?
Monosynaptic reflex
Which nerve is involved in the patellar reflex?
Femoral nerve
What is the cord segment involved in the patellar reflex?
L4, L5, L6
What is the primary action of the patellar reflex?
Contraction
What is the receptor sensitive to in the Golgi tendon organ reflex?
Muscle tension
What is the purpose of the reciprocal inhibition in the patellar reflex?
To prevent muscles from working against each other
What is the name of the receptor that detects muscle stretch in the patellar reflex?
Muscle spindle
What is the function of the Golgi tendon organ reflex?
To mitigate the force of muscle contraction
What is the patellar reflex also known as?
Knee-jerk reflex
What is the method to test the motor system in animals?
Applying gentle pressure to the plantar or palmar surface of the pelvic or thoracic limbs
What is the normal response when pressure is applied to the plantar or palmar surface of the pelvic or thoracic limbs in animals?
The limb is easy to flex
How many main components can the motor system be divided into?
2
What is the origin of Lower Motor Neurons (LMN) in the spinal cord?
Ventral horn of the spinal cord
Where do Upper Motor Neurons (UMN) typically originate?
Brain
What is the function of Upper Motor Neurons (UMN)?
Project to and control Lower Motor Neurons (LMN)
What is the name of the pathway that Upper Motor Neurons (UMN) belong to?
Corticomedullary pathway
What is the direction of the green arrowheads in the diagram?
From Upper Motor Neurons to Lower Motor Neurons
What type of synapse occurs between Upper Motor Neurons and Lower Motor Neurons?
Indirect synapse with local synapses
What is the result of loss of facilitatory UMNs?
Paresis or paralysis
What is the primary function of LMNs?
To initiate motor movement
What is the characteristic of muscle tone in LMN lesions?
Decreased to absent muscle tone
What is the characteristic of muscle atrophy in UMN lesions?
Mild and chronic
What is the location of UMNs in the CNS?
CNS neurons that communicate with LMNs
What is the level of the spinal cord where LMNs innervating the limbs are confined?
Cervical and lumbar intumescences
What is the result of a high cervical lesion?
Tetraparesis
What is the characteristic of reflexes in UMN lesions?
Increased reflexes
What is the problem in a lesion that results in paresis or paralysis, with decreased to absent muscle tone and reflexes?
Paresis
Study Notes
Patellar Reflex (Quadriceps, Knee-Jerk Reflex)
- Elicited by tapping the tendon of the quadriceps femoris muscle located immediately distal to the patella
- Tests the stretch reflex mediated by the femoral nerve
- This is the most reliable test of the stretch reflex
- Cord segment involved: L4, L5, L6
Stretch Reflex
- Main action: contraction
- Secondary action: reciprocal inhibition, inactivation of antagonist muscle
- Stretch reflexes and other muscle contractions often accompanied by reciprocal inhibition, which prevents muscles from working against each other
Inverse Stretch Reflex (Golgi Tendon Organ Reflex)
- Main action: reduced stimulation, inhibited at the level of the spinal cord
- Secondary action: reciprocal stimulation
- Responds to contraction, causes muscle relaxation, and prevents excessive tension on the muscle
Flexor Reflex (Withdrawal Reflex)
- Coordinated polysynaptic reflex in which all the flexor muscles of a limb contract in response to a noxious stimulus
- Alpha motor neurons to the limb flexor muscles are stimulated, while those to extensor muscles are inhibited
- Reciprocal innervation
- The force and duration of the withdrawal reflex are proportional to the intensity of the noxious stimulus applied
Extensor Tone
- Muscle tone is important for maintaining normal posture and providing support for the joints to stabilize their position
- It refers to the muscle's continuous resistance to being stretched (resting tension)
- It is regulated by the local spinal cord reflexes and by higher levels of the brain
- Muscle tone (extensor tone) is evaluated during neurological examination
Motor System
- Can be divided into 2 main components: Upper Motor Neuron (UMN) and Lower Motor Neuron (LMN)
- Upper Motor Neurons:
- Completely contained within the CNS
- Cell body is located in a motor nucleus of the brainstem or the motor cortex of the forebrain
- Their axons connect to lower motor neurons
- Exert their effect by stimulating or inhibiting LMNs
- UMN system is responsible for initiation of voluntary movement, maintenance of muscle tone for support against gravity, and regulation of posture
- Lower Motor Neurons:
- Cell body is located in the ventral horn of the spinal cord or in cranial nerve nuclei
- Their axons directly innervate skeletal muscle
- LMNs are responsible for the transmission of motor signals to muscles
Upper Motor Neurons vs. Lower Motor Neurons
- UMN signs:
- Paresis or paralysis
- Normal to increased reflexes
- Normal to increased extensor muscle tone
- Mild/chronic muscle atrophy
- LMN signs:
- Paresis or paralysis
- Decreased to absent reflexes
- Decreased to absent extensor muscle tone
- Severe/fast muscle atrophy
A short quiz on the patellar reflex, a monosynaptic reflex involving the quadriceps femoris muscle and the spinal cord alpha motor neurons.
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