Reflex & Muscle Tone Flashcards
(31 cards)
What is a reflex?
A rapid, involuntary response to a stimulus that is processed through a reflex arc.
What is a reflex arc?
A neural pathway that controls a reflex, consisting of:ReceptorSensory neuronIntegration center (CNS)Motor neuronEffector (muscle/gland)
What are the 5 components of a reflex arc?
Stimulus detected by a receptorActivation of a sensory neuronProcessing in CNS (spinal cord or brainstem)Activation of a motor neuronResponse by an effector (muscle/gland)
What are extrafusal fibers and their innervation?
Muscle fibers that generate force, innervated by α motor neurons.
What are intrafusal fibers and their innervation?
Muscle spindle fibers that detect stretch, innervated by γ motor neurons.
What do Group Ia afferents detect?
Speed and rate of muscle stretch (wrap around central region of muscle spindle).
What do Group II afferents detect?
Static length of muscle fibers at rest.
What do Golgi tendon organs detect, and which afferents are involved?
Muscle tension; they involve Group Ib afferents.
What is a monosynaptic reflex?
A reflex involving a direct synapse between sensory and motor neurons (fast and simple).
What is a polysynaptic reflex?
A reflex involving at least one interneuron between sensory and motor neurons (slower and complex).
What is the stretch reflex? (Myotatic)
Also called deep tendon reflex, it maintains muscle tone by causing a muscle to contract when stretched.
What is an example of the stretch reflex?
The patellar (knee-jerk) reflex.
What is the pathway of the stretch reflex?
Stimulus: Muscle stretchAfferent: Group IaIntegration: Spinal cordEfferent: α motor neuronResponse: Muscle contraction
What is the inverse stretch reflex?
A polysynaptic reflex that causes muscle relaxation in response to excessive tension detected by Golgi tendon organs.
What neurons are involved in the inverse stretch reflex?
Group Ib afferents → inhibitory interneuron → inhibits α motor neuron → muscle relaxes.
What is the withdrawal (flexor) reflex?
A protective reflex that moves a body part away from a painful stimulus, polysynaptic and bilateral.
What happens on the ipsilateral side during the withdrawal reflex?
Flexors contract and extensors relax.
What happens on the contralateral side during the crossed-extensor reflex?
Extensors contract and flexors relax to maintain balance.
What does hyperreflexia suggest?
Upper motor neuron (UMN) damage—usually contralateral to the lesion.
What does hyporeflexia suggest?
Lower motor neuron (LMN) damage—usually ipsilateral to the lesion.
Why test the patellar reflex in a patient with back pain?
To assess spinal nerve function; diminished reflex may indicate nerve compression (e.g., L4 radiculopathy).
During the patellar reflex, which group of afferent fibers transmits the stretch signal to the spinal cord?A. Group Ib afferentsB. Group II afferentsC. Group Ia afferentsD. γ motor neurons
C. Group Ia afferents
Which of the following best describes the inverse stretch reflex?A. Monosynaptic, causes muscle contraction in response to stretchB. Polysynaptic, causes relaxation in response to tensionC. Monosynaptic, inhibits antagonist muscle groupD. Polysynaptic, causes contraction of the contralateral limb
B. Polysynaptic, causes relaxation in response to tension
A patient presents with hyporeflexia in the right lower limb. Which of the following is the most likely cause?A. Left-sided upper motor neuron lesionB. Right-sided lower motor neuron lesionC. Left-sided cerebellar strokeD. Peripheral sensory neuropathy of the left leg
B. Right-sided lower motor neuron lesion
