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40 Cards in this Set

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  • Back

Reflex

Involuntary, stereotyped response to a sensory stimulus

What are the 3 required components of a reflex?

Receptor


Sensory (afferent) neuron


Motor (efferent) neuron

What nerves to spinal reflexes involve?

Sensory - dorsal root ganglion neurons


Motor - ventral horn


Interneurons are also often involved to connect the sensory and the motor

Monosynpatic Reflex

One synapse


Does not utilize an interneuron

Disynaptic reflex

2 synapses


Utilizes a motor neuron

Multisynaptic reflex

Many neurons and synapses

What are the 3 principal spinal (segmental) reflexes involving the limbs?

Muscle stretch reflex


Flexor withdrawal


Golgi tendon organ

Muscle Spindle

Stretch receptor embedded within the muscle

In the muscle stretch reflex, what does the sensory neuron synapse on?

alpha motor neurons

What kind of reflex is the muscle stretch reflex?

Monosynaptic

Knee-Jerk Reflex Process

1. Patellar tendon is tapped --> stretch the quadriceps muscle


2. Muscle spindles are stretch --> excite sensory neurons


3. Sensory neuros synapse on alpha motor neurons and gamma motor neurons


4. Alpha motor neurons cause the contraction of the muscle


5. Gamma motor neurons reset the muscle spindle to maintain sensitivity and muscle tone

In the case of peripheral nerve injury, what would happen to the muscle stretch reflex?

Hyporeflexia


Areflexia




Due to disruption of the reflex arc

In the case of CNS injury, what would happen to the muscle stretch reflex?

Hyperreflexia due to the disruption of inhibitory input

Clonus

Repetitive vibratory movements characteristic of an upper motor neuron injury

Triceps reflex: muscles invovled

Triceps brachii

Triceps reflex: spinal cord segments

C6, C7, (C8)

Triceps reflex: peripheral nerve

radial

Biceps reflex: muscles

biceps brachii

Biceps reflex: spinal cord segments

C5, C6

Biceps reflex: peripheral nerve

musculocutaneous

Knee-jerk reflex: muscles

quadriceps femoris

Knee-jerk reflex: spinal cord segments

L3, L4

Knee-jerk reflex: peripheral nerve

femoral

Ankle-jerk reflex: muscles

gastrocnemius


Soleus

Ankle-jerk reflex: spinal cord segments

S1, S2

Ankle-jerk reflex: peripheral nerve

tibial

What are the 2 major functions of the gamma motor neurons?

Maintain the sensitivity of the muscle spindle


Determine muscle tone

Muscle tone

Slight tension in a muscle that allows for normal function

What nerves are involved in maintaining normal muscle tone?

Gamma motor neurons and alpha motor neurons

What is the activity of muscle tone controlled by?

Descending motor systems --> inhibitory control

How is muscle tone assessed clinically?

By passively extending and flexing the limbs

What is an increase in muscle tone indicative of?

Injury to the descending control of the gamma loop


Upper motor neuron lesion

What is a decrease in muscle tone indicative of?

peripheral nerve injury


lower motor neuron lesion

Spasticity

Velocity-dependent resistance to passive stretch and typically results form injury to the descending motor systems controlling the muscle stretch reflex

Rigidity

Characterized by increased uniform resistance that persists throughout the whole range of motion and typically results from injury to the basal ganglia

Flexor Withdrawal Reflex

1. Pain receptors activate excitatory interneurons


2. Interneurons synapse with flexor muscles to withdraw limb


3. Flexion is facilitated because the afferents synapse with inhibitory neurons which synapse with antagonistic extensor muscles

What kind of reflex is the flexor withdrawal reflex?

Disynpatic

Where are golgi tendon organs located?

Junction between the muscle fiber and the tendon

What kind of information does the golgi tendon organ provide?

Amount of tension in an organ

Golgi tendon organ reflex

1. Afferent fiber of golgi tendon organ innervates inhibitory neurons that project to motor neurons supplying the same muscle from which the afferent originates


2. Activation of afferent --> inhibition of motor neurons supplying the muscle that experiences the stretch --> relaxation of the muscle