Muscle Spindle
Reflex Classifications
Reflex Types
Mixed Bag
100

Muscle spindles are surrounded by:

Extrafusal muscle fibers

100
  • Reflexes can be classified by:
  • Development (innate vs acquired)
  • Response (somatic vs visceral (autonomic))
  • Complexity of circuit (monosynaptic vs polysynaptic)
  • Processing site (spinal vs cranial)
100

Name five different types of reflexes.

  • Stretch reflex
  • Tendon reflex
  • Flexor reflex
  • Cross-extensor reflex
  • Superficial reflex
100

To smoothly coordinate skeletal muscle, the nervous system must receive information about:

  • Length of muscle from muscle spindles
  • Amount of tension in muscle from tendon organs
  • Proprioceptors
200

Muscle spindles are made up of:

Bundles of small specialized intrafusal muscle fibers

200

What is the difference between a monosynaptic reflex and a polysynaptic reflex?

  • Monosynaptic: Sensory neuron synapses directly onto motor neuron
  • There is at least one interneuron between sensory neuron and motor neuron
200

Describe superficial reflexes

  • Caused by gentle cutaneous stimulation
  • Depend on upper motor pathways and cord-level reflex arcs
200

What are the steps in a general reflex arc?

  • Sensory receptor recognizes stimulus, if stimulated sensory input goes to:
  • Sensory neuron which then goes to spinal cord
  • Integration center (interneuron) to motor
  • Motor neuron
  • Effector (muscle contraction)
300

The function of extrafusal muscle fibers is to:

Maintain tone and contract muscle

300

What are the two kinds of inborn reflexes and what do they activate?

  • Somatic reflexes: activate skeletal muscles
  • Autonomic (visceral) reflexes: activate visceral effectors (smooth or cardiac muscles or glands)
300

Describe the flexor reflex:

  • Spinal reflex-brain not involved but can override though
  • Withdraw reflex
  • Initiated by painful stimulus
  • Causes automatic withdrawal of threatened body part
  • Ipsilateral and polysynaptic
  • Protective
300

What is reciprocal inhibition? Give example

  • Afferent fibers synapse with interneurons that inhibit motor neurons of antagonistic muscles
  • If antagonists relax, they cannot resist shortening of stretched muscle caused by main reflex arc
  • Ex: in patellar reflex, stretched muscle quads contracts and antagonists hamstrings relax
400
  • Describe the sensory region
  • Central region of intrafusal fibers
  • Wound with dendrites of sensory neurons
  • Synapses onto gamma motor neurons
400
  • Describe inborn (intrinsic) reflexes and learned reflexes. Give examples of each
  • Inborn (Intrinsic) reflex: predictable motor response to stimulus; no help from brain. Ex: maintain posture, control visceral activities, spinal reflexes
  • Learned reflex: results from practice/repetition. Ex: riding a bike, driving a car, etc.
400

Summarize the stretch reflex

  • Spinal reflex initiated by stretching muscle spindles
  • Causes stretched muscle to contract, relaxes antagonist
  • Monosynaptic except antagonist inhibition is polysynaptic (has an interneuron)
  • Ipsilateral (same side of body)
400

What is the Babinski reflex? What may it indicate if found in an adult?

  • a reflex action in which the big toe remains extended or extends itself when the sole of the foot is stimulated
  • Normal in infants
  • If found in adult may indicate CNS damage
500

What are gamma efferents and what are their functions?

  • Axons of the motor neurons
  • Complete reflex arc that synapses back onto intrafusal fibers
  • They are important in voluntary muscle contractions
  • Allow CNS to adjust sensitivity of muscle spindles
500
  • Name five general characteristics of polysynaptic reflexes:
  • Involve pools of interneurons
  • Are intersegmental in distribution
  • Involve reciprocal inhibition
  • Have reverberating circuits which prolong reflexive motor response
  • Several reflexes cooperate to produce coordinated, controlled response
500

What is the tendon reflex and why is it important?

  • Opposite of the stretch reflex- muscle relaxation and lengthening in response to tension
  • Polysynaptic
  • Responsible for smooth onset and termination of muscle contraction
  • Prevents tear of muscles and tendons
500
  • The higher centers in the brain can inhibit spinal reflexes by:
  • Stimulating inhibitory neurons
  • Creating IPSPs at reflex motor neurons
  • Suppressing postsynaptic neurons
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