Neural organization and simple reflexes
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Neural Organization and Simple Reflexes. Anterior Motor Neurons. Alpha motor neurons give rise to large type A alpha fibers (~14 microns). stimulation can excite 3 - 100 extrafusal muscle fibers collectively called a motor unit Gamma motor neurons

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Neural Organization and Simple Reflexes

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Neural organization and simple reflexes

Neural Organization and Simple Reflexes


Anterior motor neurons

Anterior Motor Neurons

  • Alpha motor neurons

    • give rise to large type A alpha fibers (~14 microns).

    • stimulation can excite 3 - 100 extrafusal muscle fibers collectively called a motor unit

  • Gamma motor neurons

    • give rise to smaller type A gamma fibers (~5 microns)

    • stimulation excites intrafusal fibers, a special type of sensory receptor


Neural organization and simple reflexes

The Muscle Spindle

  • - sense muscle length and change in length

Figure 54-2; Guyton and Hall


Physiologic function of the muscle spindle

Physiologic Function of the Muscle Spindle

  • Compares length between the intrafusal and extrafusal muscle fiber.

  • Opposes a change in length of the muscle.

  • When the muscle is stretched the spindle returns it to its original length.

  • Leads to the stretch reflex.


Components of the stretch reflex

Components of the Stretch Reflex


The patellar reflex

The Patellar Reflex


The withdrawal reflexes

The Withdrawal Reflexes

  • A painful stimulus causes the limb to automatically withdraw from the stimulus.

  • Neural pathways for reflex:

    • nociceptor activation transmitted to the spinal cord

    • synapses with pool of interneurons that diverge the to the muscles for withdrawal, inhibit antagonist muscles, and activate reverberating circuits to prolong muscle contraction

    • duration of the afterdischarge depends on strength of the stimulus


Components of a flexor withdrawal reflex

Components of a Flexor Withdrawal Reflex


Crossed extensor reflex

Crossed Extensor Reflex

  • Painful stimulus elicits a flexor reflex in affected limb and an extensor reflex in the opposite limb.

  • Extensor reflex begins 0.2 - 0.5 seconds after the painful stimulus.

  • Serves to push body away from the stimulus, also to shift weight to the opposite limb.


The flexor withdrawal crossed extensor reflexes

The Flexor Withdrawal/Crossed Extensor Reflexes


Reflexes that cause muscle spasm

Reflexes that Cause Muscle Spasm

  • Pain signals can cause reflex activation and spasm of local muscles.

  • Inflammation of peritoneum can cause abdominal muscle spasm.

  • Muscle cramps caused by painful stimulus in muscle:

    • can be due to cold, ischemia, of overactivity

    • reflex contraction increases painful stimulus and causes more muscle contraction


Origins of the cranial nerves

Origins of the Cranial Nerves

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Origins of the cranial nerves1

Origins of the Cranial Nerves

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The olfactory nerve

The Olfactory Nerve

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Cranial nerves controlling the extra ocular muscles

Cranial Nerves Controlling the Extra-ocular Muscles

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Figure 14.23


The trigeminal nerve

The Trigeminal Nerve

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The facial nerve

The Facial Nerve

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The vestibulocochlear nerve

The Vestibulocochlear Nerve

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The glossopharyngeal nerve

The Glossopharyngeal Nerve

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The vagus nerve

The Vagus Nerve

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The accessory and hypoglossal nerve

The Accessory and HypoglossalNerve

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