Cranial nerves

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Cranial nerves


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USMLE® Step 1 questions

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High Yield Notes

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Cranial nerves

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USMLE® Step 1 style questions USMLE

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An examiner touches the forehead, cheeks, and chin of a patient with a cotton wisp to test the sensation of light touch in these regions. Which of the following cranial nerves is tested by the examiner?  

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Cranial nerve palsies

osteopetrosis p. 473

Cranial nerves p. 301, 523

branchial arch derivation p. 644

common lesions p. 550

locations of p. 521

nerve and vessel pathways p. 522

nuclei of p. 523

reflexes of p. 523

Glossopharyngeal nerve (NaNth cranial nerve)

Gustatory pathway

cranial nerves in p. 550

Medulla (brain)

cranial nerves and nuclei p. 521, 522


cranial nerve p. 523

Vagus nerve (NaNth cranial nerve)


The cranial nerves consist of 12 pairs of nerves originating directly from the brain and brainstem. They supply both motor and sensory information from the brain to other parts of the body, primarily supplying the region of the head and neck.

The nervous system is divided into the central nervous system, so the brain and the spinal cord, and the peripheral nervous system, which is further divided into the somatic and the autonomic nervous systems. Broadly speaking, the nervous system is split into an afferent and an efferent division. The afferent division brings sensory information - like vision, smell, touch, and proprioception - from the outside world into the brain. On the other hand, the efferent division brings motor information from the brain to the periphery, ultimately resulting in contraction of skeletal muscles to trigger movement through the somatic nervous system, as well as the contraction of the smooth muscles to trigger activity of the glands and organs through the autonomic nervous system.

Now, neurons are the main cells of the nervous system. And they’re composed of a cell body, which contains all of the cell’s organelles, and when there’s a group of neuron cell bodies found in the central nervous system, the whole thing is called a nucleus, while a group of neuron cell bodies that are located outside of the central nervous system is called a ganglion. Neurons also have nerve fibers that extend out from the neuron cell body - these are either dendrites that receive signals from other neurons, or axons that send signals along to other neurons. Where two neurons come together is called a synapse, and that’s where one end of an axon releases neurotransmitters, further relaying the signal to the dendrites or directly to the cell body of the next neuron in the series.


The cranial nerves are a set of 12 nerves that originate in the brain and the brainstem. They supply the muscles and skin of the head, and some of the muscles within the neck, and provide some visceral innervation in the chest and abdomen. The cranial nerves are numbered I through XII, starting with the nerve closest to the brainstem. The olfactory nerve (I) is unique in that it doesn't supply any muscles or skin; it's responsible for smell perception. The remaining 11 cranial nerves supply various muscles and skin in the head, as well as some mucous membranes and glands. Each nerve has a specific function, such as tasting food (II), controlling blinking (III), or supplying sensation to part of the face (V).


  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "The naming of the cranial nerves: A historical review" Clinical Anatomy (2013)
  6. "Midbrain dopaminergic neurons: A review of the molecular circuitry that regulates their development" Developmental Biology (2013)

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