CN 11: Accessory Nerve (Scheme, Origin, Pathway, Branches)

Uploaded December 2023 | Updated September 2026, 3 weeks ago

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Content:
0:00 Introduction
00:33 Accessory Nerve Scheme
03:00 Nuclei of Accessory Nerve
04:33 Course of Accessory Nerve
05:30 Internal Branch
05:54 External Branch
06:31 Recap

Provides motor function to the sternocleidomastoid and the trapezius, and goes together with the Vagus nerve to innervate muscles in the pharynx, larynx and soft palate.

Nucleus and course:
- Nucleus ambiguus
○ Give off the cranial root (radix cranialis)
○ Located in the medulla oblongata
- Spinal nucleus of accessory nerve (nucleus spinalis nervi accessorii)
○ Spinal roots (radix spinalis) from spinal segments C1–C6 lateral to the anterior horn, in the lateral funiculus
○ Ascend laterally to the spinal cord between the motor and sensory roots of the spinal nerve, and reach the posterior cranial fossa via the foramen magnum
- When the cranial root and the spinal root meets, they form the Trunk of the acessory nerve (truncus nervi accessorii), which leaves the cranium through the jugular foramen.

Branches:
- Internal branch (ramus internus)
○ joins the vagus nerve and participates in the pharyngeal branch and the recurrent laryngeal nerve of the vagus nerve, to innervate the pharynx, larynx and muscles of the soft palate.
- External branch (ramus externus)
○ Receives fibers from the anterior ramus of spinal nerve from C2, C3 and C4 (of the cervical plexus), and then innervates the sternocleidomastoid and trapezius

Sources:
- Singh, I. (2017). Human neuroanatomy (10th ed.). ® Pulmonary plexus (plexus pulmonalis)
- Kozlowski, T. (2017). Memorix Anatomy: The Complete Study Guide. 2nd ed. Thieme Medical Publishers.

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CN 11: Accessory Nerve (Scheme, Origin, Pathway, Branches) | Neuroanatomy

$Action Potential Made Easy - Nerve Physiology 🌐 Website: https://taimtalksmed.com/ 🫀 Help keep this content free: youtube.com/channel/UCEr7pkSXVsHcBLLBcJAGV-Q/join 🔬 Get 10% off anatomy lab models (affiliate link): https://anatomywarehouse.com?aff=34 📲 Other Links: Instagram: https://www.instagram.com/taimtalksmed/ Discord: https://discord.com/invite/DENMUpS8ey This video is about the general physiology of a nerve (Potentials, Polarizations, Permeability, and Excitability) Content: 0:00 Introduction 1:25 Basic Physiological Rules of a Cell 3:25 Rules of Transport Across the Membrane 3:36 Passive Transport 6:24 Active Transport 8:40 Membrane Potentials 13:54 Action Potentials 17:55 Impulse Conduction 19:40 Saltatory Conduction 20:25 All-or-None Law Basic physiological rules of the cell: - More negative inside the cell than on the outside. - Difference in extracellular and intracellular fluid - Nernst Equation calculates the charged ions across a membrane Transport through the cell membrane: Passive Transport: - Simple diffusion (has to be small, lipophilic and no charge) - Facilitated diffusion (Ion channel and Gated channels) - Filtration - Electrokinetic transport - Osmosis Active Transport: Primary Active Transport: Na/K Pump, Ca Pump Secondary Active Transport: Na/Glucose, Na/Amino Acids, Na/H Nerve: Functionally divided into three parts: Receptive Part: Dendrites Integrating part: Cell body and Axon Hillock Transmitting part: Axon Resting Potential: Typically -70 mV - Chemical gradient outside, Electrical Gradient inside = Electrochemical gradient outside - Sodium and Potassium goes in and out of cell throguh Ion Channels - Sodium potassium pump pumps 3 sodium out, 2 potassium in Action potential: - Voltage-Gated Channels - Excitability - Two gates on VG-Channel - Activation gate and inactivation gate - Changes of excitability during an action potential - Permeability of cell membrane during different stages of action potential: 1. resting state: Sodium and Potassium are unable to pass through the gated channels. Inside the cell: Negative 2. Depolarization: Sodium starts flowing in, inside the cell: positive 3. After depolarization comes repolarization, where the sodium channel close, and the potassium channel opens. Outflux of potassium brings cells back to more negative than the initial state (Hypoerloarization). This is the refractory period Conduction of action potential through a nerve axon. - Continous Conduction (Unmyelinated) - Saltatory Conduction (Myelinated) All-Or-None Law - Either we get a action potential, or not. - Chemical Synapse with Ligand gated channels, or chemically gated channels - Excitatory or Inhibitory #nervephysiology #physiology #nerve #neuron #actionpotential$

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