Cranial + Spinal Nerves

Question 1

Vegas nerve (X)

Answer 1

Special mixed cranial nerve that goes to the viscera in the body and into the organs in the ventral body cavity.

Question 2

Cranial nerves definition

Answer 2

12 pairs of nerves that come out of the brain, labeled 1-12 in Roman numerals. 11 cranial nerves go to the head and the vegas nerve goes to the viseral organs. The nerves are composed of efferent, afferent, and sometimes both (mixed) neurons.

no such thing as a purely efferent neron

Question 3

Afferent Neuron

Answer 3

Neurons from special senses (eyes, ears, nose, tongue)
* Somatic senses from the skin, muscles, joints of the head
* Visceral senses from organs in the ventral cavity + some places in the head + neck

Question 4

Efferent Neuron

Answer 4

Somatic + parasympatheic multipolar neurons with their cell bodies in the grey matter of the brain stem.
No pure “efferent” neurons
- Any nerve carrying somatic motor signals out to muscles
- All carrying somatic sensory neurons back from muscle
- Almost all are efferent

Question 5

Somatic motor neurons

Answer 5

Efferent neurons that go to muscles in the face, head, and neck.

Question 6

Parasympathetic efferent neurons

Answer 6

Neurons that go to some places in the head + to organs in the ventral cavity .

Question 7

Olfactory Nerve
I

Answer 7

Composed of bipolar afferent neurons coming from the the nasal cavity through the ethmoid bone sinuses to synapse on the olfactory bulb (below the frontal cortex).
The cell bodies are in the nasal cavity

Question 8

Optic Nerve
II

Answer 8

Afferent bipolar neurons with cell bodies in the retina. It recieves signals from other neurons then passes them through the optic canal in sphenoid bone.
Some of the neurons cross to the other side of the brain through the Optic Chiasma then synaps in the thalmus and continue on to the primary visual cortex (occipital).

Question 9

Oculomotor
III

Answer 9

Efferent Parasympathetic Autonomic
motor neurons for internal eye muscles
that constricts the pupils and lens focus on distance.
Emerges from the anterior midbrain (near pons) and goes out the superior orbital fisure in the sphenoid.

Question 10

Trochlear
IV

Answer 10

Emerges from the posterior midbrain, wraps around the midbrain from behind and emerges through the superior orbital fisure in the sphenoid.

Question 11

Trigeminal
V

Answer 11

Biggest mixed nerves that start at the pons -> superior orbital fissure + 2 other holes
- 3 branches that innervate different parts of the head - exit the cranium through different holes
- Afferent signals from the skin, face + eyelids
- Mucus membranes in the mouth and nasal passages
- Somatic efferent + afferent signals to muscles that open/close jaw

Question 12

Abducens
VI

Answer 12

have ducts - pons –> superior orbital fissure in the sphenoid
- 3-6 activate extrinsic eye muscles - moves the eyeball in the socket
- Have some returning somatic fibers from these muscles

Question 13

Facial
VII

Answer 13

Emerges from the inferior pons → inner ear in temporal bone
- Mixed neurons
- Somatic afferent efferent for muscles of the face – except for chewing for the trigeminal nerves + anterior tongue
- Afferent gustatory (taste) signals from the anterior tongue
- Parasympathetic efferents for saliva glands in mouth + tear glands

Question 14

Vestibulocochlear
VIII

Answer 14

• Pons/medulla border → inner ear in temporal bone
• Mostly afferent, signals from the ear
• Efferent fibers regulate the sensitivity of ear receptors
• 2 senses in the ear, carries signals for both
  1. Vestibular - balance
  2. Hearing - detected in cochlea
• Bipolar cell bodies are in the inner ear - signaled by other cells in the ear

Question 15

Glossopharyngeal
XI

Answer 15

• Medula → jugular foreman in occipital bone
• Somatic afferent/efferent to posterior tongue muscles + some muscles in the pharynx
• Afferent gustatory (taste) signals from the posterior tongue
• Efferent parasympathetic of salivary gland
• Afferent visceral signals from blood vessels in the neck - for O2, CO2, + blood pressure

Question 16

Vegas
X

Answer 16

• Medulla → jugular foreman in occipital bone
• Only cranial nerve that leaves the head + neck
• Innervates organs in the ventral cavity
• 90% of efferent parasympathetic fibers
• Visceral afferent - 70% of axons
• Somatic efferent/ afferent to larynx (voice box) + pharynx (back of throat)
• Contains recurrent laryngeal

Question 17

Recurrent laryngeal

Answer 17

Branch of the Vegas nerve that goes down + around aortic arch + then back up to larynx

Because we evolved from fish - no necks - and evolution didn’t change the route

Question 18

Accessory
XI

Answer 18

• Enter cranium through foreman magnum → exit through the jugular foreman (in the occipital bone)
• Don’t come out of the brain - do pass through the cranium
• Come out of cervical nerves - spinal nerves in the neck
• Somatic efferent/ afferent - Sternoclediomastoid + traps

Question 19

Hypoglossal
XII

Answer 19

Comes out of the medulla → exits through hole in occipital bone
Controls parts of the tongue & important for swallowing

Question 20

Efferent cranial neurons

Answer 20

• Somatic + parasympatheic
• Multipolar neurons
• Cell bodies are in the grey matter of the brain stem

Question 21

Afferent neurons of special senses
(except taste)

Answer 21

Bipolar neurons with their bodies in sensory organs.

Question 22

Afferent somatic + visceral
cranial nerves

Answer 22

Pseudounipolar (soma is in the middle of the axon)
Cell bodies in ganglia near the spinal cord

Question 23

Efferent neurons of spinal nerves

Answer 23

• Multipolar with their cell bodies in the grey matter of the spinal cord and exit on the ventral root
• Somatic efferent neurons are in the ventral horn
• Autonomic in lateral north

Question 24

Afferent neurons of spinal nerves

Answer 24

• Only somatic + visceral afferent senses
• Pseudounipolar
• Cell bodies are in the dorsal root ganglia

Question 25

Spinal Nerves organization

Answer 25

C1 - C7 - emerge above C1 - C7 C8 emerges below C7 T 1 - 12 - below thoracic L1 - S1 - below lumbar S2 - S5 - below sacral Co 1 - out of coccyx After leaving the spinal cord they branch and go to different parts of the body Carry efferent motor signals to that part of the body Carry afferent sensory signals back

Question 26

Dorsal Root

Answer 26

Axons of afferent neurons coming out of the spinal cord with the ventral root's efferent neurons to form a spinal nerve.

Question 27

Ventral root

Answer 27

Axons of efferent neurons coming off the spinal cord that merge with the dorsal root's afferent neurons to form a spinal nerve.

Question 28

Spinal Nerve

Answer 28

Mixed efferent + afferent neurons Exits out between vertebrae Quickly splits into several rami

Question 29

Dorsal Ramis

Answer 29

Goes to the back - Deep muscles of the back - Skin of back - Segmental innervation of back muscles

Question 30

Ventral Ramis

Answer 30

Biggest Ramis - Goes to the anterior skin of the trunk + anterior trunk muscles - All muscles, skin, joints of limbs - Superficial muscles of the back - Segmental innervation of intercostal + abdominal muscles

Question 31

Ramus Communicans

Answer 31

Go into trunk ganglia - Carry sympathetic signals - Afferent visceral

Question 32

Segmental Innervation

Answer 32

Spinal nerves innervate a stripe of tissue near where they emerge from the vertebrae

Question 33

Nerve Plexuses

Answer 33

Multiple spinal nerves merge, split, + merge again from segmental innervation. - Interweaving combos of spinal nerves - Nerves that emerge are made up of axons of neurons of several spinal nerves

Question 34

Cervical Plexus

Answer 34

C1 - C5 - Simple split - merge - split - Muscles + skin of neck + posterior head - Some anterior trunk muscles

Question 35

Phrenic Nerve

Answer 35

Nerve of the cervical plexus that goes to the diaphragm at the bottom of the thoracic cavity - important for breathing

Question 36

Brachial Plexus

Answer 36

C4 - T1 Shoulder + Neck - Goes to arms + hands; skin, joints, + muscles - All torso muscles that move arms + scapula; pectoralis major + minor, seratus anterior, lats + others - Super large + complex; combine - branch - SEVERAL times and the nerves get mixed up

Question 37

Lumbar Plexus

Answer 37

L1 - L4 Contains the femoral nerve Not so complex, merge + split to: - Some deep abdominal muscles - Anterior + medial thigh muscles - Knee + hip joints - Skin on the bottom of the foot + down medial leg

Question 38

Femoral Nerve

Answer 38

Passes in front of the hip bones + femur. Goes to: - Anterior thigh muscles (quads, sartorius) - Knee + hip joints - Some medial skin

Question 39

Sacral Plexus

Answer 39

L4 - S4 - overlaps with lumbar Not so complex, branch + recombine Goes to: - Glutes, whole posterior leg, lateral thigh, entire calf + foot, skin of external genetalia + anus - Other pelvic structures - Anal sphincter, external urethral sphincter - Sciatic Nerve

Question 40

Sciatic Nerve

Answer 40

Very large with 2 nerves in one sheath going to the calf + foot