Cranial + Spinal Nerves Flashcards
Vegas nerve (X)
Special mixed cranial nerve that goes to the viscera in the body and into the organs in the ventral body cavity.
Cranial nerves definition
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
Afferent Neuron
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
Efferent Neuron
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
Somatic motor neurons
Efferent neurons that go to muscles in the face, head, and neck.
Parasympathetic efferent neurons
Neurons that go to some places in the head + to organs in the ventral cavity .
Olfactory Nerve
I
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
Optic Nerve
II
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).
Oculomotor
III
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.
Trochlear
IV
Emerges from the posterior midbrain, wraps around the midbrain from behind and emerges through the superior orbital fisure in the sphenoid.
Trigeminal
V
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
Abducens
VI
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
Facial
VII
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
Vestibulocochlear
VIII
- 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
Glossopharyngeal
XI
- 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
Vegas
X
- 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
Recurrent laryngeal
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
Accessory
XI
- 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
Hypoglossal
XII
Comes out of the medulla → exits through hole in occipital bone
Controls parts of the tongue & important for swallowing
Efferent cranial neurons
- Somatic + parasympatheic
- Multipolar neurons
- Cell bodies are in the grey matter of the brain stem
Afferent neurons of special senses
(except taste)
Bipolar neurons with their bodies in sensory organs.
Afferent somatic + visceral
cranial nerves
Pseudounipolar (soma is in the middle of the axon)
Cell bodies in ganglia near the spinal cord
Efferent neurons of spinal nerves
- 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
Afferent neurons of spinal nerves
- Only somatic + visceral afferent senses
- Pseudounipolar
- Cell bodies are in the dorsal root ganglia
Spinal Nerves
organization
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
Dorsal Root
Axons of afferent neurons coming out of the spinal cord with the ventral root’s efferent neurons to form a spinal nerve.
Ventral root
Axons of efferent neurons coming off the spinal cord that merge with the dorsal root’s afferent neurons to form a spinal nerve.
Spinal Nerve
Mixed efferent + afferent neurons
Exits out between vertebrae
Quickly splits into several rami
Dorsal Ramis
Goes to the back
- Deep muscles of the back
- Skin of back
- Segmental innervation of back muscles
Ventral Ramis
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
Ramus Communicans
Go into trunk ganglia
- Carry sympathetic signals
- Afferent visceral
Segmental Innervation
Spinal nerves innervate a stripe of tissue near where they emerge from the vertebrae
Nerve Plexuses
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
Cervical Plexus
C1 - C5
- Simple split - merge - split
- Muscles + skin of neck + posterior head
- Some anterior trunk muscles
Phrenic Nerve
Nerve of the cervical plexus that goes to the diaphragm at the bottom of the thoracic cavity - important for breathing
Brachial Plexus
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
Lumbar Plexus
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
Femoral Nerve
Passes in front of the hip bones + femur.
Goes to:
- Anterior thigh muscles (quads, sartorius)
- Knee + hip joints
- Some medial skin
Sacral Plexus
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
Sciatic Nerve
Very large with 2 nerves in one sheath going to the calf + foot
