2: Anatomy - PNS Flashcards
Which structures connect neurons and allow them to receive information?
Dendrites
Which structures carry action potentials away from a neuron?
Axon
What is the purpose of myelin?
Insulates nerve axons to increase conduction velocity
Which cells produce myelin in the
a) CNS
b) PNS?
a) Oligodendrocytes
b) Schwann cells
What is a collection of nerve cell bodies called in the
a) CNS
b) PNS?
a) Nucleus
b) Ganglion
What are neurons called when they have
a) one dendrite
b) 2+ dendrites?
a) Unipolar
b) Multipolar
In which nervous system are the bodies of
a) multipolar
b) unipolar neurons found?
a) CNS
b) PNS
Motor neurons tend to be ___.
Sensory neurons tend to be ___.
(unipolar / multipolar)
Motor neurons are multipolar
Sensory neurons are unipolar
Are autonomic neurons classed as motor or sensory?
Motor
What are nerves?
Collections of axons in tracts, with connective tissue and blood vessels
What is the modality of a nerve?
Can a nerve have more than one modality?
What type of nerve it is e.g somatic motor/sensory, visceral afferent/autonomic, special sensory
Yes - they commonly have >1 modality bundled together
What are the names of the twelve cranial nerves?
What are their modalities?
What is the mnemonic for remembering the modalities of the twelve cranial nerves?
Some say marry money but my brother says big brains matter more
S - sensory, M - motor, B - both
Which cranial nerve emerges directly from the pons?
CN V (Trigeminal nerve)
Which cranial nerve emerges from the posterior aspect of the midbrain and wraps around to be seen from the anterior aspect?
CN IV (Trochlear nerve)
What is CN XI called and where does it emerge from?
Spinal accessory nerve
Cervical spinal cord
Which cranial nerves emerge from the ponto-medullary junction?
CN VI, VII, VIII
How many spinal nerves are found at each spinal level (e.g cervical, thoracic, lumbar…)?
C 8
T 12
L 5
S 5
C 1
How many cervical vertebrae are there?
How many cervical spinal nerves are there?
7 vertebrae
8 vertebrae
Because from C1 - C7, spinal nerves emerge ABOVE the vertebrae
Then the C8 nerve emerges BELOW the C7 vertebrae
And from the thoracic spine onwards, spinal nerves emerge BELOW the vertebrae
Which vertebral foramen do spinal nerves emerge from?
Intervertebral foraminae
Where do
a) cervical spinal nerves
b) thoracic, lumbar, sacral and coccygeal spinal nerves
emerge relative to their vertebrae?
a) C1 - C6 have spinal nerves ABOVE them, C7 has one above AND below (making 8 in total)
b) BELOW
What structures are found between the anterior and posterior horns and anterior and posterior rami of spinal nerves?
Anterior/posterior rootlets > “/” roots
Spinal nerve
Immediately splits again into anterior and posterior rami
Which aspects of the body wall are supplied by
a) anterior rami
b) posterior rami?
a) Anterolateral
b) Posterior
Which type of axon is given off/received by the
a) anterior root
b) posterior root?
a) Anterior root gives off motor axons (including autonomics i.e sympathetics and parasympathetics, which are the same as visceral efferents)
b) Posterior root receives sensory axons (somatic sensory, special sensory and visceral afferents)
The anterior root gives off motor neurons, which include somatic motor, sympathetics and, sometimes, parasympathetics.
At which levels are parasympathetics given off by spinal nerves?
Which nerves carry all other parasympathetic fibres?
Sacrum (S1 - S5)
Cranial nerves III, VII, IX and X
Spinal nerves supply specific slices of the body depending on where they are found.
What areas of the body are given
a) general sensation
b) muscle innervation by spinal nerves?
a) Dermatomes
b) Myotomes
Do dermatomes always overlap with myotomes?
Can you give an example?
No
C3/4/5 - dermatomes are the neck, shoulder and upper arm while these spinal nerves also supply the diaphragm
Can dermatomes overlap?
Yes
Which dermatomes align with the
a) male nipple
b) umbilicus?
a) T4
b) T10
Which landmarks can be found at
a) T4
b) T10?
a) Male nipple
b) Umbilicus
Which spinal nerves supply general sensation to the upper limb?
C5 - T1
i.e the brachial plexus
What is a nerve plexus?
Intertwined anterior rami from different spinal levels
What are the vertebral levels of the cervical plexus?
Which notable skeletal muscle is supplied by it?
C1 - C4
Diaphragm
What are the spinal nerves supplying the brachial plexus?
C5 - T1
What are the spinal levels supplying the lumbosacral plexus?
L1 - S4
(Lumbar L1 - L4
Sacral L5 - S4)
At which vertebral levels is the sympathetic chain found?
What is another name for the sympathetic outflow?
T1 - L2
Thoracolumbar outflow
The spinal cord has anterior and posterior horns for motor and sensory neurons respectively.
What is special about the spinal cord between T1 and L2?
Lateral horn, which contains sympathetic fibres
Where in the spinal cord do sympathetic neurons travel after passing into the lateral horn?
Anterior root (as all motor neurons do)
Sympathetic nerves need to get to the sympathetic chain to synapse.
How do they get from the anterior horn to the sympathetic chain?
Anterior rootlets > Anterior roots
Then hitch a ride on White rami communicantes to sympathetic chain, where most synapse
How do postsynaptic sympathetic fibres get back to the anterior or posterior rami (depending on where they’re going) after synapsing at the sympathetic chain?
Gray rami communicantes
What are the purposes of the
a) white rami communicantes
b) gray rami communicantes
in terms of sympathetic nerves?
a) Get presynaptic sympathetic fibres from spinal nerve to sympathetic chain
b) Get postsynaptic sympathetic fibres from sympathetic chain to anterior or posterior rami
Remember some sympathetic nerves have weird paths (adrenal medulla)
What is special about sympathetic fibres supplying the
a) head and neck
b) adrenal medulla?
a) Travel alongside arteries
b) Synapse directly on surface of adrenal medulla
Which cranial nerves transmit parasympathetic fibres?
CNs III, VII, IX, and X
What are the symptoms of Horner’s Syndrome?
Miosis (pinpoint pupil)
Ptosis (droopy eyelid)
Reduced sweating
Increased skin warmth and redness
What is damaged in patients who have Horner’s syndrome?
Sympathetic supply to head and neck
Horner’s syndrome is caused by an impaired sympathetic supply to the head and neck.
What is usually supplied by sympathetics and, when these nerves are damaged, cause miosis, ptosis, reduced sweating and increased warmth/redness?
Miosis - dilator pupillae
Ptosis - levator palpebrae superioris
Reduced sweating - eccrine sweat glands
Warmth/redness - arteriole smooth muscle
