2: Anatomy - PNS

Question 1

Which structures connect neurons and allow them to receive information?

Answer 1

Dendrites

Question 2

Which structures carry action potentials away from a neuron?

Answer 2

Axon

Question 3

What is the purpose of myelin?

Answer 3

Insulates nerve axons to increase conduction velocity

Question 4

Which cells produce myelin in the

a) CNS
b) PNS?

Answer 4

a) Oligodendrocytes

b) Schwann cells

Question 5

What is a collection of nerve cell bodies called in the

a) CNS
b) PNS?

Answer 5

a) Nucleus

b) Ganglion

Question 6

What are neurons called when they have

a) one dendrite
b) 2+ dendrites?

Answer 6

a) Unipolar

b) Multipolar

Question 7

In which nervous system are the bodies of

a) multipolar
b) unipolar neurons found?

Answer 7

a) CNS

b) PNS

Question 8

Motor neurons tend to be ___.

Sensory neurons tend to be ___.

(unipolar / multipolar)

Answer 8

Motor neurons are multipolar

Sensory neurons are unipolar

Question 9

Are autonomic neurons classed as motor or sensory?

Answer 9

Motor

Question 10

What are nerves?

Answer 10

Collections of axons in tracts, with connective tissue and blood vessels

Question 11

What is the modality of a nerve?

Can a nerve have more than one modality?

Answer 11

What type of nerve it is e.g somatic motor/sensory, visceral afferent/autonomic, special sensory

Yes - they commonly have >1 modality bundled together

Question 12

What are the names of the twelve cranial nerves?

What are their modalities?

Answer 12

Question 13

What is the mnemonic for remembering the modalities of the twelve cranial nerves?

Answer 13

Some say marry money but my brother says big brains matter more

S - sensory, M - motor, B - both

Question 14

Which cranial nerve emerges directly from the pons?

Answer 14

CN V (Trigeminal nerve)

Question 15

Which cranial nerve emerges from the posterior aspect of the midbrain and wraps around to be seen from the anterior aspect?

Answer 15

CN IV (Trochlear nerve)

Question 16

What is CN XI called and where does it emerge from?

Answer 16

Spinal accessory nerve

Cervical spinal cord

Question 17

Which cranial nerves emerge from the ponto-medullary junction?

Answer 17

CN VI, VII, VIII

Question 18

How many spinal nerves are found at each spinal level (e.g cervical, thoracic, lumbar…)?

Answer 18

C 8

T 12

L 5

S 5

C 1

Question 19

How many cervical vertebrae are there?

How many cervical spinal nerves are there?

Answer 19

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

Question 20

Which vertebral foramen do spinal nerves emerge from?

Answer 20

Intervertebral foraminae

Question 21

Where do

a) cervical spinal nerves
b) thoracic, lumbar, sacral and coccygeal spinal nerves

emerge relative to their vertebrae?

Answer 21

a) C1 - C6 have spinal nerves ABOVE them, C7 has one above AND below (making 8 in total)

b) BELOW

Question 22

What structures are found between the anterior and posterior horns and anterior and posterior rami of spinal nerves?

Answer 22

Anterior/posterior rootlets > “/” roots

Spinal nerve

Immediately splits again into anterior and posterior rami

Question 23

Which aspects of the body wall are supplied by

a) anterior rami
b) posterior rami?

Answer 23

a) Anterolateral

b) Posterior

Question 24

Which type of axon is given off/received by the

a) anterior root
b) posterior root?

Answer 24

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)

Question 25

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?

Answer 25

**Sacrum** (S1 - S5) **Cranial nerves III, VII, IX** and **X**

Question 26

**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?

Answer 26

**a) Dermatomes** **b) Myotomes**

Question 27

Do **dermatomes** always overlap with **myotomes**? Can you give an example?

Answer 27

**No** C3/4/5 - dermatomes are the neck, shoulder and upper arm while these spinal nerves also supply the diaphragm

Question 28

Can dermatomes overlap?

Answer 28

**Yes**

Question 29

Which dermatomes align with the a) **male nipple** b) **umbilicus**?

Answer 29

**a) T4** **b) T10**

Question 30

Which landmarks can be found at a) **T4** b) **T10**?

Answer 30

**a) Male nipple** **b) Umbilicus**

Question 31

Which spinal nerves supply general sensation to the **upper limb**?

Answer 31

**C5 - T1** i.e the brachial plexus

Question 32

What is a **nerve plexus**?

Answer 32

Intertwined **anterior rami** from different spinal levels

Question 33

What are the **vertebral levels** of the **cervical plexus**? Which notable **skeletal muscle** is supplied by it?

Answer 33

**C1 - C4** Diaphragm

Question 34

What are the **spinal nerves** supplying the **brachial plexus**?

Answer 34

**C5 - T1**

Question 35

What are the spinal levels supplying the **lumbosacral plexus**?

Answer 35

**L1 - S4** (Lumbar **L1 - L4** Sacral **L5 - S4**)

Question 36

At which vertebral levels is the **sympathetic chain** found? What is another name for the sympathetic outflow?

Answer 36

**T1 - L2** Thoracolumbar outflow

Question 37

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**?

Answer 37

**Lateral horn**, which contains sympathetic fibres

Question 38

Where in the spinal cord do **sympathetic neurons** travel after passing into the **lateral horn**?

Answer 38

**Anterior root** (as all motor neurons do)

Question 39

**Sympathetic nerves** need to get to the **sympathetic chain** to synapse. How do they get from the **anterior horn** to the **sympathetic chain**?

Answer 39

**Anterior rootlets \> Anterior roots** Then hitch a ride on **White rami communicantes** to sympathetic chain, where most synapse

Question 40

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?

Answer 40

**Gray rami communicantes**

Question 41

What are the purposes of the a) **white rami communicantes** b) **gray rami communicantes** in terms of sympathetic nerves?

Answer 41

**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)

Question 42

What is special about sympathetic fibres supplying the a) head and neck b) adrenal medulla?

Answer 42

**a) Travel alongside arteries** **b) Synapse directly on surface of adrenal medulla**

Question 43

Which cranial nerves transmit **parasympathetic fibres**?

Answer 43

**CNs III, VII, IX, and X**

Question 44

What are the symptoms of **Horner's Syndrome**?

Answer 44

**Miosis** (pinpoint pupil) **Ptosis** (droopy eyelid) **Reduced sweating** **Increased skin warmth and redness**

Question 45

What is damaged in patients who have Horner's syndrome?

Answer 45

**Sympathetic supply to head and neck**

Question 46

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**?

Answer 46

**Miosis** - dilator pupillae **Ptosis** - levator palpebrae superioris **Reduced sweating** - eccrine sweat glands **Warmth/redness** - arteriole smooth muscle