Anatomy of the Spinal Cord and Spinal Nerves

Question 1

Where is the spinal cord located?

Answer 1

In the vertebral canal of the vertebral column.

Question 2

What is the structure of the spinal cord?

Answer 2

Central core of gay matter (neuron cell bodies etc.) and surrounding white matter (axons etc.)

Question 3

How many pairs of spinal nerves are there and what are they?

Answer 3

31 pairs. 
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal

Question 4

What is each spinal nerve formed from?

Answer 4

The union of anterior (central) root and posterior (dorsal) root

Question 5

What does each spinal nerve divide into?

Answer 5

Anterior ramus and posterior ramus.

Question 6

Where does the spinal cord begin?

Answer 6

Begins at foramen magnum at base of skull (continuous with medulla of brainstem), travels from vertebral levels C1 to L1/L2 in adults (L3 in infants).

Question 7

What is conus medullaris?

Answer 7

The tapered inferior end of the spinal cord.

Question 8

How are spinal nerves names?

Answer 8

named according to their exit point from the spine - intervertebral foramen or anterior and posterior sacral foramen.

Question 9

Where do cervical spinal nerves exit from?

Answer 9

Exit above corresponding pedicle.

Question 10

Where do throacic and lumbar spinal nerves exit from?

Answer 10

Below corresponding pedicle.

Question 11

Where do sacral spinal nerves exit from?

Answer 11

Rami exit via sacral foramina (S1-4) or sacral hiatus

Question 12

Where are nerve roots located?

Answer 12

In the vertebral canal.

Question 13

What is the cauda equine?

Answer 13

The nerve roots inferior to cord.

Question 14

What are the meninges of the spinal cord?

Answer 14

Pia - innermost layer, attached to surface of spinal cord.
Arachnoid - middle layer
Dura - outermost layer, thickest.

Question 15

Subarachnoid space

Answer 15

Between pia and arachnoid, filled with cerebrospinal fluid (CSF); brain and spinal cord floats in CSF

Question 16

Subdural space

Answer 16

Between dura and arachnoid, potential space

Question 17

Epidural space

Answer 17

Between dura and vertebrae, contains fat and blood vessels (but in cranial cavity, a potential space)

Question 18

Where are the dura, arachnoid and subarachnoid space present?

Answer 18

From foramen magnum to sacral hiatus.

Question 19

Internal filum terminale

Answer 19

Extension of the pia, anchors conus medullaris of spinal cord to dura inferiorly (at S2).

Question 20

External filum terminale

Answer 20

Extension of dura, anchors dura (dural sac) at S2 to sacrum/coccyx

Question 21

Denticulate ligaments

Answer 21

Projections of pia from spinal cord to arachnoid/dura

Question 22

What are the clinical correlations of the lumbar spine?

Answer 22

Sample CSF
Measure CSF pressure
Deliver drugs or radiological contrast (myelography) from/to subarachnoid space.

Question 23

Lumbar puncture

Answer 23

Lumbar cistern, with CSF and cauda equine, from L1/2 vertebra (spinal cord termination; L3 in newborn) to S2 vertebra (dural sac termination). Usually accessed between L3 and L4, or L4 and L5 spinous processes of vertebrae.

Question 24

What is a spinal nerve formed from?

Answer 24

The union of the posterior (dorsal) root (sennsory axons - afferent fibres) and anterior (ventral) root (motor axons - efferent fibres).

Question 25

Sensor fibres

Answer 25

Afferent fibres. Convey information from the body to the CNS. Axons in spinal nerves, dorsal root and spinal cord.

Question 26

Where are primary sensory neuron cell bodies located?

Answer 26

In spinal ganglia (dorsal root ganglia, DRG)

Question 27

Somatic motor (efferent) fibres

Answer 27

Innervate skeletal muscle fibres, causing muscle contraction.

Question 28

Where are lower motor neuron (LMN) cell bodies found?

Answer 28

in ventral (anterior) horn of spinal cord.

Question 29

Where are axons of somatic motor fibres found?

Answer 29

Cord, ventral root and spinal nerves.

Question 30

Visceral motor fibres

Answer 30

Efferent fibres. Control cardiac muscle, smooth muscle, or glands. Are part of the autonomic nervous system.

Question 31

Visceral motor neuron cell bodies

Answer 31

Located in the lateral horn of spinal cord. Sympathetic (thoracolumbar) division of ANS: T1-T12 and L1-L2 segments. Parasympathetic (craniosacral) division of ANS: S2-S4 (others in brainstem in cranial cavity) Second set of neuron cell bodies in ganglia.

Question 32

Where are visceral motor neuron axons located?

Answer 32

Ventral roots and spinal nerves.

Question 33

What are rami?

Answer 33

Rami are mixed nerves: sensory and motor fibres.

Question 34

What do spinal nerves divide into?

Answer 34

Dorsal (posterior) rami: to muscles and skin of the back. Ventral (anterior) rami: to muscles and skin of anterolateral trunk and limbs.

Question 35

What are dermatomes?

Answer 35

Dermatomes are regions of skin supplied by a single spinal cord segment (pair of spinal nerves including dorsal and ventral rami).

Question 36

What are myotomes?

Answer 36

Myotomes are muscle fibres supplied by a single spinal cord segment.

Question 37

Lower limb dermatomes

Answer 37

L1-5, S1-3. Adjacent dermatomes overlap.

Question 38

What is the difference between cutaneous nerves and dermatomes?

Answer 38

Cutaneous nerves are identifiable by dissection, they are peripheral nerves that supply an area of skin. They usually contain axons from more than one spinal nerve and contain sensory fibres and autonomic fibres. Dermatomes are a region of skin supplied by a single spinal cord segment (pain of spinal nerves) and cannot be identified by dissection.

Question 39

What are the cutaneous nerves of the thigh?

Answer 39

Lateral cutaneous nerve of the thigh (lateral femoral cutaneous nerve) - separate branch from lumbar plexus. Anterior cutaneous nerve of the thigh from femoral n. Posterior cuteneous nerve of the thigh - separate branch from sacral plexus. Obturator n. others supply small areas.

Question 40

Cutaneous nerve of the leg

Answer 40

Sural n (and lateral sural, medial sural) Saphenous n - from femoral n Superficial fibular n

Question 41

Cutaneous nerves of the foot

Answer 41

``` Superficial fibular n Deep fibular n Medial plantar n Lateral plantar n Sural n Saphenous nn ```

Question 42

Anterior rami

Answer 42

Ventral ramus forms a cervical plexus (complex branching of axon fibres) C1-4: cervical plexus - neck C5-T1: brachial plexus - upper limbs T1-L1: intercostal etc. nerves - trunk L1-S5: lumbar (L1-L4) and sacral plexuses (S4-S5) - lower limbs, pelvis, perineum

Question 43

What is a plexus?

Answer 43

A mesh or not of nerve fibres

Question 44

Lumbar and sacral plexuses

Answer 44

Ventral rami of spinal nerves L1-L4 (lumbar plexus) and L4-L5, S1-S4 (sacral plexus)