Structure and function of the spinal cord

Question 1

Where does the spinal cord extend from and to?

Answer 1

medulla at the cranial border of the atlas

to the first lumbar vertebra

Question 2

What is the conus medullaris?

Answer 2

The spinal cord narrowing off at L1

Question 3

What is the terminal filum?

Answer 3

Attaches to the coccyx

The carrying on of the pia and dura past the lumbar vertebrae

Question 4

What is the cauda equina?

Answer 4

The bundle of spinal nerves arising from the end of the spinal cord
Contains lumbar/sacral dorsal/ventral roots

Question 5

Where is the spinal cord located?

Answer 5

Sits within the vertebral column
Surrounded by meninges
Well protected

Question 6

How is the spinal cord divided?

Answer 6

Into four regions corresponding to which spinal nerves form that region exit the vertebral column

Question 7

What are the two points of enlargements?

Answer 7

Cervical enlargement

Lumbosacral enlargement

Question 8

What are the vertebral divisions and how many vertebrae are in each division?

Answer 8

7 cervical
12 thoracic
5 lumbar
5 sacral

Question 9

What are the different spinal nerves and how many are there?

Answer 9

C1-C8 spinal nerves
T1-T12 spinal nerves
L1-L5 spinal nerves
S1-S5 spinal nerves

Question 10

What does the lumbar cistern contain?

Answer 10

the cauda equina (lumbar/sacral dorsal/ventral roots)

Question 11

Describe the cervical enlargement

Answer 11

C4-T1 level, origin of the brachial plexus, innervation to upper limbs

Question 12

Describe the lumbosacral enlargement

Answer 12

T11-L1, origin of lumbar and sacral plexi, innervation to the lower limb

Question 13

What is the terminal filum made of?

Answer 13

Pia internally, dura externally

Question 14

What are spinal nerves?

Answer 14

Spinal nerves connect the periphery to the spinal cord

Question 15

How many spinal nerves are there?

Answer 15

31 pairs, each formed by a dorsal and ventral root (which sort of connect to form one thing)

Question 16

What role do dorsal and ventral roots have?

Answer 16

Dorsal - afferent- cell bodies of primary sensory neurons (pseudounipolar)

Ventral - efferent - motor neurons

Question 17

Describe the inner core of vertebrae

Answer 17

Grey matter - contains neuronal cell bodies. H shaped.
Ventral (front), lateral (side) and dorsal (back) horns.
Lateral horns only in thoracic spine!
Different amounts of grey matter - expanded at levels supplying the limbs e.g. cervical

Question 18

Describe the outer area of a vertebra

Answer 18

White matter
myelinated axon
White columns/tracts or funiculi

Question 19

Describe the general rules of grey matter organisation

Answer 19

Dorsal horn - neurons receiving sensory input
Lateral horn - preganglionic sympathetic neurons
Ventral horn - motor neurons
There are also interneurons between/within these levels

Question 20

Describe white matter organisation

Answer 20

Contains tracts
Long ascending tracts carrying sensory/afferent information to brain centres
Long descending tracts carrying efferent/motor impulses from brain centres
Tracts to/from the cerebral hemispheres cross - their axons cross the midline i.e. left cerebral hemisphere controls right side of body

Question 21

Describe the tract organisation of the spinal column

Answer 21

Dorsal column - ascending tracts (afferent/sensory)
Lateral column (descending and ascending tracts (mixed)
Ventral column (mainly descending tracts (efferent/motor)

Question 22

What are the two types of sensory information carried in ascending tracts?

Answer 22

1. Proprioceptive - information originating from within the body e.g. muscles, joints, tendons
2. Exteroceptive - information originating from outside the body e.g. skin (pain, temperature, touch)

Question 23

Describe the general ascending tract circuit

Answer 23

first order neuron (primary sensory)

• enters spinal cord via dorsal root
• brings info from the periphery into the CNA
• synapses onto second order neuron

Second order neuron

• ascends spinal cord or brainstem
• synapses onto third order neurons often in the thalamus, going up to the cerebral cortices

Third order neuron
- projects to the cerebral cortex

Question 24

What does the dorsal column-medial lemiscus pathway detect?

Answer 24

fine touch (from cutaneous mechanoreceptors)
- tactile discrimination, vibration sense
proprioception
- from muscle spindles, golgi tendon organs, joints
provides brain with positional information§

Question 25

1st order neurons of the dorsal column - medial lemniscus pathway

Answer 25

enter spinal cord and ascend dorsal column on same side within the fasciculus gracilis (more medial) and the fasciculus cuneatus (lateral)
Fibres ascend the dorsal column uncrossed
Longest neurons in the body
1st order neurons synapse on second order neurons in the medulla

Question 26

How are the axons of the dorsal column medial lemniscus organised topographically?

Answer 26

Fasciculus gracilis terminates in the nucleus gracilis (gracile)

• information from lower limb
• more medial

Fasciculus cuneatus terminates in the nucleus cuneatus

• information from the upper limb
• more lateral

Question 27

Describe the second order neurons of the dorsal column medial lemniscus system

Answer 27

Cross in the medulla and ascend to the thalamus

- form the medial lemniscus (a large ascending bundle of axons which cross in the medulla)

Question 28

Where from and to do the third order neurons project?

Answer 28

From the thalamus to the somatosensory cortex

Question 29

What does a lesion on one side of the spinal cord result in?

Answer 29

E.g. in multiple sclerosis
loss of tactile discrimination and proprioception on the same side of lesion
Symptoms include sensory ataxia
- loss of coordination and balance without visual cues
- clinical test: Romberg’s sign - severe swaying on standing with eyes closed/ feet together

Question 30

What type of sensory innervation is the spinothalamic tract responsible for?

Answer 30

Pain, temperature and crude touch (from nociceptors)

Question 31

Describe the first order neurons of the spinothalamic tract

Answer 31

Enter the dorsal horn and form the tract of Lissauer
Collateral branches given off at tip of dorsal horn and run up or down 1-2 segments
Synapse in dorsal horn with second order neurones

Question 32

Describe the second order neurons of the spinothalamic tract

Answer 32

Cross in the dorsal horn at each level
Ascend in the anterolateral column to the thalamus
- fibres from the lower limb are lateral
-fibres from the upper limb are medial

Question 33

Describe the third order neurons of the spinothalamic tract

Answer 33

Project from the thalamus to the somatosensory cortex

Question 34

What happens if there is damage to the anterolateral column?

Answer 34

If there is a lesion on one side of the spinal cord, there is a loss of pain, temperature and crude touch on the opposite side

Outside compression of cord: loss of lower limb pain first (fibres sit laterally)

Inside grey matter tumour: loss of upper limb pain first (fibres sit medially)

Question 35

What are spinocerebellar tracts?

Answer 35

Ascending tracts responsible for unconscious muscle proprioception (from muscle spindles, golgi tendon organs) - unconscious because not going to higher brain centres

Allow smooth motor coordination