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Flashcards in Functional organisation of spinal cord Deck (44):
1

List the functional roles of the spinal cord?

Segmental reflexes

Inter-segmental reflexes

Pattern generators

Processing and transmission of somatosensory information

Relay of descending motor command

Relay of descending autonomic commands

2

What is the spinal cord surrounded by?

Meninges and CSF

3

At what level is a lumbar puncture performed? Why?

L3/4

The spinal cord terminates at L1/2

4

Describe the organisation of grey and white matter in the spinal cord?

White matter external

Grey matter internal

5

How is the grey matter arranged in the spinal cord?

Dorsal horns

Ventral horns

6

How does the arrangement of the spinal cord change along its length?

Proportion of grey and white matter changes

More white matter towards the top, as more fibres have joined closer to the brain

Only a thin layer of white matter in the sacral region 

7

Where do nociceptors enter the spinal cord?

Where do they make their connections?

Enter at dorsal root

Make connections in dorsal horn 

8

What do nociceptor fibres do after they have made their connection in the dorsal horn?

Project across spinal cord at the level that they enter

Travel up to brain on contralateral side in the anterolateral system

9

Where do mechanoreceptor fibres enter the spinal cord? 

Where do they make their connections?

Enter at the dorsal root 

Make some local connections, the project up to the brain ipsilaterally

10

Where do muscle spindle fibres enter the spinal cord?

Where do they make their connections?

Dorsal root

Make connections locally, then project up to brain ipsilaterally 

11

Is most of the white matter in the spinal cord ascending or descending tracts?

Ascending (sensory) tracts 

12

What is located in the ventral horn of the spinal cord?

Motor neurons

13

Describe the topography of motor nerves within the spinal cord?

Medial: innervate more proximal muscles

Lateral: innervate more distal muscles

There is also topographical organisation superiorly and inferiorly 

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14

What are a-motor neurons?

The main motor neurons that cause muscles to contract

15

Why are motor neurons referred to as the 'final common pathway'?

They are at the bottom of a massive structure/pathway

16

Describe the pathway of nociceptor, muscle spindle and mechanoreceptor pathways within the spinal cord?

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17

Define a motor unit?

Define a motor neuron pool?

Motor unit: a collection of muscle fibres innervated by a single motor neuron

Morot neuron pool: all of the motor neurons that innervate a particular muscle 

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18

What is the role of the muscle spindle?

Detect stretch within a muscle 

This tells us about muscle length

19

Are muscle spindles intrafusal fibres or extrafusal fibres?

Intrafusal fibres

20

Where are muscle spindles found within muscles?

Intrafusal fibres

Within connective tissue sheath/capsule 

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21

Which types of muscles have muscle spindles?

All muscles except the extra-ocular muscles

22

Are muscle spindles contractile?

Can contract, but their main function is to detect muscle stretch

23

How do muscle spindles receive information about stretch?

Group I and II afferent axons wrap around swollen parts of the fibres

Transduce stretch into nerve impulses

24

What are the two sensory structures within muscles?

Muscle spindles

Golgi tendon organs

25

What is the function of golgi tendon organs?

Detect muscle force

26

Describe the arrangement of muscle spindle and golgi tendon organs in relation to muscle fibres (ie. in series or parallel)?

Golgi tendon organs are in series with muscles

Muscle spindles are in parallel with muscles

27

How can muscle spindle function be tested clinically?

Monosynaptic stretch reflexes

28

Describe the neurology of the monosynaptic stretch reflex?

Pull tendon > muscle spindles detect stretch > AP travels to dorsal root via spindle afferent > spindle afferent makes an excitatory connection with motor neurons that innervate the same muscle > muscle contraction 

At the same time, the spindle afferent connects with inhibitory motor neuron > contraction inhibited in anatgonist muscle 

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29

Describe the response to placing an increased load on a muscle?

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30

Describe how golgi tendon organs respond to an increase in force?

GTO detects increased force > transmits AP along Golgi afferent > makes connection within inhibitory interneuron >  muscle contraction inhibited

At the same time, the Golgi afferent links to an excitatory interneuron, which cause the antagonist muscle to contract

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31

Is the response of the Golgi tendon organ a monosynaptic reflex?

No

Interneurons are involved

32

Is the response of muscle spindles a monosynaptic reflex?

Yes

There are no interneurons involved

33

What type of reflex is the cross-extensor reflex?

Bilateral

34

In which type of animal is the bilateral cross-extensor reflex important?

Quadrupeds

35

Which type of receptors are involved in the bilateral cross-extensor reflex?

Nociceptors 

(This is a withdrawal reflex)

36

Describe how the cross-extensor reflex occurs?

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37

Are interneurons all the same length?

No, there is variation in the length of connections

 

38

Where are longer and shorter interneurons found within the spinal cord? 

Why is the arrangement like this?

Shorter connections tend to be found laterally, as distal muscles are generally used for dextrous, complex movement

Longer connections tend to be found medially, as proximal muscles that maintain posture require lots of connections between muscles, so inter-segmental coordinations and connections are required 

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39

Is the distinction between upper and lower motor neurons a functional or anatomical one?

Functional

40

What are upper and lower motor neurons?

Lower motor neurons innervate muscles (final common pathway)

Upper motor neurons include any neurons that affect the excitability of lower motor neurons and therefore affect the outcome of the final common pathway 

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41

Where might upper motor neurons be found?

Brain stem

Cortex

Basal ganglia

42

Are most interneurons excitatory or inhibitory?

Inhibitory

43

What happens when there is a lesion in the descending motor pathway (lower motor neurons)?

Lower motor neurons below the lesion lose their inhibitory input > become more excitable and maybe spontaneously active 

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44

What happens to reflexes in stroke?

Exxagerated reflexes contraletrally