Functional organisation of spinal cord

Question 1

List the functional roles of the spinal cord?

Answer 1

Segmental reflexes

Inter-segmental reflexes

Pattern generators

Processing and transmission of somatosensory information

Relay of descending motor command

Relay of descending autonomic commands

Question 2

What is the spinal cord surrounded by?

Answer 2

Meninges and CSF

Question 3

At what level is a lumbar puncture performed? Why?

Answer 3

L3/4

The spinal cord terminates at L1/2

Question 4

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

Answer 4

White matter external

Grey matter internal

Question 5

How is the grey matter arranged in the spinal cord?

Answer 5

Dorsal horns

Ventral horns

Question 6

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

Answer 6

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

Question 7

Where do nociceptors enter the spinal cord?

Where do they make their connections?

Answer 7

Enter at dorsal root

Make connections in dorsal horn

Question 8

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

Answer 8

Project across spinal cord at the level that they enter

Travel up to brain on contralateral side in the anterolateral system

Question 9

Where do mechanoreceptor fibres enter the spinal cord?

Where do they make their connections?

Answer 9

Enter at the dorsal root

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

Question 10

Where do muscle spindle fibres enter the spinal cord?

Where do they make their connections?

Answer 10

Dorsal root

Make connections locally, then project up to brain ipsilaterally

Question 11

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

Answer 11

Ascending (sensory) tracts

Question 12

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

Answer 12

Motor neurons

Question 13

Describe the topography of motor nerves within the spinal cord?

Answer 13

Medial: innervate more proximal muscles

Lateral: innervate more distal muscles

There is also topographical organisation superiorly and inferiorly

Question 14

What are a-motor neurons?

Answer 14

The main motor neurons that cause muscles to contract

Question 15

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

Answer 15

They are at the bottom of a massive structure/pathway

Question 16

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

Answer 16

Question 17

Define a motor unit?

Define a motor neuron pool?

Answer 17

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

Question 18

What is the role of the muscle spindle?

Answer 18

Detect stretch within a muscle

This tells us about muscle length

Question 19

Are muscle spindles intrafusal fibres or extrafusal fibres?

Answer 19

Intrafusal fibres

Question 20

Where are muscle spindles found within muscles?

Answer 20

Intrafusal fibres

Within connective tissue sheath/capsule

Question 21

Which types of muscles have muscle spindles?

Answer 21

All muscles except the extra-ocular muscles

Question 22

Are muscle spindles contractile?

Answer 22

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

Question 23

How do muscle spindles receive information about stretch?

Answer 23

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

Transduce stretch into nerve impulses

Question 24

What are the two sensory structures within muscles?

Answer 24

Muscle spindles

Golgi tendon organs

Question 25

What is the function of golgi tendon organs?

Answer 25

Detect muscle force

Question 26

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

Answer 26

Golgi tendon organs are in series with muscles Muscle spindles are in parallel with muscles

Question 27

How can muscle spindle function be tested clinically?

Answer 27

Monosynaptic stretch reflexes

Question 28

Describe the neurology of the monosynaptic stretch reflex?

Answer 28

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

Question 29

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

Answer 29

Question 30

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

Answer 30

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

Question 31

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

Answer 31

No Interneurons are involved

Question 32

Is the response of muscle spindles a monosynaptic reflex?

Answer 32

Yes There are no interneurons involved

Question 33

What type of reflex is the cross-extensor reflex?

Answer 33

Bilateral

Question 34

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

Answer 34

Quadrupeds

Question 35

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

Answer 35

Nociceptors | (This is a withdrawal reflex)

Question 36

Describe how the cross-extensor reflex occurs?

Answer 36

Question 37

Are interneurons all the same length?

Answer 37

No, there is variation in the length of connections

Question 38

Where are longer and shorter interneurons found within the spinal cord? Why is the arrangement like this?

Answer 38

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

Question 39

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

Answer 39

Functional

Question 40

What are upper and lower motor neurons?

Answer 40

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

Question 41

Where might upper motor neurons be found?

Answer 41

Brain stem Cortex Basal ganglia

Question 42

Are most interneurons excitatory or inhibitory?

Answer 42

Inhibitory

Question 43

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

Answer 43

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

Question 44

What happens to reflexes in stroke?

Answer 44

Exxagerated reflexes contraletrally