Neruo 4.1 The Lower Motoneurone Flashcards Preview

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Flashcards in Neruo 4.1 The Lower Motoneurone Deck (29):
1

Define the function of a motoneurone

Supplies skeletal muscle to set muscle tone and bring about movement.

2

Motoneurones can be categorised as upper or lower motoneurones. Where is the cell bodies of each located?

Upper - Cell bodies in brain and synapse within the CNS

Lower - cell bodies in spinal cord (lamina IX) or in cranial nerve motor nuclei

3

How can upper motoneurones be further categorised? Where are their cell bodies located?

Cortical efferents and brainstem efferents

Cortical - cell bodies in cerebral cortex

Brainstem - cell bodies in the sub cortical brain areas

4

In what part of the spinal cord can descending tracts be found?

Anterior or lateral funiculus

5

How do motoneurones ensure there are no uncontrolled limb movements?

when not in use lower motoneurones are always under inhibition from the upper motoneurones and the brain.

Cortex removes this inhibition when muscle movement is desired.

6

What are the clinical signs of lower motoneurone lesions?

Muscle weakness, hypotonia or atonia, hypo or areflexia, atrophy, fasciculations

7

What is the difference between a LMN and an alpha-motoneurone?

usually synonymous term.

8

Define a motor unit

an alpha-motoneuron and all the muscle fibres it supplies

9

Define a reflex / reflex arc

involuntary, unlearned, repeatable, automatic reaction to a specific stimulus that does not require the brain to be intact.

10

What are the 5 components necessary for a reflex arc?

  1. a receptor e.g. muscle spindle
  2. an afferent fibre e.g. muscle spindle afferent
  3. An integration centre e.g. lamina IX of spinal cord
  4. An efferent fibre e.g. alpha motoneurone
  5. An effector e.g. muscle

11

What are the 2 types of LMNs?

alpha - innervates skeletal muscle fibres.

Gamma - innervates infrasual spindles found in muscle spindles which gives info on muscle length 

12

Describe how a reflex arc occurs

tap tendon of skeletal muscle which produces vibration in the belly of the muscle and stretches the muscle spindle which produces an AP and is sent to the sensory neuron which synapses with an alpha-motoneurone to trigger contraction of muscle

13

How is motor neurone generated?

Tonic contraction of LMNs. Muscle fibres contract randomly to produce sufficient tone but prevent fatiguing of muscles

14

Explain the 'size principle' with regards to increasing muscle tone

when tone needs to be increased the LMNs recruit fibres according to their size, with the smallest motor units contracting first and the largest contracting last

15

Why is motor tone suppressed in the new born?

to allow easier passage out of the vagina.

16

What are the spinal levels of diaphragm?

C3-5

17

What are the spinal levels of biceps?

c5-c6

18

What are the spinal levels of  wrist?

c8 - t1

19

What are the spinal levels of  nipple?

T4

20

What are the spinal levels of umbilicus?

T10

21

What are the spinal levels of  Hip flexion?

L1-2

22

What are the spinal levels of quadriceps?

L3-4

23

What are the spinal levels of  knee flexion?

S1

24

What are the spinal levels of great toe?

L5

25

What are the spinal levels of foot plantar flexion

s1-2

26

What are the spinal levels of urinary sphincter and anal sphincter tone?

S2-4

27

In which muscles is tone always present (even in sleep)?

breathing muscles, extra ocular, urinary and anal sphincter

28

What happens in hypertonia?

usually a result of UMN lesion, results in decreased inhibition signals being sent to the motor units, resulting in hypertonia

29