Overview of the control of movement 02.03.23

Question 1

How does a movement begin?

Answer 1

In the motor cortex then it is sent down the UMN to the LMN pathway which will activate the muscle.
Crosses the neuromuscular junction to activate the muscle

Question 2

How do we smoothen the execution of muscle movement?

Answer 2

Via the extra pyramidal pathway

Question 3

How is feedback then sent back to the brain?

Answer 3

By the afferent - sensory nerves
Brain receives this feedback and co-ordinate the movement

Question 4

What projections does the primary motor cortex have?

Answer 4

Primary motor cortex projects long axons through internal capsule and brainstem into the spinal cord and will terminate in an area called the anterior horn cell of the spinal cord (2nd order neuron)

Question 5

What are 3 features of the UMN disorders?

Answer 5

• Spasticity
• Spastic weakness/ pyramidal weakness
• Brisk reflexes

Question 6

What are the common causes of UMN disorders?

Answer 6

• Brain/brain stem - Strokes, Tumours, Demyelination (MS)
• Spinal cord – MS, cord compression, spinal cord degenerative causes- Hereditary spastic paraparesis (partially able to move leg), Vit B12 deficiency

Question 7

Where do the neurons sit in the spinal cord for LMNs?

Answer 7

In the anterior part of the spinal cord (peripheral)
They project out axons from here to muscles

Question 8

What are the features of the LMN disorder?

Answer 8

• Flaccid weakness
• Reduced tone
• Muscle wasting (fasciculations - twitching)

Question 9

What is the deep tendon reflex arc? (sensory)

Answer 9

• Knee jerk
• Tap patella tendon in the knee
• Tendon gets stretched when we tap on it
• Muscle spindles sense this stretch
• Stretch receptors send signal to spinal cord (sensory)

Question 10

What is the deep tendon reflex arc? (motor)

Answer 10

• Signals enter into the dorsal root ganglion which projects onto spinal cord
• anterior horn cell sends signal down motor neuron to effector muscle to contract the muscle

Question 11

What information do muscle spindles send?

Answer 11

Afferent information - lots of it that needs to be processed

Question 12

What are some causes of the LMN injury?

Answer 12

• At the neuron: MND, Polio
• At the roots: radiculopathy
• At the nerves: neuropathies

Question 13

What are 3 causes of peripheral nerve damage?

Answer 13

1. Diabetes
2. Idiopathic (spontaneous)
3. Alcohol/ toxins/ drugs

Question 14

What stimulates the vesicles to exocytosis?

Answer 14

Calcium causes vesicles to release the ACh to the synapse for it to bind to the ACh receptors on the post-synaptic neuron

Question 15

What does binding of the ACh to the receptors cause

Answer 15

• Opens the intrinsic ion channel, resulting in a cation entering
• This results in a local depolarisation of the sarcolemma
• This results in opening of the sodium channels causing an influx of Na+
• depolarisation of the sarcolemma that travels
  down the t-tubules and ultimately causes the
  release of Ca2+ from the sarcoplasmic reticulum - CONTRACTION.

Question 16

What happens to unbound ACh in synaptic cleft?

Answer 16

• Unbound ACh in synaptic cleft defuses away or is
  hydrolysed (inactivated) by acetylcholinesterase
  (AChE)

Question 17

What is the structure of the skeletal muscle?

Answer 17

• Lots of muscle fibres make a muscle cell - bundles
• muscle fibres are made of myofibrils
• These myofibrils are made of units called sarcomeres

Question 18

What is the structure of a sarcomere?

Answer 18

• Sarcomeres are made of thick and thin filaments
  – Z line is the end of the sarcomere
  – Thick and thin filaments slide over one another to
  shorten the muscle during contraction

Question 19

What is the sliding filament theory?

Answer 19

• During contraction thin filaments slide over thick
  filaments
• Thick filaments= myosin and have “heads”
• Thin filaments = actin, these slide
• Ca and ATP required for sliding and attachment