Lecture 15

Question 1

What distinguishes reflex movements from voluntary movements?

Answer 1

• Reflexes are automatic and rapid
• Voluntary movements are initiated consciously and involve higher brain centres

Question 2

What is the stretch reflex important for?

Answer 2

Maintaining balance and posture

Question 3

What structure detects muscle stretch?

Answer 3

Muscle spindles

Question 4

What is the function of the tension (Golgi tendon) reflex?

Answer 4

To prevent muscle damage from excessive force by causing muscle relaxation

Question 5

What is the purpose of the withdrawal reflex?

Answer 5

Rapidly withdraw a limb from a painful stimulus

Question 6

What are the three levels of the motor control hierarchy?

Answer 6

• Highest level: Prefrontal Cortex - plans voluntary actions
• Middle level: Motor Program formation (brainstem, cerebellum, basal nuclei)
• Lowest level: Execution through motor neurons

Question 7

What does the corticospinal tract control?

Answer 7

Fine voluntary motor control, especially of limbs

Question 8

Where do corticospinal tract fibers decussate (cross)?

Answer 8

In the medulla oblongata

Question 9

What brain region organises the timing of muscle contractions for smooth, accurate movements?

Answer 9

Cerebellum

Question 10

What happens when the cerebellum is injured?

Answer 10

• Ataxia
• Dysmetria
• Tremors
• Hypotonia
• Slurred speech
• Abnormal eye movements

Question 11

What is the role of the basal nuclei?

Answer 11

Planning, initiating, and monitoring voluntary movements

Question 12

What happens in Parkinson’s disease at the neural level?

Answer 12

Loss of dopamine neurons in the substantia nigra → reduced direct pathway activation and increased indirect pathway activation → impaired movement initiation

Question 13

What are central pattern generators (CPGs)?

Answer 13

Neural circuits in the spinal cord and brainstem that produce rhythmic patterns of motor output without sensory feedback

Question 14

How do central pattern generators contribute to orofacial motor control?

Answer 14

Allow for rhythmic actions like chewing to continue automatically, modified by sensory feedback

Question 15

What is the key neural pathway for a stretch reflex?

Answer 15

Muscle spindle → afferent neuron → spinal cord → α-motor neuron → muscle contraction (monosynaptic)

Question 16

What structure triggers the tension reflex?

Answer 16

The Golgi tendon organ

Question 17

What happens during the withdrawal reflex?

Answer 17

Painful stimulus triggers flexor activation and extensor inhibition on the same side, opposite on the contralateral side (crossed-extensor reflex)

Question 18

What triggers the jaw-jerk reflex?

Answer 18

Stretching of the muscles controlling jaw movement (tests trigeminal nerve function)

Question 19

What is the function of the jaw-unloading reflex?

Answer 19

To protect teeth from sudden hard contact by depressing the mandible

Question 20

Which brain region organises thoughts and initiates voluntary movement?

Answer 20

The prefrontal cortex

Question 21

What part of the brain holds a motor map of the body?

Answer 21

The primary motor cortex

Question 22

How does the basal nuclei contribute to movement?

Answer 22

By initiating and selecting appropriate motor programs and suppressing unwanted movements

Question 23

What is the cause of motor symptoms in Parkinson’s disease?

Answer 23

Degeneration of dopaminergic neurons in the substantia nigra, leading to imbalance between the direct and indirect pathways

Question 24

What is the role of the cerebellum in movement?

Answer 24

It integrates sensory input with motor commands to produce smooth, coordinated, and accurate movements

Question 25

What is dysmetria?

Answer 25

Inability to judge distances accurately, often resulting from cerebellar damage

Question 26

How are motor programs refined over time?

Answer 26

Through practice and sensory feedback, requiring fewer corrections

Question 27

How is breathing rhythm regulated by CPGs?

Answer 27

By balancing inspiration and expiration based on metabolic demands and feedback from stretch and chemoreceptors

Question 28

How does sensory feedback modify chewing movements?

Answer 28

Sensory information from the mouth modifies the chewing rhythm to ensure efficient food processing

Question 29

What functions is the Prefrontal cortex involved in?

Answer 29

- Cognitive function - Social behaviour - Used to recall and consider information not currently available from the environment - Recall of past events can be used to help plan future events

Question 30

What happens to the 1st neuron in the Corticospinal Tract?

Answer 30

* Cell body in primary motor cortex * Descends to brainstem * Crosses midline of body in medulla oblongata * Continues down spinal cord to level of exit * Terminates in ventral horn of spinal cord

Question 31

What happens in the 2nd neuron in the Corticospinal Tract?

Answer 31

* Cell body in ventral horn of spinal cord * Exits spine and has stimulatory synapse at NMJ of target muscle fibres

Question 32

What happens in the 1st neuron in the Brainstem Pathway?

Answer 32

* Cell body in brainstem * Descends down spinal cord to level of exit * Terminates in ventral horn of spinal cord

Question 33

What happens in the 2nd neuron in the Brainstem Pathway?

Answer 33

* Cell body in ventral horn of spinal cord * Exits spine and has stimulatory synapse at NMJ of target muscle fibre(s)

Question 34

What does the direct pathway in the Basal Nuclei do?

Answer 34

Enhances motor activity

Question 35

What does the indirect pathway in the Basal Nuclei do?

Answer 35

Reduces activation of cortical neurons

Question 36

What do Neurons in Substantia Nigra release?

Answer 36

Dopamine - Essential for proper basal nuclei function and resultant movement