Motor Systems

Question 1

Lower motor neurones

Answer 1

found in brainstem and spinal cord
arranged in groups according to individual muscles
their axons leave at the ventral roots of spinal cord and go to neuromuscular junction of the individual muscle fiber

Question 2

Motor Unit

Answer 2

Combination of one motor neuron and all muscle fibers that innervates with it

Question 3

…

Answer 3

The size of motor unit in a given muscle is related to the degree of fine control involved in the use of that muscle.

Question 4

In spinal cord, neurons for axial muscles (ie for posture in torso) are ____ and distal muscles are more ____

Answer 4

In spinal cord, neurons for axial muscles (ie for posture in torso) are medial and distal muscles are more lateral

Question 5

Neurons for flexers are ______ and those for extensor are ______

Answer 5

Neurons for flexers are dorsal and those for extensor are ventral

Question 6

Axial-distal mapping is reflective of the location of this pathways that descend the brainstem and spinal cord.

Answer 6

True

Question 7

3 kinds of Muscle Fibers ?

Answer 7

Red fibers and white fibers (Types IIa and IIb)

Question 8

3 kinds of motor units

Answer 8

slow-twitch (stand), fast twitch fatigue resistant (walk), fast twitch fatigable (jump)

Question 9

Motor units are recruited in order of size
grades the force of muscle contraction
recruits small to large (slow twitch to fast twitch)
this is why our movement are smooth.

Answer 9

size principle

Question 10

Basal ganglia and cerebellum control _______ (via _____) by influencing output from cortex to ______ and ______.

Answer 10

Basal ganglia and cerebellum control motor (via thalamus) by influencing output from cortex to brainstem and spinal cord.

Question 11

BG and Cb project to ________.

Answer 11

BG and Cb also project to brainstem nuclei

Question 12

Association cortex, BG, Cb control the ___________________ but do not have direct influence on __________.

Answer 12

Association cortex, BG, Cb control the choice, design and monitoring of motor movements but do not have direct influence on lower motor neurons (indirect).

Question 13

Lower motor neurosis also affected by __________ and _________ (automatically putting one foot in front of the other while you walk, type, play piano , …. )

Answer 13

Lower motor neurosis also affected by reflexes and motor programs (automatically putting one foot in front of the other while you walk, type, play piano , …. )

Question 14

What are the descending motor pathways and what are they associated with ?

Answer 14

• vestibulospinal tract (postural adjustment and head movement)
• corticospianal tract (voluntary movement)
• reticuloapinal tract and rebrospinal tract (alternate path for voluntary movement)
• tectospianal tract (from superior colliculus to cervical spinal cord - for reflexive turning of head in response to visual info)

Question 15

_______ and ________ tract end in lateral spinal cord influence _________ muscle. All others end in _________ and influence _______ muscle.

Answer 15

cortiospinal and rubrosinal tract end in lateral spinal cord influence distal muscle. All others end in medial and influence axial muscle.

Question 16

Describe the course of motor movement, or Modulation of Motor Cortex.

Answer 16

Association cortex “decide” that a motor movement is going to happen.
Premotor cortex devises plan for the movement and passes plan on to primary motor cortex.
M1 (primary motor cortex) then issues command (via brainstem nuclei and interneurons) to lower motor neurone to fire.
Premotor also sends some direct commands to lower motor neurons. BG, thalamus , Cb do not . They plan and monitor movement.

Question 17

_________ is somatopically mapped (the homunculus)

Areas that generate fine movements are given more cortical space than this with only gross movements.

Answer 17

Primary motor cortex (M1)

Question 18

• Primary motor cortex contain very large neurons called _______________. They are ________ neurons.
• Axons project through pyramids in brainstem to spinal cord (strikingly only 3% of Corticospinal Tract is axons from Betz cells)
• Only 1/2 of Corticospinal Tract originate in M1

Answer 18

Betz cells , Pyramidal neurons

Question 19

Corticospinal Tract (CST) arises in many areas, which are :

Answer 19

• Primary motor cortex (on precentral gyrus and deep within central salcus).
• Premotor cortex (anterior to M1 on lateral surface), has 4 subdivisions (so far), also has somatotopic map.
• Supplementral motor cortex (anterior to M1 on medial surface), 5-6+ subregions, somatotopically organised.

Question 20

___________ in premotor (ventral rostral) area fire booth when watching the action and when performing the action.

Answer 20

Mirror neurons

Question 21

The collection of fibres that leave the cortex and end in the brainstem (through the IC and reticular formation) are called ____________
esp for fine motor control regions of face (lips and tongue)

Answer 21

corticobulbar tract (bulb is old term for medulla)