Chapter 9 - Organization Of The Motor System

Question 1

What are the 4 regions in the neocortex involved in skilled movement?

Answer 1

POSTERIOR CORTEX (occipital and parietal) - Specify movement goals and send information to prefrontal cortex (“top down” influence)

PREFRONTAL CORTEX - Generates plans for movements

Premotor CORTEX - selects specific motor programs or actions

PRIMARY MOTOR CORTRX - sends controlled neural signals to lower motor neurons thay synapse on muscle

Question 2

What is the CORTICOSPINAL TRACT?

Answer 2

1. The primary motor pathway in the CNS
2. Originates in the precentral gyrus (primary motor cortex) M1
3. Consists of other cortical areas, not just the M1

Question 3

How does the CORTICOSPINAL tract work?

Answer 3

Axons from layer 5 of M1 form the CORONA RADIATA (made of pyramidal cells

2. In turn this inferiorly coalescing into the posterior portion of the internal capsule which passes between the CAUDATE AND PUTAMEN (vulnerable to stroke)
3. As the internal capsule leaves the cerebrum it furthers coalesces to form CEREBRAL PENDUNCLES
4. There is then hemidecussation of the pyramids

Question 4

What are the 2 CORTICOSPINAL TRACTS and how are they formed?

Answer 4

95% of fibers descending from each hemisphere decussate in the brain stem

1. Lateral CORTICOSPINAL tract - neurons originate in motor cortex and following decussation in the medullary pyramids the LCT descends contralaterally to control fine muscle moments of the contralateral body
2. MEDIAL CORTICOSPINAL TRACT (ventral CORTICOSPINAL tract) - conduct signals form precentral gyrus to the motor centres in the middle thoracic region

Question 5

Where does cerebral blood flow increase during movement?

Answer 5

1. HAND AREA OF PRIMARY SOMATOSENSORY AND PRIMARY MOTOR CORTEX - when subjects use a finger to push a lever
2. PREMOTOR CORTEX - when performing a sequence of movements
3. PREFRONTAL, TEMPORAL, PARIETAL CORTEX - when subjects use a finger to find a route through a maze

Question 6

What is a SKELETAL MUSCLE?

Answer 6

Structure that converts ATP into mechanical movement of the skeleton under control of the nervous system

Question 7

What is a muscles physiology?

Answer 7

Made up of thousands of MUSCLE FIBERS that run the length of the muscle

Within each there are thousands of MYOFIBRILS in parallel

Question 8

How are muscles controlled?

Answer 8

by the central nervous system VIA LOWER MOTOR NEURONS
- lower motor neurons arise in spinal cord segments and pass through central roots on their way to the target muscle Fibres

Question 9

What is the neuromuscular junction?

Answer 9

It is where LOWER MOTOR NEURONS synapse with muscles

• a special synapse consists of a presynaptic motor NEURON and post synaptic muscle fiber
• releases ACH and bonds to nicotinic ACH receptors that depolarizes muscle fiber cussing a cascade that results in muscle contraction

Question 10

What are the 8 steps in picking up a coffee mug?

Answer 10

1. Visual system inspects mug to determine what to grasp.
2. This visual cortex relays this information to areas of the motor cortex that plan and initiate movement (frontal-love motor area
3. This information is sent to the spinal cord area that connects to arm and hand muscles
4. Motor neurons carry message to muscles of the hand and forearm
5. As you grasp the mug information from your fingers sensory receptors travel up the spinal cord saying it’s been grasped to sensory cortex
6. Spinal cord carries information to the brain
7. Basal ganglia judges amount of force to grasp object. Cerebellum corrects movements timing and accuracy (errors)
8. Sensory cortex receives information that it’s been grasped