Sensorimotor System 1

Question 1

What does it mean that the sensorimotor system is hierarchically organized?

Answer 1

It has levels, like a company hierarchy, where top levels (association cortex) set general goals and bottom levels (muscles) execute specific actions.

Question 2

What is a parallel hierarchy in the sensorimotor system?

Answer 2

Parallel connections: Multiple pathways link levels, allowing flexible control.

Question 3

What is meant by functional segregation in the sensorimotor system?

Answer 3

Each level contains different units or structures that perform distinct functions, like separate departments in a company.

Question 4

How does information flow in the sensorimotor system versus sensory systems?

Answer 4

Sensorimotor system: Flows down from cortex to muscles.

Sensory system: Flows up from receptors to cortex.

Question 5

Why is hierarchical organization advantageous for the sensorimotor system?

Answer 5

Higher levels can focus on complex goals while lower levels handle the details of execution.

Question 6

How does sensory input guide motor output?

Answer 6

Sensory feedback from eyes, balance organs, skin, muscles, and joints fine-tunes motor actions and directs their continuation.

Question 7

Which movements are not influenced by sensory feedback?

Answer 7

Ballistic movements—brief, high-speed, all-or-none movements (e.g., swatting a fly).

Question 8

How are most motor adjustments controlled?

Answer 8

Unconsciously by lower levels of the sensorimotor hierarchy, without involving higher levels.

Question 9

How does sensorimotor learning change control of movements?

Answer 9

Initially, movements are consciously controlled, but with practice they become smooth, integrated sequences managed by lower CNS levels.

Question 10

Give examples of skills that demonstrate this shift in control.

Answer 10

Typing, swimming, knitting, basketball, dancing, piano playing.

Question 11

What role does sensory feedback play in learned motor sequences?

Answer 11

It continues to adjust movements automatically without conscious intervention.

Question 12

General Model of Sensorimotor Function

Answer 12

Key Principles:
* Hierarchical structure: Top levels set general goals; lower levels execute movements.
* Functional segregation: Different levels and areas have specialized roles (e.g., secondary motor cortex).
* Parallel connections: Multiple pathways link levels, allowing flexible control. Feedback pathways: Sensory input continuously adjusts motor output.

Question 13

What is the Sensorimotor Association Cortex (top level) divided into?

Answer 13

Posterior parietal association cortex (PPC) Dorsolateral prefrontal association cortex (DLPFC) Both are composed of several distinct areas with specialized functions.

Question 14

Describe the Flow of Control in muscle movement?

Answer 14

1. Association cortex: Sets goals and plans.
2. Motor signals descend through the hierarchy.
3. Skeletal muscles execute voluntary movements (e.g., picking up an apple).

Question 15

What is the main role of the posterior parietal association cortex (PPC) in sensorimotor function?

Answer 15

Involved in spatial information and awareness of the body in space.
- Proprioception

Question 16

Which sensory systems provide input to the PPC?

Answer 16

Visual, auditory, and somatosensory systems.

Question 17

Where does the PPC send its output?

Answer 17

To dorsolateral prefrontal cortex, secondary motor cortex, and the frontal eye field for controlling movements and attention.

Question 18

What happens when the inferior PPC is electrically stimulated in humans?

Answer 18

Low current: patients feel an intention to act.

High current: patients feel they have performed the action, but it does not actually occur.

Question 19

What deficits result from PPC damage?

Answer 19

Problems in: Spatial perception and memory, Accurate reaching and grasping, Eye movement control, Attention.

Question 20

What is apraxia and how is it related to PPC damage?

Answer 20

Apraxia means trouble doing planned movements, even though muscles work fine. It happens when the posterior parietal cortex (PPC) is damaged — this area helps plan and guide movement.

Question 21

What is contralateral neglect?

Answer 21

Inability to respond to stimuli on the opposite side of a brain lesion. Often occurs with right PPC damage, causing patients to ignore the left side of space.