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Cognitive neuroscienceThe Neural Mind
Contents and reading path

Chapter 2

Sensation, Perception and Action

  1. 2.1How does the world become an experience?
  2. 2.2From stimulation to nerve signals
  3. 2.3Vision and visual perception
  4. 2.4Hearing and the direction of sound
  5. 2.5When the senses work together
  6. 2.6The cup in a noisy café
  7. 2.7How does a movement take shape?
  8. 2.8Prediction, feedback and learning
  9. LabThe visual lab

Perception and motor learning – in preparation

Reading path
Coming chapters (planned content)
  1. 1. Introduction to Cognitive Neuroscience
  2. 3. Attention
  3. 4. Memory and Learning
  4. 5. Language
  5. 6. Thinking and Executive Functions
  6. 7. Decision-Making
  7. 8. Emotion and Motivation
  8. 9. Social Cognition
  9. 10. Metacognition and Consciousness

Chapter 2 · Section 7

How does a movement take shape?

Reaching the cup requires information about both world and body — and cooperation among several motor systems.

You see the cup on the table. To grasp it, however, the nervous system also needs an estimate of where your hand is. Reaching for the same cup differs when you are sitting, standing or already holding something. The reach, the opening of the grip and your posture need to fit the task together.

Motor control is the organisation and regulation of movement. It is not simply sending a finished command and then waiting. Information from the body and surroundings continues to contribute while the hand moves. Moving your eyes or hand also changes the information available: sensing and acting belong together.

Knowing where the body is

Proprioception provides information about the body’s own position and movement. Muscle spindles contribute signals about muscle length and its change; receptors in tendons contribute information about force. Alongside other bodily signals, these help the nervous system estimate the arm and hand even when you are not looking at them. Vision and proprioception can therefore complement one another without providing identical information.

On the way to the cup, vision can inform about both cup and hand, whereas proprioception informs about your own body. Once the fingers make contact, touch and information about load become available. If the cup is heavier than expected, grip and posture need to be adjustable. Control is therefore an ongoing interaction, not a one-off order.

From nervous system to muscle fibres

Neural control of skeletal muscles belongs to the somatic nervous system, not the autonomic system. Lower motor neurons in the spinal cord and certain brainstem nuclei innervate skeletal muscles. For the arm muscles, these neurons have their cell bodies in the spinal cord. Axons from cortex do not run all the way directly to muscle.

One alpha motor neuron together with all the skeletal muscle fibres it innervates forms a motor unit. A muscle contains many such units. Which units are activated and how they are activated contribute to muscle force; the figure shows the principle, not the number of fibres in a particular human unit.

One motor unitOne alpha motor neuron has a cell body on the left and an axon branching to three symbolic skeletal muscle fibres on the right. Each branch ends at a neuromuscular junction. The number of fibres is illustrative, not a measurement.Alpha motor neuronSkeletal muscle fibresCell bodyAxonAll fibres from the same neuronOne neuron + its muscle fibres = one motor unit
Figure 2.8. One motor unit. An alpha motor neuron branches its axon to the skeletal muscle fibres belonging to the unit. Three fibres are shown symbolically; the contacts are neuromuscular junctions.Original schematic illustration.

Many contributions, no compulsory queue

Brainstem and spinal circuits bring descending information together with sensory signals. Reflex regulation and voluntary movement interact: a reflex is not simply something switched off when you choose to move. Body position and task demands influence how sensory information is used.

Several cortical areas contribute to relating the task to the body and organising movement. Basal ganglia influence action selection, initiation and vigour within networks, among other functions. The cerebellum contributes to coordination, prediction and adaptation, among other functions. Roles overlap and interact; none of these structures is a solitary on/off switch or a final correction stage.

Motor control in interacting networksCortex, basal ganglia and cerebellum form a network of bidirectional functional relations. Descending and sensory information meet in brainstem and spinal circuits. Lower motor neurons innervate muscles; the body provides new sensory information. Lines summarise functional relations, not direct anatomical tracts.Cortextask and movementBasal gangliaselection, initiation, vigourCerebellumcoordination and adaptationdescending informationBrainstem and spinal cordintegrate sensory and central contributionslower motor neuronsMuscles and bodymovement and new signalssensoryinformation
Figure 2.9. Interacting motor systems. Functional relations in a simplified network. A line may summarise multiple connections and intervening structures; this is not an anatomical map or a compulsory processing order.Original schematic illustration.

Think of grasping the cup as a shared task for several systems. The goal needs to be related to the body’s current state, movement needs to remain adjustable, and experience can change the next attempt. The next section distinguishes immediate regulation from prediction and learning.

Sources for this section
  • Scientific referencePurves, D. et al. (eds., 2001). Neuroscience (2nd ed.). Neural Centers Responsible for Movement.Interacting motor systems, descending influences and spinal circuits. Open the source ↗ (new tab)
  • Scientific referencePurves, D. et al. (eds., 2001). Neuroscience (2nd ed.). The Motor Unit.Alpha motor neurons and the skeletal muscle fibres they innervate. Open the source ↗ (new tab)
  • Scientific referencePurves, D. et al. (eds., 2001). Neuroscience (2nd ed.). Mechanoreceptors Specialized for Proprioception.Sensory information from muscles and tendons about the body. Open the source ↗ (new tab)
  • Scientific referenceBostan, A. C. & Strick, P. L. (2018). The basal ganglia and the cerebellum: nodes in an integrated network. Nature Reviews Neuroscience, 19(6), 338–350. DOI: 10.1038/s41583-018-0002-7.An integrated-network perspective on basal ganglia, cerebellum and cortex; not an exhaustive atlas. Open the source ↗ (new tab)
  • Figure provenance and model limitations are described on the sources page. About sources and figures