PSY324 Motion

Hierarchical & Parallel Movement Control

Nervous system produces movement; somatosensory system guides it.

Spinal cord → motor reflexes
Brainstem →movement timing/control
Cerebrum → voluntary movement

Neuroprosthetics

Use brain–computer interfaces (BCI) to restore lost functions.

Translate brain activity into movement or speech.

Advances allow communication and control, but limitations remain.

Sequentially Organized Movement

1. Vision locates target

2. Motor cortex plans movement

3. Spinal cord sends command

4. Motor neurons activate muscles

5. Fingers detect touch

6. Spinal cord sends feedback

7. Basal ganglia + cerebellum adjust

8. Sensory cortex perceives grasp

Visual input → motor planning (frontal lobe) → spinal cord → muscles move.

Sensory feedback returns to brain → basal ganglia & cerebellum adjust movement.

Afferent

sensory info goes to brain.

posterior root (sensory)

back of our spine

Prefrontal cortex

→ plans

Premotor cortex

organizes movement sequences.

Damage → movements become poorly sequenced/disorganized.

Primary Motor Cortex (M1)

Controls precise movements (hands, fingers, mouth).

Damage → difficulty shaping/grasping objects.

Movement Control in the Brain

Simple → motor + sensory cortex

Sequence → premotor cortex

Complex → multiple areas (prefrontal, temporal, parietal)

Brainstem

controls basic movements (posture, walking, coordination).

Spinal Cord Injuries

Quadriplegia → paralysis of arms + legs (neck injury).

Paraplegia → paralysis of lower body (lower spine injury).

Reflexes can still occur without brain control.

Motor Cortex

plans and initiates movement.

Control of Muscles

Muscles work in pairs:
Extensor → moves limb away
Flexor → moves limb toward

Acetylcholine triggers muscle contraction.

Basal Ganglia

input from neocortex,allocortex(including motor cortex) + substantia nigra (dopamine).

learning, habits, motivation, and emotion.

Basal Ganglia Disorders

Hyperkinetic → too much movement (e.g., Huntington’s, Tourette).

Hypokinetic → too little movement (e.g., Parkinson’s).

Volume control th

Globus pallidus = “volume control” of movement.

Direct pathway → allows movement.
Indirect pathway → blocks movement.

Mesolimbic DA Pathway

Dopamine from VTA → nucleus accumbens.

Involved in reward, motivation, and reinforcement.

Cerebellum (Anatomy)

Flocculus → eye movement & balance

Lateral → limbs/hands
Medial → face & body midline

Cerebellum (Function)

1) Timing (movements and perception)

2) movement accuracy (error correction - compare intended vs actual movement)

Cerebellum (Error Correction Loop)

Cortex sends motor instructions to the spinal cord + copy to cerebellum.

Sensory feedback shows actual movement and report to the cerebellum;

Cerebellum compares → corrects errors.

Somatosensory System

touch, temperature, pain, body position, movement.

2 skin types

More receptors = more sensitivity.
Hairy → less sensitive
Glabrous (hands, feet, lips) → more receptors, more sensitive

Somatosensory Receptors

• Nociception → pain, temperature, itch

• Hapsis → touch & pressure (identify objects)

• Proprioception → body position & movement

Duration of receptor response

• Rapidly adapting → fires at start & end of stimulus

• Slowly adapting → fires as long as stimulus continues

Proprioception & touch (hapsis)

→ fast, large myelinated axons

Somatosensory Pathways to the Brain

ipsilateral - Touch/proprioception on the same side

contralateral - Pain/temperature/itch cross over on the opposite side

Spinal reflexes

• Monosynaptic → 1 synapse (e.g., knee-jerk)

• Multisynaptic → multiple neurons involved

→ Fast, automatic, spinal cord (no brain needed)

Monosynaptic reflex (knee-jerk)

1. Tap → muscle stretches

2. Sensory neuron detects stretch

3. Signal → spinal cord (1 synapse)

4. Motor neuron activated

5. Muscle contracts → leg kicks

Gate theory of pain

• Pain depends on balance of signals in pathways

• Touch ↓ pain

• Less touch → ↑ pain

• Touch (large fibers) → activates interneuron → blocks pain

• Pain (small fibers) → inhibits interneuron → pain passes

→ Rubbing area = less pain

Treating pain

• Endogenous opioids → block pain (natural)

• Opioid drugs → mimic this → ↓ pain

• Brain stimulation / descending pathways → close pain gate → ↓ pain

Periaqueductal gray (PAG)

brain pain inhibitor

Vestibular system

• 3 semicircular canals + otolith organs

• Detect:

  • Head movement (direction & speed)

  • Position relative to gravity

How vestibular system works

• Head moves → fluid moves → bends hair cells

• Bending → signals sent to brain

• Direction of bend → increase or decrease activity

Vestibular disorders

• Vertigo → false spinning sensation (inner ear problem)

• Ménière’s disease → inner ear disorder → vertigo + balance loss

Somatosensory cortex damage

• ↓ touch, proprioception, object recognition

• Impaired simple movements (grasping)

• Brain can reorganize (plasticity)

Somatosensory cortex & complex movement

• Dorsal stream → guides action (unconscious movement)

• Ventral stream → helps recognize objects (conscious)

• Both integrate with somatosensory info

anterior root (motor)

front side

Premotor

→ sequences

Primary motor

→ executes movement

Cerebral palsy

difficulty making voluntary movements, often from early brainstem/brain damage.

Locked-in syndrome

→ person is awake and aware but almost completely paralyzed, usually able to move only the eyes.

Pain/temperature (nociception)

→ slow, small (less myelin) axons

efferent

motor commands go from brain to body