4PSYC003W - Motor and Sensory systems_2024

Biological Psychology: MOTOR & SENSORY PROCESSES

Overview

• Sensation

  • General principles

  • Characteristics of sensory systems

  • Classification of receptors

• Brain: control of movement

  • Organisation of the Motor Cortex

  • Associated motor areas

  • Cortical control – descending pathways

• Skeletal Muscle

  • Anatomy

  • Muscular contraction

  • Sensory feedback from muscles

  • Reflexive control of movement

  • Monosynaptic stretch reflex

Nervous System Breakdown

• Central Nervous System (CNS)

  • Includes the brain and spinal cord

• Peripheral Nervous System (PNS)

  • Sensory (afferent) division

  • Motor (efferent) division

    • Somatic sensory

      • General: Touch, pain, pressure, vibration, temperature

    • Visceral sensory

      • General: Chemical changes, irritation in body wall, nausea, hunger

  • Special: Hearing, taste, smell, equilibrium, vision

• Autonomic Nervous System (ANS)

  • Sympathetic and Parasympathetic divisions

Sensation vs Perception

• Sensation: Awareness of external or internal conditions

• Perception: Conscious registration and interpretation of a sensory stimulus

Phases of Sensation

1. Detecting a Stimulus

• A stimulus capable of initiating a nervous system response must be present

  • Can be light, heat, pressure, mechanical, or chemical energy

2. Transduction

• Receptor or sense organ transduces stimulus into a nerve impulse

  • Membrane of receptor depolarizes, causing a generator/receptor potential

  • When potential reaches threshold level, an action potential (AP) is initiated

3. Into the Brain

• Impulse conducted along afferent pathways to the brain

  • Most impulses pass through thalamus, directing information to relevant sensory areas of the cortex

4. Registration in the Sensory Cortex

• Impulses translated into sensations within sensory areas of the cerebral cortex

  • Each sensory area corresponds to specific sensations

  • Some impulses initiate motor activities (reflexes) from spinal cord or brain stem

Characteristics of Sensory Processes

• Projection: Brain refers sensations to point of stimulation

• Adaptation: Decreased sensitivity to continued stimuli (not pain)

• After-images: Persistent sensations post-stimulus removal

• Modality: Specific type of sensation experienced

Classification of Receptors

By Location

• Exteroceptors: Sensitive to external environment (hearing, sight, smell)

• Visceroceptors: Monitor internal conditions (pain, fatigue, hunger)

• Proprioceptors: Provide information about body position and movement

By Type of Stimulus Detected

• Mechanoreceptors: Detect mechanical changes (touch, pressure)

• Thermoreceptors: Detect temperature changes

• Nociceptors: Detect pain

• Photoreceptors: Detect light

• Chemoreceptors: Detect taste, smell, and body fluid chemicals

• Osmoreceptors: Detect osmotic pressure of fluids

By Simplicity/Complexity

• Simple Receptors: Somatic and visceral senses (e.g. touch, pressure)

• Complex Receptors: Special senses (e.g. sight, hearing)

Control of Movement

• Movement Definition: Changing position in space

• Involves specialized motor systems and several stimuli

  • Voluntary Control: Intentional movements

  • Rapid Stretch: Monosynaptic stretch reflex (MSR)

  • Stumbling: Postural reflex

  • Startle Reflex: Engaging multiple muscle groups

Sensory Feedback and Control Strategies

Feedback Control

• Monitored by sensory systems, signals relayed to CNS

• Limited by speed of movement, e.g. 700 ms response to visual clues, movement 150-200 ms

Feedforward Control

• Optimal movement predicted from current sensory conditions and past strategies

  • E.g. Walking on snow, predicting ball trajectories

Initiation of Movement

• Parietal Cortex (PPC): Sensory input regarding spatial location

• Prefrontal Cortex (PFC): Decision making for action

• Primary Motor Cortex (PMC): Prepares motor sequences

• Primary Motor Area (M1): Executes required movements

Motor Cortical Organisation

• Somatotopic Organisation: Motor cortex representations for body areas

  • Motor homunculus detailed by Penfield and Rasmussen

Connectivity and Pathways

Intrahemispheric Connectivity

• Connections between areas responsible for specific body parts (e.g. hand, foot)

Interhemispheric Connectivity

• Communication between left and right hemispheres impacting motor control

Somatic Motor Pathways

• Upper Motor Neurons (UMNs): Extend to Lower Motor Neurons (LMNs)

  • Direct Pathways: From cerebral cortex for voluntary movement

  • Indirect Pathways: From motor centers in brain (e.g. basal nuclei)

Major Motor Pathways

• Lateral Corticospinal Tract: Controls fingers, hands, and arms

• Rubrospinal Tract: Influences forearm and hand movements

• Corticobulbar Tract: Controls facial and tongue movements

• Ventral Corticospinal Tract: Influences trunk and upper leg movements

Feedback from Muscles

• Golgi Tendon Organ: Monitors muscle tension

• Muscle Spindle: Provides feedback on muscle length and stretch

Monosynaptic Stretch Reflex (MSR)

• Rapid contraction of muscles in response to stimuli

  • E.g. Knee-jerk response, weight in hand activating reflex

• One synapse involved makes it monosynaptic

Skeletal Muscle Anatomy and Function

• Skeletal muscles attached to bones, facilitating movement via contraction

• Motor Unit: Alpha neuron and muscle fibers it innervates define muscle contraction precision

Action Potentials and Muscle Contractions

• Single impulses lead to muscular twitches; series of impulses create sustained contractions

• Strength measured through average firing rates of motor units.