17-upper-motor

Halloween Reminder

  • Casual introduction; mention of Halloween celebration and costumes.

  • Reminder: No class on Tuesday due to Election Day.

Spinal Cord Control

  • Overview of the spinal cord's role in controlling bodily functions and movements.

  • Importance of descending inputs from the brainstem and motor cortex for movement.

  • Next week's focus: Basic game study to analyze practical movements.

Feeding Behavior in Animals

Dog Behavior

  • Dogs eating grass may indicate sickness or a deficiency; instinctively seek micronutrients.

Fruit Flies and Tumors

  • Fruit flies with gut tumors lose aversion to bitter compounds and seek them to self-treat.

Motor Neurons

Anatomy of Motor Neurons

  • Ventral horn (motor neurons) vs dorsal horn (sensory neurons).

  • Medial to lateral map aligns with muscle groups; motor neurons in the lateral edge control fingers/toes, trunk muscles in medial areas.

Definitions

  • Motor pool: All alpha motor neurons innervating a muscle group.

  • Motor unit: A single motor neuron innervating multiple muscle fibers (3 for eye muscles, up to 1000 for trunk muscles).

  • Proprioceptor feedback essential for understanding how alpha motor neurons and proprioceptors communicate for muscle tone.

Muscle Tone Regulation

  • Alpha motor neurons maintain muscle tone; muscle tone decreases during sleep due to descending input.

  • Gamma motor neurons: Control intrafusal fibers, which affect muscle spindle function.

  • Discussion on proprioceptive feedback and muscle tone dynamics.

Proprioception and Reflexes

Proprioceptor and Golgi Tendon Organs

  • Proprioceptors measure muscle stretch; Golgi tendon organs measure muscle tension to prevent damage.

  • Joint receptors mentioned, now considered less significant in proprioception after hip replacements.

  • Reflex arcs illustrated by the pin-stepping analogy, activating flexors and inhibiting extensors.

Descending Inputs from the Brain

Brainstem Pathways

  • Two main bundles in the spinal cord: medial white matter (posture/control) and lateral white matter (fine movement).

  • Pathway injury implications: lesioned lumbar pathways result in preserved gluteal muscle functions.

Brainstem Tracts

  • Vestibulospinal tract: Regulates balance and posture.

  • Reticulospinal tract: Coordinates and regulates overall muscle activity related to posture and locomotion.

  • Collicular spinal tract: Responsible for head and eye movements via superior colliculus.

Motor Cortex Functionality

Anatomy of the Motor Cortex

  • Primary motor cortex responsible for executing movements via Bet cells (corticospinal neurons).

  • Premotor cortex as the planning area integrating sensory input for motor actions.

Pyramidal Decussation

  • 90% of Bet cell axons cross at the pyramidal decussation; controls contralateral body movements.

  • 10% of axons remain ipsilateral for trunk and posture.

Homunculus Representation

Motor Cortex Mapping

  • Topography of motor cortex mimics sensory cortex; hands/face have more extensive motor representation than legs.

  • Jacksonian March: Seizures in motor cortex exhibit a predictable pattern from feet to face.

Motor Unit Dynamics

  • Bet cells contribute to central pattern generators, orchestrating coordinated movements.

  • Explanation of how motor cortex activates movements through connective circuitry, not individual muscle control.

Mirror Neurons

  • Mirror neurons activate during observation or thought of an action, linking intention to movement.

  • Spooky aspect: Empathy and shared behavioral reflection through mirror neurons.

Neurological Conditions

Upper vs Lower Motor Neuron Issues

  • Lower motor neuron conditions involve decreased muscle tone and reflexes due to neuron damage.

  • Upper motor neuron syndrome characterized by increased tone and hyperactive deep reflexes (e.g., Babinski sign).

  • Babinski’s sign significance; diagnosed by examining reflex responses (toes curling up indicates spinal cord activity without brain input).

Summary and Implications

  • Understanding spinal cord and brain motor controls essential for grasping physiological responses and neurological disorders.

  • Highlight the impact of testing and neurological assessment in clinical settings.