1 Bi/CNS 150 Lecture 17 Wednesday November 4, 2015 Motor Systems Chapter 14, p 309 (ALS); chapter 34, 35, 37, 38 Henry Lester

22 Higher motor functions Motor cortex Basal Ganglia Corticospinal tract Motor neurons Reflexes Motor systems, “top” to “bottom”

3 Clues to Organization, from stimulation in human motor cortex. An array is implanted... to localize an epileptic focus

4 Progress in Understanding Motor Systems, 2015 Work from Richard Andersen’s lab Caltech Brain-Machine Interactions, Kandel, Box 37-3

55 Sensory & Motor Aspects of Behavior Account for Roughly Equal Times 5 1. Transduction 2. Perception (early) 3. Recognition (late perception) 4. Memory (association) 5. Judgment (valuation, preference) 6. Planning (goal formation) 7. Action Stages of Processing

Spinal reflexes and motor units Posture and muscle tone Locomotion Control of distal extremities Breathing Eye movements Speech Emotions Autonomic Nervous System (visceromotor) Examples of motor output 6

Motor output at different levels Reflexes --spinal --central "Fixed action patterns" Emotional reactions Actions Long-term plans Stimulus-coupled Stimulus-decoupled 7

8 Motor Cortex Has Layers 8

Motor System Hierarchy ganglia Motor System Hierarchy 9

Key Motor Tracts 10 Decussation in hindbrain

Damage to Motoneuron (Cell body or axon) Example: Amyotrophic lateral sclerosis (ALS) “Lou Gehrig’s Disease” 11 “Upper” motoneurons also degenerate Loss of motor unit innervation leads to weakness or paralysis of muscle Fasciculations (spontaneous contractions of muscle fibers); detected with electromyography (EMG) Atrophy of muscles, due to loss of trophic factors from motoneuron Hyporeflexia or areflexia Average time from diagnosis to death ~ 3 yr

The Basal Ganglia and ventral midbrain: Most Nuclei are GABAergic 12 “striatum” Dopaminergic. Future lecture on Parkinson’s disease Glutamatergic

13 The Basal Ganglia: Major inputs “striatum”

14 The Basal Ganglia: Projections among nuclei

Behaviors in Basal Ganglia Diseases Three common characteristics: tremor and other involuntary movements changes in posture and muscle tone slowness of movement without paralysis Cause either excess or diminished movement Cognitive changes (via caudate nucleus) 15

Motor unit: motoneuron and all innervated muscle fibers; variable number of fibers, depending on force required Alpha-motoneuron: final common pathway Motoneuron terminals, endplates, muscle action potentials, muscle contraction When MN fires, all muscle fibers contract Recruitment: adding muscle units to increase force of contraction Some Spinal Cord Motor Concepts 16

Fewer Myelinated Fibers in Lower Spinal Cord 17

The Motor Unit 18

Myelin Dorsal Horn Sensory Ventral Horn Motor Ventral Root Motor Motoneuron in Typical Spinal Cord Cross Section Motoneuron 19

Electrophysiology of the Motor Neuron and Muscle Fiber Previous Lectures 20

Herniated Disks Compress Nerve Roots (L5 most common) 21

Force increased by recruiting motor units Motoneurons of different sizes: small MNS to small, slow motor units; large MNs to large, fast motor units Size principle: smallest motor units (and smallest force) first; then larger motor units Muscle fibers: slow (red); fatigue resistant (intermediate); fast, fatigue (white) Motor Unit Size & Physiology 22

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Sensorimotor integration in absence of supraspinal input Motoneurons get input from sensory fibers, interneurons and descending fibers Stretch reflexes Flexion-withdrawal reflex Crossed extensor reflex 97% of spinal cord neurons are interneurons. Reflexes must be coordinated; this is complex 24 Tracts Groups of interneurons

Ipsilateral part of the crossed extensor reflex: Interneurons inhibit extensors when the flexors are commanded, and vice-versa 25 Figure 35-2B

A Feedback Loop Controls Muscle Function 26

27 Spindles Detect Stretch, Due to Elongation of the Muscle and of the Spindles Themselves External Stretch Modified from Figure 35-3 External Stretch

28 Golgi Tendon Organs Detect Stretch, Due to Muscle Contraction Modified from Figure 35-6

Damage in the Motor System Lower Motor NeuronUpper Motor NeuronBasal Ganglia ParalysisParesis (weakness)No paralysis Muscle atrophyNo atrophy Areflexia & atoniaHyperreflexia, hypertonia, spasticity Parkinson’s: rigidity, resting tremor, bradykinesia Huntington’s: chorea, hyperkinesia Ipsi deficit in spinal cord Contra deficit above decussation; Ipsi deficit below decussation Contra 29

30 Anterior Cingulate Cortex Lesions in this region cause impairment in one of the hierarchically highest levels of the motor system: the will to act. Patients with lesions to ACC can exhibit "akinetic mutism": they are not paralyzed and are conscious but respond poorly to their surroundings. They sometimes respond to very automatic things, like picking up a phone that rings next to their bedside (but then say nothing). They often recover, and then explain that while in this state, they were fully conscious but just lacked motivation to do anything and so did not respond or act on their surroundings.

31 Links Between Perception and Action: Why Can’t You Tickle Yourself?

End of Lecture 17

33 Primary Motor Cortex BA 4 Premotor/supplementary Motor cortex BA 6 Frontal Eye Fields BA 8 Broca’s Area (left side) BA 44, 45 Prefrontal Cortex (Frontal Association Areas) Motor Areas of Cortex

34 Sensory & Motor Aspects of Behavior Account for Roughly Equal Times 34

35 1. Transduction 2. Perception (early) 3. Recognition (late perception) 4. Memory (association) 5. Judgment (valuation, preference) 6. Planning (goal formation) 7. Action Stages of Processing

Intrafusal fibers in parallel with extrafusal muscle fibers Two types of sensory fibers – primary (Group Ia fibers) and secondary (Group II fibers) spindle afferents Group Ia – change in length (dynamic) Group II – length (static) Golgi tendon organ measures tension of muscle contraction Sensory information goes to spinal cord segment, dorsal column nuclei (proprioception), and cerebellum 1. Sensory Organs in Muscle Participate in the Feedback Loop Extrafusal fibers 36

Small MNs that project out ventral roots to intrafusal fibers Activity in gamma-MNs contracts the intrafusal muscles and makes the spindle apparatus more sensitive In turn, the group Ia and II fibers become more active Gamma-bias impacts muscle tone 2. Gamma motoneurons in muscle participate in the feedback loop Extrafusal fibers 37

Mirror Neurons 38 Links Between Perception and Action: Mirror Neurons