2019-04-01 16:49:02

Today's Topics

  • Exam 3 next Thursday, April 11
  • Warm-up
  • Wrap-up on the neuroscience of action

Warm-up

Which of the following sensory questions is the purview of exteroceptive systems?

  • Do I have a fever?
  • Is it warm enough outside to play frisbee?
  • Am I hungry?
  • Am I tired?

Which of the following sensory questions is the purview of exteroceptive systems?

  • Do I have a fever?
  • Is it warm enough outside to play frisbee?
  • Am I hungry?
  • Am I tired?

Which of the following would not be useful in measuring a neuron's receptive field?

  • Recording from the neuron
  • Stimulating the skin/retina/cochlea with different patterns & intensities
  • Characterizing the stimulation patterns that change responses
  • Using fMRI to record from sensory cortex

Which of the following would not be useful in measuring a neuron's receptive field?

  • Recording from the neuron
  • Stimulating the skin/retina/cochlea with different patterns & intensities
  • Characterizing the stimulation patterns that change responses
  • Using fMRI to record from sensory cortex

The flow of calcium (\(Ca^{++}\)) ions into the cell affects which of the following:

  1. The exocytosis of neurotransmitter
  2. The contraction of muscle fiber
  3. Neurotransmitter reuptake
  4. both 1. and 2.

The flow of calcium (\(Ca^{++}\)) ions into the cell affects which of the following:

  1. The exocytosis of neurotransmitter
  2. The contraction of muscle fiber
  3. Neurotransmitter reuptake
  4. both 1. and 2.

Neuroscience of action

Muscle contraction

Muscles are sensory organs, too!

Two muscle fiber types

Two muscle fiber types

  • Intrafusal fibers
    • Sense length/tension
    • Contain muscle spindles linked to Ia afferents
    • ennervated by gamma (\(\gamma\)) motor neurons
  • Extrafusal fibers
    • Generate force
    • ennervated by alpha (\(\alpha\)) motor neurons

Monosynaptic stretch (myotatic) reflex

  • Muscle stretched (length increases)
  • Muscle spindle in intrafusal fiber activates
  • Ia afferent sends signal to spinal cord
    • Activates alpha (\(\alpha\)) motor neuron
  • Muscle contracts, shortens length

Monosynaptic stetch (myotatic) reflex

  • Gamma (\(\gamma\)) motor neuron fires to take up intrafusal fiber slack

Monosynaptic stretch (myotatic) reflex

Why doesn't antagonist muscle respond?

Why doesn't antagonist muscle respond?

  • Polysynaptic inhibition of antagonist muscle
  • Prevents/dampens tremor

Brain gets fast(est) sensory info from spindles

How the brain controls the muscles

  • Pyramidal tracts
    • Pyramidal cells (Cerebral Cortex Layer 5) in primary motor cortex (M1)
    • Corticobulbar (cortex -> brainstem) tract
    • Corticospinal (cortex -> spinal cord) tract
  • Crossover (decussate) in medulla
    • L side of brain ennervates R side of body

Corticospinal tract

How the brain controls the muscles

  • Extrapyramidal system
    • Tectospinal tract
    • Vestibulospinal tract
    • Reticulospinal tract
  • Involuntary movements
    • Posture, balance, arousal

Extrapyramidal system

Disorders

  • Parkinson's
  • Huntington's

The Faces of Parkinson's

Parkinson's

  • Slow, absent movement, resting tremor
  • Cognitive deficits, depression
  • DA Neurons in substantia nigra degenerate
  • Treatments

Huntington's

Huntington's

  • Formerly Huntington’s Chorea
    • "Chorea" from Greek for "dance"
    • “Dance-like” pattern of involuntary movements
  • Cognitive decline
  • Genetic + environmental influences
  • Disturbance in striatum
  • No effective treatment

Huntington's

Final thoughts

  • Control of movement determined by multiple sources
  • Cerebral cortex + basal ganglia + cerebellum + spinal circuits

Next time…

  • Vision

References

Ramirez-Zamora, Adolfo, Lucy Gee, James Boyd, and José Biller. 2016. “Treatment of Impulse Control Disorders in Parkinson’s Disease: Practical Considerations and Future Directions.” Expert Review of Neurotherapeutics 16 (4): 389–99. doi:10.1586/14737175.2016.1158103.