Psychology 210

1. Psychology 210 Lecture 6 Kevin R Smith

2. The motor system • Outline • Muscles • Reflexes • Brain motor system • Disorders of movement

3. Types of Muscles • Smooth muscle • Digestive tract • Arteries • Reproductive system • Controlled by autonomic nervous system • Striated muscle: Two types • Cardiac muscle • Skeletal muscle

4. Reflexes • Monosynaptic reflexes • Involves only one synapse (two neurons) • Polysynaptic reflexes • Involve more than one synapse

5. Sensory neuron from muscle to spinal cord Motor neuron from spinal cord to muscle Monosynaptic reflexes

6. Reciprocal inhibition When one muscle is voluntarily contracted, the other is automatically inhibited Polysynaptic reflexes

7. Polysynaptic reflexes • Flexion reflex • Jerking hand away from hot surface • Pain receptors transmit info to interneurons in spinal cord • Interneurons excite the muscles and inhibit the reciprocal muscles • Leads to the action

8. Reflexes change…. • Born with • Rooting • Stepping • Babinski • Grasping • All are gone by 1 year of age • Never actually gone, but rather inhibited

9. Pathway to the Brain • Two routes • Lateral pathway • Voluntary movements • Ventromedial pathway • Automatic processes

10. Lateral pathway • Information comes from the motor cortex or the red nucleus to the spinal cord • Contralateral organization

11. Ventromedial pathway • Posture • Coordinating head and trunk movements with eye movements • Respiration, coughing, sneezing

12. Cerebellum • Does not appear to initiate movements • Plays a role in coordinating movements • Contracts and relaxes the muscles at the right times to produce a sequence of movements • Receives information from motor cortex via the pons • Sends excitatory information back to motor cortex via the thalamus

13. Basal Ganglia • Collection of cell bodies • Caudate nucleus • Putamen • Globus pallidus • Like the cerebellum, receives information from the motor cortex and sends it back to the motor cortex via the thalamus • The information is inhibitory though

14. The Basal Ganglia • Damage can lead to Parkinson’s Disease • Theory • Less dopaminergic activity in Basal Ganglia • Less inhibition of thalamus • Overstimulation of thalamus • Less activity in frontal lobe

15. Symptoms of Parkinson’s Disease • Difficulty moving • Tremor in resting body parts • Frozen facial expressions • Stooped posture • Loss of balance, frequent falls • Autonomic disturbances • Premature death

16. Causes of Parkinson’s Disease • Degeneration of substantia nigra (midbrain) • Less dopaminergic activity in basal ganglia • Genetics in early-onset cases • Correlates with exposure to toxins: • Synthetic heroin • Agricultural chemicals • Solvents

17. Treatments of Parkinson’s Disease • L-DOPA • Precursor to Dopamine • Leads to an increase in the amount of dopaminergic activity throughout the body • Benefit: increases in dopamine levels in the basal ganglia lead to a decrease in the PD symptoms • Cost: BAD side effects • Increases in dopamine levels throughout the body lead to issues with the liver and other organs • ONLY treats the symptoms, not the cause

18. Motor cortex • Primary motor cortex • Supplementary motor area (SMA) • Premotor area

19. Primary motor cortex

20. Motor Homunculus

21. SMA and Premotor areas

22. SMA • Involved in the planning of controlled movements • Receives information from the visual pathway and send info to primary motor cortex and the brainstem

23. Premotor areas • Involved in the sensory guidance of movements • Orienting the body correctly to pick up a glass • The fine coordination needed comes from the cerebellum

24. Feedback • Motor systems are highly intertwined with feedback from the visual system • Gives the ability to change a movement throughout the movement

25. Disorders of the motor system • Toxins • Myasthenia gravis • Muscular dystrophy • Polio • Lou Gehrig’s disease • Huntington’s Disease • Parkinson’s Disease

26. Toxins • Cholinergic agonists (e.g. black widow spider toxin) overstimulate the neuromuscular junction, producing convulsions followed by paralysis. • Cholinergic antagonists paralyze muscles: • Curare • Botulinum toxin • Cobra venom

27. Myasthenia gravis • Autoimmune disorder • Results in the breakdown of acetylcholine (ACh) receptors on the muscle fiber • Symptoms include extreme weakness, fatigue, droopy eyelids, slurred speech, difficulty swallowing and breathing • Treatments include medications that suppress the immune system or inhibit acetylcholinesterase (AChE)

28. Muscular dystrophy • Heritable conditions involving the muscle protein dystrophin. • Premature muscle growth is followed by degeneration. • Gene therapy may provide effective treatments soon.

29. Polio • The polio virus destroys alpha motor neurons. • Without neural input, muscles degenerate. • Vaccination may eradicate polio world-wide in the next few years.

30. Lou Gehrig’s Disease • aka Amyotrophic Lateral Sclerosis • Motor neurons in the spinal cord and brainstem degenerate. • 5-10% of cases are due to genetic defects • The rest are sporadic: no known cause • Correlated environmental factors include vigorous activity and viruses. • Treatments for symptoms are being developed

31. Huntington’s Disease • A genetically programmed degeneration of neurons • Produces involuntary, jerky movements, depression, hallucination and delusions.

32. Huntington’s Disease • Heritable condition • Parents with HD pass it on 50% of the time • Antibiotics and fetal tissue transplants and maintaining activity may provide treatment in the future.