Psychology 210 Lecture 6 Kevin R Smith

The motor system Outline Outline MusclesMuscles ReflexesReflexes Brain motor systemBrain motor system Disorders of movementDisorders of movement

Types of Muscles Smooth muscle Smooth muscle Digestive tractDigestive tract ArteriesArteries Reproductive systemReproductive system Controlled by autonomic nervous systemControlled by autonomic nervous system Striated muscle: Two types Striated muscle: Two types Cardiac muscleCardiac muscle Skeletal muscleSkeletal muscle

Reflexes Monosynaptic reflexes Monosynaptic reflexes Involves only one synapse (two neurons)Involves only one synapse (two neurons) Polysynaptic reflexes Polysynaptic reflexes Involve more than one synapseInvolve more than one synapse

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

Polysynaptic reflexes Reciprocal inhibition Reciprocal inhibition When one muscle is voluntarily contracted, the other is automatical ly inhibitedWhen one muscle is voluntarily contracted, the other is automatical ly inhibited

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

Reflexes change…. Born with Born with RootingRooting SteppingStepping BabinskiBabinski GraspingGrasping All are gone by 1 year of age All are gone by 1 year of age Never actually gone, but rather inhibitedNever actually gone, but rather inhibited

Pathway to the Brain Two routes Two routes Lateral pathwayLateral pathway Voluntary movements Voluntary movements Ventromedial pathwayVentromedial pathway Automatic processes Automatic processes

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

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

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

Basal Ganglia Collection of cell bodies Collection of cell bodies Caudate nucleusCaudate nucleus PutamenPutamen Globus pallidusGlobus pallidus Like the cerebellum, receives information from the motor cortex and sends it back to the motor cortex via the thalamus Like the cerebellum, receives information from the motor cortex and sends it back to the motor cortex via the thalamus The information is inhibitory thoughThe information is inhibitory though

The Basal Ganglia Damage can lead to Parkinson’s Disease Damage can lead to Parkinson’s Disease Theory Theory Less dopaminergic activity in Basal GangliaLess dopaminergic activity in Basal Ganglia Less inhibition of thalamusLess inhibition of thalamus Overstimulation of thalamusOverstimulation of thalamus Less activity in frontal lobeLess activity in frontal lobe

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

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

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

Motor cortex Primary motor cortex Primary motor cortex Supplementary motor area (SMA) Supplementary motor area (SMA) Premotor area Premotor area

Primary motor cortex

Motor Homunculus

SMA and Premotor areas

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

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

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

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

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

Myasthenia gravis Autoimmune disorder Autoimmune disorder Results in the breakdown of acetylcholine (ACh) receptors on the muscle fiber 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 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) Treatments include medications that suppress the immune system or inhibit acetylcholinesterase (AChE)

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

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

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

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

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