Psychology 210Psychology 210

Lecture 6Lecture 6

Kevin R SmithKevin R Smith

The motor systemThe motor system

OutlineOutline• MusclesMuscles• ReflexesReflexes• Brain motor systemBrain motor system• Disorders of movementDisorders of movement

Types of MusclesTypes of Muscles

Smooth muscleSmooth muscle• Digestive tractDigestive tract• ArteriesArteries• Reproductive systemReproductive system• Controlled by autonomic nervous Controlled by autonomic nervous

systemsystem Striated muscle: Two typesStriated muscle: Two types

• Cardiac muscleCardiac muscle• Skeletal muscleSkeletal muscle

ReflexesReflexes

Monosynaptic reflexesMonosynaptic reflexes• Involves only one synapse (two neurons)Involves only one synapse (two neurons)

Polysynaptic reflexesPolysynaptic reflexes• Involve more than one synapseInvolve more than one synapse

Monosynaptic reflexesMonosynaptic reflexes

Sensory neuron Sensory neuron from muscle to from muscle to spinal cordspinal cord

Motor neuron Motor neuron from spinal from spinal cord to musclecord to muscle

Polysynaptic reflexesPolysynaptic reflexes

Reciprocal Reciprocal inhibitioninhibition• When one When one

muscle is muscle is voluntarily voluntarily contracted, contracted, the other is the other is automaticalautomatically inhibitedly inhibited

Polysynaptic reflexesPolysynaptic reflexes

Flexion reflexFlexion reflex• Jerking hand away Jerking hand away

from hot surfacefrom hot surface• Pain receptors Pain receptors

transmit info to transmit info to interneurons in interneurons in spinal cordspinal cord

• Interneurons excite Interneurons excite the muscles and the muscles and inhibit the reciprocal inhibit the reciprocal musclesmuscles

• Leads to the actionLeads to the action

Reflexes change….Reflexes change….

Born withBorn with• RootingRooting• SteppingStepping• BabinskiBabinski• GraspingGrasping

All are gone by 1 year of ageAll are gone by 1 year of age• Never actually gone, but rather inhibitedNever actually gone, but rather inhibited

Pathway to the BrainPathway to the Brain

Two routesTwo routes• Lateral Lateral

pathwaypathway Voluntary Voluntary

movementsmovements

• Ventromedial Ventromedial pathwaypathway

Automatic Automatic processesprocesses

Lateral pathwayLateral pathway

Information comes from the motor Information comes from the motor cortex or the red nucleus to the cortex or the red nucleus to the spinal cordspinal cord

Contralateral organizationContralateral organization

Ventromedial pathwayVentromedial pathway

Posture Posture Coordinating head and trunk Coordinating head and trunk

movements with eye movementsmovements with eye movements Respiration, coughing, sneezingRespiration, coughing, sneezing

CerebellumCerebellum Does not appear to initiate movementsDoes not appear to initiate movements Plays a role in coordinating movementsPlays a role in coordinating movements

• Contracts and relaxes the muscles at the Contracts and relaxes the muscles at the right times to produce a sequence of right times to produce a sequence of movementsmovements

Receives information from motor Receives information from motor cortex via the ponscortex via the pons

Sends excitatory information back to Sends excitatory information back to motor cortex via the thalamusmotor cortex via the thalamus

Basal GangliaBasal Ganglia

Collection of cell bodiesCollection of cell bodies• Caudate nucleusCaudate nucleus• PutamenPutamen• Globus pallidusGlobus pallidus

Like the cerebellum, Like the cerebellum, receives information receives information from the motor cortex from the motor cortex and sends it back to and sends it back to the motor cortex via the motor cortex via the thalamusthe thalamus• The information is The information is

inhibitory thoughinhibitory though

The Basal GangliaThe Basal Ganglia

Damage can lead to Parkinson’s Damage can lead to Parkinson’s DiseaseDisease

TheoryTheory• Less dopaminergic activity in Basal Less dopaminergic activity in Basal

GangliaGanglia• 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 Symptoms of Parkinson’s DiseaseDisease

Difficulty movingDifficulty moving Tremor in resting body partsTremor in resting body parts Frozen facial expressionsFrozen facial expressions Stooped postureStooped posture Loss of balance, frequent fallsLoss of balance, frequent falls Autonomic disturbancesAutonomic disturbances Premature deathPremature death

Causes of Parkinson’s DiseaseCauses of Parkinson’s Disease

Degeneration of substantia nigra Degeneration of substantia nigra (midbrain)(midbrain)

Less dopaminergic activity in basal Less dopaminergic activity in basal gangliaganglia

Genetics in early-onset casesGenetics 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 DiseaseTreatments of Parkinson’s Disease

L-DOPAL-DOPA• Precursor to DopaminePrecursor to Dopamine• Leads to an increase in the amount of Leads to an increase in the amount of

dopaminergic activity throughout the bodydopaminergic activity throughout the body• Benefit: increases in dopamine levels in the Benefit: increases in dopamine levels in the

basal ganglia lead to a decrease in the PD basal ganglia lead to a decrease in the PD symptomssymptoms

• Cost: BAD side effectsCost: BAD side effects Increases in dopamine levels throughout the body Increases in dopamine levels throughout the body

lead to issues with the liver and other organslead to issues with the liver and other organs ONLY treats the symptoms, not the causeONLY treats the symptoms, not the cause

Motor cortexMotor cortex

Primary motor cortexPrimary motor cortex Supplementary motor area (SMA)Supplementary motor area (SMA) Premotor areaPremotor area

Primary motor cortexPrimary motor cortex

Motor HomunculusMotor Homunculus

SMA and Premotor areasSMA and Premotor areas

SMA SMA

Involved in the Involved in the planning of planning of controlled controlled movementsmovements

Receives Receives information from information from the visual pathway the visual pathway and send info to and send info to primary motor primary motor cortex and the cortex and the brainstembrainstem

Premotor areasPremotor areas

Involved in the Involved in the sensory guidance sensory guidance of movementsof movements

Orienting the body Orienting the body correctly to pick up correctly to pick up a glassa glass

The fine The fine coordination coordination needed comes from needed comes from the cerebellumthe cerebellum

FeedbackFeedback

Motor systems are highly intertwined Motor systems are highly intertwined with feedback from the visual systemwith feedback from the visual system

Gives the ability to change a Gives the ability to change a movement throughout the movement throughout the movementmovement

Disorders of the motor systemDisorders of the motor system

ToxinsToxins Myasthenia gravisMyasthenia gravis Muscular dystrophyMuscular dystrophy PolioPolio Lou Gehrig’s diseaseLou Gehrig’s disease Huntington’s DiseaseHuntington’s Disease Parkinson’s DiseaseParkinson’s Disease

ToxinsToxins Cholinergic agonists Cholinergic agonists

(e.g. black widow spider (e.g. black widow spider toxin) overstimulate the toxin) overstimulate the neuromuscular junction, neuromuscular junction, producing convulsions producing convulsions followed by paralysis.followed by paralysis.

Cholinergic antagonists Cholinergic antagonists paralyze muscles:paralyze muscles:• CurareCurare• Botulinum toxinBotulinum toxin• Cobra venomCobra venom

Myasthenia gravisMyasthenia gravis Autoimmune disorderAutoimmune disorder Results in the breakdown of Results in the breakdown of

acetylcholine (ACh) receptors on the acetylcholine (ACh) receptors on the muscle fibermuscle fiber

Symptoms include extreme weakness, Symptoms include extreme weakness, fatigue, droopy eyelids, slurred speech, fatigue, droopy eyelids, slurred speech, difficulty swallowing and breathingdifficulty swallowing and breathing

Treatments include medications that Treatments include medications that suppress the immune system or inhibit suppress the immune system or inhibit acetylcholinesterase (AChE)acetylcholinesterase (AChE)

Muscular dystrophyMuscular dystrophy

Heritable conditions Heritable conditions involving the muscle involving the muscle protein dystrophin.protein dystrophin.

Premature muscle Premature muscle growth is followed growth is followed by degeneration.by degeneration.

Gene therapy may Gene therapy may provide effective provide effective treatments soon.treatments soon.

PolioPolio

The polio virus The polio virus destroys alpha destroys alpha motor neurons.motor neurons.

Without neural Without neural input, muscles input, muscles degenerate.degenerate.

Vaccination may Vaccination may eradicate polio eradicate polio world-wide in the world-wide in the next few years.next few years.

Lou Gehrig’s DiseaseLou Gehrig’s Disease

aka Amyotrophic Lateral Sclerosis aka Amyotrophic Lateral Sclerosis Motor neurons in the spinal cord and Motor neurons in the spinal cord and

brainstem degenerate.brainstem degenerate. 5-10% of cases are due to genetic defects5-10% of cases are due to genetic defects

• The rest are sporadic: no known causeThe rest are sporadic: no known cause Correlated environmental factors include Correlated environmental factors include

vigorous activity and viruses.vigorous activity and viruses. Treatments for symptoms are being Treatments for symptoms are being

developeddeveloped

Huntington’s DiseaseHuntington’s Disease

A genetically A genetically programmed programmed degeneration of degeneration of neuronsneurons

Produces Produces involuntary, jerky involuntary, jerky movements, movements, depression, depression, hallucination and hallucination and delusions.delusions.

Huntington’s DiseaseHuntington’s Disease

Heritable conditionHeritable condition• Parents with HD pass it on 50% of the Parents with HD pass it on 50% of the

timetime Antibiotics and fetal tissue Antibiotics and fetal tissue

transplants and maintaining activity transplants and maintaining activity may provide treatment in the future.may provide treatment in the future.