Chapter 11 - Motor Control and Plasticity

Explain how we know that some reflexes are mediated by the spinal cord.

Spinal cord anatomy: a) Dorsal roots transmit sensory information b) Ventral roots contain motor fibers

Spinal animals research: a) Animals with spinal cord disconnected from brain still show reflexes b) Demonstrates reflexes can occur without brain involvement

Reflex pathways in spinal cord: a) Short pathways: Direct links between dorsal and ventral roots b) Longer loops: Connect spinal cord segments to each other

Example: Knee-jerk reflex (Figure 3.20 reference) a) Simple, unvarying response to sensory stimulus b) Occurs even when spinal cord is disconnected from brain

Offer evidence of motor planning versus connecting reflexes.

Limitations of reflex-only perspective: a) Cannot explain complex behavior sequences (e.g., speech) b) Speech errors (spoonerisms) reveal overall plan

Motor plan/program evidence: a) Complex set of muscle commands established before behavior starts b) Anticipation of future actions (e.g., speech sounds placed incorrectly but within overall pattern)

Examples of planned behaviors: a) Skilled acts (e.g., piano playing) b) Simple escape behaviors (e.g., crayfish)

EMG evidence: a) Figure 11.2: Shows leg adjustment before arm movement in knob-pulling task b) Demonstrates preparation and sequencing of actions

What is closed-loop motor control?

Maximizes accuracy, involves continuous feedback, e.g., driving a car, components include transducer, error detector, controller, advantages are accuracy and flexibility, disadvantage is slower execution

What is open-loop motor control?

Maximizes speed, no external feedback, preprogrammed activity, e.g., throwing a baseball, advantages are rapid execution, disadvantage is potential for error

What is the trade-off between accuracy and speed in motor control systems?

Closed-loop systems prioritize accuracy over speed, open-loop systems prioritize speed over accuracy

What is blended control in daily life?

Combination of open-loop and closed-loop components, balancing speed and accuracy based on task requirements

What is the role of the skeletal system in motor control?

Determines possible movements; joints determine types of possible movements

Describe the function of muscles in motor control.

Work through contraction (shortening); arranged antagonistically around joints; types include fast-twitch and slow-twitch fibers

Explain the concept of neuromuscular junction (NMJ) in motor control.

Connection between motor neuron and muscle fiber; involves acetylcholine (ACh) as neurotransmitter

What is a motor unit in motor control?

Consists of a single motor neuron and all innervated muscle fibers; innervation ratio varies based on muscle function

Outline the hierarchical organization of motor control systems.

Includes skeletal system, spinal cord, brainstem, primary motor cortex, nonprimary motor cortices, cerebellum, and basal ganglia

What is muscular dystrophy (MD)?

Group of disorders causing muscle wasting

What is Duchenne muscular dystrophy?

Most prevalent form that affects boys, caused by a mutation in the dystrophin gene on the X chromosome, with gene therapy approaches being developed

How does snake venom, like bungarotoxin, affect neuromuscular junctions?

It blocks postsynaptic ACh receptors and prevents neuromuscular transmission

What is myasthenia gravis?

An autoimmune disorder where antibodies attack ACh receptors or associated proteins, leading to symptoms like muscle weakness, especially in the head and neck. Treatment involves immunosuppression or thymus removal.

What is the structure of muscle spindles?

Contain intrafusal muscle fibers; Two types of sensory endings: primary (annulospiral) and secondary (flower spray)

What is the function of muscle spindles?

Monitor muscle length and velocity of stretch; Primary endings have a phasic response, secondary endings have a tonic response; Gamma motor neurons adjust spindle sensitivity

What is the structure of Golgi tendon organs?

Located in tendons; Sensory nerve endings interwoven with tendon fibers

What is the function of Golgi tendon organs?

Monitor muscle tension and force of contraction; Detect overloads to prevent mechanical damage

How do muscle spindles and Golgi tendon organs differ in the information they provide?

Muscle spindles primarily respond to stretch, providing information about muscle length and velocity; Golgi tendon organs primarily respond to tension, providing information about muscle force

Why is proprioception important?

Essential for coordinating movement; Loss of proprioception severely impairs motor function; Visual information can partially compensate for proprioceptive loss

List the sequence of events that underlie the stretch reflex.

Stretch reflex sequence (Figure 11.11): a) Weight added, pulling hand down b) Muscle is stretched c) Afferents from muscle's sensory neuron (SNA) are excited d) Spindle afferents connect monosynaptically to motor neurons controlling the stretched muscle e) Motor neurons stimulate the muscle to oppose stretch

Additional aspects: a) Negative feedback system to restore limb position b) Inhibition of antagonistic muscles via interneurons

Describe the role of central pattern generators in locomotion.

Central pattern generators: a) Neural circuitry responsible for generating rhythmic patterns of behavior b) Located in the spinal cord c) Can function independently of brain influences or afferents

Characteristics: a) Generate endogenous rhythms for repetitive movements (e.g., walking) b) Modulated by sensory feedback and brain input c) Similar across species (cats, birds, humans)

List four strategies being explored to restore movement control following spinal cord damage.

Stem cell insertion (Figure 11.12): a) Differentiate into new neurons b) Send new axons across the break

Transplantation of glial cells: a) Promote regeneration in CNS b) Guide axonal regeneration

Use of neurotrophic factors and cell adhesion molecules: a) Entice axons to grow across damaged region b) Help axons reconnect to targets c) Develop synthetic materials for axon regeneration

Peripheral nerve transplantation: a) Form a "bridge" around injured spinal cord b) Utilize peripheral nerves' ability to regrow and reconnect

Additional approach: Electrode implantation a) Implant electrodes on dorsal roots below injury b) Use computer algorithms to stimulate desired behavior

Describe the pathology of amyotrophic lateral sclerosis and theories of its origins.

Amyotrophic lateral sclerosis (ALS) pathology: a) Spontaneous death of motor neurons in brainstem and spinal cord b) Progressive muscle wasting and paralysis c) Usually fatal within 2-4 years of diagnosis

Theories of ALS origins: a) Premature aging b) Neurotoxins c) Viruses d) Immune responses e) Endocrine dysfunction

Genetic factors: a) 10% of cases are hereditary b) SOD1 gene mutation in 20% of heritable cases

SOD1 mutation research: a) Transgenic mice studies suggest toxic gain of function b) Abnormal SOD1 protein may affect astrocytes, microglia, or muscle targets

Trace the pathways of the pyramidal motor system from cortex to spinal cord.

Pyramidal motor system pathway: a) Originates from neuronal cell bodies in cerebral cortex b) Axons pass through brainstem, forming pyramidal tract c) Crosses midline (decussates) at medulla d) Descends in lateral corticospinal tract of spinal cord

Hemispheric control: a) Right hemisphere controls left side of body b) Left hemisphere controls right side of body

Primary motor cortex (M1) involvement: a) Many axons originate from M1 b) Some monosynaptic connections with spinal motor neurons in primates c) Mostly polysynaptic routes to influence spinal motor neurons

What are the key characteristics of the Primary Motor Cortex (M1)?

Located in precentral gyrus, anterior to central sulcus; Executive motor control mechanism; Damage causes partial contralateral paralysis, especially in distal muscles; Organized with large regions for complex movements (e.g., hands); Neurons encode both muscles and movements; Involved in motor learning and skill acquisition; Shows plasticity in response to training and experience

What are the main features of the Nonprimary Motor Cortex?

Located anterior to M1; Includes Supplementary Motor Area (SMA) and Premotor Cortex; Can contribute to behavior directly and indirectly through M1; Involved in higher-level motor planning and organization

Contrast the types of motor activity influenced by the supplementary motor cortex versus premotor cortex.

Supplementary Motor Area (SMA): a) Located mainly on medial aspect of hemisphere b) Important for planning internally generated movements c) Bilateral damage results in inability to move voluntarily d) Crucial for planning movement sequences

Premotor Cortex: a) Located anterior to primary motor cortex on lateral surface b) Directs movement in response to external cues c) Activated when motor sequences are guided externally by stimuli d) Composed of multiple subareas serving different functions e) Involved in categories of behaviors like defensive movements and feeding

Where are mirror neurons found?

a) Found in premotor cortex (area F5) and other frontal and parietal areas

When do mirror neurons fire?

b) Fire when performing a specific action and when observing the same action

Who possesses mirror neurons?

c) Present in monkeys, adult humans, and children

What are the potential functions of mirror neurons?

a) Understanding others' actions b) Facilitating imitation c) Enabling cooperative tasks d) Providing a neural basis for empathy

How are mirror neurons potentially related to autism?

a) Reduced activation in mirror neuron regions during imitation tasks b) Underactivation when mimicking emotional facial expressions c) May contribute to difficulties in understanding others' thoughts and actions d) Could explain social and language challenges in autism

Describe the two major extrapyramidal pathways to the spinal cord.

Reticulospinal tract: a) Originates in the reticular formation of the brainstem b) Sends axons down the spinal cord c) Synapses on spinal interneurons

Rubrospinal tract: a) Originates from the midbrain's red nucleus b) Sends axons down the spinal cord c) Synapses on spinal interneurons

What are the components of the basal ganglia?

Caudate nucleus, putamen, globus pallidus, substantia nigra, and subthalamic nucleus

What is the function of the basal ganglia in motor behavior?

Determines amplitude and direction of movement, involved in movement initiation, important for learned motor skills, works with motor cortex to initiate and terminate movements

How does the basal ganglia interact with the cortex in motor behavior?

Forms a loop from cortex through basal ganglia and thalamus back to cortex, activity correlates more strongly with primary motor cortex (M1)

What are the key roles of the cerebellum in motor behavior?

Elaborates neural 'programs' for skilled movements, crucial for motor and non-motor learning, monitors ongoing activity to produce smooth movements, important for coordination and ongoing motor control

What sensory inputs does the cerebellum receive?

Sensory inputs and motor system inputs

How does the activity of the cerebellum correlate with motor behavior?

Activity correlates with supplementary motor area (SMA)

How does the size of the cerebellum vary across species?

Size varies based on movement complexity

What are the three major components of the cerebellar cortex?

Spinocerebellum (including vermis), Cerebrocerebellum (lateral portions), Vestibulocerebellum (nodule and flocculus)

What are the functions of the Spinocerebellum (including vermis)?

Receives sensory information about body position, Anticipates subsequent movement, Modulates descending motor pathways

What are the results of damage to the Spinocerebellum?

Abnormalities of gait and posture, Ataxia (loss of coordination) of the legs

What are the functions of the Cerebrocerebellum (lateral portions)?

Involved in planning complex movements, Functions in higher-level cognition and motor learning

What are the results of damage to the Cerebrocerebellum?

Diverse motor problems, Decomposition of movement (broken up gestures), Cognitive deficits

What are the functions of the Vestibulocerebellum (nodule and flocculus)?

Connected to vestibular nuclei, Receives information about body orientation, Helps maintain posture and guide eye movements

What are the results of damage to the Vestibulocerebellum?

Errors in gaze, Difficulty tracking visual objects as the head moves

What is plegia?

Paralysis (complete loss of voluntary movement)

What is paresis?

Weakness (partial loss of voluntary movement)

What is spasticity?

Increased rigidity in response to forced movement of the limbs

What is apraxia?

Inability to carry out complex movements despite intact language comprehension, motivation, and absence of paralysis or weakness

What are the common symptoms of Parkinson's disease?

Slow movement (bradykinesia), Resting tremors of hands and face, Rigid bearing when walking, Loss of facial muscle tone (masklike appearance), Difficulty with routine motor tasks, Non-motor symptoms: sleep disorders, depression, cognitive decline

What is the underlying brain cause of Parkinson's disease?

Progressive degeneration of dopamine-containing cells in the substantia nigra, Loss of dopaminergic projections to the basal ganglia (caudate nucleus and putamen), Formation of Lewy bodies (abnormal protein aggregates) in affected brain regions

What are the common treatment approaches for Parkinson's disease?

L-dopa administration: Enhances dopamine levels in surviving cells, Deep brain stimulation (DBS): Electrical stimulation of basal ganglia sites, Experimental treatments: a) Fetal neuron or stem cell transplantation b) Cell sorting and growth factor infusion to improve transplant success

What is the genetic cause of Huntington's disease?

Single dominant gene (HTT) on chromosome 4; Abnormal lengthening of the huntingtin protein due to CAG trinucleotide repeats; 35 or more CAG repeats lead to disease development

What are the symptoms of Huntington's disease in the early stages?

Subtle behavior changes; Clumsiness; Twitches in fingers and face

What are the symptoms of Huntington's disease in the progressive stages?

Involuntary jerks throughout the body; Aimless eye movements; Jerky leg movements; Writhing of the body

What are the symptoms of Huntington's disease in the advanced stages?

Intellectual deterioration; Depression; Psychotic state (in some patients)

What is the outlook for Huntington's disease?

Disease usually develops over 15-20 years; Progressive destruction of basal ganglia, especially caudate nucleus and putamen; No cure currently available; Potential treatments being explored: Antisense oligonucleotides (ASOs) to target abnormal huntingtin mRNA, Drugs targeting abnormal huntingtin protein