Motor Control and Reflexes Quiz

Consciousness

• State of consciousness: Level of arousal (awake, asleep, etc.)
• Measured by behavior and brain activity
• Conscious experience: Thoughts, feelings, desires, ideas, etc.
• This is the capacity to experience one's existence, rather than just reacting to stimuli like an automaton.
• A laptop, for example, would not be considered conscious.

The Electroencephalograph (EEG)

• Measures the activity of neurons near the scalp in the gray matter of the cortex.
• Voltage (typically 20-100 microvolts) is measured
• Frequency is related to responsiveness levels.
• Amplitude is linked to synchronous neural activity.
• EEG patterns change during different mental states and sleep stages

EEGs and Mental States

• Alpha rhythm: Observed when relaxed with eyes closed, has slow frequencies
• Beta rhythm: Seen when alert, has fast frequencies

Stages of Sleep

• Awake: Characterized by low amplitude, high frequency waves
• NREM (Non-Rapid Eye Movement) sleep: Slow-wave sleep, has progressively higher amplitude and lower frequency waves as sleep deepens, (stages 1-4). Specifically:
  • Stage 1: Transition to sleep.
  • Stage 2: Light sleep.
  • Stage 3: Deeper sleep.
  • Stage 4: Deepest sleep. (NREM Stages 3 & 4 are sometimes combined).
• REM (Rapid Eye Movement) sleep: Characterized by low amplitude, high frequency waves, associated with dreaming, temporary skeletal muscle inhibition, rapid eye movements

Physiological Changes During Sleep

• Reflects changes in brain activity at each sleep stage
• During REM sleep, there is an increase in eye movements, and inhibition of skeletal muscle. Also, heart rate and respiration rates increase.
• Sleep apnea is a sudden reduction in respiration.

States of Consciousness and Brain Regions

• Preoptic area of hypothalamus: Plays a critical role in regulating sleep.
• Suprachiasmatic nucleus (SCN) of the hypothalamus: Regulates the circadian rhythm.
• Reticular activating System: A critical neural network involved in regulating arousal and consciousness

Regulating States of Consciousness

• Aminergic neurons (Norepinephrine, serotonin) and cholinergic neurons (acetylcholine) are active in different states of consciousness.
• These neurons are influenced by the presence and level of certain neurochemicals
• Chemical factors are involved in the regulations of states of consciousness.
• The interplay between these chemicals results in specific states of consciousness.
• Histamine and GABA are two specific chemicals involved in regulating consciousness.

Motivation and Emotion

• Motivation: Produces goal-directed behavior.
• Emotions: Accompany our conscious experiences.

Mesolimbic Dopamine Pathway

• A key part of the brain's reward pathway.
• Dopamine is the primary neurotransmitter.

Self-Stimulation Experiments

• Continuous activation of reward-related areas of the brain.

Limbic System

• Involved in emotions
• Includes the olfactory bulb, hippocampus (memory) and amygdala

Altered States of Consciousness

• Schizophrenia: Diverse set of problems in basic cognitive processing, including delusions and hallucinations; affects about one out of every 100 people.
• Mood disorders:
  • Depression: Decreased activity in the anterior limbic system. Treatments increase serotonin and norepinephrine levels.
  • Bipolar disorder: Swings between mania and depression. Treatments include lithium, which reduces certain synaptic signaling pathways.

Learning and Memory

• Declarative memory: Conscious experiences put into words.
  • Short-term: Hippocampus and other temporary lobe structures.
  • Long-term: Many parts of the association cortex.
• Procedural memory: Skilled behavior.
  • Short-term: Widely distributed.
  • Long-term: Basal nuclei, cerebellum, premotor cortex.
• Sleep: Plays a role in consolidating short-term memories into long-term memories
• Hippocampus: Important structure in learning and memory

Inside the Brain

• H.M.: Amnesic patient who underwent medial temporal lobe removal affecting different brain areas.

Language

• Broca's area: Usually in the left hemisphere; articulation.
• Wernicke's area: Usually in the left hemisphere; comprehension.
• Aphasia: Language deficit

Parietal Damage

• Sensory neglect: A condition resulting from parietal lobe damage characterized by a reduction in awareness of one side of the body or one side of space.

When Things Go Wrong

• Descriptions of cases of brain damage, or brain diseases. Cases are often cited with the use of specific medical terminology.

Motor Behavior

• Purposeful or goal-directed: Voluntary and reflexive.

Muscle Control: Extension vs. Flexion

• Extension: Extensor muscle contracts, agonist, increases the angle
• Flexion: Flexor muscle contracts, agonist, decreases the angle
• Antagonistic muscles have opposing actions during movements

Reciprocal Innervation of Muscles

• Coordinated activation and relaxation of flexor and extensor muscles.
• Maintaining limb position is a balance of flexor and extensor muscle tension.

Motor Neurons

• Only excitatory (acetylcholine).
• Alpha: Innervate skeletal (extrafusal) muscle.
• Gamma: Innervate muscle spindle (intrafusal) muscle.
• Cell bodies located in the ventral horn of the spinal cord (spinal nerves).
• Receive input mainly from interneurons.

Spinal Afferent (Sensory) and Efferent (Motor) Pathways

• Sensory information travels up the spinal cord in the dorsal columns.
• Descending motor commands travel down the spinal cord.
• Interneurons also are located in different levels throughout the spinal cord.

Spinal Interneurons

• Receive inputs from different receptor types involved with movement and sensory information.
• Involved in complex movements
• Involved in length monitoring of muscles on both sides of the body
• Coordinating complex movements

Spinal Reflexes

• Withdrawal reflex: Protects limbs from injury.
• Stretch reflex: Controls muscle length (monosynaptic and polysynaptic).
• Inverse stretch reflex: Controls muscle tension.
• Reflexes can be modified, these reflexes can be overridden

Flexion Withdrawal Reflex

• Polysynaptic: Involves multiple interneurons.
• Involves inhibition of ipsilateral extensor, and excitation of ipsilateral flexor.
• Cross-extensor reflex: Involves inhibition of contralateral flexor, and excitation of contralateral extensor.

Magnitude of Withdrawal Reflex

• Depends on the magnitude of the pain stimulus.
• Recruitment of interneurons increases in response to greater stimuli
• Feedback loops in the spinal cord are involved in the response

Properties of Withdrawal Reflex

• Ipsilateral, contralateral, polysynaptic, irradiation, afterdischarge

Monosynaptic Stretch Reflex (Knee Jerk)

• Excitation of motor neuron innervating the ipsilateral extensor.
• Inhibition of motor neuron innervating the ipsilateral flexor.
• Activation and stretch receptor causes the reflex

Muscle Spindle and Golgi Tendon Organ

• Muscle spindle: Parallel to muscle fibers, reports muscle length, vital for the stretch reflex and muscle length control
• Golgi tendon organ: In series with muscle fibers, reports muscle tension, involved with the inverse stretch reflex and controlling muscle tension

Muscle Spindle Properties

• Reports muscle length.
• Afferents (la and II): Types of nerve fibers, La (primary) detects changes in muscle length, II (secondary) detects static length.
• In parallel with extrafusal muscle fibers.
• Intrafusal fibers: Maintain muscle spindle sensitivity.
• Alpha-gamma coactivation.

Response of la (primary) and II (secondary) Afferents

• la primary: Signals dynamic and some static changes in muscle length.
• II secondary: Signals static muscle length.

Muscle Spindles Can Lose Sensitivity

• Results with voluntary flexion and extension as muscles lengthen and shorten.
• Muscle spindle collapses leading to reduction in sensitivity.

Gamma Motor Neurons Maintain Muscle Spindle Sensitivity

• Alpha-gamma coactivation maintains sensitivity.
• Intrafusal fibers contract and muscle spindle is stretched.

Alpha-Gamma Coactivation

• Motor command, alpha and gamma motor neuron activation.
• Extra-fusal muscle activation and shortening is linked to maintaining spindle sensitivity.
• Change in length activates the muscle spindle

Properties of Stretch Reflex

• Resists changes in muscle length.
• Mono- and polysynaptic components.
• Feedback from muscle spindles.

Properties of Golgi Tendon Organ

• Reports muscle tension.
• In series with extrafusal muscle fibers.
• Ib afferents.
• Underlies inverse stretch reflex.

Motor Control Involves Many Brain Areas

• Corticospinal pathway: Skilled movements.
• Extrapyramidal pathway: Trunk and posture.
• Voluntary movements have an involuntary component.
• Multiple brain regions are involved with motor control
• Middle level: Executes individualized muscle contractions. Also makes corrections based on sensory information.
• Brain stem: Plays a critical role with muscle contraction, and control
• Cerebellum: Involved with timing, planning, error correction and learning new motor skills.
• Basal Nuclei: Determine the sequence of movements necessary for the execution of an action
• Higher Centers: Conscious initiation of movement

Direct Cortical Control of Movement

• Corticospinal and extrapyramidal pathways.
• Crossing of the pathways in the medulla.
• Involvement with alpha and gamma motor neurons.

Descending Motor Pathways

• Corticospinal: Originates in the primary motor cortex, compact and direct to spinal cord, controls contralateral muscles, predominately involved with hands and feet, and skilled voluntary movements
• Extrapyramidal: Originates from neurons in the brainstem, diffused and indirect via the brainstem, involved in trunk and postural muscles, controls upright posture, balance, and walking

Muscle Tone

• Resistance of skeletal muscles to stretch.
• Normal: Slight and uniform.
• Damage to descending pathways:
  • Hypertonia: Abnormally high muscle tone
  • Spasticity: Overactive motor reflexes
  • Rigidity: Constant muscle contraction.
• Damage to motor neurons:
  • Hypotonia: Abnormally low muscle tone
  • Atrophy: Loss of muscle mass
  • Decreased or missing reflexes

Basal Nuclei (Ganglia)

• Structure: A group of nuclei located deep within the brain.
• Function: Involved in regulating movement, muscle tone, and posture.

Basal Nuclei Movement Disorders

• Parkinson's disease: Reduced dopamine input to basal nuclei, resulting in akinesia, bradykinesia, muscular rigidity, and resting tremor.
• Huntington's disease: Widespread loss of neurons in the brain, especially in the basal nuclei, resulting in hyperkinetic disorders, like choreiform movements.

Deep Brain Stimulation

• A surgical treatment to help control movement disorders like Parkinson's disease through stimulating specific areas of the brain.