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NEU_LEC_11__12

Motor System I

Neuromuscular Junction

  • Components:

    • Presynaptic terminal

    • Calcium channel

    • Synaptic bulb

    • Cytoplasm

    • Synaptic vesicle

    • Ligand-gated channel

Processes at the Neuromuscular Junction

  • Nerve Impulse:

    • When initiated, neurotransmitters (e.g., Acetylcholine) are released.

    • Ligand-gated channels open based on neurotransmitter binding.

    • Generation of postsynaptic potentials, leading to muscle contraction.

Page 2: Course Concepts

  • Focus Areas:

    • Concepts & terminology

    • Types of movements

    • Muscle contraction

    • Proprioception

    • Motor cortex

Overview of Sensory Information Processing

Sensory Pathways

  • Ascending Tracts:

    • Dorsal Column;

    • Spinothalamic Pathway

Processing Centers

  • Touch: Processed by the primary somatosensory cortex.

  • Pain: Processed by the primary somatosensory cortex and cingulate gyrus.

Coordination of Movement

  • Communication between sensory and primary motor cortex via neurons.

  • Commands dispatched from motor cortex to spinal cord for muscle activation.

Motor Neurons

Definition & Function

  • Specialization: Carry commands from brain to muscles via spinal cord.

  • Neurotransmitter Role: Acetylcholine release leads to muscle contraction at the neuromuscular junction.

Motor Units

Structure

  • Composition: Connection between axon branches of a motor neuron and all muscle fibers it serves.

Neuromuscular Junction Functionality

Key Events

  • Motor neurons synapse with muscle fibers, leading to contraction upon Acetylcholine release.

Muscle Contraction Mechanics

Activation Process

  1. Nerve impulse reaches neuromuscular junction: release of Acetylcholine (ACh).

  2. ACh binds to muscle fiber receptors causing contraction.

  3. Voltage-gated Ca2+ channels facilitate ACh release through exocytosis.

  4. ACh diffuses across synaptic cleft and binds to its receptors on the sarcolemma.

Reflex Action Overview

Basic Attributes

  • Characteristics: Fast, automatic responses to stimuli, processed in the spinal cord.

  • Includes:

    • Sensory information conveyed to spinal cord.

    • Command returned via motor neurons to provoke muscle response.

Example Reflex Pathway

  1. Pain receptors activated (hot object).

  2. Signal transmitted via afferent and interneurons to motor neuron.

  3. Output results in muscle contraction.

Types of Reflexes

  • Examples:

    • Pupillary reflex in response to light

    • Withdrawal reflex

    • Knee-jerk reflex

Behavioral Changes via Muscle Movement

Categories

  1. Reflexes: Involuntary responses.

  2. Movements: Simple muscle contractions for relocation of body parts.

  3. Acts: Complex sequences requiring a motor plan (e.g., walking).

Motor Plans

Importance

  • Motor plans essential for executing acts; involves pre-established sequences of muscle contractions.

Muscle Coordination

Anatomy

  • Skeletal muscles operate through antagonistic and synergistic relationships.

    • Antagonists: One contracts while the other relaxes (e.g., biceps and triceps).

    • Synergists: Assist primary movers during actions.

Muscle Contraction Mechanism

Cellular Interaction

  • Muscle fibers have actin (thin) and myosin (thick) filaments.

  • Role of Calcium ions: Triggers sliding motion of filaments leading to contraction.

Proprioception Overview

Functionality

  • Monitors body movement and position via specialized receptor cells.

Types of Proprioceptors

  1. Muscle Spindle: Detects stretching and signals muscle contraction.

  2. Golgi Tendon Organ: Inhibits contraction if muscle is excessively stretched, protecting from damage.

Motor Cortex

Structure and Function

  • Location: Frontal lobe, comprising primary motor cortex, supplementary, and premotor cortex.

  • Generates commands and modulates muscle movements based on incoming information.

Pathways for Motor Commands

Classification

  1. Pyramidal System: Controls fine movements; primarily from the primary motor cortex.

  2. Extrapyramidal System: Manages gross motor functions, originating from nonprimary motor regions.

Movement Disorders

Examples

  • Parkinson's Disease:

    • Symptoms: Rigidity, tremors, slow movements; affects dopaminergic pathways.

  • Huntington’s Disease:

    • Symptoms: Hyperkinetic movements, cognitive deficits; involves basal ganglia damage.

Treatment Options for PD

  1. Pharmacological: L-DOPA increases dopamine levels.

  2. Surgical: Deep brain stimulation can alleviate symptoms.

  3. Future therapies: Stem cells aim to replace lost neurons.