Control of Body Movement: Integrative Physiology I (Study Guide)

Control of Body Movement

Overview

This study guide covers the neural and physiological mechanisms underlying the control of body movement, focusing on the integration of sensory input, motor output, and reflexes. It is designed to help students understand the organization and function of neural circuits involved in voluntary and involuntary movements.

Neurons Involved in Movement

Types of Neurons

Neurons are specialized cells that transmit information throughout the nervous system. In the context of body movement, three main types of neurons are involved:

Neuron Type	Location	Function
Afferent Neurons	Peripheral nervous system (PNS), sensory organs	Transmit sensory information from receptors to the central nervous system (CNS)
Interneurons	CNS (brain and spinal cord)	Integrate information between afferent and efferent neurons; process and relay signals
Efferent Neurons	CNS to muscles/glands	Transmit motor commands from CNS to effectors (muscles or glands)

Voluntary vs. Involuntary Movements

Comparison and Integration

• Voluntary Movements: Initiated consciously by the brain, often involving planning and coordination (e.g., walking, writing).

• Involuntary Movements: Occur without conscious control, often as reflexes or automatic responses (e.g., knee-jerk reflex, heartbeat).

• Integration: Many movements are a combination of both, such as maintaining posture while walking.

Example: Catching a ball involves voluntary movement (reaching out) and involuntary reflexes (adjusting grip strength).

Somatic Muscle Movement: Neural Pathways

Development and Action

• Afferent Information: Sensory input from receptors (e.g., muscle spindles, skin) is sent to the CNS.

• Integration: Interneurons in the CNS process sensory information and determine the appropriate response.

• Efferent Information: Motor commands are sent via efferent neurons to skeletal muscles, resulting in movement.

• Action: The muscle contracts or relaxes to produce the desired movement.

Autonomic vs. Somatic Reflexes

Comparison

• Somatic Reflexes: Involve skeletal muscles; usually conscious or voluntary (e.g., withdrawal reflex).

• Autonomic Reflexes: Involve smooth muscle, cardiac muscle, or glands; involuntary (e.g., heart rate regulation).

Example: The pupillary light reflex is autonomic, while the patellar reflex is somatic.

Types of Reflexes

Definitions

• Visceral Reflex: Controls internal organs (e.g., baroreceptor reflex).

• Spinal Reflex: Mediated by the spinal cord without brain involvement (e.g., stretch reflex).

• Cranial Reflex: Mediated by the brain (e.g., blinking).

• Polysynaptic Reflex: Involves multiple synapses and interneurons.

• Monosynaptic Reflex: Involves a single synapse between sensory and motor neuron (e.g., patellar reflex).

• Ipsilateral Reflex: Response occurs on the same side as the stimulus.

• Contralateral Reflex: Response occurs on the opposite side of the stimulus.

• Bilateral Reflex: Both sides of the body respond.

• Postural Reflex: Maintains body posture and balance.

Somatic Neuromuscular Junction

Stimulation and Inhibition

• Stimulation at the neuromuscular junction is always excitatory, leading to muscle contraction.

• Inhibition of somatic reflexes occurs at the level of the CNS, not at the neuromuscular junction itself.

Example: Inhibitory interneurons in the spinal cord can prevent motor neuron activation, thus inhibiting movement.

Proprioceptors and Receptors

Types and Functions

Receptor	Location	Function
Proprioceptor	Muscles, tendons, joints	Sense body position and movement
Stretch receptor	Muscle spindle	Detects muscle stretch
Tension receptor	Golgi tendon organ	Detects muscle tension
Joint receptor	Joint capsules	Detects joint position and movement

Skeletal Muscle Stretch Reflex

Components

Component	Location	Function
Muscle spindle	Within skeletal muscle	Senses muscle stretch
Alpha motor neuron	Spinal cord to muscle	Stimulates extrafusal muscle fibers to contract
Gamma motor neuron	Spinal cord to muscle spindle	Adjusts sensitivity of muscle spindle
Extrafusal fiber	Main muscle mass	Contracts to produce movement
Intrafusal fiber	Inside muscle spindle	Detects changes in muscle length

Muscle Spindle Stretch Reflex Steps

1. Muscle is stretched, activating the muscle spindle (stretch receptor).

2. Sensory (afferent) neuron sends signal to spinal cord.

3. Motor (efferent) neuron is activated, causing muscle contraction.

4. Alpha-gamma coactivation ensures both extrafusal and intrafusal fibers contract, maintaining spindle sensitivity.

Alpha-Gamma Coactivation

• Alpha motor neurons stimulate extrafusal fibers (main muscle fibers).

• Gamma motor neurons stimulate intrafusal fibers (within muscle spindle).

• Coactivation is necessary to maintain spindle sensitivity during muscle contraction.

Muscle-Spindle vs. Golgi Tendon Organ Reflex

• Muscle-Spindle Reflex: Responds to muscle stretch; causes contraction to resist stretch.

• Golgi Tendon Organ Reflex: Responds to muscle tension; causes relaxation to prevent damage.

Classification of Reflexes

Key Reflex Types

• Agonist muscle: Main muscle responsible for movement.

• Antagonist muscle: Muscle that opposes the action of the agonist.

• Stretch (myotatic) reflex: Maintains muscle length.

• Withdrawal (flexor) reflex: Removes body part from harmful stimulus.

• Crossed extensor reflex: Supports body during withdrawal reflex.

• Reciprocal inhibition: Inhibition of antagonist muscles during movement.

Voluntary Movement: Neural Control

Phases and CNS Involvement

Phase	Function	CNS Structures Involved
Planning the movement	Sensory info, appropriate movements, movement refinement	Cerebral cortex, basal ganglia, cerebellum
Initiating the movement	Initiation of movement, refinement	Motor cortex, basal ganglia
Executing the movement	Modification and execution of movement	Motor cortex, spinal cord

Key Elements in Voluntary Movement

• CNS Integration: Coordination between different brain regions.

• Muscle memory: Learned patterns stored in the CNS.

• Sensory input: Feedback from proprioceptors and other receptors.

• Central pattern generators: Neural circuits that produce rhythmic movements (e.g., walking).

• Feedforward reflexes: Anticipatory adjustments before movement.

• Movement coordination: Integration of multiple muscle groups for smooth action.

Additional info: Some explanations and table entries were expanded for clarity and completeness based on standard Anatomy & Physiology content.