Lab_2.5_Reflex_Arcs

Chapter Overview

• Focus on the spinal cord and spinal nerves

• Integrate information from chapters 14.2 and 14.3 in the Anatomy & Physiology textbook by OpenStax.

Functions of the Spinal Cord

• Process Reflexes:

  • The spinal cord plays a critical role in generating quick reflex actions.

• Integrate EPSPs & IPSPs:

  • Integrates excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) for overall nervous system function.

• Conduct Sensory Impulses:

  • Transmits sensory impulses to the brain.

• Conduct Motor Impulses:

  • Sends motor impulses to effectors (muscles and glands).

Anatomy Review

• Spinal Nerves Overview:

  • Composed of 31 pairs of spinal nerves:

    • Cervical Nerves: 8 pairs

    • Thoracic Nerves: 12 pairs

    • Lumbar Nerves: 5 pairs

    • Sacral Nerves: 5 pairs

    • Coccygeal Nerve: 1 pair

• Plexuses:

  • Branching networks formed by the ventral (anterior) rami of spinal nerves.

Spinal Nerves & Plexuses

• Cervical Plexus:

  • Innervates skin and muscles of the head, neck, superior chest, shoulders, and diaphragm.

  • Phrenic nerve originates from C3, C4, and C5, innervating the diaphragm.

• Brachial Plexus:

  • Supplies almost the entire nerve supply to the shoulders and upper limbs.

• Lumbar Plexus:

  • Innervates the anterolateral abdominal wall, external genitalia, and part of the lower limbs.

• Sacral Plexus:

  • Innervates the buttocks, perineum, and lower limbs.

  • In particular, the sciatic nerve is prominent.

Internal Anatomy of the Spinal Cord

• Sensory & Motor Processing:

  • Allows sensory and motor information to be processed in an organized manner.

• Homeostasis Maintenance:

  • Essential for propagating nerve impulses and integrating information.

  • Includes:

    • White Matter Tracts: Conducts impulses to and from the brain.

    • Gray Matter: Receives and integrates incoming and outgoing information, playing a key role in spinal reflexes.

Reflexes & Reflex Arcs

• Definition of Reflex:

  • A reflex is a fast, predictable, automatic response to environmental changes.

• Types of Reflexes:

  • Somatic Reflexes: Effectors are skeletal muscle.

  • Autonomic Reflexes: Effectors are smooth and cardiac muscle, and glands.

• Integration Centers:

  • Spinal cord for spinal reflexes, brainstem for cranial reflexes.

Reflex Arc Vocabulary

• Ipsilateral Response:

  • Same side response.

• Contralateral Response:

  • Opposite side response.

• Monosynaptic Reflex:

  • One synapse between sensory and motor neuron.

• Polysynaptic Reflex:

  • More than one synapse between sensory and motor neuron.

• Reciprocal Innervation:

  • Opposing muscle groups respond oppositely to the effector’s response.

Specific Reflex Types

• Stretch Reflex:

  • Controls muscle length via contraction.

• Tendon Reflex:

  • Controls muscle tension via relaxation.

• Flexor (Withdrawal) Reflex:

  • Moves a limb to avoid injury or pain.

• Crossed-Extensor Reflex:

  • Maintains balance during withdrawal reflex.

Clinical Connection

• Reflex Diagnostics:

  • Reflexes help diagnose nervous system disorders and locate injured tissues.

  • Examples include:

    • Patellar Reflex (Knee Jerk)

    • Achilles Reflex (Ankle Jerk)

• Importance:

  • Abnormal or absent reflexes may indicate damage along specific reflex arcs.

Sex and Spinal Cord Injuries

• Erection Center:

  • Located between T10/L2 and S2-S4 for all genders.

• Psychogenic Pathway:

  • Messages travel from the brain via the spinal cord to genital nerves.

• Reflexogenic Pathway:

  • Activates parasympathetic nervous system responses due to touch sensation bypassing the brain.

• Reflex Erections:

  • Most paralyzed individuals can achieve reflex erections with physical stimulation, unless S2–S4 pathway is damaged.

• Pregnancy and Delivery:

  • Minimal difficulties in pregnancies post spinal cord injury, due to the regulation of birth by the endocrine system (like oxytocin).