Lecture Notes: Spinal Cord Anatomy and Physiology

Key Topics

• Anatomical features of the spinal cord
• Functions related to homeostasis and spinal reflexes
• Protection of the spinal cord
• Internal anatomy of the spinal cord
• Physiology of the spinal cord
• Reflexes and reflex arcs

Spinal Cord Anatomy

Anatomical Features

• The spinal cord starts at the medulla oblongata, exiting the foramen magnum.
• Ends at L2 level of the lumbar vertebrae.
• Structures include cervical and lumbar enlargements.
  • Cervical enlargement near the cervical region.
  • Lumbar enlargement near the lumbar region.

Protection

• Vertebrae: Spinal cord travels down the vertebral column.
• Meninges: Three connective tissue layers protect the spinal cord:
  • Dura mater (outermost)
  • Arachnoid mater
  • Pia mater (innermost)
• Cerebrospinal Fluid (CSF): Flows in the subarachnoid space, providing nutrients and waste removal.

Functions of the Spinal Cord

• Conducts sensory impulses to the brain and motor impulses to effectors.
• Integrates EPSPs and IPSPs (from Chapter 12).
• Maintains homeostasis through reflex processing.

Internal Anatomy of the Spinal Cord

• 31 pairs of spinal nerves attach to the spinal cord at different levels.
• White Matter: Conducts information to and from the brain.
  • Divided into columns: posterior, lateral, and anterior.
• Gray Matter: Processes sensory and motor information.
  • Divided into horns: posterior, lateral, and anterior.
• Motor Neurons:
  • Autonomic system: cell bodies in lateral gray horn.
  • Somatic system: cell bodies in anterior gray horn.

Spinal Reflexes

• Definition: Fast, involuntary, unplanned responses to stimuli.
• Reflex Arc Components:
  1. Sensory receptor
  2. Sensory neuron
  3. Integration center (interneurons)
  4. Motor neuron
  5. Effector (muscle or gland)
• Types of Reflexes:
  • Somatic Reflex: Involves skeletal muscle contraction.
  • Autonomic Reflex: Involves involuntary effectors (to be covered in Chapter 15).

Protection of the Spinal Cord

• Denticulate Ligaments: Anchor the spinal cord within the meninges.
• Connective Tissue Layers:
  • Epineurium: Outermost covering.
  • Perineurium: Surrounds fascicles within nerves.
  • Endoneurium: Wraps individual axons within fascicles.

Plexuses of the Body

• Cervical Plexus: C1-C5, includes phrenic nerve affecting diaphragm.
• Brachial Plexus: C5-T1, supplies shoulder and arm, includes median, radial, ulnar nerves.
• Lumbar Plexus: L1-L4, supplies abdominal wall, external genitalia, anterior thigh.
• Sacral Plexus: L4-S4, includes sciatic nerve, supplies buttocks, perineum, lower limbs.

Reflex Types

• Stretch Reflex: Monosynaptic, ipsilateral (e.g., knee-jerk reflex).
• Tendon Reflex: Polysynaptic, involves reciprocal inhibition to prevent tendon damage.

Additional Topics

• Spinal Cord Injuries:
  • Monoplegia, Paraplegia, Hemiplegia, Quadriplegia: Varying degrees of limb paralysis.
  • Cauda Equina: Nerve roots extending from L2.

Review the animations and PowerPoint slides for detailed visuals and further understanding. Contact the instructor for any questions.