Spinal Cord Anatomy and Functions Quiz

Introduction to Chapter 13

• The chapter aims to identify and describe anatomical features of the spinal cord and spinal nerves.
• It discusses the functions of the spinal cord and spinal nerves and how they maintain homeostasis.
• It explains spinal reflex arcs.

Functions of the Spinal Cord

• Processes reflexes.
• Integrates EPSPs and IPSPs.
• Conducts sensory impulses to the brain and motor impulses to effectors.

Spinal Cord Anatomy

• Protected by bone (vertebrae).
• Protected by connective tissue (meninges).
• Protected by fluid (cerebrospinal fluid).

Meninges

• Composed of three layers: dura mater, arachnoid mater, and pia mater.

External Spinal Cord Anatomy

• The spinal cord begins at the foramen magnum and ends at the level of L2.
• The spinal cord has two enlargements: cervical and lumbar.
• The cervical enlargement correlates with sensory input and motor output to the upper extremities.
• The lumbar enlargement handles motor output and sensory input to and from the legs.

Spinal Cord Internal Anatomy

• White matter is on the outside of the spinal cord.
• Gray matter is on the inside of the spinal cord.
• In the brain, the white matter is on the inside, and the gray matter on the outside.

Sensory and Motor Processing

• The internal spinal cord anatomy allows sensory and motor information to be processed.

Comparison of Spinal Cord Segments

• Cervical segments have relatively large diameters and significant white matter.
• Thoracic segments have smaller diameters and less gray matter.
• Lumbar segments are nearly circular with large anterior and posterior gray horns and less white matter.
• Sacral segments are relatively small but have large amounts of gray matter.
• Coccygeal segments are much smaller.

External Cord Anatomy: Roots and Rootlets

• Two bundles of axons called roots connect each spinal nerve to a segment of the cord.
• The smaller bundles are called rootlets.
• Posterior (dorsal) roots and rootlets contain sensory axons that transmit nerve impulses from sensory receptors to the central nervous system.

External Cord Anatomy: Ganglion

• The posterior (dorsal) root has a swelling called the posterior (dorsal) root ganglion.
• Sensory neurons' cell bodies are located within the posterior (dorsal) root ganglion.
• The anterior (ventral) root and rootlets contain motor neurons' axons that transmit nerve impulses from the CNS to effectors (muscles and glands).

Epidural Anesthesia

• Commonly given to women in labor.
• A needle is placed between the bones of the posterior spine to the ligamentum flavum.
• The needle remains superficial to the dura mater.
• Local anesthetic is used to provide pain relief during a Cesarean section.

Lumbar Puncture

• A needle inserted into the subarachnoid space for withdrawing CSF or for introducing a drug or contrast agent.
• CSF is collected to diagnose meningitis or other CNS diseases.
• Agents such as antibiotics, chemotherapeutic agents, analgesics, or contrast media for radiographic procedures are injected.
• CSF pressure in the subarachnoid space (SAS) can be measured.

Spinal Nerves

• Spinal nerves connect the central nervous system (CNS) to sensory receptors, muscles, and glands.
• There are 31 pairs of spinal nerves.
• Anterior and posterior roots attach a spinal nerve to a segment of the spinal cord.
• Spinal nerves have connective tissue coverings: epineurium, perineurium, and endoneurium.

Peripheral Nerves

• Spinal nerves are arranged in fascicles surrounded by perineurium, with the entire nerve sheathed by epineurium.

Peripheral Nerves: Emergence and Branches

• 31 pairs of spinal nerves emerge from the cord at regular intervals (segments).
• Spinal nerves exit the vertebral column from the intervertebral foramina.
• Spinal nerves split into branches: anterior ramus, posterior ramus, and rami communicantes (connections to sympathetic ganglia).

Peripheral Nerves: Plexuses

• Anterior rami of spinal nerves form large plexuses (e.g., cervical, brachial, celiac, lumbar, sacral, coccygeal).
• The anterior rami either travel alone (intercostal nerves) or join to form plexuses.

Branches of Spinal Nerves

• Shortly after passing through the intervertebral foramen, a spinal nerve divides into several branches known as rami.
• Rami supply muscles of the back.

Dermatomes

• Certain segments of the skin are supplied by spinal nerves.
• Dermatomes are areas of skin innervated by specific spinal nerves.

Cervical Plexus

• Supplies skin and muscles of the head, neck, superior part of shoulders, chest, and diaphragm.
• The Phrenic nerve is a primary component, supplying the diaphragm.

Brachial Plexus

• Supplies nerves to the shoulders and upper limbs.
• A lesion of the median nerve can result in carpal tunnel syndrome.

Nerve Plexuses: Long Thoracic Nerve

• Emerges from the brachial plexus to supply the serratus anterior muscle.
• The long thoracic nerve is susceptible to injury due to its long, relatively superficial course.
• An injury to this nerve can cause a "winged scapula."

Nerve Plexuses: Brachial Plexus Injuries

• Erb's palsy is a paralysis of the arm that occurs in infants when the head and neck are pulled to one side during childbirth.
• A similar injury can occur in adults from traumatic falls.
• Injuries to the brachial plexus or peripheral nerves can affect the median nerve, leading to numbness, tingling, and pain in the hand and fingers.

Nerve Plexuses: Ulnar Nerve

• The ulnar nerve is a major nerve in the brachial plexus, emerging from the medial and lateral cords.
• It supplies the medial half of the hand.
• Striking the medial epicondyle of the humerus (the “funny bone”) can damage the ulnar nerve.
• Damage results in abnormal sensations and the inability to abduct or adduct the little and ring fingers.

Lumbar Plexus

• Supplies nerves to the lower abdominal walls, anterior thigh muscles, and medial thigh skin.
• The femoral nerve and obturator nerve are key components of the lumbar plexus.

Sacral Plexus

• Supplies nerves to the buttocks, most of the posterior thigh, and the posterior leg and foot.
•  The primary nerve is the sciatic nerve.

Spinal Cord Physiology

• The spinal cord maintains homeostasis through the propagation of nerve impulses and the integration of information.
• White matter tracts conduct nerve impulses to and from the brain.
• Gray matter receives and integrates incoming and outgoing information to perform spinal reflexes.

Sensory and Motor Tracts (review)

• Sensory and motor tracts are essential pathways for information transmission within the spinal cord.

Reflexes and Reflex Arcs

• A reflex is a fast, involuntary, unplanned response to a stimulus.
• Reflexes are vital for maintaining homeostasis.
• The spinal cord's gray matter serves as the integrating center for spinal reflexes.

General Components of a Reflex Arc

• A reflex arc is composed of sensory receptors, sensory neurons, interneurons, motor neurons, and effectors.

Reflex Arcs: Vocabulary Terms

• Ipsilateral refers to the same side of the body.
• Contralateral refers to the opposite side of the body.
• Monosynaptic refers to reflex arcs with only one synapse.
• Polysynaptic refers to reflex arcs with more than one synapse.
• Reciprocal innervation describes neural circuits simultaneously contracting one muscle and relaxing its antagonist.

Stretch Reflex

• Causes contraction of a muscle that has been stretched.
• Sensory neurons respond to muscle-spindle stretches.
• Motor neurons to the same muscle cause contraction.

Tendon Reflex

• Causes relaxation of the muscle attached to the stimulated tendon.
• Sensory neurons respond to tendon stretches.
• Motor neurons to the antagonist muscles are stimulated, leading to relaxation of the stretched muscle.

Flexor (Withdrawal) Reflex

• Causes withdrawal of a limb to avoid injury or pain.
• Sensory neurons respond to harmful stimuli.
• Motor neurons to flexor muscles are excited, while those to extensors are inhibited.

Crossed-Extensor Reflex

• Maintains balance during a withdrawal reflex by extending the opposite limb.
• Sensory pathway transmits information of the pain stimulus to the spinal cord.

Reflexes: Important Spinal Reflexes

• Patellar reflex: leg extends when patellar tendon is stretched.
• Achilles reflex: calf contracts when Achilles tendon is stretched.
• Babinski reflex: Normal in infants; abnormal extension indicate CNS damage.

Disorders of the Spinal Cord

• Traumatic injuries (monoplegia, paraplegia, hemiplegia, quadriplegia).
• Damage depends on the severity and location of spinal cord section or segment compression.
• Spinal cord compression is a disorder of the spinal cord caused by various issues.
• Degenerative diseases, like multiple sclerosis and amyotrophic lateral sclerosis (ALS), cause damage to the spinal cord.
• Shingles is an acute infection characterized by the herpes zoster virus affecting the PNS

Test your knowledge on the anatomy and functions of the spinal cord with this quiz. Explore key structures, their roles, and how cervical and thoracic nerves contribute to the body's motor and sensory functions. Perfect for students studying anatomy or related fields!