Anatomy Quiz: Spinal Cord and Nerves

Chapter 13: The Spinal Cord and Spinal Nerves

• This chapter identifies and describes the 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 in the body.
• It also explains spinal reflex arcs.
• The spinal cord processes reflexes, integrates EPSPs and IPSPs, and conducts sensory impulses to the brain and motor impulses to effectors.

Spinal Cord Anatomy

• The spinal cord is protected by bone (vertebrae), connective tissue (meninges), and fluid (cerebrospinal fluid).
• The meninges consist of three layers: dura mater, arachnoid mater, and pia mater.

External Spinal Cord Anatomy

• The spinal cord begins as an extension of the medulla oblongata at the foramen magnum and ends at the level of L2.
• The spinal cord has two enlargements: cervical (C4-T1) and lumbar (between L1 and L4).
• The cervical enlargement controls sensory input and motor output to the upper extremities, while the lumbar enlargement handles these functions for the legs.
• Two bundles of axons called roots connect each spinal nerve to a segment of the cord. Posterior roots contain sensory axons, and anterior roots contain motor axons.
• The cauda equina are the roots of the lower spinal nerves that angle downwards alongside the filum terminale.

Internal Spinal Cord Anatomy

• In the spinal cord, white matter is on the outside and gray matter is on the inside.
• Structures include the posterior/anterior gray horns, gray commissure, anterior/posterior white commissure, anterior/posterior white funiculi and central canal.

Sensory and Motor Processing

• The spinal cord's internal anatomy allows for the organized processing of sensory and motor information.
• Spinal nerves connect the CNS to sensory receptors, muscles, and glands.

Spinal Cord Segments (Table 13.1)

• Cervical segments are relatively large in diameter, with a large oval shape and relatively large amounts of white matter, and small lateral gray horns in lower segments,.
• Thoracic segments have a small diameter, with relatively small amounts of gray matter, except for C1-C4.
• Lumbar segments are nearly circular, with very large anterior and posterior gray horns and small lateral gray horns.
• Sacral segments are relatively small with relatively large amounts of gray matter. Anterior and posterior gray horns are large and thick.
• Coccygeal are similar to lower sacral segments but are smaller.

Spinal Nerves

• Spinal nerves connect the central nervous system to sensory receptors, muscles, and glands of the peripheral nervous system.
• 31 pairs of spinal nerves.
• Anterior and posterior roots connect spinal nerves to a segment of the spinal cord.

Connective Tissue of Spinal Nerves

• Spinal nerves have layers of connective tissue coverings.
• The outermost layer is the epineurium
• The perineurium surrounds nerve fascicles
• The endoneurium surrounds individual nerve fibers (axons).

Peripheral Nerves

• Spinal nerves exit the spinal column at intervertebral foramina, and branch into anterior and posterior rami.
• Rami communicantes connect spinal nerves to sympathetic ganglia.

Peripheral Nerve Plexuses

• Nerve plexuses are formed from anterior rami of spinal nerves.
• Major plexuses in the body include cervical, brachial, lumbar, sacral, and coccygeal plexuses.

Branches of a Spinal Nerve

• Shortly after exiting, spinal nerves branch into anterior and posterior rami and rami communicantes.

Dermatomes

• Specific skin segments are supplied by spinal nerves; these regions are called dermatomes.

Cervical Plexus

• Supplies skin and muscles of the head, neck, superior shoulders and upper chest; and diaphragm.
• Phrenic nerve supplies diaphragm.

Brachial Plexus

• Provides nerve supply for shoulders and upper limbs, including the median nerve (important for carpal tunnel syndrome).
• Lesions of the median nerve can cause carpal tunnel syndrome.

Nerve Plexuses (Long Thoracic Nerve)

• The long thoracic nerve emerges from the brachial plexus to supply the serratus anterior muscle.
• This nerve is susceptible to injury, which can result in "winged scapula."

Nerve Plexuses (Injury)

• Erb's palsy and similar injuries can occur from birth canal trauma.
• The ulnar nerve is large and unprotected, and damage can affect the 4th and 5th fingers, impairing abduction and adduction.

Median Nerve Injury & Carpal Tunnel Syndrome

• Median nerve injury, either at the plexus or elsewhere, can cause numbness, tingling, and pain in the palm and fingers, often associated with typing and hand motions.
• Carpal tunnel syndrome is a specific kind of median nerve injury.

Lumbar Plexus

• Lumbar plexus supplies motor and sensory innervation to the hip, thigh, and lower leg.
• Major nerves include the femoral and obturator nerves.

Sacral Plexus

• Sacral plexus lies inferior to the lumbar plexus and supplies the posterior hip, thigh and lower leg.
• The sciatic nerve, the largest nerve in the body, is a major nerve of the sacral plexus.

Spinal Cord Physiology

• Spinal cord pathways conduct nerve impulses to and from the brain.
• Gray matter integrates incoming and outgoing information to perform spinal reflexes.

Sensory and Motor Tracts

• Specific tracts within the spinal cord carry sensory information (ascending tracts) and motor commands (descending tracts).

Reflexes and Reflex Arcs

• Reflexes are rapid, involuntary responses to stimuli, crucial for homeostasis.
• Gray matter in the spinal cord acts as the integrating center for spinal reflexes.

Reflex Arcs: Components

• Sensory receptors, sensory neurons, integrating centers (in the spinal cord), motor neurons, and effectors (muscles or glands) are components of a reflex arc.

Types of Reflex Arcs

• Monosynaptic: Simplest reflex arc with one synapse. One example is the stretch reflex.
• Polysynaptic: More complex with multiple synapses. Some examples are the flexor reflex, crossed-extensor reflex and the tendon reflexes.

Stretch Reflex

• Causes muscle contraction in response to stretching.

Tendon Reflex

• Causes muscle relaxation in response to tension on the tendon.

Flexor (Withdrawal) Reflex

• Causes withdrawal of a limb from a painful stimulus.

Crossed-Extensor Reflex

• Maintains balance during a withdrawal reflex.

Important Spinal Reflexes

• Patellar reflex: Leg extension in response to patellar tendon stretch.
• Achilles reflex: Calf muscle contraction in response to Achilles tendon stretch.
• Babinski reflex: Normal in infants; abnormal in adults indicates corticospinal tract damage.

Spinal Cord Disorders

• Traumatic injuries (monoplegia, paraplegia, hemiplegia, quadriplegia) o Degree of injury (spinal cord section or compression) and location effect the outcome of damage
• Spinal cord compression: compression from bone, blood, abscess, tumor or ruptured disk.
• Degenerative diseases (ALS - Lou Gehrig's disease)
• Shingles: infection of peripheral nerves by herpes zoster virus (causing chicken pox).
• Poliomyelitis (Polio): viral infection causing paralysis.

Test your knowledge on the anatomy and functions of the spinal cord and spinal nerves. This quiz covers key components such as nerve pairs, meninges layers, and the role of various nerves. Perfect for students studying human anatomy or preparing for exams.