Anatomy of the Spinal Cord and Nerves

Introduction

• The chapter aims to identify and describe 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.
• Students will learn about spinal reflex arcs.
• The purpose of the spinal cord is to process reflexes, integrate EPSPs and IPSPs, and conduct sensory and motor impulses.

Functions of the Spinal Cord

• Processing reflexes
• Integrating EPSPs and IPSPs
• Conducting sensory impulses to the brain and motor impulses to effectors

Spinal Cord Anatomy

• Protective components include bone, connective tissue (meninges), and cerebrospinal fluid (CSF).

Protection of the Spinal Cord

• Bone (vertebrae): Protects the spinal cord
• Connective tissue (meninges): Dura mater, arachnoid mater, and pia mater.
• Fluid (cerebrospinal fluid): Provides further cushioning and support.

Meninges

• Dura mater (outermost): Tough, protective layer.
• Arachnoid mater (middle): Thin membrane with CSF.
• Pia mater (innermost): Delicate membrane that adheres to the spinal cord.

External Anatomy of the Spinal Cord

• Begins as an extension of the medulla oblongata at the foramen magnum and ends at L2.
• Cervical plexus (C1-C5): nerves that supply the head, neck, shoulders and chest, including the diaphragm.
• Brachial plexus (C5-T1): nerves serving the upper limbs.
• Thoracic nerves (12 pairs): connect to the thoracic wall.
• Lumbar plexus (L1-L4): nerves supplying the lower abdominal wall and the anterior thigh.
• Sacral plexus (L4-S4): nerves supply the buttock, perineum, posterior thigh, and leg.
• Coccygeal plexus (Co): one pair of nerves.
• The cauda equina, or "horse's tail," are the roots of the lower spinal nerves that angle down alongside the filum terminale.
• Two prominent enlargements exist: cervical and lumbar, both associated with the extremities (motor and sensory input/output)

External Cord Anatomy

• Consist of roots and rootlets
• Posterior root (dorsal): contains sensory axons.
• Anterior root (ventral): contains motor axons
• Ganglion: contains cell bodies of sensory neurons

Epidural Anesthesia

• Used during labor and some surgical procedures.
• A needle is placed between the vertebrae to introduce anesthetic.
• The needle must remain between the bone and the dura mater.

Lumbar Puncture

• A method to withdraw cerebrospinal fluid (CSF).
• Useful in diagnosing diseases impacting the CNS.
• Often used to diagnose meningitis, assess pressure, etc.
• Site: between lumbar vertebra 3 and 4, or 4 and 5.

Spinal Nerves

• 31 pairs.
• Connect the central nervous system to sensory receptors, muscles, and glands in the peripheral nervous system.
• Two types of spinal nerve branches: anterior and posterior rami.

Connective Tissue Covering of Spinal Nerves

• Epineurium: surrounds the entire nerve.
• Perineurium: surrounds fascicles of nerve fibers.
• Endoneurium: surrounds individual nerve fibers (axons).

Peripheral Nerves

• The paths of communication between the spinal cord and specific areas of the body.
• Arranged in fascicles surrounded by perineurium, with the entire nerve sheathed by epineurium.
• Emerge from the cord at regular intervals (segments) between adjacent vertebrae.
• Branch almost immediately into three main branches: anterior ramus, posterior ramus, and rami communicantes.

Peripheral Nerves (cont)

• Anterior rami often combine to form plexuses (interconnected networks).
• The important plexuses are: cervical, brachial, lumbar, sacral, and coccygeal.

Branches of a Spinal Nerve

• Rami: Branches of a spinal nerve after passing through the intervertebral foramina
• Anterior rami typically form plexuses
• Posterior rami serve the muscles and skin of the back

Dermatomes

• Specific segments of the skin connected to particular spinal nerves.
• A dermatome is innervated by a specific segment of the spinal nerve.

Cervical Plexus

• Supplies skin and muscles of the head, neck, superior part of shoulders, chest, and diaphragm.
• Includes the phrenic nerve, crucial for diaphragm function.

Brachial Plexus

• Supplies skin and muscles of the upper limbs.
• Made up of several cords and branches with specific functions for each.
• Important nerves: musculocutaneous, axillary, radial, median and ulnar.

Nerve Plexuses

• Combined networks of interlinked spinal nerves.
• The long thoracic nerve is susceptible to injury from trauma or stretch, causing winging of the scapula.
• Injuries include Erb's palsy, median nerve injury, and carpal tunnel syndrome.
• The ulnar nerve is important for hand movements.

Lumbar Plexus

• Serves the lower abdominal wall and anterior thigh.
• Major nerves: femoral and obturator.

Sacral Plexus

• Serves the buttock, perineum, posterior thigh, and leg.
• Chief nerve: sciatic (composed of tibial and common fibular nerves), essential for lower limb function.

Spinal Cord Physiology

• Maintains homeostasis through nerve impulses passing through white matter tracts.
• Gray matter integrates sensory input and motor output for spinal reflexes.

Sensory and Motor Tracts

• Sensory (ascending) tracts bring messages from the body to the brain.
• Motor (descending) tracts carry messages from the brain to the body.

Reflexes and Reflex Arcs

• Fast, involuntary responses to stimuli.
• Vital for maintaining homeostasis.
• Spinal reflexes use gray matter as the integrating center.

Reflexes (cont)

• Vocabulary: ipsilateral/contralateral, monosynaptic/polysynaptic, reciprocal innervation.
• Reflex arcs: stretch reflex, tendon reflex, flexor reflex, crossed-extensor reflex, and the patellar and achilles' reflexes.
• The babinski reflex is specific to infants

Disorders

• Traumatic injuries: monoplegia, paraplegia, hemiplegia, quadriplegia.
• Transection: severing of the spinal cord.
• Spinal cord compression - by bone, blood/pus, tumors.
• Degenerative diseases: multiple sclerosis, amyotrophic lateral sclerosis (ALS).
• Shingles: acute infection from herpes zoster virus.
• Poliomyelitis (Polio): caused by polio virus, causing paralysis

This quiz covers essential topics related to the anatomy and functions of the spinal cord and its associated nerves. Questions focus on spinal cord structures, sensory neurons, reflex functions, and related medical conditions. Test your knowledge on these crucial elements of the nervous system.