Introduction to the nervous system and Spinal cord

What is a spinal cord injury?

Damage to the spinal cord resulting in loss of function such as mobility or sensation.

What are common causes of spinal cord injury?

Trauma (car accidents, gunshots, falls, etc.) and diseases such as polio and spina bifida.

What spinal injury did Christopher Reeve sustain?

A cervical spinal injury after a fall from a horse.

What happened to Christopher Reeve after his injury?

He became paralyzed from the neck down after shattering his first and second cervical vertebrae.

What usually results from cervical (neck) injuries?

Full or partial tetraplegia (quadriplegia).

What are the objectives of studying the nervous system and spinal cord?

Define structural and functional divisions of the nervous system, understand spinal nerves/dermatomes/myotomes, study meninges and spinal cord anatomy, learn spinal cord structural features, study spinal cord pathways, and understand spinal cord development.

What is the nervous system?

The most complex system in the human body.

What is the basic structural unit of the nervous system?

The neuron.

What are the functions of the nervous system?

Coordinates muscle activity, monitors organs, processes sensory input, and initiates actions.

How are neurons organized functionally?

Neurons form circuits.

What are the structural subdivisions of the nervous system?

Central nervous system (CNS) and peripheral nervous system (PNS).

What structures make up the CNS?

The brain and spinal cord.

What structures make up the PNS?

The nerves going to and from the CNS.

What are the functional subdivisions of the nervous system?

Somatic and visceral divisions.

What does the somatic part of the nervous system innervate?

Skin and most skeletal muscle derived from embryonic somites.

What is the primary role of the somatic nervous system?

Receiving and responding to information from the external environment.

What does the visceral part of the nervous system innervate?

Organ systems, smooth muscle, glands, and other visceral structures.

What is the primary role of the visceral nervous system?

Detecting and responding to information from the internal environment.

What is another name for the visceral motor component?

The autonomic nervous system (ANS).

What is the autonomic nervous system (ANS)?

The involuntary, reflexive visceral motor division of the PNS that regulates organ function and homeostasis.

What functions are controlled by the autonomic nervous system?

Organ function regulation and maintenance of homeostasis.

Is autonomic control voluntary or involuntary?

Mostly involuntary and reflexive.

What structures are innervated by the ANS?

Smooth muscle, cardiac muscle, and secretory cells (glandular epithelium).

What components make up the ANS?

Motor and sensory components.

What is the function of ANS sensory nerves?

Monitor changes in the viscera.

What is the function of ANS motor nerves?

Innervate smooth muscle, cardiac muscle, and glands.

When is the sympathetic nervous system most important?

During emergencies requiring fight-or-flight responses.

What is the fight-or-flight division of the ANS?

The sympathetic nervous system.

When is the parasympathetic nervous system most important?

During non-emergencies that allow rest and digestion.

What is the rest-and-digest division of the ANS?

The parasympathetic nervous system.

What body functions are regulated by the ANS?

Digestion, circulation, respiration, excretion, reproduction, and body temperature.

What spinal levels give rise to the sympathetic division?

T1-L2/L3.

What ganglia are associated with the sympathetic division?

Paravertebral and prevertebral ganglia.

What structures give rise to the parasympathetic division?

Brainstem cranial nerves and spinal levels S2-S4.

Where are parasympathetic ganglia located?

Close to their target muscles or organs.

What does GSA stand for?

General somatic afferent.

What are general somatic afferent (GSA) neurons?

Somatic sensory neurons carrying information from the periphery into the CNS.

What is another name for GSA fibers?

Somatic sensory afferents.

What does GSE stand for?

General somatic efferent.

What are general somatic efferent (GSE) fibers?

Somatic motor fibers carrying information from the CNS to skeletal muscles.

What is another name for GSE fibers?

Somatic motor efferents.

What does GVA stand for?

General visceral afferent.

What are general visceral afferent (GVA) neurons?

Visceral sensory neurons associated with the ANS.

What sensations are primarily carried by GVA neurons?

Chemoreception, mechanoreception, and stretch reception.

What does GVE stand for?

General visceral efferent.

What are general visceral efferent (GVE) neurons?

Visceral motor neurons associated with the ANS.

What is a dermatome?

An area of skin supplied by a single spinal cord level or a single spinal nerve.

How is sensory innervation of a dermatome supplied?

By dorsal root fibers from a specific spinal cord segment.

How do somatic sensory fibers enter the spinal cord?

Through the posterior region of the spinal cord at a specific level.

What is a myotome?

The portion of a skeletal muscle innervated by a single spinal cord level or spinal nerve.

How are myotomes related to embryonic development?

Each spinal nerve supplies muscles that developed from the corresponding somite.

What are the functions of the spinal cord?

Mediates motor reflexes, conducts sensory information to the brain, contains motor pathways to muscles, and contains autonomic efferents.

What is gray matter in the CNS?

Aggregations of neuronal cell bodies, forming structures such as cortex and nuclei.

What is white matter in the CNS?

Bundles of neuronal axons forming tracts, fibers, and columns.

What is gray matter in the PNS?

Ganglia.

What is white matter in the PNS?

Nerve fibers.

How many pairs of spinal nerves are there?

31 pairs.

How many cervical spinal nerves are there?

8 pairs.

How many thoracic spinal nerves are there?

12 pairs.

How many lumbar spinal nerves are there?

5 pairs.

How many sacral spinal nerves are there?

5 pairs.

How many coccygeal spinal nerves are there?

1 pair.

What is the conus medullaris?

The tapered terminal end of the spinal cord.

What is the cauda equina?

A collection of spinal nerve roots extending below the conus medullaris.

What is the filum terminale?

A fibrous extension anchoring the spinal cord inferiorly.

What are the enlargements of the spinal cord?

The cervical enlargement and lumbar enlargement.

How does white matter change along the spinal cord?

It increases in a caudal-to-rostral direction.

Why is gray matter increased in the cervical and lumbosacral enlargements?

For innervation of the limbs.

Where is the lateral horn normally found?

Only in thoracic and upper lumbar segments.

Which spinal region contains the greatest amount of white matter?

The cervical region.

Why does the cervical spinal cord contain the most white matter?

Higher levels contain more ascending and descending fiber traffic.

Where is gray matter maximal in the spinal cord?

The cervical and lumbar enlargements.

Where do afferent fibers enter the spinal cord?

Through the dorsal roots.

What is found in the dorsal root ganglia?

Cell bodies of sensory neurons.

Where do efferent fibers leave the spinal cord?

Through the ventral roots.

What do alpha motor neurons innervate?

Extrafusal skeletal muscle fibers.

What is the function of alpha motor neurons?

Produce muscle contraction and force.

What do gamma motor neurons innervate?

Intrafusal muscle spindle fibers.

What is the function of gamma motor neurons?

Adjust spindle sensitivity and help regulate muscle tone.

What is the shape of spinal cord gray matter in cross section?

An H-shaped or butterfly-shaped outline.

What lines the central canal of the spinal cord?

Ependymal epithelium.

What is the function of the dorsal horns?

Sensory processing.

What is the function of the ventral horns?

Motor output.

What is the function of the lateral horn/intermediate zone?

Contains sympathetic efferent neurons.

In which spinal segments is the lateral horn present?

Thoracic and upper lumbar segments.

Where are the cell bodies of sensory neurons located?

In the dorsal root ganglion.

Where are motor neuron cell bodies located?

In the ventral horn.

What are the three funiculi of white matter in the spinal cord?

Dorsal, lateral, and ventral funiculi.

What structures are found in the dorsal funiculus?

The fasciculus gracilis and fasciculus cuneatus.

What is the fasciculus gracilis?

The medial tract within the dorsal funiculus.

What is the fasciculus cuneatus?

The lateral tract within the dorsal funiculus.

What is the dorsolateral tract of Lissauer?

A tract located between the apex of the dorsal horn and the surface of the spinal cord.

What are Rexed's laminae?

A system for dividing spinal cord gray matter introduced by Rexed in 1952.

Which Rexed laminae are located in the dorsal horn?

Laminae I-VI.

Which Rexed laminae are located in the ventral horn?

Laminae VII-IX.

What is the intermediolateral cell column (IML)?

A gray matter column containing preganglionic sympathetic neurons.

At what levels is the IML present?

T1-L3.

What type of neurons are found in the IML?

Preganglionic sympathetic neurons (GVE).

What is the intermediomedial cell column (IMM)?

A gray matter column containing preganglionic parasympathetic neurons.

At what levels is the IMM present?

S2-S4.