Comprehensive Neuroanatomy and Spinal Cord Development Quizlet

What two structures constitute the central nervous system (CNS)?

The brain and the spinal cord.

What constitutes the peripheral nervous system (PNS)?

All nervous tissue outside the brain and spinal cord — the 12 pairs of cranial nerves and the 31 pairs of spinal nerves (plus their roots, ganglia and branches).

Are the dorsal (sensory) and ventral (motor) roots CNS or PNS structures?

PNS structures that attach to the spinal cord.

List the three functions of the spinal cord.

1. Sensory and motor innervation of the entire body inferior to the head, via spinal nerves. 2. Two-way conduction pathway for signals between body and brain. 3. Major center of reflexes.

How many pairs of cranial nerves does the PNS contain?

12 pairs.

How many pairs of spinal nerves does the PNS contain?

31 pairs.

How many cervical spinal nerves are there?

8 cervical.

How many thoracic spinal nerves are there?

12 thoracic.

How many lumbar spinal nerves are there?

5 lumbar.

How many sacral spinal nerves are there?

5 sacral.

How many coccygeal spinal nerves are there?

1 coccygeal.

What type of conduction pathway is the spinal cord?

Two-way conduction pathway.

What does the spinal cord connect?

The body and the brain.

What are the four stages in the development of the spinal cord?

1. Neural plate 2. Neural fold 3. Neural tube 4. Spinal cord.

Which germ layer gives rise to the spinal cord?

Ectoderm.

What does the ectoderm differentiate into first?

Neuroectoderm.

What is the groove that divides the spinal cord into dorsal and ventral portions called?

The sulcus limitans.

What do the alar plates in the developing cord represent?

The dorsal portions, which are the location of sensory input.

What do the basal plates in the developing cord represent?

The ventral portions, which are the location of motor function output.

What forms the central canal of the spinal cord?

The lumen of the neural tube narrows as dorsal and ventral column cells proliferate.

In which two directions does the closing neural tube extend?

Cranially (to become the brain) and caudally (to become the spinal cord).

What are neural crest cells and what do they form?

Lateral ectodermal cells pulled along during neural tube closure; they form sensory nerve cells (e.g., dorsal root ganglia) and other structures.

Name the three neural tube defects covered in this lecture.

1. Spina bifida (occulta, meningocele, myelomeningocele) 2. Anencephaly 3. Iniencephaly.

Name the three forms of spina bifida from mildest to most severe.

1. Occulta 2. Meningocele 3. Myelomeningocele.

What is spina bifida occulta?

The mildest form: a vertebral arch defect with no protrusion of meninges or cord.

What protrudes in a meningocele?

Only the meninges protrude; nerves and spinal cord remain safe inside.

What protrudes in a myelomeningocele?

The spinal cord (and nerve roots) protrude out with the meninges, resulting in neurological deficits.

Describe anencephaly.

Failure of the cranial end of the neural tube to close, leading to absence of the skull vault and brain; the condition is invariably fatal.

What is absent in iniencephaly?

The brain, skull, and cervical vertebrae are deficient.

What does neuroectoderm condense to form?

The neural plate.

What is the process called when the neural plate forms the neural tube?

Neurulation.

When does the closure of the neural tube begin?

At the end of week 3.

When is the closure of the neural tube complete?

By the end of week 4, i.e., by day 28.

Through what bony canal does the spinal cord run?

The vertebral canal.

What is the conus medullaris?

The tapered, cone-shaped inferior end of the spinal cord, usually at L2.

What is the filum terminale?

A long filament of connective tissue — an inferior extension of pia mater — that anchors the spinal cord.

What is the difference between filum terminale internum and externum?

Internum: the pial filament running within the dural sac, from conus medullaris to S2. Externum: the dural continuation from S2 down to the coccyx.

What is the cauda equina?

The collection of descending lumbar and sacral nerve roots below the conus medullaris.

Why does the cauda equina exist?

Because the cord does not reach the inferior end of the vertebral column, so those roots must descend some distance.

What are the two enlargements of the spinal cord?

Cervical enlargement (C5-T1) for upper limb nerves and lumbosacral enlargement (L1-S3) for lower limb nerves.

What shape is the spinal cord's gray matter in cross-section?

Shaped like the letter H.

What does the gray matter contain?

Neuron cell bodies, unmyelinated axons, dendrites, and neuroglia.

What is the crossbar of the H of gray matter called?

The gray commissure.

What do the dorsal (posterior) horns contain?

Interneurons that receive information from sensory neurons.

Where are the cell bodies of the neurons feeding the dorsal horns located?

In the dorsal root ganglia.

What do the ventral (anterior) horns contain?

Cell bodies of motor neurons.

Where do the axons of the ventral horns go?

Out of the cord via the ventral roots to supply muscles and glands.

At which spinal levels are the ventral horns largest?

The cervical and lumbar segments.

What does the lateral horn contain?

Visceral (autonomic) motor neurons.

Where is the white matter of the spinal cord located?

In the outer region of the cord.

What is the composition of the white matter?

Myelinated and unmyelinated axon tracts.

Into what three columns is the white matter divided?

Dorsal (posterior), ventral (anterior), and lateral columns.

What do the dorsal, ventral, and lateral columns contain?

Ascending and descending fibers.

What are the three types of white matter fibers?

Ascending, descending, and commissural.

What does ascending white matter carry?

Sensory information from sensory neurons to the brain.

What does descending white matter carry?

Motor instructions from the brain to the spinal cord.

What does commissural white matter carry?

Information from one side of the cord to the other.

Which matter is central and which is peripheral in the spinal cord?

Gray matter is central; white matter is peripheral.

Where does the spinal cord extend from?

From the foramen magnum at the base of the skull.

To which lumbar vertebra does the spinal cord extend?

To the 1st or 2nd lumbar vertebra (L1/L2).

What is the cervical enlargement of the spinal cord?

C5-T1 (upper limb).

What is the lumbosacral enlargement of the spinal cord?

L1-S3 (lower limb).

What do dorsal roots carry?

Sensory information.

What do ventral roots carry?

Motor information.

What is the composition of the spinal nerve?

Mixed (both sensory and motor fibers).

What does the dorsal ramus innervate?

The muscles and skin of the back and posterior neck.

What does the ventral ramus innervate?

Muscles and skin of the lateral and anterior trunk, and limb muscles.

What are rami communicantes?

Branches connecting the spinal nerve to the sympathetic trunk ganglion.

What is the dorsal root ganglion (DRG)?

A swelling on the dorsal root containing cell bodies of sensory neurons.

What are rootlets?

Small fascicles that emerge from the cord to form dorsal and ventral roots.

What protects the spinal cord?

The vertebrae, meninges, and cerebrospinal fluid (CSF).

What are the three meninges from outside in?

Dura mater, arachnoid mater, pia mater.

What is the position and tissue type of the dura mater?

Outermost layer; dense fibrous connective tissue.

What is the appearance of the arachnoid mater?

Weblike threads surrounding the brain and spinal cord.

What is the position and tissue type of the pia mater?

Innermost layer; delicate connective tissue clinging tightly around the brain and spinal cord.

What are the three meningeal spaces?

Epidural space, subdural space, subarachnoid space.

What is contained in the subarachnoid space?

Cerebrospinal fluid (CSF).

What are denticulate ligaments?

Lateral extensions of pia mater that anchor the spinal cord.

Where is CSF formed?

By the choroid plexus in the ventricles of the brain.

How many anterior and posterior spinal arteries are there?

1 anterior spinal artery and 2 posterior spinal arteries.

Where does the anterior spinal artery originate?

From the vertebral arteries in the cranial cavity.

Where do the posterior spinal arteries originate?

From the PICA vessels off the vertebral arteries.

Where do the segmental spinal arteries arise from, by body region?

Neck: vertebral & deep cervical arteries; Thorax: posterior intercostal arteries; Abdomen: lumbar arteries.

How do the segmental spinal arteries enter the vertebral canal?

Through the intervertebral foramina, at every level.

What do the segmental spinal arteries give rise to?

Anterior and posterior radicular arteries, which supply the ventral and dorsal roots, and segmental medullary arteries.

What is the artery of Adamkiewicz?

The great anterior segmental medullary artery, the largest reinforcing branch to the anterior spinal artery.

Which artery supplies the anterior two-thirds of the spinal cord in cross-section?

The anterior spinal artery.

What do the posterior spinal arteries supply?

The dorsal columns and posterior territory of the spinal cord.

How many segmental medullary arteries are there approximately?

8-10.

What is a nerve plexus?

A network of nerves formed ONLY by the ventral rami of spinal nerves.

Why can destruction of a single spinal nerve not completely paralyze a limb muscle?

Because fibers from the ventral rami cross each other within the plexus.

Name the four main plexuses and their root values.

Cervical: C1-C4; Brachial: C5-T1; Lumbar: L1-L4; Sacral: L4-S4.

What does the cervical plexus innervate?

The skin of the neck and shoulder, and the muscles of the neck and shoulder.

What are the cutaneous branches of the cervical plexus?

Lesser occipital, greater auricular, transverse cervical, and supraclavicular nerves.

What does the ansa cervicalis supply?

The infrahyoid muscles of the neck.

What is the root value of the phrenic nerve?

C3-C5.

What does the phrenic nerve innervate?

The diaphragm.

What is the mnemonic for the phrenic nerve?

C3, 4, 5 keeps you alive.

Where is the brachial plexus located?

In the neck and armpit (axilla).

What does the brachial plexus innervate?

The upper limb.