GAS Spinal Cord

What are the 3 major functions of the spinal cord

Provides sensory and motor innervation inferior to the head; conducts signals bidirectionally between body and brain; serves as a major reflex center.

What are the four embryonic stages leading to formation of the spinal cord

Neural plate → neural fold → neural tube → spinal cord.

What embryonic tissue gives rise to the neural plate

Neuroectoderm, derived from ectoderm.

What process converts the neural plate into the neural tube

Neurulation.

What structure divides the developing neural tube into dorsal and ventral portions

Sulcus limitans.

The dorsal portion of the developing neural tube becomes what adult functional division

Alar plate; sensory function.

The ventral portion of the developing neural tube becomes what adult functional division

Basal plate; motor output.

What happens to the lumen of the neural tube as the spinal cord develops

It narrows to form the central canal.

What neural tube defects are listed in the lecture

Anencephaly, spina bifida (occulta, meningocele, myelomeningocele), and iniencephaly.

What three structures protect the spinal cord

Vertebrae, meninges, and cerebrospinal fluid (CSF).

What is the order of the meninges from superficial to deep

Dura mater → arachnoid mater → pia mater.

Which meningeal layer is the tough, leathery outer layer

Dura mater.

Which meningeal layer is web-like and loosely surrounds the CNS

Arachnoid mater.

Which meningeal layer tightly adheres to the spinal cord

Pia mater.

Where is CSF located around the spinal cord

Subarachnoid space.

Where is CSF produced

Choroid plexus in the brain.

What are two major functions of CSF

Provides a liquid cushion against blows/jolts and helps clear CNS metabolic waste.

During a lumbar puncture, which meningeal layers must the needle penetrate to enter the subarachnoid space

Dura mater and arachnoid mater.

Why can a lumbar puncture be performed without directly injuring the spinal cord

The cauda equina roots are pushed aside.

What is the superior extent of the spinal cord

Foramen magnum.

What is the usual inferior extent of the spinal cord

L1–L2.

What is the tapered inferior end of the spinal cord called

Conus medullaris.

Where does the conus medullaris usually terminate

Around L2.

What structure extends inferiorly from the conus medullaris and anchors the cord to the coccyx

Filum terminale.

What is the function of the filum terminale

Anchors the spinal cord so it does not move excessively with body movement.

Why do lumbar and sacral nerve roots descend within the vertebral canal

The spinal cord terminates at L1/L2 while their corresponding intervertebral foramina are more inferior.

What is the collection of descending lumbar and sacral nerve roots called

Cauda equina.

What two regions of the spinal cord have prominent enlargements

Cervical and lumbosacral enlargements.

What spinal levels are associated with the cervical enlargement in this lecture

C5–T1.

What spinal levels are associated with the lumbosacral enlargement

L1–S3.

How many pairs of spinal nerves are there

31 pairs.

How many cervical spinal nerves are there

8 pairs, C1–C8.

How many thoracic spinal nerves are there

12 pairs, T1–T12.

How many lumbar spinal nerves are there

5 pairs, L1–L5.

How many sacral spinal nerves are there

5 pairs, S1–S5.

How many coccygeal spinal nerves are there

1 pair, Co1.

What two roots attach each spinal nerve to the spinal cord

Dorsal and ventral roots.

What fiber types are found in the dorsal root

Sensory only.

What fiber types are found in the ventral root

Motor only.

What fiber types are present in a spinal nerve trunk

Both sensory and motor.

What fiber types are present in the dorsal ramus

Both sensory and motor.

What fiber types are present in the ventral ramus

Both sensory and motor.

What is the key difference between a spinal nerve root and a ramus

Roots are medial to the spinal nerve and are sensory-only or motor-only; rami are lateral branches and are mixed.

What structures are innervated by dorsal rami

Muscles and skin of the back and posterior neck.

What structures are innervated by ventral rami

Lateral/anterior trunk, superficial and intermediate back muscles, and limb muscles.

Which rami innervate the true back/epaxial muscles

Dorsal rami.

Which rami supply hypaxial muscles and the limbs

Ventral rami.

Where is white matter located in the spinal cord

Externally, surrounding the gray matter.

What is the major composition of spinal cord white matter

Myelinated and unmyelinated axon tracts.

What are the three columns/funiculi of spinal cord white matter

Dorsal/posterior, lateral, and ventral/anterior columns.

What is the function of ascending spinal cord tracts

Carry sensory information toward the brain.

What is the function of descending spinal cord tracts

Carry motor instructions from the brain toward the spinal cord.

What is the function of commissural fibers

Carry information from one side of the spinal cord to the other.

What shape does spinal cord gray matter have in cross-section

H shape.

What structures are found in gray matter

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

What is the gray commissure

The crossbar of the gray-matter H containing fibers crossing between sides of the CNS.

What are the two major horns of spinal cord gray matter

Dorsal/posterior and ventral/anterior horns.

What is the primary function of the dorsal horn

Receives sensory input.

Where are the cell bodies of sensory neurons associated with the dorsal roots located

Dorsal root ganglia, outside the spinal cord.

What is found in the ventral horn

Motor neuron cell bodies.

Where do axons of ventral horn motor neurons travel

Through the ventral roots toward muscles and glands.

At which regions are ventral horns particularly large

Cervical and lumbar segments because of limb innervation.

What is a nerve plexus

A network formed by ventral rami of spinal nerves.

Why does a plexus allow a single limb muscle to receive fibers from multiple spinal nerves

Ventral ramus fibers intermingle and redistribute within the plexus.

What is the clinical advantage of a muscle receiving fibers from multiple spinal nerves

Damage to one spinal nerve is less likely to completely paralyze the muscle.

Which spinal nerves form the cervical plexus

C1–C4 ventral rami.

What areas are supplied by the cervical plexus

Skin and muscles of the neck and shoulder.

Which nerve arising from C3–C5 supplies the diaphragm

Phrenic nerve.

What is the classic mnemonic for the phrenic nerve's spinal levels

C3, 4, 5 keeps you alive.

Which spinal nerve levels form the brachial plexus

C5–T1.

What major body region is innervated by the brachial plexus

Upper limb.

What is the organizational sequence of the brachial plexus

Roots → trunks → divisions → cords → branches.

What are the three brachial plexus trunks

Upper, middle, and lower.

What are the two divisions of each brachial plexus trunk

Anterior and posterior.

What are the three cords of the brachial plexus

Lateral, medial, and posterior.

What are the five major terminal nerves of the brachial plexus

Musculocutaneous, median, ulnar, axillary, and radial.

Which major nerve primarily innervates the flexors of the arm

Musculocutaneous nerve.

Which nerve supplies the deltoid and teres minor

Axillary nerve.

Which nerve supplies the extensors of the arm and forearm

Radial nerve.

Which nerve supplies all forearm flexors except the 1.5 muscles described in the lecture

Median nerve.

Which nerve supplies flexor carpi ulnaris and the medial half of flexor digitorum profundus

Ulnar nerve.

Which spinal nerve levels form the lumbar plexus

L1–L4.

Where is the lumbar plexus located

Posterior abdominal wall.

Which major nerve of the lumbar plexus innervates the anterior thigh/quadriceps

Femoral nerve.

Which major nerve of the lumbar plexus innervates the medial thigh/adductors

Obturator nerve.

Which spinal nerve levels form the sacral plexus

L4–S4.

Which major nerve arises from the sacral plexus and supplies the posterior thigh and most of the leg

Sciatic nerve.

What is notable about the sciatic nerve

It is the thickest and longest nerve in the body.

How many anterior spinal arteries supply the spinal cord longitudinally

One.

How many posterior spinal arteries are present

Two.

Where does the anterior spinal artery originate

Vertebral arteries in the cranial cavity.

The posterior spinal arteries arise from what vessels

PICA vessels off the vertebral arteries.

What are the major sources of segmental spinal arteries in the neck

Vertebral and deep cervical arteries.

What are the major sources of segmental spinal arteries in the thorax

Posterior intercostal arteries.

What are the major sources of segmental spinal arteries in the abdomen

Lumbar arteries.

Through what structures do segmental spinal arteries enter the vertebral canal

Intervertebral foramina.

What do anterior and posterior radicular arteries accompany

The ventral and dorsal roots, respectively.

Approximately how many segmental medullary arteries reinforce the longitudinal spinal vessels

Approximately 8–10.

What is a dermatome

An area of skin innervated by sensory fibers of a single spinal nerve.

Do adjacent dermatomes have completely discrete borders

No. They can show overlap.