Spinal Cord Anatomy, Neural Pathways, and Meninges

Comprehensive vocabulary flashcards covering the gross anatomy, ascending and descending tracts, spinal nerves, reflexes, meninges, and ventricular CSF flow of the spinal cord and nervous system.

Conus medullaris

The tapered lower tip of the adult spinal cord, which terminates at approximately the $L1$ to $L2$ vertebral level.

Cauda equina

The collection of lower nerve roots hanging down below the end of the spinal cord resembling a horse's tail.

Cervical enlargement

A widened region of the spinal cord where nerve supplies for the upper limbs (arms) originate.

Lumbar enlargement

A widened region of the spinal cord where nerve supplies for the lower limbs (legs) originate.

Endoneurium

The innermost connective tissue layer that wraps around each individual nerve axon.

Perineurium

The middle connective tissue layer that wraps around a fascicle, which is a bundle of axons.

Epineurium

The outermost tough connective tissue coat that wraps and protects the entire nerve.

Gray commissure

A horizontal bar of gray matter that connects the right and left halves of the spinal cord gray matter.

Posterior (dorsal) horn

The region of spinal gray matter containing somatic and visceral sensory nuclei that receives incoming sensory signals.

Lateral horn

The gray matter region containing visceral autonomic motor neurons, found exclusively in the thoracic and upper lumbar cord levels.

Anterior (ventral) horn

The region of spinal gray matter housing cell bodies of somatic motor neurons that innervate skeletal muscles.

Funiculus

One of the three major anatomical white matter columns (posterior, lateral, or anterior) in the spinal cord containing nerve tracts.

Tract

A distinct bundle of axons located in the central nervous system (CNS) that shares a common origin, destination, and functional modality.

Decussation

The anatomical crossing over of nerve fibers across the midline from one side of the central nervous system to the other.

Posterior column pathway

An ascending sensory pathway that conducts fine (discriminative) touch, vibration, and conscious proprioception, crossing over in the medulla.

Fasciculus gracilis

The medial division of the posterior funiculus carrying fine touch and proprioceptive sensations from the lower body below about $T6$.

Fasciculus cuneatus

The lateral division of the posterior funiculus carrying fine touch and proprioceptive sensations from the upper body above about $T6$.

Spinothalamic pathway

An ascending sensory pathway carrying crude touch, pressure, pain, and temperature that decussates in the spinal cord near its entry level.

Spinocerebellar pathway

An ascending sensory pathway carrying unconscious proprioceptive information from muscles, tendons, and joints directly to the cerebellum.

First-order neuron

The sensory neuron that detects a stimulus and carries the signal from peripheral receptors into the spinal cord, with its soma in the dorsal root ganglion.

Second-order neuron

An interneuron with its cell body in the dorsal horn or medulla that decussates across the midline and ascends to the thalamus.

Third-order neuron

A sensory neuron whose cell body resides in the thalamus and whose axon terminates in the primary somatosensory cortex of the cerebrum.

Upper motor neuron (UMN)

A descending motor neuron that originates in the cerebral motor cortex or brainstem and synapses onto a lower motor neuron in the spinal cord.

Lower motor neuron (LMN)

A motor neuron originating in the anterior horn of the spinal cord or brainstem motor nucleus that directly innervates skeletal muscle fibers.

Lateral corticospinal tract

A direct pyramidal motor tract running in the lateral funiculus that decussates in the medulla pyramids and controls precise, skilled voluntary limb movements.

Anterior corticospinal tract

A direct pyramidal motor tract situated in the anterior funiculus that decussates at the spinal exit level to control axial trunk muscles and posture.

Rubrospinal tract

An indirect descending motor pathway originating in the red nucleus of the midbrain that regulates limb flexor tone and precise movements.

Vestibulospinal tract

An indirect descending motor pathway from vestibular nuclei of the brainstem that regulates balance, posture, and head and neck positions.

Reticulospinal tract

An indirect descending motor pathway originating in the brainstem reticular formation that modulates posture, muscle tone, and walking.

Tectospinal tract

An indirect motor tract originating in the superior colliculus of the midbrain that mediates reflexive head and neck turning toward visual and auditory stimuli.

Corticobulbar tract

A direct motor pathway from the motor cortex ending in the brainstem to control cranial nerves for head and facial muscles without entering the spinal cord.

Dorsal root ganglion

An enlargement along the dorsal root of a spinal nerve that contains the cell bodies of pseudounipolar sensory neurons.

Dermatome

A specific segment of skin innervated by sensory fibers from a single spinal nerve.

Nerve plexus

A network formed by interwoven ventral rami of spinal nerves that exchange fibers before emerging as named peripheral nerves.

Phrenic nerve

A vital peripheral nerve arising from spinal roots $C3$, $C4$, and $C5$ within the cervical plexus that innervates the diaphragm.

Intercostal nerves

Anterior rami of spinal nerves $T2$ through $T12$ that travel along the ribs without forming a plexus, innervating the chest and abdominal wall.

Reflex arc

The neural circuit underlying a reflex, sequentially composed of a receptor, sensory neuron, integration center, motor neuron, and effector.

Monosynaptic reflex

A rapid reflex pathway characterized by a single direct chemical synapse between a sensory afferent neuron and a motor efferent neuron.

Polysynaptic reflex

A reflex arc that includes one or more interneurons mediating between sensory and motor neurons, generating coordinated, multi-muscle responses.

Muscle spindle

A specialized stretch receptor embedded within skeletal muscles that monitors muscle length and rate of stretch.

Intrafusal fibers

Modified skeletal muscle fibers packaged inside the sensory muscle spindle capsule.

Extrafusal fibers

Standard force-producing skeletal muscle fibers situated outside the muscle spindle that are innervated by alpha motor neurons.

Hyperreflexia

An abnormal condition characterized by exaggerated reflex responses, commonly resulting from loss of upper motor neuron inhibitory signals.

Dura mater

The thick, tough, outermost meningeal layer composed of dense connective tissue that lines the cranial vault and vertebral canal.

Arachnoid mater

The delicate, avascular middle meningeal layer featuring web-like connective trabeculae extending across the subarachnoid space.

Pia mater

The delicate, highly vascularized innermost meningeal layer that adheres tightly to the surface of the brain and spinal cord.

Epidural space

The adipose- and vein-filled space located between the spinal dura mater and the surrounding bony vertebrae.

Subarachnoid space

The true meningeal fluid space located between the arachnoid mater and pia mater that contains cerebrospinal fluid and major blood vessels.

Arachnoid granulations

Villus projections of arachnoid membrane protruding into the superior sagittal sinus that filter CSF back into venous circulation.

Choroid plexus

A vascular network of permeable capillaries enveloped by ependymal cells located within brain ventricles that secretes cerebrospinal fluid.

Interventricular foramen

The anatomical channel (foramen of Monro) that provides cerebrospinal fluid passage from the lateral ventricles into the third ventricle.

Cerebral aqueduct

A slender channel (aqueduct of Sylvius) running through the midbrain that conveys cerebrospinal fluid from the third to the fourth ventricle.

Blood-CSF barrier

A selective physiological barrier established by tight junctions connecting ependymal cells of the choroid plexus to control chemical transport into CSF.

Hydrocephalus

A pathological build-up of cerebrospinal fluid within the ventricles resulting from flow obstruction, impaired reabsorption, or excessive production.