Chapter 13: The Spinal Cord and Reflexes

Vocabulary practice flashcards covering gross and cross-sectional spinal cord anatomy, spinal nerves and plexuses, motor pathways, and somatic and autonomic reflex arcs from Chapter 13.

Spinal Cord

An organ in the central nervous system measuring about 18 inches from the foramen magnum to L1; it carries sensory impulses to the brain through ascending tracts, motor impulses from the brain through descending tracts, and processes spinal reflexes.

Meninges

The three protective connective tissue coverings surrounding the spinal cord, organized from superficial to deep as dura mater, arachnoid mater, and pia mater.

Epidural Space

A large adipose-filled space located outside the dura mater of the spinal cord that cushions the cord and allows the administration of epidural anesthesia.

Subarachnoid Space

The fluid-filled space between the arachnoid mater and pia mater that contains cerebrospinal fluid (CSF) to cushion the spinal cord.

Conus Medullaris

The tapered, cone-shaped inferior termination of the spinal cord located near vertebral level L1.

Filum Terminale

An extension of the pia mater extending from the conus medullaris to the coccyx, functioning to stabilize the spinal cord within the vertebral foramen.

Mixed Nerve

A nerve containing both sensory (afferent) and motor (efferent) nerve fibers, such as all 31 pairs of spinal nerves.

Spinal Enlargements

The cervical and lumbar enlargments of the spinal cord possessing increased diameters because they house the motor neuron cell bodies supplying the upper and lower limbs.

Cauda Equina

A collection of nerve roots resembling a horse's tail that descends through the lower vertebral canal past L1 before exiting at their respective intervertebral foramina.

Gray Horns

Subdivisions of spinal cord gray matter (posterior, lateral, and anterior) containing neuronal cell bodies and unmyelinated fibers.

White Columns

Three regions of white matter in the spinal cord (posterior, lateral, and anterior) containing myelinated axons that carry sensory information upward and motor commands downward.

Central Canal

A narrow central channel running longitudinally through the spinal cord containing cerebrospinal fluid, forming a continuous extension of the brain's fourth ventricle.

Ganglion

A group of nerve cell bodies outside the central nervous system (instead are in the peripheral nervous system.)

Dorsal Root Ganglion

An enlargement on the dorsal (posterior) root containing the cell bodies (perikarya) of unipolar sensory neurons.

Anterior Gray Horn

The anterior region of the spinal cord containing gray matter, housing the cell bodies (perikarya) of somatic motor neurons whose axons exit through the ventral root.

Upper Motor Neuron

in a direct motor pathway, this is a pyramidal cell whose cell body resides in the precentral gyrus of the cerebral cortex and whose axon descends through white matter tracts to synapse with a lower motor neuron.

Lower Motor Neuron

A motor neuron situated in the anterior gray horn of the spinal cord whose axon exits via the ventral root to innervate skeletal muscle fibers.

Flaccid Paralysis

Muscles become limp, and you lose muscle tone b/c the motor neuron/nerves supplying them are damaged.

Spastic Paralysis

A state characterized by involuntary stiffness, rigidity, and increased muscle tone resulting from lesions to upper motor neurons or descending motor pathways in the brain and spinal cord.

Nerve Plexus

A network of nerves formed when the ventral rami of nearby spinal nerves branch and mix together to supply different parts of the body.

Phrenic Nerve

A vital motor and sensory nerve arising from the cervical plexus that innervates the diaphragm.

Brachial Plexus

A plexus that is a network of nerves that originates from the spinal nerves C5–T1. median, radial, musculocutaneous, axillary, and ulnar nerves arise from it.

Radial Nerve

A major nerve of the brachial plexus (C5–T1) that wraps around the humerus & innervates most of the muscles on the dorsal side of the arm and hand. (Muscles innervated by this nerve produce elbow and wrist extension.)

Femoral Nerve

The principal nerve derived from the lumbar plexus (L1–L4) that innervates the muscles of the anterior thigh, including the quadriceps femoris.

Sciatic Nerve

The largest nerve in the body, originating from the sacral plexus (L4–S4), which innervates the posterior thigh, lower leg, and foot.

Dermatome

a part of skin that is supplied by a specific spinal nerve

Reflex Arc

The specific pathway of a reflex consisting of a receptor, an afferent sensory neuron, an integration center, an efferent motor neuron, and an effector.

Monosynaptic Reflex

A fast reflex arc consisting of only two neurons (one sensory and one motor) with a single chemical synapse in the central nervous system.

Polysynaptic Reflex

A reflex arc involving multiple synapses and at least one interneuron

Ipsilateral Reflex

A reflex arc where sensory input enters and motor output exits on the same side of the central nervous system.

Contralateral Reflex

A reflex arc in which sensory input enters on one side of the spinal cord and triggers an efferent motor response on the opposite side of the body.

Muscle Spindle

A sensory stretch receptor within skeletal muscles that monitors muscle length to prevent overstretching.

Stretch Reflex

A monosynaptic, ipsilateral somatic reflex initiated by muscle spindles that causes contraction of the stretched muscle, exemplified by the patellar reflex.

Golgi Tendon Organ

A receptor located inside a tendon that monitors tension and contraction force to protect muscles from excessive contraction.

Golgi Tendon Reflex

A polysynaptic, ipsilateral somatic reflex triggered by Golgi tendon organs that induces muscle relaxation when muscle tension becomes excessive.

Withdrawal Reflex

An ipsilateral, polysynaptic somatic flexor reflex activated by nociceptors to rapidly withdraw a limb from a painful or damaging stimulus.

Crossed Extensor Reflex

A contralateral polysynaptic reflex accompanying the withdrawal reflex that stimulates extensor muscles in the opposite limb to maintain balance and support body weight.

Plantar Reflex

A superficial somatic reflex evaluated by stroking the lateral sole of the foot; the normal adult response is downward curling (flexion) of the toes (negative Babinski sign).

Positive Babinski Sign

An abnormal response in individuals over infancy consisting of dorsiflexion of the great toe with fanning of the other digits upon plantar stimulation, signaling damage to upper motor pathways.

Pupillary Reflex

A bilateral, polysynaptic autonomic reflex where light detected by photoreceptors via the optic nerve initiates motor signals along the oculomotor nerves to constrict both constrictor pupillae muscles.