Chapter 13 Spinal Cord

Coccygeal Nerves-

1 pair of nerves arising from the coccyx known as Filium Terminale.

Cranial Nerves

12 pairs of nerves that leave the brain. Relay information between brain and the body.

Thoracic Nerves

12 pairs of spinal nerves that originate in the thoracic region. Anterior divisions and posterior divisions The anterior rami of nerves (intercostal nerves) run from T2-T12.

Lumbar Nerves

5 pairs of nerves emerging from the lumbar vertebrae. Anterior rami- L1-L4 split into anterior and posterior divisions which give rise to the peripheral branches of the plexus.

Sacral Nerves

5 pairs of nerves. Half of them arising through the sacrum on the left side and the other half on the right side. Each nerve emerges in two divisions: one division through the anterior sacral foramina and the other division through the posterior sacral foramina.

arachnoid mater

A fine, delicate membrane in the middle of the pia mater and dura mater that envelops the brain and spinal cord.

Spinal Cord

A mass of nerve tissue located in the vertebral canal from which 31 pairs of spinal nerves originate it also connects all parts of the body to the brain.

central canal

A microscopic tube running the length of the spinal cord in the gray commissure

Cervical Plexus

A network formed by nerve axons from the anterior rami of the first four cervical nerves and receiving gray rami communicantes from the superior cervical ganglion.

Lumbar Plexus

A network formed by the anterior branches of spinal nerves L1 through L4

Sacral Plexus

A network formed by the anterior rami branches of spinal nerves L4 through S3

Brachial Plexus

A network of nerve axons of the anterior rami of spinal nerves C5, C6, C7, C8, and T1

Plexus

A network of nerves, veins, or lymphatic vessels.

contralateral reflex

A reflex where the response occurs on the opposite side of the response

Rami

A short distance after passing through its intervertebral foramen, a spinal nerve divides into several branches which are called rami.

intersegmental reflex arc

A single sensory neuron can activate several motor neurons which in turn stimulates more than one effector.

epidural space

A space between the dura mater and the wall of the vertebral canal that contains a cushion of fat and connective tissue that helps protect the spinal cord.

Ganglia

A structure containing a number of nerve cell bodies, typically linked by synapses, and often forming a swelling on a nerve fiber.

crossed extensor reflex

A withdrawal reflex. When the reflex occurs the flexors in the withdrawing limb contract and the extensors relax, while in the other limb, the opposite occurs.

Posterior Root

Also called (dorsal) root, contain only sensory axons, which conduct nerve impulses from sensory receptors in the skin, muscles, and internal organs into the central nervous system.

Rami Communicantes

Branches of spinal nerve that are components of the autonomic nervous system.

Spinal Nerves

Connect the CNS to sensory receptors, muscles and glands in all parts of the body. There are 31 pairs of spinal nerves They originate from posterior and anterior roots

gray matter

Contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia. appears grayish, rather than white, because the Nissl bodies give it a gray color and there is little or no myelin in these areas.

anterior white commissure

Found anterior to the gray commissure, and connects the white matter of the right and left sides of the spinal cord -aggregations/bundles of myelinated and unmyelinated axons located in the brain and spinal cord

interneuron

Mainly located within the CNS between sensory and motor neurons, which then process incoming information from sensory neurons, and elicit a motor response by activating the appropriate motor neurons.

posterior median sulcus

Narrow furrow on posterior side that also penetrates the white matter of the spinal cord and divides it into left and right sides.

Filum Terminale

Non-nervous fibrous tissue of the spinal cord that extends inferiorly from the conus medullaris to the coccyx (p. 494, 13th ed.).

contralateral reflex arc

Sensory impulses enter one side of the of the spinal cord and motor impulses exit on the opposite side. An example of this is the crossed extensor reflex.

Posterior Rami

Serve the deep muscles and skin of the posterior surface of the trunk, its singular form is called a posterior (dorsal) ramus.

Anterior Rami

Serve the muscles and structures of the upper and lower limbs and the skin of the lateral and anterior surfaces of the trunk, its singular form is called an anterior (ventral) ramus.

Meningeal Branch:

Spinal nerves give off a meningeal branch, which re-enters the vertebral cavity through the intervertebral foramen and supplies the vertebrae, vertebral ligaments, blood vessels of the spinal cord, and meninges.

pia mater

The delicate, innermost membrane enveloping the brain and the spinal cord.

Coccygeal Plexus:

The roots (anterior rami) of spinal nerves S4-S5 and the coccygeal nerves form a small coccygeal plexus. From this plexus arises the anococcygeal nerves, which supply a small area of skin in the coccygeal region.

conus medularis

The tapered portion of the spinal cord inferior to the lumbar enlargement

dura mater

The tough, outermost membrane enveloping the brain and spinal cord.

denticulate ligaments

Triangular-shaped membranous extensions of the pia mater. Suspend the spinal cord in the middle of its dural sheath

reciprocal innervations

When components of a neural circuit simultaneously cause contraction of one muscle and relaxation of its antagonist

anterior median fissure

Wide groove on the anterior side that penetrates the white matter of the spinal cord and divides it into left and right sides.

knee jerk (stretch) reflex

a contraction of the skeletal muscle in response to stretching a muscle, elicited by tapping on tendons attached to muscles- e.g. the patellar reflex

reflex arc

a pathway that follows nerve impulses that produce a reflex. it includes five functional components: sensory receptor, sensory neuron, integrating center, motor neuron, and effector.

monosynaptic reflex

a reflex which has only one synapse between the sensory neuron and a motor neuron in the CNS.

polysynaptic reflex

a reflex which involves two or more types of neurons and more than one CNS synapse.

posterior column tract

a sensory tract that conveys nerve impulses for discriminative touch, light pressure, vibration and conscious proprioception.

spinothalamic tract

a sensory tract that transmits sensations of pain, warmth, coolness, itching, tickling, deep pressure, and crude touch.

lateral white columns

area of the spinal cord, between the points of exit and entry of the anterior and posterior nerve roots

posterior white columns

area of white matter in the middle to posterior side of the spinal cord, composed of the gracile fasciculus and the cuneate fasciculus

indirect pathway tracts

carry signals from the brainstem that coordinate visual stimuli with body movements, maintain posture and regulate skeletal muscle tone

nuclei

clusters of neuronal cell bodies that form functional groups in the gray matter of the spinal cord and brain.

gray commissure

connects the gray matter of the right and left sides of the spinal cord.

motor tracts

consists of axons that carry nerve impulses FROM the brain.

sensory tracts

consists of axons that conduct nerve impulses TOWARD the brain.

posterior gray horns

contains cell bodies and axons of interneurons as well as axons of incoming sensory neurons

anterior gray horns

contains somatic motor nuclei -cluster of cell bodies of somatic motor neurons that provide nerve impulses for contraction of skeletal muscles

tracts

each column (anterior, posterior, lateral) contains distinct bundles of axons having a common origin or destination and carrying similar information that may extend long distances up or down the spinal cord

horns

gray matter on each side of the spinal cord is subdivided into regions called horns

white matter

helps maintain homeostasis through nerve impulse propagation. Surrounds the inner core of grey matter in the spine

direct pathway tracts

include lateral and anterior corticospinal tracts; carry signals from the cerebral cortex that result in voluntary movement of the skeletal muscle

lateral gray horns

present only in thoracic and upper lumbar segments of the spinal cord; contain autonomic motor nuclei-clusters of cell bodies of autonomic motor neurons that regulate activity of cardiac and smooth muscles and glands

spinal reflexes

response when integration takes place in the spinal cord gray matter

cauda equina

the roots of the lower spinal nerves angle inferiorly alongside the filum terminale in the vertebral canal like wisps of hair. Accordingly, the roots of these nerves are collectively called the cauda equina, meaning "horse's tail"

subdural space

thin space between the dura mater and arachnoid mater; contains interstitial fluid

meninges

three protective, connective tissue coverings that encircle the spinal cord and brain; from superficial to deep they are dura mater, arachnoid mater, and pia mater

ipsilateral reflex

A reflex where the stimulus occurs on the same side as the response.

Anterior Root

Also called (ventral) root, contain axons of motor neurons, which conduct nerve impulses from the central nervous system to effectors (muscles and glands).

flexor (withdrawal) reflex

An ipsilateral and polysynaptic reflex arc that makes the body respond to a stimulus (such as pain) by taking away the extremity. Such as stepping on a tack and then withdrawing your leg.

anterior white columns

large bundle of fibers located between the anterior median fissure of the spinal cord and the anterolateral sulcus of the spinal cord