A&P chapter 13 Spinal Cord

desending tract

In the descending tracts, motor signals are carried from the brainstem in a pathway typically involving two neurons, upper and lower motor neurons.

medullary cone

Inferior to the lumbar enlargement, the cord tapers to a point

lumbar cistern

Inferior to the medullary cone, the subarachnoid space is called the lumbar cistern and is occupied by the cauda equina and CSF.

spinocerebellar tract

travel through the lateral column. i. They carry proprioceptive signals from the limbs and trunk to the cerebellum.

5 ascending tracts

There are five major ascending tracts: The gracile fasciculus, the cuneate fasciculus, the spinothalamic tract, the spinoreticular tract, and two spinocerebellar tracts.

4 descending tracts

There are four descending tracts: the corticospinal; the tectospinal; the lateral and medial reticulospinal; and the lateral and medial vestibulospinal tracts.

subarachnoid space

This space is called the subarachnoid space and is filled with cerebrospinal fluid

ipsilateral

When a tract does not decussate, its fibers are said to be ipsilateral.

contralateral

When the origin and destination of a tract are on opposite sides of the body, they are said to be contralateral.

white matter

White matter has a bright, pearly white appearance due to the abundance of myelin; it consists of bundles of axons, called tracts (fasciculi).

coccygeal

coccygeal ligament that anchors the cord and meninges to vertebra Co1.

muscle spindles

1. Muscle spindles are among the body's proprioceptors; they inform the brain of muscle length and body movements.

spinal nerve roots

1. Spinal nerve roots give rise to each plexus and may also include smaller branches called trunks, anterior divisions, posterior divisions, and cords. 2. These nerves have somatosensory and motor functions. a. One of the most important somatosensory functions is that of proprioception, information about body position and movement.

dermatomes

Each spinal nerve except C1 receives sensory input from a specific skin area called a dermatome. 1. Dermatomes may overlap at their edges by as much as 50%.

third order

carries the signal the rest of the way to the cerebral cortex.

corticospinal

1. The corticospinal tracts carry motor signals from the cerebral cortex for precise, finely coordinated movement. i. The fibers form ridges called pyramids on the anterior surface of the medulla oblongata and so were once called pyramidal tracts.

AlS

3. Amyotrophic lateral sclerosis (ALS) - Lou Gehrig disease a. Destruction of motor neurons and muscular atrophy. b. Also sclerosis (scarring) of lateral regions of the spinal cord. c. Astrocytes fail to reabsorb the neurotransmitter glutamate from the tissue fluid. i. Accumulate to toxic levels.

lateral and medial reticulospinal

3. The lateral and medial reticulospinal tracts originate in the reticular formation of the brainstem. i. They control muscles of the upper and lower limbs, especially to maintain posture and balance. ii. They also contain descending analgesic pathways that reduce pain signals. to sights and sounds.

spinothalamic tract

3. The spinothalamic tract and some smaller tracts form the anterolateral system that passes up the anterior and lateral columns of the spinal cord. i. It carries signals for pain, temperature, pressure, tickle, itch, and light or crude touch.

break down of spinal cord

3. There are 31 pairs of mixed spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal

spinoreticular tract

4. The spinoreticular tract carries pain signals resulting from tissue injury. i. First order sensory neurons synapse with second-order neurons in the posterior horn.

first order

A first-order neuron detects a stimulus and transmits a signal to the spinal cord or brainstem.

flex reflex

A flexor (withdrawal) reflex is the quick contraction of flexor muscles to withdraw a limb from an injurious stimulus.

second order

A second-order neuron continues as far as the thalamus, a "gateway" at the upper end of the brainstem.

somatic reflex employ

A somatic reflex employs a reflex arc that involves the following pathway. 1. Somatic receptors in the skin, a muscle, or a tendon. 2. Afferent nerve fibers. 3. An integrating center in the gray matter of the spinal cord or brainstem consisting of one or more interneurons. 4. Efferent nerve fibers. 5. Skeletal muscles.

intersegmental reflex arc

An intersegmental reflex arc has input and output that occur at different segments of the spinal cord and thus affect muscles in different locations.

golgi tendon organs

Golgi tendon organs are proprioceptors located in a tendon near its junction with a muscle.

lumbosacral region

In the lumbosacral region, the lumbar enlargement gives rise to nerves to the pelvic region and lower limbs.

poliomyelitis and ALS

Poliomyelitis and ALS 1. Both diseases cause destruction of motor neurons and production of skeletal muscle atrophy from lack of innervation.

reflexs

Reflexes are quick, involuntary, stereotypic reactions of glands or muscles to stimulation. 1. Reflexes have four characteristics. a. They require stimulation b. They are quick c. They are involuntary d. They are stereotyped

spina bifida

Spina bifida - congenital defect in which one or more vertebrae fail to form a complete vertebral arch for enclosure of the spinal cord.

arachnoid mater

The arachnoid mater consist of a simple squamous epithelium adhering to the inside of the dura and a loose mesh of fibers spanning the gap between the arachnoid membrane and the pia mater.

lower motor neurons

The axon of the upper motor neuron terminates on a lower motor neuron in the brainstem or spinal cord. c. The axon of the lower motor neuron then innervates the muscle or other target organ.

anterior

The cord exhibits the anterior median fissure

flexor reflex crossed extension reflex

The flexor reflex employs an ipsilateral reflex arc while the crossed extension reflex employs a contralateral reflex arc.

gracile fasciculus

The gracile fasciculus carries signals from the mid-thoracic and lower parts of the body; it composes the entire posterior column below T6, and is joined at T6 by the cuneate fasciculus. i. Its fibers carry signals for proprioception, vibration, and touch from the lower limbs, and visceral pain. .

gray matter

The gray matter has a relatively dull color because it contains little myelin; it consists of somas, dendrites, and proximal parts of the axons of neurons.

lateral and medial vestibulospinal tracts

The lateral and medial vestibulospinal tracts begin in the brainstem vestibular nuclei. i. The vestibular nuclei receive impulses for balance from the inner ear. ii. The tract passes down the anterior column of the spinal cord and facilitates control of the extensor muscles of the limbs, helping one to keep balance. iii. The medial vestibulospinal tract splits into ipsilateral and contralateral fibers; it plays a role in the control of head position.

cauda equina

The lumbar enlargement and medullary cone give rise to a bundle of nerve roots called the cauda equina that occupy the vertebral canal from L2 to S5.

pia mater

The pia mater is a delicate, translucent membrane that closely follows the contours of the spinal cord.

epidural space

The space between the sheath and the vertebral bones, called the epidural space, is occupied by blood vessels, adipose tissue, and loose connective tissue.

meninges

The spinal cord and brain are enclosed in three fibrous connective tissue membranes called meninges

3 columns of the spinal cord

The three columns are posterior (dorsal), lateral, and anterior (ventral), and each consists subdivisions called tracts, or fasciculi.

The upper motor neuron

The upper motor neuron begins with a soma in the cerebral cortex of brain stem.

stretch reflex

When a muscle is stretched, it contracts to compensate, an action called the stretch (myostatic) reflex.

dura mater

a loose-fitting sleeve called the dural sheath around the spinal cord.

poliomyelitis

a. Caused by the poliovirus. b. Destroys motor neurons in brainstem and anterior horn of spinal cord. c. Signs of polio include muscle pain, weakness, and loss of some reflexes. i. Followed by paralysis, muscular atrophy, and respiratory arrest. d. Virus spreads by fecal contamination of water.

ascending tracts

carry sensory information up the cord.

4 regions of the spinal cord

cervical, thoracic, lumbar, and sacrum

3 principle functions of the spinal cord

conduction locomotion reflexes

cross extension reflex

crossed extension reflex is the contraction of extensor muscles in the limb opposite the one affected by the flexor reflex.

decussation

decussation meaning that they cross over from one side of the body to the other side.

3 nerons

first order second order third order

cervical enlargement

gives rise to nerves of the upper limbs.

cuneate fasciculus

joins the gracile fasciculus at T6 and occupies the lateral portion of the posterior column. i. It carries the same type of sensory signals as gracile fasciculus, but originating from the upper limb and chest.

posterior

posterior median sulcus posteriorly.

spinal cord

the spinal cord is a cylinder of nervous tissue that arises from the brainstem at the foramen magnum, and then passes through the vertebral canal as far as the intervertebral disc between L1 and L2.

cord gives rise to

to 31 pairs of spinal nerves.

tectospinal

turning the head in response to sight and sound