Chapter 13 The spinal cord, spinal nerves, and somatic reflexes

where does the inferior margin of the spinal cord end?

L1 or slightly beyond.

What is the perineurium?

layers of overlapping squamous cells that wrap fascicles: bundles of nerve fibers.

inferior to the lumbosacral enlargement, the cord tappers to a point called the what?

medullary cone (conus medullaris).

what is conduction of the spinal cord?

nerve fibers conduct sensory and motor information up and down the spinal cord (connecting different levels of the trunk with each other and with the brain).

what does the cervical enlargement give rise to?

nerves of the upper limbs.

what is gray matter composed of?

neuron cell bodies (the somas, dendrites, and proximal parts of the axon).

where is the lateral horn of the spinal cord visible from?

on each side of the gray matter from segment T2 through L1 of the spinal cord.

what is quadriplegia?

paralysis of all four limbs.

what is paraplegia?

paralysis of both lower limbs.

what is hemiplegia?

paralysis of one side of the body.

what is a segment of the spinal cord?

part of the spinal cord supplied by each pair of spinal nerves.

what is paresis?

partial paralysis or weakness of the limbs.

what are the smaller branches of spinal nerves called?

peripheral nerves.

what is neural integration of the spinal cord?

pools of spinal neurons receive input from multiple sources, integrate the information, and execute an appropriate output (control of the bladder/urination).

what are the two kinds of peripheral nerve fibers and how do they differ?

sesnory (afferent) fibers carry signals from sesnroy receptors to the CNS; motor (efferent) fibers carry signals from the CNS to the muscles and glands.

both sensory and motor fibers can also be described as?

somatic or visceral, general or special

a somatic reflex employs a reflex arc, in which signals travel along a pathway: what are the five steps?

somatic receptors, afferent nerve fibers, integrating center, efferent nerve fibers, effectors.

Reflexes include glandular secretion and contraction of all three types of muscle, but the reflexes of skeletal muscle are called?

somatic reflexes that involve the somatic nervous system.

the spinal cord has a central core of gray matter that is shaped like what?

somewhat like a butterfly or an H-shape

what is the most serious form of spina bifida?

spina bifida cystica.

How does the spinal cord communicate with the rest of the body?

spinal nerves.

what are the fasciculi of white matter?

subdivisons of the culumn (also known as tracts).

gray matter is the site of what?

synaptic contact between neurons and all neural integration of the spinal cord (the processing of information).

what are the two longitudinal grooves on the posterior and anterior sides of the spinal cord?

the anterior median fissure and the posterior median sulcus.

the arachnoid mater is consistent of what?

the arachnoid membrane- five or six layers of squamous to cuboidal cells adhering to the inside of the dura.

many fibers of the spinal cord have their origins where?

the brainstem.

what are the two areas where the spinal cord is a little thicker than elsewhere?

the cervical enlargement and the lumbosacral enlargement.

what is the space between the dural sheath and the vertebral bones?

the epidural space.

Lumbar punctures (spinal tap) take samples of CSF from where?

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

in what region is spina bifida common in?

the lumbosacral region.

effectors:

the muscles that carry out the response.

contralateral means what?

the origin and destination of a tract are on opposite sides of the body.

where does the lumbosacral enlargement issue nerves to?

the pelvic region and lower limbs.

what is the difference between posterior (dorsal) roots and anterior (ventral) roots of spinal nerves?

the posterior (dorsal) roots carry sesnory fibers while the anterior (ventral) roots carry motor fibers.

what are the names of the three funiculi?

the posterior (dorsal), laterla, and the anterior (ventral) funiculi.

what do the meninges seperate?

the soft tissue of the central nervous system from bones of the cranium and vertebral canal.

what is locomotion of the spinal cord?

the spinal cord contains central pattern generators: groups of neurons that coordinate repetitive sequences of contractions for walking.

a looser array of cells and collagenous and elastic fibers spanning the gap between the arachnoid membrane and the pia mater is referred to as the what?

the subarachnoid space (filled with cerebrospinal fluid).

what are the meninges?

the three fibrous membranes (the dura mater, arachnoid, and pia mater) that line the skull and vertebral canal and enclose the brain and spinal cord.

how much of the ventral canal does the spinal cord assume?

the upper two thirds.

reflexes require stimulation:

they are not spontaneous actions like muscle tics but responses to sensory input.

what are reflexes?

they are quick, involuntary, stereotyped reactions of glands or muscles to stimulation.

describe the composition of peripheral nerves.

they are surrounded by schwann cells forming neurilemma and myelin sheath around the axon.

why are mixed nerves considered mixed?

they contain both afferent (sensory) and efferent (motor) fibers.

reflexes are quick:

they generally involve only a few interneurons, or none, and a minimum synaptic delay.

reflexes are stereotyped:

they occur in essentially the same way every time; the response is very predictable.

reflexes are involuntary:

they occur without intent and they are difficult to surppress.

the core of gray matter consists of what?

two posterior (dorsal) horns which extend toward the posterolateral surfaces of the cord.

the posterior (dorsal) horns of gray matter extend towards what?

two thicker anterior (ventral) horns which extend toward the anterolateral surfaces.

what do purely sesnory nerves composed only of afferent fibers include nerves for?

vision and smell.

we refer to white matter as white why?

white matter has a bright, pearly white appearance due to abundantly myelinated axons.

the central area of gray matter is shaped by a butterfly and surrounded by what?

white matter in three columns.

defects of spina bifida begin how many weeks after development?

four weeks.

bundles of axons of the white matter are classified as what?

funiculi or columns.

what connects the left and right side of the spinal cord?

gray commissure (a median bridge).

the spinal cord consists of two kinds of nervous tissue called what?

gray matter and white matter.

somatic receptors:

in the skin, muscles, or tendons.

What are reflexes of the spinal cord?

involuntary responses to stimuli that are vital to posture, coordination and protection (pain or injury).

when the origin and the destination are on the same side of the body, we call this what?

ipsilateral (which does not decussate).

gray matter of the spinal cord has a dull color because?

it contains little myelin.

what is the difference between the central canal in adults versus children.

it is collapsed in most adult spinal cords, but in some places (and in young children) it remains open.

Why is the dura mater tough?

it is composed of multiple layers of dense irregular connective tissue (about as thick as a kitchen glove).

nerves have a high metabolic rate and need a plentiful blood supply that is furnished by what?

it is furnished by blood vessels that penetrate connective coverings.

folic acid is used to reduce the risk of spina bifida and has been added as what to make sure everyone consumes a healthy amount.

a B vitamin to flour.

what is the cuada equina?

a bundle of nerve roots that occupy the vertebral canal from L2 to S5.

what is in the middle of the gray commissure?

a central canal lined with ependymal cells and filled with CSF.

what is a ganglion?

a cluster of neruonsomas outside the CNS.

what is spina bifida?

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

what is a nerve?

a cordlike organ composed of numerous nerve fibers (axons) bound together by connective tissue.

describe the pia mater.

a delicate, transparent membrane composed of one or two layers of squamous to cuboidal cells and delicate collagenous and elastic fibers.

What does the dura mater form?

a loose fitting sleeve called the dural sheath that wrap the spinal cord.

integrating center:

a point of synaptic contact between neurons in gray matter of spinal cord or brainstem.

what are ganglions enveloped with?

an endoneurium continuous with that of the nerve

the epidural space is occupied by what?

blood vessels, adipose tissue, and loose connective tissue.

the white matter of the spinal cord is composed of what?

bundles of axons called tracts that carry signals from one level of the CNS to another.

what leads into and out of ganglions?

bundles of nerve fibers among neurosomas.

afferent nerve fibers:

carry information from receptors to posterior horn of spinal cord or the brainstem.

efferent nerve fibers:

carry motor impulses to muscles.

ascending tracts do what?

carry sensory information up the cord.

what are the four regions of the spinal cord?

cervical, thoracic, lumbar, and sacral region.

what does the pia mater do?

closely follows the contours of the spinal cord and continues inferiorly as a fibrous terminal filum that fuses with dura to form coccygeal ligament.

define complete transection.

complete severance of the spinal cord followed by immediate loss of motor control below lower levels of injury, above C4 poses the threat of respiratory failure, and spinal shock.

descending tracts do what?

conduct motor impulses down the cord (carry motor information down the cord).

what are the four functions of the spinal cord?

conduction, neural integration, locomotion, and reflexes.

white matter consists of bundles of axons that do what?

course up and down the spinal cord providing communication between different levels of the CNS.

decussation is what?

crossing of the midline that occurs in many tracts so that brain senses and controls contralateral side of body.

what is the spinal cord?

cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull.

What is the epineurium?

dense irregular connective tissue that wraps entire nerve.

at regular intervals along the cord, extensions of the pia mater called what extend through the arachnoid to the dura, anchoring the cord and limit side-to-side homework?

denticulate ligaments.

list the three fibrous membranes from superficial to deep.

dura mater, arachnoid mater, and pia mater.

what is the endoneurium?

external to the neurilemma, each fiber is surrounded by a basal lamina and a thin sleeve of loose connective tissue (endoneurium).

1 out of how many babies are diagnosed with spina bifida?

1 out of 1,000.

what is the average height and width of the spinal cord?

1.8cm thick and 45cm long.

in the united states, how many people are paralyzed each year by spinal trauma?

10-12,000.

how early before conception should mothers being folic acid?

3 months before conception.

how many pairs of spinal nerves are there?

31 pairs.

what percent of spinal cord trauma is caused by vehicular accidents?

55%

knowing the location and function of the spinal tracts is essential in diagnosing spinal cord injuries.

Fibers in a given tract have similar origin, destination and function.