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

___________ reflex are invariable and ______. While withdrawal reflexes can last for several seconds

Monosynaptic, brief

Define reinforcement as it pertains to spinal reflexes

Reinforcement is an enhancement of spinal reflexes; it occurs when the postsynaptic neurons enters a state of generalized facilitation caused by chronically active excitatory synapses

A weight lifter is straining to lift a barbell above his head. Shortly after he lifts it to chest height, his muscles appear to relax and he drops the barbell. which reflex has occurred?

The tendon reflex -monitors the external tension proudced during a muscular contraction and prevents tearing or breaking of the tendon.

Person with polio has lost the use of his leg muscles. In which area of his spinal cord would you expect the virus-infected motor neurons to be?

The infected neurons would be in the anterior gray horns of the spinal cord, where the cell bodies of somatic motor neurons are located.

acquired reflexes

are learned and typically are more complex

Spinal nerves are called mixed because they

contain sensory and motor fibers

The ventral rot of each spinal segment

control peripheral effectors contain axons of somatic and visceral motor neurons

visceral reflexes

control the activities of other systems

Somatic reflexes

control the skeletal muscles

The filum terminale ( a strand of fibrous tissue), which originates at the ________ _________ ultimately becomes part of the _________ ___________

conus medullaris coccygeal ligament

polysynaptic reflex

has at least one interneuron between the sensory afferent and motor efferent, there is a large delay between stimulus and response

Gray matter is the region of _______ and _________ initiation, and white matter carries information from place to place

integration and command

Neuronal pools are functional groups of ________ neurons

interconnected

the stretch, tendon, and withdrawal reflexes involve _________ reflex arcs

ipsilateral (ipsi same, lateral side) -the sensory stimulus and motor response occur at the same side of the body

Define neuronal pool

is a functional group of interconnected neurons organized within the CNS

flexor reflex

is a withdrawal reflex affecting the muscle of a limb. the crossed extensor reflex complements withdrawal reflexes

gray matter

is the region of integration and command initiation

Reflexes are ______, automatic responses to ________

rapid stimuli

Stretch reflex

(patellar, knee-jerk) is a monosynaptic reflex that automatically regulates skeletal muscle length and muscle tone.

There are __ __ pair of spinal nerves.

31

summarize the stretch reflex specifically the patellar reflex

-monosynaptic reflex -the stimulus (increasing the muscle length) activates a sensory neuron, which triggers an immediate motor response (contraction of the stretched muscle) that counteracts the stimulus.

Name the five circuit patterns and their functions in the neuronal pools

1-Divergence: a mechanism for spreading stimulation for multiple neurons or neuronal pool in the CNS 2-Convergence: a mechanism for providing input to a single neuron from multiple sources 3-Serial processing: Neurons or pools work sequentially 4-Neurons or pools process the same information simultaneously 5-Reverberation: a positive feedback mechanism

Explain the five steps in a reflex arc

1-arrival of stimulus and activation of receptor 2-Activation of sensory neuron 3-information processing to CNS 4-Activation of a motor neuron 5-response to effector

list the four things all polysynaptic reflex have

1-involve pools of interneurons 2-are intersegmental in distribution (in which many segments interact to produce a coordinated motor response) 3-Involve reciprocal inhibition 4-have reverberating circuits, which prolongs the reflexive motor response.

explain the four steps in sensory information processing to spinal cord

1-the sympathetic nerve carries sensory information from the visceral organs 2-the ventral ramus carries sensory information from the ventrolateral body surface structures in the body wall, and the limbs 3-the dorsal ramus carries sensory information from the skin and skeletal muscle of the back 4-the dorsal root of each spinal nerve carries sensory information to the spinal cord. *A spinal nerve collects sensory information from peripheral structures and delivers it to sensory nuclei in the thoracic or superior lumbar segments of the spinal cord. The dorsal and ventral and white rami also contain sensory fibers

List seven steps in motor commands

1-the ventral root of each spinal nerve contain the axons of somatic motor and visceral motor neurons 2-the spinal nerve forms just lateral to the intervertebral foramen, where the dorsal and ventral root unite 3-the dorsal ramus contains somatic motor and visceral motor fibers that innervate the skin and skeletal muscle of back 4-the axons in the relatively large ventral ramus supply the ventrolateral body surface, structures in the body wall, and limbs 5-The white ramus is the first branch from the spinal nerve and carries visceral motor fibers to nearby sympatheic ganglion. These preganglionic axons are myelinated, this branch has a light color and is therefore known as the white ramus 6-the gray ramus contains postganglionic fibers that innervate glands and smooth muscles in the body wall or limbs. These fibers are unmyelinated and have a dark gray color. 7-a sympatheic nerve contains preganglionic and postganglionic fibers innervating structures in the thoracic cavity *A spinal nerve distributes motor commands that originate in motor nuclei of the thoracic or superior lumbar segments of the spinal cord.

what are the four classifications that reflexes are based on?

1-their development 2-nature of the resulting motor response 3-the complexity of the neural circuit involved 4-the site of information processing

Identify the basic characteristics of polysynaptic reflexes

All polysynaptic reflexes involve pools of interneurons, are intersegmental in distribution and involve reciprocal inhibition

injury to which of the nerve plexuses would interfere with the ability breathe?

Damage to the cervical plexus, more specifically to the phrenic nerve

During a withdrawal reflex of the foot, what happens to the limb on the side opposite the stimulus? what is this response called?

During a withdrawal reflex, the limb on the opposite side is extended. This response is called a crossed extensor reflex.

Differentiate between sensory nuclei and motor nuclei

Sensory nuclei receive and relay sensory information from peripheral receptors. Motor nuclei issue motor commands to peripheral effectors

Nerve plexus

a complex, interwoven network of nerves

A disease that damages myelin sheaths would affect which portion of the spinal cord?

a disease the damages myelin sheaths would affect the columns in the white matter of the spinal cord, because the columns are composed of bundles of myelinated axons

neuronal pool

a functional group of interconnected neurons

Define a reflex

a rapid, automatic response to a specific stimulus. Important mechanism for maintaining homeostasis

what does a positive Babinski reflex show?

abnormal in adults; it indicated possible damage to descending tracts in the spinal cord

gray commissures

contain axons that cross from one side of the spinal cord to the other

white matter

carries information from place to place

Name the four major plexus

cervical, brachial, lumbar, sacral

The white matter can be divided into six _____(funiculi. each of which contain ______(fasciculi).

columns Tracts

Compression of which nerve produces the sensation that your leg has "fallen asleep"?

compression of the sciatic nerve produces the sensation that your leg has "fallen asleep"

side to side movements of the spinal cord are prevented by

denticulate ligaments

A sensory region monitored by the dorsal rami of a single spinal segment is

dermatome

dermatome

each pair of nerves monitors a region of the body surface

The adult spinal cord includes two localized _______, which provide innervation to the limbs. The spinal cord has 31 segments, each associated with a pair of dorsal roots and a pair of ______ ______

enlargements ventral roots

Denticulate ligaments

extend from the pia mater to the dura mater

Anterior gray horns

function in somatic control

Tendon reflex

monitors the tension produced during muscular contractions and prevents damage to tendons

Withdrawal reflexes

move affected portions of the body away from a source of stimulation

what sensory receptors are involved with the stretch reflex?

muscle spindles

An example of a stretch reflex triggered by passive muscle movement is the

patellar reflex

Spinal nerves form ______ that are named according to their level of emergence from the vertebral canal.

plexuses

facilitation can produce an enhancement of spinal reflexes know as _______. Spinal reflexes may also be inhibited, as when the _____ _____ in adults replaces the ____ ______sign

reinforcement plantar reflex babinski sign

descending tracts

relay information from the brain to the spinal cord

Ascending tracts

relay information from the spinal to the brain

Innate reflexes

result from genetically determined connections that form between neurons during development

Posterior gray horns contain

somatic and visceral sensory nuclei

why do cervical nerves outnumber cervical vertebrae?

the first cervical nerve exits supeiror to vertebra C1 (between the skull and vertebra); the last nerve exists inferior to C7. there are thus 8 cervical nerves but only 7 cervical vertebrae

monosynaptic reflex

the simplest reflex arc-a sensory neuron synapses directly on a motor neuron, which acts as the processing center

What is the minimum number of neurons in a reflex arc?

two. One must be sensory neurons that brings the impulses to the CNS, and the other a motor neuron that transmits a response to the effector

lateral gray horns contain

visceral motor neurons

for the patellar (knee-jerk) reflex, how would the stimulation of the muscle spindle by gamma motor neurons affect the speed of the reflex?

when intrafusal fibers are stimulated by gamma motor neurons, the muscle spindles become more sensitive. As a result, little if any stretching stimulus would be needed to stimulate the contraction of the quadriceps muscles in the patellar reflex. The reflex response would appear more quickly.

A typical spinal nerve has a ____ ____ (containing myelinated axons), a _____ ______ (containing umyelinated fibers that innervate glands and smooth muscles in the body wall or limbs), a ____ _______ (providing sensory and motor innervation to the skin and muscles of the back),and a _____ ______(supplying the ventrolateral body surface, strucutres in the body wall, and the limbs)

white ramus gray ramus dorsal ramus ventral ramus

An anesthetic blocks the function of the dorsal rami of the cervical spinal nerves. Which areas of the body will be affected?

would affect the skin and muscles of the back of the neck and the shoulders