Lecture Connect 17: The Spinal Cord and Somatic Reflexes

What are the four components of a monosynaptic somatic reflex arc?

-Efferent nerve fiber -Skeletal muscle -Receptor in skin, muscle or tendon -Afferent nerve fiber

Place the components of a reflex arc in order.

1. receptor 2. afferent nerve fiber 3. integration center 4. efferent nerve fiber 5. effector

The spinoreticular tract is found in which columns of the spinal cord?

Anterior and lateral

Within the spinal cord, which tracts carry information up to the brain?

Ascending

Where do signals ascending through the spinocerebellar tract terminate?

Cerebellum

In response to stretching, a muscle reflexively does which of the following?

Contracts

Which tract will have its origin and destination of opposite sides of the body?

Contralateral

Which tract carries signals for precise, finely coordinated limb movements?

Corticospinal

In which reflex does a contralateral extensor muscle contract?

Crossed extension

What factor accounts for the fact that the right side of the brain communicates with the left side of the body, and vice versa?

Decussation

Which carries the nerve signal to the effector in a reflex arc?

Efferent nerve fiber

Where is the origin of sensory signals carried by the cuneate fasciculus?

From vertebra T6 and up

Where do the nerve fibers of the gracile fasciculus terminate in the medulla oblongata?

Gracile nucleus

Which stimulus causes a muscle to reflexively contract?

Increased stretch

Name the fiber type that has sarcomeres at the ends of the cell, but lack sarcomeres at the middle.

Intrafusal fibers

Within a muscle, how are intrafusal fibers structurally different from extrafusal fibers?

Intrafusal fibers have sarcomeres at their ends; the middle lacks sarcomeres.

What do muscle spindles monitor?

Muscle length and body movements

Where do the first-order neurons of the spinocerebellar tract originate?

Muscles and tendons

What is a reflex involving one or more interneurons called?

Polysynaptic

Muscle spindles are classified as what type of receptor?

Proprioceptor

Which accurately describes a reflex?

Quick, involuntary, stereotyped

Which tract originates in the reticular formation?

Reticulospinal

Which tracts carry signals that control muscles of the upper and lower limbs, especially for posture and balance?

Reticulospinal

Where are the receptors for somatic reflexes found?

Skin, muscle, and tendons

Which is responsible for the inhibition of antagonistic contraction during a reflex response?

Spinal cord interneurons inhibit alpha neurons to the antagonists.

Which neurons would need to be inhibited in order for reciprocal inhibition to occur?

The alpha motor neurons to the antagonistic muscle

In descending pathways, which motor neurons have their somas in the cerebral cortex or brainstem?

Upper

What is the source of the sensory signals carried by the cuneate fasciculus?

Upper limbs and chest

A reflex in which a contralateral extensor muscle is contracted is called a ____________ extension reflex.

crossed

Because the nerve tracts of the spinal cord undergo ____________, the right side of the brain communicates with the left side of the body, and vice versa.

decussation

True or false: Conscious awareness of a stimulus is required for a reflex response to occur.

false

In a sensory pathway, which neuron detects the stimulus and transmits the signal to the spinal cord or brainstem?

first

Which order neurons of the spinocerebellar tract originate at muscles and tendons?

first

The nerve fibers of the gracile fasciculus terminate at the ____________ nucleus of the medulla oblongata.

gracile

Fibers from the cuneate fasciculus end on the ______ side of the medulla oblongata.

ipsilateral

Conscious awareness of the stimulus ______ required for a reflex response to occur.

is not

In descending pathways, the upper motor neurons synapse with ______ motor neurons in the brainstem or spinal cord.

lower

In descending tracts, which motor neuron innervates the target organ?

lower

The ______ motor neurons (which are the motor neurons connecting the brainstem and spinal cord to muscle fibers) of the descending pathway innervate skeletal muscle.

lower

A __________ reflex arc consists of only one synapse between two neurons

monosynaptic

Which type of reflex arc consists of only an afferent neuron and an efferent neuron?

monosynaptic

Within the spinal cord, what type of information do the descending tracts carry?

motor

Which are functions of the spinal cord?

neural integration, reflexes, locomotion, conduction

The spinoreticular tract carries what type of signals?

pain

The third-order neurons of the spinoreticular tract runs from the ______ to the thalamus.

pons

properties of a reflex

requires stimulation, quick, involuntary, stereotyped

In a sensory pathway, which neurons run from the spinal cord or brainstem to the thalamus?

secondary

____________ reflexes use receptors located in the skin, muscle, and tendons.

somatic

Signals for proprioception are carried by the anterior and posterior __________ tract.

spinocerebellar

___________ reflex occurs in response to excessive tension on a tendon

tendon

Where do the third-order neurons of the spinoreticular tract run from the pons to?

thalamus

In a sensory pathway, which neurons run from the thalamus to the sensory cerebral cortex?

third order

Consider the two motor neurons that form descending pathways. The neurons called the ___________ motor neurons have their somas in the cerebral cortex or brainstem.

upper