Spinal Cord and Spinal Nerves

Ascending signals in the spinal cord travel via gray matter, while descending signals travel via white matter.

“The anterior horn contains motor neurons that affect the axial muscles while the posterior horn receives information regarding touch and sensation.”

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Ascending tracts carry sensory signals up the spinal cord, descending tracts carry motor impulses down.

Gray matter = neuron cell bodies with little myelin, site of info processing.

White matter = abundantly myelinated axons, carry signals from one part of the CNS to another

Voluntary motor signals typically begin in an upper motor neuron in the thalamus.


The upper motor neuron begins with a soma in the cerebral cortex or brainstorm and has an axon that terminates on a lower motor neuron or brainstem

Most nerves are motor nerves.

Most nerves are “mixed nerves” – mix of sensory (afferent fibers) and motor (efferent fibers)

A nerve fiber is enclosed in its own fibrous sleeve called perineurium.

A perineurium surrounds a BUNDLE of nerve fibers

A ganglion is a swelling along a nerve containing the cell bodies of peripheral neurons.

A dermatome is a nerve innervating a specific region in the skin.

A dermatome is an area of the skin that is mainly supplied by a single nerve.

Posterior root ganglia contain somas of unipolar neurons.

A posterior root ganglion (or spinal ganglion) (also known as a dorsal root ganglion), is a cluster of nerve cell bodies (a ganglion) in a posterior root of a spinal nerve.

Somatic reflexes are responses of skeletal, smooth, and cardiac muscles.

Somatic reflexes are unlearned skeletal muscle reflexes that are mediated by the brainstem and spinal cord.

The stretch reflex is the tendency of a muscle to stretch when it is overcontracted.

The stretch reflex is the tendency of a muscle to CONTRACT when it is stretched.

The upper motor neurons that control skeletal muscles begin with a soma in the __________.
Precentral gyrus of the cerebrum


Many upper motor neurons synapse with lower motor neurons in the ___________.
Anterior horn
Which of the following sensory functions involves neurons in the posterior root ganglion?
Which of the following is not considered a region of the spinal cord?
Which of the following is not a function associated with the spinal cord?
Protect neurons in both the ascending and descending tracts
Which of the following fractures would be the least likely to cause a spinal cord injury?
A fracture of vertebra L4
The middle layer of the meninges is called the __________.
Arachnoid mater
Epidural anesthesia is introduced to the epidural space between the __________ to block pain signals during pregnancy.
Dural sheath and vertebral bones
Voluntary motor impulses leave the spinal cord via the _________ of gray matter.
Anterior horn

“The anterior horn contains motor neurons that affect the axial muscles while the posterior horn receives information regarding touch and sensation.”

Cerebrospinal fluid fills the space between the __________.
Arachnoid mater and pia mater
Which of the following structures is the richest in lipid content?
White matter
Which of the following is contained within gray matter?
Neurosomas, dendrites, and proximal parts of axons of neurons
Motor commands are carried by __________ from the brain along the spinal cord.
Descending tracts
Second-order neurons synapse with third-order neurons in the __________.

Ascending tracts carry SENSORY signals up the spinal cord. Sensory signals typically travel across 3 neurons from their origin in the receptors to their destination in the brain:

First-order neuron: detects a stimulus and transmits a signal to the spinal cord or brainstem
Second-order neuron: continues as far as a “gateway” called the thalamus at the upper end of the brainstem
Third-order neuron: carries the signal to cerebral cortex

Nerve fibers are insulated from one another by __________.
A ganglion is a _________.
Cluster of neurosomas in the PNS
There are __________ pairs of spinal nerves.
The connective tissue that surrounds a fascicle is called the __________.
Which of the following nerves originates in the lumbosacral plexus?
A patient with no sensation in the left thumb would most likely have nerve damage of the __________ spinal nerve.
A mixed nerve consists of both __________ and ___________.
Afferent; efferent fibers
Which of the following branches of a spinal nerve has the somas of only sensory neurons?
Posterior (dorsal) root

SENSORY = posterior root

The bundle of nerve roots that occupy the vertebral canal from L2 to S5 is called the __________.
Cauda equina
“Somatosensory” does not refer to sensory signals from __________.
The viscera
Neurosomas of the anterior root are located in the __________.
Gray matter
A __________ is a cordlike organ composed of numerous __________.
Nerve; axons
Which one of the following best describes the order of a somatic reflex?
Somatic receptor, afferent nerve fiber, interneuron, efferent nerve fiber, skeletal muscle
Which of the following is not a property of reflexes?
Reflexes do not require a stimulus.
A nurse pricks your finger to type your blood. You flinch at the pain, pulling your hand back. This is called the __________ reflex.
Flexor (withdrawal)
Reflex arcs that only use two neurons are called ____________ reflex arcs.

Only one synapse between the afferent and efferent neuron- quick

In the patellar tendon reflex arc, the patellar ligament is stretched, which stretches the quadriceps femoris muscle of the thigh. This reflex will cause the quadriceps femoris to __________ and the hamstrings to __________.
Contract; relax
Tendon organs are __________.

Proprioceptors = sense organs specialized to monitor the position and movement of body parts. Muscle spindles (stretch receptors embedded in muscles) are propioreceptors.

Tendon organs are priorioceptors located in a tendon near its junction with a muscle.

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