what did you learn ch. 16

A posterior root ganglion

attached to the posterior root located medial to the pedicles of the adjacent vertebrae

the posterior horns of the spinal cord

contain the axons of sensory neurons and the cell bodies of interneurons

lumbar cord part

Slightly larger than the thoracic part (11-13 mm in transverse diameter) Less oval, almost circular Relative amount of white matter is reduced both in proportion to gray matter and in comparison to cervical part Anterior and posterior horns are very large; small lateral horns present in first two sections of lumbar part only

Which of the following is not generally involved in a reflex?

inhibition of an effector by a stimulus from a motor neuron

The anterior horns of the spinal cord

primarily house the cell bodies of somatic motor neurons

a withdrawal reflex example

quickly pulling the arm away after touching something hot.

The gray matter in the spinal cord

s centrally located and shaped like an H or a butterfly

the main nerves of the sacral plexus

sciatic nerve, which divides into the tibial and common fibular nerves

The main nerves of the lumbar plexus

the femoral nerve and the obturator nerve.

Which nerve innervates the posterior thigh and leg muscles, plantar foot muscles, and skin of the sole of the foot?

tibial

sacral cord part

very small almost circular Proportion of gray matter to white matter is largest in this spinal cord part Anterior and posterior horns relatively large compared to the size of the cross section

coccygeal nerve

1 (Col)

The spinal nerves inferior to ____________ exit below the vertebra of the same number.

C8

horns

Gray matter regions on both sides are artificially separated into three projections

The anterior rami of spinal nerves T1-T11

are called intercostal nerves

the lumbar enlargement

contains the neurons that innervate the lower limbs.

thoracic nerves

12 (T1-T12)

pairs of spinal nerves

31 pairs

lumbar nerves

5 (L1-L5)

sacral nerves

5 (S1-S5)

cervical nerves

8 (C1-C8)

the cervical enlargement

Contains the neurons that innervate the upper limbs.

cervical cord part

Largest of all spinal cord parts Oval; slightly flattened on both anterior and posterior surfaces Large proportion of white matter compared to gray matter In superior segments (C1-C5), anterior horns are relatively small, and posterior horns are relatively large In inferior segments (C6-C8), anterior horns are larger and posterior horns are even more enlarged

polysynaptic reflexes

More complex neural pathways are observed which have a number of synapses involving interneurons within the reflex arc. a tad bit slower

thoracic cord part

Smaller than the cervical part (9-11 mm in transverse diameter) Oval; still slightly flattened anteriorly and posteriorly Larger proportion of white matter than gray matter Anterior and posterior horns are enlarged only in first thoracic segment; small lateral horns are visible

monosynaptic reflex

The afferent sensory axons synapse directly on the motor neurons, whose axons project to the effector. Interneurons do not function in this type of reflex

what does a posterior root ganglion contain

The cell bodies of the sensory neurons in the posterior root

the spinal cord enlargements

The cervical enlargement The lumbar enlargement

funiculi

The peripheral white matter

the three groups of funiculi in the white matter of the spinal cord

The posterior, lateral, and anterior funiculi

conus medullaris

The tapered inferior end of the spinal cord

Which statement is true about intercostal nerves?

They originate from the thoracic region of the spinal cord.

The word root commissura most nearly means

a stream

Which structure contains motor axons only?

anterior root

The radial nerve originates from the ________ plexus.

brachial

What is the collective name for all of the axons that project inferiorly from the spinal cord?

cauda equina

nerve plexuses from superior to inferior

cervical, brachial, lumbar, and sacral plexuses

What is the benefit of having an intricate nerve plexus, rather than a single nerve that innervates a structure

damage to a single segment of the spinal cord or damage to a single spinal nerve generally does not result in complete loss of innervation to a particular muscle or region of skin.

Between the dura mater and the inner walls of the vertebrae is the

epidural space

Axons cross from one side of the spinal cord to the other through a gray matter region called the

gray commisure

denticulate ligaments

help suspend and anchor the spinal cord within the middle of the vertebral canal, thus preventing potential lateral displacement of the spinal cord.

The anterior funiculi

interconnected by the white commissure.

if its receptor and effector are on the same side of the body, a reflex arc is termed ____________; if on opposite sides, it is ____________.

ipsilateral; contralateral

the gray commissure

part of the gray matter helps connect the right and left regions of gray matter a horizontal bar surrounds a narrow central canal