Chapter 13: The Spinal Cord and Spinal Nerves

Question 1

Spinal chord start and end

Answer 1

• Cord extends from the medulla oblongata to the superior border of the second lumbar vertebra
• It terminates at the conus medullaris

Question 2

A bundle of spinal nerves called the _____ exit the cord at the conus medullaris

Answer 2

cauda equina

Question 3

List the spinal nerve groups and how many in each group

Answer 3

cervical - 8
thoracic - 12
lumbar - 5
sacral -5
coccygeal - 1

Question 4

Spinal Nerves

Answer 4

• They are paths of communication between the spinal cord and specific regions of the body.
• There are 31 pairs of spinal nerves that arise from the spinal cord
• They are mixed nerves containing both sensory & motor axons
• Nerves attach to the cord by a posterior (dorsal) root & and an anterior (ventral) root
• doral and ventral roots unite to form a spinal nerve which then emerges from the intervertebral foramen

Question 5

Each nerve in the PNS is wrapped in protective connective tissue coverings
-list 3

Answer 5

Endoneurium → encloses each axon
Perineurium → around a nerve fascicle (bundle)
Epineurium → surrounds all fascicles

Question 6

Function of Spinal Cord - 2

Answer 6

Provides a conduction pathway

Serves as an integration centre for spinal reflexes

Question 7

Conduction Pathways

Answer 7

• Sensory input travels along tracts toward the brain (ascending pathways)
• Motor output travels along tracts toward skeletal muscle & other effectors (descending pathways)
• Many of the axons in the tracts cross-over (decussate) at some point in their pathway

Question 8

Define decussate

Answer 8

Many of the axons in the spinal tracts cross-over (decussate) at some point in their pathway

Question 9

How are spinal tracts named

Answer 9

• Its position in the white matter
• Where it begins & ends
• Direction of impulse (up or down)

Question 10

Lateral spinothalamic tract

Answer 10

Located in the lateral column of white matter
Begins in spinal cord
Ends in thalamus
Is a sensory (ascending) tract

Question 11

Anterior (Ventral) corticospinal tract

Answer 11

Located in the anterior column of white matter
Begins in cerebral cortex
Ends in spinal cord
Is a motor (descending) tract

Question 12

Ascending Tracts

Answer 12

• Contain axons that convey sensory input up to the brain
• They keep the CNS informed about changes in the body’s external & internal environments
• Involves general senses (tactile, temp., pain, proprioception) & visceral senses (receptors within internal organs)
• Also involves special senses (smell, taste, vision, hearing, equilibrium)
• ex. Lateral Spinothalamic Tract

Question 13

Ascending Tracts involves 3 successive neurons:

Answer 13

i) First-order neuron conducts the sensory info from the receptor to the spinal cord
ii) Second-order neuron conducts the impulse to the thalamus
iii) Third-order neuron conducts the impulse to the primary somatosensory area of the cerebrum

Question 14

Descending Tracts

Answer 14

They contain axons that convey motor output down to effectors
Ex. Lateral Corticospinal Tract

There are two types of descending pathways to skeletal muscle:

i) Direct - have nerve impulse conning from cerebral cortex and go to skeletal muscle to control or have voluntary movements take place
ii) Indirect - have nerve impulse coming from brain stem and go to skeletal muscle to controls automatic movement of skeletal muscle (muscle tone, posture, balance)

Question 15

Desending tracts involve Includes 2 motor neurons

Answer 15

Upper motor neuron: has its cell body in the cerebral cortex (direct pathway) OR in the brainstem (indirect pathway)

Lower motor neuron: has its cell body in the brainstem or spinal cord
innervates the skeletal muscle

Question 16

Direct pathway

Answer 16

Direct - have nerve impulse conning from cerebral cortex and go to skeletal muscle to control or have voluntary movements take place

Question 17

Indirect pathway

Answer 17

Indirect - have nerve impulse coming from brain stem and go to skeletal muscle to controls automatic movement of skeletal muscle (muscle tone, posture, balance)

Question 18

2 kinds of reflex

Answer 18

a) Somatic reflex → involves contraction of skeletal muscle

b) Autonomic reflex → involves the response of smooth muscle, cardiac muscle, & glands

Question 19

Reflex Centre

Answer 19

• Spinal cord is an integration centre for reflex arcs
• A reflex is a rapid, involuntary, & predictable motor response to a certain stimulus
• Reflexes occur over specific neural pathways called reflex arcs
• A reflex arc includes 5 components:
Sensory receptor
Sensory (afferent) neuron
Integrating centre
Motor (efferent) neuron
Effector

Question 20

Why do medical professionals test reflexes?

Answer 20

• Because reflexes have predictable responses, doctors can use them to assess the health of the nervous system.
• An abnormal response (or lack of response) to a reflex test can help doctors diagnose disease in a patient.
• Ex. Automimic test done is pupillary autonomic test which is where they shine the light in your eye and the normal response is your pupil constricts to limit amount of light that cones in (to much light can damage your retina)
• You can tell that somethings wrong and can guide you on what to do next.