Chapter 13: The Spinal Cord And Spinal Nerves

Question 1

Where does the spinal cord extend to?

Answer 1

The spinal cord begins at the medulla onlongata and it ends at the conus medullaris

Question 2

Cauda equina

Answer 2

A bundle of spinal nerves that exit the spinal cord at the conus medullaris

(Horses tail)

Question 3

Grey commisure

Answer 3

The connection between the 2 sides of grey matter.

(The body of the butterfly)

Question 4

Grey matter

Answer 4

Found on the inside of the spinal cord (shaped like a butterfly). It is full of neuron cell bodies and dendrites.

Arranged by anterior, lateral, posterior horns.

Note: lateral horns only found in the thoracic and abdominal region)

Question 5

White matter

Answer 5

Surrounds the grey matter. It is full of neuron axons

Arranged by anterior, lateral, posterior columns

Question 6

Spinal nerves

Answer 6

31 pairs that arise from the spinal cord.

They are paths of communication between the spinal cord and specific regions of the body.

Contains both sensory and motor axons since there are 2 points of attachment to the spinal cord. (Dorsal and ventral roots)

Dorsal root - carries sensory (afferent) impulses
Ventral root - carries motor (efferent) impulses
The roots unite to form 1 spinal nerve with 2 different tracts

Question 7

Dorsal root ganglion

Answer 7

A bulge in the dorsal root which contains cell bodies (somas) of sensory neurons

Question 8

Nerve structure

Answer 8

Each nerve is wrapped in protective connective tissue layers

Endoneurium - enclosed each axon
Perineurium - around a nerve fascicle (bundle)
Epineurium - surrounds all fascicles (entire nerve)

Question 9

What are the 2 main functions of the spinal cord

Answer 9

1. Provide a conduction pathway (help connect the rest of the body to the brain)
2. Serves as an integration centre for spinal reflexes

Question 10

Ascending pathways

Answer 10

The term used for sensory input that travels along tracts towards the brain

(i.e. from the rest of the body ascending up to the brain)

Question 11

Descending pathways

Answer 11

The term used for motor input that travels along tracts towards skeletal muscle and other effectors

(i.e. from the brain descending to the rest of the body)

Question 12

Decussate

Answer 12

At some point in their pathway, many of the axons in the tracts cross over. They decussate.

Usually happens at the medulla oblongata

Question 13

How is a tract named?

Answer 13

1. By its position in the white matter (anterior, lateral, posterior)
2. Where is begins and ends
3. Direction of impulse (up or down)

Ex. Lateral spinothalamic tract
1. Lateral column of white matter
2. Beings in spinal cord ends in thalamus
3. Goes up (ascending) so it is sensory

Question 14

Ascending tracts

Answer 14

Function to keep the brain updated about conscious changes in the body’s external and internal environments by using general senses and receptors. (5 senses + temp, pain, etc.)

Question 15

Lateral Spinothalamic tract
(As an example of what an ascending tract looks like)

Answer 15

This tract that conveys sensory info for touch (like tickling) for the limbs, trunk, neck, back of head.

Involves 3 neurons:
First order neuron - will conduct the sensory info from the receptor to the spinal cord.
Second order neuron - conducts the impulse to the thalamus.
Third order neuron - conducts the impulse to the primary somatosensory area of the cerebrum.

Question 16

Descending tracts

Answer 16

Function to convert motor output down from the brain to effectors

Question 17

Lateral Corticospinal Tract
(As an example of what a descending tract looks like)

Answer 17

This tract brings motor output from the cerebral cortex (direct pathway) to skeletal muscles.

Includes 2 motor neurons called upper and lower neurons. And two types of descending pathways to skeletal muscle called direct and indirect.

Upper motor neuron - has its cell body in the cerebral cortex (a direct pathway), or in the brainstem (a indirect pathway)
Lower motor neuron - has its cell body in the brainstem or spinal cord.

Question 18

Direct descending pathway

Answer 18

Impulse comes form the cerebral cortex and causes voluntary movements of skeletal muscles

Question 19

Indirect descending pathways

Answer 19

Impulses come from somewhere in the brainstem and causes involuntary movements of skeletal muscles (such as keeping the head up)

Question 20

Reflex

Answer 20

A rapid, involuntary, predictable motor response to a certain stimulus.

2 kinds:
1. Somatic reflex - involves the contraction of skeletal muscle.
2. Autonomic reflex - involves the response of smooth and cardiac muscle, and glands.

Question 21

The steps of the reflex arc

Answer 21

1. Sensory receptor
2. Sensory (afferent) neuron
3. Integrating centre
4. Motor (efferent) neuron
5. Effector (usually a muscle)

Question 22

Inborn reflexes

Answer 22

You don’t have to have any prior experience to the stimulus, but the response is hardwired into your DNA

Ex. removing hand from a hot surface, blinking, swallowing

Question 23

Learned reflexes

Answer 23

Reflexes that have to be learned in order to become natural

Ex. Slamming the breaks on a car

Question 24

The stretch reflex

Answer 24

A somatic reflex

• the stretching of a muscle stimulates a sensory receptor (muscle spindle)
• the muscle spindle monitors changes in the length of the muscle
• the reflex response in contraction of the skeletal muscles

Question 25

Why do medical professionals test reflexes?

Answer 25

Because reflexes have predictable responses, so doctors can use them to test the health of the nervous system.

An abnormal response to a reflex test can help doctors diagnose a patient

Question 26

Monosynaptic reflex

Answer 26

The sensory neuron goes in an synapses directly with the motor neuron

Question 27

Polysynaptic reflex

Answer 27

The sensory neuron and synapses with an interneuron, and the interneuron synapses with the motor neurons