Section 3

Question 1

True or false: the spinal cord is encapsulated by the meninges.

Answer 1

True. This creates an extracellular environment unique from the rest of the body. Additional physical protection is provided by the vertebrae.

Question 2

True or False: Grey matter contains nerve cell bodies, short interneurons, and glial cells.

Answer 2

True.

Question 3

What does the central canal within grey matter contain?
a) Blood cells
b) Cerebrospinal fluid
c) Hormones
d) Neurons

Answer 3

b) Cerebrospinal fluid (CSF). The central canal within grey matter is filled with CSF.

Question 4

How can each half of grey matter be divided?
a) Into layers
b) Into regions called horns
c) Into branches
d) Into lobes

Answer 4

b) Into regions called horns. Each half of grey matter can be divided into regions called horns, which differ in the cell bodies they contain.

Question 5

The white matter consists of bundles of nerve fibers or axons. Each bundle is connected to a specific region of the brain to transmit information from the brain to the periphery (descending tracts of efferent neurons) or from the periphery to the brain (ascending tracts of afferent neurons). The ascending and descending tracts are named for their point of origin and termination.

Question 6

True or False: White matter consists of nerve cell bodies.

Answer 6

False. White matter consists of bundles of nerve fibers or axons.

Question 7

What is the primary function of the bundles of nerve fibers in white matter?

Answer 7

The bundles of nerve fibers in white matter transmit information from the brain to the periphery (descending tracts of efferent neurons) or from the periphery to the brain (ascending tracts of afferent neurons).

Question 8

How are the ascending and descending tracts in white matter named?

Answer 8

The ascending and descending tracts in white matter are named based on their point of origin and termination.

Question 9

Explain the main function of white matter in the nervous system.

Answer 9

The main function of white matter is to transmit information between the brain and the periphery through bundles of axons, serving as highways for signals to travel.

Question 10

Afferent and efferent connections: the ventral horn contains the cell bodies of efferent motor neurons and the lateral horn contains cell bodies for the autonomic (involuntary or unconscious, a part of the PNS) efferent fibres. The cell bodies for the afferent nerves are located outside of the spinal cord in regions called dorsal root ganglia, dorsal meaning located closer to the back of an animal. Ganglia are collections of neuron cell bodies. These cell bodies receive information from the periphery and relay it to the interneurons of the dorsal horn within the spinal cord grey matter. The dorsal root ganglia are connected to the spinal cord by two different pathways, the dorsal root containing the afferent input, and the ventral (towards the abdomen of an animal) root containing the efferent output. Note the efferent cell bodies are located within the cord. The afferent and efferent form nerves, which together connect the CNS to the rest of the body via the PNS.

Question 11

The ventral horn contains the cell bodies of ______________ motor neurons.

Answer 11

The ventral horn contains the cell bodies of efferent motor neurons.

Question 12

Where are the cell bodies for the autonomic efferent fibers located?
a) Dorsal root ganglia
b) Ventral horn
c) Lateral horn
d) Dorsal horn

Answer 12

c) Lateral horn. The cell bodies for autonomic efferent fibers are found in the lateral horn.

Question 13

What is the function of dorsal root ganglia?
a) They contain afferent cell bodies.
b) They contain efferent cell bodies.
c) They are part of the spinal cord.
d) They transmit information from the brain to the periphery.

Answer 13

a) They contain afferent cell bodies. Dorsal root ganglia house the cell bodies for afferent nerves.

Question 14

How are dorsal root ganglia connected to the spinal cord?
a) Through the dorsal root containing efferent input.
b) Through the ventral root containing afferent output.
c) Through the lateral root containing autonomic input.
d) Through both the dorsal and ventral roots.

Answer 14

d) Through both the dorsal and ventral roots. Dorsal root ganglia are connected to the spinal cord via both dorsal (afferent input) and ventral (efferent output) roots.

Question 15

What is the role of afferent and efferent nerves in connecting the central nervous system (CNS) to the rest of the body?

Answer 15

Afferent and efferent nerves form nerves that connect the CNS to the rest of the body via the peripheral nervous system (PNS). They transmit information to and from the CNS and play a crucial role in sensory perception and motor control.

Question 16

The structure of a nerve: A nerve is a bundle of peripheral afferent and efferent axons, covered in connective tissues, that are following the same pathway. Although these axons share a common pathway, they are not communicating with each other. It is also important to note that nerves do not contain the cell bodies of neurons. These are instead found within the CNS, or the ganglia in the PNS.

A single nerve contains several nerve fascicles which are bundles of myelinated or unmyelinated axons in connective tissue, as well as blood vessels.

Question 17

True or False: Nerves contain the cell bodies of neurons.

Answer 17

False. Nerves do not contain the cell bodies of neurons. These are instead found within the CNS, or the ganglia in the PNS.

Question 18

What primary function do the connective tissues in a nerve serve with respect to the axons?

Answer 18

The primary function of the connective tissues in a nerve, in relation to the axons (peripheral afferent and efferent), is to provide structural support and insulation for the axons within the nerve.

Question 19

A single nerve contains several nerve ______________.

Answer 19

fascicles. A single nerve contains several nerve fascicles.

Question 20

True or False: Axons within a nerve communicate with each other.

Answer 20

False. Although axons within a nerve share a common pathway, they do not communicate with each other.

Question 21

Where are the cell bodies of neurons found in relation to nerves?

Answer 21

The cell bodies of neurons are found within the central nervous system (CNS) or the ganglia in the peripheral nervous system (PNS).

Question 22

What do nerve fascicles contain?
a) Cell bodies of neurons
b) Connective tissue
c) Myelinated or unmyelinated axons
d) Blood vessels

Answer 22

c) Myelinated or unmyelinated axons in connective tissue. Nerve fascicles contain bundles of myelinated or unmyelinated axons in connective tissue, along with blood vessels.

Question 23

Along the vertebral column, paired spinal nerves project from between vertebrae. These nerves are named according to the regions they innervate (innervate means to synapse with another tissue)

Question 24

What do paired spinal nerves project from between?

Answer 24

Paired spinal nerves project from between vertebrae along the vertebral column.

Question 25

Where do cervical nerves emerge from, and how many pairs are there?

Answer 25

There are 8 pairs and they emerge from the neck.

Question 26

Where do thoracic nerves emerge from, and how many pairs are there?

Answer 26

There are 12 pairs and they emerge from the chest.

Question 27

Where do lumbar nerves emerge from, and how many pairs are there?

Answer 27

There are 5 pairs, and they emerge from the abdomen.

Question 28

Where do sacral nerves emerge from, and how many pairs are there?

Answer 28

There are 5 pairs and they emerge from the pelvis

Question 29

Where do coccygeal nerves emerge from, and how many pairs are there?

Answer 29

There is 1 pair and it emerges from the tailbone.

Question 30

What are the two principle functions of the spinal cord?

Answer 30

1. Serves as a communication pathway between the brain and the periphery (the body).
2. Integrating certain afferent inputs and efferent outputs which bypass the brain itself. These are called spinal reflexes, and can either be simple reflexes (unlearned responses such as pulling your hand away from something hot) or acquired reflexes (the result of practice, training, or conditioning, e.g. salivating over your favourite food).

Question 31

What is the reflex arc?

Answer 31

The neural pathway that controls a reflex

Question 32

What is the reflex arcs pathway comprised of?

Answer 32

1. Receptors in the skin: the receptor senses a physical or chemical change in the environment and produces an action potential.
2. Afferent neuron: this action potential is transmitted from the receptor to the integrating centre.
3. Interneuron: aka integrating centre. It is generally within the CNS. Simple reflexes are generally integrated within the spinal cord or brainstem whereas acquired reflexes are processed in higher brain centres. The integrating center processes the signal from the afferent neuron (the message about the stimulus) and a response is initiated.
4. Efferent neuron: the response is transmitted away from the CNS to the effector.
5. Effector: It is usually a muscle or gland that is required to carry out the desired response.

Question 33

One example of a simple spinal reflex is the stretch reflex This reflex is associated with skeletal muscles, which contain stretch receptors. When a muscle is stretched, this receptor is activated and the afferent fibre terminates directly on an efferent neuron (there is no interneuron). IN turn, the efferent neuron supplying the same muscle is activated and causes the muscle to contract. This reflex acts as a negative feedback mechanism that resists passive change in muscle length. A common example of a stretch reflex is the patellar tendon reflex.

Question 34

What is one example of a simple spinal reflex associated with skeletal muscles, stretch receptors, and muscle contraction?

Answer 34

One example of a simple spinal reflex is the stretch reflex. It’s triggered by muscle stretching, activating stretch receptors. The afferent fiber directly connects to an efferent neuron (no interneuron), leading to muscle contraction. This reflex acts as a negative feedback mechanism to resist passive changes in muscle length. The patellar tendon reflex (the knee tap doctor thing) is a common example of this type of reflex.

Question 35

What is the withdrawal reflex?

Answer 35

Another type of simple spinal reflex that is considered a protective mechanism for the body.

Question 36

What are the steps of a withdrawal reflex arc when touching something hot with your finger?

Answer 36

1. Thermal pain receptors are activated in the finger
2. Action potentials are generated in the afferent pathway, which propagates impulses to the spinal cord
3. At this stage, the afferent fiber carrying the signal from the thermal pain receptors in your finger enters the spinal cord. Inside the spinal cord, this afferent fiber has the option to interact with several interneurons, which are like middleman neurons that relay messages. In this particular situation, the afferent neuron triggers different types of interneurons: i) It stimulates excitatory interneurons, which in turn activate motor neurons responsible for the biceps muscle. ii) It also activates inhibitory interneurons, which affect motor neurons responsible for the triceps muscle, causing them to relax. iii) Some interneurons continue the signal’s journey upward to the brain for further processing.
4. One efferent pathway stimulates contraction of the biceps muscle. Another efferent pathway leads to relaxation of the triceps muscle.
5. Effectors are stimulated and allows the withdrawal of the hand.

Question 37

Why is it important for the body to have reflexes independent from the brain’s direction?

Answer 37

In this way, an entire reflex arc can be contained within the spinal cord and a reaction can be initiated even before the brain is aware. Note that the brain can modify or override this reflex, but this now becomes a conscious decision. For example, when you give a blood sample, the same withdrawal reflex is present but your brain is actively overriding the inhibitory and excitatory inputs prior to the painful stimulus.