LEC 20 - Spinal nerves and cranial nerves

Question 1

Describe the structure and function of the dorsal root ganglion.

Answer 1

The dorsal root ganglion contains the cell bodies of pseudo-unipolar neurons, which are responsible for transmitting sensory information from the body to the spinal cord.

Question 2

How do spinal nerves function in relation to sensory and motor neurons?

Answer 2

Spinal nerves contain axons of both sensory and motor neurons, facilitating the transmission of sensory input to the central nervous system and motor output to the muscles.

Question 3

Define the roles of the ventral and dorsal roots in the spinal cord.

Answer 3

The ventral roots carry motor output from the spinal cord to the muscles, while the dorsal roots carry sensory input from the body to the spinal cord.

Question 4

Describe the function of the ventral horn neurons in the spinal cord.

Answer 4

The ventral horn neurons carry motor commands from the brain to the body, specifically through alpha motoneuron efferents.

Question 5

How is the white matter of the spinal cord organized?

Answer 5

The white matter is divided into three funiculi: the dorsal funiculus (ascending ipsilateral for fine touch), the lateral funiculus (descending corticospinal), and the anterior funiculus (ascending contralateral for crude touch).

Question 6

What horns are grey matter divided into

Answer 6

Dorsal, lateral, ventral grey gorns

Question 7

Define the role of the dorsal horn neurons in the spinal cord.

Answer 7

The dorsal horn neurons carry sensory afferent feedback, such as temperature and pain, from the body to the brain.

Question 8

Define the role of the lateral horn neurons in the spinal cord.

Answer 8

Carries ANS efferents for visceral organs

Question 9

Describe the main types of general senses and their functions.

Answer 9

General senses include nociceptors (pain receptors), thermoreceptors (sensitive to temperature changes), and mechanoreceptors (which include tactile receptors and proprioceptors). They are distributed throughout the body, primarily in the skin.

Question 10

How is information from general senses transmitted in the body?

Answer 10

Information from general senses is mainly transmitted via spinal nerves.

Question 11

Define special senses and their associated sensory receptors.

Answer 11

Special senses are sensory receptors found in the head, including olfaction (smell; chemoreceptors), gustation (taste; chemoreceptors), vision (sight; photoreceptors), and hearing & equilibrium (balance; mechanoreceptors). Information from these senses is transmitted exclusively via cranial nerves.

Question 12

How is Pain, Temperature and Itch different from touch and proprioception

Answer 12

“Potentially tissue damaging [noxious]” or “protective” senses! - from evolutionary point of view an “old system” (primitive/ancient senses)

Question 13

How are touch and proprioception different from pain and temperature senses?

Answer 13

Touch and proprioception are classified as ‘new systems’ that are not harmful and serve explorative functions, conveyed through fast pathways with myelinated axons.

Question 14

Define the pathways through which pain and touch sensations are conveyed to the brain.

Answer 14

Pain, temperature, and itch sensations are conveyed via the anterolateral (spinothalamic) pathways, while touch and proprioception are conveyed through the dorsal-column (medial-lemniscus) pathway.

Question 15

How do axon types relate to their functions?

Answer 15

Different axon types are associated with specific functions: Aα for mechanoreceptors (touch & proprioception), Aβ for temperature, Aδ for pain, and C for itch.

Question 16

Describe the composition of the dorsal columns in the spinal cord.

Answer 16

The dorsal columns are composed of the gracile and cuneate fascicles.

Question 17

How do the gracile and cuneate fascicles differ in terms of the body regions they represent?

Answer 17

The gracile fascicle contains fibers from the lower body, while the cuneate fascicle contains fibers from the upper body.

Question 18

Define the pathways associated with fine touch and crude touch in the spinal cord.

Answer 18

Fine touch is associated with the dorsal columns/medial lemniscus pathway, while crude touch is associated with the anterolateral/spinothalamic pathway.

Question 19

Describe the role of the Dorsal Column - Medial Lemniscus system in sensory processing.

Answer 19

The Dorsal Column - Medial Lemniscus system is responsible for transmitting proprioception and fine discriminative touch sensations from the body to the brain, specifically to the primary somatic sensory cortex.

Question 20

How do mechanoreceptors contribute to the sensory pathway?

Answer 20

Mechanoreceptors act as the first order neurons in the sensory pathway, detecting mechanical changes such as touch and pressure, and sending signals through the dorsal root ganglion to the central nervous system.

Question 21

Describe the components of the anterolateral system.

Answer 21

The anterolateral system includes the spinothalamic pathway, which consists of the first, second, and third order neurons, and connects to various nuclei such as the medial dorsal nucleus, ventral posterior lateral nucleus, and ventral medial posterior nucleus, ultimately projecting to the primary somatosensory cortex, insular cortex, and cingulate cortex.

Question 22

How does the spinothalamic tract function in sensory processing?

Answer 22

The spinothalamic tract is responsible for transmitting sensations of pain, temperature, itch, and crude touch from the body to the brain, facilitating the perception of these sensory modalities.

Question 23

Define the role of the dorsal columns in the nervous system.

Answer 23

The dorsal columns are involved in the transmission of fine touch, vibration, and proprioceptive information, contrasting with the anterolateral system which handles pain and temperature sensations.

Question 24

Describe the pathway of pain and temperature signals from the body to the brain.

Answer 24

Receptive organs send signals through DRG axons that terminate in the marginal zone and substantia gelatinosa. These signals then move up or down a few spinal levels via the Lissauer tract, crossover at the ventral white commissure, and ascend in the lateral spinothalamic tract. They reach the VP thalamus and then the somatosensory cortex, forming a somatotopic map.

Question 25

Define the role of the anterolateral system in sensory processing.

Answer 25

The anterolateral system, also known as the spinothalamic pathway, is responsible for transmitting pain, temperature, itch, and crude touch sensations from the body to the brain.

Question 26

How do small diameter fibers contribute to the sensory pathways in the nervous system?

Answer 26

Small diameter fibers are involved in transmitting pain and temperature signals through the anterolateral system, influencing the perception of these sensations as they ascend through the spinal cord and into the brain.

Question 27

Describe the pathway of the Dorsal-Column pathway.

Answer 27

The Dorsal-Column pathway involves three neurons: the 1st neuron is located in the dorsal root ganglion, the 2nd neuron is in the dorsal column nuclei, and the 3rd neuron is in the thalamus.

Question 28

How do the 2nd neurons in the Dorsal-Column and Anterolateral systems behave?

Answer 28

The 2nd neurons in both the Dorsal-Column and Anterolateral systems decussate to the contralateral side.

Question 29

Define the role of the thalamus in sensory pathways.

Answer 29

The thalamus serves as the 3rd neuron relay point in both the Dorsal-Column and Anterolateral systems, processing sensory information before it reaches the cortex.

Question 30

How do spinal and cranial nerves differ in terms of their fibres and innervation?

Answer 30

Spinal nerves carry both sensory and motor fibres that innervate the body from the neck down, while cranial nerves can be sensory, motor, or mixed, and innervate the head.

Question 31

What special functions do cranial nerves convey, and how do they control facial functions?

Answer 31

Cranial nerves convey special senses (smell, vision, hearing, taste, etc.) and control sensory and motor functions of the face.

Question 32

What are key characteristics of cranial nerves?

Answer 32

They are numbered I-XII, arise from the brainstem (except olfactory and optic), and emerge from the anterior surface of the brain (except trochlear nerve IV).

Question 33

What are three key differences between spinal and cranial nerves?

Answer 33

Origin: Spinal nerves originate from the spinal cord; cranial nerves originate from the brain.

Structures Innervated: Spinal nerves innervate the whole body apart from the head; cranial nerves mostly innervate the head

Question 34

What is a similarity between spinal and cranial nerves?

Answer 34

Both are peripheral nerves and contain sensory ganglia with perikarya of (pseudo)unipolar sensory nerves.