Peripheral Nervous System and Spinal Cord

Question 1

What types of nerves come from the 3 horns of the spinal cord?

Answer 1

Anterior/Ventral: Motor
Intermediate/Lateral: Autonomics
Posterior/Dorsal: Sensory

Question 2

Which functional components are positioned more intermediate in the spinal cord? Visceral or Somatic?

Answer 2

Visceral

Question 3

What are the 3 meninges that wrap a peripheral nerve and their order of structure?

Answer 3

Endoneurium: surround individual fibers
Perineurium: surrounds fascicles, continuous with arachnoid and blood-nerve barrier
Epineurium: around nerve trunks, provides tensile strength and continuous with dura.

Question 4

Blood supply of a nerve is between what 2 coverings?

Answer 4

Epineurium and Perineurium

Question 5

Difference between a schwann cell that makes myelin and one that does not.

Answer 5

Those that make myelin can only invest on one segment of one fiber, but those that do not can invest on multiple nerve fibers.

Question 6

What is myelin and its function?

Answer 6

It is a membrane of glial cells made of specialized lipids and proteins that insulates the axon membrane and increases conduction velocity

Question 7

What cells produce myelin in the CNS? PNS?

Answer 7

CNS-oligodendrocytes

PNS-Schwann cells

Question 8

What is the name and function of the bare segments between myelin segments?

Answer 8

Nodes of Ranvier, they function to initiate another depolarization and continue move the signal along the neuron by means of saltatory conduction.

Question 9

During saltatory conduction, where does depolarization occur, when is it renewed, and in what direction?

Answer 9

Depolarization occurs are the Nodes of Ranvier, is renewed at the next node, and can go in either direction. (The axon hillock is the site of the initial depolarization)

Question 10

Difference between oligodendrocytes and schwann cells?

Answer 10

Oligodendrocytes can myelinate segments of multiple different axons while schwann cells can only myelinate one segment of one axon

Question 11

Where does the transition from Oligodendrocytes and schwann cells generally occur?

Answer 11

Just proximal to the foramen (varies greatly)

Question 12

Result of losing a schwann cell?

Answer 12

Slower Action potential conduction velocity

Question 13

What type of fibers are associated with pain, heat, and touch?

Answer 13

small, unmyelinated or poorly myelinated axons. (epsilon or C)

Question 14

What type of fibers are large and heavily myelinated?

Answer 14

Muscle spindle primary endings (1a), golgi tendon organs (1b), and lower motor neurons (alpha)

Question 15

What type of fibers are intermediate in size and myelination?

Answer 15

Meissner and Pacinian corpuscles (Abeta) and axons to intrafusal fibers (gamma)

Question 16

What are the 5 main sensory receptor types and what do they detect?

Answer 16

Chemoreceptors: pH, taste, metabolites, etc.
Photoreceptors: light
Mechanoreceptors: movement, auditory, vesitublar (most diverse of all 5)
Nociceptors: pain
Thermoreceptors: temperature

Question 17

Muscle spindles are also what type of specialized receptors?

Answer 17

Proprioceptors (awareness in space)

Question 18

Main function of a receptor for a neuron?

Answer 18

To turn a physical stimulus into and electrical signal that the nervous system can understand

Question 19

What do receptor potentials encode?

Answer 19

They encode the intensity and duration of a stimulus

Question 20

What is a receptive field?

Answer 20

They convey information about the location of a stimulus. In more sensitive areas like the tip of a finger, there are more receptors and smaller receptor fields but in less sensitive areas like the elbow, there is larger fields and less receptors.

Question 21

How do sensory receptors adapt and what is the exception?

Answer 21

They become less sensitive to the stimulus if it is maintained. The exception is nociceptors

Question 22

At what level does adaptation occur and give examples of slow and fast adapting receptors.

Answer 22

Adaptation occurs at the receptor level but CNS can also regulate receptor sensitivity.
Slowly adapting: muscle spindle (detect static position)
Rapidly adapting: Pacinian corpuscles and hair receptors

Question 23

What are the 2 types of encapsulated receptors in muscles?

Answer 23

Muscle spindles and golgi tendon organs

Question 24

What is the function of Muscle spindles?

Answer 24

They detect Muscle length. The ends of intrafusal fibers (in a capsule) are attached to extrafusal fibers, so when the muscle stretches, so do the intrafusal fibers.

Question 25

What is the function of Golgi tendon organs?

Answer 25

They detect muscle tension and are found in muscle-tendon junctions. Sensory fibers are branched among collagen fibers in a capsule. Muscle contraction distorts the capsule, firing sensory fibers

Question 26

Is the epidural space a real or potential space and why?

Answer 26

Yes, it is a real space because the dura mater of the spinal cord does not attach to the vertebrae.

Question 27

Describe the structure and organization of spinal nerves.

Answer 27

Dorsal and Ventral rootlets coalesce to form dorsal and ventral roots, which then coalesce to form the spinal nerves. (Each dorsal root has a dorsal root ganglion, containing cell bodies of sensory neurons)

Question 28

What is the exception to dermatomes and clinical significance?

Answer 28

Each spinal nerve innervates one dermatome except C1, which has a rudimentary dorsal root. Clinically, they allow diagnosis of the level of a cord lesion/sensory deficit

Question 29

What are spinal cord enlargements and where are they located?

Answer 29

They are areas with more motor neurons to supply the upper and lower extremities (larger anterior horn) Cervical: C5-T1 Lumbar: L2-S3

Question 30

What is the conus medullar is and filum terminal?

Answer 30

Conus medullaris is the caudal end of the cord | Filum terminalis is the extension of pia that terminates in dura that is attached to the coccyx.

Question 31

Describe the transition of spinal cord structure as you descend in levels

Answer 31

White matter is greatest at Cervical levels but decreases as you go down. The overall shape changes from oblong at cervical levels to circular at lower levels. Posterior intermediate sulcus disappears around T6. Cauda equina begins to appear at the Lumbosaccral level.

Question 32

What travels through the anterior median fissure of the spinal cord?

Answer 32

Anterior spinal artery (br. of vertebral artery)

Question 33

The 2 sides of the spinal cord communicate through what?

Answer 33

Anterior white commisure, which is at the end of the anterior median fissure

Question 34

What are 2 significant structures in the posterior horn and their function?

Answer 34

Substantia gelatinosa (Laminae II): pain and temp. Lissauer's tract: finely myelinated and unmyelinated fibers (pain) *They are very large at lumbar levels*

Question 35

Function of lower motor (alpha) neurons and location of their clusters in the anterior horn?

Answer 35

They function as the only means to move a muscle. Axial muscles are innervated by medial clusters, limb muscles are innervated by lateral clusters.

Question 36

What type of neurons innervate muscle spindles? Muscle fibers?

Answer 36

Spindles: Gamma-motor neurons | Fibers- Alpha motor neurons

Question 37

What are the 2 specialized columns in the anterior horn at cervical levels?

Answer 37

``` Spinal accessory nucleus (caudal medulla-C5) Phrenic nucleus (C3,4,5) ```

Question 38

Where are preganglionic sympathetic and parasympathetic neurons located in the spinal cord and how do they leave?

Answer 38

Sympathetic: T1-L3 (form distinct horn) Parasympathetic: S2-S4 (no distinct horn) *Both are located in the intermediate/lateral horn and exit via anterior/ventral roots

Question 39

Function and location of Clarke's nucleus.

Answer 39

Collection of neurons on medial surface of intermediate gray matter from T1-L2. It is a relay nucleus for transmission of info to cerebellum, proprioceptive info from leg.

Question 40

Posterior intermediate sulcus separates what 2 structures?

Answer 40

Fasciculus cuneatus and gracilis (sensory fibers for proprioception and tactile info)

Question 41

What is the corticospinal tract?

Answer 41

Axons from upper motor neurons in cortex that tell lower motor neurons what to do (lateral funiculi)

Question 42

Describe positional changes of the spinal cord.

Answer 42

At 3 months pregnant, the cord extends the length of the embryo and nerves exit intervertebral foramen at level of origin. When they are born, the end of the cord moves upward and nerves run obliquely. Cauda equine travels from end of cord (L1/2) to end or dura at S2

Question 43

Where is a lumbar puncture performed at?

Answer 43

L4-5 (sometimes 2-3?) (caudal equine)

Question 44

What is the other meningeal anchor of spinal cord besides film terminal?

Answer 44

Denticulate ligaments, pia-arachnoid extensions. They prevent the cord from rotating and are located in the lateral aspect of cord.

Question 45

What do all reflexes involve?

Answer 45

A receptor, an afferent neuron (cell body in dorsal root ganglion), and an efferent neuron (cell body in CNS)

Question 46

What is the ONLY reflex that doesn't involve interneurons?

Answer 46

The stretch reflex (tapping knee)

Question 47

Describe stretch reflex.

Answer 47

Monosynaptic, only 2 neurons and 1 synapse. Tapping patellar tendon stretches the spindles slightly, which goes into cord and excites alpha motor neuron to extend leg. (important in movements and maintaing posture)

Question 48

What can golgi tendon organs (1b) have the capability to do during reflexes?

Answer 48

They have inhibitory and stimulating interneurons between afferent/efferent neurons. Thought to contribute to fine adjustment of force in muscle contraction during activity.

Question 49

What do spinal arteries get help from in supplying the cord? Location of biggest one?

Answer 49

Radicular arteries, which are branches of intercostal arteries. The biggest one is the Artery of Adamkiewicz at level T12.