Week 10: Lecture 1 - Anatomy of Spinal Nerves

Question 1

What system are spinal nerves part of, and what is their function?

Answer 1

Spinal nerves are part of the Peripheral Nervous System (PNS). They carry sensory information from the periphery to the CNS and motor commands from the CNS to peripheral muscles.

Question 2

What types of fibers are found in the PNS?

Answer 2

The PNS contains motor, sensory, and autonomic fibers.

Question 3

What is the role of the spinal nerves in the peripheral nervous system (PNS)?

Answer 3

They receive sensory input from the periphery and transmit motor commands from the CNS to the limbs and trunk.

Question 4

How many pairs of spinal nerves are there and how are they distributed?

Answer 4

Spinal nerves emerging from the spinal cord to exit the vertebral canal
31 pairs:
8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal.

Question 5

Where do C1–C7 spinal nerves exit in relation to their corresponding vertebrae?

Answer 5

Above their corresponding vertebrae

Question 6

Why are there 8 cervical spinal nerves but only 7 cervical vertebrae?

Answer 6

Because the C8 spinal nerve emerges below the C7 vertebra, marking a transition.

Question 7

In the sacrum, the spinal nerves travel through which structure?

Answer 7

travel through the sacral foramina

Question 8

How far do spinal nerve roots travel to reach their intervertebral foramen from C1 to L1/L2

Answer 8

From C1 to L1/L2, spinal nerve roots travel only a short distance to reach their corresponding intervertebral foramen

Question 9

What is the conus medullaris and what structure does it give rise to?

Answer 9

The tapered end of the spinal cord at L1/L2, which gives rise to the cauda equina

Question 10

What is the cauda equina?

Answer 10

A bundle of spinal nerve rootlets below L1/L2 that resembles a horse’s tail.

Question 11

What are the four roots of each spinal cord segment?

Answer 11

Left and right anterior (ventral) roots and posterior (dorsal) roots.

Question 12

How are the anterior and posterior roots of a spinal nerve formed?

Answer 12

Each root is formed by the union of approximately 8 nerve rootlets, which come together to form either an anterior (ventral) or posterior (dorsal) root

Question 13

What type of fibers are carried by the anterior (ventral) root?

Answer 13

Efferent (motor) fibers from the CNS to muscles and autonomic ganglia.

Contains efferent nerve fibres, which carry stimuli away from the CNS towards their target structures.

Question 14

Where are the cell bodies of anterior root motor neurons located?

Answer 14

In the central grey matter of the spinal cord.

Question 15

In the central grey matter of the spinal cord, what neurons are located there?

Answer 15

Motor Neurons - controlling skeletal muscle

Preganglionic autonomic neurons

Question 16

What type of fibers are carried by the posterior (dorsal) root?

Answer 16

Afferent (sensory) fibres from the body to the CNS.

Afferent nerves which return sensory information from the trunk and limbs to the CNS

Question 17

Where are the sensory neuron cell bodies located?

Answer 17

Cell bodies are located in a structure called the spinal/dorsal root ganglion.

Question 18

What happens when anterior and posterior roots join?

Answer 18

They form a mixed spinal nerve containing both motor and sensory fibers.

Question 19

What do the posterior (dorsal) rami innervate?

Answer 19

Muscles and skin of the posterior trunk.

Question 20

What do the anterior (ventral) rami innervate?

Answer 20

Anterolateral trunk and limbs.

Question 21

Rami nerves are?

Answer 21

Mixed nerves carrying somatic motor fibers and sensory fibers

Question 22

What are intercostal nerves (the ventral rami ) and where are they found?

Answer 22

The ventral rami from T2–T12 that travel under the ribs to innervate intercostal muscles.

Question 23

What structure carries visceral motor fibers from the spinal nerve?

Answer 23

The rami communicantes (gray and white rami).

Question 24

What is a nerve plexus?

Answer 24

A reorganization or braiding of spinal nerve fibers that follow new paths to their targets

Question 25

In the cervical, lumbar and sacral regions the nerves in the periphery are not straight continuations of the spinal nerves but rather??

Answer 25

the reorganisation of the axons in those nerves to follow different courses This is identified as a nerve plexus (plexus = a braid)

Question 26

What are the four main nerve plexuses in the body?

Answer 26

Cervical plexus (C1–C4) Brachial plexus (C5–T1) Lumbar plexus (L1–L4) Sacral plexus (L4–S4)

Question 27

What is a dermatome?

Answer 27

An area of skin innervated by a single spinal nerve root.

Question 28

Why are dermatomes clinically important?

Answer 28

They help identify spinal nerve damage and are linked to referred visceral pain

Question 29

What is the dermatome distribution for the upper limbs?

Answer 29

C5 is represented in the shoulder C6 in the lateral arm and first two digits C7 in the over the 3rd finger and the posterior aspect of the arm and forearm. C8 in the fourth, middle digit and fifth digits. The L4 representation extends over the anteromedial shin L5 extends down the anterolateral shin and dorsum of the foot to the big toe S1 is in the small toe, lateral foot, sole, and calf S2, S3, and S4 innervate the perineal area in a saddle like distributio

Question 30

What is a myotome?

Answer 30

A group of muscles innervated by a single spinal nerve.

Question 31

Why are T2–L1 myotomes harder to assess?

Answer 31

Because they innervate internal trunk muscles, which are difficult to isolate for testing.

Question 32

Mytotomes level discrepancies

Answer 32

C1/C2: Neck Flexion/Extension C3: Neck Lateral FLexion C4: Shoulder Elevation C5: Shoulder Abduction C6: Elbow Flexion/Wrist Extension C7: Elbow Extension/ Wrist Extension C8: Finger Flexion T1: Finger Abduction L2: Hip Flexion L3: Knee extension L4: Ankle dorsi Flexion L5: Great Toe extension S1: Ankle plantar-flexion/Ankle Eversion/Hip Extension S2: Knee Flexion

Question 33

Which regions of the body are innervated by the posterior rami? * A. head and neck * B. upper limbs * C. posterior thoracic and lumbar * D. lower limbs

Answer 33

C: posterior thoracic and lumbar

Question 34

The anterior root carries which type of information? * A. motor only * B. sensory only * C. both motor and sensory

Answer 34

A. motor only