1 The Spinal Cord, Reflexes, and Plexuses

What are the two main divisions of the nervous system?

Central nervous system
Peripheral nervous system

What structures make up the central nervous system (CNS)?

Brain and spinal cord

What structures make up the peripheral nervous system (PNS)?

All nerves and ganglia outside the brain and spinal cord.

Between which vertebral landmarks does the spinal cord extend?

From the foramen magnum to the 2nd lumbar vertebra

What protects the spinal cord?

Vertebral column

What allows movement through connections with the spinal cord?

Spinal nerves

What can occur if the spinal cord is damaged?

Paralysis

Where is gray matter located in the spinal cord?

In the center of the spinal cord.

What shape does gray matter have in the spinal cord?

H-shaped with horns or butterfly-shaped.

Where is white matter located in the spinal cord?

Outside the spinal cord.

What type of fibers does white matter contain?

Myelinated fibers

What are the three columns found in CNS white matter?

Dorsal, ventral, and lateral columns.

What do the three columns of CNS white matter contain?

Ascending and descending tracts

Which tracts conduct action potentials toward the brain?

Ascending tracts

Which tracts conduct action potentials away from the brain?

Descending tracts

What do the posterior horns of gray matter contain?

Axons that synapse with interneurons.

What type of neurons are found in the anterior horns of gray matter?

Somatic neurons

What type of neurons are found in the lateral horns of gray matter?

Autonomic neurons

It is the fluid-filled space in the center of the spinal cord.

Central canal

What type of reaction is a reflex?

An involuntary reaction

What initiates a reflex reaction?

A stimulus applied to the periphery

Where is the peripheral stimulus transmitted to during a reflex?

To the CNS

What is the simplest type of reflex?

Stretch reflex

What is a classic example of a stretch reflex?

Knee-jerk reflex (patellar reflex)

What is another name for the withdrawal reflex?

Flexor reflex

What is the purpose of the withdrawal reflex?

To remove a limb or body part from a painful stimulus.

What type of sensory receptors initiate the withdrawal reflex?

Pain receptors

How do spinal nerves arise along the spinal cord?

From the union of dorsal and ventral roots.

What types of axons do spinal nerves contain?

Sensory and somatic neuron axons

Where are spinal nerves located?

Between vertebrae

How are spinal nerves categorized?

By the region of the vertebral column from which they emerge.

What letter identifies a cervical spinal nerve?

C

How many pairs of spinal nerves are there?

31 pairs

How many plexuses are spinal nerves organized into?

3 plexuses

Which spinal nerves form the cervical plexus?

C1–C4

What does the cervical plexus innervate?

Muscles attached to the hyoid bone and neck.

Which important nerve is contained in the cervical plexus?

Phrenic nerve

What does the phrenic nerve innervate?

Diaphragm

What are the 3 plexuses organized in the spinal cord?

Cervical, Brachial, and Lumbosacral Plexus

Which spinal nerves form the brachial plexus?

C5–T1

What areas does the brachial plexus supply nerves to?

Upper limb
Shoulder
Hand

Which spinal nerves form the lumbosacral plexus?

L1–S4

What does the lumbosacral plexus supply nerves to?

The lower limbs

What does each spinal nerve except C1 have?

A specific cutaneous sensory distribution

Which area of skin is supplied with sensory innervation by a pair of spinal nerves?

Dermatome

Which structure supplies a dermatome with sensory innervation?

A pair of spinal nerves

Which two structures give rise to the nerves that supply specific regions of the body?

The spinal cord and vertebral column

Which reflex occurs when muscles contract in response to a stretching force applied to them?

Stretch reflex