A&P Chapter 12: Spinal Cord and Spinal Nerves

Spinal Cord

-extends from the brain at foramen magnum down to the second lumbar vertebra.
-Terminates in the conus medullaris
-shorter than vertebral column

Cauda equina

group of nerves leaves the inferior spinal cord and extends downward. Resembles a horses tail.

Cervical enlargement

has nerve fibers that supply the upper limbs

lumbosacral enlargement

has nerve fibers supplying the lower limbs

Spinal cord

larger in diameter at its superior end and gradually decreases in diameter toward its inferior end

31 pairs of spinal nerves

-8 cervical
-12 thoracic
-5 lumbar
-5 sacral
-1 coccygeal

spinal nerves

exit the vertebral column through intervertebral and sacral foramina and connect with various body regions

Spinal cord surroundings

dura mater, arachnoid, and pia mater

dura mater around the spinal cord

is separated from the periosteum of the vertebral canal by the epidural space

epidural space around the spinal cord

is a true space with spinal nerve roots, blood vessels, areolar connective tissue, and adipose tissue

subarachnoid space

between arachnoid mater and pia mater; contains weblike strands of the arachnoid mater, blood vessels, and cerebrospinal fluid.

epidural anesthesia

often administered in women during childbirth by injecting anesthetics into the epidural space of the spinal cord

anterior media fissure and posterior median sulcus

two deep grooves; anterior fissure is deeper and wider

Gray matter

cell bodies of interneurons and motor neurons in addition to dendrites and unmyelinated axons; in transverse section, looks like "H" w/ anterior posterior, & lateral limb (horns)

White matter

surrounds the gray matter and is subdivided into anterior, posterior, and lateral white columns (funiculi).

Pathways

Each white matter column consists of a large bundle of myelinated axons divided into tracts or fascicles.

Gray and white commissures

-connect the two halves of the spinal cord
-contain axons that cross from one side of the spinal cord to the other

Central canal

located in the center of the gray commissure; helps circulate CSF (cerebrospinal fluid)

Ventral roots

axons of motor neurons which innervate muscles and glands

dorsal roots

the axons of these pseudo-unipolar sensory neurons extends from various parts of the body and pass through spinal nerves to…

dorsal root ganglion OR spinal ganglion

sensory neuron cell bodies are contained within here

4 main nerve plexuses

1. cervical plexus
2. brachial plexus
3. lumbar plexus
4. sacral plexus

cervical plexus

supplies nerves to the posterior head and neck, as well as to the diaphragm

brachial plexus

supplies nerves to the arm

lumbar plexus

supplies nerves to the anterior leg

sacral plexus

supplies nerves to the posterior leg

Spinal cord function

function to transmit messages to and from the brain (white matter) and to serve as a reflex center (gray matter)

reflex

automatic response to a stimulus, occurs w/o conscious though; homeostatic

Autonomic reflexes

responsible for maintaining relatively constant blood pressure, blood CO2 levels, and water intake

Somatic reflexes

remove the body from painful stimuli that cause tissue damage or keep body from suddenly falling or moving b/c of external forces

reflex arc

neural pathway that controls a reflex; basic functional unit of the nervous system that is capable of receiving a stimulus and producing a response

components of a reflex arc

1. receptor
2. sensory neuron
3. integration center
4. motor neuron
5. effector

receptor

site of stimulus

sensory neuron

transmits afferent info to the CNS

integration center

1 or more interneurons

motor neuron

transmits efferent signals to effector

effector

muscle or gland

somatic

reflexes involving skeletal muscles and somatic motor neurons

autonomic

reflexes controlled by autonomic neurons are

spinal reflexes

integrated within the spinal cord while cranial reflexes are integrated in the brain

stretch reflex

simplest reflex; contraction of muscles in response to stretching of that same muscle
Ex: knee-jerk reflex (patellar reflex)

golgi tendon reflex

prevents contracting muscles from applying excessive tension to tendons. The sensory receptors for this reflex are called golgi tendon organs; located at muscle-tendon junction.

withdrawal reflex OR flexor reflex

removing a limb or another body part from a painful stimulus

Nerve structure

organized by layers of connective tissue on the outside, around each fascicle, and surrounding individual nerve fibers.

Spina bifida

-condition that affects spine and usually apparent in birth; type of neural tube defect (NTD).
-Can occur anywhere along the spine if the neural tube does not close all the way

spinal transection

tear w/ spinal cord after a traumatic injury

spinal shock

physiologic or anatomic transection of the spinal cord that results in temporary loss or depression of all or most spinal reflex activity below the level of the injury

phantom limb pain

pain felt in arm or leg that has been amputated; although limb is gone, nerve ending at the site of amputation continue to send pain signals to the brain that make the brain think the limb is still there

Phrenic (C3-C5)

diaphragm

Radial (C5-C8, T1)

skin and muscles of posterior arm, forearm, and hand; thumb and first 2 fingers

Median (C5-C8, T1)

skin and muscles of anterior arm, forearm, and hand

Ulnar (C8, T1)

skin and muscles of medial arm , forearm, and hand; little finger and ring finger

Intercostal (T2-T12)

intercostal muscles, abdominal muscles; skin or trunk

femoral (L2-L4)

skin and muscles of anterior thigh, medial leg, and foot

Sciatic (L4-S3)

skin and muscles of posterior thigh, leg and foot