Chapter 13 Spinal Cord, Spinal Nerves, and Spinal Reflexes

Spinal dura mater

-outermost layer of spinal meninges w/increased collagen
-enclosed by epidural space (fat) (adipose tissue)
-blends with the components of the filum terminale to form the coccygeal ligament that anchors the spinal cord to the coccyx

Epidural space

Cushion of fat and network of veins in space between vertebrae and spinal dura mater

Lumbar puncture

CSF is withdrawn from between 2 lumbar vertebrae for analysis

Conus medullaris

tapered end of spinal cord

Filum terminale

fibrous extension of the pia mater; anchors the spinal cord to the coccyx

Denticulate ligaments

Specializations of the pia mater that anchor the spinal cord to the dura mater and limit the movement of the cord.

Cervical and lumbar enlargements

enlargements where the nerves serving the upper and lower limbs arise

Cauda equina

collection of spinal nerves below the end of the spinal cord

Ventral (anterior) median fissure

Narrow groove on the anterior midline of the spinal cord

Dorsal (posterior) median sulcus

Narrow groove on the posterior midline of the spinal cord

Central canal

A tiny channel found within the spinal cord and inferior medulla oblongata containing CSF

Gray commissure

a thin strip of gray matter that surrounds the central canal of the spinal cord and, along with the anterior white commissure, connects the two halves of the cord.

Dorsal horns

gray matter in the spinal cord that contains sensory neurons; contain the cell bodies of interneurons that receive somatic and visceral sensory input

Ventral horns

gray matter in the spinal cord that contains motor neuron cell bodies

Lateral horns

gray matter located in the thoracic and lumbar segments only; contain visceral motor nuclei (of the ANS sympathetic neurons)

Ventral roots

Contain Motor (efferent) fibers from ventral horn motor neurons. The fibers innervate skeletal muscles.

Dorsal roots

Contain sensory (afferent) fibers from sensory neurons in dorsal root ganglia and conduct impulses from peripheral receptors

Dorsal root ganglion/ spinal ganglion

houses cell bodies of sensory neurons

Spinal gray matter

looks like a butterfly or a modified "H" and is more centrally located than the white matter; the gray matter is divided into the anterior, lateral, and posterior gray horns and consists of nerve cell bodies and dendrites

--4 zones
--somatic sensory
--visceral - autonomic sensory
--visceral motor
--somatic motor

Somatic sensory

receives sensory information from skin, fascia, joints, skeletal muscles, special senses

Visceral sensory

receives sensory information from viscera

Visceral (autonomic) motor

controls involuntary responses (cardiac/smooth muscles, glands)

Somatic motor

motor output that is consciously or voluntarily controlled; effector is skeletal muscle

White matter

axons

Transverse (commissural fibers)

This fibers interconnect two hemispheres, including the corpus callosum (the largest), and the anterior commissure.

White columns/ funiculi

Groups of myelinated and unmyelinated nerve fibers that allow communication between different parts of the spinal cord and between the spinal cord and brain. Named according to their location

Paresthesias

caused by damage to dorsal roots or sensory tracts. Leads to sensory function loss; resulting in numbness and/or tingling

Paralysis

temporary or permanent loss of motor control

Flaccid Paralysis

a state in which the muscles are limp and cannot contract

Spastic Paralysis

a state of continual contraction of the muscles

Muscle Atrophy

loss of muscle bulk due to muscle disease, nervous system disease, or lack of use; commonly called muscle wasting

Spinal cord trauma

Localized injury to spinal cord or its roots leads to functional losses

Poliomyelitis

inflammation of the gray matter of the spinal cord caused by a virus, commonly resulting in spinal and muscle deformity and paralysis

Amyotrophic lateral sclerosis

progressive muscle atrophy caused by degeneration and scarring of neurons along the lateral columns of the spinal cord that control muscles

Spinal nerves

31 pairs of nerves arising from the spinal cord

Rootlets

Spinal nerves initially arise from the spinal cord as

Ventral roots

Contain Motor (efferent) fibers from ventral horn motor neurons. The fibers innervate skeletal muscles.

Dorsal roots

Contain sensory (afferent) fibers from sensory neurons in dorsal root ganglia and conduct impulses from peripheral receptors

Dorsal ramus

the division of posterior spinal nerves that transmit motor impulses to the posterior trunk muscles and relay sensory impulses from the skin of the back

Ventral ramus

the anterior division of spinal nerves that communicate with the muscle and skin of the anterior and lateral trunk

Nerve plexuses

cervical, brachial, lumbar, sacral;
Complex, interwoven networks of nerve fibers
Control skeletal muscles of the neck and limbs

Cervical plexuses

C1-4; innervate the neck and sections of the head, chest, and shoulders and the diaphragm

Phrenic nerve

Carries impulses to the diaphragm from the brain.

Brachial plexuses

C5-T1; Innervates shoulder and upper limbs

Reflex arc

A relatively direct connection between a sensory neuron and a motor neuron that allows an extremely rapid response to a stimulus, often without conscious brain involvement.

Somatic reflexes

involuntary stimuli transmitted to skeletal muscles from neural arcs in the spinal cord

Autonomic (visceral) reflexes

Reflexes that activate smooth or cardiac muscle and/or glands.
- generally are not consciously perceived.
- involve responses of smooth muscle, cardiac muscle, and glands.
- body functions such as heart rate, digestion, urination, and defecation are controlled by the autonomic nervous system through autonomic reflexes.

Spinal reflexes

simple, automatic behaviors that are processed in the spinal cord

Excitatory neurons

Neurons which release neurotransmitters that have a positive effect on a target and encourage the formation of action potentials.

Inhibitory neurons

Neurons that reduce the activity of other neurons in the brain

Stretch reflex

involuntary contraction of a muscle due to rapid stretching of that muscle

flexor / withdrawal reflex

Initiated by a painful stimulus
Causes automatic withdrawal of the threatened body part
Ipsilateral and polysynaptic

Monosynaptic reflex

Reflex pathway with only one synapse between the sensory and motor neurons (ex: knee-jerk).

Polysynaptic reflex

A reflex involving one or several interneurons between sensory neuron and motor neuron.