Module 12: The Spinal Cord, Spinal Nerves, and Somatic Reflexes

Module 12: The Spinal Cord, Spinal Nerves, and Somatic Reflexes

conduction

Nerve fibers conduct sensory and motor information up and down the spinal cord

neural integration

Spinal neurons receive input from multiple sources, integrate it, and execute appropriate output

locomotion

Spinal cord contains central pattern generators

reflexes

Involuntary responses to stimuli that are vital to posture, coordination and protection

spinal cord

Cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull

cervical enlargement

Gives rise to nerves of shoulder and upper limbs

lumbarsacral enlargement

Gives rise to nerves of pelvis and lower limbs

medullary cone

Cord tapers to a point inferior to lumbar enlargement

cauda equina

Bundle of nerve roots that occupy the vertebral canal from L2 to S5

filum terminale

Thin thread of fibrous tissue at end of conus medullaris; attaches to coccygeal ligament

meninges

3 fibrous membranes of connective tissue that surround the CNS (Brain and Spinal Cord)

meningitis

Viral or bacterial infection of meninges

spinal meninges

Protect spinal cord; Carry blood supply

dura mater

outer layer of spinal cord

epidural space

anesthetic injection site

subdural mater

Between arachnoid mater and dura mater

arachnoid mater

Middle meningeal layer

subarachnoid space

Filled with cerebrospinal fluid (CSF)

cerebrospinal fluid

Carries dissolved gases, nutrients, and wastes

pia mater

Inner meningeal layer; Is a mesh of collagen and elastic fibers

denticulate ligaments

Stabilize side-to-side movement

gray matter

Contains neuron cell bodies with little or no myelin; Site of information processing, synaptic integration

white matter

Abundantly myelinated axons; Carry signals from one part of the CNS to another;

posterior gray horns

Receives somatic and visceral sensory fibers

anterior gray horns

Contain somatic motor fibers

lateral gray horns

In thoracic and lumbar segments; contain visceral motors (sympathetic) neurons

gray commissure

Connects right and left sides; Has central canal line with ependymal cells and filled with CSF

spino

Ascending, sensory (up)

spinal

Descending, motor (down)

decussation

Crossing of the midline that occurs in many tracts so that brain

contralateral

When the origin and destination of a tract are on opposite sides of the body

ipsilateral

When the origin and destination of a tract are on the same side of the body; does not decussate

first order neuron

Detects stimulus and transmits signal to spinal cord or brainstem (CNS)

Second order neuron

Interneuron proceeds to the thalamus of brain (final relay point)

fasciculus gracilis

Deep touch, pressure, vibration for lower extremities

fasciculus cuneatus

Deep touch, pressure, vibration for upper extremities

medial lemniscus

Travels to the thalamus which projects up to the primary sensory cortex

spinoreticular

Carries pain signals resulting from tissue injury

spinocerebellar

Carry proprioceptive signals from limbs and trunk up to the cerebellum

upper motor neuron

Soma in cerebral cortex or brainstem

lower motor neuron

In the brainstem or spinal cord

tectospinal tract

Reflex turning of head in response to sights and sounds

reticulospinal tract

Controls limb movements important to maintain posture and balance

vestibulospinal tract

Postural muscle activity in response to inner ear signals

poliomyelitis

Signs of muscle pain, weakness, and loss of some reflexes; Spreads by fecal contamination of water; Destroys motor neurons in brainstem and anterior horn of spinal cord

lou gehrig disease (als)

Astrocytes fail to reabsorb the neurotransmitter glutamate from the tissue fluid which accumulates to toxic levels; Early signs are muscular weakness, difficulty speaking, swallowing, and using hands; Sensory and intellectual functions remain unaffected

epineurium

Covers spinal nerves

perineurium

Surrounds a fascicle (bundles of nerve fibers)

endoneurium

covers the individual nerve fibers (axons)

dorsal root

Sensory input to spinal cord

ventral root

Motor output of spinal cord

Dorsal ramus

supplies dorsal body muscle and skin

ventral ramus

skin and muscles and limbs

Chickenpox

virus remains for life in the dorsal (posterior) root ganglia

shingles

Localized disease caused by the virus traveling down the sensory nerves by fast axonal transport when immune system is compromised; Painful trail of skin discoloration and fluid filled vesicles along path of nerve

nerve plexus

Complex, interwoven networks of nerve fibers

cervical plexus

C1 to C5; Neck, major nerve is phrenic nerve (controls diaphragm)

brachial plexus

C5 to T1; Supplies upper limbs and some of shoulder and neck

lumbar plexus

T12 to L4; Supplies abdominal wall, anterior thigh and genitalia

sacral plexus

L4 to S4; Supplies reminder of lower trunk and lower limb

somatic reflexes

Quick, involuntary reactions of glands or muscle to sensory stimulation

Knee-jerk (patellar) reflex

An example of a Monosynaptic reflex is

Flexor reflex

Quick contraction of flexor muscles resulting in the withdrawal of a limb from pain

polysynaptic reflex arc

Pathway in which signals travel over many synapses on their way to the muscle

Crosses extension reflex

Contraction of extensor muscles in limb opposite of the one that is withdrawn

paraplegia

Paralysis of both lower limbs

quadriplegia

Paralysis of all four limbs

hemiplegia

Paralysis on one side of the body

paresis

Partial paralysis or weakness of the limbs