Spinal Cord and Spinal Nerves BIOL 3310 Anatomy and Physiology 1 Lecture Exam 3

Conduction

bundles of fibers passing information up and down spinal cord, connecting different levels of the trunk with each other and the brain

Locomotion

walking involves repetitive, coordinated actions of several muscle groups

Central pattern generators

pools of neurons providing control of flexors and extensors that cause alternating movements of lower limbs

Reflexes

involuntary, stereotypes responses to stimuli

involves brain, spinal cord and peripheral nerves

Spinal cord

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

passes through the vertebral canal

Where does the spinal cord end?

L1, or slightly beyond

How many pairs of the spinal nerves come off the spinal cord?

31

Segment

part of the spinal cord supplies by each pair of spinal nerves

Anterior median fissure

front longitudinal grooves on spinal cord

Posterior median sulcus

back longitudinal groove on spinal cord

What are the regions of the spinal cord?

cervical

thoracic

lumbar

sacral

Cervical enlargement

thicker area of spinal cord that supplies nerves to upper limb

Lumbar enlargement

thicker area of spinal cord that supplies nerves to the pelvic region and lower limbs

Medullary cone (conus medullaris)

cord tapers to a point inferior to lumbar enlargement

Cauda equina

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

Grey matter

neuron cell bodies with little myelin, site of information processing

White matter

abundantly myelinated axons, carry signals from one part of the CNS to another

Dura mater

forms dural sheath of tough, collagenous membrane surrounded by epidural space filled with blood vessels and loose connective tissue

Dural sheath

loose-fitting sleeve around spinal cord

Arachnoid membrane

layer of simple squamous epithelium lining dura mater and a loose mesh of collagenous and elastic fibers spanning the gap b/t this and the pia mater

Subarachnoid space

space between arachnoid membrane and the pia mater, filled with cerebrospinal fluid

Pia mater

delicate, translucent membrane that follows the contour of the spinal cord

Denticualte ligaments

extend through the arachnoid to the dura mater, anchors spinal cord to limit side to side movement

Posterior (dorsal) horns

2

receive sensory nerve fibers, synapse with interneurons in horn

Anterior (ventral) horns

2

contain cell bodies of motor neurons

Lateral horns

present in segments, T2 through L1, associated with sympathetic nervous system

Grey commissure

connects left and right sides of spinal cord

Central canal

center of commissure

What are the three bundles that make up the white matter?

large axon bundles, posterior, lateral and anterior funiculus

What are the subdivisions of funiculus?

fasciculi or tracts

What are the sectional divisions of the spinal nerves?

cervical (C1-C8)

thoracic (T1-T12)

lumbar (L1-L5)

sacral (S1-S5)

coccygeal

What are the layers of connective tissue covering the spinal nerves?

epineurium, perineurium, endoneurium

Rami

spinal nerve branches

posterior (dorsal) ramus

anterior (ventral) ramus

Plexuses

network of axons, all anterior rami minus T1-T11

Cervical plexus (C1-C5)

supply neck and phrenic nerve to diaphragm

Brachial plexus (C5-T1)

supplies upper limb and some of shoulder and neck

Lumbar plexus (L1-L4)

supplies abdominal wall, anterior thigh, genitalia

Sacral plexus (L4, L5, S1-S4)

supplies lower trunk and lower limb

Coccygeal plexus (S4, S5 and C0)

glutes

Dermatome

area of the skin that provide sensory input to the CNS via one pair of spinal nerves

Paraplegia

paralysis of lower limbs

Quadriplegia

paralysis of all four limbs

Hemiplegia

typically due to stroke or other brain injury, paralysis of one side of the body

Spina bifida

congenital defect in which one or more vertebrae fail to form a complete vertebral arch for enclosure of the spinal cord

spina bifida occulta - one arch fails to form

spina bifida cystica - multiple arches fail to form

avoided by consuming folic acid prior to conception

Poliomyelitis

caused by poliovirus, destroys motor neurons in brainstem and anterior horn of spinal cord

symptoms include muscle pain, weakness and loss of reflexes

virus spread by fecal contamination in water

Amyotrophic lateral sclerosis (ALS) Lou-Gehrig disease

destruction of motor neurons and muscular atrophy

sclerosis of lateral regions of spinal cord

astrocytes fail to reabsorb GLU, toxic levels accumulate

Chickenpox

caused by varicella-zoster virus

clears up on its own, but virus remains for life on posterior ganglia root

Shingles

caused by herpes zoster, caused by chickenpox reemerging due to failing immune system, very painful

Reflex

automatic, sudden, predictable, involuntary response to stimuli

Cranial reflexes

integrated into brainstem

Spinal reflexes

integrated into spinal cord

Somatic reflexes

have responses involving skeletal muscles

Autonomic reflexes

involve internal processes and are usually not consciously perceived

Reflex arc

pathway followed by nerve impulses to produce a reflex

sensory receptor

sensory neuron

integrating center

motor neuron

effector

Stretch reflex

contraction of skeletal muscle in response to stretching of another muscle

monosynaptic reflex, ipsilateral

Monosynaptic

2 neural junctions

Poly synaptic

2+ neural junctions

Ipsilateral

stays on one side of the spinal column

Contralateral

crosses sides of the spinal column

Reciprocal innervation

arrangement where components of a neural circuit simultaneously cause contraction of one muscle and relaxation of the antagonistic muscle

Tendon reflex

polysynaptic reflex, controls muscle tension by causing muscle relaxation when muscle tension is too great

can override stretch reflex to prevent over contracting and tendon tearing

Flexor (withdrawal) reflex

polysynaptic reflex, ipsilateral

activates interneurons on several segments of the spinal cord, intersegmental reflex arc

Crossed extensor reflex

polysynaptic reflex, contralateral

contraction of muscle in the opposite limb in response to a painful stimulus, allows balance of opposite limb