Chapter 17 Spinal Cord

dermatones vs cutaneous fields

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anterior median fissure

- wide grove on anterior side

Protective structures of the spinal cord

-1st later is hard bone skull and vertebral column. -2nd protective layer is meninges: 3 membranes lying in between bony encasement and nervous tissue in brain and spinal cord -3rd cerebrospinal fluid is a buoyant liquid suspending central nervous tissue in weightless environment +surrounding it w/ shock absorbing hydraulic cushion

Meninges

-3 protective, connective tissue coverings encircling spinal cord and brain -from superficial to deep they are 1) dura matter 2)arachnoid mater 3) pia matter -between pia and arachnoid matter is the subarachnoid space containing shock absorbing cerebrospinal fluid -SPINAL MENINGES surround spinal cord and are continuous with cranial meninges -CRANIAL meninges encircle the brain -spinal cord is protected by cushion of fat and connective tissue located in EPIDURAL space (between dura mater and wall of vertebral canal)

white columns

-anterior and posterior gray horns divide the white matter on each side into three broad areas 1) anterior white columns 2) posterior white columns 3) lateral white columns -it contains distinct bundles of axons having common origin or destination and caring similar information

central canal

in the center of gray commissure of the spinal cord -extends entire length of the spinal cord and contains cerebrospinal fluid

intercostal nerves

-anterior rami of spinal nerves t2-t12 do not enter formation of plexuses -known as intercostal/ thoracic -nerves connect directly to structures they supply in intercostal spaces and mainly distributed to a single body segment: referred to as segmental nerves -after leaving intervertebral foramen, anterior ramus nerve of t2 innervates the intercostal muscles of 2nd intercostal space and supplies skin of axilla and posteromedial aspect of arm -nerves t3-t6 extend along costal gooves of ribs and to intercostal muscles and skin of the anterior and lateral chest wall -nerves t7-12 supply intercostal muscles, ab muscles and overlying skin -posterior rami of intercostal nerves supply the deep back muscles and skin of the posterior aspect of the thorax

anterior white commissure

-anterior to the grey commissure -Connect white matter of right and left sides to spinal cord

filum terminale

-arising from conus medullaris -extension of the pia mater that extends inferiorly and fuses with the arachnoid mater and dura mater to anchor the spinal cord to the coccyx

spinal nerves

-associated with the spinal cord and like nerves of peripheral nervous system, or parallel bundles of axons in their associated neuroglial cells wrapped in many layers of connective tissue -spinal nerves connect the central nervous system to sensory receptors, muscle, glands in all parts of body -31 pairs of spinal nerves -31 pairs emerge at regular intervals for spinal cord through intervertebral foramina

internal anatomy of spinal cord

-at all levels is characterized by a central letter H or butterfly shaped Grey Matter region surrounded by white matter Two grooves penetrate white matter of spinal cord and divided into right and left sides -Gray Matter consist primarily of the cell bodies of neurons, neuroglia, unmyelinated axons and the dendrites of interneurons and motor neurons -white matter consists of bundles of myelinated axon's of sensory neurons, interneurons, and motor neurons

nerve fiber

-axon and associated glial cells form the nerve fiber -sits in loose connective tissue covering

Plexuses

-axons from anterior rami of spinal nerves expect t2-t12 do not go directly into body structure supplied -form networks on left and right side of body by joining various numbers of axons from anterior rami of adjacent nerves -such a network of axons is called a PLEXUS --1) cervical plexus (c1-c5) 2) brachial plexus (c5-t1) 3) lumbar plexus (l1-l4) 4) sacral plexus (l4-s4) 5) coccygeal plexus

major motor tracts

-cerebral cortex is major player in controlling precise, vol. muscular movement -motor output to skeletal muscles travels down the spinal cord in two types of descending pathways : direct and indirect --direct pathways: lateral corticospinal, anterior corticospinal and corticobulbar -each of these tracts converys nerve impulses that orginate in the cerebral cortex and cause precise, voluntary movements of skeletal muscles. --indirect pathways: rubrospinal, tectospinal, vestibulospinal, lateral reticulospinal and medial reticulospinal -these convery nerve impulses from brain stem and other parts of brain governing automatic movements and coordinate body movements with visual stimuli -also maintain skeletal muscle tone, sustain contraction of postural muscles and play a major role in equilibrium by regulating muscle tone in response to movements of the head

sensory (ascending) tracts

-consist of axons that conduct nerve impulses from spinal cord towards brain

posterior gray horns

-contain cell bodies and axons of interneurons as well as axons of incoming sensory neurons

anterior gray horns

-contain somatic motor nuclei (clusters of of cell bodies of somatic motor neurons that provide impulses for contraction of skeletal muscles

reflex

-fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimulus -some reflexes inborn (born with) and some are learned (driving) -when integration takes place in spinal cord gray matter, SPINAL REFLEX -if reflec occurs in brain stem instead of spinal cord, reflex is CRANIAL REFLEX -somatic reflexes involve contraction of skeletal muscles -autonomic reflexes involve smooth muscle, cardiac muscle and glands (EX. heart rate, digestions, urination and defecations)

gray commissure

-forms crossbar of H/ body of butterfly

Perineurium

-holds many nerve fibers together into bundles called fasciculi -consists of collagenous sheaths with up to 15 layers of fibroblasts in a meshwork of collagen -this sheath functions as a diffusion barrier, along with tight junctions in capillaries, maintains the osmotic environment and fluid pressure within endoneurium -terminated y blending the connective tissue capsules of various types of nerve endings and muscle junctions

nuclei

-in the gray matter of spinal cord + brain these clusters form functional groups

conus medullaris

-inferior to the lumbar enlargement, spinal cord terminates as a tapering conical structure -ends at the level of the intervertebral disc between the first and second lumbar vertebrae in adults

pia mater

-innermost menix -thin, transparent connective tissue layer adhering to surface of the spinal cord and brain -thin squamous to cuboidal cells within interlacing bundles of collagen fibers and fine elastic fibers -many blood vessels that supply oxygen and nutrients to the spinal cord -triangular-shaped membranous extensions of the pia mater suspend the spinal cord in the middle of its dural sheath -these extensions are called DENTICULATE LIGAMENTS and are thickenings of the pia mater -project laterally and fuse with arachnoid mater and inner surface of the dura mater between the anterior and posterior nerve roots of spinal nerves on side side -extending along the entire length of the spinal cord, the denticulate ligaments protect the spinal cord against sudden displacement that could result in shock

vertebral column

-located within vertebral canal -vertebral foramina of all vertebrae stacked on top of eachother form canal -sturdy shelter for enclosed spinal cord -vertebral ligaments provide additional protection

Endoneurium

-loose connective tissue covering that each nerve cells in consisting of collagen fibers, fibroblasts and macrophages surrounds by endoneurial fluid derived from capillaries -this fluid nurses the neuron and provides necessary environment for function of propagating action potential

arachnoid mater

-middle layer of meningeal membranes -thin, avascular covering comprised of cells and thin, loose arrays of collagen -name comes from spider web arrangement of collagen fibers and elastic fibers -deep to the dura mater and continuous through foramen magnum with the arachnoid mater of the brain -between dura mater and arachnoid mater is thin SUBDURAL SPACE containing interstitial fluid

dura mater

-most superficial of the 3 spinal meninges -thick, strong layer composed of dense irregular connective tissue -early anatomists believed all of the body tissues developed from the dura mater -forms a sac from the level of the foramen magnum in the occipital bone where it is continuous with the meningeal dura mater of the brain, the second sacral vertebra -dura mater is also continuous with epineurium (outer covering of spinal and cranial nerves)

posterior median sulcus

-narrow groove on the posterior side

major sensory tracts

-nerve impulses from sensory receptors propagate up spinal cord to brain along 2 main routes on each side: lateral and anterior spinothalamic tracts (nerve impulses for pain, warmth, cool, itch, tickle and deep pressure, crude localized sense of touch -right and left posterior columns carry nerve impulses: 1) proprioception (awareness of postions and movements of muscles, tendons, and joints) 2) discriminiative touch: ability to feel exactly what part of the body is touched 3) two point discrimination: ability to distinguish the touching of two different points on the skin even thougn they are close together 4) light pressure sensations 5) vibration sensations

basic structure of a nerve

-neurons are conductive cells of the nervous tissue -nerves are bundles of axons and their associated neuroglial cells wrapped in layers of connective tissue -nerves consist of long cells

Epinerium

-outer connective tissue sheath -bundles all fasciculi together to form single nerve -continuous with dura mater and consists of fibroblasts and thick collagen strands that primarily parallel the long axis of the nerve -extensions of epineurium fill spaces between fascicles -makes up 50% of cross sectional area of a nerve -gives nerves necessary tensile strength to resist the forces that can so easily damage the delicate nervous tissue -nerves have more collagenous connective tissue than nervous tissue which allows nervous tissue to leave the protection of the bony skull and vertebral column and course through peripheral tissues of the body -strong collagenous sheaths protect the neurons from being torn apart by the strong tensile forces generated by muscular activities and body movements -contains small blood vessels and lymphatic vessels for the nerve

reflex arc

-pathway followed by nerve impulses that produce a reflex 1) sensory receptor 2) sensory neuron 3) integrating center 4) motor neuron 5) effector

lateral gray horns

-present only in thoracic, upper lumbar, and sacral segments of the spinal cord -contain the cell bodies of autonomic motor nuclei that regulate activity of smooth muscle, cardiac muscle and glands

Rami

-ramus is large spinal nerve branch following a certain course to different peripheral regions -2 largest branches: anterior and posterior are somatic that run in the musculoskeletal wall of the body -POSTERIOR RAMUS serves the deep muscles and skin of the posterior surface of the trunk -ANTERIOR RAMUS serves the muscles and structures of the upper and lower limbs and the muscles and skin of the lateral and anterior regions of the trunk -smaller branches (meningeal) and communicating rami form autonomic pathways to smooth muscles and glandular tissue -MENINGEAL BRANCH reenters vertebral canal through intervertebral foramen and supplies the vertebrae, vertebral ligaments, blood vessels of the spinal cord and meninges -communcating rami are components of autonomic nervous system

external anatomy of spinal cord

-roughly oval in shape, flattened slightly in anterior- posterior axis -adults: extends from medulla oblongata (most inferior part of brain) to superior border of the second lumbar vertebra. -newborns: spinal cord extends to 3rd or 4th lumbar vertebra. -early childhood: both spinal cord and vertebral grown longer as part of overall -elongation of spinal cord stops around age 4 or 5 but growth of the vertebral column continues -max diameter is 1.5cm

Rootlets

-spinal nerves arising from spinal cord as a series of small ROOTLETS -two types are anterior rootlets and posterior rootlets -anterior rootlets emerge in 2 or 3 irregular rows and contain axons of multipolar motor neurons arising form cell bodies in the anterior regions of the spinal cord gray matter --axons transmit action potentials to the muscles and glands of the body -projecting from posterolateral sulcus of the spinal cord are more rootlets -posterior rootlets contain central processes of the sensory unipolar neurons --these neurons transmits action potentials from peripheral receptor organs to the CNS -anterior roolets converge to form larger anterior roots -posterior rootlets converge to form large posterior roots and each one has a swelling called the POSTERIOR ROOT GANGLION containing the cell bodies of sensory neurons -anterior & posterior roots on each side correspond to one developmental segments level of the body -sensory posterior root and motor anterior root project laterally from the spinal cord, they form a mixed nerve called the SPINAL NERVE TRUNK which runs for a short distance before branching into 2 big branches and variable series of smaller branches.

cauda equina

-spinal nerves branch from spinal cord passing laterally to exit spinal canal through intervertebral foramina between adjacent vertebraw -due to the spinal cord being shorter than the vertebral column nerves arising from the lumbar region sacral and coccygeal do you do not leave the vertebral column at the same level they exit the cord -roots of these lower spinal nerves angle inferiorly along side the filum terminale in the vertebral canal like wisps of hair

motor (descending) tracts

-tracks consisting of axons that carry nerve impulses away from brain down spinal cord

cervical and lumbar enlargements

-when spinal cord is viewed externally has two conspicuous enlargements -cervical enlargement: superior enlargement extending from C4 to T1 --nerves to and from upper limbs arise from cervical enlargement -lumbar enlargement: inferior enlargement extending from t9 to t12 vertebra --nerves to and from the lower limbs arise from the lumbar enlargement

spinal cord functions

-white matter tracts in spinal cord are highways for nerve impulse propagations, sensory toward brain and motor toward skeletal muscles and effector tissues -gray matter receives and integrates info