Spinal CordSpinal Cord

CNS tissue is enclosed within the vertebral CNS tissue is enclosed within the vertebral column from the foramen magnum to Lcolumn from the foramen magnum to L11

Provides two-way communication to and from Provides two-way communication to and from the brainthe brain

Protected by bone, meninges, and CSFProtected by bone, meninges, and CSF Epidural space – space between the vertebrae Epidural space – space between the vertebrae

and the dural sheath (dura mater) filled with and the dural sheath (dura mater) filled with fat and a network of veinsfat and a network of veins

Lumbar TapLumbar Tap

Figure 12.30

Spinal CordSpinal Cord

Figure 12.29a

Spinal CordSpinal Cord

Conus medullaris – terminal portion of the Conus medullaris – terminal portion of the spinal cordspinal cord

Filum terminale – fibrous extension of the pia Filum terminale – fibrous extension of the pia mater; anchors the spinal cord to the coccyxmater; anchors the spinal cord to the coccyx

Denticulate ligaments – delicate shelves of pia Denticulate ligaments – delicate shelves of pia mater; attach the spinal cord to the vertebraemater; attach the spinal cord to the vertebrae

Spinal CordSpinal Cord

Spinal nerves – 31 pairs attach to the cord by Spinal nerves – 31 pairs attach to the cord by paired rootspaired roots

Cervical and lumbar enlargements – sites Cervical and lumbar enlargements – sites where nerves serving the upper and lower where nerves serving the upper and lower limbs emergelimbs emerge

Cauda equina – collection of nerve roots at the Cauda equina – collection of nerve roots at the inferior end of the vertebral canalinferior end of the vertebral canal

Cross-Sectional Anatomy of the Cross-Sectional Anatomy of the Spinal CordSpinal Cord

Anterior median fissure – separates anterior Anterior median fissure – separates anterior funiculifuniculi

Posterior median sulcus – divides posterior Posterior median sulcus – divides posterior funiculifuniculi

Figure 12.31a

Gray Matter and Spinal RootsGray Matter and Spinal Roots

Gray matter consists of soma, unmyelinated Gray matter consists of soma, unmyelinated processes, and neurogliaprocesses, and neuroglia

Gray commissure – connects masses of gray Gray commissure – connects masses of gray matter; encloses central canalmatter; encloses central canal

Posterior (dorsal) horns – interneuronsPosterior (dorsal) horns – interneurons Anterior (ventral) horns – interneurons and Anterior (ventral) horns – interneurons and

somatic motor neuronssomatic motor neurons Lateral horns – contain sympathetic nerve fibersLateral horns – contain sympathetic nerve fibers

Gray Matter and Spinal RootsGray Matter and Spinal Roots

Figure 12.31b

Gray Matter: OrganizationGray Matter: Organization

Dorsal half – sensory roots and gangliaDorsal half – sensory roots and ganglia Ventral half – motor rootsVentral half – motor roots Dorsal and ventral roots fuse laterally to form Dorsal and ventral roots fuse laterally to form

spinal nerves spinal nerves Four zones are evident within the gray matter Four zones are evident within the gray matter

– somatic sensory (SS), visceral sensory (VS), – somatic sensory (SS), visceral sensory (VS), visceral motor (VM), and somatic motor (SM)visceral motor (VM), and somatic motor (SM)

Gray Matter: OrganizationGray Matter: Organization

Figure 12.32

White Matter in the Spinal CordWhite Matter in the Spinal Cord

Fibers run in three directions – ascending, Fibers run in three directions – ascending, descending, and transverselydescending, and transversely

Divided into three funiculi (columns) – Divided into three funiculi (columns) – posterior, lateral, and anteriorposterior, lateral, and anterior

Each funiculus contains several fiber tracksEach funiculus contains several fiber tracks Fiber tract names reveal their origin and Fiber tract names reveal their origin and

destinationdestination Fiber tracts are composed of axons with similar Fiber tracts are composed of axons with similar

functionsfunctions

White Matter: Pathway White Matter: Pathway GeneralizationsGeneralizations

Pathways decussatePathways decussate Most consist of two or three neuronsMost consist of two or three neurons Most exhibit somatotopy (precise spatial Most exhibit somatotopy (precise spatial

relationships)relationships) Pathways are paired (one on each side of the Pathways are paired (one on each side of the

spinal cord or brain)spinal cord or brain)

White Matter: Pathway White Matter: Pathway GeneralizationsGeneralizations

Figure 12.33

Main Ascending PathwaysMain Ascending Pathways

The central processes of fist-order neurons The central processes of fist-order neurons branch diffusely as they enter the spinal cord branch diffusely as they enter the spinal cord and medullaand medulla

Some branches take part in spinal cord reflexesSome branches take part in spinal cord reflexes Others synapse with second-order neurons in the Others synapse with second-order neurons in the

cord and medullary nucleicord and medullary nuclei Fibers from touch and pressure receptors form Fibers from touch and pressure receptors form

collateral synapses with interneurons in the collateral synapses with interneurons in the dorsal hornsdorsal horns

Three Ascending PathwaysThree Ascending Pathways

The nonspecific and specific ascending The nonspecific and specific ascending pathways send impulses to the sensory cortexpathways send impulses to the sensory cortex These pathways are responsible for discriminative These pathways are responsible for discriminative

touch and conscious proprioceptiontouch and conscious proprioception The spinocerebellar tracts send impulses to the The spinocerebellar tracts send impulses to the

cerebellum and do not contribute to sensory cerebellum and do not contribute to sensory perceptionperception

Nonspecific Ascending PathwayNonspecific Ascending Pathway

Nonspecific Nonspecific pathway for pathway for pain, pain, temperature, and temperature, and crude touch crude touch within the lateral within the lateral spinothalamic spinothalamic tracttract

Figure 12.34b

Specific and Posterior Specific and Posterior Spinocerebellar TractsSpinocerebellar Tracts

Specific ascending pathways within the Specific ascending pathways within the fasciculus gracilis and fasciculus cuneatus fasciculus gracilis and fasciculus cuneatus tracts, and their continuation in the medial tracts, and their continuation in the medial lemniscal tracts lemniscal tracts

The posterior spinocerebellar tractThe posterior spinocerebellar tract

Descending (Motor) PathwaysDescending (Motor) Pathways

Descending tracts deliver efferent impulses Descending tracts deliver efferent impulses from the brain to the spinal cord, and are from the brain to the spinal cord, and are divided into two groupsdivided into two groups Direct pathways equivalent to the pyramidal tractsDirect pathways equivalent to the pyramidal tracts Indirect pathways, essentially all othersIndirect pathways, essentially all others

Motor pathways involve two neurons (upper Motor pathways involve two neurons (upper and lower)and lower)

The Direct (Pyramidal) SystemThe Direct (Pyramidal) System Direct pathways originate with the pyramidal Direct pathways originate with the pyramidal

neurons in the precentral gyrineurons in the precentral gyri Impulses are sent through the corticospinal Impulses are sent through the corticospinal

tracts and synapse in the anterior horntracts and synapse in the anterior horn Stimulation of anterior horn neurons activates Stimulation of anterior horn neurons activates

skeletal musclesskeletal muscles Parts of the direct pathway, called Parts of the direct pathway, called

corticobulbar tracts, innervate cranial nerve corticobulbar tracts, innervate cranial nerve nucleinuclei

The direct pathway regulates fast and fine The direct pathway regulates fast and fine (skilled) movements(skilled) movements

Indirect (Extrapyramidal) Indirect (Extrapyramidal) SystemSystem

Includes the brain stem, motor nuclei, and all Includes the brain stem, motor nuclei, and all motor pathways not part of the pyramidal motor pathways not part of the pyramidal systemsystem

This system includes the rubrospinal, This system includes the rubrospinal, vestibulospinal, reticulospinal, and tectospinal vestibulospinal, reticulospinal, and tectospinal tractstracts

Indirect (Extrapyramidal) Indirect (Extrapyramidal) SystemSystem

These motor pathways are complex and These motor pathways are complex and multisynaptic, and regulate:multisynaptic, and regulate: Axial muscles that maintain balance and postureAxial muscles that maintain balance and posture Muscles controlling coarse movements of the Muscles controlling coarse movements of the

proximal portions of limbsproximal portions of limbs Head, neck, and eye movementHead, neck, and eye movement

Extrapyramidal (Multineuronal) Extrapyramidal (Multineuronal) PathwaysPathways

Reticulospinal tracts – maintain balanceReticulospinal tracts – maintain balance Rubrospinal tracts – control flexor musclesRubrospinal tracts – control flexor muscles Superior colliculi and tectospinal tracts Superior colliculi and tectospinal tracts

mediate head movementsmediate head movements

Spinal Cord Trauma: ParalysisSpinal Cord Trauma: Paralysis

Paralysis – loss of motor functionParalysis – loss of motor function Flaccid paralysis – severe damage to the Flaccid paralysis – severe damage to the

ventral root or anterior horn cellsventral root or anterior horn cells Lower motor neurons are damaged and impulses Lower motor neurons are damaged and impulses

do not reach musclesdo not reach muscles There is no voluntary or involuntary control of There is no voluntary or involuntary control of

muscles muscles

Spinal Cord Trauma: ParalysisSpinal Cord Trauma: Paralysis

Spastic paralysis – only upper motor neurons Spastic paralysis – only upper motor neurons of the primary motor cortex are damagedof the primary motor cortex are damaged Spinal neurons remain intact and muscles are Spinal neurons remain intact and muscles are

stimulated irregularlystimulated irregularly There is no voluntary control of musclesThere is no voluntary control of muscles

Spinal Cord Trauma: Spinal Cord Trauma: TransectionTransection

Cross sectioning of the spinal cord at any level Cross sectioning of the spinal cord at any level results in total motor and sensory loss in results in total motor and sensory loss in regions inferior to the cutregions inferior to the cut

Paraplegia – transection between TParaplegia – transection between T11 and L and L11

Quadriplegia – transection in the cervical Quadriplegia – transection in the cervical regionregion

PoliomyelitisPoliomyelitis

Destruction of the anterior horn motor neurons Destruction of the anterior horn motor neurons by the poliovirusby the poliovirus

Early symptoms – fever, headache, muscle Early symptoms – fever, headache, muscle pain and weakness, and loss of somatic pain and weakness, and loss of somatic reflexesreflexes

Vaccines are available and can prevent Vaccines are available and can prevent infectioninfection

Amyotrophic Lateral Sclerosis Amyotrophic Lateral Sclerosis (ALS)(ALS)

Lou Gehrig’s disease – neuromuscular condition Lou Gehrig’s disease – neuromuscular condition involving destruction of anterior horn motor involving destruction of anterior horn motor neurons and fibers of the pyramidal tractneurons and fibers of the pyramidal tract

Symptoms – loss of the ability to speak, Symptoms – loss of the ability to speak, swallow, and breatheswallow, and breathe

Death occurs within five yearsDeath occurs within five years Linked to malfunctioning genes for glutamate Linked to malfunctioning genes for glutamate

transporter and/or superoxide dismutasetransporter and/or superoxide dismutase

Developmental Aspects of the Developmental Aspects of the CNSCNS

CNS is established during the first month of CNS is established during the first month of developmentdevelopment

Gender-specific areas appear in response to Gender-specific areas appear in response to testosterone (or lack thereof)testosterone (or lack thereof)

Maternal exposure to radiation, drugs (e.g., Maternal exposure to radiation, drugs (e.g., alcohol and opiates), or infection can harm the alcohol and opiates), or infection can harm the fetus’ developing CNSfetus’ developing CNS

Smoking decreases oxygen in the blood, which Smoking decreases oxygen in the blood, which can lead to neuron death and fetal brain damagecan lead to neuron death and fetal brain damage

Developmental Aspects of the Developmental Aspects of the CNSCNS

The hypothalamus is one of the last areas of The hypothalamus is one of the last areas of the CNS to developthe CNS to develop

Visual cortex develops slowly over the first 11 Visual cortex develops slowly over the first 11 weeksweeks

Growth and maturation of the nervous system Growth and maturation of the nervous system occurs throughout childhood and reflects occurs throughout childhood and reflects progressive myelinationprogressive myelination

Developmental Aspects of the Developmental Aspects of the CNSCNS

Age brings some cognitive declines, but these Age brings some cognitive declines, but these are not significant in healthy individuals until are not significant in healthy individuals until they reach their 80sthey reach their 80s

Excessive use of alcohol causes signs of Excessive use of alcohol causes signs of senility unrelated to the aging processsenility unrelated to the aging process