The cord is composed The cord is composed of: of:

Inner core of Gray Inner core of Gray matter.matter.

On cross sectionOn cross section It is It is H- shapedH- shaped PillarPillar or or

Butter Fly.Butter Fly. Outer core of White Outer core of White

matter.matter.

It is correlated to: It is correlated to: Amount of Muscle Amount of Muscle InnervatedInnervated. .

GreatestGreatest in:in: CervicalCervical andand

Lumbosacral Lumbosacral Segments.Segments. They innervate the They innervate the

muscles ofmuscles of thethe Upper Upper and Lower limbs.and Lower limbs.

AnteriorAnterior and and PoPosteriorsterior Gray Columns orGray Columns or HornsHorns..

They are united by:They are united by: A A thin thin Gray Gray

Commissure.Commissure. It contains the smallIt contains the small

Central CanalCentral Canal..

It ReceivesIt Receives Most of the Most of the

Termination of theTermination of the Dorsal Nerve RootsDorsal Nerve Roots entering the spinal entering the spinal cord.cord.

Contains: Contains: Lower Motor Neurons.Lower Motor Neurons. Their axons exit throughTheir axons exit through

Ventral Nerve RootsVentral Nerve Roots to to innervate the skeletal innervate the skeletal muscles.muscles.

The NeuronsThe Neurons receive Input from:receive Input from:

Descending pathways for Descending pathways for the motor control.the motor control.

Some dorsal root afferents.Some dorsal root afferents.

A small A small Intermediolateral Intermediolateral Horn Horn is present in:is present in:

Thoracic Thoracic andand Upper Upper LumbarLumbar Segments.Segments.

It contains the cell It contains the cell bodies ofbodies of PreganglionicPreganglionic Sympathetic Sympathetic Neurons.Neurons.

A similar place is found A similar place is found in: in:

22ndnd 3 3rdrd and 4 and 4thth Sacral Sacral Segments. Segments.

It gives rise toIt gives rise to Preganglionic Preganglionic Parasympathetic Parasympathetic NeuronsNeurons..

The Gay Matter can The Gay Matter can be divided into (be divided into (1010) ) Zones. Zones.

They are Numbered They are Numbered SequentiallySequentially fromfrom Dorsal to Ventral.Dorsal to Ventral.

Superficial LaminaeSuperficial Laminae Receive:Receive:

Cutaneous Afferents.Cutaneous Afferents. Deeper Laminae Receive: Deeper Laminae Receive: Proprioceptive and Proprioceptive and

Muscle Afferents. Muscle Afferents.

At theAt the Tip of theTip of the Dorsal Dorsal HornHorn (Laminae 1-111 (Laminae 1-111))

It Extends:It Extends: Throughout the Length of Throughout the Length of

the spinal cord . the spinal cord . It receives:It receives: 1. 1. Nerve Fibers associated Nerve Fibers associated

with Nociception with Nociception Temperature and TouchTemperature and Touch. .

2. 2. Input fromInput from Supraspinal Supraspinal Levels.Levels.

Large Nerve Cells.Large Nerve Cells. Position:Position: Anterior to Substantia Anterior to Substantia

Gelatinosa.Gelatinosa. Extension:Extension: Throughout the spinal cord. Throughout the spinal cord. It receives:It receives: Fibers from the Posterior Fibers from the Posterior

White Column associated with White Column associated with the sensesthe senses ofof Position and Position and Movement.Movement.

Composed of:Composed of: Thoracic Nucleus. Thoracic Nucleus. Nucleus DorsalisNucleus Dorsalis.. Occupies:Occupies: Base of the Dorsal Horn Base of the Dorsal Horn (Lamina (Lamina

V11):V11): Segments Segments C8C8- - L3L3 It receives afferents from:It receives afferents from: Muscle Spindle. Muscle Spindle. Golgi Tendon Organs.Golgi Tendon Organs. Tactile and Pressure ReceptorsTactile and Pressure Receptors. . These form the ascending fibers of These form the ascending fibers of

the the Dorsal Spinocerebellar Tract.Dorsal Spinocerebellar Tract.

(1) Alpha Neurons :(1) Alpha Neurons : Innervate Innervate Extrafusal Extrafusal

muscle fibers.muscle fibers. (2) Gamma Neurons: (2) Gamma Neurons: Innervate Innervate Intrafusal Intrafusal

muscle fibers within the muscle fibers within the muscle. muscle.

Neurons innervating Neurons innervating Muscles of the Muscles of the Neck Neck and and TrunkTrunk : :

MedialMedial . . Neurons innervating Neurons innervating

Muscles of the Muscles of the LimbsLimbs :: Lateral.Lateral.

Phrenic NucleusPhrenic Nucleus Centrally Located (C3-Centrally Located (C3-

C5).C5). Gives rise to: Gives rise to: Phrenic Phrenic

Nerve.Nerve. Essential for Breathing.Essential for Breathing. Acessory NucleusAcessory Nucleus Located in the Upper Located in the Upper

Cervical Segments.Cervical Segments. Its Axons form theIts Axons form the

Spinal Part of the Spinal Part of the Acessory Nerve.Acessory Nerve.

Completely Surrounds the Completely Surrounds the Gray Matter. Gray Matter.

More AbundantMore Abundant in the in the Upper Levels of the cordUpper Levels of the cord The The Ascending TractsAscending Tracts gain gain More Fibers at each More Fibers at each successivesuccessive level. level.

The The Descending fibersDescending fibers have have the opposite.the opposite.

Dorsal.Dorsal. Lateral. Lateral. VentralVentral

It is Dorsolateral It is Dorsolateral FasciculusFasciculus..

LocatedLocatedSuperficial to the Tip of the Superficial to the Tip of the

Dorsal HornDorsal Horn..Formed ofFormed of Ascending and Descending Ascending and Descending

branches of the Dorsal branches of the Dorsal Roots which Roots which Don’t Don’t Terminate at their Point of Terminate at their Point of Entry. Entry.

Fibers within the TractFibers within the Tract Run Varying Distances in Run Varying Distances in

Either DirectionEither Direction

Fasciculus PropriusFasciculus Proprius Occupies:Occupies: A Narrow band A Narrow band

immediately Peripheral immediately Peripheral to the Gray Matter.to the Gray Matter.

Functions:Functions: Interconnects Adjacent Interconnects Adjacent

or Distant Cord or Distant Cord Segments.Segments.

Permit Intersegmental Permit Intersegmental Coordination. Coordination.

Between the Posterior Between the Posterior Median Sulcus and the Median Sulcus and the Posterior Horn.Posterior Horn.

Composed of:Composed of: Fasciculus GracilisFasciculus Gracilis : : Medial throughout the Medial throughout the

Length of the Spinal Length of the Spinal Cord . Cord .

ContainsContains Ascending fibers fromAscending fibers from Sacral, Lumbar and Sacral, Lumbar and

Lower Thoracic.Lower Thoracic.

Fasciculus CuneatusFasciculus Cuneatus Lateral.Lateral. Receives fibers from:Receives fibers from: Upper Thoracic and Upper Thoracic and

Cervical regionsCervical regions.. The Fasciculi (Gracilis & The Fasciculi (Gracilis &

Cuneatus)are concerned Cuneatus)are concerned with with

Proprioceptive InformationProprioceptive Information ((Awareness of Posture and Awareness of Posture and Discriminitive Touch).Discriminitive Touch).

CONTAIN:CONTAIN: (1) Ascending Tracts(1) Ascending Tracts Dorsal Spinocerebellar:Dorsal Spinocerebellar: Carries information from: Carries information from:

Muscles, joints and ligaments. Muscles, joints and ligaments. For the Control of Posture and For the Control of Posture and

Coordination of Movement. Coordination of Movement.

Lateral Spinothalamic :Lateral Spinothalamic : Carries impulses of Carries impulses of Pain, Temperature, Pressure and Pain, Temperature, Pressure and

Coarse Touch (Extroceptive).Coarse Touch (Extroceptive).

(2) Descending Tracts:(2) Descending Tracts: Lateral Corticospinal:Lateral Corticospinal: Controls Controls Voluntary, Discrete and Voluntary, Discrete and

Skilled Movements.Skilled Movements. Rubrospinal:Rubrospinal: Has a control over the Tone Has a control over the Tone

of Limb Flexor Muscles.of Limb Flexor Muscles.

CONTAIN:CONTAIN: (1) Descending Tracts(1) Descending Tracts 1. Ventral 1. Ventral

CorticospinalCorticospinal 2.Tectospinal2.Tectospinal.. Mediates reflex Mediates reflex

movements in movements in response to Visual response to Visual Stimuli.Stimuli.

3.Vestibulospinal3.Vestibulospinal Has an Influence Has an Influence

upon Extensor Motor upon Extensor Motor neurons.neurons.

4. Reticulospinal4. Reticulospinal It influences It influences

Voluntary movement, Voluntary movement, Reflex activity and Reflex activity and Muscle Tone. Muscle Tone.

(2) Ascending Tracts(2) Ascending Tracts 1. 1. Ventral Ventral

SpinocerebellarSpinocerebellar.. 2. 2. Ventral Ventral

SpinothalamicSpinothalamic.. 3. 3. Medial Longitudinal Medial Longitudinal

Fasciculus.Fasciculus.

(1) Poliomyelitis(1) Poliomyelitis AcuteAcute Viral Infection of the Viral Infection of the

Lower Motor neuronsLower Motor neurons . . Rapid ParalysisRapid Paralysis and and

Wasting of the Limb.Wasting of the Limb. Can Affect the Diaphragm.Can Affect the Diaphragm. Recovery is Incomplete.Recovery is Incomplete.

Chronic Degenerative Chronic Degenerative DiseaseDisease..

A Progressive Muscular A Progressive Muscular Atrophy with Hypotonia Atrophy with Hypotonia and Wasting of the limband Wasting of the limb muscles.muscles.

Affect both the Lower Affect both the Lower Motor Neurons and the Motor Neurons and the Descending Tracts.Descending Tracts.

Degeneration of the Degeneration of the Descending Tracts cause Descending Tracts cause Spasticity and Weakness Spasticity and Weakness of the muscles.of the muscles.

SPINAL REFLEXSSPINAL REFLEXS Involuntary stereotyped Involuntary stereotyped

response that is response that is initiated by a sensory initiated by a sensory stimulus.stimulus.

The pathway is formed The pathway is formed of of afferent afferent neuronesneurones conveying impulses conveying impulses from sensory receptors from sensory receptors in the in the CNSCNS ( spinal cord ( spinal cord or brain stem) and or brain stem) and efferentefferent neurones neurones coming out from the coming out from the CNS to the effector CNS to the effector organ (muscle or gland).organ (muscle or gland).

SPINAL REFLEXSSPINAL REFLEXS Interneurons Interneurons

within the CNS within the CNS exist between the exist between the afferent and afferent and efferent efferent components.components.

Reflexes areReflexes are qualitatively qualitatively thethe same butsame but quantitativelyquantitatively they they differdiffer..

FUNCTIONS OF STRETCH FUNCTIONS OF STRETCH REFLEXESREFLEXES

(1)(1) control of muscle control of muscle tone which in turn tone which in turn determine the determine the proportion of motor proportion of motor units that are active units that are active at any one time. at any one time.

(2) control of posture (2) control of posture by keeping the anti by keeping the anti gravity muscles at a gravity muscles at a constant length in constant length in opposition to opposition to imposed stretch.imposed stretch.

STRETCH RECEPTORSSTRETCH RECEPTORS Neuromuscular spindlesNeuromuscular spindles

((muscular spindlesmuscular spindles) ) are are most numerous in the most numerous in the central non contractile central non contractile part toward the part toward the tendinous attachment of tendinous attachment of skeletal muscles.They skeletal muscles.They provide sensory provide sensory information that is used information that is used by the CNS in the by the CNS in the control of muscle control of muscle activity. Each spindle activity. Each spindle has a fusiform capsule has a fusiform capsule and contains slender and contains slender intrafusalintrafusal muscle fibers.muscle fibers.

STRETCH RECEPTORSSTRETCH RECEPTORS The nuclear bag The nuclear bag

fibers are concerned fibers are concerned with dynamic with dynamic responses and are responses and are associated more associated more with velocity and with velocity and position of position of contraction.the contraction.the nuclear chain fibers nuclear chain fibers are associated with are associated with slow static slow static contractions.contractions.

STRETCH RECEPTORSSTRETCH RECEPTORS

The intrafusal fibers The intrafusal fibers are of two types : the are of two types : the nuclear bagnuclear bag and the and the nuclear chainnuclear chain. .

There are two types of There are two types of sensory ending of sensory ending of muscle spindles : the muscle spindles : the (primary) (primary) annulospiral annulospiral and the (secondary) and the (secondary) flower sprayflower spray..

The ordinary muscle The ordinary muscle fibers outside the fibers outside the spindles are the spindles are the extrafusal fibersextrafusal fibers..

STRETCH RECEPTORSSTRETCH RECEPTORS

There are two types There are two types of sensory ending of of sensory ending of muscle spindles : the muscle spindles : the (primary) (primary) annulospiral annulospiral and the and the (secondary) (secondary) flower flower sprayspray..

The ordinary muscle The ordinary muscle fibers outside the fibers outside the spindles are the spindles are the extrafusal fibersextrafusal fibers..

STRETCH (MONOSYNAPTIC ) STRETCH (MONOSYNAPTIC ) REFLEXREFLEX

Stretching(elongationof Stretching(elongationof the intrafusal fibers the intrafusal fibers results in stimulation of results in stimulation of the annulospiral and the annulospiral and flower spray endings.flower spray endings.

Nerve impulses pass to Nerve impulses pass to the spinal cord in the the spinal cord in the afferent neurons.In the afferent neurons.In the spinal cord, they spinal cord, they stimulate the large alpha stimulate the large alpha motor neurons.the motor neurons.the efferent motor neurons efferent motor neurons stimulate the extrafusal stimulate the extrafusal fibers and the muscle fibers and the muscle contracts.contracts.

STRETCH (MONOSYNAPTIC ) STRETCH (MONOSYNAPTIC ) REFLEXREFLEX

The muscle spindle The muscle spindle afferent neurons inhibit afferent neurons inhibit the alpha motor the alpha motor neurons supplying the neurons supplying the antagonist muscles antagonist muscles ((reciprocal inhibitionreciprocal inhibition).).

GAMMA REFLEX LOOPGAMMA REFLEX LOOP

Centers in the brain and Centers in the brain and spinal cord( reticular spinal cord( reticular formation, basal ganglia and formation, basal ganglia and cerebellum)give rise to tracts cerebellum)give rise to tracts that synapse with the gamma that synapse with the gamma motor neurons.motor neurons.

Gamma efferent motor fibers Gamma efferent motor fibers cause shortening of the cause shortening of the intrafusal fibers and stimulate intrafusal fibers and stimulate the sensory nerve endings the sensory nerve endings and lowers the threshold to and lowers the threshold to externall applied stretch .this externall applied stretch .this in turn initiates the reflex in turn initiates the reflex contraction of the extrafusalcontraction of the extrafusal fibers.fibers.

FLEXOR REFLEXFLEXOR REFLEX

It is a It is a polysynapticpolysynaptic reflex reflex in which one or more in which one or more interneurons are interneurons are interposed between interposed between afferent and efferent afferent and efferent neurons. Cutaneous neurons. Cutaneous stimulation of the limbs stimulation of the limbs causes withdrawal from causes withdrawal from the stimulus.the stimulus.

All forms of cutaneous All forms of cutaneous stimulation can initiate stimulation can initiate flexor reflex but normally flexor reflex but normally they are inhibited by they are inhibited by descending tracts from the descending tracts from the brain unless the stimulus brain unless the stimulus is painful.is painful.

CROSSED EXTENSOR REFLEXCROSSED EXTENSOR REFLEX

Activation ofActivation of the the flexor reflex in a flexor reflex in a weight bearing limb weight bearing limb simultaneously simultaneously causes reflex causes reflex extension of the extension of the contralateral limb contralateral limb so as to carry the so as to carry the weight of the body. weight of the body.