Spinal Cord

      Runs through the vertebral canal Extends from foramen magnum to second lumbar vertebra Regions  Cervical     Thoracic Lumbar Sacral Coccygeal Gives rise to 31 pairs of spinal nerves  All are mixed nerves Spinal cord Enlargements  Cervical enlargement: supplies upper limbs  Lumbo -sacral enlargement: supplies lower limbs Conus medullaris- tapered inferior end  Ends between L1 and L2

Spinal Segments & Roots

Spinal segment C8, T12, L5, S5, Cx1 Anterior (Ventral) Root Posterior (Dorsal) Root Dorsal Root (Spinal) Ganglion Root - Rootlets

Spinal Segments

 Importance of the spinal segments

Coverings of Spinal cord

    Dura mater: outermost layer; continuous with epineurium of the spinal nerves Arachnoid mater: thin and web like Pia mater: bound tightly to surface    Ligamentum Denticulatum Cordotomy Forms the filum terminale  anchors spinal cord to coccyx Spaces    Epidural: external to the dura   Anesthestics injected here Epidural Anesthesia Subdural space: serous fluid Subarachnoid: between pia and arachnoid  Filled with CSF

Coverings of Spinal cord cont…

Lumbar Puncture

Lumbar Puncture – lumbar (terminal) cistern

Spinal Cord

  White Matter Anterior Funiculus (Anterior White Column) Posterior Funiculus (Posterior White Column) Lateral Funiculus (Lateral White Column) Gray Matter Anterior Horn ----------- motor Posterior Horn -------------- sensory Lateral Horn -----------------autonomic (sympathetic) Gray Commissure -------- anterior and posterior

Cord Organization

 Principles of Cord Organization 1) Longitudinal Arrangement Fibers (White Matter) ------------ White Column Cell Groups (Gray Matter) ------- Gray Column 2) Transverse Arrangement Afferent & Efferent Fibers Crossing (Commissural and Decussating) Fibers 3) Somatotopical Arrangement

Somatosensory Pathway(Dorsal Colum)

Somatosensory Pathway

Posterior column pathway carries sensation of highly localized touch, pressure, vibration.

Posterior column pathway includes:   Fasciculus cuneatus tract Fasciculus gracilus tract Carries fine touch, pressure, vibration, sterognosis and conscious Proprioceptive sensations.

Dorsal Colum tracts

dorsal cloumn pathway

Dorsal Colum Lesion

dorsal column pathway Left spinal cord injury Loss of sense of: •touch •proprioception •vibration in left leg

Dorsal Colum Lesions

 Sensory ataxia  Patient staggers; cannot perceive position or movement of legs  Visual clues help movement  Rombergism

Assessment of Dorsal Colum

Case ….

     An 85-year-old man is being evaluated for gait difficulties. On examination it is found that joint proprioception is absent in his toes. People with impaired position sense will usually fall if they stand with their feet together and do which of the following?

Flex the neck Extend their arms in front of them Flex the knees Turn the head Close their eyes

Clinical Case

 A 45 year old woman complained of pain in her right breast and progressive weakness of her right lower limb for a period of two months, she contacted her Family physician, Her Family physician referred her to a neurologist.

 The neurologic evaluation revealed weakness in the right lower limb. This was associated with spasticity (increased tone), hyperreflexia (increased deep tendon reflexes) at the knee and ankle, which also demonstrated clonus.  On the right side there was loss of two-point discrimination, touch ,vibratory sense and proprioception at levels below the hip. The left side showed a loss of pain and temperature sensation below dermatome T-7.

Clinical Case Of Spinal Cord cont..

 MRI of a patient indicated to have an extramedullary tumor expanding from the dorsal roots at spinal cord levels T-5,6.

 Based on the symptoms and clinical findings what is your diagnosis ?

Anterolateral system

The Anterolateral Pathway

 Provides sensations of “crude” touch, pressure, pain, and temperature  Ascend within the anterior or lateral spinothalamic tracts:

What is Pain?

 “An unpleasant sensory & emotional experience associated with actual or potential tissue damage, or described in terms of such damage” –       Subjective sensation Pain Perceptions – based on expectations, past experience, anxiety, suggestions   Affective – one’s emotional factors that can affect pain experience Behavioral – how one expresses or controls pain  Cognitive – one’s beliefs (attitudes) about pain Physiological response produced by activation of specific types of nerve fibers Experienced because of nociceptors being sensitive to extreme mechanical, thermal, & chemical energy. Composed of a variety of discomforts One of the body’s defense mechanism (warns the brain that tissues may be in jeopardy)

Where Does Pain Come From?

 Cutaneous Pain – sharp, bright, burning; can have a fast or slow onset  Deep Somatic Pain – stems from tendons, muscles, joints, periosteum, & b. vessels  Visceral Pain – originates from internal organs; diffused @ 1 st & later may be localized (i.e. appendicitis)  Psychogenic Pain – individual feels pain but cause is emotional rather than physical

Anterolateral System (Pain &Temp)

Left spinal cord injury spinothalamic pathway Loss of sense of: •Touch •Pain •Warmth/cold in right leg

    

Spinothalamic Tracts

Located lateral and ventral to the ventral horn Carry impulses concerned with pain and thermal sensations (lateral tract) and also non- discriminative touch and pressure (medial tract) Fibers of the two tracts are intermingled to some extent In brain stem, constitute the spinal lemniscus Fibers are highly somato topically arranged, with those for the lower limb lying most superficially and those for the upper limb lying deeply

Lateral Spinothalamic Tract

  Carries impulses concerned with pain and thermal sensations. Axons of 1 st order neurons terminate in the dorsal horn  Axons of 2 nd order neuron (mostly in the nucleus proprius), decussate within one segment of their origin, by passing through the ventral white commissure & terminate on 3 rd order neurons in ventral posterior nucleus of the thalamus  Thalamic neurons project to the somatosensory cortex

Anterior Spinothalamic Tract

    Carries impulses concerned with non- discriminative touch and pressure Axons of 1 dorsal horn st order neurons enter cord terminate in the Axons of 2 nd order neuron (mostly in the nucleus proprius) may ascend several segments before crossing to opposite side by passing through the ventral white commissure & terminate on 3 in ventral posterior nucleus of the thalamus rd order neurons Thalamic neurons project to the somatosensory cortex

Spino-reticulo-thalamic System

 The system represents an additional route by which dull, aching pain is transmitted to a conscious level  Some 2 nd order neurons terminate in the reticular formation of the brain stem, mainly within the medulla  Reticulothalamic fibers ascend to intralaminar nuclei of thalamus, which in turn activate the cerebral cortex

Pain Control Theories

 Gate Control Theory  Endogenous Opiates Theory  Phantom Pain  Refferd Pain

Gate Control Theory

   Melzack & Wall, 1965 Substantia Gelatinosa (SG) in dorsal horn of spinal cord acts as a ‘gate’ SG cells of Lamina II act as a inhibitory neurons and inhibit “T” cells of lamina IV  Larger diameter afferent fibers of touch excite both SG and T cells, Therefore afferent signals of pain sensation from T cells is blocked by stimulation of inhibitory SG cells.  Small diameter afferent fibers excite T cells and Inhibit SG cells Therefore Gate is kept

Descending Pain Inhibition

 Descending Pain Modulation (Descending Pain Control Mechanism)  Periaqueductal Gray Area (PGA) – release enkephalins  Nucleus Raphe Magnus (NRM) – release serotonin    The release of these neurotransmitters inhibit ascending neurons Stimulation of the PGA in the midbrain & NRM in the pons & medulla causes analgesia.

Endogenous opioid peptides - endorphins & enkephalins

Referred Pain?

 Dermatomal rule  Convergence  Facilitation

Grey Matter Of Spinal cord

White Matter Anterior Funiculus (Anterior White Column) Posterior Funiculus (Posterior White Column) Lateral Funiculus (Lateral White Column) Gray Matter Anterior Horn ----------- motor Posterior Horn -------------- sensory Lateral Horn ----------------- autonomic (sympathetic) Gray Commissure ------- anterior and posterior

Principles of Cord Organization

1) Longitudinal Arrangement Fibers (White Matter) ------------- White Column Cell Groups (Gray Matter) ------- Gray Column 2) Transverse Arrangement Afferent & Efferent Fibers Crossing (Commissural and Decussating) Fibers 3) Somatotopical Arrangement

Principles of Cord Organization

Lamina of Rexed Lamina I ---------- posteromarginal nucleus Lamina II ---------- substantia gelatinosa of Rolando Lamina III, IV ----- nucleus proprius Lamina V, VI Lamina VII --------- intermediate gray intermediolateral cell column (ILM) Clarke’s column (Nucleus dorsalis) intermediomedial cell column (IMM) Lamina VIII Lamina IX ---------- anterior horn (motor) cell Lamina X ----------- gray commissure

Alpha Motor Neurons

  Motor Unit Motor End Plate   Phasic Tonic

Muscle Spindle

Motor Pathways

 CNS issues motor commands in response to information provided by sensory systems, sent by the somatic nervous system (SNS) and the autonomic nervous system (ANS)    Conscious and subconscious motor commands control skeletal muscles by traveling over 3 integrated motor pathways The corticospinal pathway – voluntary control of motor activity  Corticobulbar tracts  Corticospinal tracts The medial and lateral pathways lower motor neurons – modify or direct skeletal muscle contractions by stimulating, facilitating, or inhibiting

Motor Pathways

• Contain a sequence of TWO neurons from the cerebral cortex or brain stem to the muscles • Upper motor neuron : has cell body in the cerebral cortex or brain stem, axon decussates before terminating on the lower motor neuron • Lower motor neuron: has cell body in the ventral horn of the spinal cord, axon runs in the ipsilateral ventral root of the spinal nerve and supply the muscle.

UMN LMN

Descending Spinal Tracts

  Originate from the cerebral cortex & brain stem Concerned with:  Control of movements  Muscle tone  Spinal reflexes & equilibrium  Modulation of sensory transmission to higher centers  Spinal autonomic functions

 The motor pathways are divided into two groups  Direct pathways (voluntary motion pathways) - the pyramidal tracts  Indirect pathways (postural pathways), essentially all others the extrapyramidal pathways

Direct (Pyramidal) System

 Regulates fast and fine (skilled) movements  Originate in the pyramidal neurons in the precentral gyri,  Impulses are sent through the corticospinal tracts and synapse in the anterior horn  Stimulation of anterior horn neurons activates skeletal muscles  Part of the direct pathway, called corticobulbar tracts, innervates cranial nerve nuclei

Indirect (Extrapyramidal) System

 Complex and multisynaptic pathways  The system includes: • Rubrospinal tracts: control flexor muscles • Vestibulospinal tracts: maintain balance and posture • Tectospinal tracts: mediate head neck, and eye movement • Reticulospinal tracts

Descending Spinal Tracts

 Pyramidal  Corticospinal  Extrapyramidal  Rubrospinal  Tectospinal  Vestibulospinal  Olivospinal  Reticulospinal  Descending Autonomic Fibers

Corticospinal Tracts

 Concerned with voluntary, discrete, skilled movements, especially those of distal parts of the limbs (fractionated movements)  Innervate the contralateral side of the spinal cord  Provide rapid direct method for controlling skeletal muscle

 Origin: motor and sensory cortices   Axons pass through corona radiata, internal capsule, crus cerebri and pyramid of medulla oblongata  In the caudal medulla about 75-90% of the fibers decussate and form the

lateral corticospinal tract

Rest of the fibers remain ipsilateral and form

anterior corticospinal tract

. They also decussate before termination

 Distribution:  55% terminate at cervical region  20% at thoracic  25% at lumbosacral level  Termination: Ventral horn neurons (mostly through interneurons, a few fibers terminate directly) 

Corticobulbar tracts

end at the motor nuclei of CNs of the contralateral side

Rubrospinal Tract

 Controls the tone of limb flexor muscles, being excitatory to motor neurons of these muscles  Origin : Red nucleus  Axons course ventro medially, cross in ventral tegmental decussation , descend in spinal cord ventral to the lateral corticospinal tract  Cortico-rubro-spinal pathway (Extrapyramidal)

Tectospinal Tract

 Mediates reflex movements of the head and neck in response to visual stimuli  Origin : Superior colliculus  Axons course ventro-medially around the periaqueductal gray matter, cross in dorsal tegmental decussation , descend in spinal cord near the ventral median fissure, terminate mainly in cervical segments  Cortico-tecto-spinal pathway (Extrapyramidal)

    

Vestibulospinal Tracts

Lateral Vestibulospinal Tracts Origin : lateral vestibular (Deiter’s) nucleus Axons descend ipsilaterally the ventral funiculus in Terminate on ventral horn cells throughout the length of spinal cord Has excitatory influences upon extensor motor neurons, control extensor muscle tone in the antigravity maintenance of posture

Case ..

 Following an automobile accident, an eighteen year old male was hospitalized for several weeks. A neurological exam at that time revealed the following: 1. Complete loss of conscious proprioception in the right lower limb.

2. Babinski sign on the right.

3. Inability to detect pain and temperature sensation on the medial side of the antecubital fossa (medialepicondyle) on both upper limbs.

4. Inability to detect pain and temperature at the apex of the left axilla, in all the intercostal spaces on the left, and in the left lower limb.

5. The patient could feel a gentle squeezing of both thumbs, right and left middle fingers, and the left little finger.

6. No sensation to squeezing could be detected in the right little finger.

   Ipsilateral paralysis below the lesion. Paralysis is the "Upper Motor Neuron" or spastic type; there is spasticity, slow (disuse) muscle atrophy, hypertonia, ankle clonus and a positive Babinski sign. Superficial reflexes, e.g., the abdominal and cremasteric are lost. Spastic paralysis is attributed to interruption of the lateral corticospinal tract and the accompanying lateral reticulospinal tract. Loss of these upper motor neurons deprives the anterior horn cells, i.e., lower motor neurons, of the impulses which generate contraction of skeletal muscle, hence, weakness (paresis) or paralysis. Hypertonia and hyperreflexia appear to result from loss of the inhibitory effects of these two descending motor pathways on the stretch reflexes, leaving them hyperexcitable to segmental muscle afferents

 It may be possible to also demonstrate a "Lower Motor Neuron Syndrome" or flaccid paralysis ipsilaterally at the level of the lesion. If the anterior horn cells supplying the skeletal muscles are injured at the level of the lesion then these muscles are denervated. This paralysis is of the flaccid type; muscles undergo rapid atrophy due to loss of the trophic influence of the nerves as well as disuse.  Tone and tendon reflexes are diminished since they are reflex responses and the injured lower motor neurons are the "final common pathway" to the muscle in the stretch reflex, hence, there is no reflex.

  

Loss of conscious proprioception, two-point

discrimination and vibratory sense ipsilaterally is due to interruption of the posterior white columns (fasciculus gracilis/cuneatus). This is frequently accompanied by a Romberg sign. A normal individual, standing erect with heels together and eyes closed, sways only slightly. Stable posture is achieve by 1) a sense of position from the vestibular system, 2) awareness of the position and status of muscles and joints by conscious proprioception and 3) visual input regarding our position. Closing the eyes has only slight effect on the normal individual's stance since the vestibular and conscious proprioception systems are sufficient. In a patient with an impaired posterior column conscious proprioception is diminished; when the eyes are closed loss of both systems renders the patient unstable and they are likely to sway or fall to the side.

  Pain and temperature sensation is lost below the lesion, on the opposite side beginning about one dermatomal segment below the level of the lesion. These sensations are carried by the lateral spinothalamic tract whose fibers originated on the side opposite the lesion but which crossed in the anterior white commissure. Dorsal root afferents carrying pain and temperature synapse in the dorsal gray; the second order neuron crosses in the anterior white commissure along an ascending path for a distance of about one spinal segment. Because of the oblique ascent of the crossing fibers in the anterior white commissure, injury of the spinothalamic tract is not likely to be carrying sensation from that level.

 A careful sensory evaluation may reveal that at the dermatomal level of the lesion there is a bilateral loss of pain and temperature sensation. Since the second order neurons from both sides cross in the midline below the central canal, a hemisection of the cord may interrupt the crossing fibers from both sides and produce this limited bilateral deficit.

Hemisection of Spinalcord

side Sensory disturbance Motor disturbance Reflexes At the level of lesion On the same side On the same side Below Loss of all sensation

1 2-

superfecial sensations deep sensations

1-LMNL 2-

paralysis of muscles which its supply arising from damage Loss of the dorsal column due to damage of gracil & cunite leading to loss of 1.

2.

fine touch kinesthetic 3.

4.

vibration sterognosis

UMNL

due to damage of pyramidal tract On the Opposite side

Loss of 1-

pain & temp.

due to damage of lateral spinothalamic tract.

2-

crude touch due to damage of ventral spinothalamic tract.

Above On the same side Hyperanasthesia (Hypersensitivity) increase sensitivity to 1.

pain 2.

3.

touch Temp.

Loss of all reflexes which its centers in damage segments

1-

loss of flexor withdrawal reflex

2-

increase crossed extensor reflex

Case 2….

• • A 55 year old man noticed a weakness of his left hand and loss of pain in his both arms which was progressing and causing him mental apathy and he felt he should visit neurologist .

On examination he demonstrated bilateral weakness, atrophy, and fasciculations of the intrinsic muscles of his hands and shoulders. Upper motor neuron syndrome signs, i.e., weakness, hypertonia, hyperreflexia, positive Babinski, were evident in both lower extremities. Dermatomes C-2 through T-6 demonstrated bilateral loss of pain and temperature sensation. There was bilateral impairment of position and vibratory sense below the hips.

Case 2 cont..

 MRI investigation showed a central cavitation at C-2 through T-7 which expanded symmetrically in all directions.  It involved the anterior white commissure (spinothalamic fibers) and included portions of the posterior white columns, lateral white funiculus, and anterior gray horns.

Syringomyelia

Syringomyelia

 the result of central cord cavitation affecting a few segments, and usually involving the cervical spinal cord  frequently found in Arnold-Chiari malformations affecting the upper cervical cord and medulla  mainly affects the crossing fibres of the spinothalamic tract as they decussate in the ventral white commissure => bilateral pain- temperature sensory loss over a few segments eg. only affecting the neck and upper shoulders in a cape-like distribution (or only affecting the upper limbs) with normal sensation above and below the affected dermatomes    does not affect the spinothalamic tracts in the early stages => no initial lower trunk or lower limb pain-temperature sensory loss does not usually affect the dorsal columns => normal position sense ("dissociative" sensory loss) may rarely affect the lower motor neurons to the upper limbs early in the disease course, and may eventually affect the corticospinal tracts

 A 66-year-old man found that, over a period of time, he developed progressive bilateral weakness of both upper and lower limbs beginning with the muscles of the hands. However, testing revealed that sensory functions appeared normal. Eventually, this individual was found to have wasting of muscles, fasciculations, and evidence of upper motor neuron (UMN) dysfunction, together with an increase in tendon reflexes. After a few additional Months, the patient developed facial weakness and an inability to swallow (dysphagia). Further analysis revealed abnormalities in the electromyegram (EMG) of the upper and lower extremities, denervation atrophy. However, the cerebrospinal fluid (CSF) remained normal.

Which of the following is the most likely diagnosis ?



MS



Amyotrophic lateral sclerosis (ALS)



Poliomyelitis



Myasthenia gravis



A cerebral cortical stroke