OTM 507: Neuro part 2

Lower motor neuron

Cell body in grey matter of ventral horn, axons travel to skeletal muscle, axons bundle together to form ventral root which joins with dorsal root to form spinal nerve

Cranial nerves have LMN

Upper motor neurons

Cell body in cortical areas or brainstem, project to LMN and interneurons in brainstem or spinal cord

Motor tracts

bundle of UMN in the CNS that transmit output information

Apraxia

impaired ability to carry out motor activities despite intact motor function due to difficulties planning motor activities

Cortical Spinal tract

A major descending motor tract

- Carries motor information from the motor cortex to the spinal cord

- Decussation of the cortical-spinal tract occurs in medulla

Corticobulbar tract

Goes from motor cortex to brainstem,

Decussate at brainstem where CN's III-XII transition from UMN to LMN

Synapse with LMN the control muscles of the face, tongue, pharynx, larynx, sternocleidomastoid, and trapezius

Ipsilateral and contralateral synapses

LMN lesions

weakness, atrophy, fasciculations (muscle twitches), decreased reflexes, decreased tone (flacidity)

UMN lesions

weakness, increased reflexes, increased tone (spasticity, rigidity, posturing), Babinksi, hoffmans test, clonus

Spinal Cord Injury

Sensory, LMN, UMN

All or part of spinal cord is damaged

Cerebral vascular accident (CVA)

Ischemic/hemorrhagic in any of the blood vessels of the brain

Sensory, UMN

Spasticity, weakness, Babinski, hyperreflexia

Cerebral palsy

Stroke in utero

Sensory, UMN

Cortical areas of movement impaired

Weakness, spasticity, increased tone, balance/postural deficits, contractures, possible cognitive changes, non-progressive, permanent disabilities and variable

Multiple Sclerosis

Sensory, UMN, cognitive

affects brain and spinal cord

CNS disorder, comes and goes

Weakness, hypertonia, spasticity, hyperreflexia, vision deficits, pain, coordination difficulties

Guillain Barre syndrome

Peripheral nervous system disorder that attacks Schwann cells

Sensory, LMN, autoimmune

Can follow a viral infection/vaccinations

weakness, pain, tingling, sensory deficits, autonomic dysfunction (constipation, tachycardic, diaphoretic)

Amyotrophic lateral sclerosis (ALS)

Motor neuron disease

UMN and LMN degeneration

Weakness progresses, poor prognosis

Transverse myelitis

inflammatory disease of the spinal cord

motor, sensory, autonomic functions

Sensory, UMN, LMN

LMN if anterior horn cells involved

Can recover 100% but may have residual symptoms

Spinal muscle atrophy

Genetic, LMN affected

Weakness, atrophy, hypotonia, fasciculations

Can be fatal

Gene replacement therapy promising

Peripheral nerve injury

LMN affected, compressing, stretching, trauma, nerve transmission disruption

Often sensory involvement

Carpal tunnel, Cubital tunnel, Sciatica, Herniated disc

Hypotonia

low muscle tone, low resistance to stretch

Hypertonia

higher muscle tone, high resistance to stretch

Spasticity and rigidity

Spasticity

velocity (speed) dependent resistance to stretch

Rigidity

Decerebrate, decorticate, cogwheel, lead pipe

Stretch resistance

Flaccidity

no resistance to stretch

Functional tests

pronator drift

Alternating movements: toe tap, supination-pronation, hand tapping, finger tapping

Mechanoreceptors

mechanical deformation of the receptor by touch, pressure, stretch, or vibration

Chemoreceptors

substances released by cells, includes damaged cells after injury or infection

Thermoreceptors

transmit information regarding heat or cold

Nociceptors

sensation of pain

Proprioceptors

muscle and joint

Fine touch

A variety or specific receptors

Meisner's corpuscles: light touch, vibration

Merkel's discs: pressure

Course touch

Mediated by free endings throughout the skin

Non discriminative, tickle, itch, pressure, pain

!st order Somatosensory Neurons

Peripheral sensory neurons have two axons

Distal: messages from receptor to cell body

Proximal: from cell body into spinal cord or spinal brainstem

2nd order Somatosensory Neurons

spinal cord or brainstem into thalamus

3rd order Somatosensory Neurons

Thalamus to sensory cortex

Conscious relay

Make distinctions and decisions regarding stimuli

Touch, proprioception, pain, temperature

Divergent

Transmitted to many areas of brainstem and cerebrum

Conscious and unconscious

Unconscious relay

Automatic adjustments, posture

Dorsal column-medial lemniscus system (DCML)

Discriminative touch, vibration, proprioception, Stereognosis

1. Synapse in Nucleus gracilis or cuneatus

2. Decussates in medulla

3. Thalamus

4. Cortex/ Homunculus

Fasiculus gracilis

lower limb DCML

Fasiculus cuneatus

upper limb DCML

Spinothalamic

Anterior: mechanical receptors, crude touch, pressure

Lateral: temperature, pain/nociception

Decussates in spinal cord

Reflexes grades

0: no response

1+: low response

2+: normal

3+: higher than normal

4+: hyperactive

0-1+: LMN lesion

3+-4+: UMN lesion

Ataxia

incoordination that is not a result of weakness

Positive Romberg - sensory ataxia

Use vision to compensate

Cerebellar ataxia

no change in coordination with eyes opened/closed, unable to stand with feet together with or w/o vision, normal vibratory sense, proprioception

Neuropathy

Dysfunction or pathologic condition of one or more peripheral nerves

Injury to peripheral nerve results in lack of sensation in the distribution of the nerve

Pain, sensory changes, reflex loss, Conscious proprioception and discriminative touch go first

Trauma

complete or partial severing of the spinal cord

Transection of the cord

sensation is prevented below the lesion

Hemisection of the cord

loss of pain and temp sensation contralateral below lesion

discriminative touch and proprioception are lost ipsilateral below lesion

Disease

compromises the function of specific areas in the spinal cord

Virus

infects the dorsal root ganglion

Shingles/Chicken pox/Varicella

Somatosensory cortex lesions

contralateral loss of sensation, conscious proprioception, two point discrimination, stereognosis, localization of touch and pinprick/pain stimuli, extinction test for neglect

Stroke, tumor

Cortical spinal tract (CST)

Most important descending pathway, motor control of limbs

1. arises from primary motor cortex

2. through internal capsule

3. cerebral peduncles (midbrain)

4. pons

5. Medullary pyramids

6. Decussate

7. spinal cord to anterior horn

8. Synapse with LMN

Lateral CST

85% pyramidal tract fibers descend contralaterally

Lateral white matter columns

Axons enter the sc central grey matter to synapse

Connects with LMN in ventral horn of the spinal cord

movement of more distal muscles

Anterior CST

15% CST continue into the sc ipsilaterally

decussates at appropriate level of spinal cord

Controls movements that involve multiple spinal segments

Synapse with LMN on muscles that control neck, shoulder, and trunk

Babinski reflex

Instant reflex where you stroke the bottom of the foot from the heel along the lateral side and base of the toes to the big toe

Positive sign: toes up or fanning

Negative sign: toes down

Hoffmans test

-Examiner grasps pt's 3rd digit DIP & briskly flicks the fingernail in a downward motion

-(+): thumb & forefinger come closer to one another

-Indicative of an UMN lesion

Disorders of the motor system

spinal cord injury

spinal muscle atrophy

CVA cerebral vascular accident

Cerebral palsy

Amyotrophic Lateral Sclerosis (ALS)

CTS, cubital tunnel syndrome, Sciatica, Disc prolapse

Brown-Sequard Syndrome

Hemi-section of the cord

- ipsilateral (same side) loss of vibration and loss of position sense

- contralateral (opposite side) loss of pain and thermal sense

Central cord syndrome

paint and temperature sense loss of upper extremities cause by injury to the middle portion of the spinal cord

Anterior cord syndrome

pain and temperature sense loss caused by injury to the anterior 2/3 of spinal cord

Posterior cord syndrome

vibration and proprioception sense loss caused by injury to posterior 1/3 of spinal cord

Cauda Equina Syndrome

-Injury at the L1 level and below resulting in a LMN lesion

-Flaccid paralysis w/no spinal reflex activity

Complete spinal cord injury

no motor or sensory at lowest level

Incomplete spinal cord injury

some sensory or motor spared

Transverse cord lesion

Both sides

vibration and position sense loss

pain and temperature sense loss

motor loss

Middle Cerebral artery CVA

stroke of MCA will interfere with motor cortex

Rubrospinal tract

Originates in red nucleus of the midbrain

Decussates in midbrain

Controls flexor tone in UE

Close proximity with LCST so injuries happen together

Spasticity after a stroke

Reticulospinal tract

Medial motor tract

Originates in the reticular formation of the brainstem (pons and medulla)

Controls postural muscles and proximal limb muscles

After stroke, responsible for muscle synergy

Vestibulospinal tract

Medial motor tract

Originates in vestibular nucleus of the pons and medulla

Maintains balance and posture through increased muscle tone and movement of the head and limbs

Nerve cells in vestibular nuclei receive afferents from inner ear and cerebellum

Axons descend undecussated through medulla and length of spinal cord

Synapse with neurons in anterior gray column of spinal cord

Vestibular nuclei

Brainstem nuclei that receive information from the vestibular organs through cranial nerve VIII (the vestibulocochlear nerve)

In pons and medulla

Internal capsule

contains both corticospinal and corticobulbar tracts (motor tracts); carries UMN (no LMN), a couple of its functions include carrying motor commands to lower motor neurons and sensory-related information from the thalamus to the cortex

Somatosensation

sensory information from the skin and musculoskeletal systems, superficial or cutaneous information from the skin

Touch, pain, temperature, proprioception

Learn from the world around us to react to body's needs

Necessary for accurate control of movements and protects against injury

Speed of information processing

determined by: diameter of axons, degree of axonal myelination, number of synapses in the pathway

Sensory receptors

Specialized, different receptors respond to specific stimuli

Mechanoreceptors, Chemoreceptors, Thermoreceptors, Nociceptors, Proprioceptors

Musculoskeletal innervation

muscle spindles, golgi tendon organs, joint receptors, joint, muscle, and skin receptors required for accurate proprioception

Muscle spindle

respond to stretch, more numerous in muscles that control fine motor

Golgi tendon organs

located at musculoskeletal junction, slight changes in tension associated with contraction

Joint receptors

Receptors surrounding a joint that respond to pressure, acceleration, and deceleration of the joint.

Myotatic stretch reflex

muscle perceives quick stretch, information is relayed to spinal cord to alpha motor neurons, efferent produce a contraction of stretched muscle and inhibit antagonist

All at spinal cord level

1st order sensory neurons

peripheral sensory neurons have two axons

Distal and proximal

Distal 1st order

conduct messages from the receptor to the cell body

Proximal 1st order

project from the cell body into the spinal cord or spinal brainstem

2nd order sensory neurons

spinal cord or brainstem to thalamus

3rd order sensory neurons

thalamus to sensory cortex

Homunculus

a maplike representation of regions of the body in the brain part of the post central gyrus

Discriminative touch

localization of touch and vibration and the ability to discriminate between two closely spaced points touching the skin

Stereognosis

identify object in hand without sight

Proprioception

The ability to tell where one's body is in space.

Vibration

able to sense and feel vibration in various parts of the body

Sensory ataxia

No sway with eyes open but loses balance with eyes closed