• Reflex: programmed unit of behavior
• Stimulus from a receptor (sensory nerve) automatically leads to response of an effector (motor nerve) (without input from cerebrum) 

1. Posterior Columns
2. Spinothalamic tract 
3. Spinocerebellar pathway

• Receptors in joint capsules
• muscles
• skin (tactile and pressure receptors)

• Sensory pathways ↑ parietal lobe sensory strip
• well localized touch, proprioception, vibration, & Stereognosis (close eyes and feel what object is)
• make it possible to put key in a door lock or visualize the position of any part of your body without looking

• The sense of where our body is in space: stretch receptors send info to our brain, it integrates all info and lets us know where our body is
• make it possible to put key in a door lock or visualize the position of any part of your body without looking

• Include destructive tumors, hemorrhage, scar tissue, swelling, infections, direct trauma
• Tactile (touch) sensations can be gone or diminished
• so can movement/ position sense

Spinal cord anatomy

[image]

• Neurons enter the cord and pass directly into Posterior Funiculus
• Fibers from lumbosacral region enter Lowest part of posterior columns (fasciculus/nucleus gracilis)
• Occupy most medial portions of column 
• Fibers higher up the cord occupy more lateral positions of posterior columns (fasciculus/nucleus cuneatus)

association neurons

confined to the CNS

innervate:

Bowel, bladder

sexual function

• Neurons Enter directly into posterior funiculus
• initially remain on same side of spinal cord that it enters
• Crosses over at junction between spinal cord and brainstem (in the medulla)
• Travels up the medial lemniscus to the somatic sensory cortex 

• decreases in conscious proprioception, stereognosis and some touch 
• Ipsilaterally below level of lesion
• i.e cut at right T1 level = loss of touch and vibration on right side below T1
• (would also usually affect pain and temp on the left side of the body due to same lesion affecting the right spinothalamic tract)

• Pathway for Pain & Temp 
• enters spinal cord dorsally
• Immediately crosses over to opposite side of cord (to the lateral or ventral funiculus)
• Ascends to Thalamus on opposite side
• Moves to the sensory area of the cerebral cortex

Loss of pain/temp sensation contralaterally  below level of the lesion

• Features of both pathways (therefore, usually do not completely lose) 
• Partly remains uncrossed until reaches brain stem
• Partly crosses over at lower levels
• Unilateral spinal cord lesions: light touch usually spared
• Alternate route will carry info

• Individual sensory units are smaller and more numerous in the fingers
• There are fewer receptors in the hands and much fewer in the arms

• Unconscious pathway connects with cerebellum (an unconscious organ)
• Unconscious proprioception & unconscious stereognosis
• Allows you to walk and do complex acts Subconsciously without having to think about component parts of the act (provides gait corrections)
• 1° remains ipsilateral 
• In general, one side of cerebellum connects with same side of the body
• 
  

• Junction between brain stem and spinal cord
• Level where the corticospinal pathway crosses over

• Part of the CNS
• Motor neurons Above the level of the synapse at the anterior horn of the spinal cord

• Part of the Peripheral Nervous System
• Motor neurons below the synapse at the anterior horn of the spinal cord
• Exit the spinal cord

• Due to lesion in brain or spinal cord (defect seen contralateral to lesion?)
• Spastic paralysis (ie cerebral palsy)
• NO muscle atrophy
• No fasciculations/fibrillations
• Hyperreflexia (4+): DTRs
• + Babinski reflex

• Sole of the foot is storked
• Big toe hyperextends (toward head) and other toes fan out (abduct)

• Seen on same side as peripheral lesion
• Flaccid paralysis

• Combination of UMN and LMN signs (only dz that affects both)
• Lower: 
  • muscle weakness
  • atrophy
  • fibrillations (rapid twitching of muscle)
  • Fasciculations (contractions of groups of muscle fibers)
• Upper:
  • Hyperreflexia
• Lesions on both anterior horns (motor) of grey matter (lower motor defects) & Cortiocospinal tracts (upper motor defects)

• Proprioceptive loss (posterior columns)
• Pain
• Posterior root irritation
• Particularly affects lower extremities
• can also lead to cerebral atrophy in neurosyphilis

• Due to low B₁₂ levels
• Proprioceptive loss
• UMN weakness
• Leads to degeneration of Posterior columns and cortiocospinal tracts 

• virus affects anterior horn cells (right where lower motor neuron synapses at ventral root)
• Lower motor neuron involvement
• Weakness
• Atrophy
• Fasciculations, fibrillations
• Hyporeflexia

• Sensory and lower motor neuron loss
• Peripheral nerve involvement 
• Autoimmune attack on myelin sheaths

• 2° to carotid artery occlusion (embolic) or hemorrhage 
• Upper motor neuron lesion
• Decorticate posturing (flexion of wrist and elbow and extension of ankle and knees)

• Decerebrate posturing
• Elbow extended as well as ankle and knee

• Result in motor problems
• Quality of coordinated movements affected 
• not paralysis

• Awkwardness of intentional movements
• Movements clumsy, unsteady and inappropriately change in speed, force and direction
• The finger may initially overshoot its mark, but finally reaches it: dysmetria
• Intention tremor may appear toward the end of movement
• Causes incoordination that may get worse with eyes closed
• Loss of proprioception
• Repetitive and consistent deviation to one side (past pointing) worse with eyes closed: cerebellar or vesitbular dz (get good hx to distinguish, vestibular often acute onset)
• Cerebellar ataxia

Pt has difficulty standing with feet together with eyes open or closed

Rhomberg test: sway with eyes open or closed

Cerebellar dysfunction: sway with eyes open or closed

Proprioception/Posterior column dysfunction: sway with eyes closed, can correct with eyes open

• Sensory and motor defects on contralateral side
• Tough to decide if lesion is in cerebral cortex or internal capsule
  • Test language to determine: if affected = cerebral cortex
• Cerebral cortex: Presence of higher level dysfunction:
  • agnosia or apraxia

• Ipsilateral and contralateral defects
• Because certain pathways "cross over" and others don't 

• Unilateral lesion: ipsilateral paralysis and proprioceptive loss (b/c posterior columns damaged)
• Contralateral pain-temp loss below level of lesion (damaged spinothalamic tract)

• Clinically, in localizing strokes to the brainstem look for the "cardinal" feature of:                                  * an ipsilateral peripheral cranial nerve involvement  * a contralateral weakness or sensory deficit
• Cerebellar signs, if present should be ipsilateral
• a dissociated sensory deficit overt the face or half the body usually indicates a lesion within the brainstem
• Bilaterality of both motor and sensory signs is almost certain evidence of a brainstem lesion
• vertigo (spinning) is a common early symptom of brainstem strokes

• Tumor on the 8th cranial nerve
  • causes LMN deficits
• Large tumors can press the brain stem as well
  • cause UMN deficits

• Ipsilateral motor and sensory defects
• Distinguish from internal capsule or cerebral cortical injuries by presence of LMN signs (hypotonicity, ↓ DTRs)
• Also, motor and sensory defects along a dermatomal distribution, follow innervations of the at particular nerve
• Severing a single peripheral nerve can cause severe symptoms 

• Severing a single spinal nerve Root results in little if any motor or sensory defect because of the overlap of adjacent roots
• Usually have to cut 3 or more roots to have a sig motor or sensory defect 

• impaired knee extension
• impaired hip flexion
• impaired knee jerk 

• onset and progression of symptoms
• Sudden onset: vascular cause
• Slow progressive: degenerative or cancerous process
• subacute/fluctuating course: infections, inflammatory processes or demyelinating dz

• Olfactory n. 
• sense of smell
• never becomes a peripheral nerve 
• Origin: telencephalon

• Absence of smell (anosmia): Common causes: nasal, paranasal dz, viral infections, trauma
• Decreased smell (hyposmia): Parkinsons, Alzheimers, HIV, severe DM
• Olfactory hallucinations: temporal lobe seizures

• Optic nerve
• Transmits visual information
• Defined as that extent of the visual system pathway from the back of the eyeball up to the optic chiasm
• Controls vision (visual assessment)
• Never becomes a peripheral nerve
• Origin: diencephalon

• Monocular visual field loss: lesion of the optic nerve 
• Bilateral temporal field deficit: pituitary lesion or optic chiasm lesion

• Visual loss on same side of each eye
• Lesion of optic radiations on side of brain OPPOSITE of pts deficits
• Rt visual field loss: left brain lesion

"Pie in the sky"

Temporal lobe lesion

"pie on the floor"

Parietal lobe lesion

• Oculomotor n. 
• Pupillary constriction
• Lid elevation
• Most extra-ocular movements (except superior oblique and lateral rectus)
• Origin: midbrain

• Eye movement problem: may complain of double vision
• CN3 Palsy: vascular problem from DM, hypertension, atherosclerosis
  • Pt has ptosis eye is positioned down and out
• Pupil abnormalities: 
  • Opiates: small, nonreactive
  • Mydriatic drops: large, nonreactive
• Horner syndrome: reactive to light and accommodation, ptosis, miosis and anhidrosis: sympathetic dysfunction (unilateral)
• Age: small, reactive pupils
• Argyll Robertson pupils: (neurosyphilis): small, nonreactive to light, responds to accommodation

• 3rd CN nerve disorders can impair ocular motility, pupillary fxn, or both
• Sxs include diplopia, ptosis, paresis of eye adduction, upward and downward gaze, and if the pupil is affected, pupil dilation and impaired light reflexes

• Trochlear
• Superior oblique
• moves eye down toward nose
• Origin: midbrain

• Isolated CN 4 palsy: often due to trauma
• often have vertical diplopia

• Trigeminal 
• Largest cranial nerve
• 1° sensory nerve of face and head
• Origin: pons

• Most common problem: trigeminal neuralgia (lancinating pain in 1 or more branches of trigeminal nerve)
  • Irritation of the trigeminal nerve root by neurovascular compression

• Abducens
• Lateral recurs muscle
• Moves eye laterally
• Origin: posterior margin of pons

• Horizontal double vision
• common CN 6 nerve palsies: neoplasm

• Facial
• 1° a motor nerve, to muscles of facial expression, and secretomotor innervation to salivary and lacrimal glands
• Origin: pons

• Facial nerve palsy:
• If forehead and eye are involved: peripheral nerve lesion (LMN problem) 
• Often caused by "Bell's Palsy"
• Idiopathic
• Most recover in 2-3 weeks, but can have permanent deficits
• If pt can wrinkle forehead = UMN deficit

• Vestibulocochlear 
• senses sound, rotation and gravity
• Origin: lateral to CN VII

• Cochlear portion involvement: trouble hearing and noise in ear (tinnitus)
• Hearing loss: causes are age (presbycusis) and noise
• Many drugs are ototoxic (anti-neoplastics, anti-inflammatories, diuretics, anti-malarials)

• Glossopharyngeal
• mixed nerve:
  • motor fibers to pharyngeal muscles for swallowing 
  • Parasympathetic motor fibers to salivary glands
  • sensory fibers carry messages from pharynx, tonsils, posterior tongue (taste)
  • afferent messages from the carotid sinus baroreceptors 
• origin: medulla

• Neuralgia: uncommon
• Lancinating pain in ear, base of tongue, lower jaw, tonsillar fossa
• sometimes syncope (carotid sinus innervation)

• Vagus nerve
• supplies branchiomotor innervation to laryngeal and pharyngeal muscles and parasympathetic fibers to thoracic and abdominal viscera
• origin: posterior sulcus of medulla

• Dysphagia (swallowing) and dysarthria (speech articulation) are most common clinical features of vagal dysfunction
  • pt will be drooling (unable to swallow)
  • always r/o stroke
• Weakness of muscles of pharynx and larynx
• Parasympathetic system can be overactive → hypotension

• accessory nerve
• controls sternocleidomastoid and trapezius muscles
• Origin: Cranial and spinal roots

• Nerve can be injured by intracranial or cervical trauma
• Shoulder pain, winging of scapula, weak elevation of shoulder

• Hypoglossal
• Provides motor innervation to muscles of the tongue
• Important for swallowing and speech
• Origin: Medulla

Lesions result in dysarthria

(tongue deviated to one side when protruded)