NEURO: Quiz 3 Flashcards
Sympathetic efferent pathway: T1-L2
Origin: T1-L2 Destination: Body wall (anterior and posterior) -- Erector pili muscles -- Sweat glands -- Blood vessels
Preganglionic:
– Lateral horn – Ventral root – Spinal nerve
– White rami communicantes
– Paravertebral ganglion
Postganglionic:
– Gray rami communicantes – Ventral or dorsal rami
– Anterior or posterior trunk
Autonomic system organization
Sympathetic system:
– “Thoracolumbar system” (T1-L2)
– Function: Fight, flight, and fright
– Structure:
Short preganglionic neurons – Sympathetic ganglia – Long postganglionic neurons
– Innervates:
– Organs above diaphragm (e.g., eye, heart, lungs, lacrimal glands, salivary glands)
– Organs below diaphragm (e.g., liver, pancreas, stomach, kidney, genitalia, bladder)
– Blood vessels, sweat glands, and erector pili muscles of body wall and limbs
Parasympathetic system:
– “Craniocaudal system” (CN 3, 7, 9, 10; S2-4)
– Function: Homeostasis (“Rest and digest”)
– Structure:
Long preganglionic neurons – Short postganglionic neurons (near organ)
– Innervates:
– Organs above diaphragm (e.g., eye, heart, lungs, lacrimal glands, salivary glands)
– Organs below diaphragm (e.g., liver, pancreas, stomach, kidney, genitalia, bladder)
NOTE: No parasympathetics in limbs and body wall (anywhere with sweat gland)
Sympathetic efferent pathways: T1-4
Origin: T1-T4
(1) Destination: Head, neck, and upper limbs (erector pili muscles, sweat glands, blood vessels)
Preganglionic:
– Lateral horn – Ventral root – Spinal nerve – White rami communicantes
– Superior, middle, or inferior cervical ganglion (travel up from T1)
Postganglionic:
– Gray rami communicantes (LATERAL) – Ventral or dorsal rami – Head, neck, limbs
(2) Destination: Organs above diaphragm
(A) Heart and lungs
Preganglionic:
– Lateral horn – Ventral root – Spinal nerve – White rami communicantes
– Superior, middle, or inferior cervical ganglion OR paravertebral ganglion (same level)
Postganglionic:
– Gray rami communicantes (MEDIAL) – Sympathetic nerves – Heart and lungs
(B) Eyes, lacrimal gland, salivary glands, and cranial nerves
Preganglionic:
– Lateral horn – Ventral root – Spinal nerve – White rami communicantes
– Superior cervical ganglion (ONLY)
Postganglionic:
– Gray rami communicantes (MEDIAL) – Arteries – Eyes, glands, cranial vessels
Sympathetic efferent pathway: T5-L2
Origin: T5-L2
Destination: Organs below diaphragm
-- Liver, Kidney, Pancreas
-- Intestines, Stomach
-- Urinary tract and bladder
-- Genitalia
Preganglionic:
-- Lateral horn -- Ventral root -- Spinal nerve -- White rami communicantes
-- PASS THROUGH paravertebral ganglion -- splanchnic nerve
-- Great splanchnic = T5-9
-- Lesser splanchnic = T10-11
-- Least splanchnic = T12
-- Prevertebral ganglion
Postganglionic:
-- Organs below diaphragmSympathetic efferent pathways: T12-L2
Origin: T12-L2
(1) Destination: Pelvis and lower limbs (Erector pili muscles, Sweat glands, Blood vessels)
Preganglionic:
– Lateral horn – Ventral root – Spinal nerve – White rami communicantes
– Lower paravertebral ganglion (sympathetic chain)
Postganglionic:
– Gray rami communicantes – Ventral or dorsal rami – Pelvis and lower limbs
(2) Destination: Organs below diaphragm
– Liver, Kidney, Pancreas, Intestines, Stomach, Urinary tract and bladder, Genitalia
Preganglionic:
– Lateral horn – Ventral root – Spinal nerve – White rami communicantes
– PASS THROUGH paravertebral ganglion (at same OR lower level)
– Lumbar and sacral splanchnic nerves (lower ganglia only)
– Inferior or superior hypogastric plexuses (regions of ganglia)
Postganglionic:
– Organs below diaphragm
NOTE: Two ways to get to organs below diaphragm:
T5-L2 – splanchnic nerves – prevertebral ganglia – organs
T12-L2 – sympathetic chain – lumbar/sacral splanchnic nerves – hypogastric plexus –organs
Lesser and least splanchnic overlap with lumbar and sacral splanchnic (lower levels)
Sympathetic efferent pathway origins: Body wall Head, neck, and upper limbs Lower limbs and pelvis Organs above diaphragm Organs below diaphragm
Body wall (erector pili muscles, sweat glands, blood vessels) -- T1-L2 (via paravertebral ganglion)
Head, neck, and upper limbs (erector pili muscles, sweat glands, blood vessels)
– T1-4 (via cervical ganglia)
Lower limbs and pelvis (erector pili muscles, sweat glands, blood vessels)
– T12-L2 (via lower paravertebral ganglion)
Organs above diaphragm
- T1-4
- Heart and lungs (via cervical or paravertebral ganglia)
- Eyes, glands, and cranial vessels (via superior cervical ganglion)
Organs below diaphragm
- T12-L2 (via splanchnic nerves)
- T5-L2 (via hypogastric plexuses)
Sympathetic afferent pathway
Origin:
– Internal organs and smooth muscles of large vessels in limbs
Destination: Posterior horn of spinal cord (via dorsal root ganglion)
Information: Visceral sensory (pain, discomfort, baroreceptor, chemoreceptor)
Single neuron (NO SYNAPSE):
- Organ – PASS THROUGH ganglia (prevertebral and paravertebral)
- White rami communicantes – Dorsal root ganglion – Posterior horn
Parasympathic efferent and afferent pathways
Efferent:
Origin: CNs 3, 4, 7, 10: S2-4 Path: -- Long preganglionic -- Parasympathetic ganglion (near organ) -- Short postganglionic neuron
Afferent:
Origin: Organs
Path: CN 10 or S2-4
Autonomic disreflexia
= Reaction of autonomic system to overstimulation by noxious stimulus
– In SCI patients (most often above T6)
– Characterized by:
– Vasoconstriction below level of lesion
~ Cold, clammy skin and goose bumps
– Vasodilation above level of lesion
~ Bradychardia, flushed skin, headache, sweating, increased spasticity
– Severe hypertension ~ Seizure, cerebral hemorrhage, MI (life threatening)
Cause:
- Noxious stimuli below lesion triggers sympathetic reflex (visceral afferent)
- Vasoconstriction – Increase BP
- Carotid sinus and aortic receptors detect increased BP – Vasodilation above
- Signal to vasodilate can not travel below lesion – Vasoconsriction below
Common stimuli:
- Full bladder (#1) or rectal distension
- Pressure sores, urinary stones
- Environmental changes, cutaneous irritation (e.g., folded sock)
Treatment: Medical emergency
- DO NOT LAY PERSON DOWN (increases blood flow to brain)
- Remove stimulus (e.g., catheterization)
NOTE: Occurrence decreases over time (rare > 3 years)
Referred pain
= Pain perceived at location other than site of stimulus
Mechanism:
- Visceral afferent carrying info from organ (distortion or inflammation)
- Visceral afferent runs adjacent to somatic afferent when entering posterior horn
- Brain interprets visceral afferent info as coming from somatic afferent dermatome
- Pain is referred to body surface according to spinal level visceral afferent enters
Example:
– Visceral afferent from heart enters at T3-4 – referred pain to T3-4 dermatome
Receptors
Chemoreceptors
- Smell
- Taste
- Metabolic compounds (e.g., O2/CO2 in blood)
Thermoreceptors
– Changes in temperature
Photoreceptors
– Retina (rods and cones)
Mechanoreceptors
– Physical deformation
Nocioceptors
– Pain (also part of other categories, e.g., heat)
General senses
(1) Light touch = awareness and precise location of very delicate stimuli
- - Three types:
- - Two point sense = discriminate between two points on skin
- - Stereognosis = ability to recognize object without visual input (touch only)
- - Graphesthesia = ability to recognize numbers and letters drawn on skin
(2) Crude touch = aware of touch but cannot discriminate
- - Same types of receptors as light touch, just fewer
(3) Pressure = deep touch (compression of subcutaneous tissue beneath dermis)
(4) Vibration = tuning fork over bony prominence felt by subcutaneous tissue
(5) Proprioception = limb position and motion sense (active and passive)
- - Ability to sense location and movement of one part of body in relation to other
(6) Pain
- - Two types:
- - First pain = sharp, pricking, well localized
- - Slow pain = dull, achy, burning, diffuse (usually after first pain)
(7) Temperature = distinguishing hot and cold
Sensory homunculus regions
Postcentral gyrus:
– Lower extremity/foot = Medial
– Trunk = Superior medial
– Upper extremity/hand = Superior lateral
– Face = Lateral
Encapsulated sensory receptors
= Surrounded by mechanical barrier (capsule)
Cutaneous:
- Pacinian corpuscle = Vibration
- Highly adaptive (no longer send signal if constant), but vibratio continuously changing stimulus so still sensed
- Subcutaneous
- Meissner corpuscle = Touch
- Vertical pressure
- Dermis, near border with epidermis
- Ruffini ending = Pressure
- Dermis, deeper than Meissner (requires more compression)
Muscle:
– Muscle spindles = Stretch (none with isometric contraction)
– Annulospiral endings = Onset of stretch
– Spiral around central region of intrafusal fibers
– Speed and change in length of fibers
– Slow rate of firing once muscle in constant stretch
– Flower spray endings = Maintain discharge during stretch (isometric contraction)
– On each side of annulospiral endings
– Less sensitive
Tendon:
– Golgi tendon organ = Tension in tendon
– Higher threshold than muscle spindle
– Stimulus requires greater stretch (near injury)
Nonencapsulated somatosensory receptors
= Surrounded by only thin capsule or none
- Endings around hair = Touch
- Sense movement of hair at base of hair root
- Dermis
- Merkel endings (tactile disc) = Touch
- Dermis (near border of epidermis)
- Free nerve endings = Touch, pain, temperature, itch
- Dermis, deeper
Dermatomes
= Area of skin supplied by the cutaneous fibers of a single spinal segment
C2 = Back of head C5 = Tip of shoulder (deltoid insertion) C6 = Thumb (web space) C7 = Middle finger C8 = Little finger
T4/T5 = Nipple line T10 = Umbilicus L1 = Inguinal ligament L4/5 = Big toe S1 = Small toe S5 = Perianal region
Dorsal column
Senses: Light touch, proprioception, vibration, pressure
Pathway:
First order neuron
– Lower extremity (below T6):
– DRG (cell body) – Posterior funiculus (Gracile fasiculus) – UP
– Lower medulla (Gracile nucleus) (posterior side) – SYNAPSE
– Upper extremity (above T6)
– DRG – Posterior funiculus (Cuneate fasiculus) – UP
– Lower medulla (Cuneate nucleus) (posterior side) – SYNAPSE
Second order neuron
– Gracile or cuneate nucleus (cell body)
– Decussation of medial lemniscus (anterior side) – CROSSES and UP
– Thalamus – SYNAPSE
Third order neuron
– Thalamus (cell body)
– Post-central gyrus
– Medial part (lower limb)
– Superior lateral part (upper limb)
Spinothalamic tract (anterolateral system)
Senses: Pain and temperature
– Also: crude touch, tickle, itch, bowel and bladder pressure, sexual sensation
Pathway:
First order neuron
– DRG (cell body) – tract of Lissauer
– Bifurcates (ascending and descending branches) – UP or DOWN 1-2 segments
– Posterior horn – SYNAPSE
Second order neuron
– Posterior horn (cell body) = Substantia gelatinosa (cluster of cell bodies)
– Anterior commissure – CROSS
– Anterior or lateral funiculus (Spinothalamic tract) – UP
– Thalamus – SYNAPSE
Third order neuron
– Thalamus (cell body) – Post-central gyrus
– Medial = Lower limb and foot
– Superior medial = Trunk
– Superior lateral = Upper limb and hand
– Lateral = Face
Pathway arrangements
Medial to lateral:
Dorsal column -- Sacral -- Lumbar -- Thoracic -- Cervical NOTE: As each higher level enters spinal cord from lateral side (from dorsal root), lower level is pushed medially
Spinothalamic tract: -- Cervical -- Thoracic -- Lumbar -- Sacral NOTE: As each higher level enters anterior funiculus from opposite side of cord (from anterior commissure), lower level is pushed laterally
Spinal cord lesion sensory effects:
Examples:
(1) Bilateral posterior funiculus
(2) Bilateral anterior cord
(1) Bilateral posterior funiculus
Dorsal column (touch, vibration, pressure, and proprioception)
– 1st neuron enters – cannot travel upward on either side
= Bilateral loss at and below lesion
Spinothalamic (pain and temperature)
– 1st neuron enters – synapses in dorsal horn
– 2nd neuron crosses – travels up anterior funiculus – synapses in thalamus
– 3rd neuron goes to postcentral gyrus
= No loss
(2) Bilateral anterior cord
Dorsal column:
– 1st neuron enters – travels up posterior funiculus – synapse in medulla
– 2nd neuron – cross in medulla – synapse in thalamus
– 3rd neuron goes to postcentral gyrus
= No loss
Spinothalamic tract:
– 1st neuron enters – synapse in posterior horn
– 2nd neuron crosses to anterior funiculus – cannot travel upward on either side
= Bilateral loss at and below lesion
Spinal cord lesion sensory effects
Examples:
(1) Left side cord
(2) Bilateral gray matter
(1) Left side cord
Dorsal column:
– 1st neuron enters left side – cannot travel up on left side
= Left side loss at and below lesion
– 1st neuron enters right side – can travel upward on right – crosses in medulla
= No right side loss at or below lesion
Spinothalamic tract:
At level:
– 1st neuron enters left – cannot synapse
= Left side loss at lesion
– 1st neuron enters right – synapses in posterior horn
– 2nd neuron crosses to left – cannot travel upwards
= Right side loss at lesion
= Bilateral loss at lesion
Below lesion:
– 1st neuron enters left – synapses in posterior horn
– 2nd neuron crosses right – can travel upwards
= No left side loss below lesion
– 1st neuron enters right – synapses in posterior horn
– 2nd neuron crosses left – travels up to lesion level – blocked
= Right side loss below lesion
(2) Bilateral gray matter Dorsal column: At and below level: -- 1st neuron enters -- travels up posterior funiculus -- synapse in medulla = No loss either side
Spinothalamic tract: At level: -- 1st neuron enters -- cannot synapse = Bilateral loss at level Below level: -- 1st neuron enters -- synapses -- 2nd neuron crosses -- travels up anterior funiculus to thalamus = No loss below level
Pathway levels
Postcentral gyrus (frontal section)
-- Homonculus regions (cortex)
-- Lateral ventricle
-- Thalamus
-- Basal ganglia
-- Internal capsule
Transverse sections:
Midbrain
-- Cerebral aqueduct
-- Cerebral peduncles
Pons
-- Fourth ventricle
Medulla (lower)
-- Gracile nucleus (posterior medial)
-- Cuneate nucleus (posterior lateral)
-- Decussation of the medial lemniscus (anterior)
Upper spinal cord (C1-T6)
-- Gracile fasiculus (posterior medial)
-- Cuneate fasciculus (posterior lateral)
= Split in posterior funiculus
-- No lateral horn (above T2)
Lower spinal cord (T7-Co1)
-- No split in posterior funiculus
-- No lateral horn (below L2)
Spinal cord spinothalamic components:
- Tract of Lissauer (from posterior horn)
- Substantia gelatinosa (posterior horn)
- Anterior white commissure (anterior)
Trigeminal nerve (touch)
Three branches (V-1, V-2, V-3) Origin: General sensory from face
Pathway:
First order neuron:
– Trigeminal ganglion (cell body) – Principle trigeminal nucleus (level of pons) – SYNAPSE
Second order neuron:
– Principle trigeminal nucleus (cell body) – axon crosses at mid pontine level – CROSS
– Trigeminothalamic tract – ASCENDS – Thalamus – SYNAPSE
Third order neuron:
– Thalamus (cell body) – Lateral postcentral gyrus (face region of homunculus)
NOTE: “Touch” refers to light touch only
Trigeminal nerve (pain and temperature)
Three branches
Origin: Pain and temperature from face
Pathway:
First order neuron:
– Trigeminal ganglion (cell body) – Pons
– Tract of Lissauer/Spinal trigeminal tract – DESCENDS
– Spinal trigeminal nucleus (upper cervical) – SYNAPSES (multiple)
Second order neuron:
– Spinal trigeminal nucleus (cell body) – axons CROSS
– Trigeminothalamic tract – ASCENDS
– Thalamus – SYNAPSE
Third order neuron:
– Thalamus (cell body) – Thalamocortical axons – Face region of homonculus
