Basic Movement & Spinal Cord Tracts

Question 1

Reflex:
A basic loop that happens because of a simple stimulus that elicit a simple (motor/sensory) response.
An action that is performed as a response to a stimulus and without conscious thought (automatically/planned).
Ex. Deep tendon reflex

Answer 1

motor; automatically

Question 2

(Reflex/Reflex arc):
o The nerve pathway involved in a reflex action
o ______ nerve + ______ nerve with a synapse between

Answer 2

Reflex arc; motor; sensory;

Question 2

Stepping on Glass
• (Motor/Sensory) input detected on (dorsal/plantar) aspect of the foot
• Information travels up to the spinal cord through the (dorsal/ventral) root and (dorsal/ventral) root ganglia into the (gray/white)
• Dorsal root ganglia branches off and excites and synapses w/ 3 interneurons
o Interneurons: function to modify the signal
1. Inhibitory interneuron
 Release of inhibitory neurotransmitters (IPSP) of the (flexor/extensor) muscles
2. Excitatory interneuron
 Release of excitatory neurotransmitters (EPSP) of the (flexor/extensor) muscles
3. Nociceptive input to the brain
 Relays to brain that something happened
 Damage occurred
o Inhibition of extensor muscles + excitation of flexor muscles  knee flexes (flexor withdrawal reflex)
 Before any executive processing occurs (automatic, reflexive)
 Minimize damage

Answer 2

Sensory; plantar; dorsal; dorsal; gray; extensor; flexor

Question 3

Stepping on glass:

• All happens at the level of the (brain/spinal cord) w/o any other processing that’s happening
• Other Interneurons crossing over to opposite limb
o Crossed extensor reflex
 Able to accept the load that is shifted over to the uninjured side
• The foot that stepped on glass is now in the air
 Exact opposite of flexor withdrawal
o Interneurons
 Once signal comes in from the receptors via the dorsal root ganglia and dorsal root
• Most of the process of this occurs between the interneurons
 _______ are key for reflexes and responses that we see at the spinal cord level
 Also referred to as “propriospinal neurons”
• All signaling happening at the level of the spinal cord

Answer 3

spinal cord; interneurons

Question 4

• Innervations for
o quad: (low/high) lumbar
o hamstring: (lumbar/sacral) region
o one set of innervations in high lumbar + another set at lower segments
 interneurons can travel down to innervate the appropriate muscles


Answer 4

high; sacral

Question 5

Non basic movements (volitional movements):
 Requires coordination of sensory input and motor output
o Coordination of ascending and descending information
 (Motor/Sensory) is critical for coordinated movements
• Need to feel what is going on
 End organ components and (CNS/PNS)
o Muscular integrity
 (CNS/PNS) component
o Needs to be integrated

Answer 5

Sensory; PNS; CNS

Question 6

End Organ Components
•	Receptors/Sensory organs (feelers)
o	Spindles
o	Golgi tendon organs (GTO)
o	Both sitting (within/outside) muscles themselves

Actors (Do-ers)
o	Alpha motor neuron
o	Gamma motor neuron
o	Neuromuscular junction
o	Muscle fibers
o	All must be working properly for the system to move and generate torque + force

Answer 6

within

Question 7

Motor neurons
- also known as (Higher/Lower) motor neurons
- b/c sits at (brain/cord) level
Motor unit
- Motor _____+ (skeletal/muscle) fibers/______
- 3 motor units shown (red, purple, blue)

Answer 7

Lower; cord; neuron; muscle; fascicles;

Question 8

Spinal Nerves: Sensory input (1st/2nd) order
• Focus on General Somatic (Afferent/Efferent) fibers
o Proprioceptive
 “What are WE doing”
• Information coming in at the spinal nerve levels
o 1st order: the first (sensory/motor) system that’s activates
 Muscle spindles and GTO
• Providing information to the (ventral (anterior)/dorsal (posterior)) root down
• Provides majority of the proprioceptive and protective input with respect to movement constantly
• Golgi Tendon Organs: sits (within/outside) tendons
• Muscle Spindles: sits (within/outside) muscle belly
 Also have skin and joint receptors
• Not constant information
• Skin receptors: Information when maximum stretch across of the segment
• Joint receptors: information signaling when compressed/loaded or at maximum tension
o sit w/I cortical bone, ligaments, joint capsule, cartilaginous structures

Answer 8

1st; Afferent; sensory; dorsal (posterior); within; within;

Question 9

• (Motor/Sensory) input is CRITICAL
• People continue getting injured
o b/c there are alterations w/ respect to
these receptors and how they are controlling/driving motion
o Receptors: (Mechanically/Voltage) gated ion channels
 Muscle spindles
 Joint receptors
 GTO

Answer 9

Sensory; Mechanically;

Question 10

Receptor: Muscle spindles
• Synapsing onto the proprioceptive endings
• Some input goes to cord level, some input synapsing onto motor neurons
• Embedded w/i muscle fibers
• 3 parts:
1. (Extrafusal/Sensory) fibers
 Musculoskeletal fibers (actin, myosin)
• Resulting in contraction
2. Intrafusal fibers
3. (Extrafusal/Sensory) fibers
 1a sensory fibers
 Wrapped around the (extrafusal/intrafusal) fibers
 Main function: (to detect stretch/to contract)

Answer 10

Extrafusal; Sensory; intrafusal; to detect stretch

Question 11

• When someone pulls your leg:
o Stretch to the system and body doesn’t like the stretch
o Spindle activation
 Facilitation of a muscle contraction IF we take (CNS/PNS) away
 Results in muscle (contraction/stretch)
• Muscle stretch w/ every degree of motion
o Ex. When flexing biceps  stretch to the triceps
o There is always some level of activation that is happening w/i the (spindles/GTO)
• Muscles naturally under tension/stretched during (movement/rest)

Answer 11

CNS; contraction; spindles; rest

Question 12

Testing Spindle Function: Spinal Reflexes
• 1a response through stretch reflex (Deep tendon reflex)
1. Small tap  (small/large) stretch
 Enough to activate the (1a/1b) fibers
 To create a muscle spindle action potential
2. Synapse w/ an (alpha/gamma) motor neuron
 Activation of the (agonist/antagonist) (quadriceps)
 Reciprocal inhibition
• Inhibition of the (agonist/antagonist) (hamstrings)
3. Bifurcation of the dorsal root
 (Motor/Sensory) input to the brain
• “It was just a tap, can shut it down”
• If something is wrong here
o Hyper reflexive response
 Greater magnitude of kicking
• Tap to the tendon (is/is not) what elicits the contraction!!!!!!!!!!!!!!!!!!
• It is the stretch to the (tendon/muscle) (stretch reflex)
• Deep tendon reflex tests for:
1. Are (muscle/spindle) fibers intact?
2. Is this (motor/sensory) pathway intact?
3. Is the (alpha/gamma) motor neuron intact?

Answer 12

small; 1a; alpha; agonist; antagonist; Sensory; is not; muscle; spindle; sensory; alpha

Question 13

• Summary:

1. Sensor/receptor: muscle _____ complex
2. Transmission: via (1a/1b) (motor/sensory) nerve
3. Action: Contraction of (agonist/antagonist) muscle/Inhibition of (agonist/antagonist) muscle

Answer 13

spindle; 1a sensory; agonist; antagonist

Question 14

Spinal Nerves: Motor Functional Components
• When muscle actively contracted:
o Input coming from (brain/spinal cord) (ascending/descending)
o Synapsing onto (alpha/gamma) motor neuron
 Alpha motor neuron: responsible (motor/sensory) output
• Contraction of the (extrafusal/sensory) fibers (muscle fibers)
o Muscle gets shortened
 All of structures that are wrapped around are put on (slack/tension)
 No longer good at picking up a stretch
 Laxity leads to (signaling/no signaling)
• Not able to function
• Missing large chunk of _______ input from CNS

Answer 14

brain; descending; alpha; motor; extrafusal; slack; no signaling; proprioceptive

Question 15

Spinal Nerves: Motor Functional Components

• Gamma Motor Neurons
o Sits next to alpha motor neuron
o During a volitional contraction
 (Ascending/Descending) input from brain activates both alpha and gamma motor neurons
o Alpha and gamma motor neuron recruited together
o Function: Correction of (laxity/tension)
Correction of laxity
• Intrafusal muscle fibers (Fusimotor system) are (contractile/non-contractile) tissues
o Spindle fibers wrapped around
• As muscle is being contracted
o Intrafusal fibers become under (slack/tension)
o (Alpha/Gamma) motor neurons are activated
 Results in a contraction of the (extrafusal/intrafusal) fibers
o Alpha-gamma coactivation
 Concurrent activation of alpha + gamma motor neuron
 Alpha: contraction of (extrafusal/intrafusal) fibers (skeletal)
 Gamma: pulls (extrafusal/intrafusal) fibers taught
•  Always some level of tension across structure
•  spindles able to continue signaling across the system
 Occurs during every volitional contraction under optimal circumstances

Answer 15

Descending; laxity; contractile; slack; Gamma; intrafusal; extrafusal; intrafusal

Question 16

Receptor: Golgi Tendon Organ
• Embedded w/i (muscles/tendons)
• Responsible for _____inhibition reflex
o Happening at muscle that the tendon belongs to
o Override button
 If muscle is putting out output that is (within/beyond) its capacity
 Signaling by the GTO that results in (excitation/inhibition) of the muscle
o Why do people still get injured?
 It’s a reflex loop
 Every reflex loop can be overwritten by the (CNS/PNS)
• Summary:
o Sensor/receptor: GTO
o Transmission: via (1a/1b) (motor/sensory) nerve
o Action: relaxation of (agonist/antagonist) muscle

Answer 16

tendons; autogenic; beyond; inhibition; CNS; 1b; sensory; agonist

Question 17

Non basic movements – CNS components
• Spinal Cord
• Ascending and Descending fibers/tracts
• Brain stem
• medulla oblongata
• pons
• mid brain
• Thalamus
• Necessary cortical regions
Spinal Nerves: (Motor/Sensory) input
• (Afferent/Efferent) pathways or (ascending/descending) information
o From receptor level  (dorsal/ventral) root  into (gray/white)  up to (brain/spinal cord)
• GSA (proprioceptive fibers): getting information from (proprioceptive/somatosensory) endings
• (GSA/GSE) (exteroceptive information): Nociceptive and thermal endings
Spinal Cord Motor Output
• GSE: to (skeletal/cardiac) muscle for movement

Answer 17

Sensory; Afferent; ascending; dorsal; gray; brain; proprioceptive; GSE; skeletal

Question 18

Grey Matter: Ventral Horn Organization:
Somatotopic organization: organization of the spinal cord
• Gray matter:
o Lateral aspect of the gray : (Distal/Proximal) muscles
o Medial aspect: (Distal/Proximal) muscles
o Most medial aspect: (Axial/Distal) muscles
 Along the midline of the trunk
• Ex. Paraspinals, obliques, postural muscles
o Dorsal aspect: (flexors/extensors)
o Ventral aspect: (flexors/extensors)
• White Matter
o Where the communicating tracts are
o Dorsal column: (sensory/motor)
o Lateral column: (Mix/Motor)
o Ventral column: mostly (motor/sensory)

Answer 18

Distal; Proximal; Axial; flexors; extensors; sensory; mix; motor

Question 19

Cross Section of Brain:
• Mesencephalon = (Hindbrain/Midbrain)
• Thalamus
o Sits deeply w/i the (lateral/middle) of the cortex
o Important: All sensory input from cord goes to the _____ first
 Thalamus relays information to different cortical regions for processing of information
o Damage to the thalamus can impact ability to feel what they’re doing  impacts overall motor output

Answer 19

Midbrain; middle; thalamus;

Question 20

Tract naming: start to finish

• Cortico-spinal tract: cortex to spine (ascending/descending); AFFERENT/EFFERENT))
• Spino-thalamic tract: spine to thalamus (ascending/descending); (AFFERENT/EFFERENT)

Answer 20

descending; efferent; ascending; afferent

Question 21

Sensory and Nociceptive System
- 2 major ascending systems that we’re going to focus on
- Spinal cerebellar is the 3rd (Next quarter): for refined movement
Spinal Cord Functions: Ascending Tracts
• Receives (motor/sensory) input from receptors
o Skin, skeletal muscle, tendon
 Somatosensory fibers
o Thorax, abdomen, pelvis
 Viscerosensory fibers
• Ascending system
o Somatosensory fibers that convey sensory information to
 _____ and ______ cortex

Answer 21

sensory; thalamus and cerebral cortex

Question 22

Classification of Axons
•	Myelination happens from the 
o	Oligodendrocytes in the (CNS/PNS)
o	Schwann cells in the (CNS/PNS)
•	Unmyelinated (PNS)
o	\_\_\_\_\_\_cells 
3 Axon fiber types
1.	A Fiber - (lightest/heaviest) myelination
a.	Descending in level of myelination 
b.	Cutaneous \_\_\_\_\_\_ travel faster than nociceptive + temperature information
2.	B Fiber
3.	C Fiber - (minimal myelination/no myelination)

Answer 22

CNS; PNS; schwann; heaviest; mechanoreceptors; no myelination

Question 23

Primary Somatosensory Cortex (also referred to as S_)
• Main target of the (ascending/descending) information
• (Pre/Post)central gyrus area
• Receives input (ascending) from the ______
o (Dorsal/Ventral) posterior lateral
o (Dorsal/Ventral) posterior medial
• Somatosensory cortex
o Postcentral + Posterior paracentral gyri
 Somatotopy
• Somatotopic organization
o Larger cortical regions for regions where there are greater number of (motor/sensory) receptors
o Separation based on body region
 From Neck down is handled at the (brain/spinal cord)
• Midline of the cortical region
 Everything related to the face is carried out by the (spinal cord/cranial nerves)
• Most lateral aspect of cortical region

Answer 23

1; ascending; Post; thalamus; Ventral; Ventral; sensory; spinal cord; cranial nerves

Question 24

o 3 ascending systems:
 Dorsal column medial lemniscus: for (nociceptive/proprioception)
 Anterolateral system: for (proprioception/nociceptive)
 Spinocerebellar: for control and coordination of (reflexes/movement)
Ascending Somatosensory system
• Receptor - 1st order neuron into (brain/spinal cord)  2nd neuron up to (spinal cord/brain stem)  3rd order up to the (brain stem/brain)

Answer 24

proprioception; nociceptive; movement; spinal cord; brain stem; brain

Question 25

Dorsal Column Medial Lemniscus (DCML) [Posterior Column Medial Lemniscus (PCML)]
• Modalities (information) the DCML carries:
o Discriminative touch - (gross/fine) touch
 Fine touch: ability to identify and localize touch
 Carried by (slow/fast) fibers
o Stereognosis
 Able to tell the three-dimensional structure of an object
o Two-point localization
 Ability to be precise with our tactile feeling
• “am I touching one object or 2 objects?”
• “what am I touching?”
 Information coming from epicritic (motor/sensory) fibers (skin sensory fibers) (EPR)
o Conscious Proprioception & kinesthesia
 “What am I doing?” “How am I moving?”
 Mainly muscles + tendons
• Little bit of joint capsules

Answer 25

fine; fast; sensory;

Question 26

DCML - Receptors 
•	Cutaneous tactile mechanoreceptors
o	Hair follicle
	Motion
o	(Merkel/Meissner) corpuscle
	Light touch
•	Fast Adapting
o	Stops firing because not a threat (ex. Wearing a shirt)
o	(Merkel/Meissner) cell
	Deep touch/Pressure
•	Slow Adapting
o	Continues to fire
o	Threat detection

(Meissner/Pacinian) corpuscle
 Vibration

Answer 26

Meissner; Merkel; Pacinian

Question 27

• Mechanical specificity
o Nerve fibers that go to these different receptors, only carry (different/that type) of information
o Important from a regeneration perspective after an injury
Sensory Tract Rules
• Sensory Modality
o (One/Multiple) sensory for each fiber/axon/neuron
 Only responsible for handing one type of information
 Don’t have one axon that is picking up proprioceptive input AND tactile touch
• Somatotopic organization
o Ascending tracts are arranged according to the site of (origin/insertion)
 Ex. Information from each finger is clustered around different areas of the cord

Answer 27

that type; One; origin

Question 28

o Medial-Lateral Rule
 Sensory neurons that enter a high level of the spinal cord are more (medial/lateral) within the spinal cord
 Sensory neurons that enter at a lower level of the spinal cord are more (medial/lateral) within the spinal cord
• Ex. Cervical sensory fibers are going to be laid out the most (medial/lateral) compared to the sacrum
Think of airplane seating. Is the first person to come in more lateral or medial?

Answer 28

lateral; medial; lateral

Question 29

DCML System

• Summary: carries (motor/sensory) info via skin + proprioceptive input from the muscles

Answer 29

sensory

Question 30

1. Sensory information coming in from the ____ spindle
2. Travels through (dorsal/ventral) root into the (gray/white)
3. Bifurcation occurs
   a. Half of the fibers synapse into other motor regions
   i. Resulting in inhibition or activation (reflexive motion)
   b. Other half comes out of dorsal root and goes into (dorsal/ventral) column
   i. Continues up to the (brain/spinal cord)

Answer 30

muscle; dorsal; gray; dorsal; brain

Question 31

• Dorsal root 2 functions:
o reflexive action
o Carry info up stream to the (brain/spinal cord)
• Dorsal root and Dorsal root ganglia is the (1st/2nd) order neuron
o w/i DCML
o receptor to (dorsal/ventral) gray

Answer 31

brain; 1st; dorsal

Question 32

• Two fascicles w/i the dorsal column
o Gracile fascicles: responsible for (upper/lower) half sensory input
o Cuneate fascicles: responsible for (upper/lower) half sensory input
 Medial to Lateral Rule!!
• Lower portion will be more (medial/lateral) than upper
 Ex. Cross section of spinal cord @ lumbar level = no cuneate fascicles
• If looking at a segment w/ only 1 big bump = probably looking at a lower segment b/c only Gracile fascicle is present

Answer 32

lower; upper; medial;

Question 33

From Spinal cord up to the Caudal Medulla
• Bottom most part of the medulla oblongata
1. Sensory information travels up (brain/spinal cord) in the dorsal region
2. Once it gets to the caudal medulla  information synapses off into a (1st/2nd) order neuron
a. Crosses over anteriorly and to the (same/opposite) side
i. Cross over is called a decussation
b. Travels rostrally via the (medial/lateral) lemniscus

Answer 33

spinal; 2nd; opposite; medial

Question 34

Caudal Medulla to the Pons + Midbrain
• At this point fibers have crossed over from the opposite side that the
information originated from –> into (spinal cord/thalamic) region
1. Once in the thalamic region –> will synapse onto Ventral Posterior (Medial/Lateral) region of the thalamus
2. From there, (2nd/3rd) order neuron relay information from thalamus up to ______ cortex (S1)
Effect of Lesions
• @ caudal medulla on L side –> will probably affect (right/left) sided information
• @ pons or midbrain on L side –> will probably affect (right/left) side information

Answer 34

thalamic; Lateral; 3rd; somatosensory; left; right

Question 35

Anterolateral system: the Nociceptive system
• Perceiving information as pain
• Pain is a cognitive, emotional process
o Occurs w/i the (cortex/spinal cord)
• If pain is not that harmful –> try to subdue pain before it gets to brain
• If pain is harmful –> let information travel to the brain to get away from the painful stimulus
Referred pain
• input from visceral fiber coming in through sympathetic _____–> dorsal root _____
• Skin receptors synapsing into (similar/different) regions
o Ex. Heart and pain in left side of arm (men) and pain in left shoulder, jaw (women)
o Due to commingling of the visceral fiber and integumentary fiber synapsing onto (same/different) area

Answer 35

cortex; ganglion; ganglion; similar; same

Question 36

Anterolateral System (ALS)
•	Primary drive of the nociceptive feedback system 
along w/ some other sensory input
•	Modalities ALS is responsible for:
o	Non discriminative touch
	(Fine/Crude) touch
	“I know something is touching me 
but I don’t know where
o	Temperature
o	Nociception
•	Signal that we are dealing w/ is nociceptive NOT pain
o	Pain until you think it is because it’s reaching the cord

Answer 36

Crude

Question 37

Spinal Cord Structure of ALS
• ALS sits w/i (anterior/ventral / posterior/dorsal) and (medial/lateral) aspect of the cord
o Over (dorsal/ventral) gray
• System because there are 4 different parts of the ALS
1. Spinoreticular
2. Spinothalamic
3. Spinomesencephalic
4. Spinohypothalamic-limbic
a. Emotional aspect, experience and learning from pain
• Main focus will be 1 – 3

Answer 37

anterior/ventral; lateral; ventral;

Question 38

Anterolateral System
•	Cutaneous Receptors
o	Mechanoreceptors
	Pinch
	Stretch 
	Squeeze
o	Thermoreceptors
	Temperature changes
•	Not harmful (warm & cold)
o	Thermonociceptors
	Burning or freezing of skin
•	Harmful 
o	Cutaneous nociceptors
	Tissue damage
•	Deep & Visceral Nociceptors
o	Muscle
	Excessive stretch or strenuous contraction
	Over working or over tensioning 
o	Joint
	Inflammatory mediators
o	Visceral
	Mechanical or chemical stimuli
	Referred pain

Answer 38

Got it

Question 39

ALS (also know as Pain Projection Pathway)
• 1st order + 2nd order neuron sits close to each other
1. Information comes at dorsal root level –> into (dorsal/ventral) gray area
2. Branches off into (1st/2nd) order neuron
a. Crosses over (immediately/latently)
i. Doesn’t cross over at the brainstem
3. Bifurcation occurs
a. Interneuron
b. To the 2nd order neuron
i. 2nd order neuron is in the spinal cord w/i dorsal gray
• Cross over occurs at the Anterior white ______
o Doesn’t follow the medial to lateral rule as the dorsal column medial lemniscus
 Follows the lateral to medial rule
o Crossing fiber from one side of the dorsal gray –> through anterior white ______ –> ________ system –> travel up to____ stem –> into cortical regions

Answer 39

dorsal; 2nd; immediately; Commissure; commissure; anterior lateral; brain;

Question 40

Nociceptive Modulation
• Bifurcation occurs
o Half: connects right away and fiber cross over
o Other half: interneuron synapses right (before/after) cross over happens
• ______ is important because it’s the first stopgap measure at trying to control pain from traveling all the way up to the CNS
o “Can I avoid the perception/experience of pain?”
o Gate Control Mechanism
• Gate Control/Gating mechanism
1. C-fiber
 carries nociceptive information synapses onto an _____
 Inhibits the inhibitory ______
 (Myelinated/Unmyelinated)
 Excite (1st/2nd) order
2. AB-fiber (mechanoreceptor)
 Thicker + heavily myelinated (travels faster)
 Also synapses onto same interneuron
 Excites (sends EPSP) to inhibitor interneuron
3. Interneuron is an inhibitory interneuron (releases IPSP)
 Releases neurotransmitters + endorphins + small level of endogenous opiates
 Inhibits activation of the 2nd order ALS fiber
• Subdues fiber from traveling all the way up
o Dependent on magnitude of the nociceptive information
 (Small/Large) magnitude –> not able to inhibit
 If (small/large) magnitude –> settle it down by making the mechanoreceptors of the DCML to inhibit the 2nd order neuron

Answer 40

before; Interneuron; interneuron; interneuron; Unmyelinated; 2nd; large; small

Question 41

From the ALS
• If mechano-stimulation was not enough to inhibit the firing of the 2nd order neuron
1. Information crosses over via anterior white _____–> travels up to different areas w/i ____stem
o Every region in the brainstem has similar effect to try to shut down the pain signal from getting to the brain
2. As we get from spinal cord –> into caudal medulla and pons
3. Spinoreticular fibers: part of the ALS that’s going from the spinal cord –> to area called the reticular nucleus/reticular formation
Reticular formation – 3rd order neurons
• Collection of 100 different nuclei
o Clusters of neuronal bodies that have similar functions
• Resides w/i pons and medulla
• Responsible for: ____ modulation, ____ , ____, motor control, sleep, cardiovascular control, and consciousness,
o “Can we modulate pain, if not need to be alert and aroused to act on nociceptive stimulus”

Answer 41

commissure; brain; pain; alertness; arousal

Question 42

• 2 types of Cells:
o “(ON/OFF)” cells
 Function: to arouse the system and prepare us to act on nociceptive input
o “(ON/OFF)” cells
 Driven by opiate driven control systems
 Function: to shut down nociceptive signals of small magnitude
• Signal stops at spinal reticular and doesn’t continue up to the brain –> we don’t feel pain

Answer 42

ON; OFF

Question 43

Large magnitude of Pain
•	“OFF” cells unable to shut down nociceptive signaling @ the spinal reticular formation
•	Signal continues up from the medulla and pons region through the spinal (mesencephalic/reticular)
o	Spinomesencephalic (2nd order neuron)
	Signal goes into periaqueductal gray (PAG) in the midbrain
•	Sits around the cerebral aqueduct
•	Gray b/c heavy concentration of endogenous opiates and endogenous opiate releasing cells
•	Large magnitude of pain --> rubbing area not enough --> travels up to (spino mesencephalic/spinoreticular) --> signal can’t be shut off --> travels up to mesencephalon midbrain region --> shut down signal with large amounts of opiates/endorphins = no pain felt from noxious stimulus
•	PAG input suppresses pain transmitting neurons in dorsal horn via release of endorphins & acting on the reticular formation

Answer 43

mesencephalic; spinoreticular;

Question 44

Reticulo-thalamic & Spinothalamic fibers
• Signal goes into the thalamic system
o Bypassed all stop gaps due to its (small/large) magnitude
• Spinothalamic tract target:
o Signal sent to the Ventral Posterior (Medial/Lateral) part of the thalamus to relay to (pre/post) central gyrus
 Sent to somatosensory region so that we can come up with an executive strategy to get away from noxious stimulus

Answer 44

large; Lateral; post