Exam 4 Part III

Question 1

A. The pain receptors and their stimulation: Pain receptors are:

Answer 1

all free nerve endings
sensitive to: mechanical stress or damage, extremes of hot or cold, and/or chemical substances (bradykinin: produced upon injury, histamine, acids, prostaglandins, leukotrienes, K+, etc.).
relatively non adapting

Question 2

Conditions in which pain is produced:

Answer 2

chemicals released from tissue damage (inject bradykinin under skin,
tissue ischemic damage from lack of blood flow. Who are the culprits?Lactic acid? Other chemicals from injury as above?
Muscle spasm is a common cause, directly stimulating receptors & causing ischemia.

Question 3

Two pathways exist corresponding to the 2 types of pain:

Answer 3

acute, sharp pain (Aδ) and chronic slow or aching pain (C fiber). Burn, for example: instantly remove your finger from that stove! Then a sec. later, you know how badly you have hurt yourself (the ache or throbbing comes).

Question 4

The anterior and lateral spinothalamic tracts both are part of the

Answer 4

anterolateral system.

Question 5

Most of the pain fibers terminate in the

Answer 5

reticular formation (RF) in the medulla, pons and midbrain. Then other neurons transmit this information upward to the thalamus, etc.

Question 6

. Some fast fibers go directly to the

Answer 6

. Some fast fibers go directly to the thalamus and then on to other areas, particularly somatosensory cortex. These are for pain localization.

Question 7

The significance of having all the slow fibers terminate in the RF is that

Answer 7

The significance of having all the slow fibers terminate in the RF is that this is part of the reticular activating system, which activates the nervous system, promoting defense and aversion in the case of pain.

Question 8

C. A pain control (“analgesia”) system in the brain and spinal cord.

Answer 8

Experimental pain thresholds tend to be very much the same for different people. How people react to pain and pain tolerance are very different for different people. Part of this probably has to do with the ability of the nervous system to control what pain signals make it all the way in in different circumstances.

Question 9

periaquaductal gray area of the midbrain and upper pons

Answer 9

decrease-> enkephalin secreted

Question 10

raphe magnus of lower pons and medulla

Answer 10

decrease -> 5 – HT secreted

Question 11

a pain inhibitory complex in the dorsal horns of the spinal cord [substantia gelatinosa] Enkephalin secreted also here. These 2 places for enkephalin secretion show that

Answer 11

endorphins or endogenous opiates are important in endogenous pain-management.

Question 12

“Pain–gating”?

Answer 12

“Pain–gating”? 40% of people with severe injury are unaware of injury, feel no pain. Part of the concept of pain-gating is that other kinds of stimuli can block pain.

Question 13

Another way in to the analgesia system is by

Answer 13

tactile stimulation which causes blockade at the spinal cord. Tactile stimulation near the site of pain or many segments away can cause pain suppression.

Question 14

Physical therapy emphasizes now

Answer 14

Physical therapy emphasizes now stimulating other parts of the nervous system than the areas of pain.

Question 15

Acupuncture for pain: at least part of its effect to reduce pain is

Answer 15

endorphin release from periaquaductal gray area

Question 16

H2O – can wash away

Answer 16

H2O – can wash away pain–promoting substances (Also does it

Question 17

Visceral pain can come from

Answer 17

overdistension of a hollow organ, injury, ischemia, spasm of a hollow organ (can result from mechanical stimulation of the pain endings, diminished blood flow). Pain often comes in the form of a cramp.

Question 18

Visceral pain is often diffuse because

Answer 18

Visceral pain is often diffuse because there are very few receptors in the viscera. According to Guyton, the only sensation in the viscera is pain.

Question 19

Visceral pain can often be felt as

Answer 19

Visceral pain can often be felt as referred pain on the surface of the body or in some other deep area of the body than the origin. Each spinal nerve innervates an area on the skin called a dermatome. Referred pain tends to follow dermatomes.

Question 20

Referred pain”

Answer 20

Referred pain” (not the usual meaning) can be caused secondarily by reflex muscle spasm. The painful stimulus may originate in a ureter and that can cause reflex spasm of the lumbar muscles.

Question 21

Hyperalgesia =

Answer 21

Hyperalgesia = hypersensitivity to pain

Question 22

Hyperalgesia primary

Answer 22

Primary: excessive sensitivity of the pain receptors themselves,

Question 23

hyperalgesia secondary

Answer 23

Secondary: facilitation of sensory transmission. It can result from lesions of the spinal cord or of the thalamus (“thalamic pain syndromes”).

Question 24

herpes zoster

Answer 24

It infects a dorsal root ganglion & causes pain in that dermatome = shingles. (Also tend to have blistering, usually at the thorax.) Immunosuppression later → virus moves down axons and can cause skin infection. Can have postherpetic neuralgia.

Question 25

A headache is not due to direct pain in the brain, but

Answer 25

A headache is not due to direct pain in the brain, but stretching the dura or the blood vessels of the dura can cause intense pain.

Question 26

meningitis –

Answer 26

meningitis – inflammation of the meninges

Question 27

sub-arachnoid hemorrhage:

Answer 27

sub-arachnoid hemorrhage: “the worst headache a person has ever had”

Question 28

low CSF pressure – removal of 20 ml prevents normal

Answer 28

low CSF pressure – removal of 20 ml prevents normalflotation of the brain and the weight of the brain stretches the dural surfaces.

Question 29

Migraine –

Answer 29

Migraine – only theories: often seems to involve vasoconstriction followed by more long-lasting vasodilation, both of which can cause pain.

Question 30

Alcoholic headache –

Answer 30

Alcoholic headache – toxicity (irritates the tissue) and dehydration (reduced brain flotation): reduced ADH effects → ↑ urine

Question 31

Constipation headache –

Answer 31

occurs even when the spinal cord is severed. Perhaps either due to toxic products or loss of fluid into the tissues (distension causes venous pooling) resulting in reduced brain floatation.

Question 32

extracranial muscle spasms

Answer 32

From muscle spasm – emotional or physical tension causes muscles of the head and neck to become spastic, “tension headaches”

Question 33

extracranial irritation of nasal structures

Answer 33

Irritation of nasal structures including sinuses – “not an intense type of pain”

Question 34

extracranial irritation of the eye

Answer 34

Eye disorders – attempts to focus can cause strain or spasm, UV can burn the conjunctiva or retina

Question 35

extracranial causes of headaches

Answer 35

muscle spasms
irritation of nasal structures
irritation of the eye

Question 36

G. Thermal sensations –

Answer 36

G. Thermal sensations – all free nerve endings

Question 37

thermal sensations

Answer 37

Freezing cold = cold receptors and pain receptors.

Burning hot = hot and pain and sometimes cold receptors. Burning hot can sometimes feel cold at the same time.

Question 38

thermal sensations are

Answer 38

rapidly adapting, thus the misperception after holding one hand in cold water and one in hot and then both in tepid. The previously hot hand feels the water as cold and the previously cold one feels the water as hot. These receptors signal changes in T not absolute T.

Question 39

the stretch reflex is

Answer 39

monosynaptic and ipsilateral.

Question 40

the stretch reflex

Answer 40

The stretch reflex (= myotatic reflex), e.g., the knee jerk
The mallet hits the tendon which stretches the quadriceps femoris muscle which causes the intrafusal fiber to be stretched. This causes the midportion of the muscle spindle to be stretched which excites the IA afferent (labelled proprioceptive nerve). This excites a synapse onto the alpha motor neuron. The extrafusal muscle (the quadriceps in this case) contracts and the leg kicks. This is the stretch reflex. It is a monosynaptic reflex. Its purpose is to “oppose sudden changes in muscle length.”

Question 41

The stretch reflex is used to assess

Answer 41

The stretch reflex is used to assess the degree of facilitation coming from other places in the spinal cord and from higher areas.

Question 42

If facilitation is greatly increased, the muscle jerks can

Answer 42

If facilitation is greatly increased, the muscle jerks can be exacerbated. If facilitation is lessened or gone, the jerks can be gone. This happens immediately following spinal cord injury, is called spinal shock..

Question 43

clonus

Answer 43

Muscle jerks can oscillate = clonus.

Question 44

clonus can be used to

Answer 44

Can be used clinically to test for damage, as in contralateral motor cortex.

Question 45

Signals from γ efferents would

Answer 45

Signals from γ efferents would increase muscle tone.

Question 46

During exercise, coactivation of γ efferents when α motor neuron is firing keeps

Answer 46

During exercise, coactivation of γ efferents when α motor neuron is firing keeps muscle spindle in right range to keep stretch reflex working. (Without coactivation of γ efferents, main muscle contraction shortens spindle, so no A.P.s from it.)

Question 47

If tension on the muscle is increased, the tendon organ is

Answer 47

If tension on the muscle is increased, the tendon organ is stretched. This activates an inhibitory interneuron that inhibits the alpha motor neuron, and the muscle relaxes

Question 48

the nociceptive or pain reflex,

Answer 48

it is most powerfully elicited by painful stimuli. But it can also be elicited by a cutaneous sense in a decerebrate or chronic spinal animal.

Question 49

reflex is reciprocal inhibition

Answer 49

reflex is reciprocal inhibition between 2 groups of muscles. When the flexor is excited, the extensor is inhibited.

Question 50

C. The crossed extensor reflex

Answer 50

This allows the body to be supported while one limb is being withdrawn. It is a spinal reflex, polysynaptic and crossed = contralateral. Reciprocal inhibition is also a component of this reflex: when the flexor of one limb is excited, the flexor of the opposite limb is inhibited.

Question 51

The positive supporting reaction.

Answer 51

Supportive pressure on the footpad of a decerebrate animal (sectioning at the middle of the midbrain) results in the limb extending against the pressure being supplied.

Question 52

Rhythmic stepping motions can be observed in

Answer 52

Rhythmic stepping motions can be observed in a spinal animal or even if the lumbar cord is separated from the rest and cut down the center to prevent interaction between the 2 limbs. Forward flexion occurs and then backward extension and then this repeats itself. No sensory input is needed for it to occur.

Question 53

rhythmic stepping involves

Answer 53

It involves reciprocal inhibition (one group of neurons inhibits another and vice versa), i.e., the flexors inhibit the extensors. The flexor stimulus dies out and the extensors rebound from inhibition.

Question 54

Pain stimuli can cause

Answer 54

Pain stimuli can cause reflex muscle spasm (not known exactly how). Relief of pain relieves the spasm, as, for example, with local anaesthetic

Question 55

spinal shock

Answer 55

At first when the spinal cord is transected, all spinal reflexes cease = spinal shock. They lose their source of excitability from above. (Continual or tonic discharge from reticulospinal, vestibulospinal and corticospinal tracts.)

Question 56

After a few hours, days or weeks of spinal cord transsection (longer in humans),

Answer 56

After a few hours, days or weeks (longer in humans), excitability returns.

Question 57

It seems to be a property of neurons that, after they lose their source of excitability from without, they

Answer 57

It seems to be a property of neurons that, after they lose their source of excitability from without, they increase their own excitability to make up for the loss.

Question 58

spinal shock symptoms

Answer 58

arterial P drops – to 40 or so, due to loss of sympathetic tone
sacral reflexes (parasym.) for bladder and bowel evacuation are lost
skeletal muscle reflexes are lost.  The simplest return first (stretch, flexor, postural antigravity, stepping)

Question 59

. In a chronic spinal animal, often all the spinal reflexes are facilitated. So then if a painful stimulus or overdistension occurs, there is a mass reflex involving large portions of the cord. The pattern is:

Answer 59

flexor spasm of the body
colon and bladder evacuation
arterial P increase, so that the mean P may be 200mmHg
profuse sweating

Question 60

The triple response to injury:

Answer 60

The triple response to injury:

1) the red reaction: pressure on the capillary from the injuring object causes immediate capillary dilation,
2) the flare: redness spreading out from the injury due to arteriolar dilation and
3) the wheal: swelling spreading out with slight delay from increased permeability of capillaries, maybe due to histamine, etc..