B&B 2 Spinal Cord Flashcards Preview

Brain & Behavior > B&B 2 Spinal Cord > Flashcards

Flashcards in B&B 2 Spinal Cord Deck (119):
1

Describe the blood supply to the spinal cord

Subclavian arteries → vertebral arteries → one anterior spinal artery and two posterior spinal arteries

►Anterior spinal artery
– formed from branch of each vertebral artery and runs in the anterior median fissure → 5-9 sulcal branches to each spinal cord segment each supplying anterior 2/3 of either right or left side

►Posterior spinal arteries
– arise from vertebral arteries and run in the postero-lateral sulci supplying posterior 1/3 of cord

2

What do anterior and posterior spinal arteries give off?

give off coronal arteries that anastomose with each other to form corona around cord

3

What are the the Radicular Arteries?

Radicular Arteries: reinforce circulation to cord

– from cervical, intercostals, lumbar and sacral arteries enter vertebral canal at intervertebral foramina to anastomose with coronal arteries and from lower cervical area down with anterior and posterior spinal arteries

– Anterior and posterior spinal arteries provide major supply to upper cervical cord while in lower cervical segments large supply comes from radicular arteries

– Great radicular artery (artery of Adamkiewicz) at T12 provides major supply for lumbrosacal spinal cord

4

Which Neurotransmitters are mainly:
● excitatory?
● inhibitory?

Remember:
Neurotransmitters themselves aren’t excitatory or inhibitory, it is the postsynaptic receptor and the postsynaptic cell that determines their action
(e.g. GABA in young hippocampal cells is excitatory but in older hippocampal cells is inhibitory)

Mainly excitatory
● Ach
● Glutamate
● NE

Mainly inhibitory
● Dopamine
● GABA
● Glycine
● 5-HT (serotonin)
● Opioid peptides

5

Describe the changes that underlie spasticity in upper motor neuron (UMN) lesions?

Normally UMN plays an inhibitory role to prevent muscle spasticity but when there is an UMN lesion there will no longer be any inhibitory signals

RESULT: muscle spasticity

6

How is pain felt?

Primary afferent nociceptors (pain receptors) are located in the skin and deep somatic/visceral structures → convey signals via Aδ and C fibers which respond maximally to intense (painful) stimuli

7

Ascending pathways for pain

Spinothalamic tract

Axons enter spinal cord from spinal ganglion then travel up or down 1-2 segments in Lissaur’s tract → synapse in posterior horn → axons of secondary neurons cross midline in anterior white commissure and ascend as spinolthalamic tract

8

Descending pathways for pain modulation

Inputs from frontal cortex and hypothalamus active cells in midbrain that control spinal pain transmission via cells in the medulla → can either enhance or suppress pain

Pain suppressing activities of this pathway is mainly via opioid receptors and endogenous opioid peptides like enkaphalins and β-endorphin

9

Analgesia

Analgesia

absence of pain in response to stimulation which would normally be painful

10

Narcotics
...vs...
Opiates
...vs...
Opioids

Narcotics
= drugs that produce sleep

Opiates
= drugs that are derived from opium

Opioids
= drugs that bind to opioid receptors
(preferred term)

11

Describe Opioid Receptors

Opioid MOA?

7 transmembrane domain G protein coupled receptors

MOA:
● Postsynaptic: hyperpolarization of neurons via opening
of K channels
● Presynaptic: reduce excitatory transmitter release by
closing Ca channels
● Activation of inhibitory enkephalin interneurons in
dorsal horn of spinal cord
● Activation of inhibitory descending pathways

12

What is the most common S/E?

What is the most dangerous adverse effect of opioid overdose?

S/E: Vomiting, constipation

A/E: Slow down respiratory pacemaker ... high enough dose will cause resp arrest

13

Polymylagia
...vs...
Fibromyalgia

Tx?

Polymylagia rheumatica
– inflammatory → shoulder muscle pain & stiffness
– corticosteroids

Fibromyalgia
– non-inflammatory
– pain management: opioids: Tramadol (Ultram®)

14

Morphine

What dose?

Parenteral: 10mg

Oral: 30-60mg
(liver actively breaks it down)

15

A patient has been on morphine. We want to switch to fentanyl.

How?

Consult Equipotency Table

All opioid drugs are compared to the standard, Morphine.

Fentanyl is 100x more potent than morphine. Therefore,, 10mg morphine = 0.1mg fentanyl.

16

Patient has normal liver, but poor renal function.

Why can we not give morphine?

Morphine → hepatic conversion to morphine-6-glucuronide (active metabolite!)

If the kidney isn't working, then it won't get cleared → toxic → resp suppression!

17

What are the therapuetic uses for Opioids?

►Analgesia
– acute pain
– cancer pain
– anesthesia (blunt hemodynamic response to intubation / surgery)

►Cough Suppression
– Codeine, dextromethorphan

►Antidiarrheal therapy
– Loperamide, diphenoxylate

►Acute pulmonary edema
– IV morphine (→ pulmonary vasodilation)

18

Naloxone & naltrexone

• Antagonists at μ/δ/κ receptors
• Almost no effects when given in absence of agonists
• Rapid reversal of agonist effects (e.g., respiratory depression, sedation, miosis, analgesia)
• No tolerance
• Potential to precipitate withdrawal syndrome in dependent subjects

19

Pt presents:
• coma
• miosis
• resp depression

Tx?

ABCs
O2
Naloxone IV

(Dr Winwood had a passed out heroin OD pt arrive at the ER. IV Naloxone ... and 5 sec later the pt sat up and punched him!)

20

What are:
►T3s

►Percocet

►Demerol

►Vicodin

►T3
Acetaminophen & codeine

►Percocet
acetaminophen & oxycodone

►Demerol
Meperidine

►Vicodin
acetaminophen & hydrocodone

21

Bladder filling

Physiology?

►Sympathetic
ß-adrenergic → detrusor relaxation
α-adrenergic → IUS contraction

22

Bladder emptying

Physiology?

►Parasympathetic
Cholinergic → detrusor contraction

23

Voluntary control of urination

►Somatic Nervous System
• striated muscle
• EUS contraction

►CNS
• Pontine Micturiation Centre
• Central inhibition of urinary reflex

24

Defecation

Defecation
• spinal reflex that can be voluntarily inhibited by keeping the external sphincter contracted or facilitated by relaxing the sphincter and contracting the abdominal muscles

25

gastrocolic reflex

What is it?

Distention of stomach by food initiates contractions of rectum and, frequently, a desire to defecate

26

What part of the spinal cord must be intact for ejaculation to occur?

T10-S4

27

Male patient has complete spinal cord lesion at T4.

Can ejaculation still occur?

Yes.

It is possible to trigger ejaculation reflex via vibro-stimulation
(assuming T10-S4 is still intact!)

28

What are the 5 neurological tests we can perform for the genitalia?

Bulbocavernosus reflex
Testicular pain (squeeze)
Pain to pinprick
Anal tone
Voluntary anal contraction

29

Bulbocavernosus reflex

What does a positive result indicate?
(normal response)

What does a negative result indicate?

►POSITIVE:
B reflex is intact
Therefore, level of injury above lumbar level

►NEGATIVE:
Sacral reflex damaged
but ... 15% of healthy mean don't have it!

30

Testicular pain (squeeze)

What does a positive result indicate?
(normal response)

What does a negative result indicate?

►POSITIVE:
T9 tract to the brain is open
Therefore, level of injury is below T9

►NEGATIVE:
Level of injury T9 or above

31

Pain to pinprick

What does a positive result indicate?

What does a negative result indicate?

►POSITIVE:
Lateral spinothatlamic tracts open from genitalia to the brain

►NEGATIVE:
Either sacral dermatome is affected (pudendal nerve cannot send message) or sacral cord injury

32

Anal tone

What does a positive result indicate?

What does a negative result indicate?

►POSITIVE:
T10-S4 is open and communicating → injury above T10

►NEGATIVE:
Lesion is somewhere between T10-S4

33

Voluntary anal contraction

What does a positive result indicate?

What does a negative result indicate?

►POSITIVE:
Normal response, able to contract ext sphincter
Therefore, must be an incomplete injury that spares corticospinal tracts

►NEGATIVE:
Corticospinal tract injury anywhere along spinal cord

34

SUMMARY:
SCI above T10

SCI = spinal cord injury

►No seminal flow to mental thoughts
►No mental erection
►Reflex erection possible

►10% of men with SCI with sexual stimulation will get enough afferent input to the spinal cord to trigger the S2-S4 → T10-T12 triangle for ejaculation.

►80% of men with injury above T10 may have this reflex if a strong vibrator stimulates the afferent reflex arc (to then cause the efferent reflex for ejaculation

35

SUMMARY:
SCI in sacral area

seminal flow possible to mental thought
mental erection possible, not reflex erection
sometimes seminal flow is not possible or the seminal bolus does not get past prostate and down the urethra. This is because S2-S4 for pulsatile ejaculation is not working.

Therefore, electro-ejaculation is used to jump-start the efferent arc of the ejaculation reflex

36

What is the role of Serotonin on sex?

Inhibits
– sexual interest
– genital arousal
– orgasm

37

What is the role of Ach on sex?

No effect:
– Sexual interest

Facilitates
– genital arousal
– orgasm

38

What is the role of NE on sex?

Facilitates
– sexual interest
– orgasm
(gives you butterflys!)

Inhibits
– genital arousal
(not the time for an erection when running from tiger)

39

What is the role of Dopamine on sex?

Inhibits
– sexual interest
– genital arousal

No effect on orgasm

40

Apply it! What is the effect on erection of the following?

Cervical Injury
...vs...
Sacral Injury

Cervical Injury
– reliant on sacral reflex to get erection

Sacral Injury
– reliant on mental erection

41

Viagra

MOA?

Viagra = sildenafil

PDE5i → Inhibits PDE-5, increasing cyclic guanosine monophosphate (cGMP) to allow smooth-muscle relaxation

PDE5i simply enhance the signal that is already there. It will not create desire, it will simply enhance the erection / lubrication.

42

sildenafil

Who can we not give it to?

PDE5i must not be used in people with serious CV concern

43

CT

How is it used in imaging of spine and spinal cord?

• best for assessing the cortical bone
• primary modality for trauma
• best for the assessment of hardware position after fixation surgery
• good for detection of foraminal or spinal stenosis, especially in the lumbar spine
• best for detection of calcium or bone, e.g. calcified disc, ossification of the posterior longitudinal ligament, calcification of tumor matrix

44

MRI

How is it used in imaging of spine and spinal cord?

What is the best tool for?

►Marrow – myeloproliferative disorders, metastases, recent fractures

►Soft tissues – disc herniations, ligamentous injuries, post- discectomy

►Spinal cord – MS, tumors, myelopathy, syringomyelia, cord compression

►Infections – discitis/osteomyelitis, epidural abscess

45

MRI

What are contraindications?

– Cardiac pacemaker
– Certain cardiovascular stents or valves
– Metallic foreign bodies (eg. ocular)
– Some cerebral aneurysm clips (ferromagnetic)
– Ferromagnetic cochlear implants
– Gadolinium: Severe renal impairment (Nephrogenic Systemic Fibrosis) MUST HAVE GFR > 30!

46

Define Myelopathy

Myelopathy
= any disease or disorder of the spinal cord or bone marrow

47

How can neuronal excitation cause nerve cell death?

►Ischemia → glutamate release → activation of glutamate receptors → influx of Na → activate voltage dependent Ca channelsinflux of Ca (toxic) → neuronal injury

►Some neurons are more vulnerable to ischemia → those with glutamate receptors or those with increased intracellular Ca ??

48

An axon is severed.

What happens to the distal end?
What happens to the proximal end?

(aka ... the arm of the octupus has been chopped off)

DISTAL
Wallerian Digeneration
– axonolysis and myelinolysis caused by phagocytosis by macrophages
– usually begins within 24–36 hours of a lesion

PROXIMAL
Axonal “retraction balls”
– the organnelles keep getting pumped out and and damn up at proximal stump`

49

What are oligodendrocytes?

Generate & Maintain myelin in CNS

50

Astrocytes

What are they?

Fx?

Fibroblasts of CNS

Fx:
– support and structure
– glycolysis (energy)
– glutamate and GABA uptake
– pH regulation
– osmolarity regulation
– spatial buffering of K
– glutamine for glutamate synthesis

51

Astrocytes

What inclusions do they contain?

►Rosenthal fibres
– linear corkscrew hyaline inclusions in long-standing gliosis

►Corpora amylacea
– round inclusions of glycoprotein in astrocytic foot processes; particularly around blood vessels, or
near surfaces of CNS

52

What is Gliosis?

– nonspecific reactive change of glial cells in response CNS damage
– Involves the proliferation or hypertrophy of several different types of glial cells, including astrocytes, microglia, and oligodendrocytes
– In its most extreme form, the proliferation associated with gliosis leads to the formation of a glial scar.

53

What is Ependyma?

– Lining of ventricles

– Destruction of ependymal cells probably not replaced with other ependymal cells

– Subventricular glial nodule (granular ependymitis) → non-specific reaction of subventricular astrocytes to ependymal injury / loss (a type of gliosis)

54

Which cells in the CNS are derived from Bone Marrow?

What are their function?

Microglia

– phagocytic and APCs

NOTE: CNS normally has very few APCs present!

55

When are T cells present in CSF?

Activated T cells can breach BBB only if trafficking T cell recognizes specific CNS antigen and it is represented in context of MHC to the T cell

56

When is it appropriate to use plain film radiograph?

Good screening tool especially for osseous structure, alignment (scoliosis and kyphosis)

57

Myelography

What is it?

►Seldom performed today as it involves doing lumbar puncture and injecting radiopaque dye leading to complications such as severe headache and severe CSF leak needing epidural blood patch

►Useful for assessment of spinal stenosis when there is prominent hardware that obscures visualization with MRI or
conventional CT

►Useful for assessment in difficult cases such as detecting CSF fluid leaks, adhesions in the subarachnoid space

58

What are the 6 clinical spinal cord syndromes we discussed?

1. Complete cord injury
2. Spinal cord hemisection (BS syndrome)
3. Central cord syndrome
4. Anterior spinal artery infarct
5. Subacute combined degeneration
6. Acute cauda equina compression

59

1. Complete cord injury

Clinical Picture?

Loss of all motor, sensory & sphincter function below level of the lesion

60

1. Complete cord injury

What disorder could cause it?

Trauma, hemorrhage, cord compression by tumour or abscess

61

2. Spinal cord hemisection (BS syndrome)

Clinical Picture?

UMN weakness ipsilateral to side of lesion

Ipsilateral ↓ vibration and position sense

Contralateral loss of pain & temperature

62

2. Spinal cord hemisection (BS syndrome)

What disorder could cause it?

– Schwannoma
– penetrating cord injuries
– extrinsic cord lesions (tumor / disc)
– blunt spinal cord trauma

63

3. Central cord syndrome

Clinical Picture?

– LMN weakness at lesion level
– Variable UMN features below level of lesion
– Arm weakness > leg
– Deep tendon reflex ↓ at injury level but normal or ↑
– below Loss of pain and sensory sparing vibration and propioception

64

3. Central cord syndrome

What disorder could cause it?

Trauma
Intramedullary tumour / Syringomyelia

65

4. Anterior spinal artery infarct

Clinical Picture?

Paralysis & loss of light touch, pain & temperature

Normal vibration and position sense

66

4. Anterior spinal artery infarct

What disorder could cause it?

Thrombosis

Embolism (i.e. bends)

Surgery on descending aorta

67

5. Subacute combined degeneration

Clinical Picture?

● Gradual onset weakness (legs > arms) & gait imbalance ● UMN weakness (deep tendon reflex may ↓ with polyneuropathy)
● Absent vibration & position sense
● Pain and temperature less affected or later
● Gait ataxia & (+) Romberg
● Anemia &/or polyneuropathy frequent associations
● Demyelination of posterior & lateral columns starting in thoracic cord

68

5. Subacute combined degeneration

What disorder could cause it?

B12 deficiency

69

6. Acute cauda equina compression

Clinical Picture?

● Rapid progression of leg weakness, numbness and sphincter disturbance
● LMN features, all sensory modalities ↓
● ↓ rectal tone

70

6. Acute cauda equina compression

What disorder could cause it?

● Disc herniation
● Spine subluxation
● Epidural metastatic tumor, hematoma or abscess

71

CSF

How much in the body?

How frequently is it replaced?

● 150ml of CSF fills the ventricles and subarachnoid space

● produced at ~550 ml/day
(turnover 3.7 times a day)

72

CSF

Where is it formed?

CSF is formed continuously by ependymal cells choroid plexus in two stages

● Plasma is passively filtered across the choroidal capillary endothelium

● Secretion of water and ions across the choroidal epithelium provides for active control of CSF composition and quantity

73

CSF

Describe flow progression?

CSF made in lateral ventricles
⬇︎
via foramen of Monro
⬇︎
3rd VENTRICLE
⬇︎
via cerebral aqueduct (of Sylvius)
⬇︎
4th VENTRICLE
⬇︎
via / exit via central Magendie formamen and 2 Luschka (lateral) foramen
⬇︎
enter the subarachnoid space
⬇︎
reabsorbed via subarachnoid villi

74

Pharyngeal (branchial) apparatus

What is it?

Pharyngeal (branchial) apparatus
– group of structures which contribute to form the head & neck
– consists of four parts:

1) Pharyngeal arches
2) Pharyngeal pouches
3) Pharyngeal grooves
4) Pharyngeal membranes

75

Pharyngeal arches

How many are there?

Which CN?

NET: 4 in total

#5 is rudimentary and disappears
#4 & #6 fuse

Therefore, the total 4 are:
#1 → CN5 v2, v3
#2 → CN 7
#3 → CN 9
#4/6 → CN 10

76

Pharyngeal arches

What does each contain?

(a) muscle component
(b) cartilage
(c) CN
(d) aortic arch.

77

Pharyngeal pouches

What are they?

– paired segmented balloon‐like pockets in endoderm

– separate the pharyngeal arches internally

78

Pharyngeal grooves

What are they?

– paired clefts separating pharyngeal arches externally.

Only Cleft 1 persists in adulthood → becomes external acoustic meatus (opening for ear)

The other grooves get covered by Arch 2 which grows really fast ... congenital abnormality exists if not covered

79

Pharyngeal membranes

What are they?

– formed where the epithelia of the grooves and pouches approach each other.

80

Congenital Abnormalities of Head & Neck

Where do they originate?

Most originate during transformation of the pharyngeal apparatus into its adult derivatives.

81

What happens to Neural Crest Cells (NCC)?

NCCs, originating from the neural tube, migrate into the ventral part of the pharyngeal arches and form different tissues in this region including
– cartilage
– bone
– dentins
– tendon
– dermis
– meninges
– sensory neurons and ganglia

82

What actually forms from the pharyngeal arches?

face
nasal cavities
mouth
pharynx
larynx
neck.

83

1st Pharyngeal Arch

What does it form?

aka: "(Mandibular Arch"

Two prominences for first arch:
Mandibular & Maxillary prominences
(mouth in between)

84

Which CN provides sensation to the face?

Which CN provides motor function of facial muscles?

►Sensory:
CN V - Trigeminal
v1 - Ophthalamic
v2 - Maxillary
v3 - Mandibular (v3 = sensory & motor)

►Motor:
CN VII - Facial

85

pharyngeal arches cartilage

What do they give rise to?

►1st arch cartilage
(Meckel Cartilage)
– forms two of the middle ear ossicles, and mainly the horseshoe‐shaped primordium of the mandible & guides its early morphogenesis
– disappears as the mandible develops around it by
intramembranous ossification.

►2nd arch cartilage
(Reichert Cartilage)
– forms one of the middle ear ossicles, styloid process of temporal bone and a part of the hyoid bone.

►3rd arch cartilage
– ossifies to form the rest of the hyoid bone which is not been formed by the 2nd arch.

►4th & 6th arch cartilage
– form the laryngeal cartilages (except for the epiglottis which is derived from mesenchyme of the 3rd and 4rd arches)

86

What is the muscle action of the pharyngeal arch muscles?

Arch 1:
All muscles of mastication

Arch 2:
Muscles of facial expression

Arch 3:
Stylopharyngeus muscle

Arch 4:
Cricothyroid muscle

Arch 6:
other intrinsic laryngeal muscles

87

What are the extra-ocular muscles?

CN 3
Occulomotor

CN 4
Trochlear
Superior Oblique
"SO4"

CN 6
Abducens
Lateral Rectus
"LR6"

88

What is the tympanic membrane derived from?

1st pharyngeal membrane

(other membranes disappear)

89

Bottom line, what is the ear derived from?

Cleft 1

90

Thyroid

What is formed from?

formed from a median endodermal thickening in the floor of the primordial pharynx and forms thyroid diverticulum (primordium)

91

Thyroglossal duct

Connection that exists during development between the tongue and thryoid

Later during development, this connection is lost (normally ...)

92

What is a cyst?

Cyst
– closed sac with distinct membrane and division compared to the nearby tissue.
– moveable & painless
– basically a cluster of CELLS that have grouped together to form a sac

NOTE: an abscess is a collection of PUS

93

What are the following present in a child?

(1) lateral cyst

(2 midline cyst

Lateral cyst
= Lateral cervical cyst

Midline cyst
= Congenital thyroglossal duct cyst

94

Ectopic thyroid gland

What is it?

Incomplete descent of the thyroid gland results in a sublingual thyroid gland appearing high in the neck.

The most common type of ectopic thyroid tissue is lingual thyroid glandular tissue

95

terminal sulcus

What is it?

V-shaped groove that separates the Anterior 2/3 oral part and the Posterior 1/3 (pharyngeal part)

96

TONGUE
– Which motor nerves?
–When sensory nerves?

Anterior 2/3
(oral part )

...vs...

Posterior 1/3
(pharyngeal part)

►Anterior 2/3
Motor: CN 12
(except palatoglossu muscle)
General Sensory: CN 5v3
Special Sensory: CN 7

►Posterior 1/3
CN 9
Most posterior part: CN 10

97

Syringomyelia

Syrinx

What is it?

►Syringomyelia
– generic term referring to a disorder in which a cyst or cavity forms within the spinal cord

►Syrinx
– Greek for "tube"
– this is what we call the cyst when it is indeed a cyst that has formed in Syringomyelia

98

Again, what is Myelopathy?

Myelopathy
= any disease or disorder of the spinal cord or bone marrow

When due to trauma, it is known as "spinal cord injury"

When inflammatory, it is known as "myelitis"

When it is vascular in nature is known as "vascular myelopathy"

99

Myelopathy

Clinical Features:

►UMN signs (weakness, spasticity, clumsiness, altered tonus)

►pathological hyperreflexia and inverted Plantar reflex (positive Babinski sign)

►sensory deficits

►bowel/bladder symptoms and sexual dysfunction.

100

Our Week 2 PBL patient fell off a roof at age 16 and suffered a spinal cord injury that left him with significant sensation loss below nipple line.

20 yrs later he starts having new Sx. He is losing sensation in his arms.

On imaging we discover that he has post-traumatic syringomyelia extending from C2 to T2

What imaging shows this?

MRI

101

Baclofen

MOA?

Used to treat muscle spasms in SCI pts

stimulates GABA-B receptors leading to decreased frequency and amplotude of muscle spasms

102

How do we grade reflexes?

0 absent

1+ hypoactive

2+ NORMAL

3+ hyperactive without clonus

4+ hyperactive with clonus

103

Spinal Shock

What is it?

Phenomenon that cal occur after SCI
Most often in a complete transection

Everything is lost below the SCI site .... but ... the reflexes return after a couple of days.

104

Spinal Shock

What are the 4 phases?

► Phase 1, (0­-1 day)
• areflexia/hyporeflexia
• loss of descending facilitation

► Phase 2, (1­-3 days)
• initial reflex return
• Denervation supersensitivity

► Phase 3, (1­-4 weeks)
• initial hyper­reflexia
• Axon-­supported synapse growth

► Phase 4, (1­-2 months)
• final hyperreflexia
• Soma-­supported synapse growth

105

Middle Meningeal Artery

• runs through the Foramen Spinosum to the periosteal layer of the Dura Mater

• intimately associated with the auriculotemporal nerve

• pulsatile arterial pressure can slowly peel the dura off of the inner bone table of the skull.

RESULT: Epidermal Hemorrhage

Remember ... Subdural bleeding is usually venous in nature, rather than arterial.

106

RECEPTORS:

• Nicotinic
• GABA-α
• GABA-ß
• NMDA
• AMPA

Nicotinic Receptors
• Na enters, K exits

GABA-α Receptors
• Ligand: GABA
• Cl- enters

GABA-ß Receptors
• inhibitory receptors
• K enters → hyperpolarizes cell
• prevents opening of Na ch
• ↓ Ca conductance

NMDA receptors
• Ligand: Glumatamate
• Na & Ca enter, K exits

AMPA receptors
• Na enters, K exits

107

As compared to a normal muscle, what happens in a spastic mono-synaptic reflex arc?

⬆︎activity in Ia afferents in response to stretch

⬆︎activity in α-motor neurons in response to stretch

⬆︎activity in γ-motor neurons prior to the stretch

Hypersensitive muscle spindles

108

γ-motor neurons

Fx:
• Keep muscle spindles taut, thereby allowing the firing of a-neurons to continue discharging, leading to muscle contraction
• role in adjusting the sensitivity of muscle spindles

109

α-motor neurons
...vs...
γ-motor neurons

BOTH have cell bodies located in the anterior horn of the spinal cord.

► α-motor neurons
–most abundant
– innervate extrafusal muscle fibers
– do the actual contraction of muscle
– larger axons

► γ-motor neurons
– innervate only intrafusal muscle fibers
– smaller axons

110

Where does the spinothalamic/anterolateral system terminate in the thalamus?

VPL

111

Loss of sensation in the small (5th) finger indicates involvement of which dermatome?

C8

112

A man with retroperitoneal lymph node dissection (RPLND) for his testicular cancer had his sympathetic outflow tracts transected by the surgery.

Men with RPLND with their sympathetics damaged do not have much interference with their erections because of the recruitment of remaining nerves of the T10 - L2 chain and the undamaged reflex erection.

Only the seminal emission phase of ejaculation is altered: the propulsatile phase still occurs (even if there is no seminal bolus to propel)

The sensation of orgasm remains intact as both the lateral spinothalamic and corticospinal tracts are open.

113

Where is fasciculus gracilis & cuneatus located?

►fasciculus gracilis
– present at all levels

►fasciculus cuneatus
– present only above T6

114

Intermediolateral cell column

Where is it present in spinal cord?

T1-L2,3
(preganglionic sympathetic cell bodies)

S2-S4
(preganglionic parasympathetic cell bodies)

115

Where do lesions often occur in MS?

Around ventricles

116

The hypophyseal or pituitary fossa is located in which bone?

Sphenoid Bone

117

Spinocerebellar Tract

Spinal cord → ipsilateral cerebellum

Conveys info to the cerebellum about limb and joint position (proprioception).

Sensory neurons synapse in an area known as Clarke's nucleus (T1-L3)

IPSILATERAL

118

Clarke's nucleus contains sensory fibres

Do they cross?

No ... ipsilateral!

119

What is the denticulate ligament and filum terminale made of?

pia mater
&
glial cells