Neuro Exam 2 Practice Questions

What is the outermost layer of a peripheral nerve?

Epineurium

What is the structure and function of Epineurium?

Vascular DICT used for strength so you can move without ripping nerves; can be sewn back together

What are fascicles and where are they found?

Bundles of sensory or motor fibers found within a peripheral nerve

What wraps fascicles? What is its function?

Perineurium, creates the BNB

Where does viral infection occur and why?

Terminal ends of nerves because there is no perineurium for BNB

What is Endoneurium?

Thin layer of connective tissue wrapping each nerve process; goes AROUND the cytoplasm of the Schwann cell

Describe the structure of a peripheral nerve.

A peripheral nerve is made of many individual motor or sensory fibers. Each fiber is wrapped in Endoneurium and bundles of the fibers make fascicles which are wrapped in perineurium. The entire nerve is made up of those fascicles as well as blood vessels (vasa nevorum) and is wrapped in Epineurium.

What is vasa nevorum? Why is it important clinically?

That is the tiny blood vessels that travel inside a peripheral nerve. Vasa nevorum is “end arterial” meaning that there is no anastomosing, and if it gets blocked everything distal to the blockage dies. It is usually the first target in diabetes leading to neuropathy

How do vasa nevorum and pia mater differ in structure and function?

Vasa nevorum is NOT anastomosing while pia mater is a collection of highly anastomosing blood vessels surrounding cranial nerves. This means that a vessel blockage will usually NOT affect cranial nerves but it WILL affect peripheral nerves. Cranial nerves are more prone to edema.

Diabetes causes nerve palsies in what nerves the most often?

CN III and CN VI

What should you NOT expect to see with a 3rd nerve palsy and why?

Dilation => issues with pupillary sphincter, because the parasympathetic fibers that regulate it run along CN III and are supplied by anastomosing pia mater

CN III palsy paired with mydriasis is indicative of what?

Aneurysm compressing the parasympathetic nerves (responsible for pupillary sphincter) which run alongside CN III

What part of the spine is prone to fractures and why?

Body of the vertebra because it is made of spongy bone

How do the spinal cord and vertebrae differ in length and why?

The vertebrae are longer than the spinal cord since there are equal numbers of segments but each vertebrae is thicker than the corresponding spinal cord region’s length

What is a cistern?

Accumulation of CSF

Where would a lumbar puncture be performed and why?

Below L2 in the cauda equina region because it is surrounded by CSF and you would be unlikely to hit the spinal cord

What regions of the spinal cord have an additional horn? What is contained within that additional horn?

T1-L2 and S2-S4

T1-L2 houses pre-ganglionic sympathetic cell body

S2-S4 houses some pre-ganglionic parasympathetic cell bodies but most come off of cranial nerves

What is unique about C1?

Sensory to dura only because it has no dermatome

What comes off the spinal nerves?

Gray ramus comes off all nerves and has parasympathetic fibers

What does the dorsal primary ramus do?

Innervates the region from the back of the head to the waist

What does the ventral primary ramus do?

Innervates everything besides the back of the head and back

What structures are found within the spinal cord in the thoracic region?

Sympathetic trunk/chain ganglion, white and gray rami, ventral primary ramus, and dorsal primary ramus

What is the sympathetic trunk/chain ganglion?

Sympathetic preganglionic cell bodies

How do gray and white rami differ?

Every spinal nerve has gray but only some have white. White has myelinated preganglionic fibers and gray has unmyelinated postganglionic fibers

What are the different functions of peripheral nerves?

Somatic afferent and efferent, visceral afferent and efferent, and taste

How are neurons named?

By their speed (A, B, C) and diameter (I-IV)

What kinds of fibers are unmyelinated?

4 and C fibers

What is GSE? (name and function)

General somatic efferent, motor to skeletal muscle of somite origin

What is GSA?

General somatic afferent, proprioception to skeletal muscle and sensory to dermis

What is GVE?

General visceral efferent, motor innervation to glands, internal organs (GI) and cardiac myocytes

What is GVA?

General visceral afferent; sensory from internal organs

What is SVE?

Special visceral efferent, motor to skeletal muscle from branchial arches (muscles of facial expression- 10 zebras bit my canary)

What is SVA?

Special visceral afferent, taste and smell

What is SSA?

Special sensory afferent, hearing and vision

What functional fibers are carried by EVERY spinal nerve?

GSE, GSA, GVE, and GVA

If cranial nerves are protected from vessel blockage by pia mater, why are some cranial nerves common targets of diabetes?

The smaller central fibers with the nerve can die because they are supplied by vasa nevorum; small vessels always first targets of neuropathy

Flaccid paralysis is indicative of…

Alpha motor neuron lesion (lower neuron)

Spastic paralysis is indicative of…

Upper motor neuron lesion

CNS damage causes what kind of paralysis?

Spastic, sometimes flaccid

PNS damage causes what kind of paralysis?

Flaccid

What is an alpha motor unit? How are they different across the body?

An alpha motor neuron and all the muscle fibers it innervates. These units may be larger in less precise areas like the legs and smaller in more precise areas like the fingers

What body part has the most precise motor movements?

Eye

How do you change the length of a muscle spindle?

Relaxing or contracting the extrafusal muscle it is wrapped around. Relaxing it lengthens it and contracting it shortens it

What is the role of Ia fibers WRT muscle activity?

Ia fibers tell the nervous system if the extrafusal muscles are contracted or relaxed based on muscle spindle length; they fire when the muscle is relaxed because the muscle spindle is stretched

What is the purpose of the spinal reflex?

The spinal cord takes over certain movements, such as reflexes, so that your cerebral cortex doesn’t have to waste energy on coordinating them

How will upper vs lower motor neuron lesions affect reflexibility?

Upper lesion/disease: hyperreflexia

Lower lesion/disease: hyporeflexia

What role do A-alpha fibers play WRT muscle movement?

A alphas send information from the spinal cord back to the muscles during a spinal reflex (patellar tendon)

What is the general mechanism of the spinal reflex arc?

Extrafusal muscle relaxes > muscle spindles stretch > Ia fibers fire towards spine > excitatory synapse in the spinal cord > a-alpha fibers away from spine > synapse on muscle

What role do A-gamma fibers play WRT muscle movement?

A-gammas regulate intrafusal muscles. Firing A-gammas causes intrafusals to contract and stretch the muscle spindle

What is an extrafusal muscle fiber?

The extrafusals are skeletal muscle fibers used for skeletal muscle movement innervated by alpha motor neurons.

What is an intrafusal muscle fiber?

The intrafusals are skeletal muscle fibers used for proprioception innervated by sensory AND motor fibers (A-gamma and Ia). These make up the muscle spindle.

Describe the pathway that sets muscle tone.

Descending fibers come from cerebellum > synapse on gamma motor fiber > A gamma activation causes intrafusal muscle contraction > Ia fibers fire > synapse on alpha motor fiber > alpha motor fiber sends signal to motor end plates of muscle

What fibers are involved in Golgi Tendon organ response?

1b sensory fibers and A alpha motor fibers

How can you change your Golgi Tendon Organ threshold?

Exercise increases it

Injury lowers it

Describe the Golgi tendon organ loop.

When you reach what your body believes to be your muscle threshold, sensory fibers (1b) send a signal to an interneuron which synapses on the A alpha neuron, which then will inhibit the muscle by firing its antagonist

What is Wallerian degeneration?

Degeneration of a nerve after damage, occurs downstream of the injury

How is an upstream nerve injury resolved?

Axon reaction/apoptosis

How is a downstream nerve injury resolved?

The downstream nerve is dissolved and then has to regrow. Schwann cells remove myelin and phagocytes clear away debris and leave behind an empty tube which a new nerve will have to grow through.

What determines how a proximal reaction will be resolved?

If the damage is close to the cell body apoptosis will occur. If far enough away axon reaction will occur

How does peripheral nerve regrowth occur?

Apoptosis or axon reaction occur. Growth cones sprout and are chemotactically drawn towards the empty tube to regenerate it.

Describe the repaired nerve.

Nerve impulses will travel slower and it may not go exactly back to its original location (function diminished)

What is an axon reaction?

The repair to the cell body of a damaged nerve. Soma hypertrophies, then nucleus moves away from cell center and loses its pigmentation

What is reactive synaptogenesis? Where does it occur? What do the new nerves look like?

Occurs in CNS where nerves can’t repair, nearby nerves can send out axon sprouts to go into and innervate the area whose innervation was lost. This location now has to split its innervation with other regions

What kind of fibers are sympathetic?

GVE

Where does sympathetic exit the spinal cord?

T1-L2

Where does parasympathetic exit the spinal cord?

CN III, VII, IX, X, and S2-S4

Where is the first cell body for autonomic always found?

Hypothalamus

Are nicotinic receptors ionotropic or metabotropic?

Ionotropic

What enzyme is activated when a muscarinic receptor is used?

Adenylate cyclase

What are the actions of a1 receptors?

Dilates the eye, blood vessels of skin constriction, contraction of vas deferens smooth muscle (ejaculation)

What are the actions of a2 receptors?

Inhibits NorE release, sedation via locus ceruleus, pain modification via dorsal horn, inhibition of insulin release from b islets

What are the actions of b1 receptors?

Heart rate and contraction strength, renin release from kidney

What are the actions of b2 receptors?

Bronchodilation, vasodilation in skeletal muscle, and reduction of mast cell degranulation and histamine release

What is the locus ceruleus?

Center in the pons that controls activation of the forebrain via NorE release

Why can sympathetic and parasympathetic both use Acetylcholine at the preganglionic?

Because the preganglionic cell bodies are in separate ganglia

What receptors are on the iris sphincter?

Mostly M3

What receptors are on the iris dilator?

a1

What receptors do sweat glands have?

Mostly muscarinic, but in palms and soles adrenergic

What receptors do blood vessels have?

Adrenergic a1 in skin, but b2 in skeletal muscle

What receptors does the adrenal medulla have?

Nicotinic

What is the mechanism of action of Hydroxyamphetamine?

Causes NorE release

What is the mechanism of action of cocaine?

Prevents NT reuptake so they stay in synaptic cleft longer

What is the mechanism of action of aproclonidine?

It is a strong a2 agonist and a weak a1 agonist

What do alpha antagonists do?

Act as sympatholytic, can be used for urinary hesitancy and benign protastic hypertrophy

What is the mechanism of action of Pilocarpine?

Parasympathomimetic, causes ciliary body contraction so that aqueous drainage is increased and makes patient mitotic

When is Pilocarpine used?

In emergency situations when need to open the angle, used to be used as a glaucoma treatment

What is the mechanism of action of Atropine?

It is a non selective muscarinic blocker so causes dilation by inhibiting sphincter

What is Atropine used for?

Treatment for amblyopia. Used to dilate the healthy eye so the patient is forced to use the amblyopic eye

What eye drops are sympathomimetics?

Phenylephrine, hydroxyamphetamine, cocaine, and aproclonidine

What eye drops are sympatholytics?

Beta blockers such as timolol, alpha antagonists

What eye drops are parasympathomimetics?

Pilocarpine

What eye drops are parasympatholytics?

Tropicamide, cyclopentolate, atropine

What parts of the body are wired by the sympathetic system?

Limbs and body wall, thoracic organs, abdominal organs, head and neck

Where do all sympathetic preganglionics start?

In the intermediolateral cell column in the lateral horn

How do preganglionic sympathetic fibers enter the sympathetic trunk?

Pass through the ventral root and then white ramus and then enter the sympathetic trunk

Where are the preganglionic cell bodies for sympathetic to eye?

T1 and T2

Where are the preganglionic cell bodies for sympathetic to head and neck?

T1-T4

Where are the preganglionic cell bodies for sympathetic to heart and lungs?

T2-T6

Where are the preganglionic cell bodies for sympathetic to abdominal organs?

T6-L2

Where are the preganglionic cell bodies for sympathetics to urinary?

L1-L2/L3