New material VMED 1000 FINAL

What pre-synaptic adregenic receptor is linked to inhibition of norepinephrine release?

alpha-2 AR

What are alpha-1 ARs?

located at post-synaptic membrane in some smooth muscles (vascular and urinary bladder sphincter)

What are alpha-2 ARs?

located mainly at pre-synaptic membrane, when stimulated by the endogenous or exogenous agonist decreases release of norepinephrine

What are Beta-1 ARs?

mainly located in the post-synaptic membrane of cardiomyocytes and cause contraction upon stimulation

What are Beta-2 ARs?

mainly in post-synaptic receptors expressed in several smooth muscles located in vasculature; bronchi, urinary bladder wall, intestine, uterus, etc

What is the thoracolumbar system?

sympathetic NS, controls all sympathetic (fight/flight) responses. (even for cranial functions)

Where are paravertebral ganglia?

located along the sympathetic trunk

What are prevertebral ganglia?

ganglia located near origins of major abdominal arteries

What is the preganglionic to postganglionic fiber ratio in the sympathetic nervous system?

~ 1:20

Which neurons are cholinergic? what does this mean?

-all preganglionic neurons, sympathetic and parasympathetic

-this means they synthesize and release acetylcholine as their primary neurotransmitter

Where can nicotinic receptors be found?

in skeletal muscles and at ganglions

What type of organs have muscarinic receptors?

heart, bronchioles, pupil constriction, GI stimulation (all parasympathetic)

also sweat glands

What types of receptors are in the adrenal medulla? what is the product?

nicotinic, produce epinephrine

What is the function of the craniosacral system?

parasympathetic

Where are most parasympathetic ganglia located?

near or within the target effector organ

Why does the parasympathetic system generally produce more localized effects?

ganglia are near or within target organs, generally less divergence, approximately 3:1 ratio preganglionic to postganglionic fiber ratio

Which receptor type does parasympathetic postganglionic ACh act on?

muscarinic

What neurotransmitter is released by most sympathetic postganglionic neurons?

norepinephrine

Which receptor type does sympathetic postganglionic NE act on?

alpha and beta adrenergic receptors

What is a first order somatosensory neuron?

a sensory neuron that has a sensory receptor embedded in their free/encapsulated nerve endings

• stimulated by only “one type of energy” - mechanical, chemical, thermal

• cell bodies are in dorsal root ganglion outside CNS

Where are the cell bodies of first order somatosensory neurons most likely located?

in the dorsal root ganglion outside the CNS adjacent to the spinal cord

What is a second order somatosensory neuron?

synapses with first order in the dorsal gray horn of spinal cord (relevant segment)

• axons enter white matter and form ascending tracts within white matter

• axons decussate in the spinal cord/brainstem

  • axons terminate in thalamus

What is a third order somatosensory neuron?

has cell body in thalamus/ARAS/RF, receiving info from second order neurons via synaptic transmission, extends to cerebral cortex

What is the labeled line principle?

every part of the body is projected to a specific location within its respective cerebral cortex area. (line can be traced directly between brain and correlated body part)

What are tonic receptors?

SLOW adaptation receptors

• sensory receptors continue to transmit impulses if stimulus exists and frequency decreases only slightly

• keeps the CNS appraised of body’s status (proprioception and baroreceptors

What are Phasic receptors?

RAPID adaptation receptors

• sensory receptors adapts within seconds or milliseconds, then stop firing

• designed to register quick changes in stimulus strength (ex touch/smell)

• allows the body to ignore information that has been evaluated and found not to threaten homeostasis/well being

What could be an exception to the “standard” of phasic receptors?

pain receptors—some nociception mechanoreceptors never adapt completely to pain (hence lingering throb)

What are the two types of proprioception?

gait-automated movement, involving large muscle groups, mostly unconscious

conscious-purposeful, learned/skilled movements, fine motor skills

What monitors muscle length and tension (proprioception)?

muscle spindles

-groups of 3-10 specialized intrafusal fibers parallel to ordinary muscle fibers

-protects from over-stretching

What monitors tendon length/tension (proprioception)?

tendon organs

What monitors joint angulation/rotation (proprioception)?

joint receptors

What monitors joint angulation/rotation (proprioception)?

joint receptors

What is ataxia?

loss of conscious and/or unconscious proprioception causing incoordination of movement

What is an example of a stretch reflex?

patellar reflex

-tap (stretch) patellar tendon (pull on muscle) causes reflexive contraction of quadriceps

What can cause a graded response of +3/+4 in a patellar reflex test?

lack of inhibitory upper motor neuron

What are some types of joint receptors?

free nerve endings, ruffini endings, pacinian corpuscles, golgi tendon organs

What is the difference between conscious and unconscious proprioception?

unconscious perception: gait, integrated in the cerebellum

conscious perception: fine motor skills, integrated in the sensory cortex

Describe the ascending pathway for conscious proprioception

-first order neurons enter spinal cord via dorsal root, axons enter ipsilateral dorsal funiculus

-synapse in medulla w/ second order neurons, immediately decussate

-synapse with third order neuron in the thalamus, projects to somatosensory cortex

Describe the ascending pathway for unconscious proprioception

-1st order neurons enter dorsal root, ascend in lateral funiculus

-terminates in ipsilateral cerebellum

spinocerebellar tracts = GAIT

What is sensory ataxia?

uncoordinated gait and/or postural responses without loss of muscle strength (no paresis/paralysis)

What type of receptors is hair root plexus?

phastic-adapt rapidly and have very low threshold

What differentiates whiskers from other hair types?

presence of a surrounding blood sinus

What are pacinian corpuscles?

phastic, sensitive to alternating pressure/vibration (look like onion)

What are merkel’s disks/ruffini corpuscles?

tonic receptors, adapt slowly and register permanent touch

What is the cutaneous trunci reflex?

twitching of the skin of the thoracolumbar region upon tactile/pain stimulation caused by lateral thoracic nerve

What are cold receptors?

free nerve endings, A delta sensory fibers

What are warm receptors?

C fibers, maybe free nerve endings

What is the pit organ?

in some snakes: pit vipers, pythons, some boas

detects infrared radiation allowing generation of a thermal image

What is the upper motor neuron system?

originate in brain and stay in the CNS

-initiate voluntary movements

-maintain normal muscle tone

-regulation of posture

What are classical signs of upper motor neuron damage?

RAT

Reflex: hyperreflexia (loss of inhibitory function)

Atrophy: slow and mild muscle atrophy due to disuse

Tone: spasticity of muscles due to loss of UMN

What is the extra-pyramidal system?

neurons originate in several brainstem nuclei, and cross immediately or not at all. Axons activate and inhibit lower motor neurons of limbs, trunk, and neck

FUNCTION: controls large muscle groups for gross motor skills (smooth gait, stable posture, balance)

What are consequences of EPS dysfunction?

extra-pyramidal system

muscular weakness = unresponsive muscles = paresis to paralysis

What is the pyramidal system?

neurons originate in the motor cortex, decussate in the medulla oblongata, decussate in the medulla oblongata, descend in the lateral funiculus and synapse with LMNs in the ventral horn of the spinal cord

FUNCTIONS: controls muscles necessary for more involved, skilled, learned voluntary movements, requiring conscious thought and dexterity (very well developed in primates)

What are consequences of PS dysfunction?

pyramidal system

in domestic animals: gait remains normal, with mild postural response deficits

in primates: typical UMN signs (facial and arm/hand muscle deficits

What are signs of damage to lower motor neurons?

RAT

Reflex: decreased or absent spinal reflexes

Atrophy: quick and severe muscle atrophy

Tone: muscle weakness with flaccid paresis-paralysis

What are nociceptors?

pain neurons with free nerve endings, containing ligand-gated channels (poly-modal, meaning can carry several types of ligand-gated channels)

present in all tissues except the brain

What is the best-characterized ligand-gated receptor/channel complex?

the transient receptor potential cation channel, subfamily V, member 1 or TRPV1

activated by capsaicin, low pH, heat, and endovanilloids

How can molecules like ATP and ions like potassium be mediators of the pain signal?

normally are found inside the cell, so when outside indicates something is amiss

What is first pain?

the generation of pain

mainly A-delta fibers.

Sharp and immediate

What is second pain?

the maintenance of pain

many involved molecules/mediators (substance P, calcitonin)

“inflammatory soup”- burning/throbbing/nauseating and long lasting pain

What are the steps of pain transmission? (ascending tract)

-first order neurons (A delta and C fibers) enter spinal cord via dorsal root → → synapse with second order neurons. Glutamate and Substance p NTs

-second order neurons enter spinothalamic tract in the lateral funiculus.

-synapse with 3rd order in thalamus, sent two places.

Where do third order neurons travel for first and second pain?

ascending tracts:

first pain=somatosensory cortex for acute perception and localization

second pain=reticular formation and limbic system

What is neuropathic or neurogenic pain?

pain caused by a lesion or disease of the somatosensory nervous system

ex: phantom pain, trigeminal-mediated head shaking in horses

What is the analgesia pathway?

life-saving mechanism for extreme situations

-uses NTs like serotonin and norepinephrine

What are some consequences of pain?

-reduced food/water intake

-reduced healing/prolonged recovery times

-impaired immune function

-increased bp, tachycardia

-reduced renal function

What are the major sensory receptor types?

mechanoreceptors, chemoreceptors, thermoreceptors, nociceptors, proprioceptors

How does the olfactory system work roughly?

Olfactory receptors in the nasal mucosa detects odorants; signals travel through CN I to olfactory bulb an optic tract

What types of neurons are olfactory neurons?

bipolar

What are the supporting cells of the olfactory system?

sustenacular

What is the function of serous olfactory glands?

below epithelium, moisten surface to dissolve odorants and wash them away to maintain sensitivity

What is the vomeronasal organ?

two narrow parallel ducts embedded into the hard palate

-contains specialized receptors for pheromones

-used in the flehmen response

What cranial nerves are involved in taste sensation?

VII-rostral tongue

IX, X- caudal tongue and pharyngeal region

What embryologic structures does the eye develop from?

retina/optic nerve: neuroectoderm

lens: surface ectoderm

What are the three eye chambers?

anterior chamber: between cornea and iris

posterior chamber: between iris and ciliary body/lens

vitreous chamber: large space behind lens surrounded by retina

What are the three tunics of the eye and their functions?

fibrous tunic: cornea and sclera provide protection shape and rigidity

vascular tunic (uvea): choroid, ciliary body, and iris provide nourishment, accommodation and control of pupil size

neural tunic: retina contains photoreceptors that convert light into nerve impulses

What separates the cornea and sclera?

limbus

What is the area cribosa?

“collander” area at posterior pole of sclera where fenestrations allow exit/entry of nerves and blood vessels

What is the flow of aqueous humor?

produced in ciliary epithelium, flows from posterior chamber, through pupil, into anterior chamber, drains through iridocorneal angle

what is mydriasis? What CN are involved?

enlarged pupil (dilation)

CN II, CN V

What is pupillary miosis? What CN are involved?

smaller pupil

CN II

What is the pars caeca?

non visual part of retina, black in color

What is the most refractive part of the eye?

the cornea

What are the five corneal layers from anterior to posterior?

anterior epithelium

anterior limiting lamina

stroma

posterior limiting lamina

posterior epithelium or endothelium

What corneal layer is absent in dogs?

anterior limiting lamina

What cell types make up the corneal anterior epithelium? endothelium?

anterior-stratified squamous (NOT keratinized)

endothelium-simple squamous/low cuboidal cells

What determines corneal transparency?

precise collagen spacing

controlled hydration (less water than is typical intracellularly)

intact endothelial pump

lack of vessels and pigment

Where do corneal stem cells reside? how often can they regen?

at limbus, migrate towards center; every 7 days

What are some characteristics of corneal endothelium?

maintains stromal dehydration and transparency, but has limited regenerative capacity

What lens orientation is best for near vs far vision?

far=flat lens

near=rounded lens

What is the difference between nuclear sclerosis and cataracts?

both lens conditions:

nuclear sclerosis=normal physiology, age-related hardening and hazing in the lens from compaction of internal layers

cataracts: pathologies caused by changes in lens proteins

What is visual acuity and what determines it?

how much detail an animal can resolve

determined by density and arrangement of photoreceptors, specifically cones

What is high convergence vs low convergence?

high-many photoreceptors per one bipolar/ganglion pathway, high sensitivity but low acuity

low-few/one photoreceptors per one pathway, increased spatial acuity

What are the first three neurons in the optic pathway?

1st-photoreceptors, in neural epithelial layers (deepest of the three)

2nd-bipolar neurons in inner layer

3rd-multipolar neurons in ganglionic layer

What is the conscious visual pathway?

retina → CN II → optic chiasm → optic tract → Lateral Geniculate Nucleus → optic radiations → visual cortex

left FOV travels to left brain, right FOV travels to right brain

Does all visual info travel to the visual cortex?

no-some fibers travel to midbrain structures (for visceral info) rather than the LGN

What does it mean if there is blindness and an absent PLR?

retinal damage possible, or dysfunction in afferent pathway

What does it mean if there is blindness and an intact PLR?

blindness in the central nervous system after splitting of fibers to the thalamus

what is the difference between mesocephalic, dolichocephalic, and brachycephalic dogs

dolichocephalic-eyes deeper in orbit, crazy long nose

brachycephalic-squish-faced, more vulnerable to corneal exposure

What is the periorbita?

fibrous sheet around the eye globe, muscles, nerves, and vessels

What is the difference between bulbar and palpebral conjunctiva?

bulbar: covers visible scleral surface (more caudal)

palpebral: lines inner eyelid surface