Dr.Gibson : Study Flashcards
Describe the general pathway of how light becomes an electric impulse.
- Light passes through the layers of the retina to the photoreceptor layer
- Via phototransduction, light transfers to electrical signals
- Signal sent through photoreceptors to bipolar cells then to ganglion cells
- Axons of ganglion cells travel along the retina to the optic disc and the optic nerve
The function of photoreceptor Layer
Where light information is taken in
Stacks of membranes with rods (shades of gray) and cones (color)
The Function of the nerve fiber layer
Contains axons of ganglion cells
All axons converge to optic disc (myelination starts here)
* leaves the eye as optic nerve
The Function of the ganglion layer
Contains cell bodies of ganglion cells,
innermost cell bodies
Know the afferent and efferent branches of the menace response, in its simplest terms and understand this is a LEARNED response.
Learned response–> 12 weeks of age in dogs and cats, 7-10 days for farm animals
protects eyes from danger
CN II and IIV
Describe how vision is interpreted (vision pathway) with a focus on how the brain sees/ interprets VISUAL FIELDS and which side of the brain interprets which visual field. (blue circle/orange box diagram).
- Left visual cortex of brain interprets right visual field
- Right and Left visual fields cortex is taken in by left temporal retina and right nasal retina
- Right visual cortex of brain interprets left visual field
-Right and Left visual fields cortex is taken in by left temporal retina and left nasal retina
Understand in what clinical scenarios/lesion locations you will have absent vision/menace with normal PLRs, absent PLR with absent vision/menace unilaterally, and absent vision/menace with absent PLRs bilaterally.
Absent vision & menace, w/ normal PLRs
- Bilateral occipital cortex lesion
Absent PLR with absent vision & menace unilaterally
- Unilateral prechiasmal lesions ( retina or optic nerve)
Absent vision, menace & PLR bilaterally
- Optic Chiasmal Lesions
Understand which nuclei are associated with the vision pathway.
Normal visual pathway
1. Retina
2.Optic n
3. Optic chiasm
4 Optic tract
5. Lateral geniculate nucleus
6. Optic radiation
7. Visual cortex where vision is interpreted
Understand which nuclei are associated with the pupillary light reflex pathway.
PLR visual pathway
1. Retina
2.Optic n
3. Optic chiasm ( decussates)
4. Optic tract
5. Contralateral pretectal nucleus ( decussates #2)
6. Parasympathetic nucleus of CN III
7. CN III
8. Ciliary ganglia
9. (short) ciliary nerve
10. Pupillary sphincter m.
11. Direct response (constriction)
Describe which portion of the brain is involved in visual reflexes that are not the pupillary light reflex. (i.e. why do we drop down when a bird or butterfly attacks us!)
Visual reflexes: rostral colliculus
- dont require cortex of brain
- optic tracts ( axons) go to Rostral colliculus ( midbrain/ brainstem) to orient eye ( CN 3,4,6) and orient head position
Be able to describe the location of the upper motor neuron and their axons,
Neuron location:
1. Motor cortex ( grey) of cerebrum (pyramidal)
2. Motor nucleus of BS (extrapyramidal)
Axon Location:
1. within the CNS
What defines it as an upper motor neuron or tract.
Initiate voluntary movement, maintain muscle tone/ antigravity muscle, maintain posture
Understand which tract is the primary voluntary motor tract in the canine
Rubrospinal Tract
1. decussates immediately
2. Facilitates flexor muscle
Have a general understanding of what mammals are extrapyramidal and what mammals have a more developed pyramidal system.
Extrapyramidal system:
1. Domestic species
2. UMN nuclei in the brain stem
Pyramidal system:
1. Primates/ humans
2. UMN nuclei in motor cortex of cerebrum
Know how cerebral input effects the extrapyramidal motor system with a special focus on its what it does to flexor and extensor muscle activity
Rubrospinal and medullary Reticulospinal tract facilitate: flexor activity
Pontine reticulospinal and vestibulospinal tracts inhibit extensor activity
Know the upper motor neuron signs with a special focus on muscle tone and reflexes. (I.e How do I tell if a lesion is C1-C5 or C6-T2) GO TO PPT
Animal circles towards the lesion
Maybe seizures
Head pressing
Behavior change
Paresis
Hypertonicity/ Spasticity (m. tightness/stiffness)
Hyperreflexia (Patellar reflex)
Increased extensor tone
Increase normal reflexes
UMN bladder (difficult to express)
Protraction Affected
Know the lower motor neuron signs with a special focus on muscle tone and reflexes. (I.e How do I tell if a lesion is C1-C5 or C6-T2)
Absent/ decreased tone and reflexes
severe muscle atrophy
LMN bladder ( leaking constantly)
Exteroreceptors
Stimuli in the immediate environment
- temperature and touch
- special senses: vision, taste, hearing
Interoceptors
Internal, visceral environment of the body
Proprioceptors
Detect muscle stretch, tension, position of movements of joints
- Understand the general pathway for how a signal goes from the receptor to the spinal cord to the somatosensory cortex
1.PNS—> 2.CNS
1. Skin, fingertips (receptors)–> 2. Spinal Cord) central pathway in CNS–> Brain ( thalamus to cerebral cortex)
Understand what classification/type of nerve is involved in transmitting the signal from the receptor to the spinal cord.
Spinal tracts
- Group of axons in CNS, travel in white matter
- Nociception tracts
- Spinothalamic ( skin, viscera, body)
- Spinocervicothalamic (skin) - Temperature
- Spinothalamic - Touch/ Pressure
- Fasciculus cuneatus ( Thoracic limbs)
- Fasciculus gracilis ( pelvic limbs)
Know the basic function of the spinal tracts (i.e. which are involved in nociception, which are involved in temperature, and which are involved in touch/proprioception).
Understand that the somatosensory cortex is where sensory signals are interpreted by the brain and that the amount of cortex dedicated to specific body parts varies between species.
(Humans devote a lot of space to finger tips, horses to their lips, and rats/cats to their whiskers)
Be able to discuss which part of the brain receives conscious input from proprioceptors and which part receives unconscious/subconscious proprioceptive information. (Somatosensory-Proprioception)
- Conscious input from proprioceptors–> Cerebral Cortex
- Unconscious/Subconscious proprioceptive information–> Cerebellum
Have a general understanding that muscle spindles detect muscle stretch and golgi tendon organs detect tension
Muscle spindle
1. in skeletal muscle
2. called an “intrafusal” fiber
3. Recognizes muscle stretch
Have a general understanding that muscle spindles detect muscle stretch and golgi tendon organs detect tension
Golgi tendon organ
1.@ junctions of a muscle and tendon
2.detects tension
3.too much stretch= golgi tendon organ reflex
Be able to describe what side of the body you would find proprioceptive deficits with lesions of the cortex and lesions of the spinal cord
Cerebral cortex lesions lead to contralateral proprioception deficits
Unilateral spinal cord damage results in ipsilateral proprioception deficit
Understand why proprioceptive tracts are the first to be damaged in spinal cord compression and what clinical signs indicate severe spinal cord compression
Spinal cord compression
Proprio fibers damaged first because:
1. large axons, heavy myelination,
Severe spinal cord compression
1. Proprio–>2. motor function–> legs–> bladder–> Conscious pain sensation
Describe which side of the body the cerebellum receives proprioceptive information from in terms of contralateral or ipsilateral.
Cerebellar lesions lead to ipsilateral proprioception deficits
Be able to, in general, describe the function of the spinocerebellar pathway.
General proprio–> execution of coordinated movement
Travels up to the ipsilateral cerebellum
Be able to, in general, describe the function of the cerebrocerebellar pathway
Critical for planning & control of precise movement of extremities
Comes down from contralateral cortex
Be able to, in general, describe the function of the vestibulospinal pathway
Coordinates eye position, neck turns and limbs with position/ movement of head ( ipsilateral effect)
Understand which structures send signals to the cerebellum.
- Afferent signals
- Excitatory
- Pathways listed above
Understand the function of the deep cerebellar nuclei and their role in facilitating the outflow of information from the cerebellum.
Function: Send signal out from the cerebellum
Sends out the modulated plan from the cerebellum
What clinical signs might be seen in an animal with cerebellar disease?
- Intension tremor
- tremors from making movements - Hypermetria
- uncoordinated movements - Truncal Ataxia
Understand the effect that the vestibular nuclei have on the ipsilateral limb’s extensor and flexor muscles normally.
the vestibular nuclei Facilitate ipsilateral motor neuron to extensor muscle
and
Inhibit ipsilateral motor neuron to flexor muscle
Be able to tell the difference between peripheral and central vestibular syndromes.
- You will NOT have to localize any further than peripheral or central (i.e I will not ask
you about right vs left). Though now is a good time to try to understand it!
Be able to describe why paradoxical vestibular syndrome occurs. You will NOT be asked to localize a paradoxical vestibular syndrome case, but now is a good time to try to understand it!
No inhibitory signals to ipsilateral vestibular nuclei
leads to pushing away from the side of lesion
Know which clinical sign can always be trusted to help you localize in vestibular syndrome.
Paw Placement test
- severe are on same side of lesion
Have a general understanding of the 5 steps of the nociceptive pathway.
- Transduction: turning noxious stimulus to an electrical signal
- Transmission: sending signal from receptor to CNS
- A-delta fibers and C fibers - Modulation: reduces activity of pain transmission at level of spinal cord
- Projection: Sending info via ascending pathway to higher brain centers
- Projection: Sending info via ascending pathway to higher brain centers
- Perception: how we feel the pain
Understand WHERE modulation of pain occurs. You will not be asked about pain modulation theories.
Pain modulation at the level of the spinal cord
Be able to describe the differences between the withdrawal reflex and pain! 100% you will
get a question on this – it is SOOOOO important!
Withdrawal reflex
- doesn’t equal deep pain sensation
Can severe spinal cord in two
- If LMN present, Withdrawal reflex present
Pulling leg away from pain= Not withdrawal reflex
Deep pain
- must have a cortical response
- they must cry out, turn around, or try to bite you
Describe the ability of nociceptors to adapt.
Nociceptors are non-adapting
- won’t adapt to persisting stimulus
Have a general appreciation of the types of nociceptors that exist (do not need to know specific temperatures or chemicals)
Mechano-sensitive
Mechano-thermal
Chemical
Polymodal
Silent
Mechano-sensitive
respond to intense pressure, stretch or strain
(A-delta fiber)
Mechano-thermal
Respond to extreme temperature: < 5 oC / 41 oF ; >45 oC / 113 oF)
(A-delta fiber)
Chemical
Respond to chemicals released from tissue
damage (i.e: bradykinin, prostaglandin, substance P,
histamine) or from external chemicals (i.e.: topical
capsaicin) (C-fiber)
Polymodal
Sensitive to combinations of mechanical,
thermal, and chemical (C-fiber)
Silent
Silent nociceptors must be first activated or “awakened” by tissue inflammation before responding to a mechanical, thermal, or chemical stimulus. Most visceral
nociceptors are silent nociceptors
Understand A-delta
- myelinated: associated with thermal and
mechanosensitive nociceptors - Fast pain, easy to localize location
Understand C fibers
- unmyelinated: associated with chemical,
polymodal, silent receptors - Slow pain, difficult to localize specific location
Describe in general terms endolymph . Understand where each can be found and know what structure makes endolymph.
Transmits sound waves to hair cells
Found inside scala media
High in potassium
(similar to intracellular fluid)
More positive electric potential
Created by melanocytes in the stria vascularis
Describe in general terms, perilymph. Understand where each can be found
Transmits sound waves to endolymph
Found in scala vestibuli and scala tympani
High in sodium and chloride
Low in Potassium
(similar to extracellular fluid)
Less positive electric potential
Have a general sense of how you, the veterinarian, can assess for auditory disorders.
- Basic/ early investigative testing
- Breed/genetics
- Behavior
-Reflexive response to sound
- Otoscopic Exam - Advanced
- CT/ MRI
- BS auditory Evoked Response ( BAER)
Understand, in general terms, how a signal gets from the olfactory mucosa to the cortex.
- Axons pass through cribriform plate and synapse in the olfactory bulb neurons
- then to Olfactory tract
- Synapse in piriform cortex, limbic center( behavior), brain stem ( reflex)
Understand that the thalamus is NOT required for perception of smell in the primary olfactory cortex. Some portions of pathway may still utilize it for higher processing centers, but it is not required.
Thalamus not required for perception of smell in primary cortex
Understand that noxious smells or chemical odors will stimulate the trigeminal nerve, not the olfactory neurons.
Noxious smells/ chemical orders will stimulate CN V ( trigeminal) and not olfactory neurons
Understand that the limbic system is complex but is involved in behavior and emotion.
Behavior and emotion
Have a general idea of the clinical signs that can be seen in veterinary patients with the limbic system is damaged.
Docile animals become aggressive and vice versa
Rabies Virus
- dumb form, furious form
Altered cognition
sexual aberrations
altered use of sensory system
