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)