Lecture 19: Vertebrate Brain Flashcards
1
Q
What is the subphylum craniata?
A
- Newer term for subphylum vertebrata
- Subgroups:
- Hagfishes (craniates without vertebrae)
- Vertebrates (craniates with vertebrae)
2
Q
Cranial end of neural tube of all craniates is characterized by three primary brain vesicles
A
- Prosencephalon: Future forebrain
- Mesencephalon: Future midbrain
- Rhombencephalon: Future hindbrain
– Differentiation of these three vesicles occurs: Localized thickenings of lateral walls and floor, and Evaginations
3
Q
Describe the Comparative anatomy of the early neural tube
A
- Prosencephalon is not divided into alar and basal plates like rest of neural tube.
- Two pairs of evaginations from prosencephalon (ray-finned fishes):
- Telencephalic vesicles: Become cerebral hemispheres
- Optic vesicles: Become retinas of the eye and become associated with diencephalon
4
Q
What is the myelencephalon?
A
- Major derivative is the medulla oblongata:
- Becomes continuous with the spinal cord.
- Gray matter in mesencephalon is organized into discrete nuclei interspersed among myelinated (white) fiber tracts.
- Gray matter in the spinal cord is continuous and is located more centrally and surrounded by myelinated fiber tracts.
- See Slide 8
5
Q
Describe the myelencephalon in agnathans
A
- The myelencephalonis more developed than other areas of the brain.
- Large neurons run the length of the tail:
- Thought to be involved in swimming.
- The myelencephalon is well developed in all the rest of the vertebrates.
- See Slide 9 and 10
6
Q
Describe the myelencephalon in teleosts, amphibians, and mammals
A
- Teleosts:
- Vagal lobes associated with myelencephalon in teleosts:
- Site of sensory nucleus (nucleus solitarius) in alar plate which may cause an enormous bulge on either side of brainstem.
- May be associated with sense of taste.
- Amphibians:
- Vagal lobes disappear from myelencephalon.
- Mammals:
- Well-developed myelencephalon
- See Slide 11
7
Q
Describe the metencephalon (cerebellum) in agnathans and chondrichthyes
A
- Agnathans:
- Cell bodies of cerebellum are on the surface
- Cerebellum does not bulge out as it does in other craniates.
- Chondrichthyes:
- Well-developed cerebellum:
- Restiform bodies: Equillibrium
8
Q
Describe the metencephalon cerebellum in teleosts
A
- Cerebellum is better developed in the more active fishes.
- Larger in fishes than in amphibians because swimming involves schooling, vertical movements, adjusting to water currents and keeping the dorsal part of the body from tipping over.
9
Q
Describe the metencephalon cerebellum in amphibians and reptiles
A
- Amphibians:
- Cerebellum poorly developed.
- Aquatic urodeles rely more on spinal cord reflexes and primitive hindbrain nuclei for muscle swimming coordination.
- Reptiles:
- Poorly developed metencephalon:
- Cerebellum is more developed in swimmers.
- Floccular lobes: May correspond to restiform bodies.
- See Slide 14
10
Q
Describe the metencephalon cerebellum in birds
A
- Very large cerebellum:
- Associated with flight
- Well-developed floccular lobes
11
Q
Describe the metencephalon cerebellum in mammals
A
- Well-developed cerebellum:
- Controlled by motor cortex in cerebral hemispheres.
- Connected to brainstem by three pairs of large fiber tracts called peduncles:
- Superior to midbrain
- Middle to the pons?? Not totally sure. But not a big deal.
- Inferior to medulla
12
Q
Describe the structure of the mesencephalon
A
- The roof of the mesencephalon is the tectum which displays a prominent pair of optic lobes in all craniates.
- Gray matter masses
- Serve as reflex and relay centers for impulses from retina
- Especially large in birds
- Chondrichthyes:
- Well-developed optic lobes and tracts.
- Amphibians:
- Well-developed optic lobes and tracts.
- In amniotes there are two pairs of dorsal lobes:
- Optic lobes (superior colliculi)
- Auditory lobes (inferior colliculi)
- Collectively, the above two lobes = corpora quadrigemina
- The floor (basal plate) of the mesencephalon is the tegmentum:
- Large fiber tracts
- Red nuclei in mammal
- Note that most reptiles have optic lobes, but snakes have developed corpora quadrigemina.
- See Slide 19-20
13
Q
Describe the major components of the diencephalon
A
- Epithalamus:
- Pineal body
- Parapineal body (organ)
- Choroid plexus
- Habenulae
- Thalamus
- Hypothalamus:
- Optic chiasma is cephalic boundary
- Infundibular recess and stalk
- Posterior pituitary (pars nervosa)
14
Q
Describe the epithalamus in agnathans
A
- Both parietal and pineal bodies are present:
- Pineal body is more posterior; parietal body is more anterior
- Parietal body is usually photosensitive
- Pineal and parietal bodies in lampreys serve as a photoreceptor
- Pineal body is vestigial or absent in hagfishes
15
Q
Describe the epithalamus of gnathostomes
A
- Pineal body serves as an endocrine gland that is stimulated by light via the retina.
- In some gnathostomes pineal organ is vestigial or absent:
- Crocodilians
- Some permanently aquatic mammals
- Pineal organ is relatively large in primates and sheep
- Median eye was a consistent feature among Devonian placoderms and osteichthyes:
- Probably a pineal derivative and may have been photosensitive
- The parietal eye (parapineal structure) in Sphenodon and lizards is photosensitive.
- Lies under a single translucent midline scale:
- Consists of a cornea, lens, and retina with photoreceptive cells
- Median eye in larval frogs is transitory and regresses in the adult to form an endocrine organ.
- Called the frontal or stirnorgan
- Not sure is it is a pineal or parietal derivative
- Produces melatonin
- Median eyes do not form retinal images but monitor photoperiod
