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
16
Q
Describe the habenulae
A
- Elevations of habenular nuclei:
- Associated with olfaction
- Associated with reflex responses associated with odors.
- Largest in sharks and bloodhounds
- Inconspicuous in birds
- Poorly developed in aquatic mammals
17
Q
Describe the thalamus and it’s functions
A
- Paired masses of nuclei in lateral walls of third ventricle
- Includes relay nuclei for both motor and sensory pathways
- Includes association nuclei
- 80 percent of diencephalon
- Separated from hypothalamus via:
- Hypothalamic sulcus (groove)
- Functions:
- Relays all sensory information except smell to the cerebral cortex.
- Provides crude awareness.
- Initial autonomic response of the body to intense pain (physiologic shock).
- Interpretation center for crude pain, temperature, light touch, pressure.
- Plays a role in arousal and alerting.
- Plays a role in complex reflex movements.
18
Q
Describe the sensory region of the thalamic relay nuclei
A
- Medial geniculate body:
- Auditory
- Projects to primary auditory cortex in temporal lobe
- Lateral geniculate body:
- Visual
- Projects to primary visual cortex in occipital cortex
- Ventral posterior nucleus:
- General sensations and pain
19
Q
Describe the motor region of the thalamic relay nuclei
A
- Ventral lateral:
- Voluntary motor
- Ventral anterior:
- Voluntary motor and arousal
- Subthalamic:
- Voluntary motor
20
Q
Describe both the reticular region and the anterior region of the thalamic relay nuclei
A
- Reticular
- Modifies neuronal activity in the thalamus.
- May be involved in: Regulating sleep-wakefulness cycle and levels of awareness.
- Anterior
- Concerned with certain emotions and memory.
- Receives input from: Hippocampus and Mamillary bodies
21
Q
What is the hypothalamus?
A
Complex of nuclei that form floor and ventrolateral walls of third ventricle.
22
Q
What is the function of the hypothalamus in craniates?
A
- Major center for homeostasis
- Controls autonomic nervous system:
- Anterior nuclei generally associated with parasympathetic functions.
- Posterior nuclei generally associated with sympathetic functions.
- Regulates gonads and pituitary gland via neurohormones
- Monitors sodium chloride and glucose content of blood
- Regulates appetite
- Associated with temperature regulation in endotherms
- Connected to thalamus
- Connected to basal nuclei
- Connections with limbic system: Associated with emotional responses
- Connected to hippocampus: Ancient olfactory cortex
23
Q
Describe the major function of the hypothalamus in mammals (and other higher vertebrates)
A
- Involved in psychosomatic disorders
- Associated with rage and aggression
- Controls normal body temperature
- Produces ADH and oxytocin
- Regulates food intake
- Maintains extracellular fluid volume
- Biorhythm oscillator
- Sexual center
24
Q
Describe the hypothalamic nuclei
A
- Mammillary bodies:
- Involved in olfactory reflexes and emotional responses to odors
- Relay stations for olfactory neurons to inferior colliculi
- Supraoptic nuclei :
- Send projections (axons) that release neurohormones into capillaries in the posterior pituitary:
- Oxytocin and Vasopressin
- Suprachiasmatic nuclei:
- Located immediately above optic chiasma
- Acts as a master biologic clock, controlling circadian and circannual rhythms.
- Set to light-dark cycle by a direct retinal projection to the suprachiasmatic nucleus
25
Describe the components of the telencephalon
* Cerebrum:
- Paired right and left hemispheres, each with a ventricle (lateral ventricles)
- Note that ray-finned fishes do not have a divided cerebrum.
* Olfactory tract and bulbs:
- Develop as anterior extensions from the floor of the telencephalon
* Striatum:
- Refers to the collection of basal nuclei (basal ganglia) that develop in the floor of the telencephalon
* Lamina terminalis:
- Original cephalic boundary of the neural tube
- Separates the two lateral ventricles
26
Describe the cerebrum in agnathans, fish, amphibians, and reptiles
* The primitive roof of the telencephalon is the pallium.
- It lacks a true cortex.
- It serves as a primitive sensory and association area and receives information from the olfactory apparatus and some from the thalamus.
* Agnathans, fishes and amphibians:
- Primitive pallium without a cortex
* Reptiles:
- Major development is a massive thick, ridge-like structure that develops from the floor of each lateral ventricle and bulges into the ventricle itself.
- Dorsal ventricular ridge
- Receives visual, auditory, and somatic sensory stimuli from the thalamus and projects to the striatum (globus pallidus)
- Additional size increase due to neurons associated with neck and upper limb movement
- Pallium is associated with neurons in crocodilians = beginnings of cerebral cortex.
27
Describe the cerebrum in birds
* Retain basic reptilian pattern
* Add another layer of neurons on top of the dorsal ventricular ridge:
- = avian ridge
- Associated with processing of sensory information from the optic nerves, especially in birds of prey
- May also play a role in homing and stereotyped behavior such as nest building
- See slide 35 for crappy picture.
28
Describe the cerebrum in mammals
* Major addition is a neocortex:
- Cerebral hemispheres make up about 80% of brain mass in mammals.
- A cortex consists of multiple layers of gray matter build from the bottom up.
- Neocortex sits on top of the original pallium.
- May have as many as 13 billion neurons in humans
- Surface area is increased in many mammals by the presence of sulci and gyri.
- - Lacking in monotremes and many marsupials
- Neocortex is typically divided into lobes:
- - Frontal
- - Parietal
- - Temporal
- - Insula (not always considered a separate lobe)
- - Occipital
29
Describe the occipital lobe of the cerebrum
* Integrates eye focusing movements.
* Correlates visual images with visual memory.
* Involved in conscious perception of vision.
* Separated from parietal lobe:
- Parietooccipital sulcus
30
Describe the parietal lobe of the cerebrum
* Somatesthetic interpretation: Postcental gyrus.
* Understanding speech.
- Auditory association cortex.
- Wenicke’s area.
- - Formulating words to express thoughts and emotions.
31
Describe the frontal lobe of the cerebrum
* Voluntary motor control:
- Precentral gyrus.
* Motivation
* Aggression
* Mood
* Personality
* Cognitive processes
* Verbal communication:
- Broca’s area.
32
Describe the temporal lobe of the cerebrum
* Receives/interprets olfactory and auditory sensations.
| * Responsible for storage of memory related to auditory and visual experiences.
33
Describe the insula
* Not observed from surface.
* Involved with memory.
* Psychic cortex:
- Highest levels of brain function: Abstract thought and Judgment
34
Describe the internal capsule and the corpus callosum
* Mammals:
- Internal capsule: Connects cortex with brainstem
- Corpus callosum: Connects neocortex of two hemispheres
- See Slides 41-43
35
What is the striatum?
* The striatum forms the floor of the telencephalon and is made up of the telencephalic basal nuclei.
- Other basal nuclei are found in the diencephalon and mesencephalon.
- The globuspallidus is the primitive basal nucleus found in fishes and all other vertebrates.
- In fishes, the globus pallidus:
- - Receives input from: The pallium and the thalamus
- - Projects to: Motor nuclei associated with cranial and spinal nerves
36
Describe the striatum in amphibians, birds, and mammals
* Amphibians:
- Additional nuclei added to the striatum:
- - Enables the cerebrum to participate in more extensive motor activities involving somatic muscles, especially limb muscles.
* Birds:
- Well developed striatum
* Mammals:
- Additional nuclei have been added to the striatum:
- - Caudate nucleus
- - Putamen
- - Amygdaloid nucleus
- Collectively, these nuclei make up the basal ganglia (nuclei).
-- See Slide 46-47
