Brain Anatomy Part 1 (Week 1, Mod 8)

Describe the embryological development of the CNS… what did it develop from?

Is initially derived from the neural plate of the embryo:

• Specialized layer of ectoderm

  • Bends in, and embryo folds in on itself to form the neural tube

  • The neural crest is formed at the point where the two borders connected to form the tube

The neural crest forms the PNS

The neural TUBE forms the CNS

What 3 regions does the neural tube divide into when forming the CNS? What are these referred to as collectively?

Called the primary vesicles:

• Prosencephalon (forebrain)

• Mesencephalon (midbrain)

• Rhombencephalon (hindbrain)

Further divisions develop as the embryo matures… what are these referred to as collectively?  Describe the divisions that occur within the prosencephalon, mesencephalon, and rhombencephalon. What structures do these give rise to?

Are called the secondary vesicles

Forebrain → divides into telencephalon and diencephalon

• Telencephalon:

  • Forms the cerebral hemispheres

  • Houses the lateral ventricles (in the brain)

• Diencephalon:

  • Forms thalamus and hypothalamus 

    • Also epithalamus and pineal gland 

Midbrain → only the mesencephalon 

• Forms the midbrain

• Includes cerebral peduncles (little feet) that connect cerebrum and midbrain 

Hindbrain → divides into metencephalon and myelencephalon

• Metencephalon:

  • Forms the pons and cerebellum 

• Myelencephalon:

  • Forms medulla oblongata 

What are the 4 main divisions of the ADULT brain?  What do they control?

Cerebrum 

• Higher control centre

• Mediates cognition/thought processing

  • Receives and interprets sensory info

  • Initiates VOLUNTARY muscle action 

  • Interacts with limbic system (moods, fear, pleasure, and memory)

• Divided into Left and right hemispheres

Cerebellum 

• gate/balance/tone

• Monitors position in space AND controls adjustments

• Can influence speech

• SMOOTH MUSCLE MOVEMENT

Diencephalon  

• processing information (sensory/motor)

• Circadian and sleep wake cycle

• Integrates endocrine and nervous systems

• Thalamus acts as a relay centre 

• Hypothalamus endocrine centre 

Brainstem 

• controls body physiology

• Breathing/heart rate etc

  • Midbrain

  • Pons 

  • Medulla oblongata

What are the 2 main physical differences between the brains of higher mammals and lower mammals?

In higher mammals the cerebrum has hills (Gyri) and  valleys (sulci)

• Deeper sulci provide boundaries for the lobes of the brain

Lower mammals have smoother surfaces

Folding greatly enhances the surface area and vastly increases the potential for neuronal networks 

What does species variation in brain anatomy typically indicate?

The brains are organized in a way that is SUITABLE FOR THEIR LIFESTYLE

• Specific regions evolved to achieve complex cognition where needed; depends on animal’s lifestyle 

  • Cerebrum - higher thought

  • Cerebellum - gait and tone

  • Limbic system - emotion and memory 

Some species can also have specific, specialized pathways 

• Ex: crows can problem solve

• Ex: salmon, though smooth brain, can return to the same spawn site after years at sea 

The cerebrum is divided into several lobes, whose boundaries are defined by major fissures and smaller sulci… what are the 4 major landmarks that divide the forebrain into lobes?

1) Longitudinal fissure 

• Divides the brain into the 2 main hemispheres 

2) Cruciate sulcus

• Only called this in animals… termed the “central sulcus” in humans

  • Placed ACROSS the brain, perpendicular to the longitudinal fissure

• Defines the division between the frontal and parietal lobes (can be seen on dorsal view)

3) Lateral sulci (aka Sulcus Sylvius)

• Seen on the lateral aspect in the center of the brain (see image)

• Separates the temporal lobe from the frontal and parietal lobes

4) Rhinal sulcus 

• Separates the olfactory lobe from the rest of the forebrain… is MUCH more pronounced in dogs 

What are the 5 lobes of the canine brain? What are their functions?

1) Olfactory lobe (bulb)

• smell

2) Frontal lobe

• Higher functions:- behaviour, speech, problem solving

• Voluntary movement / motor functions

3) Parietal lobe

• Involved in perceiving sensory input such as touch, temperature

• Associated with movement and orientation

4) Temporal lobe

• Processes sound, vestibular sensations, smells (olfaction).

• Also involved in perception and emotion

5) The occipital lobe:

• Processing visual information

Describe the dorsal anatomy of the brain… What 3 major characteristics can be clearly identified?

1) Longitudinal fissure

2) Left and right hemispheres

3) CRUCIATE SULCUS

Describe the lateral anatomy of the brain… what 5 major characteristics can be clearly identified?

1) Olfactory bulb

• MUCH more pronounce in dogs; transports odor signals to the cerebrum 

2) Rhinal sulcus 

3) SYLVIAN GYRUS 

4) Cerebellum 

5) Brain stem 

Describe the ventral view of the brain… what are the 5 main characteristics that can be clearly identified? Give a brief description of each…

1) Pituitary gland

• Nestled into the center of the brain, between the optic chiasm and the midbrain 

2) Optic chiasm

• An X-shaped structure at the base of the brain, where the two optic nerves partially cross

3) Midbrain

• Smallest part of the brainstem 

• Is responsible for processing sensory information and controlling motor control and involuntary actions, like eye movement

4) Pons

• Between the midbrain and medulla oblongata; acts as a bridge between the two

• Also has neurological function and contains important nerve connections for cranial nerves

5) Medulla oblongata

• The lower and longest part of the brainstem

• Connects the brain to the spinal cord

What are the 3 main components of the brainstem? Overall, what neurological functions does it serve?

Brainstem is composed of the midbrain, pons, and medulla oblongata

Function:

• Controls most involuntary actions

  • Breathing, coughing, sneezing, eye movement, sleep-wake cycles, facial expressions

• Also processes stimuli via cranial nerves 

  • Interacts w/ optic nerves and olfactory bulb

• Important for physiological function

  • Regulates heart rate / bp

• Also interacts with the pituitary gland

What secondary vesicle forms the inside of the brain?  What are the 6 major structures it contains?

The diencephalon is the internal portion of the brain.

Associated structures:

1) Epithalamus 

• Forms the roof of the diencephalon 

• Associated with the pineal gland (light sensitive; controls circadian rhythm and melatonin release)

2) Thalamus

• Relay station for sensory INPUTS and motor OUTPUTS 

3) Pituitary 

4) Hypothalamus 

• Autonomic and endocrine control; MAINTAINS BODY HOMEOSTASIS 

5) The Limbic System (and associated structures)

• Hippocampus

• Amygdala

6) Corpus callosum

• Thick tract between the left and right hemispheres

• Shares info between the two sides 

What is “white matter” of the brain mainly composed of? Overall, what is its function?

White matter is mainly composed of axons of neurons

Function: connects different regions of the brain together; is essentially what allows the brain to function 

What are 4 major structures of white matter that can be found in the brain?  What is there function?

• Corpus callosum

  • Connect left and right hemispheres found only in placental mammals (not marsupials/monotremes or reptiles, birds, etc)

• Internal capsule

  • Connect cerebral hemispheres with brain stem

• Peduncles of the cerebellum

  • Connects cerebellum with pons and medulla oblongata

• Corona radiata

  • Can associate with the internal capsule to relay information to and from cerebrum via thalamus and brainstem

  • Is essentially the fan-like branches of white matter that connects the cerebral cortex to the internal capsule

What is the rostral colliculus within the brain?  What is the caudal colliculus?

Rostral colliculus (latin small hill)

• Relays visual information to the visual cortex

Caudal colliculus

• Relays auditory information 

• e.g. movement of head towards sound

What is the deep nuclei of the brain? What 2 major characteristics is it composed of, and what are their functions?

The deep nuclei is an organized cluster of neurons

Composed of the:

• Basal ganglia

  • Mass of grey matter within the cerebrum

  • Controls fine movement/balance/Tone and motivation/reward

  • Receives signals from motor cortex

  • Area of damage in Parkinson's Disease

• Limbic system including hippocampus

  • Emotion and memory (rabies virus)

  • Hippocampus affected in Alzheimer's disease

Describe the thalamus of the brain… what are some defining characteristics? What, in general, does it do?

• Thalamus is bilobed structure

  • Connection between called interthalamic adhesion

    • Visible in mid sagittal section

• Sensory information (not olfaction) converge on thalamus

  • From thalamus directed to region of cortex

• Thalamus composed of nuclei-clusters of neurones receiving inputs

  • Has multiple regions that perform different functions

• Some nuclei connects to midbrain

  • e.g lateral geniculate nuclei and vision

What are the 3 main functions of the hypothalamus?

• Autonomic NS control

• Endocrine function

• Controls homeostasis