Neurobiology

Question 1

What are the three germ layers that tissue layers are derived from? Through what process do they form?

Answer 1

• Ectoderm
• Mesoderm
• Endoderm

They form via gastrulation.

Question 2

Explain the process of neurulation in chordates.

Answer 2

A flexible notochord develops during gastrulation and sends signals that triggers neurulation.

Process of neurulation:
1. (Differentiation) Cells located in the ectoderm of embryonic chordates differentiate to form a neural plate
2. (Folding) The neural plate bends, folding inwards to form a groove flanked by a neural crest
3. (Separation) The infolded groove closes off, separates from the neural crest to form the neural tube
4. (Elongation) The neural tube elongates as the embryo develops and forms the forms the central nervous system
5. (PNS formation) The cells of the neural crest differentiate to form the components of the peripheral nervous system.

Question 3

Explain the development of neurons with regards to the neural tube.

Answer 3

(Differentiation)

The neural tube contains multipotent stem cells that differentiate to form:
–> Neurons
–> Glial cells – provide physical/nutritional support for neurons

(Neurogenesis)

Neurons are produced by progenitor neuroblasts.

Question 4

How do immature neurons end up in their final positions, and why?

Answer 4

Through neural migration – two methods
–> Glial guidance – glial cells provide a scaffolding network to direct immature neurons
–> Somal translocation – neuron forms an extension at cell perimeter, translocates soma along this length

The precise final position of neurons allows for the formation of neural circuitries. This migration process is critical for the development of brain/spinal architecture.

Question 5

What is spina bifida? Where does it occur and why? What are the two main types?

Answer 5

Spina bifida is a birth defect that causes incomplete closure of the neural tube. Vertebral processes don’t fuse, leaving spinal cord nerves exposed and prone to damage.

Commonly seen in the lumbar and sacral areas – slowest regions of closure. May be caused by not enough folate in diet during pregnancy

Types
- Occulta –> splits are small enough that spinal cord does not protrude
- Cystica –> Meningocele (cyst) or a myelomeningocele (cyst with spinal elements) forms

Question 6

What causes axons to grow from immature neurons? What is the function of their growth?

Answer 6

Chemical signals from surrounding cells cause axons and dendrites to grow from each immature neuron; axons either remain within the CNS or extend through the PNS.

They are able to carry impulses to other neurons or to effector cells in different parts of the body.

Question 7

Explain axon growth with regards to the growth cone.

Answer 7

An axon has a growth cone at its tip containing filipodia (motile growth filaments).

–> Filipodia extend, expanding the internal cytoskeleton within the growth cone
——> Direction of expansion is controlled by chemical stimuli from surrounding cells
———-> Cells may release chemoattractant or chemorepellent signals

Question 8

What is a synapse? What and how are they formed?

Answer 8

Synapse: a junction at which a neuron transmits a signal to another cell–they typically transmit chemical signals.

Developing neurons form multiple synapses to create communication pathways.

In synapse development, structures are assembled in the membranes on either side of the synapse and in the synaptic cleft.

Question 9

What are the different types of synaptic formation, and what are the four different types of synapses in the CNS?

Answer 9

• CNS –> neurons form a synapse with another axon, dendrite, or soma
• PNS –> neurons form a synapse with a muscle fibre (neuromuscular) or gland (neuroglandular)
• Some neurons may form synapses with capillaries and secrete chemicals directly into the bloodstream (neurosecretory)

Types of synapses
- Axo-dendritic
- Axo-somatic
- Axo-axonic
- Dendro-dendritic

Question 10

Explain how synapses are lost.

Answer 10

During embryonic / early post-natal development, multiple synapses are formed to maximize available connections.

When transmission occurs at a synapse, chemical markers are left that strengthen the synapse. Inactive synapses do not have these markers; they become weaker and eventually are eliminated.

Question 11

What is neural pruning?

Answer 11

Neural pruning: the loss of unused neurons by removing excess axons and eliminating their synaptic connections. Unused neurons eliminate themselves through apoptosis.

Question 12

What is evidence of neural pruning and what is its purpose?

Answer 12

Infant and adult brains typically have the same total number of neurons, but infant brains form approx twice the number of synaptic connections found in adult brains.

Purpose: reinforces complex wiring patterns associated with learned behavior.
–> Influenced by environmental factors
–> Mediated by chemical signal release from glial cells.

Question 13

What is neuroplasticity and what is its function? What are the two primary ways that it is achieved?

Answer 13

Neuroplasticity: the capacity for the nervous system to change/rewire its synaptic connections.

It enables
- Reinforcement of certain connections (learning)
- Circumvention of damaged regions

Two primary mechanisms
- Rerouting:
–> creating or re-establishing existing nervous connection via an alternate neural pathway
- Sprouting:
–> growth of new axon/dendrite fibres to enable formation of new neural connections

Question 14

What happens during a stroke?

Answer 14

Inadequate blood flow to a localised area of the brain deprives it of oxygen and glucose. Cell respiration ceases in neurons, which become irreparably damaged and die.

Question 15

Define the two main types of strokes.

Answer 15

Ischemic strokes: caused by a clot within the brain, restricting oxygenation to an associated region of the brain

Hemorrhagic strokes: ruptured blood vessels cause bleeding within a section of the brain

Question 16

How does recovery from strokes typically work?

Answer 16

Parts of the brain take on new functions to supplement damaged areas – possible due to neuroplasticity.

Question 17

How is the brain formed by the neural tube in embryonic development? What else is formed?

Answer 17

The anterior end of the neural tube expands and develops into the brain in cephalization (the development of a head).

–> Remainder of neural tube develops into the spinal cord
–> Cells comprising the neural crest differentiate to form most of the PNS

Question 18

What are the three primary structures of the embryonic brain?

Answer 18

• The forebrain
• The midbrain
• The hindbrain

Question 19

Outline how each of these structures become the identifiable components of the developed brain.

Answer 19

forebrain –> telencephalon + diencephalon –> cerebrum + thalamus

midbrain –> mesencephalon –> parts of brainstem

hindbrain –> metencephalon + myelencephalon –> pons/cerebellum + medulla oblongata

Question 20

What are the three main external structures and three main internal structures of the human brain?

Answer 20

External structures
1. Cerebral cortex
2. Cerebellum
3. Brainstem

Internal structures
1. Hypothalamus
2. Pituitary gland
3. Corpus callosum

Question 21

What is the cerebral cortex? Name and explain the functions of its four lobes. (Fight Paya To Overcome)

Answer 21

Cerebral cortex: The outer layer of the cerebral hemispheres; processes the most complex tasks of the brain

Frontal lobe: controls motor activity and tasks associated with the dopamine system (memory, attention, etc)

Parietal lobe: responsible for tactility and spatial navigation (proprioception)

Temporal lobe: involved in auditory processing and language comprehension

Occipital lobe: visual processing centre of the brain, responsible for sight perception

Question 22

What is the cerebellum and what is its role?

Answer 22

Cerebellum: separate structure at the base of the brain, under cerebral hemispheres

Responsible for coordinating unconscious functions e.g. posture, balance, movement

Question 23

What is the brainstem and what is its role?

Answer 23

Brainstem: posterior part of the brain that connects to the spinal cord; includes pons, medulla oblongata, midbrain

The medulla is used in autonomic control of gut muscles, breathing, blood vessels, and heart muscle.

Question 24

What is the hypothalamus and what is its role?

Answer 24

Hypothalamus: region of the brain functioning as the interface with the pituitary gland

It maintains homeostasis through coordinating the nervous and endocrine systems
–> synthesizes hormones secreted by posterior pituitary (neurohypophysis)
–> releases factors that regulate secretion of hormones by anterior pituitary

Question 25

What is the function of the pituitary gland?

Answer 25

It produces hormones that regulate other glands and target hormones.
–> Anterior lobe (adenohypophysis) secretes hormones such as FSH, LFH, growth hormone, prolactin
–> Posterior lobe (neurohypophysis) secretes hormones such as ADH, oxytocin

Question 26

What is the corpus callosum and what is its function?

Answer 26

Corpus callosum: bundle of fibres connecting the two cerebral hemispheres; largest white matter structure in the brain

It serves as a conduit allowing information to transmit between the two sides of the brain.

Question 27

Wild carrrrrd! Make sure you can identify the parts of the brain in a photo, diagram, and scan!

Answer 27

https://old-ib.bioninja.com.au/options/option-a-neurobiology-and/a2-the-human-brain/brain-sections.html

Question 28

How is animal experimentation used to identify localisation of function in the brain? What is a major criticism of animal experimentation? Give one example of a disease that animal studies have been used to develop treatments for.

Answer 28

• Stimulating regions with electrodes
• Removing regions via lobotomy
• Animal experimentation can cause major suffering to and kill the animal
• Animal studies are limited by the differences between animal and human brains

Possible disease examples
- Multiple sclerosis
- Epilepsy
- Parkinson’s disease

Question 29

What are lesions and how are they used in understanding brain function? Give an example of a lesion study. What makes the effects of lesions difficult to identify?

Answer 29

Lesions: abnormal areas of brain tissue that indicate the effect of the loss of a brain area. They can be identified via autopsy or scans of the brain (CT scans / MRI).

In lesion studies, the position of the lesion is used to relate damage to the brain to observed changes in behaviour/capacities.

Possible example
- Split brain patients have been used to identify the specific roles of the left and right cerebral hemisphere.

The effects of lesions can be difficult to identify because many functions may involve multiple brain areas.

Question 30

What is an autopsy and how is it used to identify brain function? Give an example of its use. What is a limitation of autopsies as studies?

Answer 30

Autopsy: A post-mortem examination of a corpse via dissection in order to evaluate causes of death.

Comparisons can be made between the brains of healthy and diseased corpses to identify affected brain areas.

Possible example
- Cadavers who suffered from aphasia (language impairment) in life demonstrate damage to specific areas

Autopsies of specific cases of brain damage are extremely rare and must be waited for.

Question 31

What is fMRI and how is it used to identify brain function? Explain its process.

Answer 31

fMRI record changes in blood flow within the brain to identify activated areas.

• Increased blood flow in active parts of the brain is made visible, often by injecting a harmless dye.
• Subject placed in scanner, high-resolution scan of brain taken
• Series of low resolution scans taken while subject is given stimulus; show activated parts of brain during response to stimulus

Question 32

Give an example of what makes the results of fMRI studies evident, and an example of how fMRI studies have been used.

Answer 32

Oxygenated haemoglobin responds differently to a magnetic field than deoxygenated haemoglobin.

fMRI studies have been used to diagnose ADHD and dyslexia, and monitor recovery from strokes.

Question 33

Explain the visual cortex and its function.

Answer 33

Each of the two cerebral hemispheres has a visual cortex in the occipital lobe of the cerebrum.

In the visual cortex, neural signals originating from light-sensitive rod/cone cells in the retina are processed.

Question 34

Explain Broca’s area and its function. What happens when Broca’s area is damaged?

Answer 34

Located in the frontal lobe of the left cerebral hemisphere.

Controls the production of speech.

If damaged, an individual cannot produce meaningful speech despite being understanding meaning and being capable of producing sound.

Question 35

Explain the nucleus accumbens and its function.

Answer 35

Located within each cerebral hemisphere.

Involved in the pleasure reward pathway; secretes neurotransmitters responsible for pleasure (dopamine) and satiety (serotonin)

Communicates with other centres involved in mechanisms of pleasure e.g. ventral tegmental area (VTA).

Question 36

Describe the cerebral cortex.

Answer 36

The cerebral cortex is the outermost layer of neural tissue found in the cerebrum of humans and other mammals.

It is composed of gray matter – has a highly complex architecture of neurons.

It processes complex tasks such as memory, perception, consciousness, and thought.

Question 37

How does the cerebral cortex differ between mammals and other animals?

Answer 37

Only mammals have a cerebral cortex; the regions of the brain performing those structures are organized in clusters of cells rather than layers.

Question 38

Explain how the cerebral cortex differs between humans and other animals, and how these differences are facilitated.

Answer 38

In humans, the cerebral cortex forms a larger proportion of the brain and is much more highly developed than in any other mammal.

It has become greatly enlarged throughout evolution; that disproportional enlargement is responsible for our capacity for cognitive thought.

The increase in total area is mediated by gyrification (extensive folding) to form gyrus (wrinkled peaks) and sulcus (troughs). This significantly increases surface area without increasing volume, so the brain can fit within the cranium.

Question 39

What is a reliable indicator of potential cognitive capability with regard to the cerebral cortex? Give examples.

Answer 39

Extent of gyrification – primates and humans have a much greater degree of folding compared to rats for example.

Question 40

What are the cerebral hemispheres? Explain their function. How is information passed between them?

Answer 40

Cerebral hemispheres: two hemispheres that the cerebrum is organized into.

They are responsible for higher order functions –> memory, speech, cognitive thought, problem-solving, attention, emotions.

This involves association of stimuli from different sources – including the eye, ear, and memories.

Interhemispheric communication is facilitated by the corpus callosum, which is formed by a bundle of myelinated nerve fibres embedded within the brain.

Question 41

How are tasks localized within the cerebral hemispheres? State where the most sophisticated processes occur and give an example of localization.

Answer 41

Some activities are localized to a single side of the cerebral hemispheres.

e.g. Speech production is coordinated by Broca’s area, which is located in the left frontal lobe of the brain.

The most sophisticated thought processes (reasoning, decision-making, planning) occur in the frontal and prefrontal lobes of the cerebral cortex.

Question 42

Where do sensory stimulus and motor control come from for the respective hemispheres? What is this phenomenon known as?

Answer 42

Left hemisphere:
- Sensory stimulus and motor control from right side of body

Right hemisphere:
- Sensory stimulus and motor control from left side of body

The processing of information on the opposite side of the body is known as contralateral processing.

Question 43

Give two examples of how brain function is lateralized to each respective hemisphere.

Answer 43

Possible answers:

Left hemisphere
- Speech, language, and comprehension
- Analysis and calculations
- Time and sequencing
- Recognition of words, letters, numbers

Right hemisphere
- Creativity
- Spatial ability
- Context/perception
- Recognition of faces, places, and objects

Question 44

Outline how the cerebral hemispheres receive sensory input from:
–> the ears
–> the skin, muscle, and other internal organs
–> the eyes

Answer 44

Signals from the ear pass to the auditory area in the temporal lobe.

Signals from the skin, muscles, and internal organs pass via the spinal cord to the somatosensory cortex of the parietal lobe.

Signals from the eye pass to the visual cortex in the occipital lobe.