MT #1

Question 1

Morula

Answer 1

Cell divisions initially form a ball of cells, called the morula

Question 2

Blastula

Answer 2

Cell divisions initially form a ball of cells, called the morula, which then hollows out to form the blastula

Question 3

Describe the locations and primary functions of the following major regions and subdivisions of the brain: frontal

Answer 3

located at the very front of the brain. Involved in voluntary movement (motor cortex), reasoning, planning, problem-solving, and speech production (Broca’s area).

Question 4

Describe the locations and primary functions of the following major regions and subdivisions of the brain: parietal

Answer 4

located on both sides of the brain behind the frontal lobe. Involved in sensory processing (touch, pressure, pain, temperature), spatial awareness, and proprioception.

Question 5

Describe the locations and primary functions of the following major regions and subdivisions of the brain: temporal

Answer 5

located on both sides of the brain, under the parietal lobes and behind the frontal lobe. Involved in hearing, memory, language comprehension (Wernicke’s area), and emotional processing.

Question 6

Describe the locations and primary functions of the following major regions and subdivisions of the brain: occipital

Answer 6

back of the brain. Involved in vision processing, color recognition, object recognition, and motion detection.

Question 7

Describe the locations and primary functions of the following major regions and subdivisions of the brain: insula

Answer 7

Deep below temporal and frontal lobes. Involved in taste perception, visceral sensation, emotion processing, and consciousness.

Question 8

Describe the locations and primary functions of the following major regions and subdivisions of the brain: pineal body

Answer 8

near the center of the brain, between the two hemispheres, and above the midbrain. Produces and regulates hormones, such as melatonin.

Question 9

Describe the locations and primary functions of the following major regions and subdivisions of the brain: thalamus

Answer 9

on top of brainstem. Is a relay station for sensory and motor signals to the cerebral cortex. Is involved in consciousness, sleep, and alertness.

Question 10

Describe the locations and primary functions of the following major regions and subdivisions of the brain: hypothalamus

Answer 10

below the thalamus at the base of the brain. Regulates various autonomic functions, such as body temperature, hunger, thirst, sleep, and hormone secretion via the pituitary gland.

Question 11

Describe the locations and primary functions of the following major regions and subdivisions of the brain: midbrain

Answer 11

upper portion of the brainstem, just underneath the thalamus. Controls eye movement, auditory and visual reflexes, and relays motor and sensory signals.

Question 12

Describe the locations and primary functions of the following major regions and subdivisions of the brain: pons

Answer 12

middle part of brainstem between midbrain and medulla. Relays information between the brain and spinal cord, regulates breathing, and contributes to sleep and arousal.

Question 13

Describe the locations and primary functions of the following major regions and subdivisions of the brain: medulla

Answer 13

lower portion of the brainstem that becomes part of the spinal cord. Controls autonomic functions including heart rate, blood pressure, and respiration. Manages reflexes (coughing, sneezing, and swallowing).

Question 14

Describe the locations and primary functions of the following major regions and subdivisions of the brain: cerebellum

Answer 14

Below the occipital lobe in the back of the brain. Helps coordinate movement, balance, posture, and fine motor control. Aids the execution of voluntary actions (but does not initiate movements).

Question 15

Describe how neurons communicate with each other

Answer 15

• Neurons have a resting membrane potential of -70mV due to the uneven distribution of ions. When a neuron is stimulated, ion channels open, which allows sodium ions to rush in and depolarize the membrane.
• If depolarization reaches the threshold (-55mV), an action potential is triggered. The action potential propagates down the axon by opening voltage-gated sodium channels.
• After the depolarization, potassium ions exit the neuron, which repolarizes the membrane. Then, the action potential reaches the axon terminal (presynaptic neuron).
• The voltage-gated calcium channels open, allowing calcium to enter the terminal. Calcium triggers vesicles filled with neurotransmitters to fuse with the membrane and release their contents into the synaptic cleft.
• Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic neuron.
• Depending on the neurotransmitter and the receptor type, the postsynaptic neuron can experience either an excitatory postsynaptic potential (depolarization) or an inhibitory postsynaptic potential (hyperpolarization).
• Neurotransmitters are removed by the synapse via reuptake, enzymatic degradation, and diffusion away from the synapse.

Question 16

Define neurotransmitter and list at least one neurotransmitter and its corresponding receptor.

Answer 16

A neurotransmitter is a chemical messenger that transmits signals across a synapse. Neurotransmitters are released from a presynaptic neuron to bind to receptors on the postsynaptic neuron. This influences whether the neuron will generate an action potential. An example neurotransmitter is acetylcholine. Its receptor is the nicotinic acetylcholine receptor, which is ionotropic and fast-acting. The receptor is found at the neuromuscular junctions and in the central nervous system.

Question 17

Contrast neurons and nerves.

Answer 17

Neurons:
- Individual cells that transmit electrical and chemical signals.
- Consists of a cell body, dendrites, and an axon.
- They process and transmit information via impulses and neurotransmitters.
- They are found in the brain, spinal cord, and peripheral nervous system.
- There are sensory neurons, motor neurons, and interneurons.

Nerves:
- Bundles of axons from multiple neurons that transmit signals between the central nervous system and the body.
- Composed of many axons wrapped in connective tissue.
- They enhance communication by carrying signals to and from the brain, spinal cord, and body.
- They are located in the peripheral nervous system.
- There are cranial nerves and spinal nerves.

Question 18

What is a glial cell?

Answer 18

A glial cell is a supportive cell in the nervous system that provides structural, metabolic and protective support to neurons. They do not transport electrical impulses like neurons. They help maintain homeostasis, form myelin, and participate in immune defense, instead.

Question 19

Describe the difference between neurons and glia.

Answer 19

Neurons:
- Transmit electrical and chemical signals for communication.
- Generate action potentials and release neurotransmitters.
- There are a limited number of neurons.

Glial Cells:
- They support, protect, and maintain the environment for neurons.
- They can divide and regenerate throughout life.
- There are astrocytes, oligodendrocytes, Schwann cells, microglia, and ependymal cells.

Question 20

Astrocytes

Answer 20

maintain blood-brain barrier, regulate neurotransmitter levels, and provide nutrients.

Question 21

Ependymal cells

Answer 21

line brain ventricles and help produce CSF.

Question 22

Oligodendrocytes

Answer 22

produces myelin in the CNS.

Question 23

Schwann cells

Answer 23

produces myelin in the PNS.

Question 24

Microglial

Answer 24

act as immune cells of the CNS by removing debris and pathogens.

Question 25

Explain the nature of the blood-brain barrier

Answer 25

A selectively permeable barrier that protects the brain from harmful substances while allowing nutrients to pass through. It helps maintain the brain’s stable environment by preventing toxins, pathogens, and large molecules from entering the CNS. Oxygen, glucose, and specific small, lipid-soluble molecules are allowed to pass.

Question 26

Describe the structure of the blood-brain barrier

Answer 26

The blood brain barrier is composed of specialized endothelial cells that line the blood vessels in the brain. Endothelial cells form tight junctions, which prevents the passage of molecules. These cells lack pores (unlike capillaries) in other body regions. The end-feet of astrocytes extend to surround blood vessels and help nutrient exchange to reinforce the barrier. There are pericytes that are embedded in the walls of the capillaries, which regulate blood flow and contribute to the integrity of the barrier. The basement membrane provides structural support and an additional filtration layer.

Question 27

What is the difference between a motor neuron and sensory neuron?

Answer 27

Motor neuron: - Efferent neurons - Carry signals from the CNS to muscles and glands to create a movement or response. - Sends signals from brain and spinal cord to effectors (muscles / glands). - Ex., neurons that stimulate muscle contraction, such as those in the somatic nervous system controlling voluntary movement. Sensory neuron: - Afferent neurons - Carry sensory information from the PNS (body) to the CNS - Sends sensory information from receptors to the brain / spinal cord. - Ex., neurons that detect stimuli such as touch, temperature, and pain.

Question 28

List the different ventricles

Answer 28

Lateral ventricles → one in each hemisphere. They are the largest ventricles and are connected to the third ventricle via the interventricular foramen. Third ventricle → midline of the brain between the diencephalon. Drains into the fourth ventricle via the cerebral aqueduct. Fourth ventricle → between the brainstem and cerebellum. CSF flows into the central canal of the spinal cord and into the subarachnoid space around the brain.

Question 29

What is the function of the ventricles

Answer 29

The ventricles contain the choroid plexus, which produces CSF. This CSF flows through the ventricles and into the subarachnoid space, cushioning the brain and spinal cord. CSF absorbs shocks, reduces the brain’s weight, helps deliver nutrients, and removes metabolic waste.

Question 30

Explain how the neural plate gives rise to the brain and spinal cord

Answer 30

The neural plate arises from the ectoderm in response to signals from the notochord and mesoderm. Specifically, the inhibition of BMP signaling by molecules including noggin and chordin. The ectodermal cells then adopt a neural fate. The neural plate thickens and begins to fold inward, forming a neural groove bordered by neural folds. The folds elevate and fuse to form the neural tube, which is a precursor to the central nervous system. The rostral portion of the neural tube balloons into three primary brain sections: the forebrain, midbrain, and hindbrain. The rest of the tube elongates, forming the spinal chord. Closure of the neural tube is tightly regulated. If it does not close properly, neural tube defects may occur, such as spina bifida or anencephaly.

Question 31

Define inducing factor

Answer 31

A diffusible signaling molecule secreted by one group of cells that influences the development, fate, or behavior of nearby cells. These factors are often concentration-dependent, which means that cells respond differently depending on the distance from the source. Inducing factors include families of proteins, such as Sonic Hedgehog, BMPs, WNTs, and retinoic acid. They activate specific intracellular signaling pathways, causing differential gene expression and shaping tissue patterning and organogenesis.

Question 32

Describe the general principle in how cell fate is determined.

Answer 32

Cell fate can be determined by a combination of intrinsic factors (ex., inherited gene expression profile) and/or extrinsic factors (ex., morphogens and interactions with neighboring cells). Cells initially are pluripotent, but as they receive positional and chemical cues from the environment, specific transcription factors are activated, which direct the cells toward specialized identities (e.g., neuron or glial cell). This process is often governed by signal gradients and temporal dynamics. Key mechanisms can include inductive signaling, lateral inhibition, and cell to cell communication.

Question 33

Outline development of the dorsoventral axis

Answer 33

The dorsoventral axis of the neural tube is established by opposing gradients of signaling molecules that create distinct zones of gene expression along the dorsal-ventral plane. Ventral patterning is driven by sonic hedgehog, which is secreted first by the notochord and then by the floor plate of the neural tube. High concentrations of sonic hedgehog induce the formation of ventral cell types, such as motor neurons and interneurons. Dorsal patterning is shaped by BMPs and WNT proteins, which are secreted by the roof plate and overlying ectoderm. These induce sensory neuron progenitor domains, each expressing unique combinations of homeodomain and bHLH transcription factors, which define the distinct neural cell types. This layered patterning ensures the correct spatial arrangement of sensory, interneuron, and motor neuron populations.

Question 34

How does formation of the rostrocaudal axis differ from the dorsoventral axis?

Answer 34

The rostrocaudal axis determines the identity of neural structures from the head to the tail. It is primarily patterned by gradients of retinoic acid, WNT, and FGF signaling, which affect the expression of Hox genes. Hox genes are key regulators of positional identity, especially in the hindbrain and spinal cord. These genes are expressed in overlapping areas and confer regional identity (ex., cervical, thoracic spinal cord segments). Brain regions, such as forebrain, midbrain, and hindbrain, are specified early (partly independent of Hox genes), via separate mechanisms involving Otx2 and Gbx2. The dorsoventral axis is patterned perpendicularly to the rostrocaudal axis and determines the functional domains (ex., motor vs sensory neurons) within the sections of the neural tube. The axis relies on vertical signaling from the notochord and ectoderm, mostly via sonic hedgehog (ventral) and BMPs/WNTs (dorsal). Overall: The rostrocaudal axis specifies the regional identity (ex., brain vs spinal cord). The dorsoventral axis shapes cell type and function with a region.

Question 35

Describe how cells acquire neuronal or glial identities.

Answer 35

Neural stem cells in the ventricular zone first generate neurons, then later glial cells via the process regulated by both intrinsic and extrinsic factors. Intrinsic factors (ex., neurogenin and mash1) promote neuronal differentiation. Factors, such as Notch signaling, become more active later and push progenitors toward glial fate, including astrocytes and oligodendrocytes, Early progenitors tend to become neurons, while those that are later are more likely to be glial. Environmental cues, such as local cytokines and growth factors also shape the fate. The regulated sequence ensures proper cell type composition in the brain as it develops.

Question 36

Discuss the importance of “birthday” for neurons. (4 points)

Answer 36

The “birthday” of neurons determines its layer position in structures such as the cortex, where earlier-born neurons settle deeper, while later-born neurons migrate past that to more superficial layers (inside-out pattern). The birthday can also influence the identity of a neuron, its connectivity, and functional roles. It also reflects exposure to different signaling environments during development, affecting fate decisions.

Question 37

Radial migration

Answer 37

Cells (primarily excitatory neurons) move along radial glial fibers from the ventricular zone to the cortical plate. Creates the laminar structure of the cortex.

Question 38

Tangential migration

Answer 38

Cells (primarily inhibitory interneurons) migrate parallel to the surface of the brain, often from the ganglionic eminence to the cortex. This is critical for balancing excitation and inhibition in neural circuits.

Question 39

Free migration

Answer 39

Some cells move independently (rather than following glial scaffolds). This is especially true in intermediate zones. This allows flexibility in navigation, especially during complex pathfinding.

Question 40

Define the neurotrophic factor hypothesis and describe its importance in cell survival. (10 points)

Answer 40

The neurotrophic factor hypothesis states that developing neurons require target-derived trophic factors to survive. Only neurons that successfully reach and connect with targets receive enough of the factors to avoid cell death. Some examples of neurotrophic factors include NGF, BDNF, NT-3, and NT-4/5. These factors bind to Trk receptors or p75NTR, activating intracellular survival pathways. Neurons compete for the limited supplies of these factors and those that fail undergo apoptosis. This mechanism is critical as it ensures: - The correct matching between neurons and target cells. - Refinement of neural circuits. - Elimination of excess neurons to optimize efficiency and energy usage.

Question 41

Explain how a neuronal target can alter a neuron and give an example. (10 points)

Answer 41

Neuronal targets are able to influence the structure, function, neurotransmitter phenotype, and survival of the presynaptic neurons via retrograde signaling. For example, in sympathetic neurons, exposure to different target tissues can change the neurotransmitter from noradrenergic to cholinergic (ex., sweat glands in mice). The switch is driven by target-derived factors that alter gene expression in the neuron. Targets can also release neurotrophins that promote axon growth, synaptic stability, and survival. The plasticity allows neurons to adapt to their environment and refine their function based on where they form connections.

Question 42

Why does cell death occur during development? (4 points)

Answer 42

Eliminates excess neurons that fail to make functional connections. Helps refine neural circuits, ensuring precise connectivity. Removes damaged or misplaced cells, which maintains tissue health. Supports the sculpting of structures (ex., separating digits in the hand).