Review Questions Flashcards
1
Q
What is the difference between regional and systems neurobiology?
A
Regional= the study of structure and function of the anatomic parts of the nervous system.
Systems= the study of functional systems within the nervous system.
2
Q
What is the Lesion technique?
A
Method: Damaging a distinct nervous system region in an experimental animal and documenting the subsequent loss of function.
Purpose: Correlate structure with function.
3
Q
What is the Tracing technique?
A
Method: Injection of visible molecules into the periphery to be taken up by local axons and transported back to the cell body or vice versa.
Purpose: Assess connections between nervous systems.
4
Q
What is the Cytochemistry/Histochemistry technique?
A
Method: General cell staining.
Purpose: Demonstrate size and distribution of neurons.
5
Q
What is the Immunocytochemistry technique?
A
Method: Specific cell staining that utilizes antibodies to identify proteins.
Purpose: Demonstrate molecular distinctions of neurons.
6
Q
What is the Genetic Engineering technique?
A
Method: Insertion of a gene that codes for some visualizable substance into a neurons genome.
Purpose: Trace connections between molecularly defined populations of neurons and their targets.
7
Q
What is the Brain Imaging technique?
A
Methods: - Computerized Tomography (CT)
- Magnetic Resonance Imaging (MRI)
Purpose: View brain structure.
8
Q
What is the Single-cell or single unit electrophysiological recording technique?
A
Method: Placement of a microelectrode into a neuron or region of neurons to record action potential activity.
Purpose: Provide information about the type of stimulus that activates a neuron and define a neuron’s receptive field.
9
Q
What is the Functional Brain Imaging technique?
A
Methods: - Positron Emission Tomography
- Single Photon Emission Computerized Tomography
- Functional MRI
Purpose: View brain function based on local metabolism and correlate structure with function. (Identify brain networks associated with a specific function).
10
Q
What does Analysis of Complex Behaviors entail?
A
Uses functional brain imaging during well-designed behavioral tasks.
11
Q
What are the 4 types of tissues in our body?
A
- Nerve
- Muscle
- Connective Tissue
- Epithelial
12
Q
What is nerve tissue composed of?
A
Composed of Neurons and their support cells (Glial Cells).
13
Q
What does a neuron do?
A
Receives, process, and transmits signals.
14
Q
What are the two mechanisms neurons use to function?
A
Electrical and Chemical.
15
Q
GENERALLY, what is the difference between electrical and chemical mechanisms?
A
Electrical- used to convey information rapidly from one part of a neuron to another. (Action Potential)
Chemical- Used to carry information between part of one neuron and a part of a second neuron or effector cell (ex. skeletal, cardiac, and smooth muscle and glandular tissue).
16
Q
What are the regions of a neuron?
A
- Cell Body
- Dendrite
- Axon
- Presynaptic Terminals
17
Q
Describe the structure of the cell body.
A
Contains the nucleus and cytoplasm.
Nucleus- Large, with a spherical shape. Euchromatic with a prominent nucleolus.
Cytoplasm- lots of RER and polysomes. Well developed Golgi complexes and lots of mitochondria. It also has a well developed cytoskeleton which gives them a unique structure and function.
18
Q
What is the function of the cell body?
A
- Acts as the trophic center of the cell.
2. Receptive to stimuli.
19
Q
Describe the structure of a dendrite.
A
- Short, tapered, and highly branched.
- There is not golgi complex in the cytoplasm
- They have dendritic spines.
- One neuron has numerous dendrites.
20
Q
What is the function of a dendrite?
A
- Transmits signals toward the cell body.
2. Receptive to stimuli
21
Q
Describe the structure of an axon?
A
- Long, cylindrical and not highly branched.
- No RER or polysomes in the cytoplasm
- Has an Axon Hillock, which is devoid of Nissl substance.
- Terminal Arborization- the branched, distal part
22
Q
What is the function of an axon?
A
- Generates and conducts signals
2. Receptive to stimuli.
23
Q
One neuron can synapse with another at what parts of the cell?
A
- Axon
- Dendrite
- Cell Body
24
Q
Describe the structure of a presynaptic terminal.
A
- Cytoplasm contains more mitochondria and small spherical membrane bound vesicles that contain neurotransmitters.
- Active Zones- regions along the membrane which are concentrated with voltage-gated Ca++ channels and synaptic vesicles.
- No myelin sheath.
25
What is the function of a presynaptic terminal?
Signal transmission to another cell.
26
What are Molecular Transport Systems composed of and what do they do?
Composed of: well-developed cytoskeleton.
| Function: transports substances between the cell body and the processes at slow, intermediate, or fast speeds.
27
Define Anterograde.
Carries materials (i.e. organelles, macromolecules) from the cell body to the periphery.
28
Define Retrograde.
Carries material (i.e. toxins, viruses) from the periphery to the cell body.
29
What are the 3 main categories of neurons?
1. Motor (Efferent)
2. Sensory (Afferent)
3. Interneurons
30
What does a motor neuron do and what are the different types of motor neurons?
Function: Controls effector organs (i.e. muscles and glands)
1. General Somatic Efferent
2. General Visceral Efferent
3. Special Visceral (Brachial) Efferent
31
What does GSE innervate?
General Somatic Efferent
Motor innervation to skeletal muscles derived from myotomes.
32
What does GVE innervate?
General Visceral Efferent
Motor innervation to smooth muscle, cardiac muscle, and glands.
33
What does SVE innervate?
Special Visceral Efferent
Motor innervation to skeletal muscles derived from pharyngeal arches.
34
What does a sensory neuron do and what are the different types of sensory neurons?
Function: Receives sensory stimuli through specialized nerve endings called receptors.
1. General Somatic Afferent
2. General Visceral Afferent
3. Special Somatic Afferent
4. Special Visceral Afferent
35
What does GSA do?
General Somatic Afferent
Sensory input from structures associated with the body wall and extremities.
36
What does GVA do?
General Visceral Afferent
Sensory input from viscera, including smooth muscle, cardiac muscle, and glands.
37
What does SSA do?
Special Somatic Afferent
Sensory input from structures associated with the senses of vision, hearing, and balance.
38
What does SVA do?
Special Visceral Afferent
Sensory input from structures associated with the senses of smell and taste.
39
What is the function of an interneuron and what are the types?
Function: connect other neurons, most numerous amount of neurons.
1. Local- confined to small areas
2. Projection- has long axons connecting to different areas.
40
What is a multipolar neuron? give an example.
More than one dendrite and one axon.
Types: Motor and interneurons
Example: Alpha Motor Neuron
41
What is a Bipolar neuron? give an example.
One dendrite and one axon.
Types: Sensory, also can find it during the developmental stage of most neurons.
Example: Special sense organs
42
What is a pseudounipolar neuron? give an example.
a single process that is close to the cell body and divides into 2 branches, a central and peripheral axon.
- No dendrites
Type: Sensory
Example: Dorsal Root Ganglia
43
What is the function of a Glial cell?
Surrounds and supports neurons.
| Does not participate directly in synaptic interactions and electrical signaling.
44
What are the 3 different types of Macroglia?
1. Astrocyte
2. Oligodendrocyte
3. Schwann
45
What are the 2 types of Astrocytes?
1. Protoplasmic Fibrous
| 3. Radial Glial
46
What is the function of the Protoplasmic/Fibrous cell? Where is it?
Function: Blood-Brain barrier, structural support
Location: CNS
47
What is the function of the Radial Glial cell? Where is it?
Function: Guides migrating neurons and directs the outgrowth of axons.
Location: Developing CNS
48
What is the function of an Oligodendrocyte? Where is it?
Function: Myelin Production.
Location: CNS
49
What is the function of a Schwann cell? Where is it?
Function: Myelin production. Ensheaths axons, with or without myelin.
Location: PNS
50
What is the function of a Microglia? Where is it?
Function: Macrophagic Activity
Location: CNS
51
What is the function of Ependymal cells? Where are they?
Function: Line cavities (ventricles)
Location: CNS
52
Describe the structure of a myelin sheath.
- segmented, multilamellar, lipid rich, wrapping of axons.
| - formed by plasma membranes of oligodendrocytes or schwann cells.
53
What is an internode?
a single segment of myelin sheath on an axon
54
What is a node of ranvier?
interval at which an axon is not covered by a myelin sheath, located between internodes.
55
What is the difference between oligodendrocytes and schwann cells?
1. Oligodendrocytes are in the CNS and Schwann cells are in the PNS.
2. Oligodendrocytes can myelinate several internodes and axons while Schwann cells can only myelinate one internode or axon.
56
What is the function of a myelin sheath?
- Provides electrical insulation
- increases the speed of impulse conduction by saltation, which is a method where an action potential jumps from node to node.
57
What are the two principles of cellular connectionism?
1. Dynamic Polarization: Unidirectional flow of electrical signals within neurons.
2. Connectional Specificity: Each cell makes specific connections.
58
Go through the process of a neural circuit using the Myotactic Spinal Reflex example. (Knee-Jerk Reflex)
1. Hammer tap stretches the patellar ligament, sensory receptors in quadriceps activated.
2. Sensory neuron synapses/excites motor neuron in quadriceps. Sensory neuron also synapses with interneuron which inhibits the motor neuron of the knee flexors.
3. Motor neuron synapses on quadriceps, making them contract. Knee flexor muscles are relaxed because their motor neurons are inhibited.
4. Knee extension occurs.
59
Define Divergence.
One neuron activates many target cells, this is common in the input stages.
60
Define Convergence.
One neuron receives input from many cells, this is common in the output stages.
61
What are the two types of inhibition? Define them.
1. Feed forward- Enhances the effect of the active pathway by inhibiting the activity of the opposing pathway.
2. Feedback- Self-regulating mechanism, dampens the activity within the stimulated pathway to prevent it from exceeding a certain maximum.
62
What are the 5 organizing principles of the functional system?
1. Each system involves several brain regions that carry out different types of information processing.
2. Identifiable pathways link the components of a functional system.
3. Each part of the brain projects in an orderly fashion onto the next, thereby creating a topographical map.
4. Functional systems are heirarchically organized.
5. Functional systems on one side of the brain control the other side of the body (except in the cerebellum).
63
Describe the association component of the general functional system.
- Between the input and output systems.
- mediates the most complex and least well characterized brain function, aka cognition.
- largest portion of the cortex are considered as associational areas.
64
Define cognition.
Refers to the ability to attend to external stimuli or internal motivation, to identify the significance of such stimuli, and to make appropriate responses.
65
What are the 7 main parts of the brain?
1. Telencephalon (Cerebrum)
2. Diencephalon
3. Midbrain
4. Cerebellum
5. Pons
6. Medulla Oblongata
66
What is the brainstem composed of?
Midbrain, Pons, Medulla Oblongata
67
What is gray matter composed of?
-Neuronal cell bodies, dendrites, unmyelinated axons, and glial cells.
68
What is white matter composed of?
-Myelinated axons and oligodendrocytes
69
Where in the brain is gray matter?
Superficial outer layer and some deeper regions.
| -cortex and nuclei
70
What are gray matter cell bodies arranged in a layer called?
Layer, lamina, or striatum.
71
Where in the spinal cord is gray matter?
central H-shaped region, makes up the nuclei of the dorsal and ventral horn.
72
What are Rexed's lamina or columns?
Longitudinal groups of functionally related cell bodies.
73
Where in the brain is white matter?
deeper regions
74
Where in the spinal cord is white matter?
peripheral region
75
What are the 3 types of meninges?
1. Dura Mater
2. Arachnoid Mater
3. Pia Mater
76
Describe Dura Mater.
- Made of Dense CT
- continuous with periosteum in skull
- separated from vertebrae in spine (by epidural space)
- separated from arachnoid mater by subdural space
77
Describe Arachnoid Mater.
- Cellular layer
- In contact with system of trabeculae
- Cavities between the trabeculae form the subarachnoid space, and are filled with cerebrospinal fluid
78
Describe Pia Mater.
- Sheath of loose CT
| - Directly over surface of nervous tissue
79
What are the functional subdivisions of the PNS, and what are they made up of?
1. Somatic: neural elements associated with body wall and extremities
2. Autonomic: neural elements associated with internal organs or viscera
80
What are the components of the PNS?
1. Ganglia
| 2. Nerves
81
Describe a ganglia, what are the motor and sensory components?
- They are ovoid structures which contain neuronal cell bodies and glial cells supported by CT.
- Sensory (somatic and visceral): contain the bodies of pseudounipolar neurons. Associated with dorsal roots and cranial nerves.
- Motor (Visceral): Sympathetic and Parasympathetic.
82
What does a nerve fiber consist of?
An axon with its investing Schwann cells
83
Spinal Nerves contain what type of neurons?
(31 pairs)
| - GSE, GVE, GSA, GVA
84
Cranial Nerves contain what type of neurons?
(12 pairs)
| -GSE, GVE, SVE, GSA, GVA, SSA, SVA
85
What is a nerve?
A collection of axons with their associated schwann cells with CT coverings.
1 or more fascicles (bundles) of nerve fibers.
86
What is an epineurium?
Sheath of Dense CT that surrounds the entire nerve
87
What is a perineurium?
Sheath of Dense CT that surrounds bundles of nerve fibers called fascicles.
88
What is an endoneurium?
Delicate layer of loose CT that surrounds an individual nerve fiber.
89
What is the Cell membrane made up of?
1. Lipid Bilayer
2. Proteins
3. Glycocalyx
90
Describe the structure and function of the lipid bilayer.
- Phospholipids with hydrophilic heads and hydrophobic tails.
- Establishes concentration gradients because it's not permeable to ions.
- Stores charges of opposite signs but are unable to cross the membrane, establishing an electrical gradient.
91
Describe the structure and function of proteins in the cell membrane.
- associated with outer or inner layer, OR incorporated within and spanning the lipid bilayer.
- Acts as a transporter (carrier or ion channels), or receptors, enzymes, etc.
- Carriers: actively transport ions in or out of cell AGAINST their concentration gradient
- Ion channels: let specific ions cross the membrane in the direction of their concentration gradient
92
Where would you find the glycocalyx?
External surface of cell membrane
93
What are the 3 functions of the cell membrane?
1. Selective Barrier: separates intra and extra cellular compartments
2. Intercellular communication: cell recognition and attachment to other cells and extracellular molecules.
3. Signal Transduction: sends signals from a cell's exterior to interior.
94
Explain Resting membrane potential.
1. There is a Na+/K+ pump that keeps more Na+ outside of the cell and more K+ inside the cell.
2. The cell membrane is selectively permeable to K+, so sodium leaks out of the cell, making the inside of the cell more negative.
3. The resting membrane potential of a neuron is about -65mV and is uniform throughout the cell.
95
What are some alterations that can occur in the Resting Membrane Potential?
1. Depolarization
- Potential decreases (becomes more positive), due to an increase of Na+ flooding into the cell.
- This is EXCITATORY, increasing the ability for a neuron to generate an AP.
2. Hyperpolarization
- Potential increases (becomes more negative), due to an influx of Cl- in the cell.
- This is INHIBITORY, decreasing the ability for a neuron to generate an AP.
96
What are the 4 different signals a neuron produces within a cell and what are the regions where they occur?
1. Input (receptive)
2. Trigger (summing or integrative)
3. Conducting (signaling)
4. Output (secretory)
97
What is the function of the input component, and what region does it occur in?
Function: Produces graded and local signals.
Sensory: sensory receptors that respond to sensory stimuli.
Motor: Postsynaptic membrane receptors that respond to communication from other cells.
98
What are the input signals called in sensory and motor neurons?
Sensory: receptor potentials
Motor: synaptic potentials
99
What is the ionic basis for the input component signal?
- brief change in resting membrane potential due to change in membrane permeability
- could be depolarizing or hyperpolarizing
100
What are the properties of the input component signal?
1. Graded in amplitude and duration, proportional to that of the stimulus
2. Passive propagation, decreasing in amplitude with distance.
101
What is the function of the trigger component, and what region does it occur in?
Function: Makes the decision to generate an AP
-Occurs in the region with the highest concentration of voltage gated Na+ channels, which are located next to the input component.
Sensory: first node of ranvier
Motor: Axon hillock
102
What signal does the trigger component produce?
Action Potential.
| This is produced if the size of the input signal reaches threshold.
103
What is the ionic basis of the AP produced by the trigger component?
1. Upstroke- rapid depolarization
- Increase in Na+ permeability
2. Overshoot- reversal of the membrane potential
- increase in Na+ in the cell
3. Repolarization
- Decrease in Na+ permeability, increase in K+ permeability. Followed by an efflux in K+ (leaves the cell)
4. Hyperpolarization
- K+ permeability still increased, until there is so much K+ outside the cell that the cell is more negative inside than it needs to be.
104
What are the properties of the AP produced by the trigger component?
1. All-or-Nothing: All stimuli above the threshold produce the same signal (amplitude or duration)
2. Amplitude and duration influence the frequency and number of APs.
105
What is the Absolute Refractory Period?
Time following an AP during which a stimulus cannot elicit a second AP.
106
What is a Relative Refractory Period?
Time following an AP during which only a suprathreshold stimulus can elicit a second AP.
107
What is the function of the conducting component, and where does it occur?
Function: Propogates an AP
Region: Axon
108
What are the properties of the conducting component?
1. Propagation does not decrease in amplitude because it is periodically regenerated.
2. Propagation is unidirectional
3. Conduction velocity depends on axon diameter and myelination status.
109
What is the function of the output component and where does it occur?
Function: Releases Neurotransmitter
-Occurs in the active zones of the presynaptic terminal
110
What is the Ionic Basis for the release of the Neurotransmitters by the output component?
1. AP reaches the presynaptic terminal
2. Voltage gated Ca++ channels open
3. Increase in Ca++ causes synaptic vesicles to migrate and fuse with the presynaptic membrane
4. Synaptic vesicles releases neurotransmitters via exocytosis
111
What are the properties of the output component?
1. Neurotransmitters are released in discrete units (quanta)
2. Amount of neurotransmitter released depends on the amount of Ca++ that enters the presynaptic terminal, which depends on the frequency and number of APs that reach the presynaptic terminal.
3. This total number can be regulated from outside the cell.
112
What is the difference between the electrical and chemical basis of neuronal communication?
Electrical: communication WITHIN a neuron
Chemical: communication from one neuron to another
113
Synapses can occur from one neuron to what parts of another neuron?
1. Cell Body
2. Dendrite
3. Axon
114
What are neuromuscular junctions?
Specialized chemical synapses between neuron axons and skeletal muscle cells.
115
What are the differences between Electrical and Chemical signals?
Electrical
- Fast
- No threshold
- Uses Gap Junctions to connect pre and post synaptic membranes
- uni or bidirectional
Chemical
- slower (w/ synaptic delay)
- Has a threshold
- Presynaptic terminal, synaptic cleft, and postsynaptic membrane
- unidirectional flow
116
What is the function of a Neurotransmitter?
They are chemicals which are localized to and released from a presynaptic terminal that binds to receptors in the postsynaptic membrane, resulting in an effector function within the target cell.
117
What are the 2 different types of neurotransmitters and what type of synaptic transmission do they mediate?
1. Small Molecule
- rapid
2. Neuropeptides
- slow
118
What does the effect of the neurotransmitter depend on?
Depends on the receptors. There are multiple types of receptors for most neurons, so neurotransmitters can have more than one effect.
119
What are receptors made up of and where are they found?
- Glycoproteins
| Found: within the cell membrane or in the nucleus or cytoplasm
120
What is the function of a receptor?
Transduces a chemical signal (neurotransmitter) into an intracellular event.
121
What are the 2 types of receptors and what type of synaptic transmission do they mediate?
1. Ionotropic (Ion channels)
- Linked directly to ion channels
- Fast transmission
2. Metabotropic (G Protein-coupled)
- direct and indirect link to ion channels
- slow transmission
122
What are the two effects of neurotransmitters?
1. Agonist- activate a receptor
- Could be excitatory or inhibitory depending on the type of receptors in the postsynaptic cell.
2. Antagonist- binds to a receptor but does not elicit a response (ex. Beta blockers)
123
What are two changes that occur to a cell when it adapts to the environment?
1. Overstimulation
| 2. Decreased stimulation
124
What happens when cells are overstimulated?
1. Desensitization- fairly brief and transient decrease in responsiveness
2. Downregulation- slower and more prolonged process in which the number of receptors is decreased.
125
What happens when cells have decreased stimulation?
1. Supersensitivity- slower and more prolonged process in which the number of receptors are increased
126
What is fertilization and when does it occur?
Occurs at "Zero point" of embryological development
- sperm cell and ooctye fuse, forming a zygote.
- All cells are derived from a single cell
127
What is cleavage and when does it occur?
Occurs during week 1 of embryological development
| -zygote undergoes cell divisions, increasing the number of cells but not the size of the zygote
128
What is Implantation and when does it occur?
Occurs 6 days post fertilization until the end of week 2
- Embryo implants into the uterine wall
- The bilaminar embryonic disc is formed (plate of cells)
129
What is Gastrulation and when does it occur?
Occurs at the end of week 2 to week 3
- Bilaminar embryonic disc is transformed into a 3 layered disc (ectoderm, mesoderm, and endoderm.)
- Axes of the body are established
130
What does ectoderm turn into?
Nervous Tissue
131
What does the mesoderm turn into?
- CT
| - Muscle Tissue
132
What is Epithelial Tissue made from?
All 3 layers (Ectoderm, Endoderm, and Mesoderm)
133
What is a notochord and when is it formed?
Week 3 and 4 of embryological development
- Mesoderm derived structure
- Basis for development of axial skeleton and induction of neural plate
134
What is a somitomere and when is it formed?
Week 3 and 4 of embryological development
- Mesoderm derived structure
- Lies parallel to the notochord
- Basis of SEGMENTAL organization of the body
- Subdivides into a sclerotome, dermatome, and myotome.
135
Describe the steps of Neurulation.
1. The notochord induces the ectoderm to form the neural plate.
2. The neural plate creases ventrally, forming a neural groove with neural folds on each side.
3. The neural folds move together and fuse, forming the neural tube. (lumen is called the neural canal).
4. Neural crest arises from the lateral margins of the neural fold
5. Neural tube separates from the ectoderm and sinks into the posterior body wall.
136
What kind of cells line the neural canal?
1. Neuroepithelial
2. Neuroblasts
3. Glioblasts
4. Ependymal cells
137
What are the three layers formed within the Neural tube and what type of cells are they made of?
1. Ventricular Zone- Neuroepithelial cells
2. Intermediate Zone- Post mitotic Neuroblasts, forms the gray matter of CNS
3. Marginal Layer- Forms the white matter of CNS
138
What is the molecular basis for neural induction?
- A specific developmental pathway is stimulated in one group of cells (responding tissue) by a closely approximated group of cells (inducing tissue).
- Involves the release of chemical signals, their receptors, and the resulting regulation of gene expression.
- Can specify cell identity as well as influence other aspects of neural development.
139
What are two conditions that can occur due to the failure of the neural tube to close?
1. Spina Bifida- failure of the vertebral arches to form completely and fuse to cover the spinal cord.
2. Anencephaly- The brain is not formed, the surrounding meninges and skull may be absent, and there may be facial abnormalities.
140
What are the steps for Spinal Cord formation?
1. The sulcus limitans (a longitudinal groove) appears in the lateral wall of the neural tube, separating it into a dorsal and ventral half.
2. Cells migrate peripherally to form four longitudinal columns, which will become the gray matter.
3. The neural canal will become the central canal of the spinal cord.
141
What is the Alar plate and what does it form into?
Posteriorly located cell masses that will develop into the dorsal horns of the spinal cord.
Produces SENSORY neurons (dorsal root ganglions)
Sensory neurons innervate receptors in somatic or visceral structures.
142
What is the Basal plate and what does it form into?
Anteriorly located cell masses that will develop into the ventral horns of the spinal cord.
Produces MOTOR neurons (ventral roots)
Motor neurons innervates skeletal muscle.
143
The lateral horn of the spinal cord is formed from what?
Interface between Alar and Basal plates
| The motor neurons send their axons to autonomic ganglia
144
How are spinal nerves formed?
The dorsal and ventral roots join at the level of the intervertebral foramina.
145
Describe the formation of the Brain.
- Formed from the cranial portion of the neural tube
| - 3 primary vesicles are formed which will subdivide into 5 secondary vesicles.
146
What are the Primary vesicles of the brain?
1. Prosencephalon
2. Mesencephalon
3. Rhombencephalon
147
What are the secondary vesicles of the brain?
1. Telencephalon
2. Diencephalon
3. Mesencephalon (Midbrain)
4. Metencephalon (Pons, Cerebellum)
5. Myelencephalon (Medulla)
148
What does the brainstem consist of?
1. Myelencephalon
2. Metencephalon
3. Mesencephalon
149
Describe the process of Brainstem formation.
1. As the flexures develop, the walls of the neural tube spread apart to form a diamond-shaped cavity. This will become the fourth ventricle.
2. The Alar and Basal plates (still separated by the sulcus limitans) come to lie in the floor of the fourth ventricle.
3. This new rotation leads to lateral-medial orientation of the sensory and motor plates.
150
Describe the process of Cerebellum formation.
1. The lateral portion of the alar plate thicken to form rhombic lips.
2. The rostral parts of the rhombic lips join dorsal to the fourth ventricle, forming the cerebellum.
151
Describe the process of Forebrain formation.
The forebrain is exclusively derived from the alar plate.
1. The prosencephalic bulge subdivides into 2 rostral telencephalic swellings, that expand around a caudal centrally directed diencephalon.
2. Due to the rapid telencephalon growth, the basal ganglia portion folds down toward the diencephalon and the regions fuse.
3. The insula becomes overgrown by the cerebral cortex.
4. The cerebral hemispheres "rotate" into a C shape.
5. Extensive folds develop on the surface of each cerebral hemisphere.
152
Describe the Ventricular system.
- Formed from the cephalic portions of the neural canal.
- Lined with ependymal cells
- constitutes a continuous, cerebrospinal fluid-filled series of spaces extending through all the major divisions of the CNS.
- continues caudally as the central canal of the spinal cord
- communicates with the subarachnoid space.
153
What is hydrocephalus?
Dilation of the ventricular system due to increased pressure from obstructed flow of CSF.
154
What 3 embryonic tissues do the PNS structures originate from?
1. Neuroepithelial cells of the Neural crest
2. Placodes
3. Neuroepithelial lining of the Neural canal.
155
Describe the importance of the Neural Crest in the PNS.
- Gives rise to neural and non-neural elements.
Neural Elements: neurons of dorsal root ganglia, autonomic nervous system, and some sensory ganglia of cranial nerves.
Non-Neural Elements: Schwann Cells
156
What are placodes?
Specialized regions of neuroepithelium in the developing head region.
- Gives rise to some sensory ganglia of cranial nerves
157
What do Neuroepithelial Lining of the Neural Canal give rise to?
Glioblast cells
158
What are the 3 important parameters in brain organization?
1. neuron density
2. formation of axonal pathways
3. pattern of synaptic contacts
159
What is the period of overproduction?
By 24 weeks of gestation, 1.5-2 times more neurons than are present in the mature human brain are made.
160
Why does programmed cell death occur?
ensures that only the neurons who form appropriate connections succeed and survive. This is so they can maintain metabolism of the cell, and to ensure they make appropriate connections.
161
What are the two areas in the brain that have cells that can still divide after birth?
1. Olfactory
| 2. Hippocampus
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What are growth cones?
- Distal spade shaped elaborations which are capable of pathfinding, driving through fields of developing nervous tissue to reach distant targets.
- precursors to presynaptic terminals
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What do growth cones possess?
Receptors that recognize and interpret molecular cues into signals that regulate the cytoskeleton, receptors and channels on the cell surface, or gene expression.
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How do Axonal Pathways form?
1. The pathways along which axons grow provide molecular cues to guide axons to their targets.
2. These cues can be attractive or repulsive
3. The first growth cone to traverse a route may establish a pathway that is used by later growing axons.
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Where can axonal molecular cues be found?
1. Extracellular matrix (adhesion and recognition molecules)
2. soluble (chemoattractant or chemorepulsive)
3. cell membrane bound
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What is the function of a chemoattractant molecule?
- May be tropic factor, which guide a cell toward a particular target
- Could be a trophic factor (metabolism)
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What is the function of a chemorepulsive molecule?
Discourage axon growth along a particular pathway
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What are intercellular signals that control synaptogenesis used for?
Organizers rather than inducers
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What are the steps of synaptogenesis?
1. Elaboration of the Postsynaptic Apparatus in the Target Cell
- Organized by the neuron
- involves reorganization of the neurotransmitter receptors
2. Differentiation of Axon Growth cone into a presynaptic nerve terminal
- Organized by the target cell
- Involves the accumulation of synaptic vesicles and assembly of active zones in the region of the neuron that abuts the target cell.
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What is a critical period?
Time where we have the most amount of plasticity
We are most able to be influenced
-Postnatal time during which a given behavior is especially susceptible to- indeed, requires- specific environmental influences in order to develop normally.
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What is plasticity?
The ability of an experience to influence neural activity in such a way that it alters neural circuitry and thus determines behavior.
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What are some examples of Critical Periods and when are there critical periods?
1. Imprinting
2. Language Acquisition- before puberty
3. Vision- 4 months-8 years of age
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What are some mechanisms of Critical Periods?
1. Hebb's Postulate- when synaptic terminals are strengthened by correlated activity and will retain or sprout new branches, but those making uncorrelated connections will lose hold on the postsynaptic cell.
2. Circular Pattern of cellular and molecular mechanisms
- You have a correlated activity--> synaptic alterations in a target cell occur-->there is an increase in intracellular Ca++-->Modification of gene expression occurs (enhances correlated activity)-->May influence neurotrophins, receptors, extracellular matrix
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What is the Telencephalon made up of?
(Cerebrum)
- Cerebral Cortex
- Subcortical White Matter
- Basal Ganglia
- Hippocampus
- Amygdaloid
