Week 8: Nervous Tissue
Explain how the central and peripheral nervous systems interact to maintain homeostasis.
The CNS is the command center, the PNS is the messenger network, and together they keep your internal environment stable despite outside changes — that’s homeostasis in action.
Explain how saltatory conduction differs from continuous conduction, and describe why myelination makes signal transmission more energy-efficient.
Continuous = slow, every step of the way: It’s slower because each section of membrane has to depolarize in turn.
Saltatory = fast, jump between nodes of ranvier
Myelin = insulation + energy efficiency because the Na⁺/K⁺ pumps (which restore ion balance after each action potential) only need to work at the nodes, not along the entire axon. Fewer ions move, so less ATP is used
Explain why cranial nerves are essential for communication between the brain and the body.
Cranial nerves are essential because they form the direct connection between the brain and parts of the head, neck, and some internal organs. They carry both sensory information (like sight, smell, taste, and hearing) to the brain, and motor commands (like eye movement, facial expression, and swallowing) from the brain to the body.
Unlike spinal nerves, which connect through the spinal cord, cranial nerves emerge directly from the brain, allowing for fast and precise communication. Some also help regulate autonomic functions like heart rate and digestion (for example, the vagus nerve).
What are the main differences between focal and generalized seziures
Focal (partial) seizures:
Start in one specific area of the brain.
Symptoms depend on the brain region affected — e.g., twitching in one hand, unusual sensations, or brief confusion.
Can be with or without loss of consciousness.
Generalized seizures:
Involve both hemispheres of the brain from the start.
Usually cause a loss of consciousness.
Examples include tonic-clonic seizures (full-body convulsions) and absence seizures (brief staring spells).
Describe the role of the reticular formation
The reticular formation is a network of neurons in the brainstem that acts like the brain’s “alertness and filter system.” HABITUATION
It regulates arousal and consciousness, keeping you awake or letting you sleep.
It filters incoming sensory information, so the brain isn’t overloaded by irrelevant stimuli.
List the cell types and their role in both the PNS and CNS
Astrocytes:
Support and nourish neurons.
Help form the blood–brain barrier and regulate what enters brain tissue.
Maintain ion and nutrient balance in the extracellular fluid.
Oligodendrocytes:
Create myelin sheaths around axons in the CNS.
One oligodendrocyte can myelinate several axons
Microglia:
Act as the immune cells of the CNS.
Engulf pathogens, damaged cells, and debris (like little brain janitors).
Ependymal cells:
Line the ventricles of the brain and central canal of the spinal cord.
Produce and circulate cerebrospinal fluid (CSF).
PNS:
Schwann cells:
Form myelin sheaths around PNS axons — one Schwann cell per axon segment.
Help with axon regeneration after injury (unlike CNS myelin).
Satellite cells:
Surround neuron cell bodies in ganglia.
Regulate the chemical environment and provide structural support (like astrocytes of the PNS).
How does the blood-brain barrier help maintain homeostasis in the CNS, and why might it pose challenges for drug delivery?
The blood-brain barrier (BBB) protects the brain by controlling what enters from the blood. It keeps out harmful things like germs and toxins but still lets in what the brain needs — like oxygen and glucose. This helps keep the brain’s environment stable, or in homeostasis.
But the BBB also makes it hard for medicines to reach the brain because most drugs can’t pass through it. So, while it’s great at protecting the brain, it also makes treating brain diseases more challenging
The brainstem is sometimes called the “don’t even think about it” region. Explain this nickname using examples
The brainstem controls your body’s automatic, life-sustaining functions — things you don’t even have to think about. It manages your heartbeat, breathing, blood pressure, digestion, and reflexes like coughing or swallowing.
How does inflammation make the blood–brain barrier more “leaky,” and why is that a problem in MS?
Inflammation weakens the tight junctions of the blood–brain barrier, making it “leaky.” In MS, this allows immune cells to enter the CNS and attack myelin, damaging neurons and slowing nerve signals.
Explain the ways neurotransmitters are removed after synaptic transmission
Reuptake: The presynaptic neuron takes the neurotransmitter back into its vesicles for reuse.
Enzymatic degradation: Enzymes in the synapse break the neurotransmitter down into inactive parts.
Diffusion: Neurotransmitters drift away from the synaptic cleft and are eventually absorbed or degraded elsewhere.
Explain the steps of synaptic transmission
Action potential arrives:
An electrical signal (action potential) travels down the axon to the axon terminal of the presynaptic neuron.
Calcium channels open:
The depolarization causes voltage-gated calcium (Ca²⁺) channels to open, and calcium ions rush into the terminal.
Neurotransmitter release:
The influx of calcium makes synaptic vesicles fuse with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft (the small gap between neurons).
Neurotransmitter binding:
Neurotransmitters diffuse across the cleft and bind to receptors on the postsynaptic neuron’s membrane.
Postsynaptic response:
Depending on the neurotransmitter and receptor type, this binding either excites (depolarizes) or inhibits (hyperpolarizes) the postsynaptic neuron — possibly triggering a new action potential.
Signal termination:
Neurotransmitters are removed from the cleft to end the signal — by being
How does neuroplasticity influence the development and maintenance of neuronal circuits throughout life?
Neuroplasticity keeps your brain flexible — it’s how your brain grows, learns, and stays sharp throughout life. During development, it helps build and shape neuronal circuits as you learn new skills or experiences shape your brain. Synapses that are used often become stronger, while unused ones are weakened or removed
Compare the roles of the hypothalamus and the amygdala in regulating emotions and physiological responses to stress.
The amygdala is like the brain’s emotional alarm system. It detects threats or anything emotionally charged and triggers feelings like fear, anger, or anxiety. Once it senses danger, it sends a distress signal to the hypothalamus.
The hypothalamus then takes over the physical response — activating the autonomic nervous system. It increases heart rate, raises blood pressure, and releases stress hormones
Amygdala = “Uh-oh!” detector (emotional response)
Hypothalamus = “Do something about it!” (physiological response)
What role do oligodendrocytes play in the nervous system, and what happens when they are destroyed in MS?
Oligodendrocytes make myelin sheaths around axons in the CNS, which speeds up action potential conduction. In MS, they are destroyed, so myelin is lost, slowing or blocking nerve signals and causing symptoms like weakness, vision problems, and cognitive issues.
The hypothalamus is described as a “control freak.” Explain how its connections with the endocrine and nervous systems justify that description.
Endocrine control: It directs the pituitary gland, releasing hormones that regulate growth, metabolism, stress, and reproduction.
Nervous control: It connects to the autonomic nervous system, adjusting heart rate, blood pressure, digestion, and temperature.
Describe what happens to ion movement and membrane potential during depolarization and repolarization.
Depolarization = the neuron “fires” (positive inside).
Repolarization = the neuron “resets” (returns to negative inside).
Outline the steps of a somatic reflex arc, explaining the role of each component.
Receptor:
Detects a stimulus (like pain, heat, or pressure).
→ Example: sensory receptors in your skin detect a hot surface.
Sensory neuron (afferent neuron):
Carries the signal from the receptor to the spinal cord.
Interneuron (association neuron):
Found within the spinal cord. It processes the information and decides what to do — for example, send a “pull away” command.
→ It acts as the link between the sensory and motor neurons.
Motor neuron (efferent neuron):
Sends the command from the spinal cord to the effector.
Effector:
The muscle or gland that carries out the response.
→ Example: your arm muscles contract to pull your hand away from the hot surface.
The cerebral cortex is highly folded. Explain the functional advantage of this structural feature.
The folds in the cerebral cortex — called gyri (ridges) and sulci (grooves) — allow a large surface area of brain tissue to fit inside the limited space of the skull. More surface area means more neurons and more synaptic connections, which boosts the brain’s ability to process complex information.
Compare and contrast cerebellar ataxia syndrome and cerebellar cognitive affective syndrome
Cerebellar Ataxia Syndrome (motor-focused):
Caused by damage to the cerebellum’s motor regions.
Leads to movement problems: uncoordinated gait, balance issues, tremors, and difficulty with fine motor skills.
Mainly affects physical coordination, not thinking or emotions.
Cerebellar Cognitive Affective Syndrome (CCAS):
Caused by damage to cerebellar regions connected to the cortex.
Leads to cognitive and emotional problems: poor planning, language difficulties, impaired attention, and emotional blunting or disinhibition.
Physical coordination may be normal or mildly affected.
Can graded potentials change in strength?
Can action potentials change in strength?
Action Potentials:
Once the threshold is reached, an action potential always fires at the same size (same voltage change).
The strength of a stimulus instead affects the frequency of action potentials: stronger stimuli produce more frequent firing, not bigger action potentials.
Graded: yes,
A more substantial stimulus opens more ion channels, producing a larger voltage change.
A weaker stimulus opens fewer channels, producing a smaller voltage change.
Explain how EPSPs and IPSPs influence whether a neuron will fire an action potential.
EPSPs (excitatory postsynaptic potentials) and IPSPs (inhibitory postsynaptic potentials) are small voltage changes that happen when neurotransmitters bind to receptors on the postsynaptic membrane.
EPSPs make the inside of the neuron less negative (depolarized) by letting positive ions like Na⁺ in. This brings the neuron closer to threshold — the level needed to trigger an action potential.
IPSPs make the inside more negative (hyperpolarized) by letting K⁺ out or Cl⁻ in, pushing the neuron farther from threshold and making it less likely to fire.
Describe all neural circuts and give examples
Diverging Circuit
Description: One neuron sends signals to multiple neurons, spreading the message widely.
Example: A single motor neuron in the spinal cord can activate many muscle fibers for coordinated movement.
Converging Circuit
Description: Multiple neurons send input to a single neuron, integrating information from different sources.
Example: The respiratory center in the brainstem receives input from the pons, medulla, and chemoreceptors to regulate breathing rate.
Reverberating (Oscillating) Circuit
Description: Neurons form a feedback loop, sending signals around the circuit repeatedly.
Example: Used in rhythmic activities like breathing, walking, or maintaining posture.
Parallel After-Discharge Circuit
Description: One neuron stimulates several pathways that eventually converge again on one output neuron, causing a delayed but prolonged response.
Example: Found in problem-solving and reflexes, like when your eyes adjust to light changes after stepping outside.
Compare perception and consciousness
Perception is the brain’s processing of sensory information — what you see, hear, touch, taste, or smell. It’s about interpreting the environment and making sense of stimuli.
Consciousness is the broader state of being aware of yourself and your surroundings, including thoughts, feelings, and perceptions. It’s like the “whole stage” on which perception and other mental processes happen.
Explain the four types of fibers associated with the cerebral white matter
Association: conncets different parts if the cerebral cortex on the same side
commissural: connects left and right hemispheres
Corpus collosum: 90% of commisural fibers
Projection: motor pathway leading out of the cerebrum
A patient has a mutation that slows the opening of voltage-gated sodium channels in their neurons. How might this affect the speed and likelihood of action potential firing, and what symptoms might you expect as a result?
Voltage-gated sodium channels open more slowly:
During depolarization, Na⁺ influx is slower, so the membrane takes longer to reach threshold.
Effect on action potential speed:
Conduction along the axon slows down because each segment depolarizes more slowly.
Effect on likelihood of firing:
If depolarization is too slow, the neuron might fail to reach threshold, making action potentials less likely to occur.
Potential symptoms:
Slower or weaker nerve signaling could cause muscle weakness, numbness, slowed reflexes, or coordination problems.