essay questions

1. Define and explain the three fundamental characteristics of neurons: excitability, conductivity, and secretion. How does each relate to a neuron's ability to communicate and function in the nervous system?

Neurons are excitable, meaning they can respond to stimuli by generating electrical changes. They show conductivity by carrying these electrical impulses along their membranes, often over long distances. Finally, they use secretion to release neurotransmitters at their axon terminals, allowing them to pass signals to other cells. Together, these traits enable neurons to detect, transmit, and communicate information throughout the nervous system.

Describe the structure and function of the following parts of a neuron: dendrites, axon, synaptic vesicles, and neurofibrils.

Dendrites are branchlike extensions that receive signals and carry them toward the neuron’s cell body, while the axon is a long fiber that conducts impulses away from the cell body to other cells. At the axon terminals, synaptic vesicles store and release neurotransmitters into the synapse. Neurofibrils form part of the neuron’s internal support system and help transport materials throughout the cell.

A patient has been diagnosed with a brain tumor. Is the tumor more likely to have originated from neurons or glial cells? Provide a rationale based on cell biology and proliferation.

A brain tumor is far more likely to have originated from glial cells rather than neurons. Neurons rarely divide after early development, while glial cells retain the ability to proliferate throughout life. Because tumors arise from uncontrolled cell division, glial cells—not non-dividing neurons—are the typical source of brain tumors.

Compare chemically gated and voltage-gated ion channels. How do they differ in function and location within the neuron?

Chemically gated ion channels open when a specific neurotransmitter or chemical binds to them, and they are mostly found on the dendrites and cell body, where synaptic input is received. Voltage-gated ion channels open in response to changes in membrane potential and are concentrated along the axon and axon terminals, where they drive action potential propagation and neurotransmitter release.

Describe a neuron's resting membrane potential, including ion concentration gradients (Na⁺, K⁺, Cl⁻, Ca²⁺) and the state of gated channels at rest.

A neuron’s resting membrane potential is about –70 mV, created by unequal ion distributions across the membrane and selective permeability. At rest, there is more Na⁺ and Ca²⁺ outside the cell and more K⁺ and large anions inside, while Cl⁻ is generally higher outside. K⁺ leaks out through potassium leak channels more easily than Na⁺ enters, making the inside more negative. During this state, voltage-gated Na⁺, K⁺, and Ca²⁺ channels are closed, while leak channels and the Na⁺/K⁺ pump maintain the gradients and the electrical charge difference.

How are EPSPs and IPSPs generated in the receptive segment of a neuron? What is the functional significance of reaching threshold potential at the initial segment?

EPSPs are generated when excitatory neurotransmitters bind to chemically gated channels on the dendrites or cell body, allowing Na⁺ (and sometimes Ca²⁺) to enter and produce a small depolarization. IPSPs occur when inhibitory neurotransmitters open K⁺ or Cl⁻ channels, causing K⁺ to exit or Cl⁻ to enter, creating a hyperpolarization. These graded potentials summate as they travel toward the initial segment, where reaching threshold potential triggers the opening of voltage-gated Na⁺ channels. This is significant because reaching threshold is what initiates an action potential, allowing the neuron to fire and transmit information down the axon.

Describe how depolarization and repolarization occur in the conductive segment of a neuron. Include the role of ion channels and ion movement.

In the conductive segment (the axon), depolarization occurs when voltage-gated Na⁺ channels open in response to reaching threshold, allowing Na⁺ to rush into the neuron and making the inside more positive. Shortly after, these Na⁺ channels inactivate, and voltage-gated K⁺ channels open, causing K⁺ to flow out of the cell. This outward movement of K⁺ restores the negative membrane potential, producing repolarization. This coordinated opening and closing of ion channels allows the action potential to move down the axon.

Compare the propagation of an action potential in unmyelinated and myelinated axons. Include terminology like continuous conduction and saltatory conduction.

In unmyelinated axons, action potentials move by continuous conduction, depolarizing each segment of membrane sequentially. In myelinated axons, they travel by saltatory conduction, jumping between nodes of Ranvier, which makes transmission faster and more efficient.

Explain how acetylcholine (ACh) can generate either an EPSP or an IPSP depending on the type of postsynaptic receptor it binds to.

ACh can produce an EPSP when it binds to nicotinic receptors, opening Na⁺ channels, or an IPSP when it binds to muscarinic receptors that open K⁺ channels. The effect depends on the type of postsynaptic receptor, not the neurotransmitter itself.

Name the meningeal layers and the spaces between them in order from deepest (closest to the brain) to most superficial.

From deepest to most superficial: pia mater (with subarachnoid space), arachnoid mater (with subdural space), and dura mater (with epidural space). Each layer protects the brain and spinal cord and contains or borders spaces for fluid or cushioning.

Create a flowchart that tracks cerebrospinal fluid (CSF) from its formation to where excess fluid is drained. 

CSF is produced in the choroid plexus → lateral ventricles → third ventricle → cerebral aqueduct → fourth ventricle → subarachnoid space → absorbed by arachnoid villi → dural venous sinuses. This circulation cushions the brain and removes waste.

What is the function of the sensory and motor association areas of the cerebral cortex? How do these areas contribute to perception and movement?

Sensory association areas interpret incoming information to create perception. Motor association (premotor) areas plan and coordinate complex movements. Together, they allow the brain to understand stimuli and produce purposeful actions.

Describe how the hypothalamus regulates hunger and thirst. Include sensory inputs and relevant nuclei.

The hypothalamus monitors signals like blood glucose, hormones, and osmolarity. The lateral hypothalamus triggers hunger, the ventromedial nucleus signals satiety, and osmoreceptors stimulate thirst. These centers adjust behavior and autonomic responses to maintain homeostasis.

List all 12 cranial nerves by name and number, and provide a brief description of their primary functions.

I – Olfactory: smell

II – Optic: vision

III – Oculomotor: eye movement/pupil

IV – Trochlear: eye movement

V – Trigeminal: face sensation/chewing

VI – Abducens: eye movement

VII – Facial: expression, taste, glands

VIII – Vestibulocochlear: hearing/balance

IX – Glossopharyngeal: taste, swallowing

X – Vagus: parasympathetic control

XI – Accessory: neck/shoulder movement

XII – Hypoglossal: tongue movement

Trace the path of a withdrawal reflex after touching a hot surface. Use the following terms: sensory receptor, posterior root, posterior horn, somatic sensory nuclei, anterior horn, somatic motor nuclei, anterior root, spinal nerve, effector.

A sensory receptor detects a stimulus → signal travels via the posterior root → posterior horn → sensory nuclei → interneuron → anterior horn → motor nuclei → anterior root → spinal nerve → effector muscle contracts to withdraw.

Define decussation in the nervous system. Why is it important? Provide a specific example where decussation affects the outcome of a neurological injury.

Decussation is when nerve fibers cross to the opposite side of the CNS. It allows one brain hemisphere to control the opposite side of the body. For example, a left corticospinal tract injury causes right-sided paralysis.

Compare the spinal nerve pathway and the splanchnic nerve pathway in sympathetic innervation. Include where each synapses and their target structures.

In the spinal nerve pathway, preganglionic fibers synapse in sympathetic chain ganglia; postganglionic fibers go to skin, blood vessels, or sweat glands. In the splanchnic pathway, fibers pass through the chain, synapse in prevertebral ganglia, and target abdominal or pelvic organs.