Nervous System - Class

Question 1

Briefly describe the location of each brain lobe.

Answer 1

1. Frontal - at the front
2. Temporal - at the sides where the temples are
3. Occipital - at the very back!
4. Parietal (middle-back - the only space not taken up by the other 3 pretty much).

Question 2

Explain how Saltatory Conduction makes it seem like the charge ‘jumps’ from one node of ranvier to another.

Answer 2

Saltatory conduction occurs in the spots where myelin sheath is covering the axon. Inside of the axon, the positive charge generated at one node, will bump into the positive charge already in the spots where the myelin sheath is, and there will be a domino effect of charges bumping each other until they reach the next node of ranvier, and depolarization will occur there.

(saltatory conduction occurs very rapidly!)

Question 3

What are the 3 criteria for soemthing to be considered a neurotransmitter?

Answer 3

1. Synthesized in neurons
2. Released at presynaptic membrane following depolarization
3. Bind to postsynaptic receptor and cause a detectable effect

Question 4

What are the 5 classes of NEUROTRANSMITTERS?

Answer 4

Amino Acids,
Biogenic Amines,
Neuropeptides,
acetylcholine,
and “other”

–>We’re focusing on Acetylcholine and the two Biogenic Amines, Epinephrine, and Norepinephrine.

Question 5

What receptors (receptor name) do Acetylcholine and Epinephrine & Norepinephrine use?

–> What receptor type are they?

Answer 5

Acetylcholine = cholenergic Receptors
–>One is ionotropic, the other is metabotropic.

Epinephrine & Norepinephrine = adrenergic receptors

Question 6

Give a brief overview of stages in nervous system evolution.

Answer 6

Cnidarians (Jellyfish, Hydras): Primitive nerve nets, basic responses to stimuli.

Flatworms: Centralized nerve cords, allows coordinated movements.

Annelids and Arthropods: Segmented ganglia and more complex nerve cords (connected ganglia), improved movement coordination.

Mollusks: Advanced nerve cords and brain structures, support complex behaviors.

Vertebrates: Well-organized central nervous system (brain and spinal cord), supports higher cognitive functions, sensory processing, and sophisticated motor coordination.

Question 7

explain brain evolution and topography

Answer 7

Brain Evolution and Topography:
Early Evolution: Simple nerve nets in cnidarians (e.g., jellyfish) evolved into centralized nerve cords in more advanced invertebrates like annelids and arthropods.

Development of Ganglia: Clusters of nerve cells (ganglia) formed, providing more centralized control, seen in invertebrates.

Vertebrate Brains: More complex brains evolved with the development of a spinal column; vertebrates show distinct, specialized regions (forebrain, midbrain, hindbrain).

Forebrain Expansion: Particularly significant in mammals, leading to enhanced sensory processing, reasoning, and learning abilities.

Corticalization: In higher mammals, especially primates, extensive development of the cerebral cortex supports complex cognitive functions and social behaviors.

Question 8

structural and functional subdivisions of CNS and PNS?

Answer 8

CNS (Central Nervous System)

Structural: Brain and spinal cord.

Functional: Responsible for processing and integrating information; controls most functions of the body and mind.

PNS (Peripheral Nervous System)

Structural: Nerves and ganglia outside the brain and spinal cord.

Functional: Divided into the Somatic Nervous System (controls voluntary movements) and the Autonomic Nervous System (controls involuntary functions such as heart rate, digestion). The Autonomic is further split into Sympathetic (activates fight or flight response) and Parasympathetic (controls rest and digest activities).

Question 9

what is the blood-brain barrier?

–> does the brain sit in the blood?

Answer 9

Blood-Brain Barrier
Structure: A selective barrier formed by endothelial cells tightly joined together with the support of astrocytes.
Function: Regulates the passage of substances from the bloodstream into the brain, protecting it from pathogens and maintaining a stable environment for neural activity.

–> NO! the blood-brain barrier means the blood is kept OUTSIDE!
The brain itself is bathed in cerebrospinal fluid, which cushions the brain and serves as a shock absorber, providing a stable environment. Blood vessels do penetrate the brain, but the blood itself does not directly contact brain tissues due to the blood-brain barrier.

Question 10

Main regions of the vertebrate brain?

Answer 10

1. Forebrain:
   Cerebrum: Largest part, responsible for higher cognitive functions, sensation, and voluntary muscle activity.

Thalamus: Relay motor and sensory signals to the cerebral cortex.

Hypothalamus: Regulates temperature, hunger, thirst, and other homeostatic systems; also controls the pituitary gland.

2. Midbrain:
   Part of the brainstem that acts as a neural relay center and contains reflex centers for vision and hearing.
3. Hindbrain:

Cerebellum: Coordinates voluntary movements such as posture, balance, coordination, and speech, resulting in smooth and balanced muscular activity.

Pons: Connects upper and lower parts of the brain, serving as a message station between several areas of the brain.

Medulla Oblongata: Controls automatic functions such as breathing, digestion, heart rate, and blood pressure.

Question 11

why do mammals have a big forebreain and a reduced midbrain?

Answer 11

Mammals have a large forebrain and a reduced midbrain primarily due to the evolution of complex cognitive functions and behaviors, such as problem-solving, social interactions, and memory. The enlargement of the forebrain, especially the cerebral cortex, allows for enhanced sensory processing, learning, and intricate motor control. These capabilities provide a significant evolutionary advantage in varied and changing environments.

In contrast, the midbrain, while still important for auditory and visual reflexes, is relatively less significant in mammals compared to lower vertebrates, where these functions dominate neural processing. As a result, the midbrain is not as prominently developed in mammals, reflecting a shift towards more complex brain functions managed by the forebrain.

Question 12

Contrast and compare endocrine and nervous systems

Answer 12

Speed of Response: Endocrine system responds slowly with effects that can last from several hours to weeks; nervous system responds very quickly, within milliseconds.

Duration of Effect: Endocrine effects are prolonged, sustaining ongoing processes; nervous effects are typically brief, ideal for rapid on/off responses.

Type of Signal: Endocrine system uses hormones released into the bloodstream affecting distant targets; nervous system uses electrical signals and neurotransmitters affecting specific nearby cells.

Control of Effect: Hormonal effects are diffused and broadly spread, impacting multiple organs; neural effects are highly targeted to specific cells or groups of cells.

Mechanism of Action: Hormones alter cell function by changing gene expression or modifying cellular activity; neurons transmit impulses through synapses to control immediate cell functions.

Question 13

Explain how neuroendocrine cells span the divide between nervous and endocrine systems.

Answer 13

Neuroendocrine cells act as a bridge between the nervous and endocrine systems by responding to neural signals and then releasing hormones into the bloodstream. These cells receive synaptic inputs from neurons, which can trigger them to secrete specific hormones directly into the circulatory system, thereby influencing distant organs and maintaining physiological homeostasis. This dual functionality allows them to rapidly convert neural information into hormonal signals, integrating the quick responses of the nervous system with the long-lasting effects of the endocrine system.

Question 14

List the structural and functional units of the nervous system.

Answer 14

Structural Units:

Central Nervous System (CNS): Includes the brain and spinal cord.

Peripheral Nervous System (PNS): Comprises all neural elements outside the CNS, including nerves and ganglia.

Functional Units:

Neurons: Basic signaling units that transmit information via electrical and chemical signals.

Synapses: Junctions between neurons where signals are transmitted.
Neuroglia (glial cells): Support, protect, and nourish neurons; important in maintaining homeostasis and forming myelin.

Question 15

Distinguish between membrane, action, and synaptic potentials and explain the physiological basis of each.

Answer 15

Membrane Potential: The voltage difference across a cell’s plasma membrane due to the distribution of ions. It is maintained by ion pumps and channels that regulate ion flow, creating a resting potential in neurons around -70 mV.

Action Potential: A rapid, temporary change in membrane potential, where the inside of the cell becomes positively charged compared to the outside, typically reaching about +30 mV. It occurs when a neuron sends information down an axon, triggered by depolarization that reaches a threshold.

Synaptic Potential: Changes in membrane potential due to the action of neurotransmitters released from another neuron at a synapse. Can be excitatory (depolarizing) or inhibitory (hyperpolarizing), influencing the probability of firing an action potential in the postsynaptic neuron.

Question 16

Explain Electrical and chemical synapse (gap junction, ionotropic, metabotropic)

Answer 16

Electrical synapses occur through gap junctions, which consist of connexin proteins forming channels that directly connect the cytoplasm of two cells, allowing ions and small molecules to pass rapidly from one cell to another, facilitating quick signal transmission.

Chemical synapses, on the other hand, involve the release of neurotransmitters from the presynaptic neuron into the synaptic cleft. These neurotransmitters can bind to receptors on the postsynaptic neuron, which are either ionotropic or metabotropic. Ionotropic receptors are ion channels that open in response to neurotransmitter binding, leading to rapid changes in ion flow and membrane potential. Metabotropic receptors, however, activate second messenger systems that can result in more prolonged, modulatory effects on the postsynaptic neuron, influencing various cellular processes.

Question 17

rescribe reflex arc

Answer 17

A reflex arc is a neural pathway that mediates a reflex action, enabling a rapid response to a stimulus without the need for conscious brain involvement. Typically, a reflex arc begins with a sensory receptor that detects a stimulus and generates an impulse in a sensory neuron. This impulse travels to the spinal cord, where it may be directly transmitted to a motor neuron via a simple, direct pathway for a monosynaptic reflex, or it may involve one or more interneurons in a more complex polysynaptic reflex pathway. The motor neuron then carries the impulse to an effector organ (usually a muscle or gland), which reacts to the initial stimulus. This efficient pathway provides a quick, automatic response that is crucial for avoiding harm or maintaining balance and posture.

Question 18

explain habituation and sensitization.

Answer 18

Habituation and sensitization are two forms of non-associative learning where an organism adjusts its response to a stimulus through repeated exposure.

Habituation is a decrease in response to a repeated, benign stimulus, enabling an organism to ignore irrelevant stimuli and conserve energy. For example, a person may stop noticing the sound of traffic outside their home over time.
(the opposite of sensitization).

Sensitization is an increased response to a stimulus, often following a particularly strong or painful experience. This heightened sensitivity can serve as a protective mechanism, making an organism more alert to similar stimuli in the future. Both processes are fundamental to an organism’s ability to adapt to its environment by modulating the sensory input it responds to actively.

Question 19

explain how autonomic NS is regulated.

Answer 19

-The LYMBIC system regulates the ANS.

Central Regulation: The regulation of the ANS begins in the brain, particularly through the hypothalamus, which integrates information from the nervous system and endocrine system to maintain homeostasis. It sends signals to the rest of the body through autonomic pathways, adjusting body functions in response to current needs.

Peripheral Regulation: Autonomic functions are modulated at the level of the spinal cord and peripheral ganglia. Reflex arcs within the spinal cord can initiate responses independently of brain input, such as the quick withdrawal from a painful stimulus.

Neurotransmitters and Receptors: The sympathetic and parasympathetic branches use different neurotransmitters (norepinephrine for the sympathetic, acetylcholine for the parasympathetic) to communicate with target organs. The type of receptors present on the target tissues (e.g., adrenergic or cholinergic) determines their response to these neurotransmitters.

Feedback Mechanisms: Various sensors in the body (such as baroreceptors for blood pressure, chemoreceptors for blood chemistry) provide feedback to the central nervous system about the body’s status. This feedback influences autonomic output to adjust bodily functions like heart rate, digestion, and respiration to suit current conditions and needs.

Question 20

Describe the types of neurotransmitters and receptors, and how neurotransmitters are released and regulated.

Answer 20

Types of Neurotransmitters and Receptors:

Neurotransmitters: Chemical messengers that include categories like amino acids (e.g., glutamate, GABA), monoamines (e.g., dopamine, serotonin, norepinephrine), peptides (e.g., substance P, endorphins), and others (e.g., acetylcholine, ATP).
Receptors: Proteins on the surface of neurons that detect neurotransmitters. They can be broadly classified as ionotropic (fast, direct control of ion channels) or metabotropic (slow, indirect effects via signal transduction pathways).

Release and Regulation:
Release: Triggered primarily by the influx of calcium ions into the neuron when an action potential reaches the synaptic terminal. This influx prompts vesicles containing neurotransmitters to fuse with the synaptic membrane and release their contents into the synaptic cleft.
Regulation: Achieved through mechanisms like reuptake (neurotransmitters are absorbed back into the neuron), degradation (neurotransmitters are broken down by enzymes), and auto-reception (neurotransmitters bind to receptors on the neuron that released them to inhibit further release).

Question 21

Aceytylcholine?

Epinephrine?

Norepinephrine?

Answer 21

Acetylcholine:
Function: Plays a crucial role in muscle stimulation, memory formation, and learning. Used in both the central and peripheral nervous systems.
Receptors: Nicotinic (ionotropic, excitatory) and muscarinic (metabotropic, can be excitatory or inhibitory).

Epinephrine:
Function: Also known as adrenaline, it acts mainly as a hormone to mediate the body’s response to stress, enhancing blood flow to muscles, output of the heart, pupil dilation, and sugar metabolism.
Receptors: Binds to alpha and beta adrenergic receptors, which are metabotropic and found throughout the body.

Norepinephrine:
Function: Functions primarily as a neurotransmitter in the central nervous system and as a hormone in the blood, playing a key role in the fight or flight response, increasing arousal, alertness, and readiness to respond.
Receptors: Binds to alpha and beta adrenergic receptors; metabotropic, influencing both excitatory and inhibitory cellular responses.

Question 22

The Lymbic System?

Answer 22

The Limbic System:

Components: Includes structures like the hippocampus, amygdala, and parts of the thalamus.
Function: Crucial for emotion regulation, memory formation, and linking cognitive functions with emotional responses. Also involved in smell and motivation.
-Regulates the Autonomic Nervous System (ANS)

Question 23

true or false: Synapses ALWAYS work on BAISC DIFFUSION. The neurotransmitters leave the presynaptic cell via exocytosis, and then diffuse through to the post-synaptic cell.

Answer 23

True!

Synapses typically operate based on the basic principle of diffusion. Neurotransmitters are released from the presynaptic neuron via exocytosis, then diffuse across the synaptic cleft to bind to receptors on the postsynaptic cell.

Question 24

Nicotinic vs muscarinic receptors?

–>Why is one ionotropic and the other metabotropic?

Answer 24

Nicotinic receptors: These are ionotropic receptors found in the neuromuscular junction and autonomic ganglia. They open ion channels directly upon binding acetylcholine, leading to rapid depolarization and excitation.

Muscarinic receptors: These are metabotropic receptors found in various tissues including the heart, smooth muscles, and brain. They work through G-proteins and second messengers to modulate cellular responses, leading to slower, more prolonged effects than nicotinic receptors.

—>Nicotinic receptors are ionotropic because they are structured to form a channel through the plasma membrane. When acetylcholine binds to these receptors, the channel immediately opens, allowing ions like Na+ and Ca2+ to flow directly into the cell. This rapid ion movement triggers a quick, transient change in membrane potential, suitable for fast synaptic transmission, such as in neuromuscular junctions where quick muscle activation is crucial.
—>Muscarinic receptors, on the other hand, are metabotropic and do not form ion channels. Instead, they activate through a second-messenger system involving G-proteins. When acetylcholine binds to muscarinic receptors, it triggers a cascade of intracellular events that indirectly influence ion channel activity or other cellular processes through secondary messengers like cAMP or IP3. This setup is used where a more modulated, prolonged response is beneficial, such as in regulating heart rate or glandular secretion.