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Questions and Answers
What is the primary function of an axon?
What is the primary function of an axon?
The axon hillock is the point where signals are generated to travel down the axon.
The axon hillock is the point where signals are generated to travel down the axon.
True
What is the axon hillock?
What is the axon hillock?
The cone-shaped base of an axon where signals are generated.
An _______ transmits signals to other cells.
An _______ transmits signals to other cells.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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What is the term for the charge difference across a cell membrane?
What is the term for the charge difference across a cell membrane?
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The inside of a cell is positively charged relative to the outside.
The inside of a cell is positively charged relative to the outside.
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What is created by the charge difference inside and outside of a cell?
What is created by the charge difference inside and outside of a cell?
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The membrane potential is the voltage difference between the inside and outside of a cell and it is a result of the cell being ______ charged.
The membrane potential is the voltage difference between the inside and outside of a cell and it is a result of the cell being ______ charged.
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Match the concepts related to cell charge:
Match the concepts related to cell charge:
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What happens when potassium channels are opened?
What happens when potassium channels are opened?
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Opening potassium channels decreases the membrane's permeability to K+.
Opening potassium channels decreases the membrane's permeability to K+.
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What effect do opened potassium channels have on the membrane's permeability?
What effect do opened potassium channels have on the membrane's permeability?
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Opening potassium channels increases the membrane’s permeability to _____
Opening potassium channels increases the membrane’s permeability to _____
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What is the term used to describe the increase in the magnitude of the membrane potential making it more negative?
What is the term used to describe the increase in the magnitude of the membrane potential making it more negative?
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Hyperpolarization occurs when the inside of the membrane becomes less negative.
Hyperpolarization occurs when the inside of the membrane becomes less negative.
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What typically results in hyperpolarization in a resting neuron?
What typically results in hyperpolarization in a resting neuron?
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An increase in the magnitude of the membrane potential is known as _____.
An increase in the magnitude of the membrane potential is known as _____.
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What happens during the undershoot phase of an action potential?
What happens during the undershoot phase of an action potential?
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During the undershoot, the membrane potential is less negative than the resting potential.
During the undershoot, the membrane potential is less negative than the resting potential.
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What ion's permeability is higher during the undershoot phase of an action potential?
What ion's permeability is higher during the undershoot phase of an action potential?
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During the _____ phase of an action potential, the membrane potential becomes more negative than at rest.
During the _____ phase of an action potential, the membrane potential becomes more negative than at rest.
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Match the following phases of an action potential with their descriptions:
Match the following phases of an action potential with their descriptions:
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What happens during the absolute refractory period?
What happens during the absolute refractory period?
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During the absolute refractory period, a strong stimulus can still excite the nerve fiber.
During the absolute refractory period, a strong stimulus can still excite the nerve fiber.
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What is the state of excitability during the absolute refractory period?
What is the state of excitability during the absolute refractory period?
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The __________ period is when no stimulus can excite the nerve fiber, regardless of strength.
The __________ period is when no stimulus can excite the nerve fiber, regardless of strength.
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Match the following terms related to nerve fiber function:
Match the following terms related to nerve fiber function:
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Study Notes
STEM BIOLOGY GRADE 12
- Course taught by Dr. Samuel George
- Contact information provided (+20 111 625 6602)
Information on Course Access
- If unable to enroll, contact Dr. George (Whatsapp or personal account) for free enrollment.
- Reproduction, duplication, and distribution of the course materials is prohibited without permission.
- Any participant or individual who aids in reproduction, duplication, or distribution will face divine retribution.
Nervous System
- Information processing through the nervous system takes place through three stages; sensory input, integration, and motor output.
- The central nervous system (CNS) is where integration occurs—includes the brain and spinal cord.
- Neurons that carry information into and out of the CNS are part of the peripheral nervous system (PNS) .
- Neurons that form bundles are called nerves.
- Sensory neurons carry information from the eyes and other external sensors (touch, heat, taste & smell), and internal sensors (blood pressure, muscle tension) to processing centers in the brain or ganglia.
- Interneurons which form local circuits within the brain or ganglia, analyze and interpret the sensory input.
- Motor neurons relay signals to muscle cells and glands
- The resting potential of a neuron typically ranges between -60 and -80 mV.
- ions are unequally distributed between the interior and exterior of a neuron, maintaining a negative charge inside the cell relative to the outside. •
- Potassium and sodium ions play important roles in the formation of resting potential → they have a concentration gradient across the plasma membrane. •
- Ion channels allow ions to diffuse back and forth across the membrane– maintaining the resting potential
Neuron Structure and Function
- The soma (cell body) is where most organelles are located, including the nucleus.
- Dendrites receive signals from other neurons or sensory cells.
- The axon carries signals from the soma to other cells.
- The axon hillock is the cone-shaped part of the axon that initiates signals.
- Synapses are where signals transmit between neurons.
- The synaptic terminals are where neurotransmitters are released.
Synapses
- Action potentials are not transmitted between neurons and other cells but by neurotransmitters.
- A chemical synapse involves the release of a chemical neurotransmitter by a presynaptic neuron.
- An electrical synapse allows electrical current to flow directly from one neuron to another through gap junctions.
- Neurotransmitters are packaged in synaptic vesicles at nerve terminals.
Action Potentials
- Action potentials are rapid changes in the membrane potential of a neuron or muscle cell.
- The opening and shutting of ion channels in response to stimuli alter membrane permeability to specific ions, causing a chain reaction of depolarization, which leads to further depolarization ( positive feedback).
- Once the threshold is reached, more sodium channels open, causing an explosive influx of sodium into the cell, leading to depolarization
- The magnitude and duration of the action potential are the same at every point along the axon.
Action Potential Conduction
- Conduction occurs as the action potential is restated in an adjacent part of the axon because of the depolarization.
- The active spreading of the signal down the axon is due to the local currents.
The Absolute and Relative Refractory Periods
The refractory period is the period of time during which an axon is unresponsive to further stimulation 1.The absolute refractory period is when the excitatory to generate another action potential; (inactivation gate of sodium channels are closed) 2.The relative refractory period extends from the last third of repolarization to the return of the resting membrane potential→ a stronger than normal stimulus can trigger a new action potential . During this time, some sodium channels have not yet returned to their resting state.
Graded Potentials
Graded potentials- are changes in the membrane potential that vary in size and duration according to the strength of stimulus, so they are not all or none, unlike action potentials. • These graded potentials are crucial for communication across synapses.
Summation of Postsynaptic Potentials
- The cell body and dendrites receive input from hundreds to thousands of synapses
- The magnitude of the postsynaptic potential varies based on the amount of neurotransmitter released by presynaptic neurons.
- Temporal summation: two or more EPSPs (excitatory postsynaptic potentials ) occur rapidly at one synapse before the membrane potential returns to resting, leading to a supra threshold potential and firing of an action potential
- Spatial summation: two or more EPSPs occur at different simultaneous synapses in order to trigger a new action potential
Neurotransmitters
- More than 100 different neurotransmitters have been identified.
- These have been categorized by their chemical nature (acetylcholine, amino acids, biogenic amines, neuropeptides, and gases)
Receptor types
- Ligand gated ion channels, which alter transmembrane permeability to selected ions
- Metabotropic receptors which modify their interaction with other molecules and trigger signals via second messengers.
Types of Neurons
1- Multipolar neurons: consist of a single axon and several dendrites 2- Unipolar Neurons: consist of a single axon and processes that serve as both dendrites and axons. 3- Bipolar neurons: consist of a single axon and a single dendrite and form a relatively small proportion of all neurons 4- Pseudounipolar neurons: a single process that extends form the cell body and then divides into an axon and dendrite.
Sensory Pathways
- Sensory pathways detect and transmit information that allows us to experience stimuli, and they have four basic functions: reception, transduction, transmission, and perception
Sensory Receptors:
Sensory receptors detect physical or chemical stimuli → converting the energy of the stimulus into an electrical signal (receptor potential). That signal then triggers an action potential, which transmits the sensory information towards the central nervous system.
Sensory Pathways Conduction
Many types exist, including mechanoreceptors (pressure, touch), thermoreceptors (temperature), nociceptors (pain), and chemoreceptors (chemical stimuli). Sensory receptors can respond to stimuli of various intensities, adjusting the frequency and strength of action potentials sent to the CNS • Varying frequency and number of action potentials (how often sensory neurons fire and how many) conveys information about the intensity of the stimulus to the brain.
Sensory Integration
The process of sensory information occurs before, during, and after the CNS. Receptors respond to stimuli. After being processed, this information generates a specific sensation, which is not identical to the original stimulus.
Amplification and Adaptation
- Sensory receptors alter the intensity of a signal through amplification and adaptation.
- Amplification increases signal strength → enabling perception of faint stimuli.
- Adaptation decreases responsiveness to maintained, uninterrupted stimulation.
Mechano Receptors
Sense mechanical energy (touch, stretch, pressure). The resulting change in ion permeability alters the membrane potential → triggering a depolarization or hyperpolarization in response to the stimulus
• Vertebrate stretch receptors are dendrites of sensory neurons that spiral around the middle of some skeletal muscle fibers→ they are activated when the muscle is stretched.
• Most of the tactile information we receive come from mechanoreceptors that are in close contact with the surface of our skin.
• Many animals have specialized mechanoreceptors, such as whisker receptors, which enable them to sense their environment.
Thermoreceptors
Detect heat and cold. They are located in the skin and the anterior hypothalamus.
Chemoreceptors
Detect chemical stimuli. In animals, these monitor the concentration of chemicals within their body.
Electromagnetic Receptors
Detect electromagnetic energy (light, electricity, magnetism). Some chemoreceptors are specialized to detect particular molecules—pheromones for example-—used in animal communication. Pain receptors → detect noxious stimuli (which result from tissue damage or potential for damage), in order to trigger protective responses.
Chemical Regulation of Bone Development
Hormones regulate many aspects of bone development.
- Growth hormones (GH), along with sex hormones → affect bone growth and bone remodeling.
• The process of bone tissue remodeling and repair involves a dynamic and continual process of bone breakdown using osteoclasts and bone formation using osteoblasts.
Hormonal Control of Blood Calcium
The regulation of blood calcium is critical for the proper development and function of nervous and muscle systems. • Parathyroid hormone (PTH) and calcitonin →maintain the proper calcium levels.
Cardiovascular System
- Mammalian blood circulates in a closed system consisting of blood vessels→ arteries, veins, and capillaries.
- Blood pumped by the heart → reaches tissues by means of arteries.
- Blood circulated to the lungs from the heart through vessels called the pulmonary circuit.
- Blood is returned to the heart from tissues and organs via veins..
The Heart
- The contraction and relaxation of cardiac muscle is essential for maintaining blood pressure→ allowing circulation.
- Valves ensure that blood flows in a unidirectional manner throughout the heart and blood vessels by preventing blood backflow
- The sinoatrial node (SA node) is the pacemaker and initiates electrical impulses stimulating rhythmic contractions.
Blood Vessels
- Structure 1- Arteries- thick walls of smooth muscle (and elastic fibers) 2- veins- thinner walls and valves to prevent backflow 3- capillaries- extremely tiny and thin walls to allow for exchange
Blood Flow Velocity
Blood flows at higher velocities in arteries than capillaries because arteries have smaller diameter than capillaries. The large amount of capillaries has an effect on the velocity of the blood flow.
Blood Pressure
- Blood pressure is the force exerted by blood against the walls of the blood vessels.
- Blood pressure is affected by a number of factors, including the volume and viscosity (thickness) of blood, the elasticity of blood vessel walls.
- Pressure is highest in arteries, as these vessels lead directly from the heart.
• Fluids in the Body: Blood and Lymph The body contains two major interstitial fluids; a fluid called lymph, which flows through the lymphatic system, and blood which circulates throughout the circulatory system. • The composition of blood and lymph differ, although the composition of lymph is similar to the interstitial fluid.
Fluid Return by the Lymphatic System
•The lymphatic system plays a critical role in maintaining the proper fluid distribution throughout the body by collecting excessive interstitial fluid. •Lymph vessels, like veins contain valves → prevent backflow. •Rhythmic contractions of the vessel walls aid in moving lymph toward the heart, and skeletal muscle contraction plays a role in the process.
Blood Components:
- Plasma: The liquid portion of the blood, consisting of water and dissolved substances.
- Blood cells are the cellular components of blood, which are involved in carrying oxygen, defense against disease, and blood clotting.
- Red blood cells (erythrocytes): Carry oxygen from the lungs to the rest of the body.
- White blood cells (leukocytes): Defend the body against pathogens and disease.
- Platelets (thrombocytes): Involved in blood clotting.
The Respiratory System
- The system of branching tubes that deliver air to the lungs.
- The respiratory process happens inside millions of tiny air sacs called alveoli.
- Air flows into the alveoli when inspiration (inhaling) occurs-where air is filtered, warmed, and humidified in the nasal cavity
- Air leaves the alveoli during exhalation (breathing out—when abdominal and rib muscles relax).
Gas Exchange (Pulmonary Respiration)
- Oxygen diffuses from the lungs to the blood.
- Carbon dioxide diffuses from the blood to the lungs.
- The partial pressures of O2 and CO2 in the blood → influence the net flow of these gases between the air in the lungs and the blood.
Respiratory Pigments
- Respiratory pigments increase the amount of oxygen that can be carried in the blood.
- Hemoglobin is the iron-containing protein responsible for oxygen transport in blood.
Control of Breathing
- The breathing rate varies based on metabolic demands (exercise, altitude, changes in blood pH).
- Breathing control centers in the medulla oblongata regulate breathing by detecting changes in blood gases or pH and adjusting the breathing rate.
The Eye
- The eye is a complex organ designed to convert light energy to electrical signals that are transmitted to the brain, enabling vision. The eye consists of layered structures, including:
- the conjunctiva; (thin mucous membrane lining the eye)
- sclera → outermost layer
- Choroid → middle layer
- Retina → innermost layer
- the cornea (transparent portion of the sclera), pupil and iris (controls the light that enters the eye), lens (focuses light onto the retina), and the vitreous humor (fluid filling the posterior cavity of the eye).
Photoreceptor Cells
- Rods are responsible for vision in low-light conditions (night vision)—and have low sensitivity in high-light conditions
- Cones are responsible for vision in high-light conditions (color vision)—and have high sensitivity to details in high light conditions.
- Both rod and cone cells contain different light sensitivities, which are based on their visual pigments.
Visual Processing in the Retina
- Visual information originates in rods and cones in the retina→ it is process at the level of the retinal and the deeper layers (bipolar, ganglion, horizontal, amacrine)
- Several different pathways carry information from the outer portion of the retina to the brain→ allowing for better processing of the image.
The Brain: Processing of Visual Information
- The axons of ganglion cells form the optic nerves→ carry visual information from each eye to the brain.
- The optic nerves from both eyes meet at the optic chiasm→ where axons from the left visual field of each eye are routed to the right side of the brain, and axons from the right visual field are routed to the left side of the brain.
Brain Structures
- Cerebrum: Controls voluntary movements and higher-level cognitive function (learning, memory, emotion).
- Cerebellum: Integrates sensory information to coordinate movement and balance.
- Basal Nuclei: Clusters of neurons that help with planning and executing movement sequences.
- Thalamus: Receives and relays sensory information to the Cerebral cortex.
- Hypothalamus: Regulates hormone release and basic drives, such as hunger, thirst, and temperature control.
- Epithalamus: Includes the pineal gland, involved in regulating rhythms and producing melatonin.
- Midbrain: Part of the brainstem that controls some auditory and visual reflexes.
- Pons and Medulla oblongata; (part of the brainstem) →control breathing, heart and blood vessel activity, swallowing, vomiting, and other basic bodily functions.
Auditory System (Hearing)
- The Ear converts sound waves into nerve impulses that are perceived as sound/vibrations
- The Three Parts of the ear are; 1- External ear → collects sound waves. 2- Middle ear → transfer the vibrations from eardrum to the inner ear. 3- Internal ear → converts vibrations into nerve impulses.
• The structures within the inner ear- particularly the cochlea- and connected apparatus, are responsible for detecting and transmitting details in sound.
• Auditory receptors also relay signals about position and balance, enabling the brain to track movement and body position .
• Hearing involves detecting/transducing physical waves
The Skeletal System
- The skeletal system is the framework of the body, providing support, protection, and enabling movement and is composed of bones, ligaments and cartilage.
- Bones are hard due to calcium phosphate, allowing for support of the body, protection, and to enable muscle contraction.
- Ligaments connect bones to other bones
- Cartilage cushions between bones.
Joint Structures
- Fibrous- Immovable
- Cartilaginous - Slightly movable, includes the connecting bone to the rib cage, including the vertebrae in the backbone.
- Synovial → Freely movable and widely varied, includes the knee joint (hinge joint—a joint that can flex and extend but not rotate), which allow movement in a single plane.
- Ball and socket joint- allows for wider ranging movements
Diseases & Disorders of the Skeleton
- Sprains, Bursitis, Tendinitis, Arthritis, Osteoporosis
Endocrine System
- The endocrine system is a collection of glands→ regulate numerous physiological processes through hormones.
- The endocrine glands secrete hormones → that travel in the blood→ reaching the cells they act on (target cells)
- Examples of hormones and their functions:
- Insulin (↓ blood glucose levels)
- Glucagon (↑↑ blood glucose levels)
- Epinephrine (↑↑ blood sugar, metabolism & blood pressure.
Chemical Classes of Hormones
Water-soluble hormones (e.g. epinephrine, insulin) → bind to receptors → trigger intracellular signals→ activate/affect enzyme or proteins in the target cell Lipid-soluble hormones (e.g. testosterone, cortisol) diffuse across the target cell membrane → bind to receptors → affect gene expression in the nucleus
• Neuroendocrine signaling: Neurohormones release hormones that act on the hypothalamus, which regulates many other endocrine glands. • Positive feedback: The response enhances the initial stimulus (e.g., oxytocin during labor). • Negative feedback: The response inhibits the initial stimulus (e.g., the regulation of blood glucose levels by insulin and glucagon).
- Different types of hormones elicit various responses in the body depending on where they are released and how their interactions happen with target organs.
Multiple Effects of Hormones
- Many hormones elicit more than one type of response→ depending on the types of receptors
- The effects brought about by a particular hormone can vary based on different combinations of cell types or by difference in the signaling pathways
Hormones controlling Bone Development
- Growth Hormone
The process of bone remodeling and repair involves the dynamic and continuous process of bone breakdown using osteoclasts and bone formation using osteoblasts
- The process of repair involves the formation of a callus that eventually hardens and fuses to form a new bone.
• Malnutrition→ especially inadequate amounts of iodine→ can disrupt thyroid hormone production, leading to a condition called goiter.
Hormones of the Adrenal Cortex and Medulla
- The adrenal glands→ are two endocrine glands that sit atop the kidneys→ regulated by the autonomic nervous system→ play an important role in responding to stress.
- The adrenal cortex secretes steroid hormones→ to respond long-term to stress
- The adrenal medulla→secretes catecholamines → such as epinephrine and norepinephrine → to respond promptly to stress.
Gonadal Sex Hormones
- The gonads→ testes in males and ovaries in females→ are the primary sources of sex hormones.
- These hormones → regulate sexual development, reproductive cycles → and sexual behavior.
Digestive System
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The stages of food processing: ingestion digestion, absorption, and elimination.
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Digestive compartments are used in order to avoid self digestion.
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The small intestine is where most of the digestion and nutrient absorption take place.
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The larger intestine is involved in removing water→ forming feces, and plays a role in the fermentation of materials.
• Chemical digestion employs enzymes that catalyze hydrolysis to break down large food molecules.
Absorption in the Small and Large Intestines
- The small intestine's lining has many structures (villi, microvilli), increasing its surface area for absorption.
- Absorption of nutrients involves passive or active transport.
- The large intestine→absorbs water → forms feces • Waste products are expelled from the body.
Disorders of the Accessory Organs of Digestion
- Hepatitis
- Gallstones
- Malnutrition
Urinary System
The structures that filter blood→ producing urine→ that removes waste products from body fluids. The kidney functions in:
- Filtering blood to produce urine (blood filtration)
- Regulating blood volume and pressure
- Regulating the concentration of salts within the body
- Removing metabolic waste from blood and excreting it in urine.
The nephron is the functional unit of the kidney, responsible for filtering blood, reabsorbing essential substances, and secreting wastes into the urine.
The nephron and collecting duct contain cells that have roles in regulating osmolarity and maintaining homeostasis.
The Two-Solute Model
- The kidney produces hyperosmotic urine by establishing an osmolarity gradient in the tissues surrounding the loop of Henle as a means of concentrating the substances in urine to regulate fluid and electrolyte balance within the body.
Hormonal control of kidneys function
- Hormones such as ADH (Antidiuretic Hormone) and ANP (atrial natriuretic peptide) regulate the function of the kidneys.
- ADH increases water reabsorption by making the collecting duct more permeable to water in response to high blood solute concentration or dehydration
- ANP (atrial natriuretic peptide), which has the opposite effect to ADH
Digestive System Disorders
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Foodborne illness, including food poisoning and food allergies, are issues in the digestive system.
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Celiac disease and diverticulosis→ are conditions from the large intestine that can disrupt the function and normal operation of the digestive system.
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Peptic ulcers are sores in the stomach lining that result from infection by bacteria, such as H. pylori, and other conditions.
The Lymphatic System
The lymphatic system collects fluid called lymph → from around the body's tissues and organs → returns the fluid to the circulatory system at the base of the neck; plays a role in the defense against pathogens. • Lymph nodes are part of this system and serve as filters removing foreign microbes or substances.
• Spleen houses white blood cells.
The Immune System
- The overall response of the body to pathogens.
The immune system is divided into innate immune system and acquired immune system.
- Innate immunity → is non-specific in nature and has relatively very quick response to pathogens and is present from birth.
- Adaptive immunity → is specific to pathogens and has a relatively slow response that results from prior exposure.
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- Helper T cells stimulate responses from both humoral and cell-mediated components and in conjunction with other cells
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- Cytotoxic T cells destroy infected cells.
Disorders of the Accessory Organs of the Immune System
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Allergies and inflammation are involved and can occur locally and systematically causing symptoms throughout the body.
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Immunity disorders also include deficiencies in pathogens (antibodies) or cells (lymphocytes).
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HIV is a dangerous virus that directly affects the immune system and causes immunodeficiency.
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Description
Test your knowledge on the primary functions of axons and the key concepts of membrane potential. This quiz covers important definitions and critical thinking about neuronal communication and cell charge. Challenge yourself to match terms and understand the principles governing neuronal signaling.
