Themes C2.2 and C3.1

Themes C2.2 and C3.1 Summative Study Guide

Neural Signaling Notes:

* All elements must be labeled

• Neurons are cells. They have a cell body and a nucleus. 

• Saltatory conduction: neural conduction from node to node (jumping across nodes), enabling impulses to travel faster. 

  • Latin root “salt”: to jump

  • For nerve impulses to be saltatory, there must be myelin wrapped around the axon. 

  • The Nodes of Ranvier between Schwann cells enable saltatory conduction: the action potential jumps (or propagates) from node to node. 

Speed of Impulse: 

• Human neurons are about 1 micrometer in diameter. 

• Human impulses travel at a rate of around 1 meter per second. 

• Giant Squid neurons are about 500 micrometers in diameter. 

• Giant Squid impulses travel at a rate of about 25 meters per second. 

  • Giant Squids need this speed of impulse because they need to propel themselves for sudden movement. 

Impulse Movement: 

• In response to a stimulus, the soma end of the axon (the end with the cell body) becomes depolarized when Na+ ions enter the axon through the plasma membrane. 

• The depolarization spreads down the axon. Meanwhile, the first part of the membrane repolarizes. Because the Na+ channels are inactivated and additional K+ channels have opened, the membrane cannot immediately depolarize again. 

• The action potential continues to travel down the axon. 

Stages: 

• Resting potential

  • Sodium-potassium pump creates an imbalance of ionic charges across the membrane by pumping 3 Na+ ions out for every 2 K+ ions in. 

    • This results in a charge difference between the inside and outside of the membrane, where the outside is positively charged relative to the inside. 

  • The sodium-potassium pump requires energy in the form of ATP as is a form of active transport and occurs up the concentration gradient. 

• Action potential

  • Action potential begins with depolarization once the threshold potential is reached (-55mV in humans). 

  • Depolarization 

    • Reversal of charge of the inside of the membrane from negative to positive

    • Opening of sodium channels allowing Na+ to move down the concentration gradient into the membrane. (Na+ open, K+ closed)

  • Repolarization 

    • Reversal of charge of the inside of the membrane from positive to negative

    • Opening of potassium channels allowing K+ to move down the concentration gradient out of the membrane. (Na+ closed, K+ open)

Neural Impulse Sequencing: 

1. At resting potential the sodium-potassium pump creates an imbalance of ionic charges across the membrane.

2. Threshold potential is reached (-55mV in humans) → level to which a membrane must be depolarized to create an action potential or nerve impulse. 

3. Action potential begins with depolarization → opening of sodium channels allows Na⁺ to move down the concentration gradient.

4. Na⁺ continues to move down the concentration gradient. 

5. Repolarization phase of the action potential begins → opening of potassium channels allows K⁺ to move down the concentration gradient. 

6. After a brief “undershoot,” Na⁺ and K⁺ return to resting potential via active transport up the concentration gradient (sodium-potassium pump).

* The undershoot is also known as hyperpolarization or the refractory period. Another impulse cannot be sent during this phase. 

Synaptic Transmission: 

• When the impulse reaches the axon terminus, the action potential (depolarization) causes calcium ions to enter the cell through Ca+ channels. 

• This triggers vesicles filled with neurotransmitter compounds to move to the membrane. 

• Neurotransmitters are released into the synapse via exocytosis. 

• The neurotransmitters cross the synaptic cleft and bind to neuroreceptors on the postsynaptic neuron.

  • Synaptic cleft: the space between neurons

• This triggers a signal and causes ion channels to open on the postsynaptic neuron. 

Synaptic Transmission Sequencing: 

1. Action potential reaches the axon terminus

2. Calcium channels open.

3. Ca⁺² floods the neuron.

4. Vesicles containing neurotransmitters release them into the synaptic cleft via exocytosis.

5. Neurotransmitters cross the synapse.

6. Neurotransmitters bind with receptors on the postsynaptic neuron.

7. This triggers the signal in the postsynaptic neuron.

8. Neurotransmitters are then broken down by enzymes or taken back in by reuptake channels in the presynaptic neuron.

Application: Neonicotinoids: 

• Acetylcholine → motor neurotransmitter

• Neonicotinoids found in pesticides and is a neural disruptor (blocks receptors) 

• Paralyzes the insect by disrupting impulses, as neurotransmitters cannot bind to neuroreceptors on the postsynaptic neuron and therefore the impulse is not transmitted from one neuron to another. 

• May lead to CCD (Colony Collapse Disorder) in bees

Paper 2 Practice: 

Outline the role of membrane proteins in the movement of specific ions and specific times in the transmission of nerve impulses. (4 marks)

• During depolarization, Na+ channels open;

• Allowing Na+ ions to flow into the axon

• During repolarization, K+ channels open; 

• Allowing K+ ions to flow out of the axon

• The sodium potassium pump returns the axon membrane to resting potential; 

• By pumping 3 Na+ out and 2 K+ in

Outline the role of the sodium-potassium pump in maintaining the resting potential. (2 marks)

• Sodium-potassium pump pumps Na+ ions out of the axon and pumps K+ ions into the axon. 

• Requires energy/ATP/against concentration gradients/active transport

• 3 Na+ pumped out for every 2 K+ pumped in

• Results in charge difference between inside and outside where the outside of the membrane is positive relative to the inside.

Integrated Body Systems Notes: 

General Organization: 

• Cells: smallest functional units of a living organism

• Tissues: groups of similar cells that carry out a function

• Organs: groups of tissues that work together to perform a specific function

• Organ Systems: groups of organs interacting to perform a life function

• Organisms: a living being composed of interconnected and interdependent parts

Organization example: 

• Epidermal cell → Epidermis → Skin → Integumentary system → Human (Homo sapiens)

Signaling: 

• Requires both transport of materials …

  • Neurotransmitters 

  • Hormones

  • Nutrients

• and communication between organs for →

  • Growth and development (chemical)

  • Reproduction (chemical)

  • Osmoregulation (chemical)

  • Thermoregulation (chemical)

  • Mood (chemical)

  • Muscle contraction (electrical)

  • Heart rate (electrical)

  • Gland secretions (electrical)

The Nervous System: 

• Brain: the principal organ of the nervous system, responsible for processing information, controlling bodily functions, and coordinating responses to stimuli. 

  • The Cerebellum coordinates voluntary skeletal muscle movements, responsible for balance and coordination. 

  • Motor Cortex: the region connecting the hemispheres of the brain

    • Coordinates voluntary movements (conscious control)

    • Densely packed with motor neurons

    • Highly folded to increase surface area

  • The Medulla oblongata is the area of the brain responsible for coordinating vital, life-sustaining processes like ventilation rate, heart rate, and blood pressure. 

• Nerves: bundles of fibers (neurons) that transmit electrical signals between the brain, spinal cord, and other parts of the body, enabling coordination of various physiological processes. 

  • A single nerve contains multiple neurons (sensory, motor, or both) in a sheath along with blood vessels. 

  • Fascicle: a bundle of neurons within a nerve, encased in a perineurium. 

Diagram of a nerve cross section: 

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

  • Interneurons: neurons within the CNS that communicate internally and intervene between the sensory inputs and motor outputs. 

• PNS (Peripheral Nervous System): connects the CNS to muscles, organs, and sensory receptors, facilitating communication throughout the body (the parts of the nervous system outside of the brain and spinal cord). 

• Autonomic Nerves: regulate involuntary bodily functions, such as heartbeat, digestion, and respiratory rate, maintaining internal balance without conscious control. 

• Motor Neurons: neurons that carry outgoing information from the brain and spinal cord (CNS) to the muscles and glands. 

• Sensory Neurons: neurons that carry incoming information from receptor cells to the brain and spinal cord (CNS). 

The Pain Reflex Arc: 

• System of reactionary events linking a stimulus to an involuntary movement. 

• Neurons connect receptor cells to effector cells (using the smallest number of neurons possible) through neural signaling. 

  • Receptor cells: perceive a stimulus → detect pain and initiate the pain-reflex arc

  • Effector cells: generate a response

• Coordinated effort between the nervous and muscular systems. 

• Follows the “relay” from receptor cells to effector cells:

  • Receptor cells

  • Sensory neurons

  • Interneurons

  • Motor neurons

  • Effector cells

Feedback Mechanisms: 

• Negative feedback: 

  • Resets the system

    • Body temperature drops → shiver to warm muscles

    • Body temperature rises → sweat to cool down the body

• Positive feedback: 

  • Changes the system

    • Bleeding injury → clotting factors released

Epinephrine (Adrenaline) Secretion:

• Fight or flight

  • Release controlled by the brain in response to environmental stressors.

  • Epinephrine is released by the adrenal gland (impulse sent from the medulla) → epinephrine secreted into the bloodstream. 

    • Increases the production of glucose (and therefore ATP) in the body. 

    • Faster ventilation rate (airways expand) 

    • When epinephrine reaches the heart, cardiac output speeds up (heart pumping faster) → contraction of the SAN

    • Arteries expand and contract in response to the body’s needs.

Control of Heart Rate: 

• Sinoatrial node (SAN): a group of cardiac muscles in the wall of the right atrium. 

  • Acts as a pacemaker and receives signals from the cardiovascular center of the brain (in the medulla) in response to a stimulus. 

  • Branches off to two nerves:

    • Sympathetic nerve: increases the heartbeat speed. 

      • Heartbeat speed increases immediately in response to epinephrine release. 

    • Vagus nerve: makes the heartbeat slow down. 

      • The nerves are like an accelerator and brake. 

• Negative feedback controls blood pressure: when blood pressure is high, the SAN slows the heart down.

• Baroreceptors: specialized cells that detect changes in blood pressure and send signals to the CNS. 

Increase in heart rate: 

• Controlled by the sympathetic nervous system. 

Decrease in heart rate: 

• Controlled by the vagus nervous system. 

• Baroreceptors detect high blood pressure, 

Feedback Control of Ventilation Rates: 

• Regulated by chemoreceptors located in the aortic and carotid bodies. 

• Aortic chemoreceptors detect changes in pH level. 

• Carotid chemoreceptors detect changes in blood oxygen and carbon dioxide levels. They can override signals from aortic chemoreceptors. 

• An increase in carbon dioxide concentration or a decrease in pH (indicating an increase in acidity) stimulates the receptors. 

• Receptors send signals to the respiratory center of the brain (in the medulla). 

• The medulla then sends signals to the internal intercostal muscles and the diaphragm to contract.

• This prompts a faster ventilation rate and deeper breathing to expel excess carbon dioxide from the body. 

• Once carbon dioxide levels decrease and blood pH level returns to normal, chemoreceptors stop sending signals and breathing rate returns to normal. 

• Involving in homeostatic regulation, occurs in response to negative feedback mechanisms (resets the system). 

Peristalsis: 

• Contraction of the circular muscles of the intestines to digest food. 

• A coordinated series of contraction and relaxation of the intestinal muscles occuring in waves along the entire length of the GI (gastrointestinal) tract. 

• Results in the movement of food along the lumen of the GI tract. 

• Involuntary process that occurs during digestion → impulse sent by the medulla to coordinate the contraction of the intestinal muscles .

• Function: 

  • Movement of food along the digestive system. 

  • Churning of the semi-digested food to mix with enzymes and thus speed up the digestive process. 

• Process: 

  • Controlled by the CNS and enteric nervous system (regulates involuntary responses). 

  • Only occurs in one direction: away from the mouth. 

  • Food moves slowly through the intestines allowing for digestion. 

Melatonin and the Control of the Endocrine System: 

• Endocrine system: hormone system involving the brain and various glands throughout the body. 

  • Responsible for energy, growth, reproduction and responses to injuries, stress and mood. 

• Melatonin: a hormone made by the pineal gland which helps control the body’s sleep cycle and levels of tiredness (it is an antioxidant). 

• In response to low light, the brain signals to the pineal gland to secrete melatonin. 

• Circadian Rhythm: the human body functions on a 24 hour cycle, melatonin release corresponds with this cycle. 

• Production: synthesized from serotonin and influenced by light exposure. 

• Secretion pattern: peaks at night, inhibited by light (release of melatonin impacted by light exposure).