IB Bio: Topic 6 (Human Physiology --> 6.4, 6.5, 6.6)

Inhaling

* Diaphragm contracts
* Chest (rib) muscles contract
* Volume of chest cavity increases
* Air pressure decreases
* Causes air to fill lungs

Exhaling

* Diaphragm relaxes
* Chest (rib) muscles relax
* Volume of chest cavity decreases
* Air pressure increases
* Forces air out of lungs.

Muscles at inspiration

* Core muscles:
* External intercostals contract to elevate ribs
* Internal intercostals relax.
* Diaphragm contracts to expand thoracic cavity

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Muscles at expiration

* Core muscles:
* External intercostals relax
* Internal intercostals contract to pull ribs down
* Diaphragm relaxes to reduce thoracic cavity.

Gas exchange

* Absorbing one type of gas from environment and releasing another type of gas.
* Animals: Cellular respiration (Oxygen → Carbon Dioxide)
* Plants: Photosynthesis (Carbon Dioxide → Oxygen)
* Proceeds due to diffusion
* Movement from high concentration to low concentration.

Pneumocytes

* Alveoli cells
* Type 1
* Extremely thin cells of alveoli walls
* allows increased rates of gas exchange via diffusion.
* Type 2
* Secretes fluid surfactant
* helps with gas exchange
* stops walls of alveoli from sticking
* Stops lungs from collapsing.

Emphysema

* Chronic respiratory disease
* irreversible damage to alveoli
* less surface area
* smaller number of alveoli
* thicker alveoli walls or destroyed walls
* Inefficient gas exchange
* Low oxygen levels
* high carbon dioxide levels
* Symptoms: shortness of breath and Fatigue

Lung Cancer

* Caused by smoking and air pollution.
* Symptoms:
* Breathing difficulties
* Coughing
* Chest pain
* Loss of appetite
* Weight loss
* General fatigue

Neurons

* Nerve cells
* Allows communication throughout the body with a wide neural network

Neural Structure

Neurons consist of the cell body, dendrites, axon, Schwann cells, Myelin sheath, and nodes of Ranvier.

Cell body (neurons)

Contains cell nucleus and other normal cell structures.

Dendrites (neurons)

Where signal is received.

Axon (neurons)

long tube-like structure where signal is sent out.

Schwann cells (neurons)

Create Myelin sheath

Myelin Sheath

* the protective layer that surrounds and insulates the axon of a neuron.
* The myelin sheath helps to speed up the transmission of electrical impulses along the axon.
* The myelin acts as an insulator, preventing the electrical charge from leaking out and allowing the impulse to travel faster and more efficiently.

Nodes of Ranvier

Axon parts with no Myelin sheath

3 types of neurons

Sensory neurons, Interneurons and motor neurons.

Sensory neurons

* Detect stimuli (5 senses)
* Send information to central nervous system (brain and spinal cord)

Interneurons

* In brain and spinal cord (CNS)
* Processes information
* Thinking or automatic reflexes
* Connects sensory neurons to motor neurons
* Does NOT have Myelin sheaths.

Motor neuron

* Receive information from CNS to muscles for movement.

Action Potential

* Electrical signal transferred along a neuron.

Action Potential steps

1) Resting state

2) Depolarization (rising phase)

3) Repolarization (falling phase)

4) Hyperpolarization (undershoot / refractory period)

Resting State (Action Potential)

* Outside of cell: Positive (Na+ on the outside)
* Inside cell: Negative (K+ and proteins inside)
* Salty Banana
* Ion gates are closed (diffusion still occurs)
* Cell is polarized
* Charge difference between inside and outside the cell.
* Resting potential: -70mV

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Membrane permeability during Resting rate (action potential)

* Ions diffuse through membrane to reach equilibrium
* K+ diffuses more easily than Na+
* and so more K+ moves out
* More positive charges are outside
* More negative charges are inside

Sodium-Potassium Pump

* Prevents equilibrium
* Maintains resting potential @ -70mV
* Keeps Na+ outside and K+ inside
* Uses ATP for active transport of ions.

Sodium-Potassium Mechanism

1. 3 Na+ ions bind to pump and ATP is signaled
2. ATP binds to pump, ATP loses phosphate, and energy is released.
3. Pump changes shape and Na+ ions are released outside the cell.
4. 2 K+ ions bind to pump
5. Phosphate unbinds from pump
6. Pump returns to original shape and K+ ions are released into cell.

Depolarization

* Sensory neurons receive stimulation.
* Threshold level is -55mV
* Action potential will only be transmitted if stimulation is strong enough. (>-55mV)

Steps in Depolarization

* K+ gates closed