Topic 6 Human Physiology

• 6.1 Digestion and absorption • 6.4 Gas Exchange • 6.5 Neurons and Synapses

neurons 101

nervous systems; used for communication of impulses; have a cell body, cytoplasm, nucleus and outgrowths.

dendrites have short branches for impulses to communicate WITHIN body part.

axons are elongated fibres along main body for communication BETWEEN spine and body part.

myelin sheath

cylindrical fibre coated in plasma membrane/cytoplasm. speeds up nerve impulses

structure: schwann cells create lots of phosopholipid layers around shaft as a membrane. gaps between schwann cells are nodes of ranvier that nerve impulses can jump through.

resting potentials

neurons pump sodium and potassium ions across membranes, creating a resting potential gradient.

membrane is 50 times more permeable to K potassium, so some seep back, creating an imbalance.

action potentials

depolarisation: change from negative to positive

repolarisation: change back from positive to negative

this is due to sodium channels reversing the K seepage by letting in more Na, reversing the charge imbalance. because of this full reversal, it doesn’t return to resting potential.

nerve impulses

action potentials propagated along neurons’ axons in only one direction.

happens as movements caused by depolarisation in turn depolarise nearby parts.

acetylcholine secretion and reabsorption

acetylcholine causes sodium channel to open and trigger next neuron.

acetylcholinesterase is an enzyme that breaks down acetylcholine into acetate and choline to stop too many channels being opened.

neonicotenoid pesticides prohibit acetylcholinesterase from working and overload the neurons, killing the animal.

ventilation

maintaining the concentration gradient of oxygen and carbon dioxide between air in alveoli and blood in capillaries

alveoli

ballon shaped structures at the end of the branches in the lungs. used to move oxygen and carbon dioxide into/out of blood. contain type I and type II pneumocytes. 100 um diameter. increase surface area for more absorption.

type I pneumocytes

thin alveolar cells used for gas exchange. part of layer of cells known as epithelium, close to capillaries for quick diffusion.

type II pneumocytes

secrete pulmonary surfactant (phosopholipid monolayer) to create a moist surface to stop alveoli from adhering to each other, reduce surface tension. occupy 5% of epithelium surface area.

gas exchange

same as ventilation: oxygen and carbon dioxide move between lungs and blood

parts of the respiratory system

trachea > lungs > branches > bronchioles > alveoli

see also ribs > intercostal muscles; diaphragm

inspiration

diaphragm contracts and flattens while external intercostal muscles contract to change pressure and suck in air

expiration

muscles relax, pressure decreases, air is released

spirometer

device that measures volume of the lungs, such as tidal volume (normal amount breathed), inspiratory/expiratory reserve volume (max volume/exhale) ect

emphysema

lung disease that rounds the alveoli, decreasing surface area and therefore absorption

mechanical digestion

chewing, mixing food with saliva, churning in stomach, peristalsis

chemical digestion

enzymes break down large molecules, salivary amylase, stomach acid