Processes

Skin

Keratinocyte Lifecycle

  1. Keratinocyte produced in stratum basale

  2. Cell moves upward through epidermis

  3. Keratin accumulates

  4. Cell loses nucleus and organelles

  5. Becomes corneocyte

  6. Shed from skin surface

Nervous System

Stretch Reflex

  1. Muscle stretches

  2. Muscle spindle activated

  3. Sensory neuron sends AP to spinal cord

  4. Sensory neuron synapses directly with alpha motor neuron

  5. Motor neuron stimulates same muscle

  6. Muscle contracts

Keyword: Monosynaptic

Withdrawal Reflex

  1. Pain receptor activated

  2. Sensory neuron enters spinal cord

  3. Excitatory interneuron activates flexor muscle

  4. Inhibitory interneuron inhibits extensor muscle

  5. Limb withdraws from stimulus

Keyword: Polysynaptic

Crossed Extensor Reflex

  1. Pain stimulus activates withdrawal reflex

  2. Injured side flexes

  3. Interneurons cross spinal cord

  4. Opposite limb extends

  5. Balance maintained

Action Potential

  1. Threshold reached

  2. Na⁺ channels open

  3. Depolarisation occurs

  4. Na⁺ channels close

  5. K⁺ channels open

  6. Repolarisation occurs

  7. Hyperpolarisation

  8. Return to resting potential

Synaptic Transmission

  1. Action potential arrives

  2. Neurotransmitter released

  3. Neurotransmitter binds receptor

  4. Postsynaptic graded potential generated

  5. New action potential may occur

Autonomic Nervous System

General ANS Pathway

  1. Preganglionic neuron cell body in CNS

  2. Preganglionic fibre leaves CNS

  3. Synapse in autonomic ganglion

  4. Postganglionic neuron activated

  5. Postganglionic fibre reaches target organ

RAAS (if kidneys are included later)

  1. Blood pressure falls

  2. Renin released

  3. Angiotensinogen → Angiotensin I

  4. ACE converts Angiotensin I → Angiotensin II

  5. Angiotensin II causes vasoconstriction

  6. Aldosterone released

  7. Na⁺ and water reabsorbed

  8. Blood pressure rises

Vision

Phototransduction

This is VERY likely exam content.

In Light

  1. Photon hits rhodopsin

  2. Retinal changes shape (11-cis → all-trans)

  3. Na⁺ channels close

  4. Photoreceptor hyperpolarises

  5. Glutamate release decreases

  6. Bipolar cells depolarise

  7. Ganglion cells activated

  8. Action potentials generated

Visual Pathway

  1. Retina

  2. Optic nerve

  3. Optic chiasm

  4. Thalamus (LGN)

  5. Optic radiations

  6. Visual cortex (occipital lobe)

Hearing

Sound Transmission

  1. Sound enters ear canal

  2. Tympanic membrane vibrates

  3. Malleus vibrates

  4. Incus vibrates

  5. Stapes vibrates

  6. Oval window moves

  7. Fluid movement in cochlea

  8. Basilar membrane moves

  9. Hair cells stimulated

Hearing Transduction

  1. Stereocilia bend

  2. Tip links stretch

  3. MET channels open

  4. K⁺ enters hair cell

  5. Hair cell depolarises

  6. Glutamate released

  7. CN VIII activated

Auditory Pathway

  1. Cochlea

  2. CN VIII

  3. Cochlear nuclei

  4. Inferior colliculus

  5. Thalamus

  6. Auditory cortex

Taste & Smell

Olfactory Transduction

  1. Odorant binds receptor

  2. GPCR activated

  3. cAMP increases

  4. Na⁺ channels open

  5. Depolarisation occurs

  6. Action potentials generated

Olfactory Pathway

  1. Receptor neuron

  2. Cribriform plate

  3. Olfactory bulb

  4. Glomerulus

  5. Mitral cell

  6. Olfactory cortex

Taste Transduction (General)

  1. Tastant dissolves in saliva

  2. Tastant enters taste pore

  3. Receptor cell activated

  4. Receptor cell depolarises

  5. ATP released

  6. Sensory neuron stimulated

  7. Action potentials generated

Respiratory

Inspiration

  1. Diaphragm contracts

  2. External intercostals contract

  3. Thoracic volume increases

  4. Intrapulmonary pressure falls

  5. Air enters lungs

Expiration

  1. Inspiratory muscles relax

  2. Elastic recoil occurs

  3. Thoracic volume decreases

  4. Pressure rises

  5. Air leaves lungs

Gas Exchange in Lungs

  1. Alveolar PO₂ higher than blood

  2. O₂ diffuses into blood

  3. Blood PCO₂ higher than alveoli

  4. CO₂ diffuses into alveoli

  5. CO₂ exhaled

Oxygen Transport

  1. O₂ enters blood

  2. O₂ binds haemoglobin

  3. Oxyhaemoglobin formed

  4. Blood travels to tissues

  5. O₂ released

  6. O₂ diffuses into cells

Bohr Effect

  1. Active tissues produce CO₂

  2. H⁺ increases

  3. Temperature increases

  4. Haemoglobin affinity falls

  5. O₂ released more easily