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<aside> 💡 KEY TERMS - for revision

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Introduction to the nervous system

What it is

• Nerves (can be severed or injured)
• run through the body
• ‘electrical system’
• it’s role is to send signals to the brain

how do we smell

• 1 in every 50 gene dedicated to smell
• distinguish 10,000 different smells
• sniff molecules
• 95^ of nasal cavity
• back of nose is called olfactory epithelium
  • patch of skin that’s key to smell
  • has a layer of olfactory receptor cells
    • special neurons → scent smells like the taste buds of your nose
• olfactory epithelium → layer of mucus
• dog’s epithelium is 20 times bigger than human
• brain has 40 million different olfactory receptor neurons
• only neuron in the body that gets replaced regularly every 4 to 8 weeks
• olfactory tracts → bundle through the brain
• olfactory → relating to sense of smell
• epithelium → the small outer layer of skin

The nervous system

nervous system →body system that sense the environment and controls actions

• one nerve will send one type of message from the brain
• another nerve sends message back to the brain

central nervous system

• consists of brain and spinal chord
• ‘co-ordinate’ muscles and brains

peripheral nervous sytem

• all other nerves coming out from central nervous stem
• everything else coming out
• everything else coming from the central point
• spread out through the entire body
• relay information to all parts of the body

nerve

• send messages to and from the brain

neurons and nerve are the same thing

• transmit messages in the form of electrical signals to and from, and within the central nervous system

neurons generally have the same structure

• cell body → where the nucleus is located

• dendrites → branches that receive messages

• axon → a thread-like structure that carries impulses to other neurons

• myelin sheath → fatty layer that insulates axon and sometimes dendrite, protect the axon

• tentacles → dendrites

• small dot is the nucleus

• long tail is called the axon

Neurons

Sensory neuron

sensory neuron: transmits messages from sensory organs to the central nervous system

• cell body is in the middle
• cell body doesn’t have dendrites attached to it

Interneurons

interneuron: transmits messages from sensory neurons to motor neurons

• located in the spinal cord

Motor neurons

motor neuron: transmits messages from the central nervous system to “effectors” such as muscles and glands to initiate a response

Axon terminal

Axon terminal: located at the end of a neuron and contains vessels that releases neurotransmitters (chemicals) that travel across the synapse

Synapse

synapse: very small gap between neurons

• Neurons do not touch each other - they have synapses between each other
• message is transmitted chemically

Receptors

there are five primary receptors in the body, related to senses

Chemoreceptors

• sensitive to chemicals
• odour molecules in the air
• located in the nose and tongue

Thermoreceptors

• snesitive to heat changes
• located in the skin
• temperature change

Mechanoreceptors

• sensitive to touch, pressure, sound and motion
• skin, inner ear and muscles

Photoreceptors

• sensitive to light
• located in eyes

stimulus → input

• may come via your senses

Stimulus response pathway