Neurons & Neurotransmission

• (AO1) What are the 3 main types of neurons?

  Sensory, Motor and Relay
• (AO1) Where are sensory neurons found? What is their function? What is their structure?

  Found = Receptors (eyes, ears, tongue, skin)

  
  

  Function:

  1)Carry information from sensory receptors to CNS.

  How: = When nerve impulses reach brain, translated into 'sensations' (vision, hearing, taste, touch). HOWEVER, not all sensory neurons reach brain, as some neurons stop at spinal cord for quick reflex actions.

  
  

  Structure = Cell body always located in middle of axon
• (AO1) Where are motor neurons found? What is their functions? What is their structure?

  Found = CNS

  
  

  Functions:

  1)Carry messages from the CNS to organs and muscles in the body

  2)Control muscle movements

  How = When motor neurons are stimulated, they release neurotransmitters that bind to receptors on muscles to trigger a response = leads to a movement.

  
  

  Structure = has a traditional neuron shape.
• (AO1) Where are relay neurons found? What is their functions? What is their structure?

  Found = Between sensory input and motor output / response (found in brain and spinal cord)

  
  

  Functions:

  1)Carry messages from one part of the CNS to another.

  2)They connect sensory and motor neurons - communicate

  Structure = No cell body, no myelin sheath, long axon
• (AO1) Draw out a sensory, motor and relay neuron

  Diagrams:

  A) Receptor Cell

  B) Axon

  C) Myelin sheath

  D) Cell body

  E) Dendrite

  F) Cell body

  G) Axon

  H) Pre synaptic terminal

  I) Dendrite

  J) Cell body

  K) Axon

  L) Myelin sheath

  M) Neurofibril Node

  
• (AO1) Define the first 4 processes of neurotransmission

  This is the process of neurons communicating, messaging one neuron to another.

  
  

  1)Info is passed down the presynaptic neuron by the axon as electrical impulses known as action potential.

  
  

  2)At the end of the neuron (in the axon terminal) are synaptic vessels which contain chemical messengers known as neurotransmitters.

  
  

  3)When electrical impulses (action potential) reach the synaptic vessels, they release their content of neurotransmitters.

  
  

  4)The neurotransmitters then diffuse and carry the signal across the synaptic gap
• (AO1) Define the last 2 processes of neurotransmission

  5)They then bind to receptors on the post synaptic cell that then become activated

  6)Once the receptors have been activated, they either produce excitatory or inhibitory effects on the post synaptic cell
• (AO1) Define excitatory and inhibitory

  At the post synaptic neuron, a net total of the neurotransmitters is taken, which determines whether the neuron will fire.

  
  

  If the sum total is excitatory (e.g. noradrenaline), an excitatory post synaptic potential (ESPS) occurs = making the post synaptic cell MORE likely to fire.

  
  

  If the sum total is inhibitory (e.g. GABA), an inhibitory post synaptic potential (ISPS) occurs = making the post synaptic cell LESS likely to fire.
• Function of neuron parts

  Dendrite = receives signals from other neurons

  
  

  Myelin sheath = insulates the axon & speeds up transmission of the electrical impulse

  
  

  Gaps in myelin sheath (only in motor) = nodes of Ranvier (neurofibril nodes) = allows impulse to jump along the axon

  
  

  Cell body = contains the nucleus

  
  

  Receptor cell (only in sensory)= responsible for detecting stimuli from the environment (e.g. light, sound, touch, temperature). When stimulated by a specific environmental change, generates an electrical impulse that travels along the sensory neuron and to the CNS, where info is processed

  
  

  Presynaptic terminal (only in relay) = stores and releases neurotransmitters. When electrical impulse arrives at terminal, it triggers release of neurotransmitters into and across synaptic gap. These chemicals then bind to receptors on postsynaptic neuron
• What is the function of the axon

  It carries the electrical impulse away from the cell body and to the exon terminal.

  This allows communication between neurons or neurons to an effector (e.g. muscle or gland).