Structure and Function of Sensory, Relay and Motor Neurons

• there are 100 billion neurons in the human nervous system, 80% of which are located in the brain
• Neurons - conduct nerve impulses by transmitting signals electronically and chemically with primary means of communication
• Dendrites - receive signals from neurons or other receptor cells and are typically connected to the cell body
• Axon - A long slender fibre that carries nerve impulses in the form of electrical signals known as action impulses
• Myelin Sheath - most axons are surrounded by myelin sheath which insulates the axon so that the electrical impulses travel faster along the axon
• Axon terminal - connects neurons to other neurons or organs, using a process called synaptic transmission
• Sensory Neuron - found in receptor cells and carry nerve impulses to the brain and spinal cord by translating them into 'sensations' (5 senses)

  • some neurons stop at the spinal cord allowing for quick reflex actions (knee jerk)
• Relay Neurons - found between sensory input and motor responses. They are found in the brain and spinal cord and allow sensory and motor neurons to communicate
• Motor Neurons - found in the Central Nervous System (CNS) and control muscle movements. When stimulated, they release neurotransmitters that bind to the receptors on muscle to trigger a response
• Synaptic Gap - Each neuron is separated from the next by a small gap called a synapse - this is the conjunction of the end of the axon of one neuron and the dendrite or cell body of another neuron
• Fight or Flight Process:

  • stressful/dangerous situations entered
  • Amygdala activation, sending distress signals to hypothalamus
  • hypothalamus activates the Sypathomedually (SAM) Pathway, stimulating the adrenal medulla and Sympathetic Nervous System
  • Adrenal Medulla secretes adrenaline and noradrenaline causing physiological changes
• Physiological Changes during F/F:

  • Increased heart rate - increase blood flow and adrenaline to body
  • Increased breathing rate - increase oxygen intake per breath
  • Pupil dilation - increase light intake and vision
  • Sweat production - regulate temperature
  • reduce non essential fluids (saliva) - increase energy for essential organs
• Response to chronic (ongoing) stressors: if the brain continues to perceive something as a job (eg. a stressful job) a second system kicks - the HPA axis

  • Hypothalmus
  • Pituitary gland
  • Adrenal gland
• HPA (H) - the hypothalamus releases a chemical messenger corticotrophin releasing hormone (CRH) into the bloodstream
• HPA (P) - on arrival to the pituitary gland, CRH causes the pituitary to release adrenocorticotrophic hormone (ACTH), then transported to the adrenal gland via the bloodstream
• HPA (A) - ACTH stimulates the adrenal cortex releasing stress related hormones eg. cortisol, responsible for several fight or flight responses. some are positive (quick bursts of energy), and some are negative (lowered immune system)
• why may F/F be unhelpful today:

  • F/F triggers, adrenaline
  • Sweat, quick reaction time etc
  • unhelpful during real life task and fighting irl isn't good