Biopsych

• nervous system:

  • is a specialised network of cells and our primary communication system - it is based on electrical and chemical signals, whereas endocrine system based on hormones
  • has 2 main functions:
  • first function - to collect, process and respond to info in environment
  • second function - to co-ordinate the working of diff organs and cells in the body
• CNS:

  • made up of brain and spinal cord
  • outer layer of brain - cerebral cortex is highly developed in humans and is what distinguishes our higher mental functions from those of animals
  • the brain is divided into 2 hemispheres
  • spinal cord= extension of the brain and responsible for reflex actions
  • spinal cord passes messages to and from the brain and connects nerves to PNS
• PNS:

  • pns transmits messages, via millions of neurons to and from nervous system
  • further subdivided into ANS AND SNS
  • ANS: autonomic nervous system governs vital functions in body like breathing, stress responses, heart rate (further subdivided into sympathetic and parasympathetic nervous system)
  • SNS: somatic nervous system governs muscle movement and receives info from sensory receptors
• endocrine system

  • works alongside the nervous system to control vital functions in the body through the actions of hormones
  • it works more slowly that nervous system but has widespread and longer lasting effects
  • glands- organs in body that produce hormones (key- pituitary gland 'master gland' as it controls release of hormones from all the other endocrine glands in body)
  • hormones - secreted in bloodstream and affects any cell in body that has receptor for that particular hormone (thyroxine produced by thyroid, affects cells in heart)
• Endocrine system and ANS work together (stressful event):

  • stressor perceived by hypothalamus which activates pituitary
  • the sympathetic nervous system is now aroused
  • adrenaline (stress hormone) is released from adrenal medulla into bloodstream - this delivers the aroused state causing changes in target organs in the body (e.g. increase heart rate, digestion of pupils, less saliva)
  • immediate and automatic - this response happens when threat is perceived
  • parasympathetic nervous system (Rest and digest) takes over once threat has passed - returns body to resting state
• • sympathetic state - increased heart rate, increased breathing rate, dilated pupils, inhibited digestions, stops saliva
  • parasympathetic state - decreased heart rate, decreased breathing rate, constricts pupils, normal digestion and saliva
• neurons - 100 billion nerve cells (neurons) in the human nervous system

  80% of which are located in brain

  by transmitting signals electrically and chemically, these provide the nervous system with its primary means of communication
• 3 types of neurons:

  • sensory: carry messages from PNS to CNS - they have long dendrites and short axons - located in PNS
  • relay: connect sensory neurons to motor neurons - they have short dendrites and short axons - most are in brain and visual system
  • motor: connect CNS to effectors like muscles and glands - have short dendrites and long axons - may be in CNS and PNS
• structure of neurons are all the same:

  • cell body: includes nucleus which contains genetic material of the cell
  • dendrites: branchlike structures that protrude from cell body - carry nerve impulses from neighbouring neurons towards cell body
  • axon: carries electrical impulse away from the cell body down the length of the neuron (covered in fatty layer of myelin sheath that protects axon)
  • terminal buttons at the end of the axon communicate with the next neuron in the chain across a gap called synapse
• electrical transmission:

  • when a neuron is in resting state, the inside of cell is negatively charged compared to the outside
  • when neuron is activated, the inside of cell becomes positively charged causing action potential to occur
  • this creates an electrical impulse that travels down the axon towards end of neuron
• a synapse: each neuron is separated from the next by an extremely tiny gap called synapse
• chemical transmission:

  • signals within neurons are transmitted electrically but signals between neurons are transmitted chemically across the synapse
  • when the electrical impulse reaches the end of the neuron, it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles
  • once neurotransmitter crosses gap, its taken up by postysynaptic receptor site on the next neuron, so the impulse only ever travels in 1 direction
  • the chemical message is converted back into an electrical impulse and the process of electrical transmission begins
• neurotransmitters are chemicals that diffuse across the synapse to the next neuron in the chain - each neurotransmitter has its own specific molecular structure that fits perfectly into a postsynaptic receptor site like a lock and key - each has its own functions
• excitation and inhibition:

  neurotransmitters generally have either an excitatory or inhibitory effect on the neighbouring neuron.

  • adrenaline - generally excitatory, increasing the positive charge of the postsynaptic neuron; making it more likely the postsynaptic neuron will fire
  • serotonin - generally inhibitory, increasing the negative charge of the postsynaptic neuron, making it less likely the postsynaptic neuron will fire
  • dopamine is an unusual neurotransmitter as its equally likely to have excitatory or inhibitory effects on the postsynaptic neuron
• summation: excitatory and inhibitory influences influences are summed and must reach a certain threshold in order for the action potential of the postsynaptic neuron to be triggered

  if the net effect of the neurotransmitters is inhibitory then the post synaptic neuron is less likely to fire. it is more likely to fire if the net effect is excitatory