Biopsych

• Nervous system


  A special network of cells that is our primary internal communications system
• Functions of the nervous system

  • To collect, process and respond to environmental information
  • To coordinate the organs and cells
• Central nervous system (CNS)


  Made up of the brain and spinal cord
• Brain


  • The brain's outer layer, the cerebral cortex, is highly developed in humans and distinguishes our higher intelligence from other animals
• Spinal cord


  An extension of the brain responsible for reflexes
• Peripheral nervous system (PNS)


  Transmits messages, via millions of neurons, to and from the central nervous system
• Subsystems of the PNS

  • Somatic nervous systems (controls muscle movements and receives information from sensory receptors)
  • Autonomic nervous system (controls bodily functions e.g. breathing, heart rate, arousal)
• Sympathetic nervous system


  Increases bodily activity, quick
• Parasympathetic nervous system


  Decreases bodily activity, slow
• Endocrine system


  Instructs glands to release hormones directly into the bloodstream
• Gland


  Organ in the body that releases substances such as hormones
• Hormones


  Chemical substances that circulate the bloodstream, only affecting target organs. Produced in large quantities and have powerful effects
• Fight or flight response


  The way an animal responds when stressed. The body becomes physiologically aroused in readiness to fight the aggressor or flee
• Adrenaline


  Hormone produced by adrenal glands that are a part of the stress response. Has strong effects on the cardiovascular system - fast heart rate, contracting blood vessels, dilating air passages
• The endocrine system works alongside the nervous system to control vital functions in the body
• The endocrine system is much slower than the nervous system but has a widespread and powerful effect
• Thyroxine


  Impacts the heart cells (increase heart rate) and metabolic rates and, in turn, affects growth rates
• Pituitary gland


  The major endocrine gland, located in the brain, which controls the release of hormones from all other glands in the body
• Fight or flight response

  1. Part of brain called the amygdala (in limbic system) sends distress signal to hypothalamus which triggers activity in sympathetic branch of the ANS

  2. ANS changes from normal resting state (parasympathetic state) to physiologically aroused (sympathetic state)

  3. Adrenaline is released from adrenal medulla

  4. Adrenaline triggers physiological changes in the body (increased heart rate) which creates physiological arousal necessary for fight or flight response

  5. Once the threat has passed, the PNS returns the body to its resting state
• Sympathetic state (accelerate)


  • Increases heart rate
  • Increases breathing rate
  • Dilated pupils
  • Inhibits digestion
  • Inhibits saliva production
  • Contracts rectum
  • Glucose is released
• Parasympathetic state (break)


  • Decreases heart rate
  • Decreases breathing rate
  • Constricts pupils
  • Stimulates digestion
  • Stimulates saliva production
  • Relaxes rectum
  • Glucose is stored
• Neuron


  The basic building blocks of the nervous system, neurons are nerve cells that process and transmit messages through electrical and chemical signals
• Types of neurons


  • Sensory neurons (carry messages from the PNS to the CNS)
  • Relay neurons (connect the sensory neurons to the motor or other relay neurons)
  • Motor neurons (connect the CNS to the effectors such as muscles and glands)
• Sensory neurons


  • Long dendrites and short axons
• Relay neurons


  • Short dendrites and short axis
• Motor neurons


  • Short dendrites and long axons
• Structure of a neuron

  • Cell body (contains the nucleus which holds genetic material)
  • Dendrites (branch-like structures that protrude from the cell body)
  • Axon (carries impulses away from the cell body, in the form of an electrical signal called action potential, down the length of the neuron. This is covered in a fatty layer of myelin sheath)
  • Myelin sheath (protects the axon and speeds up electrical transmission of the impulse. It being too long would have the opposite effect so there are gaps called the nodes of Ranvier)
  • Nodes of Ranvier (speed up transmission of the impulse by forcing it to jump across the gaps along the axon)
  • Axon terminal (the end of the axon. Communicate with the next neuron in the chain, across the synapse)
• How a neuron works

  1. The cell body has a nucleus containing DNA

  2. Information travels by electrical impulse

  3. The axon extends from the cell body to the synaptic terminal. It is covered in a fatty layer called the myelin sheath, each cell is called a Schwann cell and the part where the axon is exposed is called a Node of Ranvier

  4. The synaptic terminal contains synaptic vesicles (sacs containing neurotransmitters)
• Electric transmission


  When a neuron is in a resting state the inside of the cell is negatively charged compared to the outside. When a neuron is activated by a stimulus, the inside of the cell becomes positively charged for a split second causing an action potential to occur. This creates an electrical impulse that travels down the axon towards the next neuron
• Synaptic transmission


  The process of the neighbouring neurons communicating with each other by sending chemical messages across the synaptic cleft
• Neurotransmitter


  Brain chemicals that are released to relay signals across the synapse
• Excitation


  The neurotransmitter increases the positive charge of the postsynaptic neuron, increasing the likelihood that the neuron will fire and pass on the electrical impulse
• Inhibition


  The neurotransmitter making the postsynaptic neuron more negative, decreasing the likelihood that the neuron will fire and pass on the electrical impulse
• Chemical transmission - synapse


  1. When the electrical impulse reaches the end of the neuron (presynaptic terminal), it triggers the release of neurotransmitters from synaptic vesicles

  2. These then diffuse across the synaptic cleft (gap) to the postsynaptic neuron

  3. When released the neurotransmitters have to be taken up immediately by the postsynaptic neuron or it will be reabsorbed by the presynaptic neuron from which it was released

  4. If successfully transmitted, the impulse is then carried along the postsynaptic neuron until it reaches the next synapse
• Summation


  The addition of positive and negative post-synaptic potentials. A nerve cell can receive both EPSPs and IPSPs simultaneously. The EPSPs and IPSPs are summed and if the net effect on the postsynaptic neuron is inhibitory, the neuron will be less likely to fire and if the net effect is excitatory, the neuron will be more likely to fire
• Localisation of function


  Theory that different areas of the brain are responsible for different behaviours, processes or activities
• Localised brain functions


  • Motor area (frontal lobe, regulating movement)
  • Somatosensory area (parietal lobe, processing sensory information)
  • Visual area (occipital lobe, receiving and processing visual information)
  • Auditory area (temporal lobe, analysing speech-based information)
  • Broca's area (frontal lobe (left hemisphere), speech production)
  • Wernicke's area (temporal lobe (left hemisphere), language comprehension)
• Pre 19th century, scientists believed a holistic theory of the brain - all areas were involved in the processing of thought and action
• Broca and Wernicke argued for localisation of function
• If a certain area is damaged through illness or injury, the functions associated with that area will be affected