Paper 2

• Divisions of the nervous system

  • Human nervous system
  • Central nervous system (CNS)
  • Peripheral nervous system (PNS)
  • Automatic nervous system (ANS)
  • Somatic Nervous system (SNS)
  • Sympathetic system
  • Parasympathetic system
• Human nervous system


  Body wide system of nerve cells that collects information from the world, processes this info and then takes action by directing body organs and muscles via transmissions of electro chemical messages
• Central nervous system (CNS)

  Involves complex processing, includes the brain for all conscious and most unconscious processing and the spinal cord which receives and transmits information and some reflex processing
• Peripheral nervous system (PNS)

  Body wide network of messenger neurons take info away from the CNS
• Automatic nervous system (ANS)

  The part of the PNS that controls actions of internal glands, is an involuntary system (not under conscious control)
• Somatic Nervous system (SNS)


  The part of the PNS that controls skeletal muscles, it is a voluntary system (under conscious control)
• Sympathetic system


  Part of the ANS that increases bodily activities, releases noradrenaline, activities in fight/flight response, increased heart/sweat/breathing rate, dilates pupils
• Parasympathetic system

  Part of ANS that decreases bodily activities, releases acetylcholine, activates in rest (Rest and digest), decreased heart/sweat/breathing rates, constricts pupils
• The endocrine system


  • Pituitary gland
  • Hypothalamus
  • Pineal gland
  • Thyroid gland
  • Thymus gland
  • Pancreas
  • Adrenal glands
  • Ovaries
  • Testicles
• Endocrine system


  Collection of glands around the body that regulate bodily functions, growth, and psychological factors by releasing chemical messengers called hormones in the blood
• Glands, hormones they produce, and effects

  • Pituitary gland (ACTH) controls releases of hormones from other glands
  • Hypothalamus (CRH) links nervous system to endocrine system
  • Pineal gland (Melatonin) modulates sleep pattern, keeping body to day/night rhythm
  • Thyroid gland (Thyroxine) modulates metabolism
  • Thymus gland (Thymosin) stimulates development of T cells in immune system
  • Pancreas (Insulin) regulates blood sugar levels
  • Adrenal glands (Adrenaline) regulates effects of fight or flight response
  • Ovaries (Oestrogen) develops secondary characteristics in females
  • Testicles (Testosterone) leads to development of secondary sexual characteristics in males
• Types of neurons


  • Sensory neuron
  • Relay neuron
  • Motor neuron
• Sensory neuron


  Detects sensations (e.g. pain) at sensory receptors, action potential travels across nerve passing along the myelinated axon, then the electrical signal is converted into a chemical signal to cross the synapse
• Relay neuron


  After synaptic transmission, a new action potential forms in the dendrites, this neuron is in the spine, and sends a signal to the CNS but also immediately sends a signal along its axon to the motor neuron
• Motor neuron


  Detects the signals from the relay neuron via synaptic transmission and passes this signal along its own myelinated axon to stimulate an effector (e.g. muscle group in the arm moving away from the source of the pain)
• Stages of synaptic transmission

  • Action potential travels down axon of presynaptic neuron
  • Vesicles containing neurotransmitters merge with cell membrane and release neurotransmitter into synaptic cleft
  • Receptors on postsynaptic neuron detect neurotransmitters, changing chemistry within postsynaptic neuron
  • Neurotransmitters detach from receptors and return to presynaptic cell via transport protein (reuptake)
• Synapse


  Structure at the end of a nerve cell (neuron) that allows neurons to communicate by passing on chemical signals, this process is called synaptic transmission
• Neurotransmitters

  Chemical messengers released by neurons, either excitatory (stimulate/make more likely) or inhibitory (make less likely) the development of an action potential in other (postsynaptic) neurons
• Excitation


  Excitatory neurotransmitters increase the likelihood of a new action potential forming in the postsynaptic cell, causing depolarisation
• Inhibition


  Inhibitory neurotransmitters decrease the likelihood of a new action potential forming in the postsynaptic cell, causing hyperpolarization
• Summation


  Combined effect of all inhibitory and excitatory influences, resulting in a new action potential forming or not
• Synaptic transmission is unidirectional - information can only be passed between the pre and postsynaptic neurons in one direction, due to the structure of the synapse
• Stages of the fight or flight response

  • Stressor detected by hypothalamus
  • HPA axis in endocrine system activated, pituitary gland releases ACTH, detected by adrenal cortex releasing cortisol
  • Hypothalamus activates sympathetic branch of ANS, adrenal medulla triggered via sympathetic Adrenomedullin pathway, releasing adrenaline
• Fight or flight response

  Evolutionary survival mechanism in response to a threat, primes the body and mind to extreme action, body returns to homeostasis after threat has passed
• Role of adrenaline


  Psychological effects include increased anxiety, attention and alertness, physical effects include increased blood flow to brain and skeletal muscles, decreased blood flow to skin, digestive and immune systems, dilated pupils, faster breathing rate
• The fight or flight response is maladaptive in the modern world, frequently triggered by stimuli that cannot be run away from or fought, resulting in acute stress and chronic stress-related illness
• Principles of brain localization

  • Localization of function - functions performed in distinct brain regions
  • Contralateral - each hemisphere controls opposite side of body
  • Hemispheric lateralization - each hemisphere specialized for different functions
• Motor cortex


  Voluntary muscle motor movements across the body, located at back of frontal lobe, contralateral, damage results in paralysis on opposite side of body
• Somatosensory cortex


  Receives sense impressions from around the body, located in front of parietal lobe, contralateral, damage results in loss of sensation and neglect on opposite side
• Broca's area


  Responsible for speech production, located in left frontal lobe, damage results in motor aphasia/difficulty producing fluent speech
• Wernicke's area


  Responsible for speech comprehension, located in left temporal lobe, damage results in sensory aphasia/difficulty understanding speech
• Auditory cortex


  Receives and processes sound information from ears, located in both hemispheres
• Visual cortex


  Visual processing, each hemisphere receives information from opposite visual fields, located in occipital lobe
• Case studies demonstrate loss of certain functions if damage is caused to particular brain areas, suggesting localization of functions
• Modern brain scanning techniques like fMRI support older research on language centers, showing activation in associated regions during language tasks
• Motor and somatosensory functions are highly localized, but systems like language are more distributed, and some functions like consciousness appear not to be localized at all
• Findings from split-brain research


  • Information presented to left hemisphere can be spoken, but not if delivered to right hemisphere
  • Right hemisphere is specialized for face recognition
• Split-brain research has had a fundamental impact on understanding the unity of consciousness and identity, suggesting the brain is a combination of separate intelligent processes working together
• Reasons for brain plasticity


  • Learning new skills
  • Developmental changes
  • Direct trauma to brain area
  • Indirect effects of damage like swelling
• Mechanisms of functional recovery

  • Synaptic pruning - strengthening of frequently used synapses, loss of unused synapses
  • Axonal sprouting - growth of new axons to connect adjacent neurons
  • Neural regeneration - growth of new neuronal cells
  • Denervation supersensitivity - remaining axons become more sensitive to compensate for loss