NS and Endocrine System

• The central nervous system (CNS)


  • The CNS is made up of the brain and spinal cord.
  • The CNS is connected to the rest of the body by the PNS.
• The somatic nervous system:

  • conscious and voluntary.
  • It is involved in the relay of sensory and motor information to and from the CNS. It consists of sensory and motor neurones.
• Sensory neurones:


  carry information from sensory receptors to the CNS and are afferent ("moving toward") fibres.
• Motor neurons :


  carry information from the CNS to the muscles of the body and are efferent ("moving away from") fibres.
• The autonomic nervous system:


  • controls our internal organs and glands
  • involuntary.
  • It is made up of sympathetic and parasympathetic divisions.
• The sympathetic nervous system:

  • involved in preparing the body for stress-related activities.
  • fight or flight
• The parasympathetic nervous system:

  • associated with returning the body to routine, day-to-day operations.
  • rest and digest
• Neurotransmitters


  Can be classified as either excitatory or inhibitory in their action because they have one of these two effects on the neighbouring neuron
• Inhibitory neurotransmitters


  • The neurotransmitter serotonin causes inhibition in the receiving neuron, resulting in the neuron becoming more negatively charged and less likely to fire
  • Inhibitory neurotransmitters are like the nervous system's "off switches" and are generally responsible for calming the mind and body inducing sleep and filtering out unnecessary excitatory signals
  • An inhibitory neurotransmitter binding with a postsynaptic receptor results in an inhibitory postsynaptic potential (IPSP), so is less likely to fire
• Excitatory neurotransmitters


  • Neurotransmitters like noradrenaline are excitatory; they are the nervous system's "on switches"
  • They cause excitation of the post synaptic neuron by increasing its positive charge and making it more likely to fire
  • It causes an electrical charge in the membrane of that cell resulting in excitatory post synaptic potential (EPSP) making it more likely to fire
• Likelihood of a cell firing

  1. A nerve cell can receive both EPSPs and IPSPs at the same time

  2. The likelihood of the cell firing is determined by adding up the excitatory and the inhibitory synaptic input

  3. The net sum of this calculation (summation) determines whether or not the cell fires
• Dopamine


  • Can be both an excitatory or inhibitory neurotransmitter depending on the receptor it binds to
  • Dopamine is associated with rewards as the brain releases it in response to pleasure
  • It is also responsible for movement co-ordination and is implicated in Parkinson's Disease
• Serotonin


  • Is an inhibitory neurotransmitter
  • It regulates mood, appetite and sleep
  • SSRI (Selective Serotonin Reuptake Inhibitors) relieve the symptoms of depression by increasing levels of serotonin in the brain
• The dopamine hypothesis


  • excess of the neurotransmitter dopamine in certain regions of the brain is associated with the positive symptoms of schizophrenia
• Nervous system


  Made up of the brain and the spinal cord
• Peripheral nervous system (PNS)

  Relays messages from the environment to the CNS, via sensory neurones, and from the CNS to effectors, via motor neurones
• Subdivisions of the PNS

  • Autonomic nervous system
  • Somatic nervous system

  
• Autonomic nervous system


  Controls involuntary, vital functions of the body, such as maintaining heart rates and breathing rates
• Somatic nervous system


  Receives information from sensory receptors belonging to each of the 5 senses, and results in effectors being stimulated by the CNS, via motor neurones

  
• Branches of the autonomic nervous system

  • Sympathetic
  • Parasympathetic
• Sympathetic and parasympathetic nervous systems

  Work as part of an antagonistic pair during the 'rest and digest' response, and are crucial in producing the physiological arousal needed to maintain the fight or flight response
• Sympathetic nervous system


  Increases heart rates, breathing rate, causes vasoconstriction and pupil dilation
• Parasympathetic nervous system


  Decreases heart rate, breathing rates, causes vasodilation and pupil constriction
• Endocrine system


  The main chemical messenger system of the body, where hormones are secreted into the bloodstream from glands, and then are transported towards target cells in the blood, with complementary receptors
• Pituitary gland


  Considered to be the 'master' gland because it controls the release of hormones from all other glands in the body
• Thyroid


  Releases the hormone thyroxine, which increases heart rate and therefore increases the rate of growth
• Adrenal gland


  Releases adrenaline which creates the physiological arousal preceding the fight or flight response, through increasing the activity within the sympathetic branch of the nervous system
• Inhibitory neurotransmitters


  Reduce the potential difference across the postsynaptic membrane through the closure of the voltage-dependent sodium ion channels, reducing the likelihood that an action potential will be generated
• Excitatory neurotransmitters


  Increase the potential difference across the postsynaptic membrane

  = more voltage-dependent sodium ion channels

  increasing the likelihood that an action potential will be generated
• Adrenaline


  Hormone released from the adrenal medulla in response to activation of the sympathomedullary pathway
• Effects of adrenaline


  • Increase heart rate
  • Constrict blood vessels, increasing rate of blood flow and raising blood pressure
  • Divert blood away from the skin, kidneys and digestive system
  • Increase blood to brain and skeletal muscle
  • Increase respiration and sweating
• General effects of adrenaline

  • Prepare the body for action, fight or flight
  • Increase blood supply/oxygen, to skeletal muscle