Nervous system & Key Defs

• 85,000 neurons die everyday.
• The nervous system is a specialised network of cells in the human body. Primary internal communication system. Collect, process and respond to info in environment. Coordinate working of different organs and cells.
• Peripheral nervous system

  1. Autonomic nervous system - sympathetic nervous system, parasympathetic nervous system
  2. Somatic nervous system
• Somatic nervous system: carries sensory and motor info - 12 pairs of cranial nerves and 31 pairs of spinal nerves.
• Autonomic nervous system: governs vital functions - breathing, heart rate, digestion, sexual arousal, stress responses. Sympathetic = fight or flight. Parasympathetic = calms body down
• Sympathetic nervous system: gut slows digestion, salivary glands inhibit saliva, increased heart rate, liver stimulates glucose production, eye dilates pupils, lungs dilate bronchi. The parasympathetic does the opposite of all above.
• 1. Stimulus - hammer hitting knee
  2. Detected by sense organs in the peripheral nervous system
  3. Conveys a message along a sensory neuron
  4. Message reaches CNS
  5. Connects with a relay neuron
  6. Transfers back to a motor neuron
  7. Carries the message to an effector such as a muscle
  8. Causes the muscle to contract
  9. The knee jerks
• Synapse: the gap between the end of one neuron and the dendrites of the next neuron
• Action potential: process of the neurotransmitters firing. Crosses between presynaptic and postsynaptic neuron
• Neurotransmitters: chemicals released from a synaptic vesicle into the synapse by neurons. Neurotransmitters are reabsorbed into terminal buttons via reuptake, or they are broken down by an enzyme.
• Excitatory: more chance of next neuron firing.
• Inhibitory: less chance of next neuron firing.
• STAGES OF SYNAPTIC TRANSMISSION:

  1. Nerve impulses travel down axon
  2. Nerve impulses reach synaptic terminal
  3. This triggers the release of neurotransmitters
  4. The neurotransmitters are fired into the synaptic gap
  5. Neurotransmitters bind with receptors on the dendrite of the post-synaptic neuron
  6. If successfully transmitted, the neurotransmitter is taken up by the post-synaptic neuron
  7. The message will continue to be passed in this way via electrical impulses
• Central nervous system: made up of the brain and the spinal cord. The CNS (via the spinal cord) passes messages to and from the brain and connects nerves to the peripheral nervous system
• Sensory neurons: carry impulses from the PNS receptors (e.g. pain receptors in the skin) to the CNS. Long dendrites, short axons
• Relay neurons: carry impulses from sensory nerves to motor neurons. Short dendrites and short axons.
• Motor neurons: carry impulses from CNS to effector (e.g. muscles of glands). Short dendrites and long axons.
• Lateralisation: the idea that the two halves of the brain are functionally different and certain processes or behaviours are controlled by one hemisphere rather than the other. For example, the right side of the brain processes information from the left visual field, and vice versa.
• Commissurotomy: a solution for epilepsy - because it is caused by heightened, random neuron firing, surgeons can sever the connective tissue between the right and left hemispheres. Some of the side effects are split-brain thinking.
• Split brain thinking: the left hemisphere will understand what is being told, but won't be able to draw a picture of it. The right hemisphere will not be able to convert an image into linguistics, but they can draw a picture of it and then identify it.
• Neuroplasticity: mould to new information, scenarios, situations, environments etc.
• Synaptic pruning: what to retain, what to displace. The connections are lost.
• Bridging: where new connections are created due to use and new stimulus
• Axonal sprouting: healthy axons sprout new nerve endings that connect to other pathways in the nervous system. This can be used to strengthen existing connections or to repair damaged parts of the nervous system by repairing damaged conditions.
• Biological rhythms: distinct patterns of changes in body activity that conform to cyclical time periods. They can be influenced by internal body clocks or external changes to the environment.
• Ultradian rhythm: more than once in a 24 hour cycle (like a baby sleeping)
• Circadian rhythm: a type of biological rhythm that operates along a 24 hour cycle. This regulates a number of bodily processes such as the sleep/wake cycle and core body temperature.
• Infradian rhythm: less than once in a 24 hour cycle - such as hibernation or menstruation.
• Endogenous pacemakers: internal cues that influence our body clock, such as the suprachiasmatic nucleus.
• Exogenous zeitgebers: external cues that influence our body clock (light, sound temperature)
• Suprachiasmatic nucleus: found in hypothalamus. Registers light etc. and inhibits or stimulates the release of melatonin.