The nervous system

• The central nervous system (CNS)


  consists of the brain and spinal cord
• The brain (CNS)


  1)The centre of all conscious awareness

  2)Consists of a left and right hemisphere

  3)Is surround by an outer layer the cerebral cortex which is 3mm thick (only in mammals)
• spinal cord (CNS)


  1) an extension of the brain

  2) passes messages to and from the brain via electrical impulses

  3) connects nerves to the peripheral nervous system (PNS)

  4) responsible for reflex actions
• The nervous system


  A specialised network of cells in the body

  2) primary internal communication system via electrical and chemical signals

  3) divided into the peripheral and central nervous systems
• The nervous system has two main functions


  1. To collect, process and respond to information in the environment

  2. To co-ordinate the working of different organs and cells in the body
• The peripheral nervous system


  Transmits messages to and from the CNS and body
• The PNS is subdivided into the


  1) somatic (voluntary), governs muscle movement and conscious activity (e.g reading )receives info from sensory receptors

  2) autonomic (involuntary), governs breathing heart rate sexual arousal and other vital functions in the body enteric nervous systems
• The ANS is subdivided into the


  1) sympathetic (NS) prepares for action fight or flight

  2) parasympathetic (NS) calms the body , rest and digestive system
• The structure neurones


  1.cell body (soma) — contains a nucleus

  2.Dendrite(s)

  3.Axon(s) and terminal buttons

  4.myelin sheaths and nodes of ranvier
• Role of the axon and the dendrite


  D- carry impulses from neighbouring neurones towards the cell body

  A- carry impulses AWAY from the cell body towards terminal buttons (synaptic knob)
• Myelin Sheath and Nodes of Ranvier


  MS - a fatty layer that cover axons , provides protection and speeds up e- impulse transmission

  They have gaps NoR that speed the impulse by forcing it to jump along the gaps ( if the MS was continuous the impulse would be slower)
• Motor neurones (structure


  Cell body oriented to either end of cell covered in small dendrites and one long axon that goes into many axon terminals

  - myelinated
• Relay neurone (structure


  Cell body with a cell body with small dendrites and a longISH axon

  - not typically myelinated
• sensory neurones ( structure


  Cell body oriented in the middle of the neurone and has long axon on one end and long dendrite on the other

  - myelinated
• location of neurones : motor


  Cell body may be in the CNS but the long axons form part of the PNS
• Location of neurone relay


  Make 97% of all neurones

  Typically found in the brain or visual system
• Location of neurone sensory


  Located outside the CNS

  In the PNS in ganglia ( clusters )
• synaptic transmission


  Neighbouring neurones communicate with each other via neurotransmitters that diffuse across a synapse
• How do neurotransmitters travel


  Impulses become neurotransmitters

  Held in vesicles in the presynaptic nerve terminals

  Travel across a synapse

  To the post synaptic receptor sites on a dendrite of a neighbouring nerve cell
• Excitatory neurotransmitters


  E - neurotransmitters such as adrenaline increases the positive charge of the postsynaptic neurone making it more likely the postsynaptic neurone passes the impulse
• inhibitory neurotransmitters


  E.g serotonin

  Increase the postsynaptic neurones negative charge

  Decreasing the likelihood of the PS neurone passing the impulse on
• Describe the structure of neurotransmitters and postsynaptic receptor sites


  Each neurotransmitter has its own specific molecular shape that fits perfectly into a PS knob similar to the lock and key of enzymes