the nervous system

• the two main functions of the nervous system is to control the body and to sense the environment
• the two subsystems of the nervous system are the central nervous system and the peripheral nervous system
• the central nervous system is made of the brain and the spinal cord
• the peripheral nervous system transmits messages via neurons to and from the central nervous system
• the PNS is made of the autonomic nervous system and the somatic nervous system
• the autonomic nervous system controls involuntary actions e.g breathing, heart rate etc
• the somatic nervous system controls voluntary actions such as muscle movement
• the ANS is divided into two subsystems: the sympathetic nervous system and the parasympathetic nervous system
• the sympathetic nervous system gets the body ready for action - fight of flight
• the parasympathetic nervous system helps the body restore to normal conditions and calm down - rest and digest
• examples of the sympathetic nervous system is increased heart rate, dilated pupils and inhibits saliva production
• examples of the parasympathetic nervous system are decreased heart rate, constricted pupils and stimulates saliva production
• a difference between the autonomic nervous system and the somatic nervous system is that the ANS controls internal organs and glands, the SNS controls muscles and movement
• there are three types of neuron: sensory, relay and motor
• sensory neurons carry information from receptors to the CNS
• relay neurons connect sensory and motor neurons
• motor neurons carry impulses away from the CNS to effectors (muscles or glands)
• the cell body of a neuron includes the nucleus which holds the genetic information
• the dendrites carry impulses from other neurons towards the cell body
• axons carry impulses away from the cell body
• the myelin sheath protects the axon and speeds up the electrical information
• the nodes of Ranvier are gaps between the myelin sheath which speeds up transmission as the action potential jumps along the axon
• a synapse is where two neurones meet, one sends an impulse across the gap to another neurone
• step 1 of synaptic transmission: electrical impulse (action potential) reaches presynaptic nerve terminal which contains neurotransmitters
• step 2 of synaptic transmission: the release of neurotransmitters from the synaptic vesicles
• step 3 of synaptic transmission: the neurotransmitter diffuses across the synaptic cleft (gap) and binds with receptors on the postsynaptic membrane
• the synapse is the point where one neuron (presynaptic) can send a chemical message to an adjacent neuron (postsynaptic)
• neurotransmitters are chemical messages released by synaptic vesicles, these can perform an excitatory or inhibitory function
• the direction of travel can be only one way, due to the neurotransmitters being released from the presynaptic neuron and received to the postsynaptic neuron through receptors (uni-directional)
• excitatory neurotransmitters increase the likelihood of a new action potential forming in the postsynaptic cell - this is because they make the electrical charge more positive and are more likely to fire. this is called depolarisation
• inhibitory neurotransmitters decrease the likelihood of a new action potential forming in the postsynaptic cell - this is because they make the electrical charge more negative and are less likely to fire. this is called hyperpolarisation
• summation is the combined effect of the excitatory and inhibitory neurotransmitters influence on the post synaptic neuron. if the threshold is reached, a new action potential will form in the postsynaptic cell
• reuptake is where neurotransmitters are reabsorbed into the presynaptic cell after transmitting a neural impulse

  this happens at transport proteins and prepares the cell to fire again
• psychoactive drugs interfere with the system to achieve their effects by inhibiting or increasing the transmission of certain neurotransmitters e.g SSRIs block the reabsorption of serotonin to increase its level in the synapse
• cocaine also blocks the reabsorption of dopamine to increase its signal
• the muscle at the end of a neuron is called the effector, which is activated by the motor neuron
• the reflex arc is the pathway of the nervous system from the sensory neurone to the effector
• a neuron is a cell that carries electrical impulses around the body, allowing for communication within the nervous system