The nervous system and endocrine systems

• The nervous system


  The nervous system is a specialised network of cells, consisting of the central nervous system and peripheral nervous system. It communicates using electrical signals and serves two main functions, to collect, process and respond to information in the environment, and to co-ordinate the working of different organs and cells in the body.
• The Central Nervous system


  The central nervous system consists of the brain and spinal chord.
• The brain


  The brain is the centre of all conscious awareness. Its outer layer is the cerebral cortex, 3mm thick and is only found in mammals.

  It is highly developed in humans and is what distinguishes our higher mental functions from those of other animals. Only a few things e.g. sponges, or jellyfish, do not have brains.
• The spinal cord


  The spinal cord is an extension of the brain. It passes messages to and from the brain and connects the nerves to the PNS. It is also responsible for reflex actions such as pulling your hand away from a hot surface.
• The peripheral nervous system


  The PNS transmits messages via millions of neurons, to and from the CNS. The PNS is divided into the Automatic nervous system and the somatic nervous system.
• The automatic nervous system


  Part of the PNS, the ANS governs vital functions in the body such as breathing, heart rate digestion, sexual arousal and stress responses
• The somatic nervous system


  Part of the PNS, the SNS governs muscle movement and receives information from sensory receptors.
• The endocrine system 


  The endocrine system works more slowly than the nervous system, but has widespread powerful effects, It is a system of glands that release hormones into the bloodstream and affect any cell in the body with a receptor for that particular hormone. Most hormones affect cells in multiple organs, leading to diverse and powerful responses. For example, the thyroid releases thyroxine which affects the heart, and cells throughout the body increasing metabolic rates and effecting growth rates.
• The pituitary gland


  Known as the 'master gland' the pituitary gland is located in the brain and controls the release of hormones from all other endocrine glands in the body.
• Gland


  a gland is an organ in the body that synthesises substances such as hormones
• Hormone


  a biochemical substance that circulates in the blood and affects target organs.
• Fight or Flight Response

  The endocrine system and ANS often work together. When a stressor is identified, the hypothalamus activates the pituitary gland and triggers activity in the sympathetic branch of the ANS. The ANS goes from a parasympathetic state to a sympathetic one. Adrenaline is released from the adrenal medulla triggering changes necessary for flight or fight. This is an automatic response. Once the threat has passed, the parasympathetic system returns the body to its resting state. Its actions are antagonistic to the sympathetic system.
• Parasympathetic system


  The parasympathetic system is part of the ANS and returns the body to its natural parasympathetic state after arousal. Its actions e.g. decreasing heart rate, stimulating digestion, constricting pupils, are antagonistic (opposite) to the sympathetic nervous system, reducing activity in the body. It is also referred to as the rest and digest response.
• Sympathetic system


  Responsible for the state of arousal in the flight or fight. The sympathetic state is characterised by increased heart rate, increased breathing rate, dilated pupils, inhibited digestion, inhibited saliva production and contracted rectum.