Bio-psych

• The nervous system

  The nervous system consists of the central nervous system (CNS) and the peripheral nervous system (PNS). Communications using electrical signals. It functions to collect, process and respond to information, and coordinate the working of organs and cells in the body.
• The central nervous system


  The CNS is made up of the spinal cord and brain. The brain is the centre of conscious awareness, its outer layer is the cerebral cortex and is 3mm thick, only found in mammals. It is highly developed in humans and is what distinguishes us from other animals and it is divided into hemispheres. The spinal cord is an extension of the brain. It passes messages to and from the brain and connects nerves to the PNS, as well as being responsible for reflexes.
• The peripheral nervous system

  The PNS transmits messages via millions of neurons to and from the CNS. It is divided into the Automatic nervous system (ANS) which controls vital functions such as breathing, heart rate, digestion and stress responses, and the Somatic nervous system (SNS) which controls muscle movement and receives information from sensory receptors.
• The endocrine system


  The endocrine system instructs glands to release hormones directly into the bloodstream. These hormones are carried to the target organs in the body. Communicates using chemicals. It is slower than the nervous system and includes glands such as the thyroid which releases thyroxine to regulate metabolism. The pituitary gland is known as the master gland located in the brain as it controls the release of hormones from all other glands in the body.
• Fight or flight


  The endo system and ANS work together, for example, in a stressful event, the stressor is identified by the hypothalamus, it activates the pituitary gland, which triggers activity in the sympathetic branch of the ANS. Adrenal medulla releases Adrenaline into the bloodstream and triggers physiological changes in the body e.g. increased heart rate for flight or flight. This happens automatically when threat is detected.
• Post-fight or flight


  Once the threat has passed the system returns to its resting state. The parasympathetic system is the opposite of the sympathetic and reduces activities that were increased by the sympathetic system. This is known as the 'rest and digest' response.
• Sympathetic state

  increased heart rate, increased breathing rate, dilated pupils, inhibits digestion, inhibits saliva production, contracts rectum
• Parasympathetic state


  Decreases heart rate, decreases breathing rate, constricts pupils, simulates digestion, stimulates saliva production, relaxes rectum
• 100 billion neurons in the nervous system, 80% of neurons are located in the brain.
• Sensory Neurons

  Sensory neurons have long dendrites and short axons. They carry messages from the PNS to the CNS.

  
• Relay neurons


  Relay neurons have short dendrites and short axons. They connect sensory neurons to the motor neurons or other relay neurons.

  
• motor neurons

  Motor neurons have short dendrites and long axons. They connect the CNS to the effectors such as muscles and glands.

  
• Structure of a neuron

  cell body- includes a nucleus with the genetic material and dendrites branch off it

  dendrites- carry nerve impulses from neighbouring neurons to the cell body

  axon- carries the impulses away from the cell body covered in the myelin sheath a fatty protective layer that speeds up transmission

  Terminal buttons- communicate with the next neuron across the synapse
• location of neurons

  Cell bodies of motor neurons may be in the CNS but have long axons which form part of the PNS.

  Sensory neurons are located in the PNS in clusters known as Ganglia

  Relay neurons make up 97% of all neurons and are mostly found within the brain and visual system.
• Electrical transmission


  when a neuron is in its resting state, the inside is negatively charged compared to the outside. When it is activated by a stimulus, the inside becomes positive causing action potential to occur. This creates an electrical impulse to travel down the neuron to the end.
• Chemical transmission


  neurons communicate within groups called neural networks, separated by gaps called the synapse. When an electrical impulse reaches the end of a neuron (presynaptic terminal) it triggers the release of neurotransmitters from the synaptic vesticles.
• Neurotransmitters


  Brain chemicals that are released from the synaptic vesicles that relay signals across the synapse. They are received by the postsynaptic receptor site on the dendrites of the next neuron where the message is converted back to an electrical signal. Each neuron has a specific molecular structure that fits perfectly to a postsynaptic receptor site. Each type has specialist function.
• Excitation


  when a neurotransmitter increases the positive charge of a postsynaptic neuron, increasing the likelihood it will pass on the electrical impulse.
• Inhibition


  When a neurotransmitter, such as serotonin, increases the negative charge of the postsynaptic neuron. This decreases the likelihood it will pass on the electrical impulse.
• Summation


  Whether a postsynaptic neuron fires is decided by the process of summation. The excitatory and inhibitory influences are summed. If the sum effect is inhibitory it will be less likely to fire, if it is excitatory it is more likely to fire. Once an electrical impulse is created it travels down the neuron. The action potential is only triggered if the sum of signals reaches the threshold.