Biopsychology

• The Nervous System 


  Consists of the central nervous system and the peripheral nervous system. Communicates using electrical signals.
• Central Nervous System (CNS)

  Consists of the brain and the spinal cord and is the origin of all complex commands and decisions.
• Peripheral nervous system (PNS)

  Sends information to the CNS from the outside world, and transmits messages from the CNS to muscles and glands in the body.
• Somatic nervous system (SNS)

  Transmits information from receptor cells in the sense organs to the CNS. It also receives information from the CNS that directs muscles to act.
• Autonomic nervous system (ANS)

  Transmits information to and from internal bodily organs. It is 'autonomic' as the system operates involuntarily (i.e. automatic). It has two main divisions: the sympathetic and parasympathetic nervous systems.
• The nervous system 


  It is a specialised network of cells in the human body and is our primary internal communication system. It is based on electrical and chemical signals whereas the endocrine system is based on hormones. The nervous system has two main functions:

  • To collect, process and respond to information in the environment.
  • To co-ordinate the working of different organs and cells in the body.
  • The nervous system is divided into two subsystems:
  • Central nervous system (CNS).
  • Peripheral nervous system (PNS).
• The CNS


  It is made up of the brain and the spinal cord.

  • The brain is the centre of all conscious awareness. The brain's outer layer, the cerebral cortex, is only 3 mm thick. It is only found in mammals.
  • The brain is highly developed in humans and is what distinguishes our higher mental functions from those of other animals. The brain is divided into two hemispheres.
  • The spinal cord is an extension of the brain. It passes messages to and from the brain and connects nerves to the PNS. It is also responsible for reflex actions.
• The peripheral nervous system (PNS)

  The PNS transmits messages, via millions of neurons (nerve cells), to and from the central nervous system. The peripheral nervous system is further subdivided into the:

  • Autonomic nervous system (ANS) governs vital functions in the body such as breathing, heart rate, digestion, sexual arousal and stress responses.
  • Somatic nervous system (SNS) governs muscle movement and receives information from sensory receptors.
• Endocrine system 


  One of the body's major information systems that instructs glands to release hormones directly into the bloodstream. These hormones are carried towards target organs in the body. Communicates via chemicals.
• Gland 


  An organ in the body that synthesises substances such as hormones.
• Hormones


  Chemical substances that circulate in the bloodstream and only affect target organs. They are produced in large quantities but disappear quickly. Their effects are very powerful.
• Fight to Flight response

  The way an animal responds when stressed. The body becomes physiologically aroused in readiness to fight an aggressor or, in some cases, flee.
• Adrenaline 


  A hormone produced by the adrenal glands which is part of the human body's immediate stress response system. Adrenaline has a strong effect on the cells of the cardiovascular system - stimulating heart rate, contracting blood vessels and dilating air passages.
• The endocrine system- glands and hormones

  The endocrine system, working with the nervous system, controls vital body functions through hormone production by various glands (e.g., thyroid gland producing thyroxine), which are released into the bloodstream and affect multiple cells and organs; the pituitary gland, known as the "master gland," regulates the release of hormones from other endocrine glands.
• The endocrine system- Fight to flight response (Endocrine and ANS working together)

  If a stressor is sensed, the hypothalamus activates the pituitary gland, shifting the ANS from the parasympathetic state to the sympathetic state, causing adrenaline release from the adrenal medulla, & increasing heart rate to trigger the fight-or-flight response. This occurs fast, causing physical changes like 'butterflies' in the stomach. After the threat passes, the parasympathetic nervous system counteracts the sympathetic response, returning the body to resting state: the rest and digest response.
• Neuron


  The basic building blocks of the nervous system, neurons are nerve cells that process and transmit messages through electrical and chemical signals.
• Sensory neurons


  These carry messages from the PNS (peripheral nervous system) to the CNS. They have long dendrites and short axons.
• Relay neurons


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


  These connect the CNS (central nervous system) to effectors such as muscles and glands. They have short dendrites and long axons.
• Neurons


  There are 100 billion neurons (nerve cells) in the human nervous system, 80% of which are located in the brain. By transmitting signals electrically and chemically, these neurons provide the nervous system with its primary means of communication.
• Types of neurons


  There are three types of neurons: sensory neurons, relay neurons and motor neurons.
• The structure of a neuron

  Neurons have a basic structure that includes a cell body (soma) with a nucleus, dendrites that receive nerve impulses, and an axon that transmits impulses away from the cell body, covered by a myelin sheath for protection and speed. The myelin sheath has gaps called nodes of Ranvier, which help electrical impulses jump across, and at the axon’s end, terminal buttons communicate with the next neuron across a synapse.
• Location of neurons


  The cell bodies of motor neurons may be in the central nervous system (CNS) but they have long axons which form part of the peripheral nervous system (PNS). Sensory neurons are located outside of the CNS, in the PNS in clusters known as ganglia. Relay neurons make up 97% of all neurons and most are found within the brain and the visual system.
• Electrical transmission- the firing of a neuron

  When a neuron is in a resting state the inside of the cell is negatively charged compared to the outside. When a neuron is activated by a stimulus, the inside of the cell becomes positively charged for a split second causing an action potential to occur. This creates an electrical impulse that travels down the axon towards the end of the neuron.
• Synaptic transmission 


  The process by which neighbouring neurons communicate with each other by sending chemical messages across the gap (the synapse) that separates them.
• Neurotransmitter


  Brain chemicals released from synaptic vesicles that relay signals across the synapse from one neuron to another. Neurotransmitters can be broadly divided into those that perform an excitatory function and those that perform an inhibitory function.
• Excitation 


  When a neurotransmitter, such as adrenaline, increases the positive charge of the postsynaptic neuron. This increases the likelihood that the postsynaptic neuron 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 that the postsynaptic neuron will pass on the electrical impulse.
• Chemical transmission


  Neurons communicate with each other within groups known as neural networks. Each neuron is separated from the next by an extremely tiny gap called the synapse. Signals within neurons are transmitted electrically. However, signals between neurons are transmitted chemically across the synapse. When the electrical impulse reaches the end of the neuron (the presynaptic terminal) it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles.
• Neurotransmitters

  Neurotransmitters are chemicals that transmit signals across the synapse to the next neuron by fitting into specific receptor sites on its dendrites, converting the chemical message into an electrical impulse. This process is one-way, as neurotransmitters are released from the presynaptic neuron and received by the postsynaptic neuron. Different types of neurotransmitters, like acetylcholine (ACh), have unique functions, such as causing muscle contractions at the junctions where motor neurons meet muscles.
• Excitation and inhibition 


  Neurotransmitters have either an excitatory or inhibitory effect on the neighbouring neuron. For instance, the neurotransmitter serotonin causes inhibition in the receiving neuron, resulting in the neuron becoming more negatively charged and less likely to fire. In contrast, adrenaline (an element of the stress response which is both a hormone and a neurotransmitter) causes excitation of the postsynaptic neuron by increasing its positive charge and making it more likely to fire.
• Summation 


  The firing of a postsynaptic neuron depends on summation of excitatory and inhibitory signals: if the overall effect is inhibitory, the neuron is less likely to fire, while an excitatory effect makes it more likely to fire, creating a positive charge inside the neuron; an action potential occurs only when the combined signals reach a certain threshold.