H human bio unit 3

• The nervous system can be divided into two main sections:

  Central nervous system (CNS) consists of the brain and spinal cord.

  Peripheral nervous system (PNS) consists of peripheral nerves.
• The peripheral nervous system can be further divided into the somatic nervous system (SNS) and the autonomic nervous system (ANS).
• The somatic nervous system controls the body’s skeletal muscles

  This involves both sensory and motor pathways

  The somatic nervous system allows voluntary control of the skeletal muscles
• The central nervous system receives information from receptors via sensory neurons and decides an appropriate response.

  Nerve impulses are then sent along motor neurons to effectors to bring about the response.

  Effectors can be muscles or glands.
• The autonomic nervous system regulate the internal environment  by controlling organs such as heart, blood vessels and bronchioles.

  This control is involuntary and automatic.

  Nerves of the ANS arise in the brain and leave the spinal cord at various points to reach effectors.
• The autonomic nervous system is further divided into  the sympathetic system and the parasympathetic system.
• The sympathetic and parasympathetic nervous systems are described as antagonistic.

  This means they affect many of the same structures but have the opposite effect on them.
• The sympathetic system is involved in “fight or flight” responses.

  It prepares the body for action by increasing heart rate and breathing rate, it diverts blood from the gut to the skeletal muscles.

  It reduces the rate of peristalsis and intestinal secretions.
• •The parasympathetic system is involved in “rest and digest” responses.

  •It calms the body down by decreasing heart rate and breathing rate, it allows blood to flow to the gut.

  •It increases the rate of peristalsis and secretions in the digestive system.
• In a converging neural pathway impulses from several sources are channelled towards a common destination, one neuron. 

  Converging neural pathways increase the sensitivity to excitatory or inhibitory signals. 
• Some of the visual receptors in the eye (the rods) have multiple synapses with just one neuron.

  This increases sensitivity to dim light by intensifying the signal passed along the optic nerve.
• To diverge means to branch out.

  In a diverging neural pathway, impulses from one neuron travel to several neurons so affecting more than one destination at the same time.

  This allows information from the original source to be transmitted to several places.
• Diverging pathways from a common starting point allows impulses to be transmitted simultaneously to the different muscles of the hand for example.

  This allows fine motor control of the fingers and thumb for writing.
• In a reverberating pathway, neurons later in the pathway link with earlier neurons, sending the impulse back through the pathway. 

  This allows repeated stimulation of the pathway. 

  This enables repeated activities like breathing.
• •The cerebral cortex is the outer layer of the cerebrum.

  •The cerebral cortex is the centre of conscious thought

  .•It also recalls memories and alters behaviour in the light of experience.
• There is localisation of brain functions in the cerebral cortex.
• The cerebral cortex contains sensory, motor and association areas
• sensory areas: receives information from receptors.
• motor areas: send motor impulses to effectors.
• association areas: involved in language processing, personality, imagination and intelligence.
• Information from one side of the body is processed in the opposite side of the cerebrum.  
• The left cerebral hemisphere deals with information from the right visual field and controls the right side of the body and vice versa.
• Transfer of information between the cerebral hemispheres occurs through an area (containing a bundle of nerve fibres) called the corpus callosum.
• •Memory is the capacity of the brain to encode, store  it and  retrieve  information when it is required.

  •Memories include past experiences, knowledge and thoughts.
• •Encoding involves converting nerve signals into a form which can be received and interpreted by the brain so it can be stored and used at a later date.

  •Information is encoded using shallow encoding or elaborative encoding.
• •Repetition is an example of shallow encoding whereas linking information to previous memories  allows elaborative encoding.
• •Memory is thought to involve three separate interacting levels.
• •All information entering the brain passes through the sensory memory (SM) and then, if selected, enter the short-term memory (STM).

  •From there it may be transferred to the long-term memory (LTM) or be discarded.
• The first level of memory is sensory memory.

  This lasts less than a second and represents  all of the visual or auditory input.

  Sensory memory retains all the visual and auditory input received for a few seconds.

  Only selected images and sounds are encoded into short-term memory (STM). 
• Short term memory has a limited capacity and holds information for a short time.  This is known as the memory span and is usually about seven items.

  Items are held in STM for around 30 seconds then moved to long term memory or lost by displacement (old memories “pushed out” by new one) or decay (loss of information).
• Items can be maintained in the STM by rehearsal.

  This involves repeating a piece of information to yourself over and over.

  It extends the time information is stored in STM.
• When given a list of objects to memorise, recall is best for objects at the beginning and end of the list.

  This is known as the serial position effect.

  Recall is better for the objects shown at the start (primacy effect) or end (recency effect) of the sequence.
• Primacy effect -

  The first few objects are remembered because they have been rehearsed.

  The first objects may have been encoded and transferred to the long-term memory (LTM) and can be retrieved.
• Recency effect -

  The last objects are remembered because they are still present in the STM.
• Serial position effect -

  The middle objects are not retained, they are forgotten before they can be rehearsed, encoded and stored in the LTM.
• Short-term memory has a limited capacity (memory span) of about 7±2 pieces of information. These are retained for around 30 seconds.
• If more items go into the STM they displace the previous items. Other items are lost through decay, the breakdown of a fragile ‘memory trace’ by neurons briefly becoming activated.
• The capacity of STM can be improved by ‘chunking’.

  Chunking involves taking individual units of information and grouping them into smaller units (chunks).
• Chunking is a useful method of increasing its memory span.

  STM can also process data as well as store it

  This working memory model explains why the STM can, to limited extent, perform simple cognitive tasks as well as store data
• The long-term memory (LTM) is thought to have an unlimited capacity and hold information for a long time.

  Successful transfer of information from the STM to the LTM is promoted by the processes of rehearsal, organisation and elaboration of meaning.