Download U3 Neurobiology Summary

Higher Human
Unit 3 Neurobiology & Communication Summary
(BOLD is essential)
1 Divisions of the nervous system and parts of the brain
(a)Structures and functions of the central nervous system (CNS)
(b) Structures and functions of the peripheral nervous system (PNS) to include the autonomic nervous
system (ANS) to include the somatic nervous system (SNS).
The nervous system analyses sensory information from the body and the external environment, stores
some aspects and makes decisions regarding appropriate responses and behaviours. It makes motor
responses by initiating muscular contractions or glandular secretions. The nervous system can be divided
both structurally and functionally.
On a structural basis, the nervous system is divided into the central nervous system (CNS) and the
peripheral nervous system. The CNS is comprised of the brain and spinal cord and the peripheral NS is
comprised of the sensory and motor neuron pathways which pass information via impulses to and from
the CNS. Sensory neurons, following a stimulus, carry impulses from receptors, which may be in the sense
organs, e.g. eyes, ears, etc, or internal, e.g. thermoreceptors in the hypothalamus.
Following processing by the CNS, motor neurons transmit impulses to effectors, muscles and endocrine
glands, which bring about a response, e.g. muscle contraction, hormone release.
On a functional basis the nervous system can be divided up into the somatic nervous system (SNS) and the
autonomic nervous system (ANS).
The somatic nervous system, which includes the spinal nerves, controls the body’s skeletal muscles. This
involves both sensory and motor nerves and is mostly, but not entirely, voluntary. Reflex actions, for
example, are controlled by the SNS but are involuntary.
The autonomic nervous system regulates internal structures and organs such as the heart, blood vessels
(e.g. vasodilation/vasoconstriction), alimentary canal, sweat glands, etc. through involuntary actions
involving sensory and motor neurons, often to exert homeostatic control. It normally works automatically
without conscious control although, exceptionally, some individuals may be able to exert some degree of
conscious control. The nerves comprising the ANS arise in the brain and emerge from the spinal cord at
various points to reach the organs that they stimulate.
The autonomic nervous system is split in to the sympathetic and parasympathetic nervous system; the SNS
and PNS are described as being antagonistic to one another; this means that they act in opposition to one
another. They can control the heart rate, breathing rate and digestive processes.
In general terms, the sympathetic NS acts as an “accelerator” and the parasympathetic NS as a “brake”.
The sympathetic NS, for example, speeds up heart rate, breathing rate and increases blood pressure in
preparation for action and increased energy usage – the fight or flight reaction. At the same time blood is
diverted away from the gut and skin.
The parasympathetic NS slows down and reverses the actions of the sympathetic NS, heart rate and blood
pressure return to normal, peristalsis resumes, intestinal secretions increase and blood flow to the gut
increases – the rest and digest response. The effects of the parasympathetic nervous system help the body
to conserve resources and store energy.
(c) The functions of the medulla and cerebellum in the
central core of the brain.
The central core contains the medulla (ANS) that regulates
the basic life processes of breathing, heart rate, arousal
and sleep and the cerebellum which is responsible for
controlling balance, posture and movement.
(d) The functions of the limbic system
Functions include processing information for memories and influencing emotional and motivational
states.
(e) Cerebral cortex is the centre of conscious thought; it also recalls memories and alters decision making
behaviour in the light of experience.
The cerebral cortex also receives sensory information and coordinates voluntary movement.
(f) Different parts of the cerebrum control different aspects of
nervous function. The motor and sensory areas run across the
top of the cerebrum with other association areas of the
cerebrum controlling language, personality, imagination and
intelligence. Information from one side of the body is processed
in the opposite side of the cerebrum, transfer of information
occurs through the corpus callosum, a number of nerves which
link the left and right hemispheres of the cerebrum.
Some association areas deal with thought processes. The left cerebral hemisphere deals with information
from the right visual field and controls the right side of the body and vice versa.
2 Perception and memory
(a) Perception is the process by which the brain analyses and makes sense out of incoming sensory
information.
The three areas of perception involve segregation of objects, perception of distance and recognition.
(i) Segregation of objects.
When we view an object we firstly try to make sense of its shape. Any enclosed area
represents an object which will stand out from its background. This is called the
figure and ground phenomenon. The enclosed area appears to stand out from the
background even though there is no depth to the image.
The brain then tries to organise visual stimuli into coherent patterns, which can be
altered by simple additions or subtractions; the brains tries to form ordered
relationships.
Figure-ground
phenomenon
This is assisted by visual cues such as relative size, where objects appear to get
smaller the further away they are, superimposition where objects that partially block the view of another
are deemed to be nearer, and relative height in the field of view where closer objects appear to be lower
down (have lower bases) than distant objects.
(ii) Perception of distance.
When we look at an object, each eye views the object from a slightly different position relative to the other
eye. We therefore “see” a slightly different image with each eye. The closer the object, the greater the
disparity (difference) between the two images. The brain merges the two images into one producing a
binocular disparity image which allows us to make an accurate judgement of distance. This will have
helped in hunting and is now important, for example, in sports.
Perceptual constancy as objects become nearer and the viewing angle changes.
As objects become closer or further away from us the size of the image they make on out retinas will
increase or decrease in size. We do not, however, perceive these objects as shrinking or increasing in size,
they have size constancy. This depends partly on past experience and stored knowledge. (We know what
size familiar objects are.)
A similar process applies to shape; for example, as a door opens
its shape appears to change from a rectangle to a trapezoid to a
very small rectangle. We do not believe however, that the
shape of the door has changed, it has shape constancy. This,
too, depends on past experience and stored knowledge.
(iii) Recognition.
The ability to perceive an object’s physical properties such as shape, colour and texture is called object
recognition. Of these properties shape is considered to be the most important in the recognition of
objects rather than detail. When a person perceives a shape a subconscious attempt is made to match the
shape descriptions with one already stored in memory. If not recognised it could then be recognised as
being similar, but not identical to an image held in the brain this is called inference in recognition. The
brain then infers that the object is related in some way to one or more of these visual images. It could be a
familiar object seen from a different angle.
Perceptual set is the tendency of a person to perceive certain aspects of
available sensory information and ignore others.
Perceptual set is affected by expectation, context and past experience. It
influences the way a stimulus is perceived.
If a group of people are shown various pictures of young women and then
the image alongside they will tend to see a young woman. If they are shown
a series of pictures of old women then they will perceive an old woman.
(b) Memory as storage, retention and retrieval of information.
Young or old?
All information entering the brain passes through sensory memory and enters short-term memory.
Information is then transferred to long-term memory (LTM) or discarded.
Memories include past experiences, knowledge and thoughts.
(i) Sensory memory — lasts a few seconds and retains all of the visual or auditory input.
Stimuli from the outside world are continuously being perceived as sensory images by the brain.
These images are very short lived between 0.5 and 2 seconds. Only a few are selected and transferred to
the short term memory.
(ii) Short-term memory (STM).
Short term memory allows us to remember information for a few seconds before it is
replaced by more. Short term memory has a limited capacity, or memory span, it can retain about 7 pieces
of information for about 30 seconds, e.g. a phone number or car number plate. If more items go into the
STM items are lost by displacement.
More information can be retained in the STM if it is organised.
Chunking can increase STM span by organising information of smaller units into a chunk e.g. telephone
numbers can be chunked to give an area code which reduces 4 numbers to one piece of information—0141
for Glasgow, etc.
Rehearsal involves repeating information to yourself many times. This extends the length of time the
information is held in the STM and increases the chance that it will be transferred to the LTM. If
information is not rehearsed the memory will decay and be forgotten.
Serial position effect is where the first few and last few items from a string of facts are remembered best.
The first few items are remembered as there has been time to rehearse them and they are now in the
LTM. The last few are remembered because they are still in the STM.
Working memory is an extension of the STM. It process, manipulates and controls information while held
in the STM. This enables simple cognitive tasks to be carried out
(iii) Long-term memory (LTM).
LTM is thought to be able to hold an unlimited amount of information. During encoding the items are
organised into categories such as personal facts and useful skills.
The transfer of information from the short to long term memory happens upon successful encoding of the
information in the STM. Once in the LTM it is then stored and may be retrieved at a later date.
Successful transfer of information from the STM to LTM is promoted by rehearsal, organisation and
elaboration of meaning.
Rehearsal facilitates the transfer of information from the STM to the LTM.
Organisation is where information is grouped or categorised in a way that is logical and meaningful to the
learner.
Elaboration is where facts are easier to transfer into the LTM if they are part of a bigger ‘story’, e.g.
phosphofructokinase is easier to remember as part of the whole respiratory pathway than a single fact.
Encoding is the conversion of one or more nerve impulses into a form that can be received and held by the
brain and retrieved later from the STM or LTM. The quality of the memory is affected by the attention
given to the task of encoding the material.
Information encoded by repetition is an example of shallow encoding.
Information encoded by linking it to previous memories is an example of elaborative encoding.
Contextual cues aid the retrieval of information from the LTM.
A contextual cue is a signal or reminder relating to the conditions or circumstances that were present at
the time when the information was encoded into the LTM.
(iv) Location of memory in the brain.
Episodic (the memory of events and experiences) i.e. remembering that…., and semantic memory (the
record of general knowledge, non-personal facts and concepts) are stored in the region of the cerebral
cortex where the sensory information was first received and encoded.
Procedural memories (skills) e.g. how to swim, how to read, are linked to the motor cortex. Emotional
memories involve links between the cortex and the limbic system. Spatial memory is located in the
limbic system and is responsible for holding information about a person’s environment and spatial
orientation.
3 The cells of the nervous system.
(a) Nerves are bundles of nerve fibres which carry electrical impulses from one part of the body to the
other. Nerve cells or neurons consist of a nerve cell body and nerve fibres.
The nerve cell body contains the nucleus and cytoplasm containing organelles including ribosomes which
make various proteins including enzymes needed for the synthesis of neurotransmitters.
Dendrites are nerve fibres that receive nerve impulses and carry them towards the cell body.
An axon is a nerve fibre which carries impulses away from the cell body.
The direction in which a nerve impulse travels is always dendrite-cell body-axon.
Long axon fibres are covered in a myelin sheath which insulates the axon and speeds up impulse
conduction from node to node.
Myelination is the development of myelin round axon fibres of individual neurons.
Myelination is not complete at birth and so nervous control increases over the first two years as many
more neurons are myelinated. Myelination continues from birth to adolescence. As a result responses to
stimuli in the first two years of life are not as rapid or coordinated as those of an older child or adult.
Certain diseases destroy the myelin sheath causing a loss of coordination.
A motor neuron has short dendrites which make contact
with other neurones in the CNS, a nerve cell body and a
long myelinated axon that carries impulse to the many
axon terminals within a muscle.
Motor neuron
Sensory neurons have one or
several dendrites making contact
with receptors in a sense organ,
these merge to form a myelinated fibre which carries impulses to the cell body, a
short axon and axon branches make contact with the CNS neurones.
Sensory
neuron
An inter neuron connects a sensory and a motor neuron.
Inter neuron
Glial cells.
Physically support neurons and produce the myelin sheath.
Glial cells also maintain a homeostatic environment around the neurones and remove debris by
phagocytosis.
(b) Neurotransmitters at synapses.
Neurotransmitters relay messages from nerve to
nerve within and outwith the brain. Neurones
connect with other neurones, muscle fibres and
endocrine at a synaptic cleft. Neurotransmitters are
stored in vesicles and released into the cleft on arrival
of an impulse. They diffuse across the cleft and bind
to receptors on nerve endings.
Neurotransmitters must be removed from the synaptic cleft to prevent continuous stimulation of postsynaptic neurones by enzymes or reuptake.
Examples of neurotransmitters are acetylcholine and noradrenaline.
Acetylcholine is broken down by an enzyme and the non-active products are reabsorbed by the
presynaptic neurone and resynthesised into active transmitter.
Noradrenaline is reabsorbed directly into the presynaptic membrane and stored in a vesicle ready for
reuse.
Receptors determine whether the signal is excitatory or inhibitory. Synapses can filter out weak stimuli
arising from insufficient secretion of neurotransmitters. Summation of a series of weak stimuli can
trigger enough neurotransmitter to fire an impulse.
(c) Function of converging, diverging and reverberating neural pathways.
Converging path ways are where two or more neurones feed impulses to one
neurone e.g. from rod cells in the eye. Converging neural pathways increase
the sensitivity to excitatory or inhibitory signals.
Diverging neural pathways mean that an impulse in one neurone can have a
simultaneous effect in many parts of the body.
Reverberating pathway neurones later in the pathway synapse with earlier
ones sending the impulse back through the circuit.
Plasticity of response is created when new neural pathways are developed to create new responses,
bypass areas of brain damage, to suppress reflexes or responses to sensory impulses.
Major plasticity following brain damage is when undamaged cells form new neural pathways which take on
the function of the damaged area.
Minor plasticity is when the brain suppresses reflexes e.g. blinking or suppresses sensory impulses causing
distraction from a task.
(d) Neurotransmitters, mood and behaviour.
The functions of endorphins and dopamine.
Endorphins are neurotransmitters that stimulate neurones involved in reducing the intensity of pain.
Increased levels are also connected with euphoric feelings, appetite modulation and release of sex
hormones. Endorphin production increases in response to severe injury, prolonged and continuous
exercise, stress and certain foods.
Dopamine induces the feeling of pleasure and reinforces particular behaviour in the reward pathway.
The reward pathway involves neurons which secrete or respond to the neurotransmitter dopamine. The
reward pathway is activated on engagement of beneficial behaviours, e.g. eating when hungry.
There are a number of disorders related to defects in neurotransmitters.
Disorder
Cause
Treatment
Loss of cells synthesising
Alzheimer’s disease
Cholinesterase inhibitors
acetylcholine.
Loss of dopamine synthesising Monamine oxidase inhibitors and the potential
Parkinson’s disease
neurons.
use of adult stem cells
Schizophrenia
Overactive dopamine system The use of dopamine antagonists
General anxiety
Imbalance in serotonin and
The use of GABA agonists and beta blockers
disorders
norepinephrin
Norepinephrin re-uptake inhibitors and
Depression
Low levels of serotonin
monoamine oxidase enzyme inhibitors
Agonists bind to and stimulate receptors mimicking the neurotransmitter. Antagonists bind to specific
receptors blocking the action of the neurotransmitter. Other drugs inhibit the enzymes which degrade
neurotransmitters or inhibit re-uptake. Many drugs used to treat neurotransmitter related disorders are
similar to neurotransmitters.
(e) Mode of action of recreational drugs.
Recreational drugs can mimic neurotransmitters. They cause changes in neurochemistry leading to
changes in mood, cognition, perception and behaviour.
Many recreational drugs affect neurotransmission in the reward circuit of the brain.
Recreational drugs interact with neurotransmitters in different ways by stimulating the release of
neurotransmitters, imitate their action (agonists), block their binding (antagonists), and/or inhibit their reuptake/enzymatic degradation.
Drug addiction/tolerance.
Sensitisation is an increase in the number and sensitivity of neurotransmitter receptors as a result
of exposure to drugs that are antagonists and leads to addiction.
Desensitisation is a decrease in the number and sensitivity of receptors as a result of exposure to
drugs that are agonists and leads to drug tolerance.
4 Communication and social behaviour
(a) The effect of infant attachment.
Early infant attachment is important in laying the foundation for the future formation of stable
relationships.
Secure attachment and insecure attachment, responses of detachment, anger or inconsistent responses.
Socialisation and learning. Humans have a long period of dependency on adults providing time for
socialisation and learning to occur. Authoritative control generally results in greater social competence
than permissive control.
(b) The effect of communication.
The importance of non-verbal communication in the formation of relationships between individuals and
how it can signal attitudes and emotions as well as acting as an aid to verbal communication.
Verbal communication is used in the transmission of knowledge, development of culture and social
evolution.
(c) The effect of experience. Learning is a change in behaviour as a result of experience. The repeated
use of a motor skill results in a motor pathway being established.
Human behaviour may be learned by observation and imitation.
Reinforcement, shaping and extinction of behaviour as seen in trial and error learning.
Generalisation and discrimination.
Generalisation is the ability to respond in the same way too many different but related stimuli.
Discrimination is the ability to distinguish between related stimuli and give different responses.
Discrimination is taught by reinforcing the desired response. Learning to discriminate is an essential
part of a child’s preparation for coping with everyday life.
(d) The effect of group behaviour and social influence.
Social facilitation-Increased performance in competitive/audience situations.
De-individuation- Loss of personal identity in a group leading to diminished restraints on behaviour.
Internalisation - changing of beliefs as a result of persuasion.
Identification - changing of beliefs to be like an admired influencing source.