The Brain and The Brain and BehaviourBehaviour

The central nervous system

• The central nervous system is one of the two major divisions of the human nervous system.

• The central nervous system comprises the brain and spinal cord. The spinal cord connects the brain and the peripheral nervous system.

• The peripheral nervous system includes all parts of the nervous system that lie outside the brain and the spinal cord.

The Brain

• It is encased in a hard, protective skull and weighs, on average, around 1.5 kg in adults.

• It has the consistency of firm jelly and is covered by a strong plastic like membrane.

• There is a small gap between the brain and the skull, which is filled with fluid.

The Cerebral CortexThe Cerebral CortexThe cerebral cortex is the convoluted outer layer or covering

of the two cerebral hemispheres.

The surface area of the cerebral cortex bends and folds inwards so that its surface area can fit into the limited amount of space available in the skull.

If flattened out the cerebral cortex would cover about 4 A4 pages.

The cerebral cortex is involved with information-processing activities such as perception, language, learning, memory, thinking, problem-solving as well as the planning and control of voluntary body movements.

Some areas of the cerebral cortex are dedicated to specific functions.

The areas of the cerebral cortex and their main functions can be can be organised into three broad categories:

1. The various sensory cortex areas which receive and process information from our different senses

2. The motor cortex area which receives, processes and sends information about voluntary body movements

3. Association cortex which integrate sensory, motor and other information and are involved in the more complex mental abilities, such as perceiving, thinking and problem-solving.

It is believed that the larger the size of the cerebral cortex, the more intelligent the organism will be.

Cerebral HemispheresCerebral HemispheresThe cerebral cortex is described as having two halves,

called cerebral hemispheres.

The cerebral hemispheres are two almost symmetrical brain structures that appear to be separated by a deep groove (known as the longitudinal fissure) running from the front to the back of the brain.

Although the hemispheres appear to be separated, they are connected at several points by strands of nerve tissue. The largest and most important of these strands is the corpus callosum.

The left hemisphere receives information from the right side of the body just as the right hemisphere receives information from the left side of the body.

Remember!! Contralateral Organisation

•Left hemisphere controls movement on the right side of the body.

•Right hemisphere controls movement on the left side of the body.

Corpus CallosumCorpus Callosum

The interaction between the two hemispheres of the brain occurs mainly through the corpus callosum.

The corpus callosum is a strand, or bridge of nerve tissue that connects the left and right cerebral hemispheres and serves as the main communication pathway between them.

This means that information can be exchanged between the two hemispheres when performing their many functions as we think, feel and behave throughout everyday life.

Four lobes of the cerebral cortexFour lobes of the cerebral cortex

The cerebral cortex of each hemisphere can be divided into four anatomical regions called cortical lobes.

Cortical lobes are areas of the brain associated with different structures and functions. The four lobes are named after the bones of the skull that cover them.

• Frontal lobe• Parietal lobe• Occipital lobe • Temporal lobe

The lobes contain areas of the cortex that have specialised sensory or motor functions, as well as areas of the cortex generally referred to as association cortex.

The sensory areas of the lobes receive and process information from sensory receptors in the body.

The sensory area that receives and processes visual information is called the primary visual cortex. It is located in the occipital lobe.

The sensory area that processes auditory information is called the primary auditory cortex and is located in the temporal lobe.

Sensory information from the skin and from skeletal muscles is processed in the somatosensory cortex located in the parietal lobe.

The motor areas receive and process information about voluntary body movements; that is intentional movements such as when you scratch your nose.

There is only one primary motor area in the brain. This is called the primary motor cortex and is located in the frontal lobe.

The association areas of each lobe integrate information from different brain areas and are mainly involved in complex cognitive processes such as perceiving, thinking, learning, remembering, reasoning and so on.

Association areas are located on all four lobes of each hemisphere and may receive and process information from sensory and/or motor areas, as well as from other structures or other association areas of the brain in other lobes.

Frontal LobeFrontal LobeThe frontal lobe is the largest of the four lobes and

occupies the upper forward half of each cerebral hemisphere, right behind your forehead.

In the forward section of each frontal lobe are association areas that receive information from other lobes to enable us to perform complex mental functions.

The frontal lobes are also involved in personality, the control of emotions, and expression of emotional behaviour.

Primary Motor CortexLocated at the rear of each frontal lobe and running

roughly across the top of your head is a strip of neural tissue called the primary motor cortex.

The primary motor cortex is specifically involved in controlling voluntary bodily movements through its control of skeletal muscles.

The motor cortex in the left frontal lobe controls voluntary movements on the right side of the body and vice versa.

The amount of cortex devoted to a particular body part corresponds to the complexity or fineness of its movements.

Broca’s AreaBroca’s AreaA specific cortical area located in the left frontal lobe next to

the motor cortex areas that control the muscles of the face, tongue, jaw and throat is an area called Broca’s area.

Broca’s area is responsible for the production of articulate speech, coordinating movements of the muscles required for speech and supplying this information to the appropriate motor cortex areas.

Broca’s area is also involved in understanding the meaning of words and the structure of speech such as adjectives, prepositions and conjunctions. It is also involved in understanding the grammatical structure of sentences.

Damage to Broca’s AreaDamage to Broca’s Area

Damage to Broca’s area often produces speech that is very deliberate, consisting of a few words with very simple grammatical structure, but damage rarely results in the total loss of speech.

This type of speech impairment is known as Broca’s aphasia.

Aphasia is a form of language loss or impairment due to brain damage, injury or disease.

In Broca’s aphasia speech consists of very short sentences, typically three or four words, and these words are mainly verbs and nouns.

The smaller parts of speech are often ommitted such as to and the, as are proper grammatical endings of words such as ing and ed.

Parietal LobeParietal LobeThe parietal lobe is located behind the frontal lobe and

occupies that upper back half of the brain, but not the rear-most area.

The parietal lobe in each hemisphere receives and processes sensory information from the body and skin senses and other sensory areas in the brain. It also sends information to other areas of the brain.

Located at the front of each parietal lobe, just behind and parallel to the primary motor cortex in the frontal lobe, is a strip of cortex called the primary somatosensory cortex.

The primary somatosensory cortex receives and processes sensory information from the skin and body, enabling us to perceive bodily sensations.

Different areas of the primary somatosensory cortex are involved with sensations of touch received from specific body parts. Furthermore, the amount of cortex devoted to a particular body part corresponds to the sensitivity and amount of use of the body part.

Occipital LobeOccipital LobeThe occipital lobe is located at the rear-most area of each

cerebral hemisphere; that is at the back of your head.

The occipital lobe is primarily involved in vision.

Damage to the occipital lobe can produce blindness, even if the eyes and their neural connections to the brain are normal.

The primary visual cortex is located at the base of each occipital lobe and this is where visual information from the two eyes is received and processed.

Temporal LobeTemporal LobeThe temporal lobe is located in the lower, central, area of the

brain, above and around the top of each ear.

The temporal lobe in each hemisphere is primarily involved with auditory perception, but also plays an important role in memory, in aspects of visual perception such as our ability to recognise faces and identify objects, and in our emotional responses to sensory information and memories.

The primary auditory cortex in each temporal lobe receives and processes sounds from both ears, receiving and processing different features of sound and therefore playing a vital role in the identification of sounds.

The two main features of sound are frequency (which we perceive as pitch) and amplitude or intensity (which we perceive as loudness).

Verbal sounds such as words are mainly processed in the primary auditory cortex of the left hemisphere and non-verbal sounds (such as music) are mainly processed in the primary auditory cortex of the right hemisphere.

Damage to the temporal lobe as a result of a stroke or severe blow to the head can level a person with the ability to describe someone’s facial features, to identify their sex, and to judge their approximate age, but without the ability to recognise the person as someone that they know, even if it is their mother.

Wernicke’s AreaWernicke’s AreaA specific area in the temporal lobe of the left hemisphere only, next

to the primary auditory cortex and connected to Broca’s area by a bundle of nerves is called Wernicke’s area.

Wernicke’s area is involved with comprehension of speech; more specifically, with interpreting the sounds of human speech.

When a word is heard, the auditory sensation is processed by the primary auditory cortex of the left temporal lobe, but the word cannot be understood until the information has been processed by Wernicke’s area.

This area is also thought to be involved with not only understanding words, but also for locating appropriate words from memory to express intended meanings when we speak or write.

Hemispheric Specialisation

Hemispheric Specialisation

• Overall, the two cerebral hemispheres appear to be two replicas of each other in terms of size, shape and function.

• The function of the sensory and motor areas of the left and right hemispheres are generally the same, however, each hemisphere does have some specialised functions which are not duplicated by the other hemisphere.

• Hemispheric specialisation: The idea that one hemisphere has greater control over a particular function.

How do we know what we know??

• The earliest evidence of hemispheric specialisation came from observations of people who had suffered a stroke or an injury affecting one hemisphere but not the other.

• It was observed that damage to the LEFT hemisphere often resulted in difficulties with language related activities (VERBAL TASKS) such as understanding speech, talking fluently, reading and writing. It also noted that the left hemisphere processes information in a step by step and analytical way.

• Damage to the RIGHT hemisphere often resulted in difficulties with visual and spatial tasks not dependent on language (NON VERBAL TASKS), such as reading a map.

What is each hemisphere specialised in?

LEFT:• Verbal Task (involve the recognition of words) eg.

Reading, writing, understanding of speech

• Analytical tasks (involve breaking down a task into its key parts and then approaching it in a step by step way) eg, following instructions on how to bake a cake.

• Left hemisphere receives and processes sensory information from the right side of the body.

• Controls voluntary movement on the right side of the body

Right:• Non verbal tasks (tasks that are not dependent on language

skills) eg. Completing a jigsaw puzzle.

• Spatial and visual thinking eg. Reading a map, visualising a place in your mind, recognising faces.

• More involved in recognising emotions from facial cues (signals), such as raised eyebrow and smiling.

• Right hemisphere receives and processes information from the left side of the body and controls voluntary movements on the left side of the body.

The Reticular Activating System (RAS) and Thalamus

• Two other important brain structures are involved in our ability to be awake and alert and to attend to stimuli in our internal and external environments.

• These are the reticular activating system and the thalamus.

Reticular Activating System (RAS)

• Before incoming sensory information (neural impulses sent from outside the body to the brain) reaches the cerebral hemispheres, it must pass through the reticular activating system.

• The reticular activating system is a network of neurons that extends in many directions from the top of the spinal cord up to the thalamus. It influences our state of physiological arousal and alertness.

• Nerve fibres from sensory neurons have side branches into the RAS, which filter incoming sensory information, sorting it into ‘important’ and ‘unimportant’ categories.

• These side branches stimulate the RAS to send its own nerve impulses upward toward the cortex, arousing it to a state of alertness and activity.

• This stimulation keeps the cortex alert and active which we then experience as being in a state of consciousness awareness.

• Once alerted to the fact that new information is on its way, the brain is ready to process the sensory information.

• Unimportant information is ignored.

• This is what we know as ‘selective attention’- our ability to voluntarily redirect our attention to a specific stimulus while ignoring others.

• Eg. When you are trying to cross a busy road without traffic lights the RAS allows you to filter out unwanted sensory information and concentrate on what is important.

• The RAS is not only involved in keeping us alert when we are awake- it is also involved in the control of sleeping and waking, and is often referred to as the brain’s arousal centre.

• Experiments in which researchers have removed the RAS from animals show that without it they cannot be awakened, due to lack of arousal. If the RAS is electrically stimulated in sleeping animals they will awaken immediately.

• Damage to the RAS will profoundly disrupt the sleep-wake cycle and can result in coma or a vegetative state.

• Many general anaesthetics work by reducing the activity of the RAS, making the patient unconsciousness.

The thalamus: the sensory switching station

• The thalamus is a structure that sits on top of the brain stem and acts as a sensory relay station.

• Information from all senses (except smell) pass through this structure.

• The thalamus is a brain structure that filters information from the senses and transmits the information to the cerebral cortex.

• Eg. Information from the eyes enters the thalamus and is relayed to the primary visual cortex in the occipital lobe.

• The flow of information is not one way- there is a constant flow of information between the thalamus and other cortical areas.

• In addition to incoming sensory information, the thalamus receives information about our state of arousal from the reticular formation.

• This means the thalamus also has a crucial role in influencing our level of alertness.

• The thalamus also appears to play a role in attention.

• It filters the vast amounts of information that need to be attended to and highlights some while de-emphasising others.

• This is crucial when we are in need of resting the brain (eg sleep) as the thalamus stops information from passing through to the cortex.

The spinal cord• The spinal cord is a long column of nerve tissue

that extends from the base of the brain and is encased in the spinal column which runs from the skull to the lower back.

• The bones of the spinal cord are called vertabrae.

• The two main functions of the spinal cord are:

To pass sensory information from the Peripheral Nervous System to the brain.

To pass motor information from the brain to the Peripheral Nervous System so that the appropriate actions can be taken.

• When the spinal cord is damaged, the brain loses both sensory input from and control over the body.

• The spinal cord is the linking ‘pipeline’ that integrates the central nervous system and peripheral nervous system, which work together to transmit information around the body.

• This information is transmitted via NEURONS.

TYPES OF NEURONSTYPES OF NEURONS• There are three main types of neurons, each of which

has a different role in the nervous system.

• These are:

- Sensory neurons

- Motor neurons

- Interneuron's

• Sensory neurons and motor neurons are found primarily in the PNS, whereas interneuron’s are only found in the CNS.

SENSORY NEURONSSENSORY NEURONS• Sensory neurons (also called afferent neurons) are

specialised cells that receive information from both the external environment and from within the body and transmit the information to the CNS.

• Their main role is to help us sense the external world and changes within our body.

• Generally there are different types of sensory neurons, each of which is specialised to respond only to a particular type of stimulation. Eg. The sensory neurons in the ears respond to sound waves, but not light.

MOTOR NEURONSMOTOR NEURONS

• Motor neurons (also called efferent neurons) transmits messages from the CNS to the muscles, glands and organs.

• They enable muscles to move, cause glands to secrete chemicals and activate internal organs such as the heart, lungs and intestines.

INTERNEURONSINTERNEURONS• Interneurons exist only within the CNS.

• Interneurons provide neural links between sensory and motor neurons and have a specialised role of carrying and integrating messages between sensory and motor neurons.

• When information from a sensory neuron arrives at the CNS, an interneuron receives, organises and integrates the information. They also connect with the motor neurons to send messages back through the PNS.

Neurons

• The major difference between sensory and motor neuron activity is the direction of the neural impulse and what happens at their destinations.

STUDIES ON COGNITIVE PROCESSES OF THE BRAIN

• The brain is not always perfect as shown through perceptual anomalies or ‘irregularities’ like when we perceive motion that doesn’t actually occur (motion after effect), when we fail to notice changes that are occurring (change blindness) and when we involuntarily experience sensations that do not have a physical basis at that time (synethesia).

• When looking at the irregularities of the brain we examine these phenomena, which are all experienced by people with intact, undamaged brains.

• Other people with brain damage experience the world very differently to those without damage.

• We will also look at this and the way this effects a persons life.

- Aphasia

- Spatial neglect

- Split-brain studies

APHASIA

• The word ‘aphasia’ is a general term used for clinical purposes to describe individuals with a language disorder.

• Aphasia refers to a language disorder apparent in speech (comprehension or production), writing or reading, produced by injury to brain areas specialised for these functions.

• Aphasia is often classified into three main areas:- Fluent aphasias in which there is fluent speech but

there are difficulties in either auditory verbal comprehension or the repetition of speech spoken by others

- Nonfluent aphasias in which there are difficulties in articulating clearly but auditory verbal comprehension is good

- Pure aphasias in which there are specific impairments in reading, writing or the recognition of words.

• The most common cause of aphasia is stroke, causing loss of blood supply to areas of the brain associated with language.

• Some aphasia sufferers can speak fluently but they cannot read, others may understand what they read but cannot speak, some can write but not read, some can read but not write, some can read numbers but not letters, and others can sing but not speak.

Broca’s aphasia• In the late 1800’s, French physician Paul

Broca studied patients with damage to the lower left frontal lobe, close to the motor cortex.

• This later became known as Broca’s area.

• He discovered that while patients with damage to this area could understand what was said to them and knew what they wanted to say in response, they simply could not say it.

• In Broca’s aphasia a person has difficulty in speaking, although they continue to understand speech.

• A typical patient will speak slowly and laboriously, and use simple sentences.

• Usually only the concrete words (verbs and nouns) are pronounced and the connecting words are omitted (to, the or –ing).

• Eg. ‘Boy went beach’ instead of ‘The boy went to the beach’.

• The sentence is not articulate and incomplete.

• Some patients cannot speak at all.

• Broca’s aphasia:

http://www.youtube.com/watch?v=f2IiMEbMnPM

Wernicke’s aphasia• Around the same time, German physician

and psychiatrist Carl Wernicke studied patients with a different language disorder.

• This was the inability to understand speech or to produce coherent language.

• He identified a part of the brain in the left temporal lobe close to the primary auditory cortex as being the area responsible for language comprehension- Wernicke’s area.

• Wernicke’s aphasia is a type of aphasia in which a person has considerable difficulty comprehending speech and speaking in a meaningful way.

• Unlike Broca’s aphasia, speech is often fluent and grammatically correct, but what is said is nonsense.

• Words are used inappropriately and sometimes made up words are used.

• The patient often is not even be aware that what they are saying does not make sense.

• Eg. When describing a picture of a woman washing the dishes and her two children stealing cookies from the cookie jar behind her the patient says:

“Well, this is…mother is always here working her work out of here to get her better, but when she’s looking the two boys looking in the other part. One their small tile into her time here. She’s working another time because she’s getting to. So two boys work together and one is sneaking around here making his work and further funnas his time he had.”

• Tono man:

http://www.youtube.com/watch?v=Fw6d54gjuvA

• Wernicke’s aphasia:

http://www.youtube.com/watch?v=aVhYN7NTIKU

Language functions• There are other areas of the brain that have been

linked to language that complement the functions outlined in Broca and Wernicke’s areas.

• It has also been found that the right hemisphere may also have a role in language.

• Some patients with major destruction to the left hemisphere may be capable of swearing or using emotionally charged words, or singing, and learning well known phrases.

• Some can sing phrases that they are unable to say, thereby making use of the right hemisphere’s musical function.

Spatial neglect• Read intro page 217. • Spatial neglect is an attentional disorder in

which individuals fail to notice anything either on their left or right side.

• They tend to behave as if one side of their world does not exist.

• Most commonly observed in stroke victims or accident victims who have extensive damage to the rear area of the parietal lobe of the right hemisphere.

• They mostly neglect the left side of their world.

• Read studies pg 218.

• Spatial neglect is widely considered to be a disorder involving failure of attention, and not due to impairment of memory processes, the visual system or any other sensory system.

• Its much greater occurrence with damage to the right rather than the left parietal lobe highlights the importance of this lobe in attention and spatial recognition.

• Many patients insist that there is nothing wrong with their perception of the world.

• Some do however, make a gradual recovery.

Split brain studies

• Much of our knowledge on hemispheric specialisation comes from researchers Roger Sperry (1914-1994) and Michael Gazzaniga (1939-).

• These researchers demonstrated that there is more to hemispheric specialisation than just language functions.

• How is it possible to test only one side of the brain?

• One way is to work with people who have had a split-brain operation.

• Split brain surgery involves surgically cutting the corpus callosum thereby disconnecting one hemisphere of the brain from the other.

• Another less common procedure is the WADA test in which a sedative is injected into an artery which sedates only one side of the brain.

Split brain surgery

• In the 1940’s there was very little remedy for people who suffered from severe epileptic seizures (10-15 a day).

• In recognising the need for new treatments, American neurosurgeon William Van Waganen decided to contain seizure activity by cutting the corpus callosum and stopping the communication between the two cerebral hemispheres.

• Animals studies showed that there were no obvious effects of this surgery and in the 1940’s the first of the human split-brain surgeries began.

• There was little evidence of impairment and patients appeared to remain ‘normal’, however there was little or no improvement in the occurrence of the seizures.

• The surgery was abandoned until the 1950’s when Sperry and a student of his, Roger Myers conducted successful split brain operations with cats.

• Through this experimentation it was found that the earlier split-brain operations may have been unsuccessful because the corpus callosum and other neural connections had not been completely severed.

• The split-brain surgeries were conducted on 11 epileptic patients, completely cutting the corpus callosum and other nerves, leaving some patients virtually seizure free afterwards and with minimal side-effects.

• Sperry and Gazzaniga however discovered that the surgery had left some patients with a unique condition.

Effects of having a split brain• Surgery that cuts the corpus callosum interrupts

the exchange between the two cerebral hemispheres, so information registered in one hemisphere is unable to be transferred to the other.

• This means the brain cannot integrate information registered separately in each hemisphere.

• Eg. Information registered in the right hemisphere cannot be transferred to the left (language centres) and therefore cannot be verbalised.

• Problems arise for split-brain patients when a response requires information from one hemisphere to be integrated with information from the other hemisphere.

• Eg. When registering visual information, it is registered on the retina of each eye and travels to each hemisphere. Info from the right portion of a persons vision (right visual field) goes to the left hemisphere where the speech centre allows you to articulate this information verbally. If you receive information only to your left visual field, the information will only travel to your right hemisphere and if you had a split-brain operation it would be unable to pass to the left hemisphere and therefore be unable to be articulated verbally.

Perceptual anomalies• Perception occurs when sensory information

reaching the brain is meaningfully interpreted. • Touch, taste, smell, sight, hearing. • This allows us to make sense of the world. • However sometimes we make errors in our

perceptions and this can lead to perceptual anomalies.

• Perceptual anomaly refers to an irregularity in perception. It usually involves an inconsistency or mismatch between the perceptual experience and physical reality.

• Eg. When driving along a highway you may see a puddle on the road ahead. As you drive the road stays dry and the puddle remains in the distance. In reality there is not puddle it is a layer of hot air beneath cool air but the brain misinterprets it and you see it as a puddle.

• Three types of anomalies:

- Motion after-effect

- Change blindness

- Synesthesia

Motion after-effect• Motion after-effect refers to the

phenomenon that occurs when, after staring at a moving image for a period of time and then looking immediately at a stationary one, we perceive the stationary image to be moving in the opposite direction to the moving image.

• http://www.michaelbach.de/ot/mot_adaptSpiral/

• One explanation for motion after-effect is that the neurons in the visual cortex that respond to the motion become fatigued over time. When you stare at a moving object, these cells signal movement in one direction. When you shift your attention to something else, these neurons fail to fire. However, as neurons that signal movement in the opposite direction are more active they therefore interpret the movement as the opposite direction.

Change blindness• Change blindness refers to a failure to

notice changes in a visual scene.

• This failure to notice is usually because the changes occur at the same time as a disruption to our vision and, in particular, a disruption to our attention.

• Change blindness illustrates the importance of attention in cognitive processes and the important roles of the RAS and thalamus as a sensory filter.

• http://www.youtube.com/watch?v=vBPG_OBgTWg

Inattentional blindness• Inattentional blindness is the failure to notice an

object in the environment, because attention was not focused on it.

• There is no visual disruption or reliance on memory. • It is possible that these phenomena occur because

of a failure to store the information in the first place. It may also occur because we are unable to compare the new information with the old information.

• http://www.youtube.com/watch?v=IGQmdoK_ZfY&feature=related

Synesthesia • Synesthesia is a perceptual experience in

which stimulation of one sense produces additional unusual experiences in another sense.

• It is involuntary and occurs automatically and is consistent across time.

• Grapheme-colour synesthesia is the most common form and is when the experience of viewing letters or numbers actually produces the experience of colours.

• Although the causes of synesthesia are yet to be clearly determined, there are some factors that are associated closely with synesthesia:

- It is most likely to run in families, suggesting a genetic link

- It is most common in drug users (LSD)- People with one type of synesthesia are more

likely to have another form- Creative people are more likely to have

synethesia- Synesthesia can develop over the course of a

lifetime, not everyone is born with it.

• http://www.youtube.com/watch?v=veoN1mh7RME

Brain research methods. • Neuroimaging can capture detailed

images of the living intact brain as people engage in different mental processes or make behavioural responses.

• Functional neuroimaging refers to scanning techniques that provide views of some particular aspect of brain function by showing images of the brain at work.

Brain research methods

Summarising brain research methods.docx

Ethical principals in brain research

• Psychologists are not medically qualified and therefore are not legally or ethically permitted to administer any medical procedures.

• Any neuroimaging device involves medical procedures and can therefore not be administered by a psychologist.

• A psychologist may work on a team with medical experts to administer these kinds of treatments.

THE HUMAN NERVOUS SYSTEM

Central Nervous System

The Central Nervous System (CNS) comprises the brain and spinal cord. The spinal cord connects the CNS with the Peripheral Nervous System.

The roles of the CNS are to integrate and coordinate all incoming neural information and to initiate messages sent to different parts of the body, the CNS does not have direct contact with the outside world.

The CNS relies on the Peripheral Nervous System to provide it with information about both the external world and the body’s internal environment, and to carry messages from the CNS to various parts of the body.

Peripheral Nervous System

The Peripheral Nervous System (PNS) is the entire network of nerves located outside the Central Nervous System.

It extends from the top of the head, throughout the body to the tips of the fingers and toes and to all parts of the skin.

The PNS has two main functions:1. To carry information from the sensory organs to the CNS2. To convey information from the CNS to the muscles, organs

and glands.

It enables communication to occur between the CNS and all other parts of the body outside the brain and spinal cord.

Human Nervous System

In the human nervous system, messages can only travel in one direction along the neuron. To accommodate this, the PNS has two different pathways for communicating information to and from the CNS.

One of these pathways consists of a set of neurons- the sensory neurons- that carry information from the sensory organs, muscles and glands to the CNS.

The other pathway consists of a set of neurons- motor neurons- that carry instructions or messages from the CNS to muscles, organs and glands.

You are able to feel the heat of a wood fire because of the coordination of the and the . The heat

given from the fire is received by the neurons of the skin, which are part of the . The sensory neurons then transmit the information to the

. The brain then organises and interprets the information in a meaningful way, which enables you

to know how hot the flame is. If you decide it is too hot, the brain sends messages via the neurons which

are part of the to the muscles in your legs to move a few steps away from the fire.

The peripheral nervous system can be subdivided into two quite distinct nervous systems, each of which has different functions- the

somatic nervous system and the autonomic nervous system.

THE SOMATIC NERVOUS SYSTEM

The Somatic Nervous System is a network of sensory (afferent) nerves that carry information received by sensory receptors in the

body to the CNS, and motor (efferent) nerves that carry information from the CNS to control voluntary movements of skeletal muscles.

The Sensory function of the SNS is activated when you sense or feel something on your skin for example and the SNS sends

signals from that point to your brain via the spinal cord, resulting in you experiencing the sensation.

The motor function of the SNS is demonstrated whenever you voluntarily move a body part.

THE AUTONOMIC NERVOUS SYSTEM

The Autonomic Nervous System is a network of nerves that connects the CNS to the body’s internal organs and glands providing feedback to the brain about their activities.

The ANS is called autonomous because many of the organs, glands and processes under its control are self-regulating and not usually under voluntary control.

Eg. Heartbeat, digestion, perspiration.

Regardless of our level of awareness or alertness, the ANS keeps the vital organs and systems of our body functioning thus maintaining our survival.

Divisions of the ANS

The ANS is made up of two distinct divisions, the sympathetic and parasympathetic nervous systems.

The sympathetic nervous system is responsible for increasing the activity of most visceral muscles, organs and glands in times of vigorous activity, stress or threat.

The parasympathetic nervous system is responsible for decreasing the activity of most visceral muscles, organs and glands, and keeping the body functioning in a normal state.

While the two nervous systems are both active at the same time, one system usually dominates the other at any given time.

The Sympathetic Nervous System

Enhances survival by providing an immediate response, in a split second, to any kind of emergency.

When an emergency is perceived, neurons in the SNS activate target organs and glands to respond in the required way. The result is that:

• heart rate and blood pressure increase, • breathing rate increases so more oxygen can be taken in, • sugar and fat are released from storage to provide instant energy to

the skeletal muscles, • the pupils dilate to allow more light to enter the eye and enhance

vision, • and sweat glands increase their production of sweat which cools the

body.

The Parasympathetic Nervous System

The PNS generally has the effect of counterbalancing the activities of the SNS.

It has two main functions:

1. It keeps the systems of the body functioning efficiently and in times of minimal stress and in the absence of threats, helps it to maintain the internal body environment in a steady, balanced, state of normal functioning (homeostasis).

2. It also restores the body to a state of calm, once the need for activity of the SNS has passed.

The PNS dominates the SNS most of the time as it is involved in basic everyday functioning.

DescriptionDescription FunctionFunction

SomaticSomatic Network of sensory nerves that carry Network of sensory nerves that carry info to the CNS received by sensory info to the CNS received by sensory and motor nerves that carry info and motor nerves that carry info from the CNS to control voluntary from the CNS to control voluntary movements of the skeletal muscles.movements of the skeletal muscles.

Initiates all skeletal muscle activity Initiates all skeletal muscle activity enabling you to perform voluntary enabling you to perform voluntary actions such as scratching your actions such as scratching your head, talking, riding a bike, dancing, head, talking, riding a bike, dancing, chewing and wriggling your toes. chewing and wriggling your toes.

AutonomicAutonomic The Autonomic Nervous System is a The Autonomic Nervous System is a network of nerves that connects the network of nerves that connects the CNS to the body’s internal organs CNS to the body’s internal organs and glands providing feedback to the and glands providing feedback to the brain about their activities.brain about their activities.

Heartbeat, digestion, perspiration. Heartbeat, digestion, perspiration.

Regardless of our level of awareness Regardless of our level of awareness or alertness, the ANS keeps the vital or alertness, the ANS keeps the vital organs and systems of our body organs and systems of our body functioning thus maintaining our functioning thus maintaining our

survival.survival.

SympatheticSympathetic Enhances survival by providing an Enhances survival by providing an immediate response, in a split immediate response, in a split second, to any kind of emergency. second, to any kind of emergency. When an emergency is perceived, When an emergency is perceived, neurons in the SNS activate target neurons in the SNS activate target organs and glands to respond in the organs and glands to respond in the required wayrequired way

heart rate and blood pressure heart rate and blood pressure increase, breathing rate increases so increase, breathing rate increases so more oxygen can be taken in, sugar more oxygen can be taken in, sugar and fat are released from storage to and fat are released from storage to provide instant energy to the provide instant energy to the skeletal muscles, the pupils dilate to skeletal muscles, the pupils dilate to allow more light to enter the eye and allow more light to enter the eye and enhance vision, and sweat glands enhance vision, and sweat glands increase their production of sweat increase their production of sweat which cools the body.which cools the body.

ParasympatheticParasympathetic The PNS generally has the effect of The PNS generally has the effect of counterbalancing the activities of the counterbalancing the activities of the SNS. It dominates the SNS most of SNS. It dominates the SNS most of the time as it is involved in basic the time as it is involved in basic everyday functioning. everyday functioning.

It keeps the systems of the body It keeps the systems of the body functioning efficiently and in times of functioning efficiently and in times of minimal stress and in the absence of minimal stress and in the absence of threats, helps it to maintain the threats, helps it to maintain the internal body environment in a internal body environment in a steady, balanced, state of normal steady, balanced, state of normal functioning (functioning (homeostasis). homeostasis). It also It also restores the body to a state of calm, restores the body to a state of calm, once the need for activity of the SNS once the need for activity of the SNS has passed.has passed.

•OLD COURSE

Research on hemispheric specialisation:

• There are 3 main approaches to conducting research on hemispheric specialisation:

1. Studying individuals with brain damage

2. Studying people who have had a split brain operation.

3.Studying people with intact, and damaged brains.

1. Studying people with brain damage

• People who have suffered brain damage include those who have suffered a stroke, have suffered head injuries through a car or sporting accident, or for a medical reason, have had to have part of their brain surgically removed.

• This research has been crucial in localising the functions of each hemisphere. For example, Broca's and Wernicke’s pioneering studies on damage to the specific parts of the left hemisphere that are involved in speech production and speech comprehension. Their research clearly showed that language and language- dependent verbal tasks are a specialised function of the left hemisphere.

• Similarly, the role of the right hemisphere in spatial tasks is evident in people with Neglect Syndrome, a disorder caused by damage to the right hemisphere. Sufferers behave as if the left side of their world does not exist. For example, they may eat all the food on the right side of their plate.

Case Studies:

• Sometimes one of the best methods of brain research is to conduct a case study. Case study: A detailed account of a single individual

• Eg. Phineas Gage, Albert Einstein• Advantages: Rich source of information and

detail• Disadvantages: Time consuming, problems with

generalising as cases are extraordinary.

• Phineas Gage is probably the most famous patient to have survived severe damage to the brain.  He is also the first patient from whom we learned something about the relationship between personality and the function of the front parts of the brain.

• The tamping iron was 3 feet 7 inches long and weighed 13 1/2 pounds.  It was 1 1/4 inches in diameter at one end and tapered over a distance of about 1-foot to a diameter of 1/4 inch at the other.  The tamping iron went in point first under his left cheek bone and completely out through the top of his head, landing about 25 to 30 yards behind him.  Phineas was knocked over but may not have lost consciousness even though most of the front part of the left side of his brain was destroyed.  Dr. John Martyn Harlow, the young physician of Cavendish, treated him with such success that he returned home to Lebanon, New Hampshire 10 weeks later.

• Some months after the accident, probably in about the middle of 1849, Phineas felt strong enough to resume work.  But because his personality had changed so much, the contractors who had employed him would not give him his place again.  Before the accident he had been their most capable and efficient foreman, one with a well-balanced mind, and who was looked on as a shrewd smart business man.  He was now fitful, irreverent, and grossly profane, showing little deference for his fellows.  He was also impatient and stubborn, yet impulsive and indecisive, unable to settle on any of the plans he devised for future action.  His friends said he was "No longer Gage."

2. Studying people who have had a split brain operation.

• A split brain operation involves surgically cutting the corpus callosum, the main bundle of nerves/tissue that connects the two hemispheres.

• This procedure was first used in the 1940’s to minimise or stop recurring seizures in severe cases of epilepsy that could not be treated by any other means. By severing the corpus callosum, the

seizures were unable to pass over the hemispheres.

• Important information gained from split-brain research is how the left and right hemisphere function when they cannot exchange information, and therefore cannot communicate together. For example, Sperry (1974) found that a split brain patient can recognise a picture of an object but not name it.

3.Studying people with intact and damaged brains.

• This refers to the study of people who have not undergone brain surgery and do not have a brain injury or disease.

• New technology allows the study of brain functions ie: - Electrical stimulation of the brain (ESB)– Electroencephalograph (EEG)– Computerised Axial Tomography (CAT)– Positron emission tomography (PET)– Magnetic Resonance Imaging (MRI)– Functional Magnetic Resonance Imaging (fMRI)– The Wada test

Electrical Stimulation of the Brain (ESB)

• ESB involves precisely regulated electric current to stimulate a specific area of the brain leading to either activation or inhibition of stimulated area.

• Wilder Penfield mapped the brain using numbered tags, and by eliciting either a physical, emotional or experiential response.

Electrical Stimulation of the Brain (ESB)

• Advantages:

-Identifying function and location.

-hemispheric specialisation.

-Disadvantages:

-Only useful for people undergoing brain surgery.

-Invasive risks.

-Generalisation difficult.

The Wada test:

• The Wada test is used on patients with intact brains before surgery to find out in which hemisphere the language centres are located.

The WADA test:

• Sodium amytal (a fast acting barbiturate) is injected into either the left or right carotid artery (an artery in your neck)

• These arteries send blood primarily to the cerebral hemisphere on the same side as the injected artery

ie. Injecting the left artery results in anaesthetising the left hemisphere (and so the right side of the body)

The WADA test:

What happens?• Patients are asked to put both arms in the air and count

backwards from 100.• The arm on the opposite side of the injection will fall limp

(indicating that the anaesthesia has taken effect)• If patients continue to count backwards the language

centre must be on the other side from the injected artery.• If the patient stops counting, the language centre must

have been anaesthetised and is on the same side as the injection.

Electroencephalograph: (EEG)

• EEG is a device that detects, amplifies and records general patterns of electrical activity of the brain.

• Described in rhythms or patterns as alpha, beta, delta, theta.

• Used to diagnose brain-related medical conditions

Electroencephalograph: (EEG)

• Advantages:

-Non invasive

-Less expensive than PET and MRI, can be used widely and over long periods

• Disadvantages:

-Doesn’t provide detail on specific brain structures.

Computerised (axial) Tomography (CAT)

• A CT is a neuroimaging technique that produces a computer enhanced image of a cross section (slice) of the brain from X-rays taken at different angles.

• Needs a radiologist.• Contrast/iodine injected into the bloodstream to

highlight brain’s blood vessels with no ill effect.

Computerised (axial) Tomography (CAT)

• Advantages:

-Non invasive

-precisely locates brain damage.

• Disadvantages

-Only structural, not functional information.

Positron Emission Tomography (PET)

• PET produces a computer-generated image that provides information about brain function and activity during various tasks.

• Tracks blood flow and detects increased neural activity as a result of glucose consumption.

• Harmless radioactive substance injected.• Colour coding- red is most active

Positron Emission Tomography (PET)

• Advantages:-Detailed images of brain functioning.-Use on people without brain damage-More sensitive than CAT/MRI-Colour coding easy to analyse.• Disadvantages:-Injection-Session must be kept short-Can’t eliminate other causes of brain activity at time of the

scan

Magnetic Resonance Imaging (MRI)

• MRI is a neuroimaging technique that uses harmless magnetic fields and radio waves to vibrate atoms in the brain’s neurons to produce an image of the brain.

• Coloured image assembled by computer indicates high and low level activity.

Magnetic Resonance Imaging (MRI)

• Advantages:-Identifies structural abnormalities.-Detects very small changes.-Can detect prosopagnosia (identifying faces but not

objects) and akinetopsia (lack of motion perception)-No x-rays or radioactive substances.Disadvantages:-No metallic devices can be present.-Still does not assess brain function.

Functional Magnetic Resonance Imaging (fMRI)

• fMRI is a neuroimaging technique that enables the identification of brain areas that are particularly active during a given task by detecting changes in oxygen levels in the blood flowing through the brain.

• Colour variation reflects degree of activity.• Can take numerous images in succession

leading to more detailed, precise images.• 3D displays.

Functional Magnetic Resonance Imaging (fMRI)

• Advantages:-No radiation.-More detail than PET.-Colour coding• Disadvantages:-Still cannot eliminate other influences on

brain activity of brain at a given point.