the brain (chapter 3)
Complexity of the brain
- the brain is covered in three transparent, 'skin-like' membranes and encased in hard, bony skull. - protecting the brain is a watery like fluid (cerebrospinal fluid) that circulates between the membrane. Provides a cushion against knocks to the head thus protecting the brain from injury. - arteries carry nutrients and oxygen-rich blood throughout the brain. Without this blood, brain tissues quickly die.
Organisation of the nervous system
- the nervous system spreads throughout the entire body, from the tips of your toes and fingers to the top of your head. - a single system made up of different subsystems commonly referred to branches or divisions. - two main divisions CNS and PNS - CNS comprises the brain and the spinal cord. - PNS includes all parts of the nervous system that lie outside the brain and the spinal cord -
First brain experiments- Brain ablation experiments 1. Pierre Flourens pioneers experimental ablation 2. Karl Lashley's search for the location of learning and memory
- brain ablation involves, destroying or removing selected brain tissue followed by an assessment of subsequent changes in behaviour. - sometimes called lesioning because it involves brain injury, usually irreversible. 1. - 1820s in controlled laboratory experiments with animals - working mainly with rabbits and pigeons, he developed techniques of damaging or removing small areas pf brain tissue to observe the effects on the brain - varied the location from which he removed brain tissue found that the: - brain stem had specialised functions. damage caused some animals to stop breathing. - cerebellum appeared to coordinate movement. - removal of small bits of tissue in a specific area of the cortex would result in loss of movement criticised - possibility that behavioural changes he observed were caused by injury to brain parts beyond the cortex. - he did not write reports on his research, so his findings were difficult to test. 2 - beginning in the 1920s Lashey (1890-1958) used ablation in experiments to find the location of learning and memory in the brain - rats, monkeys and chimpanzees were taught various tasks and then bits if their cortical tissue were removed with the goal of producing amnesia for the memory of learnt tasks - found that learning and memory were located throughout the brain. - mass action is the idea that the large areas of the brain function as a whole in complex forms if a part is destroyed then a loss of function will depend on the amount of cortex that is destroyed. - equipotentiality is the idea that any healthy part of the cortex can take over the part if an injured part. - these principles reflect a holistic view.
Neuroimaging techniques: Structural neuroimaging
- computerised tomography (CT) brain imaging device that takes a series of 2D X-rays of slices of the brain and uses a computer to construct a 3D image of the brain. can show the difference between a healthy and abnormal brain allowing areas of damage to be identified. - magnetic resonance imaging (MRI) uses harmless magnetic fields to vibrate atoms in the brain's neurons and generate a computer image of the brain.
Structure of a neuron: Dendrites
- each dendrite separates out like the branches of a tree. - receives info from other neurons
Split-brain experiments
- involves cutting the band of nerve tissue connecting the two hemispheres - tissue is called the corpus collosum - disconnecting the hemispheres was found to reduce the incidence and severity of epileptic seizures. - the procedure is only performed in very serious cases of epilepsy where drugs and other medical procedures have not been effective.
Structure of a neuron: Myelin
- not all neurons are myelinated. - myelin is a white, fatty substance that coats and helps insulate the axon from the activity of the other nearby axons.
Neuroimaging techniques: Functional neuroimaging
- positron emission tomography (PET) - functional magnetic resonance imaging - a brain imaging and recording device measures the amount of brain activity that occurs while the participant is undergoing a task. - requires an injection of radioactive glucose - brain regions engaged in high levels of activity require more oxygen which = INCREASE IN GLUCOSE CONCENTRATION - therefore brain functioning can be identified when completing a task. (fMRI) - other functional neuroimaging techniques - a technique is based on standard MRI - measures subtle changes in blood oxygen levels in the functioning brain. - technique enables the identifictaion of brain areas that are particularly active during a gievn task by detecting changes in oxygen levels in blood flowing through the brain. - when an area in the barin is active- increased blood flow- more oxygen required by active neurons.
Structure of a neuron: Axon
- single, tube-like, extension that transmits mental info away from the soma to other neurons or cells. - most neurons have only one axon. many axons have branches that allow a message to ge sent to multiple cells.
Structure of a neuron: Axon terminals
- small branches at the end of an axon are axon collaterals are axon terminals. each axon terminal has a small knob like button. - terminal button is a structure that stores and secretes a chemical called neurotransmitter that is manufactured by the neuron and carries its messages to other neuron cells.
Structure of a neuron: Soma
- soma or cell body, combines the neural info received from the neuron's many dendrites and sends it to the axon.
First brain experiments- Electrical stimulation of the brain 1. Gustav Fritsch and Eduard Hitzig discover the motor cortex 2. Wilder Penfield maps the cerebral cortex
- weak electrical signals are generated continuously by neurons throughout the brain. - electrical activity in the brain can either be stimulated or detected using an electrode. - assumed that if electrical stimulation (of a specific brain area) initiate a response, such as movement of a body part, then that area controls or is involved in the response. - ESB may not just initiate a response, it may also interfere with the functions of a specific brain area, thereby inhibiting (blocking) a response. 1 2 - 20th century ESB procedures were perfected by neurosurgeon Wilder Penfield who used ESB to map the cerebral cortex (on patients used as research patients) - He invented a new treatment for patients with severe epilepsy.
Approaches over time to understanding the role of the brain: brain versus heart debate
An issue on whether the brain or heart is the location of or structure primarily responsible for human mental processes.
frontal lobe - prefrontal cortex
Association area involved with sophisticated mental abilities such as reasoning, planning, problem-solving, decision making and symbolic thinking; attention; regulation of emotions and expression of emotional reactions; self-awareness; aspects of personality such as initiating appropriate and inhibiting inappropriate behaviour.
Hindbrain: Medulla
The medulla is the lowest part of the brain and a continuation of the spinal cord, so it connects to the brain. The medulla controls vital bodily functions such as swallowing, breathing, heart rate, blood pressure, vomiting, salivating, coughing and sneezing, all of which occur automatically and are essential for survival. This is why a serious injury to the medulla, as could occur through a blow to the back of the head, is often fatal. Some parts of the medulla are also involved in sensations such as touch, pressure and vibration.
Glial cells: Astrocytes
Glial cells (sometimes called glia and neuroglia) provide support for neuronal function. For example, they surround neurons and hold them in place, supply nutrients and insulation, and aid in the repair of neurons and elimination of waste materials. In contrast to neurons, glial cells tend to be smaller and can readily multiply and divide, but they cannot generate or carry an action potential so they are not directly involved in the transmission of messages between neurons. However, without glial cells, neurons could not function. Astrocytes These star-shaped cells (also called astroglia) have numerous roles and are the largest and most numerous of the glial cells. They provide structural support for neurons by holding them in place, nutritional support by regulating local blood flow to provide more supplies to neurons when they are active, secrete chemicals that keep neurons healthy, assist recovery of damaged neurons and are also involved in the formation of new connections between neighbouring neurons.
Parasympathetic nervous system
In everyday situations in the absence of threat and when there is minimal stress, the parasympathetic nervous system helps to maintain the internal body environment in a steady, balanced state of normal functioning. The parasympathetic nervous system generally has the effect of counterbalancing the activities of the sympathetic nervous system. It restores the body to a state of calm, once the need for sympathetic nervous system activation has passed.
frontal lobe - primary motor cortex
Initiates and controls voluntary bodily movements (left controls right side of body and vice versa)
Hindbrain: Pons
Just above the medulla is the pons, a small bundle of neural tissue about 2.5 cm long. The pons is involved in sleep, dreaming and arousal from sleep ('waking'), as well as helping control breathing and coordination of some muscle movements. The pons also serves as a 'bridge' that connects parts of the brain with one another by relaying messages between the cerebral cortex and cerebellum and between the medulla and midbrain. For example, information from the ear first enters the brain from the pons, and messages for voluntary movements are passed on from the motor areas of the cerebral cortex to the cerebellum.
Midbrain: Reticular formation
Midbrain As the name suggests, the midbrain is in the central part of the brain. It is about 2.5 cm long and contains neural pathways connecting upper and lower brain areas. The midbrain is a collection of structures involved with movement, processing of visual, auditory and tactile sensory information, sleep and arousal. The midbrain receives a large amount of information from the eyes and ears and processes this to help produce orienting movements. For example, if you are walking and hear a car braking suddenly and loudly, the sound registers in your midbrain, which then triggers muscles in your neck and for eye movements to enable you to turn your head to look in the direction of the sound. This is coordinated movement, but not as complex as coordination by the cerebellum. Running through the centre of the midbrain and the hindbrain (which includes the brain stem) and upward to the forebrain is the reticular formation, a network of neurons, about the thickness of your middle finger. When viewed through a microscope, it resembles white netting or lacing, which is why it is called reticular (reticular means 'like a network'). The reticular formation helps screen incoming information so as not to overload the brain, alerts higher brain centres to important information, helps maintain consciousness, and regulates arousal (such as awakening from sleep) and muscle tone (tension).
Types of neurons: Interneurons
Motor neurons (also called efferent neurons) carry messages from the CNS to the cells in skeletal muscles, organs and glands to stimulate activity. They enable muscles to move so we can walk or speak, cause glands to secrete chemicals and help control the function of internal organs such as the heart, lungs and intestines. Skeletal muscles respond to messages from the CNS to start, stop or change movement. Motor neurons are located in the lower brain stem and spinal cord. All outgoing neural information must pass through them to reach the muscles. Motor neurons essentially control all actions and therefore all forms of behaviour.
Types of neurons: Motor neurons
Motor neurons (also called efferent neurons) carry messages from the CNS to the cells in skeletal muscles, organs and glands to stimulate activity. They enable muscles to move so we can walk or speak, cause glands to secrete chemicals and help control the function of internal organs such as the heart, lungs and intestines. Skeletal muscles respond to messages from the CNS to start, stop or change movement. Motor neurons are located in the lower brain stem and spinal cord. All outgoing neural information must pass through them to reach the muscles. Motor neurons essentially control all actions and therefore all forms of behaviour.
Forebrain: Thalamus
Often described as the gateway from the lower part of the brain to the cortex in the upper part Filters information from almost all the sense receptor sites (except the nose), then passes it to relevant areas of the brain for further processing of the brain Information from the cerebral cortex also passes through the thalamus to lower brain structures, the spinal cord and out to the peripheral nervous system. For example, the thalamus has neurons that relay messages between motor cortex areas and movement control centres in the brainstem (such as the cerebellum) Plays a role in attention by filtering the vast amounts of incoming to-be-attended-to sensory information, highlighting some inputs and de-emphasising others - damage may lead to visual or hearing impairments, or the inability to feel sensations when touched Areas of the thalamus that are connected to the reticular formation and RAS are crucial to the regulation of arousal - damage can lead to lowered arousal (lethargy to coma)
Gilal cells: Schwann cells
Schwann cells predominantly have functions similar to those of oligodendroglia, except they form the myelin sheath around axons in the PNS.
Forebrain: Hypothalamus
The vital role in maintaining the body's internal environment by regulating the release of hormones from various glands of the body (through its control of the pituitary gland) and influencing behaviours associated with basic biological needs, such as hunger, thirst as well as sleep. Depending on exactly where and how severely the hypothalamus is damaged, it could result in an inability to regulate internal body functioning (such as maintaining a constant body temperature), problems with the normal sleep/wake cycle,an overwhelming urge to eat, uncontrollable anger, or the degeneration of sex organs and a significant reduction in sex drive (in males only) Is the part of the limbic system - an interconnected group of forebrain structures located along the base of the cerebral cortex and includes the amygdala, hippocampus and hypothalamus
Types of neurons: Sensory neurons
Sensory neurons (also called afferent neurons) receive and carry sensory information. This is received from both our external and internal environments then transmitted to the CNS. Their main role is to help us sense the external world and monitor changes within our bodies. Information is received from the external environment via sensory receptors in sense organs, and internally, within the body, from the muscles, joints, tendons, organs and glands. There are different types of sensory neurons, each of which is specialised to respond only to a particular type of stimulation. For example, the sensory neurons in the ears respond to sound waves detected by receptors within the cochlea (inner ear), but not to light. The sensory neurons in the skin that respond to heat would not respond to chemical energy, which would stimulate the sense of smell. You are able to read the words on this page because sensory neurons specialised for visual information are transmitting information from your eyes to your brain.
frontal lobe - broca's area
Speech production
CNS - brain
an intricate network of cells that plays a vital role in processing information from the body's external and internal environments and in directing responses. - kept continually formed, everchanging environments through sensory information detected and sent it by the many and varied sensory receptor cells located at or near the surface of the body and also deep within the body. - brain is more than a mass of networked cells. - brain cells are organised into many identifiable areas. - for example, some parts are dedicated to sensory or motor functions yet most parts have integrating and overlapping functions - refer to page 147 for example - many brain functions involve the activation of interconnected nerve cells that form neural pathways which link different brain areas and structures. - these pathways are often referred to as neural circuits or tracks
Hindbrain: Cerebellum
The cerebellum, located at the base of the brain (attached to the brain stem), is a cauliflower-shaped structure about the size of a tennis ball in adult brains. The cerebellum coordinates fine muscle movements and regulates posture and balance. Although the commands for movement are initiated higher up in the brain, the cerebellum organises and adjusts muscle activity to help ensure movement is smooth and precise so that it's performed more or less automatically. The cerebellum makes rapid-fire calculations about which muscles must be activated and by exactly how much. The cerebellum is involved in activities requiring a rapid and skilled sequence of movements, such as when speaking and touch-typing. It is particularly active when you learn a new movement or when you perform a sequence of movements where the next movement cannot be predicted in advance. It is also involved when you make everyday voluntary, purposeful movements, such as when reaching to pick up a cup of coffee, so that your arm and hand make one continuous movement. Damage to the cerebellum makes it difficult to coordinate muscle control for everyday activities such as reaching, walking, throwing a ball or riding a bike. There are problems with balance, and damage can also contribute to difficulties with speech, which involves intricate movement control. The cerebellum is also involved in learning and memory associated with movement in particular. For example, when we learn to walk, speak, or play a musical instrument, the necessary, detailed control information is believed to be processed and temporarily stored within the cerebellum, before it is transferred to the cerebral cortex for more permanent storage. Research findings suggest that the cerebellum may also play a role in other mental processes, including spatial learning, navigation and spatial memory (Bergland, 2015).
Role of the cerebral cortex: Cerebral hemispheres
The cerebral hemispheres are two almost-symmetrical brain areas running from the front to the back of the brain. They are connected by the corpus callosum and are referred to respectively as the left hemisphere and the right hemisphere. The left and right hemispheres not only appear to be alike in overall size, shape and structure, but they also have many of the same functions. The specific area of the hemisphere responsible for each of these functions is located in approximately the same place in each hemisphere. For example, each hemisphere has motor and sensory areas that perform the same motor and sensory functions, each for a different side of the body (i.e. contralateral function). The left hemisphere receives sensory information from the right side of the body and controls movements on the right side. The right hemisphere receives sensory information from the left side of the body and controls movements on the left side. In addition to the hemispheres having common functions, each hemisphere also has specialised functions. For example, human language is primarily a function of the left hemisphere, and the right hemisphere is primarily involved in many functions that do not depend on language, such as spatial and visual thinking and recognition of faces and tunes.
Forebrain: Cerebrum
The cerebrum is located above and in front of the cerebellum and occupies most of the forebrain. The cerebrum consists of an outer surface called the cerebral cortex and masses of neural tissue where neurons form connections with each other and receive and process incoming and outgoing information. The cerebrum and its outer cortex are primarily responsible for almost everything we consciously think, feel and do. The cerebrum (including the cortex) is divided into two cerebral hemispheres. There is one on the left and one on the right of a deep groove that runs from the front to the back (called the longitudinal fissure). Both hemispheres remain connected, mainly by the corpus callosum which enables information exchange and coordinated functioning of the brain.
Roles of the cerebral cortex: Hemispheric specialisation
The idea that one hemisphere has specialised functions or exerts greater control over a particular function is called hemispheric specialisation. The terms hemispheric dominance and hemispheric lateralisation are also sometimes used. Although each hemisphere can specialise or exert greater control in various functions, both the left and right hemispheres are actually involved in nearly all functions, usually acting together in a coordinated and interactive way. Ordinarily, we do not use the left hemisphere of our brain any more than the right hemisphere, and vice versa. The earliest evidence for 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 such as understanding speech and talking fluently. Damage to the right hemisphere often resulted in difficulties with tasks that did not depend on language. These were mainly dependent on visual and spatial abilities, such as when using a map to navigate through an unfamiliar location.
Roles of the cerebral cortex: Left hemisphere specialisations
The left hemisphere specialises in verbal and analytical functions. Verbal functions involve the use or recognition of words such as in reading, writing, speaking and understanding speech, all of which are important in language. Analytical functions essentially involve breaking a task down into its key parts and approaching it in a sequential step-by-step way. This is required, for example, when you use logical reasoning to interpret and apply a formula to solve a mathematics problem, critically evaluate an experimental design in psychology, or prepare a meal at dinner time. Analytical functions are also involved when you develop an argument for a debate, plan how to save up enough money to buy a car or find enough time to complete all the homework for six different subjects.
Roles of the cerebral cortex: Right hemisphere specialisations
The right hemisphere specialises in non-verbal functions that do not depend on language skills. Its non-verbal functions include: - spatial and visual thinking, such as completing a jigsaw puzzle, reading a map or visualising the location of objects or places - recognising faces, patterns and tunes appreciating music and artworks (but not necessarily producing them) - creative thinking - daydreaming. The right hemisphere is also more involved in recognising emotions from facial cues ('signals'), such as a raised eyebrow or trembling lips, and in non-verbal emotional expression.
Sympathetic nervous system
The sympathetic nervous system arouses the body when we experience an extreme emotion, feel threatened or suddenly experience stress, such as when riding a roller coaster or unexpectedly approached by a vicious-looking dog as we walk along the street. This system can very quickly arouse the body for an immediate response to an emergency. For example, it can instantly mobilise the body in readiness for fight to confront and fight off a threat, flight to escape a threat by running away to safety, or to freeze by keeping absolutely still and silent to avoid detection. This is an adaptive reaction called the fight-flight-freeze response (which is studied in depth in Unit 3).
Gilal cells: Microglia
These extremely small cells act like immune system cells elsewhere in the body by protecting neurons from intruders. They monitor the health of brain tissue and identify and devour foreign substances. When brain cells are damaged, microglia invade the area to help repair it. They also help clean up the nervous system by eliminating foreign matter and debris such as the remains of dead neurons.
Gilal cells: Oligodendroglia
These insulate neurons in the CNS by forming and maintaining the myelin sheath surrounding the axon, thereby preventing adjacent neurons from 'short-circuiting' and also speeding up the process of communication. They also absorb chemicals that the neuron secretes and secrete chemicals that the neuron absorbs, roles that are believed to contribute to a neuron's nutrition and function.
Central nervous system
consists of the brain and spinal cord. main functions include: - processing information through the sensory systems and other parts of the body - CNS is named 'central' cause it is located in the centre of the body - central to all our mental processes and behaviours including what you think and do (processed through the system) - CNS is important to our ability to function - entirely covered (protected) by bone (brain by the skull and the spinal cord by the spinal column) - brain and spinal cord are also covered by the meninges and suspended in cerebrospinal fluid to cushion blows
Approaches over time to understanding the role of the brain: Phrenology
eighteenth century proposed that different parts of the brain had different functions. this concept is known as localisation of brain functions. describes the study of the relationship between the skulls surface features and a person's personality and behavioural characteristics.
parietal- association areas
involved in functions such as attention, spatial reasoning and judging the position of our body in space.
temporal lobe- wernickies area
involved with comprehension of speech
Somatic nervous system
is a network of nerves that carries sensory info to the CNS and motor info from the CNS The somatic nervous system (SNS) is a network of nerves that carries sensory information to the CNS and motor information from the CNS. Sensory information is received at sensory receptor sites in the body (skin, muscles, joints and tendons) and carried along sensory neural pathways. Motor information is carried along motor neural pathways to skeletal muscles to control their activity.
Autonomic nervous system
network of nerves that carries messages between the CNS and the heart, lungs and internal organs and glans The ANS regulates, or controls, the functioning of internal organs automatically, without you having to consciously think about it. For example, the ANS regulates heart rate, breathing, digestion, salivation and perspiration, actions that occur continuously and involuntarily without your conscious control. Thus, the ANS is a system that functions fairly independently of the CNS in maintaining the body's internal states and processes.
Approaches over time to understanding the role of the brain: mind-body problem
problem involves the question whether our mind and body are distinct, separate entities or whether they are one and the same thing.
CNS - spinal cord
the spinal cord is the long, thin bundle of nerve tissue that extends from the base of the brain to the lower back. Encased in a series of bones called vertebrae, that extends further than the actual spinal cord. the spinal cord links the brain and parts of the body below the neck Two major functions of the spinal cord are to: - receive sensory information from the body (via the PNS) and send these messages to the brain for processing - receive motor information from the brain and send it to relevant parts of the body (via the PNS) to control muscles, glands and internal organs so that appropriate actions can be taken. For an example, refer to page 147
parietal - primary somatosensory cortex
receives and processes bodily sensory information
temporal lobe - primary auditory cortex
receives and processes sounds from both ears
occipital lobe- primary visual corrtex
receives and processes visual information from the eyes
Peripheral nervous system
term peripheral refers to 'outskirts' or 'outlying'. the PNS is the entire network of nerves located outside the CNS that transmits information to and from the CNS. the PNS carries information to the CNS from the sense organs, muscles and glands. PNS role is the communication of information around the body and in the body's normal functioning CNS depends on the PNS to provide it with info from the sense organs about the external and internal environment from other parts of the body. PNS has two subdivisons called somatic and automatic nervous system.
