Chapter 2: Biological Bases of Behaviour

Hindbrain

• base of the near the back of the skull

• controls activities over which we have no conscious control (eg. breathing, coordinating voluntary muscle movements and reflex actions)

Cerebellum

• part of the hindbrain

• receives information from the sensory systems, spinal cord, and other part of the brain

• used to regulate posture and balance, and coordinate fine muscle movements

Damage to the cerebellum

• affected by alcohol consumption, with excessive consumption resulting in a stumbling gait

• when injured, one walks as if they were drunk

Medulla

• base of the hindbrain in front of the cerebellum

• controls heart rate, breathing, digestion and swallowing

Damage to the medulla

• lead to an individual being placed on life support machines to regulate breathing and heart function

• if the damage is too severe, the person will be pronounced as ‘brain dead’

Midbrain

• sit on top of the hindbrain, under the cerebral hemispheres

• pass information from the spinal cord to the forebrain and vice versa

• receives messages from all the senses except smell and sends them on to higher brain regions that deal with hearing, seeing, tasting, and touching

Reticular Formation

• through the centre of thew midbrain, running from the forebrain to the hindbrain

• main function is to screen incoming information so that the higher brain centres can attend to important information and not be overloaded with less important information

• role in controlling sleeping and waking and our level of alertness

• referred to as the brain’s arousal system

Reticular Activating System (RAS)

• part of the reticular formation

• it increases or dampens down arousal level and muscke tone in response to feedback from the brain

• when RAS is low, we go to sleep

Forebrain

• most highly developed and largest part of the brain

• major role in how we think, feel and behave

• neural pathways in the forebrain connect with parts of the midbrain and hindbrain to coordinate and regulate functions of the brain

• consists of hypothalamus, thalamus, and the cerebral cortex

Thalamus

• filters information from all the senses except the nose and passes it on to the appropriate part of the brain for processing

• acts as a relay system

• role in regulating level of arousal, wakeness, energy, and attentiveness we feel through its connect to the RAS

Damage to the thalamus

• result in reduced sense of touch, or visual or hearing impairment

• arousal is reduced, resulting in lethargy or even coma

Hypothalamus

• located just below the thalamus

• extremely important role, with its main function is to regulate the release of hormones that control body temperature, biological clock, sex drive and thirst and hunger needs

Cerebrum

• most of the forebrain, located above and in front of the cerebellum

• two hemispheres; left and right

• consist of an outer layer; cerebral cortex

Cerebral Cortex

• located over and around most of the other brain structures

• responsible for the higher-level processes of the human brain; language, memory, reasoning, thought, learning, decision-making, emotion, intelligence and personality

Hemispheres

• symmetrical

• each hemisphere has sensory and motor functions that are found in virtually the same place in each hemisphere

Corpus Callosum

• thick band of fibres that joins the two hemispheres

• let messages be sent from one hemisphere to the other

Damage to the corpus callosum

• if it were cut, the two hemispheres would be unable to communicate, making normal activities, such as hand coordination very difficult

Right Hemisphere

• controls the left side of the body

• more important in terms of controlling verbal functions

• speaking, reading, writing and understanding language

• major role in reasoning or analyzing or interpreting information

Left Hemisphere

• controls the right side of the body

• controls non verbal activities that do not require language, such a drawing

• involved in spacial tasks like following maps, facial recognition, and finding ways through mazes

Lobes of the cerebral cortex

• frontal lobe

• parietal lobe

• occipital lobe

• temporal lobe

Frontal Lobe

• front of each hemisphere, in front of the parietal lobe, and above the temporal

• control voluntary movement

• abstract thinking

• regulation of emotional behaviour

• personality

Damage to the frontal lobe

• personality change may occur

• capacity for reasoning and problem solving is reduced

Parietal Lobe

• above the occipital lobe and behind the frontal

• integrates sensory information relating to touch, temperature, position in space and muscle movement

Damage to the parietal lobe

• leads to a reduction in bodily feelings

Occipital Lobe

• at the back of the brain, above the cerebellum

• receive and process visual information such as colour, shape and motion

Damage to the occipital lobe

• affect vision even if the eyes and their connecting nerves to the brain are normal

Temporal Lobe

• each side of the brain, under the cerebral hemisphere

• critical role in our ability to interpret different sounds and understand speech

Damage to the temporal lobe

• affects one’s language ability

External recording techniques

electroencephalograph (EEG)

Electroencephalograph

• measurement type is external and does not use imaging techniques

• method includes electrodes consisting of small metal discs with thin wires are pasted onto your scalp

• detects electrical charges that result from brain activity

Use and limitations of EEG

Scanning techniques- still pictures

• computed axial tomography (CAT)

• magnetic resonance imaging (MRI)

Computed (Axial) Tomography (CT/CAT)

• type of X-ray that scans the brain at different angles

• goes to the computer leading cross sectional pictures of slices through the brain

Use and limitations of CAT

• detection of tumours

• used in research to look at possible abnormalities in brain structure associated with mental illnesses

• images only show brain structure, and of inferior quality compared to MRI

Magnetic Resonance Imaging (MRI)

• uses a strong magnetic field, radio frequency pulses and computers to produce 3D images from which 2D ‘slices’ can be displayed

Use and limitations of MRI

• used in detection of tumours and other abnormalities

• does not require X-irradiation and images superior to CAT can, but MRI cannot be used if the patient’s body contains any magnetic objects in them (eg. pacemakers)

Scanning techniques- dynamic pictures

• functional magnetic resonance imaging (fMRI)

• position emission tomography (PET)

Functional Magnetic Resonance Imaging (fMRI)

• most recent form of MRI

• measures brain activity when neurons consume oxygen

• higher levels of oxygen indicate higher level of activity

• colour variations indicate level of activity

Use and limitations of fMRI

• enables observation and measurement of changes in the brain during activity

• scans can be made rapidly, they have good spatial resolution, are non invasive and do not expose patient to radioactive tracers

• less expensive than PET scans

Position Emission Tomography (PET)

• scans provide images of the brain in action by tracking a glucose solution that contains a short-lived radioactive tracer

• records are based on glucose consumption in the brain

• different colours indicate areas of low or high activity

Use and limitations of PET

• does not provide an image of the health level of the brain but problems

• used in research to show specific brain areas activated during activities such as reading, speaking, and thinking

• images are not as detailed as those from fMRI and are more expensive

Neuron

• type of cell specialised to receive, transmit, and process information

• consist of'; cell body (soma), dendrites, axon, and myelin sheath

Soma

• contains a nucleus that controls the maintenance and function of the cell

• integrates information received from dendrites and passes it to the axon

Dendrites

• fine branches from the soma that receive incoming messages from other neurons and transmit it to the cell body

Axon

• structure only found in neurons

• purpose of transferring information over distance in the nervous system

• many neurons only have one axon, but axon terminals are branched off at the end

Myelin Sheath

• speed up the transmission of electrical signals

• allow nutrients to enter the axon and waste products to leave

• protects the axon

Neurotransmitters

• chemicals that affect the way messages are passed from neuron to neuron

• carry message from a sending neuron across a synapse to receptor sites on a receiving neuron