Biological Psychology

Nervous system

The system that produces and relays messages between the brain, spinal cord and a network of neurons.

Central nervous system

Part of the nervous system made up of the brain and spinal cord that carries sensory information up the spinal cord to the brain via sensory neurons and carries motor messages to the PNS via motor neurons.

Peripheral nervous system

Nerves outside of the brain and spinal cord that carry sensory information to the CNS from the body and motor messages from the brain to organs and muscles in the body.

Autonomic nervous system

Branch of the PNS that carries motor messages from the brain to internal glands and organs via motor neurons, causing their involuntary activity, and carries sensory messages to the brain about the activity level of glands and organs via sensory neurons. Controls involuntary muscle movement.

Somatic nervous system

Branch of the PNS that carries sensory information received by the sensory receptor cells to the CNS via sensory neurons and carries motor messages from the CNS to skeletal muscles via motor neurons. Controls voluntary and involuntary skeletal muscle movement.

Sympathetic nervous system

Controls the fight or flight response. Regulates the glands and internal organ function to physically prepare the body for increased activity during heightened physical or emotional arousal.

Parasympathetic nervous system

Controls the rest and digest response. Calms the body after being under the control of the sympathetic nervous system. Maintains an energy level suitable for normal bodily functioning.

Neurons

Cells of the nervous system that communicate with each other, as well as muscle and gland cells.

Dendrites

Extensions of the cell body that receive neurotransmitters from pre-synaptic neurons and convert them into electrical nerve impulses that are conducted towards the cell body.

Cell body (soma)

Contains a nucleus that controls the activities of the neuron.

Axon

The long projection of a neuron that conducts electrical nerve impulses and carries them away from the cell body.

Axon terminals

The enlarged end points of axon branches that store neurotransmitters and release them into the synaptic cleft.

Myelin sheath

Fatty covering of the axon that acts as an insulator protecting the axon from stimuli that could interfere with electrical nerve impulses. It also increases the speed of electrical nerve impulse transmission and helps improve the conduction of the transmission.

Sensory neurons

Neurons that process sensory information from the sense organs and carry the sensory messages to the CNS.

Motor neurons

Neurons that carry motor messages from the CNS to the muscles, glands, and organs of the body.

Interneurons

Neurons that act as the connection between sensory neurons and motor neurons and transfers messages from sensory neurons to motor neurons within the CNS.

Neurotransmitters

Molecules found within the central nervous system that act as chemical messengers. They allow neurons to communicates by relaying information between them across the synapse, as well as from neurons to glands and muscle cells.

Electro-chemical signal

• Neurons can be explained as carrying electro-chemical signals, as an electrical nerve impulse (action potential) travels through the neuron, and neurotransmitters travel between the synapse of communicating neurons.

• The electrical nerve impulses are the ‘electro’ component, and the neurotransmitters are the ‘chemical’ component of the signal.

Neurotransmission steps

1. Electrical nerve impulses (action potential) travel to the axon terminal in the pre-synaptic neuron.

2. The action potential causes the neurotransmitters to be released from vesicles in the axon terminal.

3. Neurotransmitters diffuse across the synaptic cleft.

4. Neurotransmitters bind to receptor sites on the dendrite of the post-synaptic neuron.

5. Dendrite converts neurotransmitters into electrical nerve impulses which travel to the cell body.

Synapse

The axon terminal of a pre-synaptic neuron, the synaptic cleft and the dendrite of a post-synaptic neuron. It allows neural transmission to occur by converting the electrical nerve impulse from one neuron into a chemical signal and then back again into an electrical nerve impulse in another neuron.

Hindbrain

Coordinates sensory and motor messages entering and leaving the spinal cord, and is responsible for balance and coordination. Includes:

• Medulla - the lowest part of the brainstem that relays information between the spinal cord and the brain, and regulates the respiratory and cardiovascular systems. 

• Cerebellum - the convoluted structure at the lower back of the brain sitting underneath the cerebrum. It is involved in balance, judging distance, and coordination of fine motor movement.

Midbrain

Receives sensory messages from all the senses except smell, and sends information to the forebrain. Includes:

• Reticular formation - network of nuclei located within the length of the brainstem that helps maintain wakefulness and alertness and aids in the regulation of the sleep-wake cycle.

Forebrain

The largest part of the brain that plays a key role in cognition, emotion, behaviour, and processing sensory information. Includes:

• Cerebrum - the largest part of the brain consisting of white matter on the inside, and the cerebral cortex on the outside. It is split into two cerebral hemispheres.

• Thalamus - double-lobed structure located just above the brainstem that receives sensory information, except smell, and transmits information to the cerebral cortex. It also has an influence on sleep.

• Hypothalamus - sits below the thalamus and regulates sleep, eating, body temperature and sexual drive. Also regulates the release of hormones from the pituitary gland that sits beneath it.

Cerebral cortex

Outermost layer of the brain made up of nerve cell tissue that is responsible for higher order processes such as memory, language, reasoning, emotion and decision making.

• This two-four millimetre thick layer of tissue sits on top of the cerebrum and has deep furrows to increase surface area. The nerve tissue is comprised of unmyelinated neurons, and the cell bodies of neurons, which are collectively known as grey matter.

Hemispheres

• The cerebrum is the largest part of the brain and is divided into two halves known as the hemispheres. The hemispheres are connected by the corpus callosum and each hemisphere is dominant in the control of specific tasks.

• Hemispheric specialisation is the concept that each hemisphere has greater control over certain functions. Both hemispheres are involved in almost all functions but each is dominant in specialised functions.

• The hemispheres have contralateral control of the body, which means the left hemisphere controls the right side of the body, and the right hemisphere controls the left side of the body.

Corpus callosum

The thick band of nerve fibres connecting the cerebral hemispheres of the brain and allowing the transfer of information between them. This is the largest white matter structure in the human brain with myelinated axons allowing for optimum nerve impulse transmission between neurons.

Left hemisphere

• Movement of the right side of the body,

• producing speech,

• comprehending language,

• writing,

• reasoning,

• logical thinking,

• mathematic processes,

• sequential information processing.

Right hemisphere

• Movement of the left side of the body,

• ability to draw pictures,

• spatial orientation,

• experiencing and expressing emotion, as well as perceiving the emotion of others,

• music and art awareness,

• intuition,

• creativity.

Frontal lobes

• Voluntary movement

• planning and decision making

• problem solving

• ability to reason

• ability to organise information

• expression of personality

• recognition of emotions

• speech production

• impulse control

Temporal lobes

• Understanding speech

• interpreting auditory information

• processing the sense of smell

• facial recognition

• recognising body language

• recognition of emotions (partly)

• long-term memory formation

Occipital lobes

• Visual perception

• visual processing

• interpreting visual information

• facial recognition

• perception of distance and depth

Parietal lobe

• Processing sensory information relating to the sense of touch

• spatial awareness

• perception of the location and movement of body parts

• integration of sensory information

Broca’s area

• Adjacent to the primary motor cortex in the left frontal lobe.

• Controls the fine muscles responsible for the production of clear, articulate speech. These include the muscles of the tongue, cheeks, lips and jaw, as well as muscles of the larynx and pharynx.

• Broca’s aphasia - Impairment in the ability to produce articulate speech.

Wernicke’s area

• Adjacent to the primary auditory cortex in the left temporal lobe.

• Responsible for the understanding/comprehension of language and the production of meaningful speech.

• Wernicke’s aphasia - Impairment in the ability to understand language and produce meaningful speech.

Pre-frontal cortex

The front layer of the frontal lobes that coordinates executive function such as the ability to predict consequences of behaviours, as well as the ability to recognise and regulate emotions.

Primary motor cortex

A strip of cerebral cortex running through the frontal lobes that controls voluntary movement of the body. Different zones of the primary motor cortex correspond to the various parts of the body, with the size of each zone representing the importance of the body part according to how often it is used.

Primary sensory cortex

A strip of cerebral cortex running through the parietal lobes that registers and processes sensory information.

Primary auditory cortex

An area within both temporal loves that registers and processes auditory information that is received from the ears.

Primary visual cortex

An area within both occipital lobes that registers and processes visual information that is received from the eyes.

Phineas Gage (1848)

• in 1848 Phineas gage was working as a foreman building a railroad. The twenty-five year old was described as active, well organised, reasonable and calm.

• While compacting powder in a hole in preparation for blasting, he became distracted and the tamping iron hit rock. The powder exploded forcing the iron - pointy end up, into the left side of his face under his cheek bone and continued up and back, exiting through the top of his skull.

• Phineas was thrown onto his back, his limbs convulsed a few times and a few minutes later he was able to speak. His mean put him in an ox cart and he rode to a hotel in town.

• He remained conscious as his wounds were being attended to by doctors. Fractured bone pieces and some protruding brain was removed and adhesive straps kept the scalp together.

• A year later, when visited by one of the doctors who had treated him, it was discovered that Phineas applied for the position of foreman but the contractors could not give him the position due to his change in personality.

• While they described him as highly capable, efficient and polite prior to the incident, he was now impatient, impulsive, uncaring for others around him, and would often swear.

• Serious damage to Gage’s left frontal lobe caused a marked shift in personality and organisational skills. Therefore, this case contributed to the understanding that the frontal lobes of the brain are responsible for the expression of personality, problem solving and impulse control.

Roger Sperry (1959-1968)

• Before using human volunteers, Sperry conducted split-brain research on cats and monkeys. From this research he deducted that the two hemispheres worked together independently of each other, as two split brains, when the corpus callosum connecting them was cut, and that the corpus callosum allowed direct communication between the hemispheres.

• Sperry later conducted research on humans who had undergone split-brain surgery (severing of the corpus callosum) to treat their epilepsy. Optic nerves from each eye cross over at the optical chiasm so input from the left field of view is processed in the left hemisphere - irrespective of whether the corpus callosum is intact.

• Participants with a severed corpus callosum were asked to focus on a black dot in the middle of a white screen and words or pictures presented on the left of the dot were processed in the right hemisphere and vice versa. In one experiment participants were flashed a word to the right of the dot and asked to say what they saw. Participants had no trouble saying the word. When, however, participants were flashed a word to the left of the dot, they were unable to say what they saw.

• Further experiments required the participants who were unable to say what they saw to the left of the dot, to close their eyes and draw what they saw with their left hand. As voluntary movement of the left hand is controlled by the right hemisphere, and the word flashed to the left of the dot was processed in the right hemisphere (due to the optic chiasm) the participants were able to draw what they saw.

• Sperry’s split brain experiments demonstrated that the corpus callosum is required for full functioning of the brain, and that the left hemisphere is responsible for understanding language and speech articulation, while the right hemisphere can recognise language, but is unable to verbally articulate it.

Walter Freeman (1936-1945)

• Walter Freeman, with the assistance of James Watts, was the first person to perform a frontal lobotomy in the USA and used the media to help propel the popularity of his procedures. Freeman claimed that mentally ill people were obsessed with their own problems due to being too self-aware and having overactive emotions.

• He believed the thalamus was the centre of human emotion, and therefore the source of mental illness symptoms, and that severing the neural connections between the thalamus and pre-frontal cortex would eliminate excessive emotions and stabilise personality.

• Freeman and Watts used local anaesthesia on their patients so that they were able to respond to tests and report their feelings and ideas during the procedure.

• The patient’s scalp was shaved and markings were drawn on the sterilised scalp. Incisions were made on the left and right side of the frontal lobes and a pair of clamps held the shaft of a knife that was inserted into the incisions and moved in wave-like motions. The knife cut the bundles of nerve fibres connecting the pre-frontal cortex (front part of the frontal lobes) and the thalamus of the brain.

• The pre-frontal cortex is responsible for complex functions that include reasoning, decision making, and the expression of personality. Freeman’s main goal was to reduce agitation in participants, and while that was the consequence for many patients, others also developed apathy (a lack of interest), decreased concentration and a numbness in emotional reseponses.

• Advances in the development of antipsychotic medications and knowledge of the many patients who suffered due to the procedure led to the decline of Freeman’s reputation and the decline in popularity of the lobotomy procedure.

Electroencephalogram (EEG)

A functional technique that shows brain activity in real time.

How it works:

• Electrodes are placed on the scalp and electrical activity (brain waves) in the brain is detected, then carried via wired to an EEG recording machine where it is displayed.

• Electrical changes within thousands of neurons are detected at the same time (rather than from single neurons).

Uses:

• Able to help diagnose epilepsy and other seizure disorders.

• Recordings can be analysed for sleep research.

• Shows which part of the brain is being utilised during mental tasks.

• Can be used to confirm whether an individual in a coma is brain dead.

Strengths:

• Has high temporal resolution, meaning it can detect rapid changes in brain waves (within milliseconds).

• It is a safe and non-invasive process as electrical activity is measured; electricity is not run through the body.

Limitations:

• Has low spatial resolution, meaning that the precise location of neural activity is not clear. While the conductive gel helps increase temporal resolution, it also reduces the spatial resolution - as does the scalp, skull, and thick membrane surrounding the brain.

• It can be a messy procedure as conductive gel is placed on each electrode which is then pressed onto the scalp.

Computed Tomography (CT)

This structural neuroimaging technique produce still pictures.

How it works:

• A rotating x-ray beam moves 360 degrees around the patient while taking multiple x-ray images.

• A computer pieces together the many two-dimensional x-rays and produces a three-dimensional reconstruction that the technician can scroll through to view ‘slices’ of the brain.

Uses:

• Can check for fractures in the skull (better defines bone fractures than MRI scans).

• Can be used to diagnose brain tumours and aneurysms.

• Can be used to measure the size of a brain tumour.

• Can help assess brain injury from trauma (bleeding of the brain, or fluid filled spaces).

Strengths:

• Patients with pacemakers (or other metal in the body such as aneurysm clips) can have this scan.

• CT scans can image bone, soft tissue and blood vessels at the same time (unlike MRI scans which do not show bone as clearly.

Limitations:

• Patient is exposed to ionising radiation - this can slightly increase the likelihood that they will develop cancer later in life.

• This scan is not suitable for pregnant women as the ionising radiation may damage the foetus.

Magnetic Resonance Imaging (MRI)

This structural neuroimaging technique produce still pictures.

How it works:

• This type of scan uses a strong magnetic field and radio waves to produce pictures of the brain.

• The magnetic field lines up the protons (positively charged particles) in hydrogen atoms, then short bursts of radio waves tip the protons out of alignment.

• As the protons realign, they release radio signals which are detected in the scanner. Different structures (such as tissue and bone) produce different signals, allowing them to be distinguished in pictures.

Uses:

• Can be used to diagnose brain tumours and aneurysms.

• Can be used to measure the size of a brain tumour.

• Can help assess the effects of a stroke.

• Can help assess brain injury from trauma (bleeding of the brain, or fluid filled spaces).

Strengths:

• More detailed pictures are formed than those produced by CT scans (better at detecting soft tissues - such as brain tumours).

• Does not expose the patient to ionising radiation (is safer for pregnant mothers to used than CT scans, although it is not recommended during the first trimester of pregnancy when the foetus’ organs are forming).

Limitations:

• Patients cannot have magnetic metal on or in the body (such as a pacemaker).

• Some MRI scanners produce loud banging noises and require ear protection to be worn - the noise may also cause distress in some patients.

Functional Magnetic Resonance Imaging (fMRI)

This functional neuroimaging technique produces dynamic pictures.

How it works:

• This type of scan uses a strong magnetic field and radio waves to show where neurons are consuming oxygen in the brain in real time.

• The scanner creates a three-dimensional map of the brain broken up into tiny ‘volume blocks’ called voxels. When neurons in the brain communicate with each other through electrical impulses and neurotransmitters, energy is used (metabolic change occurs). Oxygen rushes to the area through the blood causing the voxel to change colour and become red, and the voxel colour returns to normal once the body stops rushing oxygen to the active neurons.

• The scanner detects the colour change because blood that is high in oxygen has iron and is more attracted to magnets than blood that is low in oxygen. The difference in magnetism is shown as shades of light and dark and is called the BOLD signal (blood oxygen level dependent signal). The higher the BOLD signal, the greater the oxygen level in the blood.

Uses:

• Can show the parts of the brain that are active when a patient is performing a task.

• It is used to help plan for tumour removal surgery. The patient is asked to do tasks that cause changes in areas of the brain responsible for producing speech, the surgeon can map where this area is and avoid it during surgery.

• Can help assess the effects of a stroke.

• Can detect the brain activity of patients with neurological conditions such as Parkinson’s disease.

Strengths:

• Has high enough spatial resolution for the scans to determine the location of neural activity, down to a few cubic millimetres.

• Does not expose the patient to ionising radiation.

Limitations:

• Patient cannot have magnetic metal on or in the body (including some types of cochlear implants, aneurysm clips and pacemakers).

• has temporal resolution lower than CT and EEG methods, meaning the scan takes longer to detect changes in neural activity. This is because the BOLD signal relies on the body’s response to metabolic changes. While the EEG can detect electrical activity within the millisecond, fMRI may take around two seconds.