This week I have continued my reading of Carlson et al. (2007) focusing on psychology, but particularly on the brain and its components, drugs and behaviour, and the controlling of behaviour and the body’s functions.
The brain and its components
The brain is the largest part of nervous system and contains 10billion -100billion nerve cells. All of the nerve cells are different sizes, shapes, functions they carry out and chemicals they produce. To understand the brain we need to look at the structure of the nervous system. The brain has 3 primary jobs: controlling behaviour, processing and storing information about the environment and adjusting the body’s physiological processes. There are two divisions which make up the central nervous system: the spinal cord and the brain. The spinal cord is connected to the base of the brain and runs along the spinal column. The brain contains three major parts:
The brain stem – controls physiological functions and automatic behaviours
The cerebellum – controls and coordinates movements
The cerebral hemispheres – concerned with perceptions, memories
The brain and spinal cord float in a liquid known as cerebrospinal fluid (CSF) that provides a cushion like protection. A blood brain barrier, ensures less substances pass from the blood to the brain to reduce toxic chemicals. A cerebral cortex, which is a 3mm layer of tissue, covers the surface of the cerebral hemisphere and has a billion nerve cells. The brain works with the body through the peripheral nervous system.
Sensory information, decision making, and controlling muscles, are all sent to the brain through neurons which make up the nervous system. To receive, process, and transmit information neurons contain; dendrites, soma, axon, and terminal buttons. Support is provided by glia, that also produces chemicals required by neurons, remove chemicals not required and help protect neurons from infections.
Neurons communicate with cells through synapse. When a message is sent from the presynaptic neuron it is received by the postsynaptic. A neuron accept s messages for lots of terminal buttons which results in terminal buttons creating synapses with several all neurons. Communication between synapses is chemical producing called neurotransmitter. When the axon is fires an actions moves down an axon causing the terminal buttons to release the neurotransmitter chemical.
Drugs and Behaviour
Chemicals that can be found in nature can affect people’s perceptions and behaviours. But some of these chemicals can be useful and are used as therapeutic remedies. By understanding how drugs affect the brain, help us to understand disorders and how to develop new methods of treatment.
Drugs can be said to alter our thoughts, the way we perceive things, the emotions we have, and the behaviour we demonstrate. This is achieved by affecting the activity of the neurons in our brain. Some drugs can stimulate or inhibit the release of neurotransmitters (chemical that is realised when neurons communicate) when the axon is firing, e.g. the venom of a black widow spider. Some drugs can stimulate (e.g. nicotine) or block postsynaptic receptors (e.g. cocaine). Finally, some drugs can impede on the reuptake of the neurotransmitter after it has been released, e.g. botulinum toxin or block receptors all together e.g. curare.
There are two important neurotransmitters that help achieve synaptic communication:
Glutamate – has excitatory efforts, every sensory organ passes messages to the brain through axons with terminals that release glutamate. One type of glutamate receptor – NMDA can be affected by alcohol. This why some ‘binge drinkers’ sometimes say they have no memory of what happened the night before when they were drunk. Likewise if a person has been addicted to alcohol for a long time this receptor can become suppressed, making it more sensitive to glutamate. So if a person stops drinking alcohol then this can strongly disrupt the balance of excitation and inhibition in the brain.
GABA – has inhibitory effects. Drugs that suppress behaviour, cause relaxation, sedation, and loss of consciousness act on a certain GABA receptor. For example if Barbiturates are taken in large quantities they can affect how a person walks, talking, cause unconsciousness, comas and even death.
Muscular movements are controlled by Acetylcholine (ACh) as well as controlling REM sleep (the part of sleep where most dreams occur), activation of neurons in the cerebral cortex and functions of the brain that are concerned with learning. ACh receptors are stimulated by the highly addicted drug nicotine. However the drug curare can block Ach receptors causing paralysis.
Dopamine is important in helping movement and helps in reinforcing behaviours. People with Parkinson’s disease are often given the drug L-DOPA to accelerate the production of dopamine. Drugs such as cocaine and amphetamine stop the uptake of dopamine and with people abusing these drugs would suggest that dopamine plays a role in enforcement.
Norepinephrine is said to increase vigilance and helps control REM sleep. Serotonin helps to control aggressive behaviour and risk taking, and drugs that have an impact on the uptake of serotonin are used to treat disorders concerned with anxiety, depression and obsessive compulsive disorders.
Control of behaviour and the body’s physiological functions
Figure 1 shows how the cerebral cortex part of the brain is split up into four parts also known as lobes – the frontal lobe, parietal lobe, temporal lobe and the occipital lobe. The areas of the cerebral cortex that receive information from the sensory organs are the primary visual cortex (concerned with visual information), the primary auditory cortex (concerned with auditory information), and the primary somatosensory cortex (concerned with information with regards to body senses).the area of the cerebral cortex concerned with the control fo movement is the primary motor cortex and the association cortex is concerned with learning, perceiving, remembering, planning and moving.
Some functions within the brain are lateralized both hemispheres are responsible for different functions. The left hemisphere takes part in analysis of information, and controls serial events (e.g. talking, understanding speed of other people, reading and writing). Whereas the right hemisphere is responsible for synthesis, puts separate elements together to create the bigger picture e.g. draw sketches, read maps. It is also involved in understanding the meanings of certain statements, and damage to this hemisphere can alter these abilities. Although they are responsible for different tasks, these hemispheres combine information through a bundle of axons connecting the two, known as the corpus callosum.
Behind the central fissure are lobers that are reponsisble for learning, perceving, and remembering:
Occipital lobe as well as lower lobes – information concerned with seeing/vision
Upper temporal lobe – information concerned with hearing/auditory
Parietal lobe - information concerned with movement/sensory
However these lobes also perform other functions such as processes concerned with perception and understanding of the body. the lobes situated at the front are responsible for motor movements, such as planning strategies for action. Similarly, the Broca’s area (left front of he cortex) is used to control speech.
Situated in the Cerebral hemispheres is the limbic system which is key when it comes to learning, memory and emotions. This is made up of lots of areas of the limbic cortex as well as the hippocampus and amydala, both of which can be found in the temporal lobe. The latter is concerned with emotions and such behaviour, e.g. aggression and the hippocampus takes part in learning and memory. People who damage the hippocampus are unable to learn anything new but can remember and recall past memories.
The brain stem is made up of three parts:
The Medulla – manages heart rate, blood pressure, rate of respiration
The Pons - manages sleep, and how awake someone is
The Midbrain – manages movements when fighting and when involved in sexual behaviour
Sensory information is received by the hypothalamus, this includes information about changes in the body’s physiological status, e.g. body temperature. It also manages the pituitary gland which is attached to the bottom of the hypothalamus. It also manages the endocrine system (endocrine glands).
Hormones are similar to neurotransmitters as there effects can be seen by stimulating receptors, but they work over a much larger distance. When these hormones combine with receptors they result in physiological reactions in the target cells (receptors in certain cells). The hypothalamus manages homoeostatic processes by its control of the pituitary gland and the autonomic nervous system. However, it can also cause neural circuits in the cerebral cortex to perform more complicated, learned behaviour.
My blog post on criminology will follow shortly
Figure 1 taken from http://samedical.blogspot.com/2010/08/nervous-system-cerebrum.html