biopsychology revision

the nervous system

key features of the nervous system

• the nervous system is a specialised network of cells and our primary communication system

• it is based on electrical and chemical signals whereas the endocrine system is based on hormones

• main functions:

1. to collect, process and respond to information in the environment

2. to coordinate the working of different organs and cells in the body

the structure and function of the central nervous system

• CNS is made up of the brain and spinal cord

• the brain is the centre of conscious awareness

• the outer layer of the brain, the cerebral cortex (3mm thick), is highly developed in humans and is what distinguishes our higher mental from those animals

• the brain hemisphere is divided into two hemisphere

• the spinal cord is an extension of the brain and is responsible for reflex actions

• it passes messages to and from the brain and connects nerves to the PNS

the structure and function of the peripheral nervous system

• the PNS transmits messages, via millions of neurons, to and from the nervous system

• the PNS is further subdivided into:

1. autonomic nervous system (ANS) governs vital functions in the body such as breathing, heart rate, digestion, sexual arousal and stress responses

2. somatic nervous system (SNS) governs muscle movement and receives information from sensory receptors

the endocrine system

key features of the endocrine system

• the endocrine system works alongside the nervous system to control vital functions in the body through the action of hormones

• it works more slowly than the nervous system (seconds instead of milliseconds) but has widespread and powerful effects

glands

• glands are organs in the body that produce hormones

• the key endocrine gland is the ‘pituitary gland’ located in the brain. it is called the ‘master gland’ because it controls the release of hormones from all the other endocrine glands in the body

hormones

• hormones are secreted in the bloodstream and affect any cell in the body that has a receptor for particular hormones

• for example, thyroxine produced by the thyroid gland affects cells in the heart and also cells throughout the body which increase metabolic rates. this in turn affects growth rates

the endocrine system and the ANS work together e.g. fight or flight

• often the endocrine system and the ANS work in parallel, for instance during a stressful event

• stressor perceived by the hypothalamus which activates the pituitary

• the sympathetic nervous system is now aroused

• adrenaline (stress hormone) is released from the adrenal medulla into the bloodstream. this delivers the aroused state causing changes in the target organs in the body e.g. increased heart rate, dilated pupils, decreased production of saliva. this is called the fight or flight response

• immediate and automatic - this response happens the instant a threat is received

• parasympathetic nervous system (rest and digest) takes over once the threat has passed. this returns the body to its resting state. this acts as a brake and reduces the activities of the body that were increased by the actions of the sympathetic branch (rest and digest)

neurons

structure and function of neurons

types of neurons

• there are 100 billion nerve cells in the human nervous system, 80% of which are located in the brin

• by transmitting signals electrically and chemically, these provide the nervous system with its primary means of communication

• there are three types of neuron

1. sensory neurons carry messages from the PNS to the CNS. they have long dendrites and short axons. located in the PNS in clusters called ganglia’s

2. relay neurons connect sensory neurons to motor or other relay neurons. they have short dendrites and short axons. of a;; neurons, 97% are relay neurons and most are in the brain and visual system

3. motor neurons connect the CNS to effectors such as muscles and glands. they have short dendrites and long axons. cell bodies may be in the CNS but long axons form part of the PNS

structure of a neuron

• neurons vary in size but all share the same basic structure:

• cell body (soma) includes a nucleus which contains the genetic material of the cell

• dendrites - branchlike structures that protrude from the cell body. these carry nerve impulses from neighbouring neurons towards the cell body

• axon - carried the electrical impulse away from the cell body down the length of the neuron

  • it is covered in a fatty layer of myelin sheath

  • gaps in the axon called nodes of ranvier speed up the transmission of the impulse

• terminal buttons at the end of the axon communicate with the next neuron in the chain across a gap called the synapse

electrical transmission: the firing of a neuron

• when a neuron is in a resting state the inside of the cell is negatively charged compared to the outside

• when a neuron is activated, the inside of the cell becomes positively charged for a split second causing an action potential to occur

• this creates an electrical impulse that travels down the axon towards the end of the neuron

synaptic transmission

synapse

• each neuron is separated from the next by an extremely tiny gap called the synapse

chemical transmission: the events that occur at the synapse

• signlas within neurons are trsmistted electrically but signals between neurons are trasmitted chemically across the synapse

• when the electrical impulse reaches the end of the neuron (the presynaptic terminal) it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles

• once a neurotransmitter crosses the gap, it is taken up by a postsynaptic receptor site ion the next neuron, so the impulse only ever travels in one direction

• the chemical message is converted back into an electrical impulse and the process of electrical transmission begins

neurotransmitters

• neurotransmitters are chemicals that diffuse across the synapse to the next neuron in the chain

• many neurotransmitters have been identified. each has its own specific molecular structure that fits perfectly into a postsynaptic receptor site, lock and key

• each has a specific function eg

  • acetylcholine (ACh) found where a motor neuron meets a muscle, causing muscles to contract

  • serotonin affects mood and social behaviour (among other things) which is why it has been implicated as a cause of depression

excitation and inhibition

• neurotransmitters generally have either an excitatory or inhibitory effect on the neighbouring neuron

• adrenaline - generally excitatory, increasing the positive charge of the postsynaptic neuron, making it more likely the postsynaptic neuron will fire

• serotonin - generally inhibitory, creasing the negative charge of the postsynaptic neuron, making it less likely the postsynaptic neuron will fire

• dopamine is an usual neurotransmitter as it is equally likely to have excitatory or inhibitory effects on the postsynaptic neuron

summation

• excitatory and inhibitory influences are summed and must reach a certain threshold in order for the action potential of the postsynaptic neuron to be triggered

• in the net effect of the neurotransmitters is inhibitory then the postsynaptic neuron is less likely to fire. it is more likely to fire if the net effect is excitatory

localisation of function in the brain

localisation of function

holistic theory replaces by localisation theory

• in the early 19th century holistic theory suggested that all parts of the brain were involved in processing thought and action

• nut specific areas of the brain were later linked with specific physical and psychological functions (localisation theory)

• if an area of the brain is damaged through illness or injury, the function associated with the area is also affected

brain is divided into two hemispheres and lateralised

• lateralisation - some physical and psychological functions are controlled by a particular hemisphere

• generally, the left side of the body is controlled by the right hemisphere, the right side of the body by the left hemisphere

outer layer of brain is called the cerebral cortex

• the cerebral cortex is like a tea cosy covering the inner parts of the brain. it is about 3mm thick and is what separates us from lower animals as it highly developed

• the cortex appears grey due to the location of cell bodies - hence the phrase grey matter

cerebral cortex of both hemispheres is divided into four lobes (frontal, parietal, occipital, temporal)

• motor area - at the back of the frontal lobe (both hemispheres). controls voluntary movement. damage may result in loss of control over fine motor movements

• somatosensory area - at the front of the parietal lobes. processes sensory injformation form the skin (touch, heat, pressure etc). the amount of somatosensory area devoted to a particular body part denotes its sensitivity

• visual area - in the occipital lobe at the back of the brain. each eye sends information fr4om the right visual field to the left visual cortex and from the left visual field to the right visual cortex

• auditory area- in the temporal lobe. analyses speech based information. damage may produce partial hearing loss - the more extensive the damage, the more serious the loss