1. AS BIOPSYCHOLOGY Flashcards
THE NERVOUS SYSTEM
Is a specialised network of cells in the human body and is our primary internal communication system.
It is based on electrical and chemical signals whereas the endocrine system is based on hormones.
The nervous system has two main functions:
· To collect, process and respond to information in the environment.
· To co-ordinate the working of different organs and cells in the body.
The nervous system is divided into two subsystems
· Central nervous system (CNS).
· Peripheral nervous system (PNS).
THE CENTRAL NERVOUS SYSTEM (CNS)
The CNS is made up of the brain and the spinal cord.
· The brain is
the centre of all conscious awareness.
The brain’s outer layer, the cerebral cortex, is only 3 mm thick and covers the brain. It is only found in mammals.
· The brain is highly developed in humans and is what distinguishes our higher mental functions from those of other animals.
· The brain is divided into two hemispheres.
THE PERIPHERAL NERVOUS SYSTEM (PNS)
The PNS transmits messages, via millions of neurons (nerve cells), to and from the central nervous system.
The peripheral nervous system is further subdivided into the:
Autonomic nervous system (ANS) governs vital functions in the body such as breathing, heart rate, digestion, sexual arousal, and stress responses.
· Somatic nervous system (SNS) governs muscle movement and receives information from sensory receptors.
· The spinal cord is an extension of the brain - it
passes messages to and from the brain and connects nerves to the PNS.
It is also responsible for reflex actions.
The endocrine system works alongside the nervous system to control vital functions in the body.
The endocrine system acts more slowly than the nervous system but has very widespread and powerful effects.
name each gland in the body, the hormone it releases and the effects.
The key endocrine gland is the
pituitary gland - known as the master gland as it releases 6 hormones (e.g. LH and fsh) and it controls the release of hormones from all the other endocrine glands in the body.
pancreas - releases insulin and glucagon which maintain blood glucose concentration
adrenal glands - release adrenaline which is important in triggering the fight or flight response e.g. by increasing heart and breathing rate.
thyroid gland - releases thyroxine which is impotant in controlling metabolism and growth rates
ovaries - produce oestrogen and progesterone which control the female sexual characteristics and maintain the menstrual cycle.
testes - produce testosterone whoch develops secondary sexual characteristics in males.
ENDOCRINE AND ANS WORKING TOGETHER: FIGHT OR FLIGHT
Often the endocrine system and the autonomic nervous system (ANS) work in parallel with one another, for instance during a stressful event.
When a stressor is perceived, the first thing that happens is a part of the brain called the
how does the ANS change
hypothalamus activates the pituitary gland and this triggers activity in the sympathetic branch of the autonomic nervous system.
The ANS changes from its normal resting state (the parasympathetic state) to the physiologically aroused sympathetic state.
SYMPATHETIC STATE
Increases heart rate
Increases breathing rate
Dilates pupils
Inhibits digestion
Inhibits saliva production
ADRENALINE: The stress hormone adrenaline is released from the adrenal medulla into the bloodstream. Adrenaline triggers
physiological changes in the body (e.g. increased heart rate) which creates the physiological arousal necessary for the fight or flight response.
PARASYMPATHETIC ACTION:
Finally, once the threat has passed, the parasympathetic nervous system
returns the body to is resting state. The parasympathetic branch of the ANS works in opposition to the sympathetic nervous system. It reduces the activities of the body that were increased by the actions of the sympathetic branch. This is sometimes referred to as the ‘rest-and-digest’ response.
There are three types of neurons:
sensory neurons, relay neurons and motor neurons.
PARASYMPATHETIC STATE
Decreases heart rate
Decreases breathing rate
Constricts pupils
Stimulates digestion
Stimulates saliva production
The cell body includes a nucleus, which contains
the genetic material of the cell.
Branchlike structures called dendrites protrude from the cell body.
These
carry nerve impulses from neighbouring neurons towards the cell body.
The axon carries the impulses
away from the cell body down the length of the neuron.
The axon is covered in a fatty layer of
myelin sheath that protects the axon and speeds up electrical transmission of the impulse.
If the myelin sheath was continuous this would have the reverse effect and slow down the electrical impulse.
myelin sheath is segmented by gaps called
nodes of Ranvier - these speeds up the transmission of the impulse by forcing it to ‘jump’ across the gaps along the axon
Finally, at the end of the axon are terminal
that communicate with the next neuron in the chain across a gap known as the synapse.
Sensory neurons are located
outside of the CNS, in the PNS in clusters known as ganglia.
LOCATION OF NEURONS
The cell bodies of motor neurons may be in the central nervous system (CNS), but they have
long axons which form part of the peripheral nervous system (PNS).
Relay neurons make up 97% of all neurons and most are found
within the brain and the visual system.
Each neuron is separated from the next by an extremely tiny gap called the synapse.
Signals within neurons are transmitted electrically.
However, signals between neurons neurotransmitter are
transmitted chemically across the synapse.
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 by a stimulus, 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.
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.
The direction of travel can only be one-way. This is because
neurotransmitters are released from the presynaptic neuron terminal and received by the postsynaptic neuron (at the receptor sites). only the postsynaptic neuron has receptor sites.
Each neurotransmitter has its own specific molecular structure that fits perfectly into a postsynaptic receptor site, similar to a lock and a key. Neurotransmitters also have specialist functions.
Neurotransmitters are chemicals that diffuse across the synapse to the next neuron in the chain. Once a neurotransmitter crosses the gap, it is taken up by a
postsynaptic receptor site on the dendrites of the next neuron (axons take signals to the synapse, dendrites take signals away).
Here, the chemical message is converted back into an electrical impulse and the process of transmission begins again in this other neuron.
Neurotransmitters have either an excitatory or inhibitory effect on the neighbouring neuron.
For instance, the neurotransmitter serotonin causes
inhibition in the receiving neuron, resulting in the neuron becoming more negatively charged and less likely to fire.
Whether a postsynaptic-neuron fires is decided by the process of summation.
The excitatory and inhibitory influences are summed: if the net effect on the postsynaptic neuron is inhibitory then
the postsynaptic neuron is less likely to fire.
In contrast, adrenaline causes
excitation of the postsynaptic neuron by increasing its positive charge and making it more likely to fire.
If the net effect is excitatory, it is
more likely to fire, (the inside of the postsynaptic neuron momentarily becomes positively charged).
Therefore, the action potential of the postsynaptic neuron is only triggered if the sum of the excitatory and inhibitory signals at any one time reaches the
threshold.
