- To collect, process and respond to infomration in the envrionment.
- To co-ordinate the working of different organs and cells in the body.
The nervous system is divided into two subsystems:
The central nervous system
Made up of the brain and the spinal cord
The brain is the centre of conscious awareness. The brains outer layer, the cerebral cortex, is 3mm thick and covers the brain. (It is only found in mammals). The brain
is highly developed in humans and distinguishes our higher mental functions from those of other animals. Also, the brain is divided into two hemispheres. The spinal
cord is an extension of the brain and it passes messages to and from the brain and connects nerves to the peripheral nervous system. It is responsible for reflex actions
like pulling your hand away from a hot plate.
The peripheral system
The peripheral system transmits messages via neurons to and from the central nervous system. The peripheral nervous system is further subdivided into the autonomic
nervous system and the somatic nervous system. The autonomic nervous system (ANS) governs vital functions in the body such as breathing, heart rate, digestion,
sexual arousal and stress responses. The somatic nervous system (SNS) governs muscle movement and receives information from sensory receptors.
The Nervous System
The peripheral system The central nervous
system
Spinal cord:
Somatic NS: Autonomic NS: Brain: centre of all extension of the
transfers info to and Transfers info to and conscious brain and is
from the sensory from the internal awareness and responsible for
receptors and the organs and regualtes psychological receiving and
CNS. Controls involuntray bodily processes transmitting info to
voluntray movements processes and from the brain
Sympathetic NS: Parasympathetic NS:
prepares body for calms the body to
action or stress. Fight or converse energy.
flight respose. Boosts Sustains or reduces
bodily activities bodily activities.
,- Specialised cells that conduct electrical impulses. Their primary role is to receive messages and transmit them to other cells.
Structure
Dendrites
Cell body - contains nucleus (genetic material of cell).
Nucleus
Dendrites - blanchlike structures carry nerve impulses from Nodes of ranvier
neighbouring neurons towards cell body.
Axon Mylein sheath
Axon - carries impulses away from cell body down the
neuron.
Axon terminals
Myelin sheath - protects axon and speeds up
electrical transmission of the impulse. ÷ Direction of nerve
Nodes of ranvier - segmented gaps in the myelin
impulse
sheath to speed up the transmission of the -
impulse by forcing it to jump across along the
axon.
Terminal buttons - commuicate with the next neuron Cell body
3 main types of neurons:
Sensory (input): Transfer info about sensory stimuli from the envrionment to the rest of the brain.
Relay (process): Carry messages to and from different parts of the CNS. Connect Motor & Sensory Neurons.
Motor (output): Convey signals from the CNS to nucleus and glands which provide commands for organs (including muscle performance, digestion, the release of
hormones).
Stimulus = a change that can be detected (drawing
pin)
Receptor = something that detects stimuli (pain
receptors)
Effector = Something that makes a response (muscle)
Nodes of ranvier
Location
Sensory neurons = located in the PNS in clusters known as ganglia.
Relay neurons = make up 97% of all neurons and most are found within the brain and the visual system.
Motor neurons = located in the CNS but they have long axons which form a part of the PNS.
Electrical transmission
When a neuron is resting inside of the cell it 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 to travel down the axon toward the end of the neuron.
stimulus receptor sensory relay motor effector response
, Sysnaptic transmission
Chemical Transmission
Presysnaptic axon
terminals 1111
- Neurons communicate in groups of neural networks.
- Each neuron is seperated by the gap called the synapse.
- Signals are transmitted electrically however
signals between neurons are transmitted Neurotransmitter Vesicle
chemically across the synapse.
- When the electrical impulse reaches the neuron it triggers the
release of the neurotransmitter from vesicles.
Neurotransmitters Receptor site Synapse
- Chemicals diffuse across the synapse to the next neuron in the
chain -
-
-
-
- Once a neurotransmitter crosses the gap it is taken by a postsysnaptic
receptor site on the dendrites of the next neuron. Postsysnaptic neuron dendrite
- The chemical message is converted back into an electrical impulse and the process of transmission begins again.
Summary
At first, the electrical nerve impulse moves down the neuron and stimulates there lease of chemicals in the brain, called neurotransmitters, at the pre-synaptic terminal. The
neurotransmitters then emerge into the synaptic fluid within the synapse (gap). The neuron adjacent has to rapidly take up the neurotransmitters from the fluid and convert
them to an electrical impulse which can then travel across that neuron to the subsequent pre-synaptic terminal. This continues the process of transmission between other
neurons. This whole procedure happens very quickly (50-100 milliseconds).
Excitation and inhibition
Not every message stimulates activation the same way. It hinges on the action potential of the post-synaptic neuron and the form of message being collected. The ‘lock
and key’ analogy helps explain this; only once the correct key (neurotransmitter) joins to the proper lock (receptor) can the door open up (allowing the flooding of ions
which cause a potential).
Excitation = increase the likelihood an electrical impulse is triggered in the postsysnaptic neuron.
Inhibitory = decrease the likelihood an electrical impulse will be triggered in the postsysnaptic neuron.
Summation
Weather a postsysnaptic neuron is fired is decided by the process of summation. the excitatory and inhibitory influences are summed. If the postsysnaptic neuron
is inhibitory it is less likely to fire however if the postsysnaptic neuron is excitatory it is more likely to fire. Once the electrical impulse is created it travels down the
neuron. Therefore, the action potential of the postsynaptic is only triggered if the sums of the excitatory and inhibitory signals is at the threshold.
How SSRI’s work
When serotonin is released from the pre-synaptic cell into the synapse, it travels to the receptor sites on the post-synaptic neuron. Serotonin that is not absorbed into the
post-synaptic neuron is reabsorbed into the sending cell (the presynaptic neuron). SSRIs increase the level of serotonin available in the synapse by preventing it from being
reabsorbed into the sending cell. This increases the level of serotonin in the synapse and results in more serotonin being received by the receiving cell (post-synaptic
neuron).
Exam Questions
Q1. Give one difference between the autonomic nervous system and the somatic nervous system. (1 mark)
The autonomic nervous system controls internal organs and glands, while the somatic nervous system controls muscles and movement.
Q2. Information can only travel in one direction at a synapse. Explain why neurons can only transmit information in one direction at a synapse. (3 marks)
The reason that information can only travel in one direction at the synapse is due to the specific function of different parts of the neuron. At the end of the pre-synaptic
neuron are synaptic vesicles that contain neurotransmitters. When an action potential reaches the vesicles, they release neurotransmitters which carry the signal over the
synaptic gap. Neurotransmitters bind to specific receptor sites that are positioned at the start of the post-synaptic neuron that then become activated. Consequently, the
information can only travel in this direction because the neurotransmitters are released from the vesicles at the end of the pre-synaptic neuron and bind to sites at the
start of the post-synaptic neuron. This would make it impossible for information to flow in any other direction.
Q3. Martha was telling her friend Sanya about her recent frightening experience. I was walking home by myself in the dark. Suddenly, i heard footsteps behind me and i
realised that someone was getting closer to me. I saw a bus at the bus stop and decided to run. I don’t think i have ever moved with such speed. I leaped on the bus -
shaking, sweating and my heart was beating so fast i nearly collapsed.
Outline the role of the central nervous system and autonomic system in behaviour. Refer to Martha’s frightening experience in your answer. (4 marks)
The central nervous system receives sensory information and controls body responses. This explains why Martha realised someone was getting closer to her. The CNS
system also perceived this as dangerous and stressful which meant that the PNS relayed this information to the rest of the body. As part of the subconscious function,
her ANS took over and coordinated motor actions, resulting in her fight or flight response of her running very quickly. This action was caused by the stimulation of the
hypothalamus activated during the SNS. During the response, the body was primarily involved in bringing oxygen to the muscles or brain. Her heart rate was increased
as more blood was pumped to the brain.
- To co-ordinate the working of different organs and cells in the body.
The nervous system is divided into two subsystems:
The central nervous system
Made up of the brain and the spinal cord
The brain is the centre of conscious awareness. The brains outer layer, the cerebral cortex, is 3mm thick and covers the brain. (It is only found in mammals). The brain
is highly developed in humans and distinguishes our higher mental functions from those of other animals. Also, the brain is divided into two hemispheres. The spinal
cord is an extension of the brain and it passes messages to and from the brain and connects nerves to the peripheral nervous system. It is responsible for reflex actions
like pulling your hand away from a hot plate.
The peripheral system
The peripheral system transmits messages via neurons to and from the central nervous system. The peripheral nervous system is further subdivided into the autonomic
nervous system and the somatic nervous system. The autonomic nervous system (ANS) governs vital functions in the body such as breathing, heart rate, digestion,
sexual arousal and stress responses. The somatic nervous system (SNS) governs muscle movement and receives information from sensory receptors.
The Nervous System
The peripheral system The central nervous
system
Spinal cord:
Somatic NS: Autonomic NS: Brain: centre of all extension of the
transfers info to and Transfers info to and conscious brain and is
from the sensory from the internal awareness and responsible for
receptors and the organs and regualtes psychological receiving and
CNS. Controls involuntray bodily processes transmitting info to
voluntray movements processes and from the brain
Sympathetic NS: Parasympathetic NS:
prepares body for calms the body to
action or stress. Fight or converse energy.
flight respose. Boosts Sustains or reduces
bodily activities bodily activities.
,- Specialised cells that conduct electrical impulses. Their primary role is to receive messages and transmit them to other cells.
Structure
Dendrites
Cell body - contains nucleus (genetic material of cell).
Nucleus
Dendrites - blanchlike structures carry nerve impulses from Nodes of ranvier
neighbouring neurons towards cell body.
Axon Mylein sheath
Axon - carries impulses away from cell body down the
neuron.
Axon terminals
Myelin sheath - protects axon and speeds up
electrical transmission of the impulse. ÷ Direction of nerve
Nodes of ranvier - segmented gaps in the myelin
impulse
sheath to speed up the transmission of the -
impulse by forcing it to jump across along the
axon.
Terminal buttons - commuicate with the next neuron Cell body
3 main types of neurons:
Sensory (input): Transfer info about sensory stimuli from the envrionment to the rest of the brain.
Relay (process): Carry messages to and from different parts of the CNS. Connect Motor & Sensory Neurons.
Motor (output): Convey signals from the CNS to nucleus and glands which provide commands for organs (including muscle performance, digestion, the release of
hormones).
Stimulus = a change that can be detected (drawing
pin)
Receptor = something that detects stimuli (pain
receptors)
Effector = Something that makes a response (muscle)
Nodes of ranvier
Location
Sensory neurons = located in the PNS in clusters known as ganglia.
Relay neurons = make up 97% of all neurons and most are found within the brain and the visual system.
Motor neurons = located in the CNS but they have long axons which form a part of the PNS.
Electrical transmission
When a neuron is resting inside of the cell it 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 to travel down the axon toward the end of the neuron.
stimulus receptor sensory relay motor effector response
, Sysnaptic transmission
Chemical Transmission
Presysnaptic axon
terminals 1111
- Neurons communicate in groups of neural networks.
- Each neuron is seperated by the gap called the synapse.
- Signals are transmitted electrically however
signals between neurons are transmitted Neurotransmitter Vesicle
chemically across the synapse.
- When the electrical impulse reaches the neuron it triggers the
release of the neurotransmitter from vesicles.
Neurotransmitters Receptor site Synapse
- Chemicals diffuse across the synapse to the next neuron in the
chain -
-
-
-
- Once a neurotransmitter crosses the gap it is taken by a postsysnaptic
receptor site on the dendrites of the next neuron. Postsysnaptic neuron dendrite
- The chemical message is converted back into an electrical impulse and the process of transmission begins again.
Summary
At first, the electrical nerve impulse moves down the neuron and stimulates there lease of chemicals in the brain, called neurotransmitters, at the pre-synaptic terminal. The
neurotransmitters then emerge into the synaptic fluid within the synapse (gap). The neuron adjacent has to rapidly take up the neurotransmitters from the fluid and convert
them to an electrical impulse which can then travel across that neuron to the subsequent pre-synaptic terminal. This continues the process of transmission between other
neurons. This whole procedure happens very quickly (50-100 milliseconds).
Excitation and inhibition
Not every message stimulates activation the same way. It hinges on the action potential of the post-synaptic neuron and the form of message being collected. The ‘lock
and key’ analogy helps explain this; only once the correct key (neurotransmitter) joins to the proper lock (receptor) can the door open up (allowing the flooding of ions
which cause a potential).
Excitation = increase the likelihood an electrical impulse is triggered in the postsysnaptic neuron.
Inhibitory = decrease the likelihood an electrical impulse will be triggered in the postsysnaptic neuron.
Summation
Weather a postsysnaptic neuron is fired is decided by the process of summation. the excitatory and inhibitory influences are summed. If the postsysnaptic neuron
is inhibitory it is less likely to fire however if the postsysnaptic neuron is excitatory it is more likely to fire. Once the electrical impulse is created it travels down the
neuron. Therefore, the action potential of the postsynaptic is only triggered if the sums of the excitatory and inhibitory signals is at the threshold.
How SSRI’s work
When serotonin is released from the pre-synaptic cell into the synapse, it travels to the receptor sites on the post-synaptic neuron. Serotonin that is not absorbed into the
post-synaptic neuron is reabsorbed into the sending cell (the presynaptic neuron). SSRIs increase the level of serotonin available in the synapse by preventing it from being
reabsorbed into the sending cell. This increases the level of serotonin in the synapse and results in more serotonin being received by the receiving cell (post-synaptic
neuron).
Exam Questions
Q1. Give one difference between the autonomic nervous system and the somatic nervous system. (1 mark)
The autonomic nervous system controls internal organs and glands, while the somatic nervous system controls muscles and movement.
Q2. Information can only travel in one direction at a synapse. Explain why neurons can only transmit information in one direction at a synapse. (3 marks)
The reason that information can only travel in one direction at the synapse is due to the specific function of different parts of the neuron. At the end of the pre-synaptic
neuron are synaptic vesicles that contain neurotransmitters. When an action potential reaches the vesicles, they release neurotransmitters which carry the signal over the
synaptic gap. Neurotransmitters bind to specific receptor sites that are positioned at the start of the post-synaptic neuron that then become activated. Consequently, the
information can only travel in this direction because the neurotransmitters are released from the vesicles at the end of the pre-synaptic neuron and bind to sites at the
start of the post-synaptic neuron. This would make it impossible for information to flow in any other direction.
Q3. Martha was telling her friend Sanya about her recent frightening experience. I was walking home by myself in the dark. Suddenly, i heard footsteps behind me and i
realised that someone was getting closer to me. I saw a bus at the bus stop and decided to run. I don’t think i have ever moved with such speed. I leaped on the bus -
shaking, sweating and my heart was beating so fast i nearly collapsed.
Outline the role of the central nervous system and autonomic system in behaviour. Refer to Martha’s frightening experience in your answer. (4 marks)
The central nervous system receives sensory information and controls body responses. This explains why Martha realised someone was getting closer to her. The CNS
system also perceived this as dangerous and stressful which meant that the PNS relayed this information to the rest of the body. As part of the subconscious function,
her ANS took over and coordinated motor actions, resulting in her fight or flight response of her running very quickly. This action was caused by the stimulation of the
hypothalamus activated during the SNS. During the response, the body was primarily involved in bringing oxygen to the muscles or brain. Her heart rate was increased
as more blood was pumped to the brain.
