U3AOS1- Nervous System

• Responsible for transmitting neural messages to and from the peripheral nervous system
• The brain is responsible for organising, interpreting and coordinating actions, thoughts and behaviours
• The spinal cord connects the brain to the peripheral nervous system. Carries motor information from the brain and sensory information from the body.

• Contains all neurons outside the CNS
• Responsible for carrying information to and from the CNS
• The PNS can be further subdivided into two different systems:
• Autonomic nervous system (ANS)
• Somatic nervous system (SNS)

• The branch of the PNS responsible for sending motor information from the CNS to the body’s skeletal muscles and bringing sensory information from the body to the CNS in order to formulate voluntary responses.
• The CNS controls these voluntary movements by transmitting information from the body’s sensations to the brain, and then coordinating the skeletal muscles to respond.

Environmental stimuli-sensory receptor-sensory neurons in PNS-ascending tract in Spinal cord- brain

Brain coordinates response-descending tracts in spinal cord-motor neurons in PNS-muscles/glands/organs respond

• The branch of the PNS responsible for connecting the CNS and the body’s visceral (non-skeletal) organs, muscles and glands like the heart and liver.
• The organs, muscles and glands involved in the ANS are mostly self regulating and they don’t require conscious mental control to operate. We do however have control over our breathing and can make it faster or slower.
• The ANS is further divided into three divisions:
• Sympathetic nervous system
• Parasympathetic nervous system
• Enteric nervous system

• Branch of the ANS responsible for activating the body’s visceral organs, muscles and glands to trigger a fight-flight-freeze response.
• This response prepares the body for dealing with high levels of activity such as exercise or escaping a threat/stressful situation.

• Branch of the ANS responsible for returning and maintaining the body’s visceral organs, muscles and glands at optimal and balanced functioning.
• This balanced level of functioning is also known as homeostasis.

• It receives and sends messages to the sympathetic and parasympathetic nervous system and is responsible for controlling the many functions of the digestive system.
• Due to its connection to the Peripheral nervous system, it can communicate directly with the CNS.
• It can also function independently of the CNS and is sometimes called the ‘second brain’
• The neural connections between the ENS and CNS are called the gut-brain axis.
• Functions include:
• Controlling movement of food through the digestive system
• Regulating secretion of digestive enzymes

Sensory receptors in the part of body in contact with sensory stimulus register sensory info. Sensory neural messages are initiated in the PNS Messages are sent along sensory neural pathways of the PNS, via spinal cord to be integrated by the brain. The brain coordinates a conscious motor response, initiates it by sending motor neural messages out to PNS via spinal cord. Skeletal muscles then receive the motor message and respond accordingly.

responses are those that occur in response to sensory stimuli that involves awareness. The somatic nervous system controls our conscious voluntary responses.

• responses are those that we are not consciously aware of, they are involuntary
• The Autonomic nervous system directs our unconscious functioning such as our heart beat, temperature control and breathing.
• These responses help to keep our body’s internal environment in a homeostatic state.

• An unconscious response to sensory stimuli that is initiated at the spinal cord, not involving the brain. It is a simple involuntary response.
• Because of this, spinal reflexes involve fewer steps, allowing them to occur more quickly and automatically without the brain’s awareness. This can enhance survival because an organism is able to respond to danger and harm more quickly than a conscious motor response.

1.The sensation of a sensory stimulus is detected by the body’s sensory receptors, which send a signal via sensory neurons to the spinal cord.

2.The spinal cord, via interneurons, immediately relays a signal via motor neurons to initiate an automatic/unconscious motor response in the skeletal muscles to the sensory stimulus.

3.As the motor neurons send messages to the tell the body to response unconsciously, sensory neurons send their neural impulses to the brain to make it aware of any pain or sensation. The brains conscious awareness is not necessary for the reflex response.

oA nerve cell responsible for transmitting, receiving and processing information to enable communication across the nervous system in the brain and the body

Similar to a domino effect, neural communication only occurs in one direction from one neuron to the next in a smooth movement

When a message, in the form of an electrical impulse, is sent to another neuron, muscle or gland. When a neuron receives this impulse, it is know as neural reception.

oNeurons are organised into networks within the nervous system. Communication occurs within these networks to allow us to think, feel and do.

Neurotransmitters are chemical substances that carry information between neurons.

Neurotransmitters are contained in small sacs and are produced by a presynaptic neuron before being released from terminal buttons (also known as synaptic buttons). From there they are passed onto other neurons around the body. This communication occurs in the space between them known as the synaptic gap.

Once released into the synaptic gap, neurotransmitters reach the receptor sites on the dendrites of the postsynaptic neuron. The message that travels within a neuron is primarily electrical

when a neuron sends an electrical impulse down the axon, this will either activate the neuron to perform its function (and cue the axon terminal to release neurotransmitters) or prevent it from performing its function

When a neurotransmitter causes the postsynaptic neuron to become more likely to fire an action potential

When a neurotransmitter causes the postsynaptic neuron to become less likely to fire an action potential.

• Neurotransmitters positively charge a postsynaptic neuron.
• One of the most common excitatory neurotransmitters in the CNS is glutamate:
• Glutamate is essential for movement, thought, learning and memory
• An insufficiency of glutamate in the brain with result in difficulty with learning and concentration
• Too much glutamate can cause over-excitation, damaging neurons and potentially leading to nervous system dysfunction such as seizures

• Neurotransmitters negatively charge a postsynaptic neuron.
• One of the most common inhibitory neurotransmitters in the CNS is gamma-amino butyric acid (GABA).
• GABA functions to counterbalance the effects of excitatory neurotransmitters such as glutamate
• An insufficiency of GABA can lead to an over-excitation of neurons, causing things such as seizures and anxiety
• GABA regulates and balances brain function

• Capable of affecting a large number of neurons at the same time. They can also influence the effects of other chemical messengers.
• Neuromodulators are released by a neuron and will diffuse (spread) through large areas of the brain Examples of neuromodulators include Dopamine and Serotonin

• -Excitatory and inhibitory effects
• -coordinate voluntary movement
• -reward base learning (pleasure)
• -motivation
• Neuromodulator that is responsible for signaling that a reward is available.
• It interprets and processes rewarding experiences and the feeling we experience when dopamine is released is desirable. This enables an individual to become motivated and repeat the behavior again.
• It is also responsible for initiating movement towards the reward which is called approach behavior.
• Treatment – Levodopa is most widely used to treat low levels of dopamine, especially in those who suffer from Parkinson’s disease. Dopamine is not responsible for the pleasure we experience when receiving a reward, but important for motivating behaviour. When it is released in areas of the brain, known as the reward system, dopamine produces states of motivation

• Inhibitory effects
• -mood regulation/stabilization
• -regulating sleep wake cycle
• -appetite, digestion, arousal
• Produced in the CNS and intestines.
• It is involved in many processes such as sleep, pain and mood regulation. Lower levels of serotonin have been associated with mood and sleep disorders. 
• Treatment – Prozac (antidepressant) has been known to boost the effects of serotonin and improve mood. It works by preventing the uptake of serotonin after it has been released so more is available.

the ability of the brain to physically change in response to experience.

Is a type of neural plasticity, that refers to the changes that occur to the synapse, which can lead to either an increase or decrease in activity between neurons

The long-lasting and experience dependent strengthening of synaptic connections. This repeated co-activation of a pre and postsynaptic neuron results in the strengthening of these synapses, making a postsynaptic neuron more receptive to the messages sent from a presynaptic neuron.

The long-lasting and experience dependent weakening of postsynaptic responses. This occurs as a result of a repeated low intensity stimulation of post-synaptic neurons

• the formation of new synapses (neural pathways) which occurs when learning takes place​
• When learning takes place, the neuron develops or sprouts bushier dendrites​. More dendritic spines on the postsynaptic terminal grow, as well as new axon terminals in the presynaptic neuron
• Interconnected groups of neurons form pathways for the learned information which becomes the memory of that information. ​

• When brain injury occurs, the synaptic connection can be damaged. An undamaged neuron that has a synapse with the damaged neuron, will form a new synapse with other undamaged neurons.
• This results in the rerouting of neural pathways
• Through LTP these new pathways will be strengthened and the previously lost function is taken over by an undamaged area

• The pruning away of existing connections.
• By removing unused or unnecessary synapses, the brain becomes more efficient