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Nervous System

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Nervous System

Picture a command centre full of computers and workers, forming the central place for an operation to be managed and orders to be carried out. Now imagine that each person has this same centre of operations in their body, called the nervous system. It practically controls everything we do, including our thoughts, feelings, and movements. It even controls our breathing.

Nervous System Definition

Considering how important the nervous system is, it's important we understand the definition of it overall. We can define the nervous system as:

The nervous system is a network of nerve cells called neurons which transfer messages to and from different parts of the body. It controls movements, responses and automatic bodily functions. It can be split into the central nervous system and the peripheral nervous system.

Neurons receive and transmit information to the cells, comprised of motor neurons, relay neurons, and sensory neurons.

Our nervous systems are crucial to supporting bodily functions and coordinating movements in response to the environment (stimuli).

Structure and function of the nervous system, a large illustration of a brain surrounded by scientists working on it, StudySmarterThe nervous system allows you to respond to the environment, clipart.me

Nervous System Structure

To understand the different parts of the nervous system, we must differentiate between the central nervous system and the peripheral nervous system. They are made up of different components, so it's important you remember their differences.

The Central Nervous System (CNS)

The central nervous system comprises the brain and the spinal cord and controls communications between the brain and the body, acting as a command centre of sorts. The peripheral nervous system connects the CNS to the body to allow the CNS to enact commands.

How does this work?

Parts of our body, such as muscles, skin, and organs, have sensory neurons (when grouped, these are known as nerves). These neurons have receptors that detect stimuli, which leads to messages being sent directly to the CNS.

  • Sensory neurons are responsible for sending messages to the brain from the body.
  • Once our brains have gathered and processed this information, it sends messages back to these body parts via the spinal cord to effectors, which prompt movement or responses.
  • Motor neurons are responsible for sending these messages back to the body.

Motor neurons function by carrying messages from the central nervous system to effectors (organs, muscles or glands) so that they can perform a function.

The spinal cord facilitates the transfer of messages to and from the brain to the peripheral nervous system. It is also involved in reflex actions e.g. startle response.

The spinal cord is the column of nerves between the brain and the peripheral nervous system

The Peripheral Nervous System (PNS)

The peripheral nervous system consists of all the nerve cells which are not in the central nervous system. The spinal cord activates the peripheral nervous system, which is collectively responsible for gathering and sending information to different body parts through nerves.

This is how our body controls automatic functions such as heartbeat, blood flow, and stimulus responses which seem 'automatic' to us.

The peripheral nervous system can be split into two sections:

Somatic nervous system Autonomic nervous system
A network of nerve fibres that transmit and receive information from the senses (for example, visual and auditory information).It also directly controls voluntary muscular movements. These nerve fibres pass information to and from the CNS using myelinated sensory and motor neurons. (Myelin acts as an insulation layer - the neurons are layered to aid faster transmission).
A network of nerves that receives and transmits information from the organs.It controls involuntary body functions (for example, heartbeat and digestion)The autonomic system operates automatically, without conscious direction (hence 'autonomous')The autonomic is further divided into two systems:

Sympathetic system Parasympathetic system
This system works by increasing activity during fight or flight.This is activated when you feel threatened or anxious. This system works by conserving the body's natural activity.It enables the body to store energy as a reserve when we are not feeling threatened.

Think of the autonomic nervous system as one that helps us react to situations, particularly those considered an 'emergency'.

It connects our brain to our endocrine system, which is a network of glands and organs that secrete hormones into the blood.

Nervous System Function: The Function of The Central and Peripheral Nervous System

It may help to clearly underline and distinguish how both parts of the nervous system function.

Central Nervous System

The CNS is responsible for receiving information from the sensory neurons and powering and regulating psychological processes. Any adequate responses are passed to the body via the peripheral nervous system.

  • Think of the brain and the spinal cord. The brain is the centre of consciousness, receiving messages from the sensory receptors and sending messages to our glands and muscles.

It may help to think of the spinal cord as an extension of the brain down the body, directing and aiding the brain to control the voluntary movements of the body.

Peripheral Nervous System

The somatic nervous system in the PNS comprises nerves that function by sending messages to and from the senses (external stimuli) and muscles (internal) to and from the spinal cord (CNS).

  • It receives directions from the CNS for body movement.

The autonomic nervous system in the PNS functions by regulating involuntary bodily actions such as rises in temperature, arousal, heart rate, and more. It has two divisions: the sympathetic and parasympathetic nervous systems:

  • If someone is experiencing a fight or flight response, the autonomic nervous system shifts from the parasympathetic system to the sympathetic system. Energy is readily available to use, and our heart rates increase, as well as our breathing and body temperature.

  • When the threat is no longer evident, the ANS returns to the parasympathetic system in control.

Did you know that when the autonomic nervous system detects a fight or flight situation, our brain produces a hormone called endorphins, known as a natural painkiller produced by the body that is released from the hypothalamus and pituitary glands?

Our blood also thickens with blood vessels restricting to prepare for any potential injury.

Structure and function of the nervous system, the sympathetic and parasympathetic nervous system illustrated, StudySmarterThe human nervous system is composed of multiple divisions, freepik.com/macrovector

Neurotransmitters

Neurotransmitters are the chemicals that are released from nerve cells in the nervous system. They function by passing chemical messages between neurons across a very small gap between the neurons, known as the synapse. This is called synaptic transmission.

An electrical impulse is triggered and travels down to the end of the neuron, where vesicles containing neurotransmitter molecules release them into the synapse. The molecules are grasped by receptors on the next neuron so that the impulse can be passed onwards.

The synapse can be thought of as an empty, in-between space crucial for transmission to occur.

The James-Lange Theory of Emotion

In the 1880s, William James and Carl Lange came up with a theory of emotion. In short, they proposed that bodily changes to external events instigate emotional responses.

For Jame and Lange, when an individual is sweating, has an increased heart rate and deeper breathing, it is these alterations which cause them to experience the emotion of fear or nervousness.

Thus, they believed that stimulus led to physiological reactions to occur.

It is an important early study investigating the fight or flight response.

Evaluating the James-Lange Theory

Whilst it was one of the earliest theories of a emotion in modern psychology, not everyone has been convinced of its accuracy.

  • The theory may be criticised as there is an inconsistency in emotional responses. For the theory to be exact, there would have to be a specific emotion that equates to a physical reaction, which we know is not the case. Whilst someone's heart rate may increase, this could insight fear, excitement, or even irritation. Similarly, the action of crying does not always signify one singular emotion.
  • Schachter and Singer also challenged the basis of the theory by suggesting that not only physiological changes occur when an individual spots a threat, but also cognitive altercations occur. ANS stimulation can result in a deeper understanding of the threatening environment.
  • in 1927, the Cannon-Bard theory of emotion was proposed as an alternative by Walter B. Cannon and Philip Bard. The theory states that external stimuli trigger feelings and physical reactions to occur simultaneously and independently of one another.

Nervous System Disorders

Parts of the nervous system can become damaged, which is considered neurological damage. If someone is a victim of this damage, it can have a direct effect on the way they think, feel, and behave. Some disorders are listed below.

  • Spinal Cord Injury: If someone is to suffer from any damage to their spinal cord, it can disrupt electrical impulses, thus signals, from being transmitted throughout the body which prohibits movement. Depending on the severity, this can result in partial or complete paralysis.

  • Prefrontal Cortex Damage: the prefrontal cortex control impulses and helps us to make rational decisions. If damage is done to this area, it can cause a shift in behaviour for people who can become more impulsive and even potentially violent.

A study by Raine et al. (1997) found that murderers had less activity occurring in the prefrontal cortex region, which may be considered one reason for their impulsive behaviour.

  • Agnosia: Agnosia is a rare disorder where someone cannot process sensory information. With visual agnosia, whilst they may be able to see an object, such as a chair, they cannot recognise that it is a chair. This is because the information sent from the eyes (organ) to the brain (CNS) cannot be comprehended.

  • Prosopagnosia: this is an extremely rare form of agnosia where an individual cannot recognise faces despite being able to see them. Around 1 in 50 people suffer with some form of prosopagnosia. It can be caused by damage to part of the frontal lobe known as the fusiform face area.


Nervous System - Key takeaways

  • The nervous system is a network of nerve cells called neurons that transfer messages to and from different body parts. It is crucial to support and maintain bodily functions and can be split into two main sections: the central nervous system and the peripheral nervous system.
  • The central nervous system (CNS) consists of the brain and the spinal cord. It controls communications between the brain and the body by coordinating messages and passing information and instructions between them.
  • The peripheral nervous system (PNS) consists of the nerve cells outside of the CNS, in charge of gathering and sending information to different parts of the body. It can be further split into the somatic nervous system and the autonomic nervous system.
  • Whilst the somatic nervous system controls voluntary bodily functions and information from sensory neurons, the autonomic nervous system controls involuntary bodily functions.
  • Nerve cells in the nervous system release neurotransmitters which travel throughout the body through synaptic transmission. Neurological damage can insight rare disorders concerning the nervous system.

Frequently Asked Questions about Nervous System

The nervous system is a network of nerve cells called neurons which transfer messages to and from different parts of the body. It controls movements, responses and automatic bodily functions. It can be split into the central nervous system and the peripheral nervous system. 

The central nervous system is the part of the nervous system which controls communications between the brain and the body by coordinating messages and passing them between the two. The central nervous system comprises the brain and the spinal cord.

The autonomic nervous system is a subsection of the peripheral nervous system and can be classified as a network of nerves which controls internal organs and glands. It controls involuntary (unconscious) bodily physiologic processes such as heartbeat and digestion and can be further divided into the sympathetic and parasympathetic sections.  

The main function of the nervous system is to transfer signals from the brain to different parts of the body, such as organs and glands and vice versa. We can think of its main function as a command centre, where all movements, sensations, and automatic functions are controlled and maintained. 

The peripheral nervous system is the part of the nervous system excluding the brain and the spinal cord. It consists of nerves throughout the body which pass on information between the brain and the rest of the body. It can be split into the somatic nervous system and the autonomic nervous system. 

Final Nervous System Quiz

Question

What is the autonomic nervous system?

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The autonomic nervous system is responsible for regulating involuntary bodily functions.

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What are some examples of bodily functions regulated by autonomic nervous system?

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Some examples are: heart rate, breathing, sexual arousal, salivation and digestion.

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What are the two important neurotransmitters within the autonomic nervous system?


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acetylcholine (parasympathetic nervous system) and norepinephrine/noradrenaline (sympathetic nervous system)

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The autonomic nervous system is split into what two parts?

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The sympathetic nervous system and the parasympathetic nervous system.

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What is the sympathetic nervous system primarily responsible for?


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The fight-or-flight response

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Is the fight-or-flight response related to the sympathetic or parasympathetic nervous system?

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Sympathetic nervous system

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What is the fight-or-flight response?


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The fight-or-flight response is what is activated when we face acute stress.

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What are some physical signs of the fight-or-flight response?

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Some physical signs are: dilated pupils, pale or flushed skin, fast heart beat and increased breathing rate.

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What is the parasympathetic nervous system responsible for?


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The parasympathetic nervous system is responsible for relaxing the body back into a normal state once the stress has passed.

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What are the physical body signs of the parasympathetic nervous system?

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The physical body signs are for example: slower heart rate, decreased breathing rate and reduced blood pressure.

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What's the enteric nervous system?

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The enteric nervous system consist of neutrons limited and confined in the gastrointestinal tract

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What is autonomic dysfunction?

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Autonomic dysfunction occurs when the nerves of the autonomic nervous system are damaged so this can affect the regulation of bodily functions.

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What are some causes of autonomic dysfunction?


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  • diabetes
  • Parkison's disease
  • peripheral nerve disorders
  • certain drugs consumption
  • spinal cord disorders
  • cancer
  • hereditary reasons

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What are some symptoms of autonomic dysfunction?

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Autonomic disorders will at times cause dizziness to the person, this is due to the reduced blood pressure. Some people may sweat too much or not sweat, becoming intolerant to the heat

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What is the main difference between the somatic and autonomic nervous system?


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The somatic nervous system is responsible for voluntary bodily movements while the autonomic nervous system is responsible for involuntary bodily functions.

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What is the purpose of the fight or flight response?

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When encountering threats like predators in the wild our ancestors adapted to mobilise all energy resources to either "fight" or "flight" to survive.  The response allows us to instantaneously take action and survive threats.

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What triggers the fight or flight response?

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The fight or flight response is triggered by threats which can include stressful events.

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What is the function of the autonomic nervous system?

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The autonomic nervous system controls involuntary actions like breathing, heart rate, digestion or blood pressure.  

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What divisions does the autonomic nervous system consist of?

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The autonomic nervous system consists of the sympathetic and parasympathetic divisions.

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What is the function of the parasympathetic division of the autonomic nervous system?

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The parasympathetic division acts as a "brake" it is responsible for the "rest and digest" activity, it involves digestion of food, storing energy, slowing down the heart rate and breathing.

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What is the function of the sympathetic division of the autonomic nervous system?

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The sympathetic division acts as an "accelerator"  it is responsible for activating the "fight or flight" response, it involves rapidly releasing energy to muscles, dilating the pupils, accelerating heart rate, blood pressure and inhibiting digestion.

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What is the fight or flight response?

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The fight-or-flight response can be defined as a stress response that involves activation of the sympathetic nervous system and release of stress hormones (adrenaline) to increase our chances of survival in situations of threat.

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What is the role of the amygdala in the fight or flight response?

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The fight-or-flight response starts with the activation of the amygdala, a brain region that responds to emotions like fear, amygdala triggers the activation of the hypothalamus. 

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How does the hypothalamus control the fight or flight response?

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Hypothalamus communicates with the autonomic nervous system and activates the sympathetic nervous system.

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What hormone is released by the adrenal glands during the rapid fight or flight response?

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Adrenaline (epinephrine)

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What are the effects of adrenaline on the body?

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The release of adrenaline causes the liver to release stored energy in a form of glucose into the bloodstream, increases heart rate, blood pressure breathing rate and stops digestion.  

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What is the function of increased levels of glucose in the bloodstream during the fight or flight response?

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Increased levels of glucose in the bloodstream allow muscles to quickly use this energy to respond to a threat by either rapidly running away or fighting. 

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What is the function of increased heart rate and inhibition of digestion during the fight or flight response?

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  • Faster heart rate increases blood flow to important organs like the heart and to important muscles, so the energy can be used in a way that increases survival.  
  • Slowing down digestion means more of the energy can go to the muscles, which again can increase our chances of survival upon encountering a predator. 

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What is the benefit of dilated pupils during the fight or flight response?

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Dilated pupils help to enhance the vision to detect or respond to a threat quicker. 

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What is the role of the parasympathetic nervous system after the fight or flight response?

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After the fight or flight response, the body returns to the "rest and digest state", the parasympathetic nervous system slows down the rate of breathing and heart rate. Blood vessels dilute lowering blood pressure. Glucose is again stored and digestion activity comes back to normal. 

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What are the effects of chronic stress on physical health?

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Chronic stress can cause headaches, cardiovascular problems, digestive problems, increased chances of heart attack or stroke, stress can even decrease the immune system function making people under stress more prone to getting a cold or other infectious diseases. 

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What is the nervous system?

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a network of nerve cells called neurones which transfer messages to and from different parts of the body.

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What is a neuron?

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A neuron acts as a messenger which receives and transmits information to the cells. 

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Which two sections can the nervous system be first split into?

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The central nervous system and the peripheral nervous system. 

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The central nervous system consists of...

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The brain

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What are sensory nerves responsible for?

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Sensory nerves report information from the body and send it one way to the brain. 

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What are motor nerves responsible for?

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Motor nerves carry messages from the central nervous system to organs, muscles or glands so that they can perform a function.

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What is the spinal cord?

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The spinal cord is the column of nerves, part of the central nervous system, existing between the brain and the peripheral nervous system. It functions as a relay from the brain. 

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What two sections can the peripheral nervous system be split into?

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The somatic nervous system and the autonomic nervous system. 

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Select examples of the 'involuntary bodily functions' which the autonomic nervous system controls. 

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Digestion

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Which part of the autonomic nervous system is in control during fight or flight?

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The sympathetic system. 

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What is Myelin?

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It is a layer of insulation fat which exists on motor and sensory neurons to promote faster transmission. 

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Which part of the peripheral nervous system control voluntary muscle movements?

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The somatic nervous system. 

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What is a synapse in neurotransmission?

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The synapse is the very small gap between neurons where neurotransmitter molecules bind with receptor molecules on the second neuron and the impulse is passed on. 

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Prefrontal Cortex damage can cause...

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a shift in behaviour 

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What is Agnosia?

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Agnosia is a rare defect where someone may not be able to to process sensory information. 

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How does the James-Lange theory differ from traditional perspectives of emotions? 

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The James-Lange theory disagrees with traditional perspectives of emotion and instead proposes that the sequence of response to stimuli differs. 

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What is the definition of a physiological response? 

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The physiological response is the body's automatic, unconscious response to a stimulus or an event. 

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How does the James-Lange theory define emotion? 

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According to the James-Lange theory, the definition of emotion is the interpretation of physiological responses to changes in bodily sensation. 

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Question

Which division of the automatic nervous system is associated with negative emotions and increased activity?  

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The sympathetic system 

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