6.1.1

Nervous System Divisions

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The Nervous System

The nervous system can be split in many different ways, but the two major parts are the central nervous system and the peripheral nervous system.

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The nervous system

  • The nervous system can be divided into two major parts: the central nervous system (CNS) and the peripheral nervous system (PNS).
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The central nervous system (CNS)

  • The CNS is made up of the brain and spinal cord.
  • The CNS is connected to the rest of the body by the PNS.
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The peripheral nervous system (PNS)

  • The PNS is made up of thick bundles of axons, called nerves, carrying messages back and forth between the CNS and the muscles, organs, and senses in the periphery of the body.
  • The PNS has two major subdivisions: the somatic nervous system and the autonomic nervous system.
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The somatic nervous system

  • The somatic nervous system is associated with activities traditionally thought of as conscious and voluntary.
  • It is involved in the relay of sensory and motor information to and from the CNS. It consists of sensory and motor neurones.
    • Sensory neurones carry information from sensory receptors to the CNS and are afferent ("moving toward") fibres.
    • Motor neurons carry information from the CNS to the muscles of the body and are efferent ("moving away from") fibres.
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The autonomic nervous system

  • The autonomic nervous system controls our internal organs and glands and is considered to be involuntary.
  • It is made up of sympathetic and parasympathetic divisions.
    • The sympathetic nervous system is involved in preparing the body for stress-related activities.
    • The parasympathetic nervous system is associated with returning the body to routine, day-to-day operations.
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Homeostasis

  • Homeostasis is a state of equilibrium, in which biological conditions (such as body temperature) are maintained at optimal levels.
  • The sympathetic and parasympathetic have complementary functions. They work in tandem to maintain the body's homeostasis.

The Central Nervous System (CNS)

The central nervous system (CNS) is made up of the brain and the spinal cord, which work together to allow the body to respond to its environment.

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The brain

  • The brain is a very complex organ made up of billions of interconnected neurons.
  • It is a bilateral, or two-sided, structure that can be separated into distinct lobes.
  • Each lobe is associated with certain types of functions. Ultimately, all of the areas of the brain interact with one another to provide the foundation for our thoughts and behaviours.
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The spinal cord

  • The spinal cord is what connects the brain to the outside world, and allows the brain to act.
  • It routes messages to and from the brain, but has its own system of automatic process, called reflexes.
  • The cord is organised into 30 segments, which correspond with the vertebrae. Each segment is connected to a specific part of the body through the peripheral nervous system.
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Reflexes

  • Reflexes are reactions to stimuli that are rapid and automatic as sensory input is immediately acted upon by the spinal cord without input from the brain.
  • When a sensory message meets certain parameters, the spinal cord starts an automatic reflex.
  • The signal passes from the sensory nerve to a simple processing centre, which starts a motor command.
  • Seconds are saved, because messages don’t have to go the brain, be processed, and get sent back.
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Importance of spinal reflexes

  • Spinal reflexes are very important for survival because they allow the body to react very quickly.

Sympathetic & Parasympathetic Nervous Systems

The sympathetic nervous system (SNS) is primarily involved in responses that help us to deal with emergencies. The parasympathetic nervous system (PNS) relaxes them again once the emergency has passed.

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Sympathetic nervous system

  • The SNS is primarily involved in responses that help us to deal with emergencies (fight or flight), such as increasing heart rate and blood pressure and dilating blood vessels in the muscles.
  • Neurons from the SNS travel to virtually every organ and gland within the body, preparing the body for the rapid action necessary when the individual is under threat.
    • E.g. The SNS causes the body to release stored energy, pupils to dilate and hair to stand on end. It slows bodily processes that are less important in emergencies such as digestion.
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Parasympathetic nervous system

  • If we think of the SNS as pushing an individual into action when faced with an emergency, then the parasympathetic nervous system (PNS) relaxes them again once the emergency has passed.
  • Whereas the SNS causes the heart to beat faster and the blood pressure to increase, the PNS slows the heartbeat down and reduces blood pressure. Another benefit is that digestion will begin again under PNS influence. Because the PNS is involved with energy, conservation and digestion, it’s sometimes referred to as the body’s rest-and-digest system.

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1Social Influence

2Memory

3Attachment

4Psychopathology

5Approaches in Psychology

6Biopsychology

7Research Methods

8Issues & Debates in Psychology (A2 only)

9Option 1: Relationships (A2 only)

10Option 1: Gender (A2 only)

11Option 1: Cognition & Development (A2 only)

12Option 2: Schizophrenia (A2 only)

13Option 2: Eating Behaviour (A2 only)

14Option 2: Stress (A2 only)

15Option 3: Aggression (A2 only)

16Option 3: Forensic Psychology (A2 only)

17Option 3: Addiction (A2 only)

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