The Nervous System.

• • he human nervous system consists of the:​
  • Central nervous system (CNS) – the brain and the spinal cord
• • Peripheral nervous system (PNS) – all of the nerves in the body​​
• • Information is sent through the nervous system as nerve impulses – electrical signals that pass along nerve cells known as neurones​
• Central Nervous System (CNS)​-

  • Brain​
  • Spinal Cord​
• Peripheral Nervous System (PNS)​- Consists of 2 divisions:​

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  • Somatic Nervous System​
  • Autonomic Nervous System​
• • Somatic Nervous System​

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  • Nerves that branch out from the CNS.​
  • They link our voluntary muscles and our major sense organs to our brain, that we have control over.​

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• • Autonomic Nervous System​

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  • They are also nerves that branch out from the CNS.​
  • But these link our involuntary smooth muscle of our glands/organs to our brain., that we have no control over.​
• • Sympathetic Nervous System (SNS): prepares the body for action (fight/flight/release) 
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  • Parasympathetic Nervous System (PNS): returns the body to normal state (rest and digest). 
• Blood pressure regulation Baroreceptors (detects pressure) monitor blood volume as it is released from the heart​

  • Sensory signals are sent from the baroreceptor to the brain (the hypothalamus)​​
  • A signal is then sent to the sympathetic (increases heart rate - Adrenaline) or parasympathetic (slows heart rate – Acetylcholine release) nervous system ​​
  • The sympathetic nervous system releases Adrenaline to increase heart rate and blood pressure​​
  • The parasympathetic nervous system releases Acetylcholine to decrease heart rate and blood pressure​
• Spinal Cord : Column of nerves from brain to tailbone – protected by vertebrae of spine​

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  • Responsible for:​

       - Conducting impulses between the brain and the rest of the body​

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  *Impulses may travel as fast at 268 miles/hr​
• The two types of nerve cells

  • Motor neurons: Link the CNS to muscles and glands​
  • Sensory Neurons: Link the CNS to the sensory organs
• Which part of the autonomic nervous system increases heart rate?(shorter word)

  sympathetic
• Which part of the autonomic nervous system decreases heart rate? (longer word)

  parasympathetic
• Stimulus (plural = stimuli) The event that makes a nerve cell likely to transmit an impulse. For e.g. pain, pressure, sound, temperature (hot/cold), light, smell.​

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• Threshold value = a stimulus has to be above a certain level for a nerve cell to fire a nerve impulse. This value is its threshold.
• • How do they occur?
  • When a stimulus, for example a bright light shining through your eye, is perceived by a neuron (in the eye), special channels in the membrane of the neuron will open, and sodium ion (Na+) flows into the cell. This positive charge will cause other channels to open allowing for even more sodium to pass through.​
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  • 2. Because Na+ is positively charged, the inside of the neuron changes its charge from negative to positive. This change in charge is what we call an Action Potential, it occurs across the length of the nerve cell.​
• How do they occur?

   Saltatory conduction = is a leap frogging effect where an action potential is only generated at particular points along a nerve making the speed of transmission faster.​

   When the impulse arrives at the end of the neuron, this triggers the release of chemicals called neurotransmitters from the neuron membrane to the synapse.​​Neurotransmitter release – and signal continues or acts on the effector to cause a response 
• The reflex pathway stimulus, receptor, sensory neurone, relay neurone, motor neurone, effector, response.
• • A reflex arc is a pathway along which impulses are transmitted from a receptor to an effector without involving ‘conscious’ regions of the brain​​
  •  As it does not involve the brain, a reflex response is quicker than any other type of nervous response​​
  •  Examples of simple reflex actions that are coordinated by these pathways are:​
  • Removing the hand rapidly from a sharp or hot object​
  • Blinking​
  • Focusing of the eye on an object​
  • Controlling how much light enters the eye​
• Reflex Arc Example – Pain response ​

  A pin (the stimulus) is detected by a pain receptor in the skin​​

  2. The sensory neurone sends electrical impulses to the spinal cord (the coordinator)​​

  3. Electrical impulses are passed on to relay neurone in the spinal cord​​

  4. The relay neurone connects to the motor neurone and passes the impulses on​​

  5. The motor neurone carries the impulses to the muscle in the leg (the effector)​​

  6. The impulses cause the muscle to contract and pull the leg up and away from the sharp object (the response)​
• The somatic nervous system is the part of the nervous system that controls voluntary muscles and somatic reflexes. The somatic nervous system is involved with motor functions with skeletal muscles.
• The two different types of peripheral system is somatic nervous system and autonomic nervous system.
• The automatic nervous system is all about what is going on in the internal environment eg: gastrointestinal or excretory, endocrine, smooth and cardiac muscle, autonomic reflexes.
• The automatic nervous system can be sympathetic or parasympathetic.
• The sympathetic nervous system increases heart rate and increases breathing rate and inactive digestion.
• The parasympathetic nervous system will decrease heart rate and active digestion.
• The neurones resting potential is more negative then positive their is a higher Na+ outside of the cell and K+ inside the cell.
• An action potential is gonna rapidly change the charge in the neurone along the axon. Ion channels opens allowing Na+ to flood inside the first region of the axon. This event is called depolarisation as the electric charge is becoming more positive in the axon as Na+ floods in and most K+ channels stay closed. This spreads the next region of the axon and carries along