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Nervous Control

Nervous Control

Nerve Organisation
• Central Nervous System (CNS): Made up of the brain and spinal cord
• Peripheral Nervous System (PNS) Made up of the pairs of nerves that originate from either the brain or the spinal chord
o Sensory Neurons: Carry nerve impulses from receptors  CNS
o Motor Neurons: Carry nerve impulses away from CNS  Effectors
• The motor Neuron system can be divided into:
o Voluntary Nervous system: Nerve impulses to body muscles is with conscious
o Autonomic Nervous system: Nerve impulses to glands, smooth muscles and cardiac muscles and is without conscious
Spinal Cord
• The spinal cord is a column of nervous tissue that runs along the back and lies inside the vertebral column for protection
• At regular intervals do pair of nerves separate off of the cord
Reflex Arc



Example: Heat



Heat from hot object



Temperature receptors in skin create nerve impulse to sensory neuron


Sensory Neuron

Passes nerve impulse to spinal cord


Intermediate Neuron

Links the sensory neurone to the motor neuron found in spinal cord


Motor Neuron

Carries nerve impulse from spinal cord to muscle in the upper arm



Muscle in upper arm, which is stimulated to contract



Hand is pulled away from hot object

Importance of the Reflex Arc
• The reflex arc is an involuntary response which allows for an instant reaction to a danger
• The reflex arc being involuntary frees up the brain to carry out more complex tasks
• The reflex arc does not have to be learnt and therefore is effective since birth
• The response is fast as the neurone pathway is short from spinal cord to receptor this is further increased by few synapses.

Nerve Communication

Nerve Communication

  • Nerve Communication


    • A stimulus is a detectable change in the internal or external environment of an organism that produces a response in the organism
    • The ability for an organism to respond to a stimulus increases its chance of survival. These organisms which survive can therefore carry out natural selection.
    • Stimulus are detected by receptors.
      • Receptors are able to transfer energy of a stimulus into a form of energy that can be processed by the organism and lead to a response
      • The response is carried out by Effectors
    • Animals use their nervous system to communicate between receptors and effectors
    • Each effector and receptor is connected to a coordinator
      • The coordinator connects information from each receptor with the appropriate effector

    Stimulus à Receptor à Coordinator à Effector à Response


    • Taxis is a simple response by direction which is determined by a direction of the stimulus
    • A motile organism will respond directly to the environment changes by moving its entire body either towards a favourable stimulus or away from an unfavourable one
    • Taxes are classified according to whether the movement is:
      • towards the stimulus (positive taxis)
      • away from the stimulus (negative taxis


    • Kinesis is an indirect movement towards/away from a stimulus determined by a more unpleasant environment causing a more rapid change in direction compared to a favourable one where changes in directions are reduced.
    • Kinesis results in an increase in random movements
    • Kinesis aims to return the organism back into a favourable environment.
    • Kinesis is particularly important for less directional stimuli
      • g. Humidity and Temperature do not have a fixed gradient from one extreme to another


    • Tropism is a growth movement of a part of a plant in response to a directional stimulus
    • Plants will grow towards and away from a stimulus
      • Plant shoots grow towards light (positive phototropism)
      • Plant roots grow away from light (negative phototropism) but towards gravity (gravitropism)
      • Plant roots grow towards water (positive hydrotropism)

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Control of Heart Rate

Control of Heart Rate


Sympathetic Nervous System: Parasympathetic Nervous System:
  • Stimulates effectors and so speeds up any activity
  • Used under stressful conditions by awareness and preparing for Fight or Flight
  • Inhibits effectors and results in them being slowed down
  • It controls activities under normal resting conditions
  • It is used to conserve energy and replenishing body reserves

The actions of the Sympathetic and Parasympathetic nervous systems work antagonistically.

Control of Heart Rate

  • Resting heart rate of an average adult is 70 BPM
  • However, the BPM must be able to change to accommodate demands for oxygen
  • Changes to the Heart Rate occurs in the Medulla Oblongata:
    • A centre which increases heart rate which is linked to the sinoatrial node by the sympathetic nervous system
    • A centre which decreases heart rate which is linked to the sinoatrial node by the Parasympathetic system

The response of each centre is determined by stimulation from receptors of:

  • Chemoreceptors: Change in chemical properties of the blood
  • Baroreceptors: Change in blood pressure


  • Found in the carotid arties (arteries leading to the brain) and aorta
  • Sensitive to changes in pH (n.b. pH alters on CO2 concentrations)
    1) Increased CO2 concentrations lowers pH
    2) Chemoreceptors detect change and increase frequency of impulses to the medulla oblongata
    3) Centre increase frequency of impulses via sympathetic nervous system to SA node which increases heart rate
    4) Increased blood flow result in more CO2 being removed by lungs and thus CO2 concentration decreases
    5) pH of the blood returns back to normal
    6) Chemoreceptors reduce impulse frequency to medulla oblongata
    7) medulla oblongata reduces frequency of impulses to SA node which therefore decreases heart rate to normal

Found within the walls of the carotid arties and the aorta

 High Blood Pressure  Low Blood Pressure
 1) Baroreceptors transmit impulse to the medulla oblongata which decrease the heart rate
2) Medulla oblongata centre send impulses via parasympathetic nervous system to the SA node of the heart which decrease the heart rate
 1) Baroreceptors transmit impulse to the medulla oblongata which increases the heart rate
2) Medulla oblongata centre send impulses via sympathetic nervous system to the SA node of the heart which increases the heart rate