Leaving Certificate Agricultural Science

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Leaving Certificate Agricultural Science
The Nervous System
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Introduction

• The function of the nervous system is to allow
  the animal to quickly detect, communicate and
  co-ordinate information about its external and
  internal environment.
• The two major parts of our nervous system are the
  central nervous system (CNS) and peripheral
  nervous system (PNS).
• The CNS is made of the brain and spinal cord.
• The cranial nerves, spinal nerves and ganglia
  make up the PNS.
• The cranial nerves connect to the brain.
• The cranial and spinal nerves contain the axons
  (fibres) of sensory and motor nerve cells.
• Nerve cells are also known as neurons.

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Types of Neurons

• Sensory Neurons
• Sensory neurons carry electrical signals
  (impulses) from receptors or sense organs to the
  CNS.
• Sensory neurons are also called afferent neurons.
  
• The cell body of sensory neurons is outside the
  CNS in ganglia.
• Motor Neurons
• Motor neurons carry impulses from the CNS to
  effector organs.
• Motor neurons are also called efferent neurons.
• The cell bodies of motor neurons are inside the
  CNS.

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Bridging the Gap The Synapse

• A synapse is a specialised junction between a
  neuron and its target cell.

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The Brain
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Parts and Functions of the Brain

• Cerebrum centre for sensory and motor control,
  language, memory, intelligence, and
  consciousness.
• Cerebellum muscle co-ordination, movement and
  balance.
• Medulla Oblongata controls breathing and heart
  rate.
• Hypothalamus osmoregulation and temperature
  control.
• Pituitary Gland secretes a wide variety of
  hormones a major endocrine gland.

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The Reflex Action

• A reflex action is a very fast unconscious
  response to an unexpected and potentially
  dangerous stimulus.
• Examples of reflex action knee jerk, eye blink,
  pupil size alteration, closure of the glottis on
  swallowing.
• A reflex arc is a specific nerve pathway involved
  in a fast, unconscious response to an unexpected
  stimulus.
• E.g. Spinal Reflex Action - the withdrawal of
  hand when finger jabbed unexpectedly with a pin.

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The Reflex Action - 2

• Pain and pressure receptors in the skin are
  stimulated.
• Sensory neurons carry the impulses to the spinal
  cord by way of the dorsal root.
• An interneuron picks up the impulse from the
  sensory and transmits it to the motor neuron.
• At the same time the impulse is also transmitted
  to the brain.
• The motor neuron stimulates the specific effector
  organ to make the appropriate response,  muscles
  in the arm are stimulated to contract pulling the
  hand away from the pin.
• The response is very fact occur before the
  brain is aware of the situation.
• The brain, having received the information, may
  transmit impulses to other muscles to modify the
  response.