The Nervous System

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• The Nervous System

WALT The structure and function of the nervous
system The motor neurone The reflex arc
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The nervous system performs 3 functions

• 1 To collect information about the internal and
  the external environment.
• 2 To process integrate the information, often
  in relation to previous experience.
• 3 To act upon the information, usually by
  coordinating the organisms activities.

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The Nervous System

• In higher animals like mammals, the nervous
  system consists of
• (1)The Central Nervous System which includes the
  brain and the spinal cord
• (2)The Peripheral Nervous System which includes
  the cranial nerves and the spinal nerves

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Brain

• The Nervous
• System

Spinal Cord
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Organisation of the nervous system

• The sensory neurons (nerve cells) which transmit
  this information and the receptors form the
  sensory system.
• The processing and integration of this
  information is performed by the CNS.
• The final function whereby information is
  transmitted to effectors, which act upon it, is
  carried out by the effector (motor) system.

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The Nervous Tissue the Nerve Impulse

• A nerve is a bundle of cells called neurones
• Nerve impulses are transmitted along neurons
• Each neuron (nerve cell) consists of a cell body
  and nerve fibres

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Types of Neurons

• There are three types of neurons
• 1.The motor neuron transmits nerve impulses
  from the CNS to the effectors
• 2.The sensory neuron transmits nerve impulses
  from the receptors to the CNS
• 3.The relay neuron connects the sensory neuron
  to the motor neuron and also neurons in the CNS

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• The portion which activates involuntary responses
  is known as the Autonomic Nervous System
• The portion that activates voluntary responses is
  called the Somatic System.
• The collection of information from the internal
  and external environment is carried out by the
  receptors.

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The Motor Neurone
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dendrites
nucleus
nucleolus
Motor Neurone
dendrites
axon
cell body
Node of Ranvier
Schwann cell
Myelin sheath
Axon
Myelin sheath
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The Nervous Tissue

• Dendron part of nerve fibre transmitting
  impulses towards the cell body
• Axon part of the nerve fibre transmitting
  impulses away from the cell body

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The Myelin sheath

• This is a fatty layer outside the nerve fibre
  it has two functions
• 1 To insulate nerve impulses (electric charges)
• 2 To speed up transmission of nerve impulses

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The Myelin Sheath

• The myelinated sheath is made up of mainly the
  membranes of Schwann cells
• These membranes contain phospholipid molecules
  that have long fatty acids.
• These prevent the movement of charged water
  soluble ions

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A Schwann Cell
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Damage to myelin Multiple Sclerosis
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The Reflex Arc

• A simple reflex action is a quick, inborn
  automatic response of an animal to a stimulus.
• It does not involve thinking (the brain) but
  inform the brain (cerebrum) later.
• The simple reflex actions are protective in
  function need not be learnt.
• The same stimulus initiates the same response at
  different times.

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The reflex arc
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The reflex arc

• - The neural pathway between the receptor and the
  effector involved in a reflex action
• - spinal reflex only the spinal cord is
  involved, e.g. knee jerk reflex, withdrawal
  reflex
• - cranial reflex involves the medulla oblongata,
  e.g. blinking, sneezing

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Reflex Arcs

• monosynaptic the reflex arc has only one
  synapse between the sensory motor neurons in
  the spinal cord
• polysynaptic reflexes involving two or more
  synapses