Mammalian Nervous System

• Sensitivity or Irritability


  The ability of living organisms to respond to a stimulus (a change in the environment)
• Stimulus


  The change in conditions of the surroundings that may affect the activities of the organism
• Receptors


  Special sensitive tissues (e.g. pain, touch and temperature receptors in the skin) or sense organs (e.g. eye, ear, tongue, nose)
• Response


  The reaction produced by the organism after receiving the stimuli, brought about by an effector
• Effectors


  Muscles, glands or organs that carry out the response
• Behaviour


  The observable reactions of the organism to the stimulus
• Coordinating systems


  • Nervous system
  • Endocrine system
• Nervous system


  • Coordinates the body's activities, enabling us to respond in an appropriate way to a given stimulus
• Structural components of the nervous system

  • CNS (Central Nervous System)
  • PNS (Peripheral Nervous System)
  • ANS (Autonomic Nervous System)
  • Nerves
• CNS (Central Nervous System)

  Brain and spinal cord
• PNS (Peripheral Nervous System)

  Nerves that link receptors to CNS and CNS to effectors
• ANS (Autonomic Nervous System)


  Regulates activities of internal organs (not under one's control)
• Components of the ANS


  • Sympathetic
  • Parasympathetic
• Functions of the nervous system

  1. Receptors detect stimuli and collect information about changes in the environment

  2. They send this information via nerves to the CNS

  3. The CNS receives the information, processes it and decides how the body should respond

  4. The CNS sends out instructions via the nerves to the appropriate effectors (muscles and glands) to carry out the required responses
• Nervous tissue


  The basic structural unit is the neurone, which is highly specialised for carrying information in the form of electric impulses
• Structure of a neurone

  • Cell body containing nucleus, cytoplasm and plasma membrane
  • Long thin fibre called the axon, covered with a fatty sheath (myelin sheath) that transmits impulses away from the cell body
  • Short fibres called dendrites that conduct impulses towards the cell body
  • Nerve endings that connect to receptor, effector or another neurone
• Functional types of neurones

  • Sensory neurone - has a single long dendrite that conducts impulses from receptors towards the CNS
  • Motor neurone - has a single long axon that conducts impulses from the CNS to effectors
  • Relay neurone - found within the CNS, passes information from a sensory neurone to a motor neurone
• Nerve


  Nerve fibres grouped together in bundles within a membrane
• Synapse


  Junction (slight gap) between the branching dendrites of one neurone and the cell body or dendrites of another neurone, where a neurotransmitter substance is released to transmit the nerve impulse
• Ganglion


  Swelling along a sensory nerve due to the accumulation of cell bodies of sensory neurones
• Arrangement of neurones in a reflex arc

  • Sensory neurone
  • Relay neurone
  • Motor neurone
• Spinal cord


  Soft, white cylindrical organ extending from the base of the brain through the vertebral column, containing grey matter (cell bodies) and white matter (nerve fibres)
• Reflex action


  1. Very rapid automatic (no conscious control) response to a specific stimulus

  2. Involves the shortest pathway from receptor to effector

  3. Components are receptor, sensory neurone, relay neurone in reflex centre (e.g. spinal cord), and motor neurone to effector
• Types of reflexes


  • Spinal reflexes - controlled by the spinal cord
  • Cranial reflexes - have their reflex centres in the brain (but are not consciously controlled)
• Brain


  Contains grey matter (cell bodies) on the outside and white matter (nerve fibres) on the inside
• The spinal cord has grey matter inside and white matter outside, whereas the brain has white matter inside and grey matter outside
• Reflex arc


  Components of a reflex
• Components of a reflex arc

  • Receptor
  • Sensory neurone
  • Relay neurone
  • Motor neurone
  • Effector
• Sequence of events in a reflex

  1. Receptor detects stimulus

  2. Sensory neurone transmits impulse to spinal cord

  3. Relay neurone in spinal cord integrates impulse

  4. Motor neurone transmits impulse to effector

  5. Effector responds
• Types of reflexes


  • Spinal reflex
  • Cranial reflex
• Spinal reflex


  Reflex actions controlled by the spinal cord, with reflex centres in the spinal cord
• Cranial reflex


  Reflex actions with reflex centres in the brain, but not consciously controlled
• Components of a spinal reflex arc

  • Receptor
  • Sensory neurone
  • Relay neurone
  • Motor neurone
  • Effector
• The spinal cord contains grey matter (bodies of motor and relay neurones) and white matter (fibres of motor and sensory neurones)
• Parts of the brain

  • Forebrain (cerebrum, pituitary gland, hypothalamus)
  • Midbrain
  • Hindbrain (cerebellum, medulla oblongata)
• Cerebrum


  Consists of two cerebral hemispheres, with the right hemisphere controlling the left side of the body and the left hemisphere controlling the right side
• Cerebral cortex


  • Outer part of the cerebrum, consisting of grey matter (nerve cell bodies)
  • Convoluted (folded) to increase surface area and pack more neurones
  • Site of higher mental activities like intelligence, memory, speech
• Functional areas of the cerebral cortex

  • Sensory area
  • Motor area
  • Association areas
• Sensory area


  Receives impulses from different receptors (sense organs) to give different sensations
• Motor area


  Sends out impulses to different effectors (e.g. involuntary muscles) to produce responses