B3.3

• What is a stimulus?

  A change in the environment which causes a response
• What is a receptor?


  The part of a control system that detects a change
• What is the processing centre?

  The part of a control system that coordinates a response
• What is an effector?


  A gland or muscle that brings about a response
• What is a response?

  Action or behaviour caused by stimulus
• What is a sense organ?

  An organ that detects stimuli
• What are the senses, their receptors and their purpose

  Hearing:Ears- Receptors for sound and balanceSight:Eyes- Receptors sensitive to lightScent and Taste:Nose and tongue- Receptors sensitive to chemicalsTouch:Skin- Receptor sensitive to pressure, pain and temperature
• What is the nervous system made up of?

  Central Nervous System (CNS)- Brain + Spinal ChordPeripheral Nervous System (PNS)- Bundles of neurons called nerves
• What are the different types of neurons?

  Sensory neurons

  Relay neurons

  Motor neurons
• What is the function of sensory neurons?

  Carry impulses from receptor cells to CNS

  Has myelin sheath which insulates axons and allows impulse to travel faster also stops impulse from travelling to other neurons

  Schwann cell in myelin sheath

  
• What are the features of relay neurons?


  Found in CNS

  
• Functions of dendrites in relay neurons

  Lots of short dendrites carry nerve impulses from sensory neurons to cell body

  Always come before cell body in any neuron
• Function of axons in relay neurons

  Lots of short axons carry nerve impulses from cell body to motor neuron

  Always come after cell body in any neuron
• Function of motor neuron


  Nerve impulses travel along axon

  Transmit impulses from CNS to a muscle or gland

  Myelin sheath insulates axon, stops impulses travelling to other neurons and speeds up nervous conduction

  Branching dendrites enables neurone to connect with many other neurones

  
• What is the cell body of a neuron?


  A rounded part of the cell that contains the nucleus and connects to the dendrite(s) and axon(s).
• What are the dendrites of a neuron?

  Thread-like extensions that receive an impulse from previous cells and carry it to the cell body
• What are the axons of a neuron?


  Thread-like extensions that receive the impulse from the dendrites and carry it to the next cell.
• What is the Myelin Sheath of a neuron?

  An insulating layer that surrounds dendrites or axons
• What are the Schwann Cells of a neuron?

  Cells that make up the myelin sheath
• What are the axon terminals of a neuron?

  Ends of the axon that carry the impulse to the next cell
• What is the nucleus of a neuron?

  The organelle within the cell body that contains the neurone's genetic information.
• What route do impulses take?

  Stimulus -> Sensory Receptor -> Sensory neurone -> Spinal chord -> Brain -> Spinal chord-> Motor neurone -> Effector -> Response
• Features of a coordinated response


  Goes to all parts of body

  Has many links

  Has different sensory receptors

  Is able to coordinate responses in different effectors
• What are reflex actions

  Automatic involuntary actions e.g. breathing

  They are often there to keep us from harming ourselves
• What is a reflex arc and why is it useful?

  Subconscious response to a stimuli

  Sometimes an extremely quick response is needed and there is not enough time for it to go through the conscious portion of the brain so the CNS is involved instead
• Describe a reflex arc for burning your hand

  1. Pain receptors in the finger sense the pain and stimulate the sensory neurone.

  2. Once the sensory neurone has been stimulated, an electrical impulse travels along it's length to the spinal chord.

  3. The sensory neurone is connected to a relay neurone via a synapse

  4. The relay neurone is triggered by a neurotransmitter which in turn triggers the motor neurone

  5. This stimulates the effector organ

  6. The relay neurones also sends a message to the brain so it knows what is going on
• What is a synapse?

  Gap in the middle of 2 neurons
• How does impulse travel along the synapse?

  1. An electrical nerve impulse travels along the first axon.

  2. When the nerve impulse reaches the dendrites at the end of the axon, chemical messengers called neurotransmitters are released.

  3. These chemicals diffuse across the synapse (the gap between the two neurons). The chemicals bind with receptor molecules on the membrane of the second neuron.

  4. The receptor molecules on the second neuron can only bind to the specific neurotransmitters released from the first neuron.

  5. The binding of neurotransmitter to the receptors stimulates the second neuron to transmit an electrical impulse along its axon.

  6. The signal therefore has been carried from one neuron to the next.
• Why are synapses important?


  An electrical impulse cannot directly cross the gap so a different mechanism has to be used.
• What is the function of receptors on the surface of synapses?

  They bind only to specific neurotransmitters
• What are vesicles? (synapses)

  Vesicles fuse with cell surface membrane releasing the neurotransmitter into the synapses
• What are problems with damage to the PNS?

  •PNS has a limited ability to regenerate

  •Minor damage to the PNS can often self heal.

  •More severe damage can be treated through surgically grafting sections of nerves over the damaged tissue
• What are problems with damage to the CNS?

  •Can lead to:

  •A loss of control of body systems

  •Partial or complete paralysis

  •Memory loss or processing difficulties

  •CNS cannot regenerate

  •Any damage is permanent unless it can be corrected by surgery
• Why is it so difficult to repair damage to the CNS? (brain)

  •Difficult to diagnose. MRI and CT scans used to locate damaged site.

  •Possible treatments

  -Radio therapy and chemotherapy

  •Brain tumors

  -Surgery

  •Remove damaged brain tissue

  -Deep brain stimulation

  •Parkinson's disease
• Why is it so difficult to repair damage to the CNS? (spinal chord)

  •Made of 31 pairs of nerves, each containing many nerve fibers

  •Identifying and repairing the damaged fiber with out damaging others in the process is extremely difficult.
• What are the different parts of the eye?

  
• Features of the conjunctiva


  Transparent

  Protects cornea
• Features of the cornea

  Transparent

  Bends light
• Features of the iris

  Coloured

  Made of muscle

  Controls the size of the pupil
• Features of the pupil


  A hole

  Allows light to enter eye