Biology, 9: Co-ordination and response

• What are the types of neurones?

  Motor

  Relay

  Sensory
• Nerves connect sense organs to the central nervous system
• Nerves, the brain, and spinal cord are made of neurones

  Each are specialized for their function

  There is endings connecting with other neurons to pass on electrical impulses

  Axon and dendrons carry the electrical impulse
• Neuron: a specialized cell transmitting nerve impulses; a nerve cell.
• Dendron: A branching extension from the body of a neurone that receives signals from other cells or nerves.
• Types of neurones

  
• Sensory neurons are specialized to carry impulses from the sensory organs to the CNS
• Relay neurons are neurons that connect sensory neurons to motor neurons, it is in the CNS.
• Motor neurons carry impulses from the CNS to effectors (muscles and glands)
• Reflex is a response to a stimulus, it is rapid and automatic and protects you.
• What is the reflex arc?

  Stimulus -> Receptor -> Sensory neurone -> Relay neurone -> Motor neurone -> Effector -> Response
• The reflex arc:
• Reflex arc

  
• In the reflex arc, impulse is sent to the brain so it is aware of what is happening

  It allows the brain to over-ride reflex response
• Reactions happens automatically and is caused by a reflex

  It is involuntarily as it is the unconscious control of the CNS
• Involuntary responses are essential to basic survival and is quick

  Voluntary responses often take longer
• What are the sense organs?

  Skin, tongue, nose, eyes, ears
• What is stimulus for skin?

  Pressure, pain, temperature
• What is stimulus for tongue?

  Chemicals in food and drinks
• What is stimulus for nose?

  Chemicals in the air
• What is stimulus for eyes?

  Lights
• What is stimulus for ears?


  Sound (hearing)

  Movement/head position (balance)
• The eye anatomy

  
• The eye is a sense organ, responding to changes in light

  Specialised light-sensitive receptor cells are cells of the retina
• Light passing through the eye and reaching light-sensitive cells causes changes in cells

  It results in electrical impulses being sent to the brain along the optic nerve
• How is the cornea adapted?

  Transparent, allowing light to pass through without interference

  Refracts the light as it enters the eye
• How is the lens adapted?

  Focuses light on retina as it enters so image falls on it

  Changes shape to focus light on the retina
• How is the pupil adapted?

  Hole allowing light into the eye
• How is the jelly inside the eye adapted?

  Maintains shape of eyeball so the distance from front-to-back (focusing distance (does not change)
• How is the retina adapted?

  It is very dark so it can absorb as much of the light entering as possible
• How is the optic nerve adapted?


  Carries electrical impulses from the retina to the brain

  Sensory neurone
• The blind spot is where the optic nerve connects with the retina, there are no light sensitive cells
• What happens when there is dim light?

  Cells not stimulated

  Pupils dilate so more light reaches the retina

  Circular muscles relax, radial muscles contract
• What happens when there is bright light?

  Cells are stimulated

  Pupils contract so less light reaches the retina

  Circular muscles contract, radial muscles relax
• What happens when the eye is looking at a far object?

  There is less light refracted

  The ciliary muscles relax

  Suspensory ligaments tighten

  Lens becomes thinner
• What happens when the eye is looking at a near object?

  There is more light refracted

  The ciliary muscles contract

  Suspensory ligaments slacken

  Lens becomes fatter
• Hormones are a chemical substance used in hormonal system

  It is produced in the endocrine glands
• Endocrine glands do not have ducts to carry away hormones produced

  Hormone is secreted into the blood, dissolved in the plasma and carried around to target organs
• Hormones:

  
• Adrenaline is produced in the adrenal glands, above the kidney

  It is released in crucial moments, e.g. in fight or flight responses