Biology Chapter 14

• Electrical impulses travel along neurones
• CNS is the brain and spinal cord
• PNS is all the nerves in the body (outside brain and spinal cord)
• Sensory neurone

  Sense organs to CNS
• Relay neurones

  Within CNS
• Motor neurone

  CNS to Effector
• Types of neurones

  
• Reflex actions are rapid and automatic
• Reflex arc

  
• Reflex arc

  Stimulus > Receptor > Sensory Neurone > Relay Neurone > Motor Neurone > Effector > Response
• Voluntary response

  Conscious action (begins from brain)
• Involuntary response

  Quick and automatic
• Synapse is a junction between 2 neurones
• Structure of a Synapse

  
• Events at synapse

  1. Impulse stimulates the release of neurotransmitter molecules from vesicles into the synaptic gap
  2. The neurotransmitter molecules diffuse across the gap
  3. Neurotransmitter molecules bind with receptor proteins on the next neurone
  4. An impulse is then stimulated in the next neurone
• Synapses ensure that impulses travel in one direction only
• Sense organs are a group of receptor cells that respond to specific stimuli:

  Light

  Sound

  Touch

  Temperature

  Chemicals
• Skin = Touch and Temperature

  Tongue = Chemicals

  Nose = Chemicals

  Ear = Sound

  Eye = Light
• Structure of eye

  Cornea: Refracts light

  Iris: Controls how much light enters pupil

  Lens: Focuses light onto retina

  Retina: Contains light receptors, some sensitive to light of different colours

  Optic nerve: Carries impulses to the brain

  
• High light intensity

  Radial and Circular muscles are antagonistic

  Radial muscles relax

  Circular muscles contract

  Pupil becomes smaller

  Less light enters the eye
• Low light intensity

  Radial and Circular muscles are antagonistic

  Radial muscles contract

  Circular muscles relax

  Pupil becomes bigger

  More light enters the eye
• When an object is near:

  Ciliary muscles contract

  Suspensory ligaments are relaxed

  Lens become thicker

  More refraction of light
• When an object is far:

  Ciliary muscles relax

  Suspensory ligaments tighten

  Lens become thinner

  Less refraction of light
• Rods

  Night vision because they have greater sensitivity

  All over retina except blind spot and fovea
• Cones:

  Colour vision

  3 different cones, sensitive to different colours

  Red, Blue and Green

  Found in fovea
• Fovea: small part in retina

  helps see colours clearly

  high concentration of cone cells
• Hormone is a chemical substance, produces by a gland and carried by the blood, which alters the activity of one or more specific target organs
• Endocrine glands: Specialized organs that produce and release hormones directly into bloodstream

  1. Adrenal glands
  2. Pancreas
  3. Testes
  4. Ovaries
• Adrenaline is produced by adrenal glands

  Responds to stress or danger

  Fight or flight hormone
• Insulin is produced by Pancreas

  Helps regulate and lower blood sugar levels
• Testosterone produced by Testes

  Main sex hormone in males
• Oestrogen produced by Ovaries

  Main sex hormone in females
• Effects of adrenaline

  1. Increased breathing rate: deliver more glucose and oxygen to muscles and other vital organs quickly
  2. Increased heart rate: blood pumped more quickly and efficiently around body, delivers more glucose and oxygen to muscles and other vital organs
  3. Increased pupil diameter: allows more light to enter retina, brain gets more info
• Adrenaline controls metabolic activity by:

  Increasing blood glucose concentration

  Increasing heart rate

  This is to provide more glucose to the muscles for respiration
• Glucagon is produced by pancreas

  Help regulate and higher blood glucose levels
• Blood glucose level too high:

  1. Pancreas detects changes
  2. Pancreas secretes insulin
  3. Insulin travels to the liver and stimulates the liver to convert glucose to glycogen
  4. Brings glucose levels down
• Blood glucose level too low

  1. Pancreas detects changes
  2. Pancreas secretes glucagon
  3. Glucagon travels to liver and stimulates break down glycogen into glucose
  4. Glucose released into blood
  5. Brings glucose levels up
• Nervous system: Neurones, brain, spinal cord

  Electric impulse

  Rapid

  Short lived

  Travel along neurones

  Small target area

  Wired system
• Hormonal system: Glands

  Chemical hormone

  Slower

  Longer lived

  Travels in blood

  Large target area

  Wireless
• Homeostasis is the maintenance of constant internal environment

  Reversing any changes that occur from set point