Coordination and Response

Coordination and response in humans

The action of the endocrine system is slow and long-term compared to CNS

• Central Nervous System
  • Brain, Spinal cord, peripheral nerves and sense organs
• Hormonal (or endocrine) system
  • Hormones secreted by endocrine glands
  • Regulate body functions like metabolism, growth

The Nervous System

• Consists of
  • Sense organs containing receptor cells
    • Receive stimuli
  • Nerves that conduct electrical impulses
    • Transmit these stimuli to ...
  • Spinal cord and brain
    • which process them and coordinate the response, which is passed as electric impulses (along nerves) to
  • effectors (muscles, or endocrine glands)
    • produce the desired response
      • eg. muscle contraction

Nerve cells = neurones

• Specialised cells making up brain, nerves and spinal cord
  • Have many endings to connect to other neurones
  • Long cell extensions (axons and dendrons) to carry electrical impulses
  • Sensory neurones, relays and motor neurones

Sense organs

• Skin for touch (pressure, pain, temperature)
• tongue for taste (chemicals in food)
• nose for smell (chemicals in air)
• eyes for sight (light)
• ears for hearing (sound vibrations), balance (movement or head position)

Eye

• light-sensitive receptor cells in retina
  • located in back of eye
  • light converted to electrical impulses, sent to brain via optic nerve
  • Cells in retina:
    • Cone cells (respond to colour, work well in bright light), clustered around fovea (most sensitive part of retina)
    • Rod cells (respond to intensity, more sensitive in low light)
• Cornea, lens, aqueous and vitreous humor all transparent
  • Vitreous humor maintains the eye-ball shape
  • Aqueous humor nourishes the eye (in addition to providing shape)
• Pupil is a hole in iris to let in light

Focusing light

• Cornea bends (refracts) the light, focusing it on the retina. Its focus is fixed.
• the lens "fine-tunes" the focus
• When focusing on distant objects:
  • Incident light rays almost parallel
  • Cornea can focus without much help from lens
    • Ciliary muscles relaxed, lens elongated
• When focusing on nearby objects:
  • ...
  • ...

Response to light

• Light-sensitive cells only respond to light above certain intensity
• They can be damaged by light of two high an intensity
• Amount of light entering through pupil controlled by iris
  • contains radial and circular muscles
    • in dim light, radial muscles contract, circular muscles relax = pupil dilated; more light let through
    • the opposite happens in bright light (pupil constricted)

Reflex responses

• Rapid, automatic responses
• Stimulus usually processed by spinal cord
  • Reflex arc: Stimulus -> receptor -> Sensory neurone -> Relay neurone in CNS -> motor neurone -> effector -> Response
• Examples: response to standing on pin, touching hot object
• Message also sent to brain
  • Can override the reflex response

Homeostasis

• Life processes require conditions (such as temperature, water concentration, alkalinity, etc.) to lie within a narrow limit of ranges
• Homeostasis =Maintaining constant internal conditions (temperature, water content, etc.)
• Homeostasis - body water content
  • Controlled by hypothalamus
    • through action of ADH on the kidney's collecting ducts*

* Will be convered in chapter on excretion

Homeostasis: Temperature Control

• Core body temperature = 37 degrees C
• Heat energy constantly released due to respiration and other chem reactions
• This heat energy is eventually transferred to the environment
• Hypothalamus monitors body temperature
• If core temperature too high
  • Sweat released, cooling the skin (how?)
  • Surface capillaries dilate (vasodilation)
• If too low
  • Vasoconstriction
  • Shivering
  • In furry mammals/birds, fur/feather become raised, trapping air (which is a good insulator)
    • Happens to a smaller extent in humans

Hormones

• Hormones are "chemical messengers"
• Made by "endocrine glands"
  • These are ductless glands => hormones directly secreted into the blood
  • Some glands produce/release multiple hormones (eg. pituatary)
• Some hormones target a specific organ; others effect various parts of the body
• Changes caused by hormones are slower and more longer lasting (compared to changes caused by CNS)

Hormones - contd.

• Adrenaline
  • Produced by adrenal glands in kidney
  • Produced during stress/excitement/fright...
    • "Fight or flight" response
  • Effects
    • Increased heart rate, breathing rate and sweating
    • hair standing on end
    • glucose released from liver and muscles
    • dilated pupils
    • paling of skin (blood redirected to muscles)
• Antidiuretic hormone (ADH)
  • Produced by pituitary in brain
  • Causes kidney to reabsorb more water
• Insulin
  • Produced by pancreas
  • Controls the concentration of glucose in blood
    1. After a carb-rich meal, glucose rises quickly in blood
    2. Rise detected by pancreas; releases insulin
    3. Insulin travels to liver
    4. Causes glucose to convert to glycogen, which is stored in liver
• Glucagon secreted by pancreas (instead of insulin) when glucose in blood falls too low

Hormones - contd.

• Testosterone
  • Produced by testes in males
  • Causes secondary sexual characteristics
  • Needed or production of sperm
• Progesterone/oestrogen
  • Produced by ovaries in females
  • Causes secondary sexual characteristics
  • Controls menstrual cycle