A-Level Biology: Control in Animals & Plants

Survival & Coordination

• Human body is controlled by two major systems:
• 1) Nervous system
• 2) Endocrine system
• These systems are linked together by the hypothalamus
• Reflex arc is an instant uncontrolled action:
• sensory neurone > relay neurone > motor neurone
• Postural reflex, e.g. knee jerk, maintains position and body control without conscious adjustment
• Endocrine System
• 7.1 - Nervous system
• The Nervous System

Nervous Coordination (I)

• Glial cells
• Packed between neurones to form neuroglia tissue:
• a) provides mechanical support and electrical insulation
• b) Schwann cells are specialised glial cells, forming myelin sheaths
• c) control nutrient and ionic balance. Break down neurotransmitters
• 
• Legenda: Glial Cell Activation

Nervous Coordination (II)

• Nissl tissues
• Contained in neurones:
• a) generate enzymes involved in impulse transmission and synthesis of trophic factors
• b) regulate growth and differentiation of nervous tissue
• When impulse is not transmitted: - charge (resting potential) across axon membrane = -70mV
• When impulse is transmitted: - action potential is a brief reversal of resting potential
• All-or-None rule: - stimulus needs the minimum intensity to initiate an action potential. Below this, there is no impulse
• Impulse takes place over: - temporal or spatial summation
• 
• Legenda: Image of a Nissl-stained histological section (showing various classes of cells (neurons and glia)

Nervous Coordination (III)

• Synapses are gaps between neurones to control impulses chemically. They release neurotransmitters that diffuse across synaptic cleft and trigger action potential in membrane
• Once it reaches post-synaptic neurone, enzymes break it down and it diffuses back across synapse
• Neurotransmitters used in the human body are:
• acetylcholine (motor neurones)
• noradrenaline (sympathetic synapses)
• serotonin, dopamine (in brain)
• Synapses: - are effected by drugs: Hallucinogens (LSD) mimic actions of other neurotransmitters Nicotine is addictive
• Curare and atropine block acetylcholine
• Muscarine mimics acetylcholine
• https://www.youtube.com/watch?v=EXqXBnxP_sE (Incorporar)
• Legenda: neurotransmitters function and parts; a simple understanding about the concept of neurotransmitters

The Human Eye

The Anatomy of the Eye

• Light entering eye: focused on retina - cornea does most refraction. Cornea and vitreous humour have the same refractive index
• - lens fine focuses using ciliary muscles:
• Distant object: ciliary muscles relax, ligaments tighten > lens becomes flat and thin
• Close-up object: ciliary muscles contract, ligaments relax > lens becomes more spherical and fat
• Iris controls pupil size:
• Dim light: radial muscles contract, circular muscles relax > pupil dilates
• Bright light: radial muscles relax, circular muscles contract > pupil constricts
• Rods respond to dim light, responsible for peripheral vision. Contain the visual pigment, rhodopsin
• Cones respond to bright light, responsible for central and colour vision. Contain the visual pigment, iodopsin
• Rods – low visual acuity
• Cones – high visual acuity
• Trichromatic theory = red, blue and green cones. Each detects different wavelength of light

Central Nervous System

• Central Nervous System : Spinal Cord, Hindbrain, Midbrain, Forebrain
• Cerebral Cortex: Sensory areas, Motor areas, Association areas
• Visual Cortex: Simple cells, Complex cells, Association areas
• Brain and spinal cord protected by:
• - Bone (skull and vertebral column)
• - Spinal and cranial meninges
• - Cerebrospinal fluid
• Opposing functions of sympathetic & parasympathetic divisions of the ANS:
• - Iris
• - Ciliary muscle
• - Lacrimal gland
• - Urinary bladder wall
• Nervous System III Senses
• W5: Development of the nervous system
• Endocrine System
• Nervous system test