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

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Caption: : Glial Cell Activation

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

Nervous Coordination (II)

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Caption: : 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 addictiveCurare and atropine block acetylcholine Muscarine mimics acetylcholine

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Caption: : neurotransmitters function and parts; a simple understanding about the concept of neurotransmitters

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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, iodopsinRods – low visual acuityCones – 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, ForebrainCerebral Cortex: Sensory areas, Motor areas, Association areasVisual Cortex: Simple cells, Complex cells, Association areasBrain 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