Coordination and response

Stimulus

Changes in internal and external environment

Homeostasis

• Maintains internal conditions

• Optimal conditions for enzymes and cell function

Factors controlled by homeostasis

• Water content

• Temperature

• pH

• Blood pressure

• Blood glucose concentration

2 main communication systems

• Endocrine system

• Nervous system

Where is body temperature maintained and controlled

Thermoregulatory centre

Types of control responses

• Nervous

• Chemical

Components of the control system

• A stimulus

• A receptor

• A coordination centre which receives and processes information from receptors

• An effector (a muscle or gland), which brings about responses to restore optimum levels

Positive tropism

• Growth towards the stimuls

Negative tropism

• Growth away from the stimulus

Phototropism

Response to light

Geotropism

Response to gravity

Auxin

Plant growth regulators that control directional growth responses

Where is auxin produced

• Tips of growing shoots and diffuses to the region just below the tip, where cell division occurs.

• Only the area behind the tip can contribute to growth by cell division and elongation.

How does the nervous system transmit information

Sent as electrical impulses through neurons at very high speeds

How does the endocrine system transmit information

Sends information as hormones, which are carried by the blood and can circulate throughout the body.

Main features of the nervous system

• Made up of nerves, brain, and spinal cord.

• It uses electrical impulses, with fast action and a short duration.

Main features of the endocrine system

• Made up of glands.

• It uses chemical hormones, with slower action and a longer duration.

The human nervous system consists of

• Central nervous system (CNS) – the brain and spinal cord

• Peripheral nervous system (PNS) – all of the nerves in the body

Nerve

Bundle of neurons

The pathway through the nervous system

stimulus → sensory neurone → relay neurone → motor neurone → effector → response

Synapse

A synapse is a junction between two neurones where their dendrites meet. It is a very small gap known as the synaptic cleft

How is the signal transferred across a synapse

The electrical signal is converted into neurotransmitters that crosses the synaptic cleft, then back into an electrical impulse when it meets the neurone on the other side.

Neurotransmitters

Chemical signalling molecules used to transfer the signal between neurons at a synapse

Process of how an impulse is passed across a synapse.

• The electrical impulse travels along the presynaptic neurone.

• This triggers the release of neurotransmitters from vesicles.

• Neurotransmitters diffuse across the synaptic cleft and bind with receptor molecules on the postsynaptic membrane.

• This stimulates the second neurone to generate an electrical impulse.

• The neurotransmitters are destroyed to prevent continued stimulation.

Why do synapses ensure impulses only travel in one direction?

To avoid confusion within the nervous system

Reflex arc

Pathway of a reflex response taken by an electrical impulse

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Suspensory ligament

Ligaments that connect the ciliary muscle to the lens

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Conjunctiva

A clear membrane that covers the white of the eye and the inside of the eyelids; it lubricates the eye and provides protection from external irritants

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Iris

controls how much light enters the pupil

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• Cornea

  transparent lens that refracts light as it enters the eye

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• Pupil

  Hole that allows light to enter the eye

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• Lens

  transparent disc that can change shape to focus light onto the retina

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• Ciliary muscle

  A ring of muscle that contracts and relaxes to change the shape of the lens

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• Sclera

  The strong outer wall of the eyeball that helps to keep the eye in shape and provides a place of attachment for the muscles that move the eye

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• Retina

  contains light receptor cells – rods (detect light intensity) and cones (detect colour)

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• Fovea

  A region of the retina with the highest density of cones (colour detecting cells) where the eye sees particularly good detail

Label the structure and its function

• Optic nerve

  sensory neuron that carries impulses between the eye and the brain

rod cells

Sensitive to light

Cone cells

Sensitive to colour

Blind spot

The point at which the optic nerve leaves the eye, where there are no receptor cells

In bright light

• Radial muscles relax

• Circular muscles contract

• Pupil constricts

In dim light

• Radial muscles contract

• Circular muscles contract

• Pupil dilates

Focusing on near objects

• Ciliary muscles contract

• Suspensory ligaments loosen

• Lens gets fatter

Focusing on distant objects

• Ciliary muscles relax

• Suspensory ligaments tighten

• Lens is pulled thin

Cooling mechanisms

• Vasodilation

• Sweating

• Flattening of hairs

Vasodilation

Increase heat loss is to supply the capillaries in the skin with a greater volume of blood, which then loses heat to the environment via radiation

Sweating

• Sweat is secreted by sweat glands

• This cools the skin by evaporation

Flattening of hairs

• The hair erector muscles in the skin relax, causing hairs to lie flat

• This stops them from forming an insulating layer by trapping air and allows air to circulate over the skin and allows heat to leave by radiation

Warming mechanisms

• Vasoconstriction

• Shivering

• Erection of hairs

Vasoconstriction

The capillaries in the skin are supplied with a smaller volume of blood, minimising the loss of heat to the environment via radiation

Shivering

• This is a reflex action in response to a decrease in core body temperature

• Muscles contract in a rapid and regular manner to warm the blood

Erection of hairs

• The hair erector muscles in the skin contract, causing hairs to stand on end

• This forms an insulating layer over the skin's surface by trapping air between the hairs and stops heat from being lost by radiation

Adrenaline

• Readies the body for a 'fight or flight' response

• Increases heart and breathing rate

Adrenaline- Source

Adrenal gland

Insulin

• Lowers blood glucose levels

• Causes excess glucose in the blood to be taken up by the muscles and liver and converted into glycogen for storage

Insulin- source

Pancreas

Testosterone

• Main sex hormone in males

• Development of male reproductive organs and secondary sexual characteristics (eg facial hair, deep voice)

Testosterone- source

Testes

Progesterone

• Maintains pregnancy

• Maintains the uterus lining to cushion the fertilised egg and allow it to develop

Progesterone- source

Ovaries

Oestrogen

• Main sex hormone in females

• Development of female secondary sexual characteristics and regulation of the menstrual cycle