CHAPTER 8 NOTES

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MAINTAINING A BALANCE:

HOMEOSTASIS - the maintenance of a relatively stable internal environment

Mechanisms used in complex organism are called homeostatic mechanisms

- this includes mostly the nervous and hormone systems

- much of regulation and control is developmental

THE PRINCIPLE OF FEEDBACK:

- minor fluctuations can occur, but sometimes considerable disturbances do occur in the internal environment

- these disturbances need to be brought under control as cells can function effectively only at an optimal temperature or concentration of substances

- information or signals about these disturbances are fed to a control centre

- the centre then interprets the signal and coordinates a response that might counteract the disturbance

- these mechanisms are called FEEDBACK MECHANISMS

- feedback mechanisms are characterised by a stimulus which is detected by a receptor, a coordinating centre and some part of an organism (effector) which carries out a response

- effectors are usually muscles/glands

NEGATIVE FEEDBACK -

If the response by the effector - the gland/organ responding to stimulation - cancels/counteracts the original disturbance/stimulus, the mechanism is referred to as a negative feedback

- negative feedback mechanisms results in returning the changed internal conditions to their optimal level/set-point.

DETECTING CHANGING CONDITIONS:

- without food or water, organisms are unlikely to survive

- organisms need to be able to detect changing external/internal conditions and coordinate their responses if they are to survive

- two systems; nervous and endocrine system are responsible for; monitoring changed and coordinating responses

NERVOUS SYSTEM:

- brain and spinal cord make up the CNS (central nervous system)

- CNS is responsible for processing, storing and coordinating information

- the other parts of a nervous system is called the PNS (peripheral nervous system)

- nerve impulses travel along defined pathways

sensory neurones - to the CNS from the source of stimulation

motor neurones - from the CNS to the effectors along different pathways

- neurones are the basic units of the nervous system

- neurones structures is directly related to its function

- neurones have extensions called fibres which nerve impulses travel

- a bundle of nerve fibres is a never

- each nerve is wrapped in a tube of connective tissue

- the peripheral nerve that connect directly the brain are the cranial nerves and the spinal nerves also connected to the spinal cord

- peripheral nerve fibres are encloses in a sheath of whitish-looking fatty material called myelin

- myelin is produced in the cytoplasm of thin cells which wrap around the fibre, leaving small gaps/nodes where adjacent myelin cells meet

- myelin sheath assists in the transmission of electrical impulses along the neurone

- damage to the myelin sheath, hinders the transmission of nerve impulses

BEGINNING THE PATHWAY - RECEPTORS DETECT STIMULI

- specialised nerve cells called sensory cells/receptors are able to detect disturbances in the environment

- receptors can be single and distributed all over the body

- no single receptor detects every kind of stimulus

- a receptor is specialised to detect a particular kind of stimulus and to pass that message on

FIVE GENERAL TYPES OF RECEPTORS:

1. chemoreceptors - are stimulated by molecules of substances that have to do with smell, taste and concentration of substances such as CO2, O2, and glucose in the blood

2. mechanoreceptors - detect pressure, touch, tension, sound vibrations, and internally position and posture of the body (balance)

3. photoreceptors - are stimulated by light such as in the retina of the eyes, and light-senstive cells in body surface

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