Human Biology Chemical Messengers

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Human Biology 3A Notes
CHAPTER 4: Chemical Messengers
Homeostasis:the maintenance of a constant internal environment Homeostasis ensures that the fluid environment of the cells: • Contains the optimum concentration of nutrients, ions, gases and water • Stays at a constant temperature – the optimum temperature for normal cell functioning • Is maintained at the optimum pressure

Feedback system: Negative feedback system:
Negative feedback: Positive feedback:
A situation where the response toa stimulus changes the original stimulus Where the response to a stimulus brings about a change opposite to, or reduces the effect of, the original stimulus Feedback that brings about a change opposite to, or reduces the effect of, the original stimulus Feedback that reinforces the original stimulus Common features of a negative feedback system:

Stimulus: Receptor: Modulator:
the change in environment that causes the system to operate detects the change control center (brain) that processes information from receptor and sends to the effector Effector:carries out a response counteracting the effect of the stimulus Response:a response is carried out (action) Feedback:is achieved because the original stimulus has been changed by theresponse

Homeostatic mechanisms are controlled by both the nervous system and the endocrine system. Nervous system:sends electrical messages to appropriate organs Endocrine system:secrete chemical messengers Endocrine system is generally slower

Endocrine system: Exocrine glands: Endocrine glands:
the body system involved in chemical communication between cells; made up of endocrine glands secrete into a duct that carries the secretion to the body surface or to one of the body cavities secrete hormones into the extracellular fluid that surrounds the cells making up the gland Hormone:a chemical secreted by an endocrine gland and often carried in the blood that affects the functioning of a cell or organ Steroid hormones:work by entering target cells and combining with a receptor protein inside the cell. Human Biology 3A Notes

CHAPTER 5: The Central Nervous System
Jennifer Nguyen
The nervous system is the communication network and control centre of the body. The nervous system is also involved in maintaining homeostasis. The nervous system is divided into two parts:
The central nervous system:
Consists of the brain and spinal cord •The control centre for the whole nervous system The peripheral nervous system:
Made up of nerves that connect the central nervous system with the receptors, muscles and glands Protection of the Central Nervous System
Structures that protect the CNS:
• Bones •Cerebrospinal fluid (CSF) •Membranes called meninges Cranium: Vertebral canal:the opening in the vertebrae through which the spinal cord part of the skull that houses and protects the brain

passes Meninges:membranes covering the brain and spinal cord (i.e. the entire CNS). The meninges is made up of three layers 1.Outer meningal layer (dura mater): closest to the skull, tough and fibrous, similar texture to a rubber glove 2.Middle meningal layer (arachnoid mater): lose mesh of fibres with a web-like appearance; provides a cushioning effect 3.Inner meningal layer (pia mater): firmly adheres to the brain and spinal cord; very delicate and contains blood vessels

Cerebrospinal fluid:
Fluids produced in the cavities of the brain •Fills the brain cavities and surrounds the brain and spinal cord •Contains few cells, glucose, protein, urea, salts •Acts as a shock absorber, cushioning any blows or shocks the CNS must sustain •CSF is formed from blood that circulates around and through the CNS and eventually re-entering blood capillaries. During circulation, takes nutrients to brain and spinal cord and carries away wastes •Brain floats in the cranium, supported by CSF Therefore the cerebrospinal fluid protects, supports and transports. THE BRAIN

Largest part of the...
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