Methods of Control Animals are very complex organisms with many cells to coordinate. This coordination and control is performed with 2 different systems. These systems often cooperate. 1.The Nervous System (electric signals) 2.The Endocrine system (chemical signals)

USES OF THE CONTROL SYSTEMS -Influencing the internal environment (Nervous + Endocrine control) -Contraction of muscles (Nervous system)

A Major reason for control Maintenance of a constant internal environment, despite and ever changing external environment = Homeostasis Why? organisms have a range of tolerance, should these tolerance levels be exceeded, the organism cannot function correctly

Principles of Feedback Feedback always begins with a stimulus and ends with a response The stimulus is detected by a receptor organ, processed by the brain and a signal is sent to an effector organ to generate a response The effector can be either a muscle or a gland depending on the type of response required

Response flow chart Pain (stimulus) Sensory neuron (receptor) Inter Neuron Brain Inter Neuron Motor Neuron Muscle (effector) Contraction (response)

Positive vs. Negative feedback Positive feedback amplifies the stimulus (makes stimulus stronger) E.g. Contractions in birth, Nerve impulses Negative feedback counter acts the stimulus (reduces stimulus stopping it from alerting receptors) E.g. Temperature regulation, Blood sugar, pain

Major Homeostatic controls Internal Temperature - Vasodilation / constriction - Sweating - Shivering Blood sugar - Insulin / Glucagon pH levels - Breathing (CO2 vs O2)

The Nervous System

100% COVERAGE OF THE NERVOUS SYSTEM Each area of the body is serviced by its own network of nerves. Every muscle has an attached motor neuron, if there is no attachment, that muscle is unable to function

NERVE PATH WAYS Somatic nerves carry signals to and from skeletal muscles, tendons and skin They are nerves responsible for voluntary responses Autonomic nerves carry signals to and from internal organs, these actions are said to be involuntary (done without conscious thought)

THE NEURONS Motor neuronSensory neuron Inter-neuron

Neuron structure Neurons are the basic unit of the nervous system. They join up together to form what we know as ‘nerves’ Neurons contain Nerve body: containing nucleus Axon: thin wire like structure that carries signals Myelin sheath: Fatty covering over the axon increasing signal speed and reducing risk of signal loss Dendrites & Axon terminals: Points of connection to other neurons

Receptor types Chemoreceptor Detect chemical stimulus: taste, smell, co2 levels, blood glucose levels Mechanoreceptors Detect changes in pressure, touch, balance Photoreceptors Detect changes in light Thermoreceptors Detect changes in temperature Pain receptors Free nerve endings in the skin

Signal Transmission The nervous systems relies on the transmission of electrical signals along the axons of nerves They way these signals are sent is fairly complex This is known as an action potential

How a signal runs along a nerve

Action potential overview Outer membrane begins is positive Inner membrane begins negative Sodium pump beings to pump Na+ into the cell, causing a small section of the inner membrane to become (+) and the outer membrane to become (–)

Action potential overview cont.. There is now this situation this As electricity is the movement of electrons from (-) to (+) the signal moves down the membrane to the positive area This then activates the next sodium pump and the cycle repeats Whilst the signal passes the depolarized area, the potassium channel is pump out K+ ions, restoring the original membrane charge that is positive outside, negative inside.

This phenomenon continues to occur along the axon until the electric signal reaches the end of the axon *sodium and potassium stores are pumped back to their original locations, ready to be used again if needed Action potential overview cont..

The synaptic cleft Neurons are not hard wired to one another, between each neuron there is a small gap called a synapse. At this point, the electrical signals stimulate the release of a chemical substances known as a neurotransmitter, which crosses the cleft Once the neurotransmitter has crossed the synapse, it reaches a receptor which once stimulates the membrane of the new neuron, and begins the electrical impulses process once again