The Internal Environment Week 9

External and Internal Environments The internal environment is the interstitial fluid through which cells exchange substances

External and Internal Environments Organisms are able to regulate their internal conditions despite the changing conditions of the external environment by constant movement of material across membranes.

Different environments Type of organism External environme nt ToleranceInternal environment Control UnicellularGeneral environment Relatively high, little mobility Contents of the cell. Closely related to external environment. Tolerate, or move away Multicellula r General environment Variable, but high ability to maintain constant internal environme nt Extracellular fluid. Often very different from external environment. High regulatio n

Homeostasi s: keeping within limits

Structure of the nervous system

The Brain

Having a brain wave A living brain shows continuous electrical activity which can be measured. A range of different ‘brain wave’ patterns is shown. A person is declared ‘brain dead’ when no electrical activity can be measured.

Stimulus-Response Model Stimulus Receptor Transmission Control Centre Effector Response Transmission

Stimulus-response model Set points and optimum conditions are maintained through negative feedback

Negative Feedback

Positive feedback mechanisms Positive feedback system in which oxytocin produced by the posterior pituitary gland stimulates contraction of the uterus and also stimulates the pituitary gland to produce even more of the hormone. Note the positive feedback nature of the inputs.

Homeostasi s: hormones in action Detecting and counteracting change. The two interrelated stages of homeostasis. Relies on negative feedback systems. If a variable slightly overshoots the optimal as a result of effector action, the counter negative feedback system will respond to correct the overshoot. Occurs continuously in the body so that optimal levels of variables are maintained

Temperature Regulation

Stimulus High CO 2 levels in blood Receptor Medulla and aortic and carotid bodies Control Centre Brain Effectors Diaphragm and intercostal muscles Response Faster, deeper breathing Transmission

Examples of factors that animals detect EnvironmentPhysical factorsChemical factors InternalTemperature, blood pressure, stress on bones and muscles Concentrations of O 2, CO 2, water, ions, wastes ExternalLight, temperature, gravity, sound Food, O 2, CO 2, water, other organisms, other chemicals

Types of sensory receptors and their stimuli Type of receptorTypes of stimuli detected Example ChemoreceptorO 2, CO 2, pH, ions, signalling molecules Receptors on dendrites of nerve cells PhotoreceptorLight and infrared radiation Rods and cones in the eye MechanoreceptorSound, touch, pressure and gravity Geotropism receptors that direct roots to grow down ThermoreceptorHeat and coldReceptors in skin sensing changes in temperature

Neurons

A typical motor neuron. Note the cell body containing the nucleus, with many branching projections, called dendrites, and the single axon that ends with many synaptic terminals that allow it to communicate with other neurons.

3 types of neuron

Neurons (a) affector (or sensory) neuron (b) effector (or motor) neuron (c) connecting neuron (or interneuron) Different kinds of neurons: Neurone animation – reference to drug use

Neurons Which type of neuron is located completely within the CNS? Relationship between different kinds of neurons.

Transmission of an impulse along and between nerve cells

Synapse

Communication by neurotransmitters Notice the gap between the axon of one neuron and the one to which it joins. Transmitter substances are produced in vesicles near the end of the axon. Synapses

Signal transduction across a synapse

Reflex Arc

Communication by neurohormones (a) Electrical impulses transmit signals along a neuron. Neurotransmitters are secreted at the axon and diffuse across a small gap to deliver a signal to the target cell, another neuron. (b) Similar to part (a), except the target is striated muscle tissue. (c) Some neurons release chemicals called neurohormones into the blood. The blood carries the appropriate signal to the target organs that then respond.

Communication by neurohormones Neurons in the hypothalamus in the brain secrete neurohormones into blood capillaries that become associated with the pituitary. Signals received by cells of the pituitary are transduced and the pituitary responds by producing a hormone as instructed. This hormone enters the bloodstream and is transported to its target cells.

Network of nerve cells

Neuron function impeded Thyrotoxic goitre A goitre is caused by the enlargement of the thyroid gland and may vary in size from a small lump to an enormous swelling.

Toxins can overwhelm neuron transmission Many animal toxins act on the nervous system, particularly at neuro- muscular synapses. Some prevent the passage of nerve impulses along a nerve. Others act on one or both sides of the neuro- muscular synapse.

Additional animations Cocaine effect

Chapter 5 and 6 Reviews Chapter 5 –Biochallenge (p.162), all questions –Chapter Review (p.163), Q. 2-6, 8-9 Chapter 6 –Biochallenge (p.196), all questions –Chapter Review (p.197), Q. 2-3, 6-8 You can start this work as we have covered some of the content, but you will not be able to do all questions. You will be submitting this work once we have finished Week 10.