Objectives – What you will need to know from this section

1. Responses in the Human Nervous System 1 Objectives – What you will need to know from this section • Outline the nervous system components: central nervous system (CNS) and the peripheral nervous system (PNS) • Receptor messages are carried through these systems by nerve cells or neurons. • Outline the structure & function of the neuron including:cell body, dendrites, axon, myelin sheath, schwann cell, and neurotransmitter vesicles& synaptic cleft • Outline impulse movement & synapse. • Explain activation & inactivation of neurotransmitter.

2. 2 • The structure and function of a neuron: variation in size and shape. • Neuron -- Three part structure:> dendrite(s) receive information and carry it towards thecellbody,> the axon conducts nerve impulses away from the cell body,> the cell body contains the nucleus and other organelles andproduces neurotransmitter chemicals. • Explain the role & position of 3 types of neuron -- sensory/motor/inter

3. The Nervous System • Organisms must be aware of what is happening around them,as this affects their survival chances. • Co-ordination of an organism’s activities is carried out by thenervoussystem • A nervous system allows an organism to detect and respond to stimuli in its internal or external environment. • A stimulus is any change in your environment e.g. a flash of light, a noise, a fly landing on your nose.

4. The nervous system relies on electrical signals, carried byspecialised cells [neurons], and is involved in fastresponses. • The central nervous system(CNS) is your brain and spinalcord. • The brain keeps a check on internal organs and activities, such as the level of carbon dioxide orwater in theblood. • The peripheral nervous system (PNS) is the nerves branchingfrom the CNS to all parts of the body.

5. LEARNING CHECK • Co-ordination of an organism’s activities is carried out by what body system? • Distinguish between the CNS and PNS. • What is a neuron? • What is an impulse?

6. NS ----- Co-ordination & Response • A stimulus is any change in your environment • A receptor is a nerve cell that detects the stimulus • A neuron is a specialised cell that carries electrical messages(impulses) around the body. • An impulse is an electrical message that is carried along aneuron.

7. Neuron structure • The cell body contains the nucleus and other organelles andproduces neurotransmitter chemicals. • A dendron is a short fibre that receives information and carries ittowards the cell body. • The axon is a very long fibre that conducts impulses away from the cell body.

8. A dendron is a short fibre that receives information and carry ittowards the cell body. • Dendrites are small branches of a dendron. • Many Schwann cells wrap their fatty cell membranes around an axon, forming a myelin sheath. • The myelin sheath insulates the neuron from electrical impulses flowing in other neurons.

9. There are three types of Neuron : • Sensory neuron –carries messages from the sense organ tothe central nervous system (CNS). • Interneuron –connects sensory and motor neurons and socarries messages within the CNS. • Motor neuron –carries impulses from the CNS to muscles andglands.

11. SYNAPSE • Synapse—region where two neurons come into close contact. • Synaptic cleft—the gap between two neurons, bridged bychemicals (neurotransmitters). • Neurotransmitter—chemical released across a synaptic cleft tocarry a signal from one neuron to another. • The chemical is then destroyed or removed

12. LEARNING CHECK • What is a stimulus? • What is a receptor? • Name the main parts of a neuron and give one function of each. • Distinguish between a sensory and motor neuron. • Distinguish between synapse and synaptic cleft. • What are neurotransmitters?

13. The Brain • The brain is composed of over 100 billion neurons, eachreceiving messages simultaneously from thousands of otherneurons. • The brain is protected by the skull bones, meninges (threemembranes) and cerebrospinal fluid.

14. The cerebrum is our conscious brain, with different parts havingdifferent jobs to do. cerebrum hypothalamus pituitary • The hypothalmus is the centre for the regulation of the internalorgans. • The pituitary ‘[master] gland secretes hormones that stimulateother glands to release their hormones.

16. 4) The brain decides to move away the hand 3) Here another sensory neuron carries the signal to the brain 5) This impulse is sent by MOTOR NEURONS to the hand muscles (the effectors) via the spinal chord… 2) The impulse is carried by SENSORY NEURONS to the spinal chord 1) Receptors in your skin detect a stimulus 6) Which then moves the hand away Stimulus Receptor Sensory NeuronCoordinator Motor NeuronEffector Response Conscious actions A conscious action is one where the brain makes a considered response. Here’s what happens:

17. Medulla oblongata • The cerebellum co-ordinates processes that we have learnedto do automatically, such as speaking. cerebellum • The medulla oblongata co-ordinates involuntary, automaticprocesses—such as breathing, heartbeat.

18. LEARNING CHECK • Name the 3 main parts of the brain and one function of each. • How is the brain protected? • What is meant by “conscious action”? • What does the term “involuntary” mean? • Distinguish between the cerebrum and the cerebellum.

19. SENSE ORGANS • Animals have specialised senses to provide them with information about their environment. • The five senses are sight, hearing, touch, taste and smell. • A receptor is a cell that can detect a stimulus • A stimulus is any change in your environment, e.g. light, sound.

20. Sense Sense Sense Organ Organ Stimulus detected Sight Sight Sight Eye Eye light [by rods and cones in the retina] Hearing Hearing Hearing Ear Ear sound [receptors in cochlea] Touch Touch Touch Skin Skin touch, pressure, temperature and pain [receptors spread throughout body] Taste Taste Taste Tongue Tongue chemicals [taste buds detect sweet, sour, salt and bitter]. Smell Smell Smell Nose Nose chemicals [receptors in the nasal cavity detect vapours]