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

 The nervous system relies on electrical signals, carried by specialised cells [neurons], and is involved in fast responses.  The brain keeps a check on internal organs and activities, such as the level of carbon dioxide or water in the blood.  The central nervous system (CNS) is your brain and spinal cord.  The peripheral nervous system (PNS) is the nerves branching from the CNS to all parts of the body.

Comparison of the endocrine and nervous systems - 1 Target organReceived by BloodCarried by GlandCells involved Cells throughout the body Message sent to Chemical (Hormone) Message Endocrine

Comparison of the endocrine and nervous systems - 1 EndocrineNervous Cells involvedGlandSense receptor MessageChemical (Hormone) Electrical(Impulse) Carried byBloodNerve cell Message sent toCells throughout the body A specific cell or tissue Received byTarget organEffector (muscle or gland)

long-lasting (hours) Duration Can be widespreadEffects Usually slowSpeed of transmission Endocrine Comparison of the endocrine and nervous systems -- 2

EndocrineNervous Speed of transmission Usually slowRapid EffectsCan be widespreadLocalised usually Durationlong-lasting (hours) Usually brief (seconds) Comparison of the endocrine and nervous systems -- 2

LEARNING CHECK Co-ordination of an organism’s activities is carried out by what 2 body systems? Distinguish between the CNS and PNS. What is a neuron? What is an impulse? List the main differences between the endocrine and nervous systems.

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

 The cell body contains the nucleus and other organelles and produces neurotransmitter chemicals.  The axon is a very long fibre that conducts impulses away from the cell body. Neuron structure  A dendron is a short fibre that receives information and carries it towards the cell body.

 Dendrites are small branches of a dendron.  A dendron is a short fibre that receives information and carry it towards the cell body.  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.

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

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

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?

 The brain is composed of over 100 billion neurons, each receiving messages simultaneously from thousands of other neurons.  The brain is protected by the skull bones, meninges (three membranes) and cerebrospinal fluid. The Brain

Conscious actions A conscious action is one where the brain makes a considered response. Here’s what happens: Stimulus Receptor Sensory Neuron Coordinator Motor Neuron Effector Response 1) Receptors in your skin detect a stimulus 3) Here another sensory neuron carries the signal to the brain 4) The brain decides to move away the hand 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 6) Which then moves the hand away

 The cerebellum co-ordinates processes that we have learned to do automatically, such as speaking.  The medulla oblongata co-ordinates involuntary, automatic processes — such as breathing, heartbeat. cerebellum Medulla oblongata

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.

 The spinal cord is well protected by the vertebrae, meninges (three membranes) and cerebrospinal fluid.  It transmits impulses to and from the brain and controls many reflex actions.

 A cross-section through the spinal cord shows a small central canal, filled with cerebrospinal fluid, surrounded by an area of grey matter, shaped somewhat like the letter H.

 Outside the grey matter, the spinal cord consists of white matter (containing axons only).  Grey matter contains cell bodies and dendrites (regions of a neuron that have no white myelin covering).

 In humans, 31 pairs of spinal nerves branch off from the spinal cord.  The dorsal root ganglion is a swelling that consists of the cell bodies of the sensory neurons.  Each spinal nerve has a dorsal root and a ventral root.  The dorsal root consists of nerve fibres carrying information into the spinal cord from the senses.

 The ventral root consists of nerve fibres carrying information out from the spinal cord, to the muscles and glands.  The cell bodies of the motor neurons are positioned within the grey matter of the cord.  The spinal cord transmits impulses to and from the brain and controls many reflex actions.

 A reflex action is a quick, automatic response to a particular stimulus. Interneuron REFLEX ACTION --- The Reflex Arc

Suppose you touch a hot flame.  In this brief instant, a message has been carried by a sensory neuron from pain receptors in the skin to the spinal cord.  Almost instantly you pull your hand away. Interneuron REFLEX ACTION --- The Reflex Arc

 In the spinal cord, the message is passed on to an interneuron and then to a motor neuron, and so into muscles that respond by contracting and pulling your hand from the flame. Interneuron

 The response is called a reflex action, as it does not involve conscious control, and is predictable and automatic.  Many of the activities of the body, such as breathing and keeping our balance, are regulated by reflex actions.  This response saves the body from injury. Interneuron