Nervous System

NERVOUS SYSTEM CNS PNS SNS ANS Parasympathetic Sympathetic Endocrine system releases chemical signals that are slow to react but the effects are long lasting. This does not involve the CNS. Messages are carried by the blood. www.SMARTutorials.com

CONTROL SYSTEMS There are two main control systems in your body. Nervous system – which has two main sections central or CNS that is made up of the spinal cord and brain and functions to coordinate all actions of the body peripheral or PNS that is made up of the bodies nerves and functions to connect the CNS to the rest of the body through neurones. PNS is further divided into somatic or SNS which is associated with the voluntary control of body movements and is made up of all neurones, sense organs, skin, skeletal muscles Autonomic or ANS which is associated with the involuntary control of body movements such as reflex and controls such things as heart rate, body temperature, digestion etc. The ANS is further divided into Parasympathetic nervous system works in actions that do not require a fast response (fight or fight response) Sympathetic nervous system works in actions that do require a fast response (rest and digest response) Endocrine system – which is a system of glands that release a number of signalling chemicals known as hormones. www.SMARTutorials.com

Parts of the nervous system The nervous system is made up of three main parts; The brain The spinal cord Nerve fibres It detects stimuli such as light, sounds, temperature, pressure, pain and co-ordinates the bodies response. www.SMARTutorials.com

Parts of the nervous system For example; If you smell something burning… Your nose (receptor) detects the stimulus (smell) Nerve fibres send the message to the brain Your brain then sends a message to move your body away or to put out the fire! www.SMARTutorials.com

EFFECTORS An effector is any part of the body that produces the response. Here are some examples of effectors: a muscle contracting to move the arm a muscle squeezing saliva from the salivary gland a gland releasing a hormone into the blood www.SMARTutorials.com

NERVE FIBRES Nerve fibres are bundles of nerve cells (neurons) that pass on electrical signals (impulses) to the brain. From the brain, nerve fibres send impulses to effectors (muscles). www.SMARTutorials.com

NEURONS There are three types of neurones Sensory neuron – carries impulses from the receptors to the spinal cord. Relay Neuron – carries impulses to and from the spinal cord and the brain Motor Neuron – carries impulses from the brain to the effector www.SMARTutorials.com

SYNAPSES Where two neurons meet, there is a tiny gap called a synapse. Signals cross this gap using chemicals. One neuron releases the chemical into the gap. The chemical diffuses across the gap and makes the next neuron transmit an electrical signal. www.SMARTutorials.com

What is a synapse? A synapse is a junction between two neurones across which electrical signals pass. The human body contains up to 500 trillion synapses. presynaptic cell postsynaptic cell www.SMARTutorials.com

The release of neurotransmitters When a nerve impulse arrives at the end of one neurone it triggers the release of neurotransmitter molecules from synaptic vesicles. synaptic vesicle neurotransmitter molecules www.SMARTutorials.com

Continuing the impulse The neurotransmitters diffuse across the synaptic cleft and bind with receptors on the next neurone, triggering another impulse. synaptic cleft nerve impulse receptor www.SMARTutorials.com

REFLEX ACTION In bright light In dim light Radial muscles of the iris relax. Circular muscles of the iris contract. Less light enters the eye through the contracted pupil. Radial muscles of the iris contract. Circular muscles of the iris relax. More light enters the eye through the dilated pupil. The way the iris in our eye adjusts the size of the pupil in response to bright or dim light is also a reflex action. www.SMARTutorials.com

Inside the eye cornea protects eye surface and focuses light rays hold lens in place suspensory ligaments retina senses light lens focuses light on retina iris regulates amount of light entering eye ciliary muscles change shape of the lens optic nerve transmits impulses to the brain www.SMARTutorials.com

Reacting to Changes To keep the conditions inside body constant is called homeostasis. Small changes inside your body can cause its cells to be damaged or destroyed. Yet, there are big changes going on outside your body. To detect a change in the environment (a stimulus) and to react to the change (a response) in a way that maintains homeostasis. Doing this without thinking, it is called a reflex. www.SMARTutorials.com

Reacting to Changes It can get very hot or very cold outside, but the temperature inside your body stays the same. How? When it gets cold outside (stimulus) you shiver (response) and keep the temperature inside your body from dropping. When it gets hot outside (stimulus) you perspire (response) and keep the temperature inside your body from rising. www.SMARTutorials.com

Other Reflexes Stimulus Response The aroma of your favorite food Salivation A nasty odor Nausea A bright light shining in your eye Pupils get smaller An insect flying towards your eye Blinking www.SMARTutorials.com

A Conscious Stimulus-Response Reaction to all stimuli in basically the same way as a reflex. The integration just gets more complex. Complex behavior involves complex integration in the brain. www.SMARTutorials.com

Thyroid gland – Thyroxine (regulates the rate of metabolism) Pituitary gland – FSH, LH (stimulates the release and maturity of follicles during menstruation) Thyroid gland – Thyroxine (regulates the rate of metabolism) Adrenal gland - corticosteroids and catecholamines including cortisol and adrenaline (regulates stress levels) Pancreas – peptides (regulates the production of shorter active digestive enzymes) Ovary – oestrogen, progesterone (regulates the growth of eggs and stabilises the growing foetus during pregnancy) Testis – testosterone (plays a key role in the health and well-being of the man) www.SMARTutorials.com