Coordination

• Changes in an organisms environment is called stimuli
• Stimuli are sensed by receptors and organisms respond using effectors
• Muscles are effectors and may react by contracting. Glands are also effectors (Salivary glands respond to good smelling food by secreting saliva)
• Animals need fast and efficient communication systems between their receptors and effectors.
• Most animals move in search of food
• Many animals needs to be able to respond very quickly yo catch their food or to avoid predators
• The way in which receptors pick up stimuli and then pass information on to effectors, is called coordination.
• There are 2 methods of sending information from the receptors to the effectors. The fast way is through nerves, the slow way is through chemicals called hormones.
• The human nervous system is made up of specialized cells called neurones.
• Each neuron contains a nucleus, cytoplasm, and call membrane. However, their structure is adapted to be able to carry signals very quickly.
• Neurons have thin fibers of cytoplasm stretching out from the cell body. The longest fiber is called the axon.
• Short fibers in neurons are called dendrons or dendrites.
• Dendrites pick up electrical signals from other neurons lying nearby. These electrical signals are called nerve impulses. The signal passes through the cell body, then along the axon, which might pass it to another neuron.
• All mammals have a central nervous system (CNS) and a peripheral nervous system.
• The CNS is made up of the brain and spinal cord. The peripheral nervous system is made up of nerves and receptors.
• The CNS is made up of neurons and its role is to coordinate the information traveling through the nervous system.
• When a receptor detects a stimulus, it sends an electrical impulse to the brain or spinal cord, which receives the impulse and sends it along the specific nerve fibers to the specific effector.
• The receptor generates a nerve impulse, which travels to the spinal cord along the axon of a sensory neuron.
• In the spinal cord, the neuron passes an impulse onto several other neurons. These are called relay neurons because they relay the impulse onto other neurons.
• Relay neurons pass impulses to other neurons, the brain, the spinal cord, or an effector.
• Effectors could be muscles in your arm. The impulse travels to the muscle along the axon of a motor neuron. The muscle then contracts and pulls away.
• The reaction where your hand pulls away from something is an example of a reflex action. Your brain is made aware of something, but you only consciously realize it, after the message has been sent to your muscles.
• Reflex actions are very useful because information gets from the receptor to the effector as quickly as possible.
• The pathway along which the nerve impulse passes - the sensory, relay, and motor neuron - is called the reflex arc.
• Reflex action: a means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors
• Reflex arc order: Stimulus, Receptor, Sensory Neuron, Relay Neuron, Motor Neuron, Effector
• Reflex actions are examples of involuntary actions as they are not under conscious mind.
• The eye is a receptor organ. Its function is to detect light and transfer the energy in the light to electrical energy in a nerve impulse.
• The part of the eye that contains the receptor cells is the retina.
• The rest of the eye simply helps to protect the retina or to focus light onto it.
• Each eye is set in a boney socket in the skull, called the orbit.
• The front of the eye is covered by a thin, transparent membrane called the conjunctiva, which helps to protect the parts behind it.
• The conjunctiva is always kept moist by the fluid made in tear glands. This fluid contains lysozyme, which can kill bacteria.
• The fluid in the tear duct is washed over your eyes every time you blink.
• Eyelids, eyebrows, and eyelashes also help to stop dirt from landing on the surface of your eyes.
• The retina is at the back of the eye . When light falls on a receptor cell in the retina, the cell sends an electrical impulse along the optic nerve to the brain.
• The brain sorts out all the impulse from each receptor cells and builds up an image.
• Some receptor cells are sensitive to light of different colors, enabling us to see colored images.
• The closer together the receptor cells are, the clearer the image the brain will get.
• The optic nerve carries impulses to the brain.