what is the function of the nervous system?. the nervous system is made of structures that control...
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What is the function of the Nervous System?
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• The nervous system is made of structures that control the actions and reactions of the body in response to stimuli from the environment
• There are two parts: the central nervous system (CNS) and the peripheral nervous system (PNS)
• The brain and the spinal cord make up the CNS• The brain is the body’s central command organ and
is constantly receiving impulses from all over your body
• The spinal cord allows your brain to communicate with the rest of your body
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The PNS Connects the CNS to Muscles and Organs
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• The PNS has two main parts – the sensory part and the motor part• Sensory gathers information and motor
responds to information• Many brain processes happen
automatically – involuntary (ex. heart beat)• Some actions of your brain you can
control – voluntary (ex. moving your arm)
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The Brain
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• There are three main areas of the brain – the cerebrum, the cerebellum and the brain stem
• Cerebrum – largest part - where you think and problem – solve and where most of your memories are stored
• It controls voluntary movements and allows you to sense touch, light, sounds, odors, pain, heat and cold
• Cerebellum – 2nd largest part – processes information from your body – allows brain to keep track of body position and coordinate movements
• Brain stem – connects brain to spinal cord – medulla is part of the brain stem – controls involuntary processes (blood pressure, body temp)
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The Spinal Cord
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• The spinal cord is made of a bundle of nerves• A nerve is a collection of nerve cell extensions
bundled together with blood vessels and connective tissue
• The spinal cord is surrounded by protective bones called vertebrae
• Special cells in your skin and muscles carry sensory information to the spinal cord
• The spinal cord carries the information to the brain • The brain interprets the impulses as pain or warmth
and sends information back to the spinal cord • Different cells in the spinal cord send impulses to
the rest of the body as a response
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How Do Signals Move Through the Nervous System?
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• The nervous system works by taking information from the environment and translating that information into an electrical signal
• Electrical signals are sent by the brain to the rest of the body by special cells called neurons
• Neurons move messages in the form of fast moving electrical energy called impulses
• Signals move through the CNS and PNS with the help of glial cells
• Glial cells don’t transmit nerve impulses but protect and support neurons
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Neurons
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• Two groups of neurons – sensory neurons and motor neurons
• Sensory neurons – gather information from in and around the body – they move this information to the brain
• Motor neurons – move impulses from the brain and spinal cord to other parts of the body
• The four main parts of the neuron are the cell body, the axon, the dendrites and the axon terminal
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• Cell body – large region that contains the nucleus and organelles
• Dendrite – a usually short, branched extension of the cell body – neuron may have one or several – cell body gathers information from the dendrites and creates an impulse
• Axon – extension of the neuron that carries the impulse away from the cell body – neuron has only one axon – can be short or long – impulses move in one direction along the axon
• Axon terminal – located at the end of the axon – where signal is changed from an electrical signal to a chemical signal called a neurotransmitter
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What Are the Main Senses?
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• Sight – your eye allows you to see the size, shape, motion and color of objects around you
• The front of the eye is covered by a clear membrane called the cornea
• Light passes through an opening called the pupil • Light hits the eyes lens – an oval-shaped piece of
clear curved material – eye muscles change the shape of the lens to focus light onto the retina
• The retina is a layer of photoreceptor cells that change light into electrical impulses
• These cells called rods and cones generate nerve impulses that are sent to the brain
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What Are the Main Senses?
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• Sensory cells in your ear turn sound waves into electrical impulses – these impulses travel to your brain
• Sound waves are funneled by the outer ear toward the middle ear – the waves make the eardrum vibrate - eardrum is a thin membrane separating the outer and middle ear
• The vibrating eardrum makes three tiny bones vibrate• The last bone vibrates against the cochlea – a fluid filled
organ in the inner ear• Inside the cochlea, the vibrations make waves in the fluid• Sensory receptors called hair cells move – their
movement causes neurons in the cochlea to send electrical impulses
• Impulses travel to the brain via the auditory nerve
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What Are the Main Senses?
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• You feel a tap on your shoulder – the tap produces impulses in sensory receptors in your shoulder that travel to the brain• Once the impulses reach your brain,
they create an awareness called a sensation• Skin has different receptors that
detect temperature, pressure, pain and vibration
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What Are the Main Senses?
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• Your tongue is covered with taste buds • Taste buds have clusters of cells
called taste cells that respond to signals in dissolved molecules of food• Taste cells react to five basic tastes:
sweet, sour, salty, bitter and savory
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What Are the Main Senses?
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• The nose is the sense organ for smell – receptors for smell are located in the nasal cavity
• Sensory receptors called olfactory cells react to chemicals in the air
• These molecules dissolve in the lining of the nasal cavity and trigger an impulse in the receptors
• The nerve impulses are sent to the brain where they are interpreted as an odor
• Your sense of taste and smell work together to allow you to taste a variety of food flavors
• Both senses detect chemical cues in the environment