What is the function of the Nervous System?

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

The PNS Connects the CNS to Muscles and Organs

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)

The Brain

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)

The Spinal Cord

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

How Do Signals Move Through the Nervous System?

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

Neurons

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

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

What Are the Main Senses?

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

What Are the Main Senses?

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

What Are the Main Senses?

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

What Are the Main Senses?

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

What Are the Main Senses?

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