CHAPTER 21 THE NERVOUS SYSTEM and SENSES

Homeostasis-maintaining a constant internal balance; responding to stimuli Stimuli- an external or internal change that brings about a stimuli

NERVE CELLS- Neurons- nerve cells that are made up of axons, dendrites and cell body. Axons- carry impulses away from the cell body Dendrites- carry impulses to the cell body

Sensory neurons- send impulses (information) to the brain and spinal cord interneurons-found in brain and spinal cord and send impulses from sensory neurons to motor neurons. Motor neurons- relay information to muscles or glands in the body.

IMPULSE TRANSFER Impulse moves from axon of one neuron to dendrites of another; moves across synapse

Synapse- space between axon and dendrites neurotransmitters-chemicals that are released that carry impulse across synapse 7Yk&feature=related 7Yk&feature=related

Central Nervous System (CNS) -made up of brain and spinal cord Peripheral Nervous System (PNS) -made up of all nerves outside of CNS; all nerves in your head and coming off of spinal cord

BRAIN Three parts 1) Cerebrum- largest part; where thinking occurs; memory is stored; movements are controlled Cortex- outer portion; have ridges and grooves that increase surface area so more complex thoughts can occur

2) Cerebellum-under cerebrum; coordinates voluntary muscle movements, maintain balance and muscle tone. i.e.) helps ride a bike

3) Brain Stem- base of brain; connects to brain to spinal cord a) Contains medulla-controls involuntary actions like heartbeat, breathing, blood pressure, coughing, sneezing, swallowing and vomiting.

SPINAL CORD -in adult is as wide as adult thumb -carries impulses from the body to the brain and from the brain to the body 7Yk&feature=related 7Yk&feature=related

Reflexes -involuntary automatic response to a stimulus -controlled in your spinal cord -brain acts after reflex to help you figure out what to do to make pain stop

Drugs -directly affect the nervous system -destroy brain and liver cells -can be a depressant and slow down responses of CNS as well as thinking processes -can be stimulant that speeds up heart rate, cause sleeplessness and can cause kidney to make more urine

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of-Liver.htm of-Liver.htm SENSES-taste, touch, smell, sight, hearing ses.htm ses.htm

anatomyvideos/ htm anatomyvideos/ htm SIGHT Nearsighted-focus in front of retina Farsighted-focus behind retina

Parts of Eye: Cornea-transparent membrane that protects the eye-allows light to enter Pupil-opening the front of the eye that allows light to enter

Retina-light sensitive area in the back of the eye -rods-detect dim light; used in night vision -cones-detect colors *impulses from these photoreceptors travel to brain along the optic nerve Iris-the part of the eye gives it its color

Lens-piece of curved material behind the pupil that allows the light to pass through but changes its direction. -focuses entering light on the retina -looking at objects close to the eye-lens is more curved -looking at objects far away- lens is flatter

Hearing -sound begins when object starts to vibrate b/c air particles push on each other and transfer energy. -waves move from outer ear to middle ear (causes tiny bones in eardrum to vibrate) to cochlea of the inner ear fluid

-neurons in cochlea convert waves to electrical impulses and sends them to the part of the brain that interprets sound. ultimedia/Videos.asp?reportid= ultimedia/Videos.asp?reportid=34284

TASTE Taste buds - contain receptors for taste; located in the papillae Four types- sweet, sour, salty, bitter

SMELL Olfactory cells- receptors for smell that are located in the upper part of your nasal cavity. -brain combines information from your taste buds and nose to give a sense of smell.

understanding-the-smell-center-video.htm understanding-the-smell-center-video.htm rks/461-how-smell-works-video.htm rks/461-how-smell-works-video.htm

Touch Touch receptors are the nerve cells that tell your brain about tactile sensations. There are several types of touch receptors, but they can be divided into two groups. (1) mechanoreceptors that tell you about sensations of pushing, pulling or movement, – The mechanoreceptors contain the most types of touch receptors.

(2) thermoreceptors that tell you about sensations of temperature.

Types of Mechanoreceptors Free nerve endings informs the brain about pain, and they are located over the entire body.

Pacinian corpuscles detects pressure, telling the brain when a limb has moved. After the brain has told a limb, such as an arm, to move, the pacinian corpuscles tells the brain that that limb has actually moved into the correct position.

The Tactile Corpuscles of Meissner are grouped on the skin of the fingertips, lips, and orifices of the body and the nipples. Only stimulated when touched, meissner corpuscles tells the brain the shape and feel of an object in the hand. They adjust constantly to the environment, which is why the brain eventually ignores clothing that you are wearing.

Thermoreceptors are the other major group of touch receptors. There are two types of thermoreceptors: A) end-bulb of Krause, which detects cold B) Ruffini's end organ, which detects heat.

The end-bulb of Krause can be found in the skin, conjunctiva, lips, and tougue

Ruffini's end organs are found over the entire body in the skin.