THE NERVOUS SYSTEM (CHAPTER 36) I) The Central Nervous System (DIVISION 1) A) A nerve impulse traveling in your body must first go to the brain (Control Center) for processing 1) Brain and spinal cord make up the CNS (a) Coordinate body s activities and respond to external stimuli II) Peripheral Nervous System (DIVISION 2) A) Consists of all the nerves that carry messages to and from the body & CNS 1) Similar to telephone wires that go to people s homes (No Start-No End) 2) Respond to External Stimuli (a) Impulses travel between the body and the CNS. A stimulus is picked up by receptors in your skin (i) The impulse is carried to the CNS (ii) The impulse is processed and another impulse is sent to a muscle B) Can be divided into two subcategories 1) Somatic nervous system 12 pairs of cranial nerves (brain), 31 pairs of spinal nerves (spinal cord) and all of their branches (like wiring harness) (a) Connected by connective tissue and contain sensory & motor neurons (b) Responsible for reflexes (message goes to spinal cord and then directly to the muscle and then after it is over, the brain is aware) (c) nerves of the SNS involve Skin, CNS, and skeletal muscles VOLUNTARY (i) pressure receptors are found in joints, muscle tissue, organs, palms, fingers, and soles of feet (ii) nerve endings act as pain receptors extend into the epidermis (a) heat receptors are deep in the dermis (b) cold receptors are closer to skin surface 2) autonomic nervous system (Two more sub-categories) (INVOLUNTARY!!!!!!!) (a) Sympathetic Operates when there is stress (i) Releases epinephrine/adrenaline (FIGHT OR FLIGHT) (b) Parasympatheic controls body functions when at rest (c) Secretes hormone noradrenaline (norepinephrine) chillin (d) Both systems affect the same organs but in opposite ways resulting organ activity depends on which system is stronger at the time
The Basic Units of the Nervous System III) Nerve Cells or Neurons A) 3 types 1) Sensory Neurons carries impulses from the body to the spinal cord & brain 2) Interneuron found within the brain and spinal cord. They process incoming impulses and pass the message to motor neurons 3) Motor Neurons carry messages away from the brain to the muscle or gland B) Three Parts = Cell Body, Dendrites, and Axon + the Synapse 1) Cell Body = very enlongated with nucleus and gated ion channels (a) Gated ion channels open or close and regulate Sodium (Na) and Potassium (K) (i) There is a charge difference between Sodium and Potassium and this is the case when there is no nerve signal = RESTING POTENTIAL (ii) A stimulus (touch, etc.) will cause Sodium to fill the neuron and reverse the charge in the cell = ACTION POTENTIAL 2) Dendrites- branchlike extensions of the neuron that receive impulses and carries them toward the cell body 3) Axon- single extension of the neuron that carries impulses AWAY from the cell body towards other muscles, glands, or neurons (a) Myelin sheath the wrapping membrane of the axon that speeds the signal so the signal can HOP through sections called NODES instead of traveling the whole length = INSULATION (i) Myelin gives nerves a white appearance referred to as white matter (ii) a blockage of the this hopping process is characteristic of the disease Multiple Sclerosis. Plaque builds up in the relay areas 4) Synapse not part of cell. It is the gap where a neuron meets with another cell. The message must get from one side to the other (a) It doesn t jump or Hop across. It is carried across by chemicals called neurotransmitters.
(i) Slowest part of nervous system. - Electricity moves faster than chemicals (ii) Neurotransmitter = acetylcholine (a) After chemical is done, enzymes break them down (b) name of enzyme = acetylcholine esterase (iii) if nerve continues to fire = muscle fatigue results (a) after a while the impulse stops receiving a response because the brain is aware of the problem (b) Transmission of Signals Process Stimulus and Response 5) Realization through receptor neurons (tap on shoulder/ stimulus) 6) The impulse is carried to the spinal cord and then to your brain 7) Brain sends impulse to motor neurons which bring the impulse to your neck and you turn around (response) using your neck muscles ANATOMY OF THE BRAIN I) Cerebrum (Front and Top) 85% of Brain A) 2 Halves or Hemispheres Left and Right Hemispheres regulates lanuage, conscious thought, intelligence, memory, language, movement, personality, vision and senses 1) Has 2 Layers (a) Outer surface or Cerebral Cortex contains grey matter (unmyelinated axons) (i) Many folds and convolutions to increase surface area and store info (ii) Increases the capacity for the thought process (b) Also has White Matter Myelinated Axons (c) 2 Hemispheres linked by a tract of neurons that let one side know what the other is doing (Can function separately if cut) II) Cerebellum (Back of Brain) A) Controls balance, posture, coordination, (movements jerky if injured) 1) Affected by Alcohol B) Rear Cauliflower shaped part of brain
III) Brain Stem A) Connects cerebrum to spinal cord B) Medulla oblongata (part of brain stem area)controls involuntary activities (breathing,, swallowing, heart & blood vessels, and digestive processes) 1) Also contains the Hypothalamus (primitive brain) (a) Regulates blood pressure, heart rate, body temp, hunger, thirst, urination, sex drive, emotions C) Pons and Midbrain connect various brain parts together by acting as pathways 1) Sensory and motor pathways cross over here causing the right side of the brain to control the left side of the body and vice versa D) Contains reticular formation network of nerves that connect the brain stem to the whole brain 1) Brain stem is important for consiousness, awareness and sleep. Allows some messages through but not others E) Spinal Cord 1) Bundles of neurons that contains gray and white matter 2) Protected by vertebral column 3) Transmits messages to and from the brain F) Protection and Brain Size 1) Skull is main protection but also has an outer layer = meninges (a) Swelling of this protective lining = meningitis 2) Bigger brain DOES NOT mean more Intelligence
I) How Scientists Study The Brain A) Stimulating the brain with electricity allows the brain s activities to be mapped by computer B) New Method Identifies which part of the brain uses the most ATP during an activity to trace the origin of the action II) Learning Vs Memory A) Both Poorly Understood by scientists B) Most Learning Occurs as a young child but we don t remember learning it (talking) C) Memory Lasts for different lengths of time 1) Short Term few seconds to a few hours (cramming, errands) 2) Long Term stores info for longer periods of time- possibly for entire life (a) Use tricks to transfer info from Short term to LONG term (mnemonic devices) (b) Most Long Term memory is stored subconsciously (You don t know you know it!)
III) Scientists and Sleep A) Mysterious process to scientists B) They Don t understand why you must sleep each night and why it affects your temper, alertness, and emotions C) They also don t understand why some need more sleep than others D) Brain is VERY active during sleep periods E) They think that sleep allows the body to restore equilibrium after a day s activities and organize information taken in during the day The Sense Organs I) Receptors A) Respond to stimuli by producing impulses in a sensory neuron (Light, Heat, Pressure) B) Receptor converts stimulus into electrical energy that travels in your system II) The Ear A) 2 Sense organs in one = 1) Sound Waves & 2) Movement of Head B) Inner Ear Canals & Chambers contain receptor cells for sense of position C) Each Receptor Cell has hairs coming from it and are stimulated by moving fluid in inner ear D) Inner Ear has 3 fluid filled canals in each plane (X, Y, Z) called semicircular canals E) Fluid moves in ONE direction and touches hairs you now know that position of your head F) Semicircular Canals detect Head Changes in Speed AND Direction G) Sensing Sound Involves sound waves entering the ear canal and striking the ear drum H) 3 Bones in ear move when eardrum moves. Bones press against Cochlea (Inner Ear) that contains hearing receptors I) Hearing Receptors have hairs that detect fluid movement in cochlea J) Hair Cells stimulate the sensory nerve that carries info to the brain K) Hairs are easily destroyed by LOUD NOISE and old age
III) Sensing Light A) Receptors in the eyes use pigments to absorb light energy B) Changes in pigment trigger nerve impulses to sensory neurons C)Path or Light: 1) Enters EYE 2) Pass through Cornea (protective covering) 3) Lens focuses light (muscles help) 4)Pupil opening in middle of iris 5) Iris controls amount of light entering eye (pupil size) 6)Retina in back of eye has light receptors and neurons (image is upside down) 7)Receptor Cells in retina called RODS sensitive to light, blurry gray shades, no color 8)Cones color, sharp images, bright light a)generates impulses to cerebrum where images are inverted again b)cones do not work correctly in color blind individuals c)blind Spot where optic nerve enters retina - no rods or cones there d)rods and cones have pigments made from carotenoids e)found in carrots helps make them when eaten f)animals can t make these and get them from eating plants IV) Touch A) receptors on tongue, lips, fingertips, face, joints, muscles, and arteries B) attached to sensory neurons V) Taste and Smell A) chemical receptors used B) taste = sour, sweet, bitter, salty C) Smell = tells us about food flavor comes from smell (NO SMELL = NO TASTE) D) Spicey foods picked up by PAIN receptors instead of chemical