NERVOUS SYSTEM, THE BRAIN, AND THE SENSORY ORGANS

Transcription

1 NERVOUS SYSTEM, THE BRAIN, AND THE SENSORY ORGANS BY: 6 TH GRADE SCA STUDENTS MODIFIED FROM COPYRIGHT 2003 PEARSON EDUCATION, INC. PUBLISHING AS BENJAMIN CUMMINGS

2 Functions of the Nervous System 1. Sensory input gathering information To monitor changes occurring inside and outside the body (changes = stimuli) 2. Integration to process and interpret sensory input and decide if action is needed. 3. Motor output A response to integrated stimuli The response activates muscles or glands Structural Classification of the Nervous System Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) Nerve outside the brain and spinal cord

3 Functional Classification of the PNS Sensory (afferent) division Nerve fibers that carry information to the CNS (spinal cord and brain) Motor (efferent) division Nerve fibers that carry impulses away from the CNS Motor (efferent) division Two subdivisions Somatic nervous system = voluntary Autonomic nervous system = involuntary

4 Organization of the Nervous System Neuron (Nerve Cell) Anatomy Neurons = nerve cells Cells specialized to transmit messages Major regions of neurons Cell body nucleus and metabolic center of the cell Processes fibers that extend from the cell body (dendrites and axons) Cell body Nucleus Large nucleolus Extensions outside the cell body Dendrites conduct impulses toward the cell body Axons conduct impulses away from the cell body

5 Neuron Cell Body Location Most are found in the central nervous system Gray matter cell bodies and unmyelinated (not insulated) fibers Nuclei clusters of cell bodies within the white matter of the CNS Ganglia collections of cell bodies outside the CNS Functional Classification of Neurons Sensory (afferent) neurons Carry impulses from the sensory receptors Cutaneous sense organs Proprioceptors detect stretch or tension Motor (efferent) neurons Carry impulses from the CNS

6 The Reflex Arc Reflex rapid, predictable, and involuntary responses to stimuli Reflex arc direct route from a sensory neuron, to an interneuron, to an effector Simple Reflex Arc

7 Types of Reflexes and Regulation Autonomic reflexes Smooth muscle regulation Heart and blood pressure regulation Regulation of glands Digestive system regulation Somatic reflexes Activation of skeletal muscles

8 Central Nervous System (CNS) CNS develops from the embryonic neural tube The neural tube becomes the brain and spinal cord The opening of the neural tube becomes the ventricles (brain chambers) Four chambers within the brain Filled with cerebrospinal fluid Regions of the Brain o Cerebrum o Cerebellum o Brain stem o Diencephalon *each region is subdivided into lobes

9 Cerebral Hemispheres (Cerebrum) Paired (left and right) superior parts of the brain Include more than half of the brain mass The surface is made of ridges (gyri) and grooves (sulci) Fissures (deep grooves) divide the cerebrum into lobes Surface lobes of the cerebrum Frontal lobe Parietal lobe Occipital lobe Temporal lobe Somatic sensory area receives impulses from the body s sensory receptors Primary motor area sends impulses to skeletal muscles Broca s area involved in our ability to speak

10 Lobes of the Cerebrum

11 Sensory and Motor Areas of the Cerebral Cortex

12 Specialized Area of the Cerebrum Cerebral areas involved in special senses Interpretation areas of the cerebrum Gustatory area (taste) Speech/language region Visual area Language comprehension region Auditory area General interpretation area Olfactory area

13 Brain Stem Attaches to the spinal cord Parts of the brain stem Midbrain, Pons, and Medulla oblongata Midbrain Mostly composed of tracts of nerve fibers Reflex centers for vision and hearing Cerebral aquaduct connects the 3 rd and 4 th ventricles to allow flow of cerebral fluid Pons The bulging center part of the brain stem, mostly composed of fiber tracts, that includes nuclei involved in the control of breathing Medulla Oblongata The lowest part of the brain stem, that merges into the spinal cord, includes important fiber tracts, and contains important control centers for.. Heart rate control, blood pressure regulation, breathing, swallowing, and vomiting

14 Cerebellum Two hemispheres with convoluted surfaces Provides involuntary coordination of body movements Protection of the CNS Scalp and skin Skull and vertebral column Meninges Cerebrospinal fluid Blood brain barrier

15 Traumatic Brain Injuries (TBI) Concussion Slight or mild brain injury Bleeding & tearing of nerve fibers happened Recovery likely with some memory loss Contusion A more severe TBI Nervous tissue destruction occurs Nervous tissue does not regenerate Cerebral edema Swelling from the inflammatory response May compress and kill brain tissue Cerebral edema Swelling from the inflammatory response May compress and kill brain tissue Subdural hematoma Collection of blood below the dura (this is a bruise on the brain)

16 Cerebrovascular Accident (CVA) Commonly called a stroke The result of a ruptured blood vessel supplying a region of the brain Brain tissue supplied with oxygen from that blood source dies Loss of some functions or death may result Alzheimer s Disease Progressive degenerative brain disease Mostly seen in the elderly, but may begin in middle age Structural changes in the brain include abnormal protein deposits and twisted fibers within neurons Victims experience memory loss, irritability, confusion and ultimately, hallucinations and death Spinal Cord Extends from the medulla oblongata to the T12 region Below T12 is the cauda equina (a collection of spinal nerves) Enlargements occur in the cervical and lumbar regions

17 Peripheral Nervous System Nerves and ganglia outside the CNS Nerve = bundle of neuron fibers Neuron fibers are bundled together by connective tissue that strengthens and insulates the neurons Spinal Nerves There is a pair of spinal nerves at the level of each vertebrae. The spinal nerves connect the CNS to all of the other areas of the body.

18 Autonomic Nervous System The involuntary branch of the nervous system Consists of only motor nerves Divided into two divisions: Sympathetic division & Parasympathetic division Sympathetic fight-or-flight Response to unusual stimulus Takes over to increase activities Remember as the E division = exercise, excitement, emergency, and embarrassment Parasympathetic housekeeping activities Conserves energy Maintains daily necessary body functions Remembered as the D division - digestion, defecation, and diuresis

19 Comparison of Somatic and Autonomic Nervous Systems

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22 The eye is the organ of vision. It has a complex structure consisting of a transparent lens that focuses light on the retina. The retina is covered with two basic types of light-sensitive cells-rods and cones. The cone cells are sensitive to color and are located in the part of the retina called the fovea, where the light is focused by the lens. The rod cells are not sensitive to color, but have greater sensitivity to light than the cone cells. Rodare located around the fovea and are responsible for peripheral vision and night vision. The eye is connected to the brain through the optic nerve. The point of this connection is called the "blind spot" because it is insensitive to light. Experiments have shown that the back of the brain (visual cortex) maps the visual input from the eyes. Being nearsighted or farsighted depends on the length of your eye. People with blue eyes all share a common ancestor. Your eyes actually see everything upside down, but your brain sorts it out. Your eyes can get sunburned too. We blink 28,000 times per day. 20/20 vision isn't perfect vision, it's just normal. The human eye can detect over 10 million different colors.

23 The ear is the organ of hearing. The outer ear protrudes away from the head and is shaped like a cup to direct sounds toward the tympanic membrane, which transmits vibrations to the inner ear through a series of small bones in the middle ear called the malleus, incus and stapes. The inner ear, or cochlea, is a spiral-shaped chamber covered internally by nerve fibers that react to the vibrations and transmit impulses to the brain via the auditory nerve. The brain combines the input of our two ears to determine the direction and distance of sounds. Your ears contain the three smallest bones in the human body: the malleus, incus, and stapes Ears help the body maintain equilibrium. The outside of the ear is called the pinna which acts as a funnel, collecting and amplifying sound for the inner ear. Your ability to hear high frequencies deteriorates as you get older, because the hair cells closest to your outer ear begin to break down. Sound travels at roughly 770 miles per hour through our atmosphere. Earwax is used to catch dirt and debris. The hardest bone in the human body is the temporal bone and it shapes the inner ear where its shape helps process sounds in the ear.

24 The receptors for taste, called taste buds, are situated chiefly in the tongue, but they are also located in the roof of the mouth and near the pharynx. They are able to detect four basic tastes: salty, sweet, bitter, and sour. The tongue also can detect a sensation called "umami from taste receptors sensitive to amino acids. Generally, the taste buds close to the tip of the tongue are sensitive to sweet tastes, whereas those in the back of the tongue are sensitive to bitter tastes. The taste buds on top and on the side of the tongue are sensitive to salty and sour Your taste buds have a lifespan that can last from 10 days to two weeks. It is possible to kill your taste buds by burning your tongue, but they regenerate rather quickly. However, smoking can actually reduce taste bud pods (called papillae) and therefore dull your taste buds more permanently. Taste buds are made up of microvilli, which are microscopic hairs that send signals to the brain to tell us how to process and identify how things taste. Your taste buds need the help of your nose s olfactory senses to send the correct message to the brain about how something tastes. The flavor of something is determined by the taste and the smell senses. When you smell an odor you are also tasting it.

25 The nose is the organ responsible for the sense of smell. The cavity of the nose is lined with mucous membranes that have smell receptors connected to the olfactory nerve. The smells themselves consist of vapors of various substances. The smell receptors interact with the molecules of these vapors and transmit the sensations to the brain. The nose also has a structure called the vomeronasal organ whose function is being sensitive to pheromones that influence the reproductive cycle. The sense of smell is sometimes temporarily lost when a person has a cold. The sense of smell comes about through the stimulation of specialized cells in our nasal cavities cells that are similar to the sensory cells of the antennae of invertebrates. The human olfactory system works when odorant molecules bind to specific sites on the olfactory receptors, which are used to detect the presence of smell. And it all comes together at the glomerulus, a structure which transmits signals to the olfactory bulb a part of the brain directly above the nasal cavity and below the frontal lobe. The end result is the subjective experience we call smell. The smell receptors are sensitive to seven types of sensations that can be characterized into 10 categories: Fragrant (e.g. florals and perfumes) Citrus (e.g. lemon, lime, orange) Chemical (e.g. ammonia, bleach) Minty and peppermint (e.g. eucalyptus and camphor) Pungent (e.g. blue cheese, cigar smoke) Fruity (all non-citrus fruits) Woody and resinous (e.g. pine or fresh cut grass) Sweet (e.g. chocolate, vanilla, caramel) Toasted and nutty (e.g popcorn, peanut butter, almonds) Decayed (e.g. rotting meat, sour milk)

26 The sense of touch is distributed throughout the body. Nerve endings in the skin and other parts of the body transmit sensations to the brain. Some parts of the body have a larger number of nerve endings and, therefore, are more sensitive. Four kinds of touch sensations can be identified: cold, heat, contact, and pain. Hairs on the skin magnify the sensitivity and act as an early warning system for the body. The sense of touch is the first to develop in humans at about 8 weeks into the gestation period. Touch stimulates the brain to release endorphins. The skin is your body s largest organ and contains more than 4 million sensory receptors. Among the body s most sensitive areas are the lips, the back of the neck, the fingertips, and the soles of the feet. The least sensitive area of your body is the middle of your back. Being touched can reduce stress, by lowering levels of hormones like cortisol, which can reduce blood pressure and heart rate. Pain is the body s warning system and that s why people have more receptors for pain than for any other sensations. Thermoreceptors perceive sensations related to temperature, but they may be stimulated when the surface of the skin drops below 41 (which is why your skin starts to feel numb in icy temperatures) or rises above 113 (at which point pain receptors take over to avoid burns).

27 Resources Explore Human Anatomy and Physiology. Edited by Eric Rodriguez, InnerBody, InnerBody.com, Jan. 2018, Human Body Systems. Carolina Biological Supply: World-Class Support for Science & Math, Carolina Biological Supply, Mar. 2018, Nervous System." Fact Monster Sandbox Networks, Inc., publishing as Fact Monster. May < Dowshen, Steven. Body Basics. Rady Children's Hospital-San Diego, The Nemours Foundation/KidsHealth., Mar. 2012,