Nervous System I. Nervous System A. 2 Groups 1. Central Nervous System (CNS) 2. Peripheral Nervous System (PNS) B. 3 Functions of the Nervous System 1. Sensory Function 2. Integrative Function 3. Motor Function C. Sensory Function 1. Sensory receptors are located at the ends of the peripheral nerves. 2. Sensory receptors gather info. based on changes that occur inside and outside the body. Example: light, sound intensities, temp. 3. Signal received is turned into a nerve impulse which goes to the central nervous system. (CNS) D. Nervous Tissue - Neurons masses of nerve cells Function 1. to react to physical and chemical changes from the surroundings 2. conduct nerve impulses to other neurons. E. Parts of Neurons 1. Cell body mainly cytoplasm, a nucleus, and many organelles. 2. Dendrites main receptor site that accepts impulses/short and highly branched. 3. Axons conduct impulses away. It is one single fiber with a side branch. F. Neuron Reproduction - 1. The nucleus does not undergo mitosis after it is developed. 2. Can not replace neurons once they are mature. G. Neuroglial Cells occurs with organs of the nervous system. 1. fills spaces 2. provides support 3. produces myelin forms myelin sheath on an axon - an insulator
4. Astrocytes found between nervous tissues and blood vessels 5. Oligodendrocytes found in rows along nerve fibers 6. Microglial cells found throughout the CNS 7. Ependymal cells covers brain parts and spinal cord. H. Nerve Impulses 1. Action potential occurs in one region of a nerve fiber membrane 2. Causes a flow to adjacent nerve fiber membrane called a local current. 3. Local current stimulates membrane to the threshold level and triggers other action potentials 4. Action potential moves away in all directions to make a nerve impulse. G. Synapse the gap that occurs between the neurons impulses must cross this gap = synaptic cleft 1. Dendrite carries impulse to neuron body 2. Impulse travels down an axon 3. Crosses the synapse 4. A different dendrite from a neighboring neuron II. A Nerve Nerve cord-like bundle of nerve fibers held together by layers of connective tissue. A. 3 types of Nerves 1. Sensory nerves conduct impulses into brain or spinal cord. 2. Motor nerves carry impulses to muscles or glands 3. Mixed nerves includes both sensory and motor fibers B. Reflexes - an automatic, unconscious response to changes occurring within or outside of the body. Example: heart rate, blood pressure, breathing rates, swallowing, sneezing, coughing and vomiting. III. Central Nervous System 1. All organs of the CNS are surrounded by bones, membranes, and fluid. 2. Underneath these coverings there is a protective covering called meninges. A. 3 Layers to the Meninges 1. Dura mater outermost layer, white fibrous connective tissues and blood vessels. 2. Arachnoid mater web like membrane that lacks blood vessels and
located between the dura and pia mater. 3. Pia mater very thin and contains many nerves and blood vessels and attached to organs IV. Spinal Cord - consists of 31 segments - each gives rise to a power of spinal nerves A. Functions of Spinal Cord 1. Conducts nerve impulses 2. Serves as a center for spinal reflexes. B. Nerve Tracts - provide two-way communication system between brain to the outer nervous system 1. Ascending Tract conduct impulses from the body parts to the brain 2. Descending Tract conducts impulses from brain to muscles & glands V. The Brain - composed of about 100,000,000 neurons and nerve fibers A. Three parts to the Brain 1. Cerebrum (largest part) - contains nerve centers associated with sensory and motor function - associated with higher mental functions including memory & reasoning 2. Cerebellum - includes centers associated with the coordination of voluntary muscular movements 3. Brainstem - contains nerve pathways by which various parts of the nervous system are interconnected and also contains nerve centers involved in regulation of various organ activities B. Parts to the Cerebrum 1. Cerebral hemispheres 2 mirrored halves - connected by a bridge called corpus callosum 2. Surface of cerebrum - has ridges called convolutions - shallow grooves called suleus
- deep grooves called fissures - longitudinal fissures separates left and right hemispheres - transverse fissures separates cerebrum from cerebellum 3. Lobes of the cerebral hemisphere - Frontal lobe speech, sight, concentration, planning, problem-solving, motor function, control of voluntary muscles - Parietal lobe understanding speech, general interpretation area, senses - Temporal lobe auditory, interpretation of sensory experiences, memory of visual and auditory patterns. - Occipital lobe combining visual images, visual recognition of objects, visual area C. Hemisphere Dominance - 90% of population is left hemisphere dominant for language related activities of speech, writing, and reading. (also right handed) - non-dominant hemisphere seems to specialize in nonverbal function, orientation of body, understanding and interpreting musical patterns. D. Ventricles 1. Interconnected cavities that are filled with cerebrospinal fluid (CSF) - clear liquid - circulates through ventricles and around brain - supports and protects by absorbing forces E. Brain stem 1. A bundle of nervous tissue that connects the cerebrum to the spinal cord Partsa. Diencephalon includes thalamus and hypothalamus Thalamus serves as a central relay station for sensory impulses from other parts of the nervous system Hypothalamus receives impulses from thalamus and other parts of the brain and sends impulses to them Important Functions: 1. regulating heart rate and blood pressure 2. regulating body temperature 3. regulating water balance (homeostasis) 4. control of hunger and regulating body weight
5. control of movements and secretions of stomach and intestines 6. release of various hormones 7. regulation of sleep and wakefulness b. Limbic System - controls emotional experience and expression c. Midbrain - beneath diencephalon and pons and related to visual and auditory functions d. Pons - rounded area under midbrain and above medulla oblongata - transmits impulses beneath the cerebrum and other parts of the nervous system - helps regulate rate and depth of breathing e. Medulla Oblongata end of brain stem - transmits all ascending and descending impulses and several vital and nonvital reflexes - associated with the cardiac center, vasometer center and respiratory center - vasometer = smooth muscles and blood vessels E. Cerebellum - 2 hemispheres - primary function is to be a reflex center for sensory information needed to coordinate muscle movement and maintain equilibrium VI. Peripheral Nervous System - consists of cranial and spinal nerves that branch out from the brain and spinal cord to all body parts. - Divided into somatic and automatic portions A. Somatic - CNS that connects the CNS to skin and skeletal muscles conscious activities B. Automatic - CNS that connects to visceral organs unconscious activities 1. Cranial Nerves - 12 pairs that connect brain to head, neck, and trunk
- most are mixed but some just for sensory or motor - names of cranial nerves indicate their function or general distribution ex. olfactory nerves = smell optic nerves = sight 2. Spinal Nerves - 31 pairs that come from spinal cord - all mixed nerves (sensory/motor) - grouped by the levels from which they arise and are numbered - each emerges by a dorsal and ventral root. - dorsal = sensory - ventral = motor example: cervical plexuses neck brachial plexuses shoulder, neck, arm, hand lumbosacral plexuses - back VII. Autonomic Nervous System - consists of the portions of the nervous system that function without a conscious effort - reflex actions controlled by the hypothalamus, brain stem, and spinal cord - 2 divisions: - Sympathetic deals with stressful and emergency situations - Parasympathetic active under normal situations