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Nervous System

Explore the intricate workings of the nervous system, from sensory input to muscle control. Learn about the central and peripheral divisions, nerve tissue components like neurons and neuroglia, the spinal cord's protective coverings, and the reflex pathways. Uncover the mysteries of how neurons transmit impulses and the significance of reflex actions. Delve into the complex structures and pathways that enable our body's intricate communication system.

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Nervous System

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  1. Nervous System Functions 1. Sensory input 2. Integration 3. Homeostasis 4. Mental activity 5. Control of muscles & glands.

  2. I. Division of the Nervous System A. Central Nervous System (CNS) 1. Brain 2. Spinal cord B. Peripheral Nervous System( PNS) 1. Nervous that are outside the CNS a. Cranial nerves b. Spinal nerves

  3. 2. Sub divisions of the PNS a. Sensory (afferent)-conducts action potential from sensory receptors to the CNS. b. Motor (efferent) – conducts action potential from CNS to PNS. (muscle or glands) a. Somatic - serves sensory nerves, receptors (skin) sensory organs (head) & motor nerves that stimulate the skeletal muscle - voluntary nervous system b. Autonomic - automatic 1. Sympathetic - involving stressful activities 2. Parasympathetic - normal functioning

  4. II. Nerve Tissue A. Neuroglia - support & maintain neurons 1. Schwann Cells - Provide insulation covering around large axons. 2. Astrocytes - Anchor neurons to blood capillaries. 3. Ependymal cells - form & circulate cerebrospinal fluid. 4. Microglia - phagocytize invading microorganisms. 5. Oligodendrocytes - insulation covering around the CNS.

  5. B. Neurons - functional unit of the nervous system 1. Structure a. Dendrites - receive impulses b. Cell body - typical to other cells 1. Nissl bodies - similar to RER 2. Neurofibrils - network of fine threads c. Axon (nerve fiber) - carries impulse away from the cell body. 1. One axon to every neuron 2. Collaterals – side branches 3. Axon hillock – site of the axon missing Nissl bodies

  6. d. Myelin sheath - insulating barrier from a schwann cell around a axon. 1. Nourishment e. Neurilemma - cytoplasm & nuclei of the schwann cell on the outer covering. f. Nodes of Ranvier - gaps where myelin sheaths are absent. g. Unmyelinated fibers - gray matter h. Myelinated fibers - white matter

  7. 2. Types of Neurons a. Mutlipolar - many dendrites (signal to muscles). b. Bipolar 1 dendrtie & axon (eyes, ears, & nose). c. Unipolar d. Sensory (afferent) to CNS. e. Association (interneurons) with in the CNS. f. Motor (efferent) from CNS.

  8. 3. Function a. Resting potential - Polarized -70 mv -more sodium ions outside the neuron than inside. -more potassium ions inside the neuron than outside. -this is maintained by the sodium potassium pump. -but overall negative due to the large negative chloride ions stuck inside.

  9. b. Action potential – (excitable) Nerve impulse + 30 mv Depolarization – sodium moves into the cell Repolarization – potassium moves outside the cell.

  10. c. Refractory period - hyperpolarized - 80 mv. Inside is more negative .

  11. 4. All or None Response a. Threshold Stimulus - minimum strength that can cause an action potential. b. Subthreshold - cannot initiate a response. c. Summation - series of subthreshold stimuli can have a cumulative effect.

  12. 5. Transmission of impulse a. Synapse b. Presynaptic c. Postsynaptic d. Synaptic end bulb e. Synaptic vesicles f. Neurotransmitters (50 different) 6. Excitatory vs. Inhibitory transmissions a. Excitatory causes a action potential (more Na allowed to enter the postsynaptic) b. Inhibitory

  13. III. The Central Nervous System A. Spinal Cord - Conduction pathway for impulses between the brain & the PNS, reflex center. Protected by bone, fluid, membrane. Compose of gray & white matter. Conduction pathway between the brain & nerves. Reflex center 42 cm long.

  14. B. Protective coverings - Meninges - membrane layers. 1. Dura mater - outermost, thick, & tough. Epidural space - space filled with fat between the bone & dura matter. 2. Arachnoid - middle layer of collagen fibers. Subarachnoid space filled with Cerebrospinal fluid (CSF) - shocking absorning & transporting. 3. Pia mater - inner most, attached to the spinal cord.

  15. C. Structures1. 31 segments each with a pair of spinal nerves. 2. Gray Matter - center of the cord (looks like an H). a. Posterior Horns - terminal endings of sensory neurons. b. Lateral Horns - motor neurons of the autonomic nervous system. c. Anterior Horns - motor neurons to skeletal muscle. 3. White Matter - Surrounds the gray matter a. Anterior Columns - b. Lateral Columns- c. Posterior Columns -

  16. D. Conduction Pathways 1. Ascending Tracts - sensory info to the brain. 2. Descending Tracts - motor info from the brain. neurons to the effectors. E. Spinal nerves 1. Mixed nerves because they contain both sensory and motor neurons. 2. Organizied into regions that they emerge. C – cervical T – thoracic L – Lumbar S – Sacral Co – Coccygeal 3. Plexus – nerves come together and separate. a. three main ones cervical c1-c4 brachial – c5-t1 lumbosacral – l1-s4

  17. E. Reflex Center 1. Reflex is an extremely rapid way of responding to an emergency situation. a. Receptor at the end of the sensory neuron. b. Sensory neuron to the CNS Associated neuron in the spinal cord (reflex center). c. Motor

  18. 2. Types of reflexes a. Somatic - actions involve skeletal muscles. 1. Withdrawal – protective 2. Pattellar - knee jerk (2 neurons, sensory to the motor) 3. Stretch reflex

  19. b. Visceral - smooth & cardiac to maintain homeostasis. 1. Breathing, vomiting, sneezing, & coughing

  20. IV Brain - integrative center of the nervous system100 billion neurons.One of the largest internal organs. A. Protective coverings - Meninges - membrane layers. 1. Dura mater - outermost, thick, & tough. Epidural space - space filled with fat between the bone & dura matter. 2. Arachnoid - middle layer of collagen fibers. Subarachnoid space filled with Cerebrospinal fluid (CSF) - shocking absorbing & transporting. 3. Pia mater - inner most, attached to the spinal cord

  21. B. Cerebrum “higher brain”- Largest structure in the brain 1. Cerebral hemispheres 2. ConvolutionsGyri - upwards foldsSulci - inward folds 3. Fissures Longitudinal Transverse 4. Four lobes a. Frontal – smell, motivation, aggression, mood. b. Parietal – touch, pain, temperature, balance, taste c. Occipital – sight d. Temporal – smell, hearing, memory

  22. 5. Sensory Functions a. small portion of the sensory input results in sensation. b. ascending tracts – sends signals to the brain. -each tract is limited ex… ex. Lateral spinothalamic tract pain & temperature. ex. Dorsal column touch, position, pressure -most tracts have 2 or 3 neurons to the brain. -almost all end in the thalamus.

  23. C. Diencephalon – between brain stem & cerebrum 1. Thalamus - relay station for sensory impulses (except smell) entering the brain. 2. Epithalamus – pineal body (puberty) 2. Hypothalamus - Primary control for the autonomic nervous system (homeostasis). a. Thermostat control for body temp b. regulates food & water uptake c. maintain walking & sleeping patterns. d. associated with emotion (rage, aggression, sex drives 1. Pituitary glands - endocrine glands

  24. D. Midbrain - reflexes for rapid eye, head & trunk movements E. Pons - Bridges the cerebrum & cerebellum F. Medulla Oblongata - part of the brain stem & most inferior brain structures 1. Cardiac & respiratory center G. Cerebellum - sends signals to the skeletal muscles

  25. Cranial Nerves

  26. Cranial Nerves

  27. V. Disorders A. Encephalitis – inflammation of the brain B. Meningitis – inflammation of the meninges. C. Rabies – viral disease transmitted by saliva of a animal bite. D. Tetanus – bacterial disease that produces a neurotoxin that affect lower motor neurons in the spinal cord & brain stem. E. MS – autoimmune disorder caused by a viral infection F. Cerebral palsy – general, defects in motor functions from several types of brain damage or birth related injury. G. Parkinsons – muscular rigidity, lack of movement H. Stroke I. Alzheimer’s disease – mental deterioration (dementia). J. Epilepsy – group of brain disorders that cause seizures K. Herpes - shingles

  28. VI. Effects of Aging A. Natural decline in functioning neurons, including sensory neurons. (balance loss, coordination, blood pressure, bladder) B. By the age of 60 up to 50% loss of lower motor neurons in lumbar region. (loss of muscle mass & increase fatigue) C. Size and weight of the brain decreases, but other neurons can compensate for this loss. D. Short term (problem solving, thinking) memory decreases slowly until the age of 60. Afterwards increase rate of memory loss, especially after 70. E. Long term memory seems to be unaffected. F. More time to fall asleep, more walking periods during the night, and longer amount of time being awake at night. G. Many older people shoe no change and some show a 10% increase in thinking ability due to education, health, motivation.

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