Fundamentals of Nervous System and Nervous Tissue Chapter 12 Nervous System The nervous system is the main system to communicate and coordinate body activities by sending electrical impulses. Nervous system forms a communication network in whole body. Endocrine system communicates through chemical messengers – hormones. 12 pairs of Cranial nerves arise from brain Brain (Part of PNS) Central NS 31 pairs of spinal nerves arise from spinal Spinal nerve cord nerve cord (Part of PNS) Somatic sensory Afferent Division Visceral sensory Peripheral NS Somatic NS Efferent Division Sympathetic Autonomic NS Parasympathetic Neuron A neuron has a cell body. Many smaller branched appendages are called Dendrites. Dendrites bring in information (nerve impulse) to the cell body. A single longer appendage is called Axon. It takes information away from cell body. It branches at the end into terminal knobs. A terminal knob secretes a chemical called Neurotransmitter in the gap to the next neuron or muscle membrane. 3-types of neurons (on basis of function) Specialized nerve cells are called Neurons. Sensory neurons bring information from sense organs like eyes to CNS. Sensory = Affrent. Somatic Sensory = coming from body wall - skin, muscles and joints; Visceral Sensroy = coming from internal organs - viscera Motor neurons take information from CNS to effectors like muscles or glands. Motor = Effrent. Somatic Motor – going to skeletal muscles and Visceral Motor – going to smooth or cardiac muscles. Inter-neurons receive information from sensory neurons and integrate it, interpret the meaning and pass instructions to motor neurons to act. Neurons (on basis # of appendages) Multipolar Neurons – many dendrites and 1 axon; most neurons in nervous system Unipolar Neurons – 1 appendage, one end acts as dendrite and other end as axon, cell body attached to the middle of appendage; sensory neuron in dorsal root ganglion of spinal nerve Bipolar Neurons – 1 dendrite and 1 axon; neurons in middle layer of retina Neuroglial Cells Neuroglial Cells are non-conducting cells and have 4 kinds: Astrocytes have many appendages, anchor neurons, form blood brain barrier, provide nourishment to neurons Oligodendrocytes form myelin sheath around axons in CNS and Schwann cells form myelin sheath in PNS. Microglial cells are phagocytes Ependymal cells secrete cerebrospinal fluid. CNS PNS 1. Nucleus: Collection of cell bodies deep in brain Ganglion: Collection of cell bodies 2. Tract: bundle of axons; tracts Columns pathways Nerve: bundle of nerve fibers; may have 1-2 ganglia 3. Gray matter – mainly cell bodies; neural cortex, Cranial nerves and spinal nerves centers, higher centers 4. White matter – mainly myelinated axons Sympathetic and Parasympathetic divisions of ANS Important Terms Polarization: + ions dominate outside nerve fiber and – ions dominate inside nerve fiber = resting potential Depolarization: Na+ enter the nerve fiber, + ions dominate inside but – ions dominate outside nerve fiber Repolarization returns back to original state, + dominate outside and – ions inside the nerve fiber. Resting Potential Resting Potential (- 70mV): is when a nerve fiber has more positive ions outside and more negative ions inside. It is not conducting any electrical impulse. It is Polarization. Na+ - K+ pump maintains the resting potential by pumping 3Na+ out and bringing 2K+ in and consumes 1 ATP each time. Action Potential (+35mV) = nerve impulse travels as a wave of depolarization from one segment of nerve fiber to next. Meninges – CNS coverings Meninges: Dura mater, Arachnoid and Pia Mater cover, just like brain, Spinal Cord. Dura Mater = tough mother, outermost covering of brain and spinal cord Arachnoid = vascular spidery middle covering Pia mater = delicate mother, is in contact with brain Outside dura mater epidural space is filled with fat and network of veins. Dura mater is not fused with bone outside. Spinal Nerve Cord Spinal Cord: has a narrow central canal lined with ependyma and filled with cerebrospinal fluid. Gray matter lies around central canal and has 2 anterior and 2 posterior extensions = Horns. The outer part is formed of white matter and has ascending and descending tracts in it. Ascending and descending pathways lie in spinal nerve cord (seen in T.S.). Brain Brain: has 6 main parts: Fore-Brain 1. Cerebrum 2. Diencephalon 3. Mid-Brain Hind Brain 4. Pons 5. Medulla 6. Cerebellum .