ANATOMY I; CHAPTER 11, NERVOUS SYSTEM Nervous system is the master control, 2 communication and coordinating system between the different body structures and systems Every activity, thought and emotion reflects its activity It functions on electro-chemical signals Function and division of the nervous system 3 Composed of neurons and neuroglial cells 1. Neurons transmit nerve impulses/signals 2.Neuroglial cells aid and protect the neurons Nervous system is divided into 2 divisions 1. Central nervous system (CNS) brain and spinal cord 2. Peripheral Nervous system (PNS) nerves that connect all the different body parts to the CNS Figure: 11.2 ;pg 387 4 General functions of the nervous system 5 A. Sensory function-sensory division (afferent) Receptors at the distal end of the peripheral nerves nerves gather information and turn it into nerve impulses and send to CNS 6 B. Motor function-motor division (efferent) 1. Carry nerve impulses from the CNS to the effectors (muscles or glands) so they can respond Figure: 11.2; page 387 7 Motor division 8 1
Two different systems 1. Somatic: Directs structures under our conscious control (voluntary/skeletal) 2. Autonomic: directs control over unconscious control. (involuntary/smooth) Autonomic is further divided into sympathetic and parasympathetic 1. sympathetic controls the fight or flight response 2. parasympathetic controls functions when at rest (pretty much) Figure: 11.2 pg. 387 9 C. Integrative Function 10 1. Sensory impulses are integrated into the brain as perceptions 2. Conscious or subconscious analysis and decisions follow. Leading to motor functions by the effectors. Figure: 11.1; page 386 11 Neuroglial cells (glial) - support cells 12 A. In CNS: 1. Microglial cells (CNS): phagocytize and destroy bacteria and cell debris 2. Oligodendrocytes: (CNS) Form myelin coverings in the brain and spinal cord 3. Astrocytes: (CNS) Provide physical support 4. Epindymal cells: (CNS) cover the inside of ventricles Figure 11.3b; pg. 388 13 Figure 11.3b; pg. 388 14 Figure 11.3a; pg. 388 15 2
Figure 11.3c; pg. 388 16 B. In peripheral nervous system (PNS) Satelite and Schwan cells are the myelin forming cells Neurons/Nerve cells Highly specialized: carry nerve impulses 1. great longevity 100 years! 2. amitotic: - can t divide/reproduce/regenerate 3. High metabolism: use a lot of energy need a lot of glucose & oxygen 17 18 Neuron Anatomy: Cell body w/ branching fibers A. Most organelles are in cell body 1. nucleus 2. nucleolus 3. mitochondria 4. golgi bodies 5. endoplasmic reticulum and ribosomes B. Nerve fibers include a solitary axon and numerous dendrites Figure: 11.4a: page 390 19 20 1. Branching dendrites carry impulses from other neurons from other neurons to the cell body. receptive region 2. The axon carries the impulse away from the cell body. a. Sits on a small mound- axon hillock b. axon connects with dendrite to continue the path of the nerve impulse 21 3. Large axons are enclosed by sheaths of myelin made up of Schwann cells and called myelinated fibers 3
a. Narrow gaps in the myelin sheath are called nodes of Ranvier they increase the speed of the nerve impulse. b. Myelin is an electrical insulator-nerve impulses are an electrical current c. The schwann cells are flat and are wrapped around the nucleus like a band-aid around a finger d. The cytoplasm & nucleus are pushed to the outer wrap this is known as the neurilemma Figure 11.4; page 390 22 c. The schwann cells are flat and are wrapped around the nucleus like a band-aid around a finger d. The cytoplasm & nucleus are pushed to the outer wrap this is known as the neurilemma 23 Figure: 11.5; pg. 392 24 25 White matter in the CNS is due to myelin sheaths in this region. Unmyelinated nerve tissue in the CNS appears gray. Peripheral nerves have some ability to regenerate because of the neurilemma (outer layer of the schwann cells) but CNS axons are myelinated with oligodendrocytes and usually can t regenerate Axons can be very!! Long and referred to as fibers. These fibers are often bundled together. If the bundles are in the PNS they re called nerves If the bundles are in the CNS they re called tracts How long can these fibers be? 26 Classification of neurons according to structure 3 types 1. Bipolar 2. unipolar 3. multipolar Bipolar: Two processes at each end, an axon and a dendrite 27 4
Unipolar: Single short process, that T s of into two branches. Multipolar: Three or more processes, one axon and the rest dendrites Table 11.1 pg. 393 28 Table 11.1 pg. 393 29 Table 11.1 pg. 393 30 31 Synapse: point where axons of one neuron meet dendrites of another neuron Nerve impulses travel from neuron to neuron The junction between the two is a synapse. There is a synaptic cleft (space) between the two When the electrical impulse reaches the synaptic knob at the terminal end of the axon neurotransmitters are released The neurotransmitters react with the postsynaptic membranes of the adjacent dendrites on the other side of the synaptic cleft Figure: 11.17; pg. 409 32 Excitatory and inhibitory actions 33 1. Some neurotransmiters increase nerve impulses 2. Other neurotransmitters decrease the impulses 3. At least 50 kinds of neurotransmitters 4. Enzymes rapidly decompose the neurotransmitters to prevent continuous stimulation 5
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