Nervous System Nerve Structure A single nerve in

Nervous System

Nerve Structure A single nerve in the body may contain hundreds of thousands of nerve fibers that run parallel to each other. Each Nerve Fiber is a long extension that is a part of an individual nerve cell = NEURON 17 -2

Nervous Tissue The nervous system is divided into a central nervous system (CNS), consisting of the brain and spinal cord, and a peripheral nervous system (PNS), consisting of nerves carrying sensory and motor information between the CNS and muscles and glands.

Types of Nervous Cells Both systems have two types of cells: A) NEURONS that transmit impulses. B) NEUROGLIAL cells that service neurons. 17 -4

Organization of the nervous system 17 -5

Neuron Structure Neurons are composed of dendrites that receive signals, a cell body with a nucleus, and an axon that conducts a nerve impulse away. 17 -6

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Structures and Functions Of A Neuron: 1. Dendrites -Receive signals from other neurons and conduct a nerve impulse (message) towards the cell body. -Many dendrites enter a cell body. 17 -8

2. Cell Body -Contains the nucleus and cell organelles needed to keep the cell alive. -Only a single axon leaves a cell body. -Relays an impulse from dendrite to axon. 17 -9

3. Axons -Conduct a nerve impulse away from the cell body. 4. Myelin Sheath -Protective lipid coating of Schwann cells (type of neuroglial cell) forms insulating layer around longer axons and dendrites 5. Nodes of Ranvier -Interrupted areas of the Myelin Sheath due to gaps between one Schwann cell and the next. 17 -10 -Speeds up transmission of impulse.

6. Axon Terminals (Synaptic Endings) - The branches found at the end of the axon. - Each terminal ends with a small swelling (axon bulb) which houses many synaptic vesicles containing neurotransmitter chemicals. 17 -11

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7. Motor End Plates (found only on motor neurons) -The ending of a motor nerve found in close proximity to effectors (muscles and organs/glands) -From here the impulse is chemically transported to the effectors causing an event to take place. 17 -13

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Types of Neurons 1. Motor Neurons 2. Sensory Neurons 3. Interneurons 17 -15

1. Motor Neurons Efferent Neuron: Carries the nerve impulse from the Central Nervous System (Exiting the CNS) and heading toward an effector (organ/gland). -Relays messages from the brain or spinal cord to the muscles and organs. - *Short Dendrites – Long Axon 17 -16

Motor (Efferent) Neurons take information from the CNS to effectors (muscles or glands). Characterized by short dendrites, a central cell body and fairly long axons. Axons are often covered with a myelin sheath to carry impulse faster and to protect the long nerve fiber. 17 -17

2. Sensory Neurons -Afferent Neuron: Carrying a nerve impulse from a central organ or receptor, having the impulse Arrive at the CNS. -Relays messages from receptors to the brain or spinal cord * Long Dendrite – Short Axon 17 -18

Sensory (Afferent) Neurons take information from sensory receptors to the CNS. Characterized by longer dendrite fiber, shorter axon fiber and a peripheral cell body. Both axon and dendrite fibers may be myelinated. 17 -19

3. Interneurons (Connector Neurons) - Carry impulses within the CNS. -Relays message from a sensory neuron motor neuron. -Make up the brain and spinal cord. * Short Dendrite – Long or Short Axon 17 -20

Interneurons (Connector/Association) occur within the CNS and integrate input. Characterized by short dendrites as well as short axon. Central cell body, but very seldom shows myelination along nerve fibers. They are found within brain and spine and act like “Head Coordinator” (Pre-wired Circuit Board) to receive and relay incoming impulses to the 17 -21 appropriate pathways.

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Types of neurons – All Three Work Together 17 -23

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Take a 2 min break https: //www. youtube. com/watch? v=6 q. S 8 3 w. D 29 PY https: //www. youtube. com/watch? v=HZh 0 A-l. WSm. Y 17 -25

Myelin Sheath Long axons are covered by a protective myelin sheath formed by neuroglial cells called Schwann cells. The sheath contains lipid myelin which gives nerve fibers their white, glistening appearance. The sheath is interrupted by gaps called nodes of Ranvier. 17 -26

Myelin sheath SCHWANN Cells are a type of NEUROGLIAL cell. Myelination serves two purposes, it protects long fragile nerve fibers and it also speeds up a nerve impulse. It speeds up impulse by allowing action potential of 17 -27 nerve impulse to skip from node to node.

Multiple sclerosis is a disease of the myelin sheath. 17 -28

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1. Give two separate names for the type of neuron shown here. A B H C G – Name for branched endings D F- Name for gaps in myelin sheath E – Name of Cells 17 -30 that form Myelin Sheath