Nervous System (1) PDF

Nervous system (1) Definition of a Neuron  Neuron is the name given to the nerve cell and all its processes. Neurons are :  Excitable cells that are specialized for : The reception of stimuli And the conduction of the nerve impulse They vary considerably in : Size a...

Nervous system (1) Definition of a Neuron  Neuron is the name given to the nerve cell and all its processes. Neurons are :  Excitable cells that are specialized for : The reception of stimuli And the conduction of the nerve impulse They vary considerably in : Size and Shape  But each possesses:  A cell body from whose surface project :  One or more processes called neurites. Those neurites responsible for :  Receiving information and conducting it toward the cell body are called Dendrites  The single long tubular neurite that conducts impulses away from the cell body is called The axon  The dendrites and axons are often referred to as : Nerve fibers Neurons are found in :  The brain  The spinal cord  The ganglia  Unlike most other cells in the body normal neurons in the mature individual do not : undergo division and replication  The nervous system can be separated into parts based on : structure and on function Structurally, it can be divided into : The central nervous system (CNS) The peripheral nervous system (PNS) Functionally it can be divided into : Somatic and Visceral parts The CNS is composed of : The brain and spinal cord The PNS is composed of : All nervous structures outside the CNS That connect the CNS to the body The PNS consists of : 1. The spinal and cranial nerves 2. visceral nerves and plexuses 3. and the enteric system. Peripheral Nervous System  Cranial nerves —12 pairs  Spinal nerves —31 pairs The 12 Cranial Nerves  There are 12 pairs of cranial nerves.  which leave the brain  and pass through foramina and fissures in the skull.  All the nerves are distributed in the head and neck  except cranial nerve X  which also supplies structures in the thorax and abdomen. The cranial nerves are named as follows: 1. Olfactory 2. Optic 3. Oculomotor 4. Trochlear 5. Trigeminal 6. Abducent 7. Facial 8. Vestibulocochlear 9. Glossopharyngeal 10. Vagus 11. Accessory 12. Hypoglossal Organization of the Cranial Nerves 1. The olfactory nerve 2. Optic nerve 3. Vestibulocochlear nerve Are entirely sensory 1. The oculomotor nerve 2. Trochlear nerve 3. Abducent nerve 4. Accessory nerve 5. Hypoglossal nerve Are entirely motor 1. The trigeminal nerve 2. Facial nerve 3. Glossopharyngeal nerve 4. Vagus nerve Are both sensory and motor nerves Spinal nerves  31 pairs that exit the vertebral column through the intervertebral foramina 8 Cervical 12 Thoracic 5 Lumbar 5 Sacral 1 Coccygeal  Each spinal nerve is connected to the spinal cord by two roots:  the anterior root and the posterior root. The anterior root consists of :  Bundles of nerve fibers carrying nerve impulses away from the central nervous system  These nerve fibers are called efferent (motor) fibers. The posterior root consists of :  Bundles of nerve fibers carrying nerve impulses to the central nervous system  These nerve fibers are called afferent (sensory) fibers. Thank you