Nervous System Lecture

NERVOUS SYSTEM Objectives • Discuss the functions of the Nervous System. • Classify Nervous System. • Define neuron. • Classify neuron on the basis of Structure, Function and Location. • Define Synapse. • Enumerate different types of synapses. • Enlist the different types of Supporting Cells of Nervous system. • Define Myelination. • Explain the formation of the brain and the spinal cord • Describe the formation of a typical Spinal Nerve. • Enumerate the different coverings of spinal nerve. • Enlist the coverings of Brain and Spinal Cord. Basic Functions of the Nervous System  Sensation: collecting sensory input by monitoring internal and external changes (stimuli) via receptors.  Integration: processing and interpretation of sensory information to determine the appropriate response.  Reaction: is the motor output, activating muscles or neurotransmitters. glands through Structural organization of Nervous System 1. Central a. Brain b. Spinal Cord 2. Peripheral a. 12 Pairs of Cranial Nerves b. 31 Pairs of Spinal Nervous tissue is divided into: • Grey matter: contains cell bodies & short processes of the neurons, the neuroglia and blood vessels. • White matter: contains long processes of the • Ganglion: Collection of cell bodies of neurons outside CNS • Nucleus: Collection of cell bodies of neurons inside CNS • Plexus: Collection of nerve fibers to form a network. Human brain The brain is located in the cranial cavity. It has four major regions: 1. Cerebrum (2 Cerebral hemispheres) 2. Diencephalon: Thalamus, Hypothalamus, Subthalamus& Epithalamus 3. Cerebellum 4. Brainstem:  Midbrain  Pons Spinal Cord • Length: 42-45 cm long, • Site: within the vertebral canal. • Beginning: medulla oblongata • Termination: conus medullaris at L2 vertebra • Gives rise to 31 pairs of spinal nerves PROTECTIO N OF THE CNS 1.Bones: Skull and the vertebral column 2.Meninges (membranes): 3 layers 3.Cerebrospinal fluid Coverings of the Brain and Spinal cord (Meninges) • Dura mater (outer) • Arachnoid mater (middle) • Pia mater (inner) Peripher al Nerves •May be sensory, motor or mixed •Cranial: • 12 pairs • attached to brain •Spinal: •31 pairs (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccyeal). •attached to spinal cord Spinal Nerves and Nerve Plexuses  31 pairs  Each spinal nerve is attached by two roots: dorsal (sensory) & ventral (motor)  Dorsal root bears a sensory ganglion (DRG)  The ventral rami form plexuses (except in thoracic region. CRANIAL NERVES 12 pairs 1. Olfactory n. (1st) 2. Optic n. (2nd) 3. Occulomotor n. (3rd) 4. Trochlear n. (4th) 5. Trigeminal n. (5th) 6. aAbducent n. (6th) 7. Facial n. (7th) 8. Vestibulocochlear n. (8th) 9. Glossopharyngeal n. (9th) 10. Vagus n. (10th) 11. Accessory n. (11th) 12. Hypoglossal n. (12th)  Dermatomes  The segment of skin supplied by a segmental spinal nerve is called a ‘Dermatome’ The Autonomic Nervous System •ANS is the subdivision of the peripheral nervous system that regulates body activities that are generally not under conscious control •It is composed of a special group of neurons supplying: •- Cardiac muscle (the heart) •- Smooth muscle (walls of viscera and blood vessels) •- Internal organs The Autonomic Nervous System •Axon of 1st (preganglionic) neuron leaves CNS to synapse with the 2nd (ganglionic) neuron. •Axon of 2nd (postganglionic) neuron extends to the organ it supplies. Divisions of the autonomic nervous system • Sympathetic division • Parasympathetic division Supplies most of the same organs, but cause opposing or • Parasympathetic: conserving energy &routine maintenance “rest &digest” • Sympathetic: mobilization & increased metabolism: Activated during exercise, excitement, and emergencies “fight, flight or fright” 18 Origin of Sympatheti c Division • T1-L2 segments of spinal cord (Thoracolumbar outflow) Origin of Parasympat hetic Division • Craniosacral 1. (Cranial outflow): Nuclei of the 3rd, 7th, 9th & 10th cranial nerves. 2. (Sacral outflow): S2-S4 segments of spinal cord