Study Guide - Nervous System 1. 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. 2. Central nervous system CNS consists of Brain and Spinal Cord. Brain Central NS Spinal nerve cord Afferent Division Peripheral NS Efferent Division

12 pairs of Cranial nerves arise from brain (Part of PNS) 31 pairs of spinal nerves arise from spinal nerve cord (Part of PNS) Somatic sensory Visceral sensory Somatic NS

Sympathetic Parasympathetic 3. Peripheral nervous system PNS consists of nerves and ganglia bringing information into or out of Central nervous System. Cranial nerves – 12 pairs arise from brain and Spinal nerves – 31 pairs arise from spinal cord. Autonomic NS

4. PNS has sensory and motor parts. Motor part includes Autonomic Nervous System. ANS has 2 parts Sympathetic and Parasympathetic Nervous Systems. 5. Specialized nerve cells are called Neurons. 6. 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 7. 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. 8. Inter-neurons receive information from sensory neurons and integrate it, interpret the meaning and pass instructions to motor neurons to act. 9. 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.

10. 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 Polarisation. Na+ - K+ pump maintains the resting potential by pumping 3Na+ out and bringing 2K+ in and consumes 1 ATP each time. 11. Action Potential (30mV): is the sudden change on stimulation. Na+ ions move in through Na+ gated channels. Now nerve fiber has more + ions inside. Action potential or nerve impulse travels from cell body side to terminal knob side of neuron. When the impulse reaches a part it becomes + inside and the part just behind it, returns to resting potential = Repolarisation, due to outward movement of K+ ions through K+ gated channels. This does not stop at – 70mV but becomes more negative (Hyperpolarisation) around -90mV. It has more Na+ inside and more K+ outside. Na+ - K+ pump starts operating and restores the original ionic balance – more Na+ outside and more K+ inside and keeps it that way until next action potential. 12. Brain: has 6 main parts: •

Fore-Brain o

1. Cerebrum

o

2. Diencephalon

•

3. Mid-Brain

•

Hind Brain o

4. Pons

o

5. Medulla

o

6. Cerebellum

13. Cerebrum is the largest part of brain. It is divided into 2 cerebral hemispheres. Longitudianal fissure divides the cerebral hemispheres. Each cerebral hemisphere has 4 main lobes a – Frontal b – Parietal c – Temporal d – Occipital, covered by respective bones. 14. Each Cerebral Hemisphere: has 1. Cerebral Cortex – formed of gray matter = cell bodies, 2. Cerebral white – formed of myelinated nerve fibers lies below gray matter and 3. Basal nuclei – lie deeper, have cell bodies and control movements. 15. Corpus Callosum: a broad band of transverse nerve fibers joins the 2 cerebral hemispheres. It is highway of information between them. It lies above the level of lateral ventricles. A narrow median band of fibers is Fornix. 16. Lateral Ventricles: two large cavities lined by ependyma and filled with cerebrospinal fluid are present in the 2 cerebral hemispheres.

17. Cerebral Cortex: The majority of nerve cell bodies = Soma lie in the surface of cerebral hemispheres. It has large number of grooves = Sulci and ridges = Gyri to increase the surface area to accommodate more neurons. Different regions are Control Centers for specific functions. A deep transverse fissure = Central sulcus divides frontal and parietal lobes. 18. Primary Areas: 1. General Motor area lies in front of central sulcus and control voluntary movements of skeletal muscles. 2. The area just behind central sulcus is the general Sensory Area to receive sensory input. 3. Primary vision area lies in visual cortex in occipital lobe. 4. Primary Gustatory Area lies on lateral side of frontal lobes and receives information about taste. 5. Primary Auditory Area lies in temporal lobes and receives information about sounds. 6. Primary Olfactory area lies in temporal lobe very close to frontal lobes and receives inputs about smells. 19. It is the seat of intelligence, imagination, calculations or processing, and memories. Most of the times we use word brain to mean cerebrum. 20. Diencephalon: lies above the midbrain. It has the 3rd ventricle in it. 2 Thalamus are lateral thick structures, in most people fuse with each other – inner mass. Thalamus is the main Relay Center. They receive sensory inputs from ascending tracts and pass it to specific parts of Cerebral Cortex via Cerebral Radiations. Epithalamus is the thin roof and has Pineal Gland and Choroid to secrete cerebrospinal fluid. Hypothalamus is the thin floor and is the main control center for secretion of hormones and therefore controls metabolism. It has centers for body temperature and fluid balance in body. Pituitary gland lies below it – lodged in Sella Turcica of sphenoid bone of cranium. 21. Brain Stem has Mid Brain, Pons and Medulla . 22. Mid-brain has 4 posterior protrusions –superior collicule control visual reflexes and inferior colliculi control auditory reflexes. 2 thick bands Cerebral peduncles lie on anterior side. A narrow Aqueduct passes through mid brain and joins 3rd and 4th ventricles. 23. Pons: is a thick band of nerve fibers and lie anterior to medulla oblongata. It joins the 2 sides of cerebellum and also lower parts of brain to cerebrum. It has breathing center in it. 24. Medulla Oblongata: is the most inferior part of brain and is continuous with spinal cord. Medula is superior to foramen magnum but spinal cord is inferior to it. 4th ventricle lies in medulla and has choroid in posterior wall to secrete cerebrospinal fluid. It has many control centers including the cardiac and breathing centers to regulate heart beat and rate of breathing. 25. Cerebellum is the 2nd largest part of brain and is responsible for maintaining body posture and balance = equilibrium of body. It has a small central lobe = vermis and 2 lateral cerebellar hemispheres. It has tree like branching pattern of gray and white matter in it.

26. 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. 27. Meninges: Dura mater, Arachnoid and Pia Mater cover, just like brain, Spinal Cord. Outside dura mater epidural space is filled with fat and network of veins. Dura mater is not fused with bone outside. 28. Blood-Brain-Barrier is formed of capillary cells with tight junctions and other features and does not allow all things in blood to enter brain. Choroid plexus is a network of fine capillaries present in the roof of all 4 ventricles and secrete Cerebrospinal fluid = CSF. CSF supports brain, provides nourishment and protection. CSF moves freely in ventricles and central canal of spinal nerve cord. It passes through foramina in roof of 4th ventricle and enters subarachnoid space. From here CSF diffused through Arachnoid Grannulations (clusters of slender extensions) into superior sagittal sinus by penetrating the inner layer of dura mater. CSF is about 150mls. 4 Choroid plexus secrete about 500mls of CSF in one day. 29. Peripheral Nervous System = Cranial nerves + Spinal nerves (and their ganglia). 30. Cranial Nerves – are 12 pairs and arise from brain and pass through cranium. Memory aid in your text book is really good. On Occasion, Our Trusty Truck, Acts Funny – Very Good Vehicle AnyHow. Capital letters represent 12 cranial nerves – OO, OTTAF – VGVAH. Fig 13.5a-b 31. Cranial nerves – Sensory cranial nerves – 1,2 and 8; Motor cranial nerves – 3, 4, 6 (eye ball muscles), 11 and 12. Mixed cranial nerves – 5, 7, 9 and 10. Tongue – Sensory nerves = Anterior 2/3rd 7th-facial; posterior 1/3rd 9th –glossopharyngeal; motor nerve – 12th –hypoglossal. Vagus is the only nerve to go past head and neck, it traverses to thorax, diaphragm, abdomen and innervates larynx, heart, lungs, diaphragm, stomach, liver, kidneys, intestines, bladder and testes/ovaries - uterus. Facial – 7th controls facial expression and supplies most of the muscles of face, cranium and neck. Trigeminal – 5th collects information from most part of skin of face and supplies muscles of mandible. 3rd, 7th, 9th and 10th cranial nerves carry Parasympathetic nerve fibers in them. All are mixed except 3rd cranial nerves. 32. Spinal Nerves: 31 pairs of spinal nerves arise from spinal nerve cord. 33. Roots of Spinal nerve: Each spinal nerve has a dorsal root and bears dorsal root ganglion. Dorsal root is sensory = affrent. Ventral root does not have a ganglion and is motor = efferent. The 2 roots combine to form spinal nerve that passes out through a gap between bodies of vertebra. 34. Rami of Spinal Nerve: each spinal nerve divides into a slender Dorsal Ramus – is sensory and supplies the skin on back; a thick Ventral Ramus – is motor and supplies the lateral and anterior sides of body. A 3rd very thin branch is Ramus Communicanis (rami communicanti) that joins to lateral ganglion of Sympathetic cord.

35. 31 pairs: 8 Cervical, 12 thoraci, 5 lumbar, 5 sacral and 1 caudal. 36. Plexi: branches of spinal nerves (except T2 – T12) combine with branches of nearby spinal nerves to form network = Plexus. Cerivical, brachial, lumbar, sacral and caudal plexi. Brachial plexus, Fig 13.9, gives rise to radial, median and ulnar nerves to arm. Sacral plexus, Fig 13.11, gives rise to Sciatic – tibial and fibular branches, Posterior femoral and pudendal branches and also to gluteal muscles. 37. Dermatome: is the part of skin innervated by a spinal nerve. Fig 13.12 38. Autonomic Nervous System: Fig 21.10 lab manual or Fig 14.5 text book.

Sympathetic = Thoracolumbar division

Parasympathetic = Craniosacral division

1. Preganglionic neurons lie in lateral horns of gray matter in thoraco-lumbar part of spinal cord and enter lateral ganglia through spinal nerves.

1. Preganglionic neurons lie in brain nuclei of cranial nerves and sacral part of spinal cord.

2. Thoraco-lumbar - Sympathetic trunks (T1T12 – L1-L5)

2. Cranio-sacral – 3rd, 7th, 9th, 10th cranial nerves and spinal nerve cord through 2nd, 3rd, 4th sacral spinal nerves

3. Post ganglionic fibers are Adrenergic and secrete epinephrine formerly called adrenalin.

3. Post ganglionic fibers are Cholinergic and secrete Acetylcholine.

4. Pre ganglionic fibers (before synapse) are much longer than postganlionic fibers

4. Pre ganglionic fibers are shorter than post ganglionic fibers

5.fight or flight – response to unusual stimuli (emergency, excitement, exercise, embarrassment), increases activity

5. maintains house-keeping activities, conserves energy, promotes digestion, defecation and diuresis – passing out enough urine