The Nervous System PDF

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Exercise #17: Histology of the Nervous System The Nervous System The functions of the nervous system are integration, coordination, monitoring and processing of sensory information, both internal and external. The Nervous system consists of two types of cells: 1. Neurons, cells that conduct nervous impulses. 2. Neuroglia or Glial cells, which are supporting cells. The neuroglia that are found in the CNS are Astrocytes, Oligodendrites, Microglia, and Ependymal cells. The neuroglia of the PNS are Schwann and Satellite cells. 1. Astrocytes help maintain the blood brain barrier. 2. Oligodendrites myelinate/insulate the axons of neurons. 3. Microglia are phagocytic and clean up debris. 4. Ependymal cells form the blood brain barrier. 5. Schwann cells’ plasma membrane myelinates the axons of neurons in the PNS. 6. Satellite cells regulate the neurons environment. Neuron Anatomy: 1. The Cell body is found in Nuclei in the CNS and Ganglia in the PNS. 2. Neuron processes are called Tracts in the CNS and Nerves in the PNS. 3. Neurofibrils are cytoskeletal structures. 4. Dendrites have receptors for neurotransmitter and generally bring nerve impulses towards the cell body. 5. Axons are nerve impulse generators that release neurotransmitter, branch into Collaterals, begin at the Axon Hillock, and end at Axon Terminals, which are contain vesicles filled with Acetylcholine. The axon terminals are separated from a dendrite or a muscle by the Synaptic cleft. 6. Myelinated Axons are covered by a Myelin Sheath, gaps between the sheath are called Nodes of Ranvier. In the PNS the Neurolemma (neuron cell membrane) of the schwann cells is the myelin sheath. Neuron types: 1. Unipolar neurons have one short process that divides into peripheral (dendrite) and central (axon). 2. Bipolar neurons have two processes extending from the cell body, an axon and a dendrite. 3. Multipolar neurons have many processes (dendrites) and one axon. Classification of Neurons: 1. Sensory/Afferent neurons carry impulses from sensory receptors to sensory bodies in the PNS, then towards the brain via the spinal cord. 2. Motor/Efferent neurons carry impulses to the viscera, muscles and/or glands. Cell bodies are found in nuclei in the CNS.

3. Association/Interneurons are found between sensory and motor neurons, cell bodies are found in the spinal cord and are involved in reflexes. Nerve A nerve is a bundle of neuron fibers wrapped in connective tissue. Types of nerves: 1. Mixed nerves are nerves that carry both sensory and motor fibers, an example is spinal nerves. 2. Sensory/Afferent are fibers that go towards the brain, and are made up of only sensory fibers. 3. Motor/Efferent nerves go away from the brain and are made up of only motor fibers. Each individual fiber (myelinated axon) is wrapped in Endoneurium, groups or bundles of these fibers are called Fascicles and they are wrapped in Perineurium. Groups of Fascicles are wrapped in Epineurium and are called nerves. Inside nerves are also blood vessels and lymph vessels. Exercise #19: Gross Anatomy of the Brain and Cranial Nerves The Central Nervous system (CNS) is made up of the Brain and the Spinal cord. The Peripheral Nervous System (PNS) is made up of The Cranial and Spinal nerves, ganglia and sensory receptors. There are both Motor and Sensory branches, the motor branches are Somatic and Autonomic which have both Parasympathetic (to the viscera) and Sympathetic (fight or flight response). Brain Development: 1. Neural tube. 2. A)Proencephalon (Forebrain) develops into both the Telencephalon and the Diencephalon. The Telencephalon develops into the Cerebrum. The Diencephalon develops into the Thalamus, Hypothalamus. B) Mesencephalon (Midbrain) brain stem/midbrain. C) Rhomboencephalon (Hindbrain) develops into the Metencephalon and the Mylencephalon. The Metencephalon becomes the Brain stem/ Pons and the Cerebellum. The Mylencephalon becomes the Brain stem/Medulla Oblongata. External Brain structures The Cerebral hemispheres of the Cerebrum are divided by the Longitudinal Fissure. The surface (cortex) ridges of the cerebrum are called Gyri and these are separated by

grooves called Sulci or large fissures. The Frontal lobe is separated from the Parietal lobe by the Central Sulcus. The Parietal and Occipital lobes are separated by a ParietoOccipital Sulcus. The Temporal lobe is separated from the frontal and the parietal by the Lateral Sulcus. Some areas of interest The Primary Somatosensory receives information from sensory receptors found in the Post Central Gyrus. The Primary Motor area sends motor impulses. It is found in the Precentral gyrus. Broca's area a motor speech area is found at the base of Precentral gyrus in the Primary motor area. The Prefrontal Cortex which is the area responsible for personality among other things is found in the Anterior frontal lobes.                            

Sheep Brain Dissection Cerebrum Dura Mater Arachnoid Mater Pia Mater Cerebellum Inferior and Superior Colliculi of the Corpora Quadrigemina Pineal Body Olfactory Bulb Olfactory Tract Optic Nerve Optic Chiasma Optic Tract Oculomotor Nerve Mammillary body Pituitary Gland Infundibulum Trochlear Nerve Trigeminal Nerve Abducens Nerve Cerebral Peduncles Pons Medulla Oblongata Corpus Callosum Septum Pellucidum Fornix Thalamus Intermediate Mass of the Thalamus Lateral Ventricles

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Third Ventricle Fourth Ventricle Hypothalamus Spinal Cord

Cerebral peduncles connect the Pons and the Cerebrum. Medulla Oblongata is made up of fiber tracts, connects the spinal cord to the brain. The Decussation of the pyramids is an area of crossover of motor tracts. Also contains the breathing and heart centers. The Cerebellum is posterior to the brain stem is called the little brain contains tracts that appear to be branched this is called the Arbor vitae (tree of life) connected to the brain stem by the Vermis. The Cerebellum is involved with awareness of position and tension of various area of the body. The Corpora Quadrigemina both superior (visual reflex centers) and inferior Auditory reflex centers) Colliculi are seen in the posterior brain stem. Internal Brain Structures Cerebral Hemispheres – Higher Brain function Fornix – Olfactory and limbic sytem function Corpus callusom- Commisure that connects cerebral hemoispheres Septum Pellucidum- Membrane that seperates cerebral ventricles. Thalamus – Major integrating and relay station for sensory impulses Intermediate Mass– (connects thalamic lobes) Hypothalamus- Autonomic center for body temperature, water balance and fat and carbohydrate metabolism, and drives (thirst, sex, hunger). Hypophysis (Pituitary)- The Master Gland. Infundibulum – Stalk that connects pituitary to brain. Optic Nerve- Concerned with vision. Olfactory Bulb- Synapse between CN #1 and Olfactory Tracts. Optic Chiasma- Crossover of medial portions of CN #2. Oculomotor, Trochlear Nerves (Eye muscle control),and Trigeminal (facial muscle control). Mamillary Body – Relay station for olfaction Cerebral Aqueduct – Takes CSF from third to fourth ventricles Corpora Quadrigemmina- both superior (visual reflex centers) and inferior Auditory reflex centers) Epithalamus- Forms roof of the third ventricle, contains Pineal body (gland) and the Choroid Plexus, which produces CSF (cerebrospinal fluid) . Pons- the bridge, made up of sensory and motor tracts between upper brain structures and medulla and spinal cord Spinal Cord- Communication, reflexes, contains oathways and neronal bodies Optic Nerve- Concerned with vision. Olfactory Bulb- Is the synapse area between CN #1 and Olfactory Tracts.

Optic Chiasma- Crossover of medial portions of CN #2. Oculomotor, Trochlear Nerves (Eye muscle control),and Trigeminal (facial muscle control). The Meninges are connective tissue that covers the brain. The three meninges are the Dura, the Arachnoid and the Pia Mater. Dura Mater is the thickest and outermost covering. It is a double-layered membrane the outer Periosteal layer ,the periosteum is derived from it, and an inner layer the Meningael, the first brain covering. The Arachnoid Mater is separated from the dura by a Subdural space. The Subarachnoid Space is filled with threads that separate the Arachnoid from the Pia Mater. In life the subarachnoid space is also filled with Cerebrospinal fluid. The Pia Mater is the innermost membrane and adheres directly to the brain. Meningitis is the inflammation of the meninges, which can lead to Encephalitis which is an infection of the neural tissue of the brain. Cerebrospinal Fluid is similar to plasma and is formed in the Choroid Plexus. The Choroid plexus are capillary knots found on the roof of the four ventricles. CSF path/flow The cerebrospinal fluid flows from the two Lateral Ventricles to the Interventricular Foramen and then to the Third Ventricle and then to the forth ventricle via the Cerebral Aqueduct. Most of the CSF goes through one of three Foramina (two Lateral Apertures and one Median Aperture) towards the subarachnoid space to the Arachnoid Villus and then to the Dural Sinuses, the Superior Saggital Sinus being the largest. Also from the forth ventricle the fluid can flow down the Central Canal of the spinal cord before reaching the dural sinuses where all CSF is sent back into circulation. Hydrocephalus is the impaired flow of CSF (water on the brain), dramatic in infants. Cranial Nerves Cranial Nerves are part of the Peripheral nervous system. There are 12 paired cranial nerves that serve the head and neck regions, only the Vagus nerve (10) extends to the thorax. The Cranial nerves are mixed nerves with the exception of #1, #2, and #8, which are only sensory. 12 Cranial nerves: 1. Olfactroy nerve- smell. 2. Optic nerve- vision. 3. Oculomotor nerve- eye muscle control.

4. Trochlear nerve- eye muscle control. 5. Trigeminal nerve- muscles of face and mouth. 6. Abducens nerve- eye muscle control. 7. Facial nerve- Facial muscles, glands ad tongue. 8. Vestibulocochlear nerve- Equilibrium and hearing. 9. Glossopharyngeal nerve- Salivary glands, taste, and the pharynx (throat). 10. Vagus nerve- digestive system (positive), heart (negative). 11. Accessory nerve- mastoid, and trapezious, the mouth and the pharynx. 12. Hypoglossal nerve- Tongue.

(See Table 19.1 for complete functions and testing for each nerve!)...