CNS Central Nervous System Brain and Spinal cord PNS Peripheral Nervous System Cranial and Spinal nerves Ganglia and sensory receptors Function of nervous system To monitor and process sensory information from the environment and inside the body Two groups of cells Features of Neurons o Neurons conducting cells o Neuroglia Supporting cells Act as nerve glue They brace protect and myelinate neurons Supporting cells of CNS Microglia Oligodendrocytes Astrocytes Ependymal cell act as phagocytes digest pathogens myelinate the extensions of the neurons control the chemical environment around neurons facilitate Microglia Oligodendrocytes Astrocytes capillary nerve exchanges Ependymal cells circulate cerebriospinal fluid Supporting cells of the PNS Schwann cells Satellite cells Schwann cells Satellite cells myelinate the extensions of neurons surround cell body of the neuron o Cell Body composed of large round nucleus surrounded by neuroplasm o Neuroplasm contains Neurofibrils intermediate filaments in the neuron provide tensile strength Nissil Bodies Specialized ER which synthesizes proteins Neuron cell bodies found in clusters in the CNS nuclei Neuron cell bodies found in clusters outside CNS ganglia together these make up the gray matter of the nervous system o Neuron Processes Dendrites Receive signals to the cell body many Axons generate and transmit action potential one jxn bt cell body and axon Axon features Axon hillock Axon terminal Myelin Sheath rings of the plasma membrane wrapped around the axon Insulates fibers and increases the speed of transmission nerve impulse end of axon where neurotransmitters are stored whitish fatty proteins covering some axons Concentric o In CNS axons are myelinated by Oligodendrocytes o In PNS by Schwann cells part of the schwann cell external to the myelin sheath Neurilemma housing the nucleus and cytoplasm Nodes of Ranvier Gaps in myelin sheath Properties of Neurons o Excitability the ability to respond to stimuli and convert them into nerve impulses o Conductivity the ability to transmit the impulse to other neurons muscles glands o They exhibit longevity o They are amitotic because neurons lack centrosomes Structural Classifications of neurons based on how many processes extend from the cell body a single process extending from the cell body that is divided into peripheral o Unipolar and central processes conducts toward CNS in the eye ear and olfactory mucosa common type of neuron in the body away from CNS o Bipolar two processes attatched to one cell body one dendrite one axon found only o Multipolar many processes from the cell body Many dendrites one axon most CNS o Sensory afferent Neurons Carry impulses from sensory receptors in the skin internal organs muscles and special sense organs toward the CNS o Motor Neurons efferent Carry impulses away from the CNS to organs muscles and o Association Neurons interneurons Conduct impulses within the CNS Structure of a Nerve o Nerve A bundle of axons in the PNS wrapped in CT o Tract A bundle of axons in the CNS wrapped in CT o Mixed Nerves contain both sensory afferent and motor afferent processes all spinal glands nerves o Sensory afferent nerves contain only sensory processes some cranial nerves o Motor efferent nerves contain only motor processes ventral nerves of the spinal cord Structure of a Nerve or a tract o Each axon is covered by Endoneurium o Fassicles are covered by Perineurium o Nerve or tract is covered by Epinuerium Nerve Impulse o Step 1 Resting state The neuron is polarized High sodium Na conc Outside high K inside cell Maintained by active sodium potassium pumps Cytoplasmic surface is more neg that the exterior face This charge separation resting membrane potential o Step 2 Stimulation The neuron is activated by a stimulus of appropriate intensity threshold stimulus Sodium gates open and Na moves into cell down its concentration gradient Interior of the cell becomes less negative and eventually positive depolarization o Step 3 Generation of Nerve Impulse Depolarization occurs when the charge across the plasma membrane changes from neg to pos When the threshold potential is reached an action potential is generated Generation of AP is an all or none phenomenon A transmitted AP nerve impulse o Step 4 Repolarization Potassium gates open and K moves out of cell down concentration gradient The membrane repolarizes o Step 5 Returning to the Resting State The sod pot pump reestablishes the concentration gradients of the RMP so the neuron can fire again Absolute Refractory Period depolar and neuron is unable to initiate new AP Relative Refractory Period sodium gates are closed an exceptionally strong stimulus can cause initiation of another AP When neuron is undergoing repolar and therefore Occurs when sodium gates are still open during Gross Anatomy of the Human Brain o 4 Major regions Cerebrum Superior portion Higher mental functions reasoning memory Separated by longitudinal fissure and connected by corpus callosum Lateral ventricles separated by membrane septum pellucidum Separated into 5 lobe Frontal parietal occipital temporal insula Gyrus is an elevated ridge sulcus is gap between ridges and fissures are deep sulcus Precentral gyrus central sulcus postcentral gyrus Back of frontal lobe Lateral sulcus Parieto occipital sulcus separates temporal and parietal lobes Cerebrum has 3 regions bodies and dendrites location of conscious mind cerebral cortex most composed of gray matter cell White matter Basal Nuclei deeper composed of tracts w myelinated axons islands of nuclei within white matter Cerebellum 2 hemis separated by longitudal fissure called vermis 2 parts thin superficial layer of gray matter Deeper white called arbor vitae Coordinates skeletal muscle contractions speacilizes in fine movements helps learn new movements and is most effected by alc intoxicaton Diencephalon important structure in it Thalamus relay center for all sensory info except smell to cerebral cortex Hypothalmus regulation of visceral activities and body fxns Emotions and instincts Secretes hormones Epithalmus contains the pineal gland which secretes the hormone melatonin Brainstem blends into the spinal cord Mid Brain o Corpora Quadrigemina pair of superior colliculi visual reflex and pair of inferior coliculi auditory reflex o Cerebral peduncles tracts in midbrain connects pons to cerebrum o Cerebral aqueduct pathway for cerebral spinal fluid Pons contains fiber tracts connecting the cerebrum to the
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