Nervous System PDF

The Nervous System  Functions of the Nervous System 1. Sensory input – gathering information To monitor changes occurring inside and outside the body (changes = stimuli) 2. Integration – to process and interpret sensory input and decide if action is needed. 3. Motor output A respons...

The Nervous System  Functions of the Nervous System 1. Sensory input – gathering information To monitor changes occurring inside and outside the body (changes = stimuli) 2. Integration – to process and interpret sensory input and decide if action is needed. 3. Motor output A response to integrated stimuli The response activates muscles or glands  Structural Classification of the Nervous System Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) Nerve outside the brain and spinal cord  Functional Classification of the Peripheral Nervous System Sensory (afferent) division Nerve fibers that carry information to the central nervous system Motor (efferent) division Nerve fibers that carry impulses away from the central nervous system Motor (efferent) division Two subdivisions Somatic nervous system = voluntary Autonomic nervous system = involuntary  Nervous Tissue: Support Cells (Neuroglia or Glia) Astrocytes Abundant, star-shaped cells Form barrier between capillaries and neurons Control the chemical environment of the brain (CNS) Microglia (CNS) Spider-like phagocytes Dispose of debris  Nervous Tissue: Support Cells Ependymal cells (CNS) Line cavities of the brain and spinal cor Circulate cerebrospinal fluid Oligodendrocytes (CNS) Produce myelin sheath around nerve fibers in the central nervous system  Neuroglia vs. Neurons Neuroglia divide. Neurons do not. Most brain tumors are “gliomas.” Most brain tumors involve the neuroglia cells, not the neurons. Consider the role of cell division in cancer!  Support Cells of the PNS Satellite cells Protect neuron cell bodies Schwann cells Form myelin sheath in the peripheral nervous system  Nervous Tissue: Neurons Neurons = nerve cells Cells specialized to transmit messages Major regions of neurons Cell body – nucleus and metabolic center of the cell Processes – fibers that extend from the cell body (dendrites and axons) Cell body, Nucleus, Large nucleolus  Neuron Anatomy Extensions outside the cell body Dendrites – conduct impulses toward the cell body Axons – conduct impulses away from the cell body (only 1!)  Axons and Nerve Impulses Axons end in axonal terminals Axonal terminals contain vesicles with neurotransmitters Axonal terminals are separated from the next neuron by a gap Synaptic cleft – gap between adjacent neurons Synapse – junction between nerves  Nerve Fiber Coverings Schwann cells – produce myelin sheaths in jelly-roll like fashion Nodes of Ranvier – gaps in myelin sheath along the axon  Clinical Application In Multiple Scleroses the myelin sheath is destroyed. The myelin sheath hardens to a tissue called the scleroses. This is considered an autoimmune disease. Why does MS appear to affect the muscles?  Neuron Cell Body Location Most are found in the central nervous system Gray matter – cell bodies and unmylenated fibers Nuclei – clusters of cell bodies within the white matter of the central nervous system Ganglia – collections of cell bodies outside the central nervous system  Functional Classification of Neurons Sensory (afferent) neurons Carry impulses from the sensory receptors Cutaneous sense organs Proprioceptors – detect stretch or tension Motor (efferent) neurons Carry impulses from the central nervous system Interneurons (association neurons) Found in neural pathways in the central nervous system, Connect sensory and motor neurons Structural Classification of Neurons Multipolar neurons – many extensions from the cell body  Structural Classification of Neurons Bipolar neurons – one axon and one dendrite Unipolar neurons – have a short single process leaving the cell body  How Neurons Function (Physiology) Irritability – ability to respond to stimuli Conductivity – ability to transmit an impulse The plasma membrane at rest is polarized Fewer positive ions are inside the cell than outside the cell  Continuation of the Nerve Impulse between Neurons Impulses are able to cross the synapse to another nerve Neurotransmitter is released from a nerve’s axon terminal The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter  The Reflex Arc Reflex – rapid, predictable, and involuntary responses to stimuli Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector  Types of Reflexes and Regulation Autonomic reflexes Smooth muscle regulation Heart and blood pressure regulation Regulation of glands Digestive system regulation Somatic reflexes Activation of skeletal muscles  Regions of the Brain Cerebral hemispheres Diencephalon Brain stem Cerebellum  Cerebral Hemispheres (Cerebrum) Paired (left and right) superior parts of the brain Include more than half of the brain mass The surface is made of ridges (gyri) and grooves (sulci)  Lobes of the Cerebrum Fissures (deep grooves) divide the cerebrum into lobes Surface lobes of the cerebrum Frontal lobe Parietal lobe Occipital lobe Temporal lobe  Specialized Areas of the Cerebrum Somatic sensory area – receives impulses from the body’s sensory receptors Primary motor area – sends impulses to skeletal muscles Broca’s area – involved in our ability to speak  Specialized Area of the Cerebrum Cerebral areas involved in special senses Gustatory area (taste) Visual area Auditory area Olfactory area  Specialized Area of the Cerebrum Interpretation areas of the cerebrum Speech/language region Language comprehension region General interpretation area  Layers of the Cerebrum Gray matter, Outer layer Composed mostly of neuron cell bodies  Layers of the Cerebrum White matter Fiber tracts inside the gray matter Example: corpus callosum connects hemispheres  Layers of the Cerebrum Basal nuclei – internal islands of gray matter Regulates voluntary motor activities by modifying info sent to the motor cortex Problems = ie unable to control muscles, spastic, jerky Involved in Huntington’s and Parkinson’s Disease  Diencephalon Sits on top of the brain stem Enclosed by the cerebral heispheres Made of three parts Thalamus Hypothalamus Epithalamus  Thalamus Surrounds the third ventricle The relay station for sensory impulses Transfers impulses to the correct part of the cortex for localization and interpretation  Hypothalamus Under the thalamus Important autonomic nervous system center Helps regulate body temperature Controls water balance Regulates metabolism  Hypothalamus An important part of the limbic system (emotions) The pituitary gland is attached to the hypothalamus  Epithalamus Forms the roof of the third ventricle Houses the pineal body (an endocrine gland) Includes the choroid plexus – forms cerebrospinal fluid  Brain Stem Attaches to the spinal cord Parts of the brain stem Midbrain Pons Medulla oblongata  Midbrain Mostly composed of tracts of nerve fibers Reflex centers for vision and hearing Cerebral aquaduct – 3rd-4th ventricles  Pons The bulging center part of the brain stem Mostly composed of fiber tracts Includes nuclei involved in the control of breathing  Medulla Oblongata The lowest part of the brain stem Merges into the spinal cord Includes important fiber tracts Contains important control centers Heart rate control Blood pressure regulation Breathing Swallowing Vomiting  Cerebellum Two hemispheres with convoluted surfaces Provides involuntary coordination of body movements  Protection of the Central Nervous System Scalp and skin Skull and vertebral column Meninges  Protection of the Central Nervous System Cerebrospinal fluid Blood brain barrier  Meninges Dura mater Double-layered external covering Periosteum – attached to surface of the skull Meningeal layer – outer covering of the brain Folds inward in several areas  Meninges Arachnoid layer Middle layer Web-like Pia mater Internal layer Clings to the surface of the brain  Cerebrospinal Fluid Similar to blood plasma composition Formed by the choroid plexus Forms a watery cushion to protect the brain Circulated in arachnoid space, ventricles, and central canal of the spinal cord  Spinal Cord Extends from the medulla oblongata to the region of T12 Below T12 is the cauda equina (a collection of spinal nerves) Enlargements occur in the cervical and lumbar regions  Spinal Cord Anatomy Exterior white mater – conduction tracts Internal gray matter - mostly cell bodies Dorsal (posterior) horns Anterior (ventral) horns Central canal filled with cerebrospinal fluid  Spinal Cord Anatomy Meninges cover the spinal cord Nerves leave at the level of each vertebrae Dorsal root Associated with the dorsal root ganglia – collections of cell bodies outside the central nervous system Ventral root  Peripheral Nervous System Nerves and ganglia outside the central nervous system Nerve = bundle of neuron fibers Neuron fibers are bundled by connective tissue  Classification of Nerves Mixed nerves – both sensory and motor fibers Afferent (sensory) nerves – carry impulses toward the CNS Efferent (motor) nerves – carry impulses away from the CNS  Spinal Nerves There is a pair of spinal nerves at the level of each vertebrae.