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Nervous system
 

Nervous system

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    Nervous system Nervous system Presentation Transcript

    • NERVOUS SYSTEM
    • NERVOUS SYSTEM
      • is the master controlling and communicating system of the body; works with other organ system;
      • electrical impulses which act as signaling device and as a means of communicating with body cells are specific and cause an immediate response;
      • three overlapping functions:
          • monitor changes occurring both inside and outside the body (stimuli); the gathered input is called SENSORY INPUT;
          • it process and interprets the sensory input and decides on the input (INTEGRATION)
          • it effects a response by activating muscles or glands (MOTOR OUTPUT)
      • Structural Classifications:
        • Central Nervous System (CNS) – consists of the brain and spinal cord;
        • Peripheral Nervous System (PNS) – outside the CNS; consists of the spinal nerves and cranial nerves
      • Functional Classification: (concerned only with PNS structures)
        • Sensory or Afferent division – consists of nerves that convey impulses to the CNS from sensory receptors located in various parts of the body;
          • Sensory fibers delivering impulses from the skin, skeletal muscles, and joints are called SOMATIC SENSORY FIBERS;
          • Sensory fibers transmitting impulses from the visceral organs are called VISCERAL SENSORY FIBERS;
        • 2. Motor or Efferent division – carries impulses from the CNS to the effector organs, the muscles and glands;
          • Somatic Nervous System – allows conscious or voluntary control of our movements;
          • Autonomic Nervous System – regulates events that are involuntary; such as the activity of smooth and cardiac muscles and glands;
              • Sympathetic NS
              • Parasympathetic NS
      • STRUCTURE AND FUNCTIONS
        • the nervous system is made up of two principal types of cells:
            • Supporting Cells
            • Neurons
      • SUPPORTING CELLS
        • these cells in the CNS are lumped together as NEUROGLIA ;
        • generally made up of cells that support, insulate, and protect the delicate neurons;
        • types of neuroglia:
          • Astrocytes – most abundant; form a living barrier between capillaries and neurons; play a role in making exchanges between the capillaries and neurons;
          • 2. Microglia – are phagocytes that dispose of debris (dead brain cells, bacteria, etc.)
          • 3. Ependymal cells – line the cavities of the brain and spinal cord; their beating cilia helps circulate CSF and forms a protective cushion around the CNS;
          • 4. Oligodendrocytes – forms myelin sheath around the nerve fibers in the CNS ;
      • Supporting Cells in the PNS comes in two major forms:
          • Schwann Cells – form myelin sheath around the nerve fibers in the PNS ;
          • Satellite Cells – act as protective, cushioning cells;
      • NEURONS
        • also called nerve cells ;
        • are the functional unit of the nervous system;
        • are highly specialized to transmit nerve impulses from one part of the body to another;
        • parts:
          • Cell Body – contains the nucleus and is the metabolic center of the cell;
          • Dendrites – neuron processes that conduct nerve impulses toward the cell body;
          • Axons – processes that conduct nerve impulses away from the cell body;
        • most long nerve fibers are covered with a whitish, fatty material, called MYELIN;
            • also protects and insulates the fibers and increases the transmission rate of nerve impulses;
            • most axons are wrapped with myelin called MYELIN SHEATH;
            • MULTIPLE SCLEROSIS
      • Clusters of neuron cell bodies in the CNS are called NUCLEI;
      • Small collections of cell bodies in the PNS are called GANGLIA;
      • Functional Classification of a Neuron:
        • Sensory / Afferent Neurons – carrying impulses from the sensory receptors to the CNS;
        • Motor / Efferent Neurons – carrying impulses from the CNS to the viscera and/or muscles and glands;
        • Interneurons – connect the motor and sensory neurons;
      • Structural Classification of Neurons (based on the no. of processes)
        • Multipolar Neurons – several processes; most common structural type;
        • Bipolar Neurons – contain two processes, an axon and a dendrite;
        • Unipolar Neurons – contain a single neuronal process;
      • Neurons have two major functional properties:
        • Irritability – ability to respond to a stimulus and convert it to a nerve impulse;
        • Conductivity – ability to transmit the impulse to other neurons, muscles, or glands;
      • REFLEXES – are rapid, predictable, and involuntary response to stimuli;
          • Occur over neural pathways called REFLEX ARC (a complete circuit consisting of a sensory neuron ending in the spinal cord, connecting neuron within the cord, and a motor neuron to a muscle );
          • Autonomic Reflexes regulate the activity of smooth muscles, the heart, and glands; ex. Salivary and Pupillary reflex
          • Somatic Reflexes includes all reflexes that stimulate the skeletal muscles;
      • CENTRAL NERVOUS SYSTEM
        • originates in the NEURAL TUBE ;
        • is the part enclosed by bone or the cranium;
        • it includes the BRAIN and the SPINAL CORD;
        • the chambers of the brain are called VENTRICLES (filled with cerebrospinal fluid )
        • Four Major Parts:
          • Cerebrum
          • Diencephalon
          • Brainstem
          • Cerebellum
      • Anatomy of the Brain
        • the brain is the largest and most complex mass of nervous tissue in the body;
      • Four major regions of the brain:
      • Cerebral Hemispheres (cerebrum)
        • are paired superior part of the brain;
        • enclose and obscure most of the brain stem;
        • Gyri – elevated ridges of tissue on the surface of the cerebral hemispheres;
        • Sulci – hollow grooves that separates the gyri;
        • The cerebral hemispheres are separated by a single deep fissure called the LONGITUDINAL FISSURE;
      • Lobes of the brain:
        • Parietal Lobe – area for somatic sensory;
        • Frontal Lobe – area for motor movement;
        • Occipital Lobe – area for vision;
        • Temporal Lobe – auditory and olfactory area;
      • A specialized area that is involved in our ability to speak is called BROCA’S AREA;
      • Areas involved in higher intellectual reasoning and language comprehension is called WERNICKE’S AREA;
      • Layers of cell bodies of Neurons:
        • Gray Matter – outermost layer; functional area;
        • White Matter – deeper layer; composed of fibers tracts carrying impulses to or from the cortex; form tracts or bundles that connect two parts of the cerebrum to other parts of the brain.
      • The cerebral hemispheres are connected by one large fiber tract called CORPUS CALLOSUM;
      • 2. Diencephalon
        • Or interbrain;
        • Sits atop the brainstem and is enclosed by the cerebral hemispheres;
        • Major structures:
            • Thalamus – encloses the third ventricle , is a relay station for sensory impulses passing upward to the sensory cortex;
            • Hypothalamus – forms the floor of the third ventricle; is an important autonomic NS center because it plays a role in regulation of body temperature, water balance, and metabolism; also secretes oxytocin and ADH;
      • 3. Brainstem
        • Is found on the lower part of the brain hidden by the cerebral hemispheres;
        • Provides a pathway for ascending and descending tracts;
        • Their nuclei form the cranial nerves and control vital activities such as breathing and BP;
        • RETICULAR FORMATION – is a diffuse mass that extends in the entire length of the brainstem;
      • Parts of Brainstem:
      • Midbrain – contains the cerebral aqueduct of Sylvius;
        • contains nuclei that act as reflex centers involved with vision and hearing;
      • Parts of Brainstem…..
      • 2. Pons – rounded structure that protrudes below the midbrain;
        • contains many fiber tracts;
        • involved in control of breathing;
        • also contains nuclei of several cranial nerves;
      • Parts of Brainstem…
      • 3. Medulla Oblongata – is the most inferior part of the brainstem;
        • also an important fiber tract area;
        • Also contains nuclei that regulate vital visceral functions;
        • Contains centers that control heart rate, BP, breathing, swallowing, and vomiting;
      • 4. Cerebellum
        • Is a large, cauliflowerlike structure that projects dorsally from under the occipital lobe of the cerebrum;
        • Provides the precise timing or good coordination of skeletal muscle activity and controls our balance, posture, and equilibrium;
        • Ataxia means clumsy, disorganized movements when the cerebellum is injured;
    • PROTECTION OF THE CNS
      • because of the delicate nature of the neurons, the body provides many protective structures to protect them:
          • Skull
          • Vertebral Column
          • Meninges – this are three connective tissue membranes that covers and protect the CNS;
              • The outermost layer (DURA MATER) is a double-layered membrane that surrounds the brain;
              • The middle meningeal layer is the weblike ARACHNOID MATER;
              • The innermost layer is the PIA MATER which clings tightly to the surface of the brain and spinal cord;
      • The FALX CEREBRI is the fold of dura mater that passes transversely across the upper end of the posterior cranial fossa in the transverse fissure;
        • also separates the occipital lobe of the cerebrum from the upper surface of the cerebellum;
      • The SUBARACHNOID SPACE is filled with CSF;
      • ARACHNOID VILLI absorb CSF into the venous blood;
      • MENINGITIS – inflammation of the meninges;
      • ENCEPHALITIS – inflammation of the brain;
          • 4. Cerebrospinal Fluid (CSF)
            • Is a watery broth similar to blood plasma;
            • Formed by the CHOROID PLEXUS;
            • Is found in and around the brain and spinal cord which forms a watery cushion that protects these fragile structures against blows and trauma;
      • EPIDURAL SPACE – is the interval between the dura mater and cranial bones ; in the SPINE, it is the space between the dura mater and the vertebral canal;
      • SUBDURAL SPACE – is the interval between the arachnoid and dura mater of the brain or the spinal cord;
      • FLOW OF CSF
      • CHOROID PLEXUS
      • LATERAL VENTRICLES
      • FORAMEN OF MONROE
      • THIRD VENTRICLE
      • AQUEDUCT OF SYLVIUS
      • FOURTH VENTRICLE
      • FORAMEN OF MAGENDIE AND LUSCHKA
      • SUBARACHNOID SPACE (space between the arachnoid and pia mater)
      • ARACHNOID VILLI DURAL SINUSES VENOUS SYSTEM
      • THE BLOOD BRAIN BARRIER
        • the brain is very dependent on a constant environment;
        • separates the neurons from blood-borne substances;
        • composed of least permeable capillaries in the body;
        • water-soluble substances like water, glucose, and essential amino acids pass easily;
        • is virtually useless against fats, respiratory gases, and other fat-soluble molecules that diffuse easily thru all the plasma membranes;
      • SPINAL CORD
        • is a glistening white continuation of the brainstem;
        • provides a two-way conduction pathway to and from the brain;
        • enclosed within the vertebral or spinal column;
        • extends from the FORAMEN MAGNUM of the skull to the 1st or 2nd lumbar vertebra;
        • it is protected and cushioned by meninges;
      • In humans, 31 pairs of spinal nerves arise from the cord;
      • Collection of spinal nerves at the inferior end of the vertebral canal is called CAUDA EQUINA;
      • the gray matter of the spinal cord is H-shaped and is found more interior;
      • the two posterior projections are the DORSAL or POSTERIOR HORNS for sensory functions;
      • the two anterior projections are the VENTRAL or ANTERIOR HORNS for motor function of the somatic nervous system (voluntary);
      • the LATERAL HORN is a bulge on each limb of gray substance in the thoracic and upper lumbar segments;
      • the gray matter surrounds the central canal of the cord which contains the CSF;
      • PLEXUSES:
        • Cervical Plexus – on each side of the body is made up of the ventral divisions of the C1-C4;
              • Supplies the skin and muscles of the scalp, neck, and part of the face;
              • The PHRENIC NERVE originates from this plexus;
        • Brachial Plexus – formed by C5-T1; lies posterior to the clavicle;
              • Supplies the shoulder and upper limb;
        • Lumbar Plexus – formed by L1-L4; lies in the posterior abdomen in the area of the psoas muscle; supplies the FEMORAL NERVE;
        • Sacral Plexus – formed by L4-S3; located within the pelvis on the posterolateral wall; the largest branch is the SCIATIC NERVE;
      • PERIPHERAL NERVOUS SYSTEM
        • consists of nerves and scattered groups of neuronal cell bodies found outside the CNS;
      • A. NERVES
        • Is a bundle of neuron fibers found outside the CNS;
          • Afferent / Sensory Nerve
          • Efferent / Motor Nerve
      • B. CRANIAL NERVES (CN)
        • arise directly from the base of the brain (brainstem), and are not associated with the spinal cord;
        • The 12 pairs primarily serve the head and neck except for the CN X (vagus) which extends to the thoracic and abdominal cavities;
        • most cranial nerves are mixed (both motor and sensory function);
        • “ OOOTTAFAGVAH”
      • CN I – olfactory n. II – optic n.
      • III – oculomotor n. IV – trochlear n.
      • V – trigeminal n.
      • VI – abducens n. VII – facial n.
      • VIII – auditory n.
      • IX – glossopharyngeal n X – vagus n.
      • XI – spinal
      • accessory n.
      • XII – hypoglossal n.
      “ Pls. read your book!”
      • AUTONOMIC NERVOUS SYSTEM
        • is the motor subdivision of the PNS that controls body activities automatically;
        • regulates cardiac muscle activity, smooth muscle contraction, and secretion of exocrine glands;
        • has a chain of two motor neurons:
          • Preganglionic axons – axons before the ganglion; leaves the CNS to synapse with the second motor neuron in a ganglion outside the CNS;
          • Postganglionic axons – the axon extends to the organ it serves;
      • two divisions (usually they are antagonistic)
          • Sympathetic NS (thoracolumbar division) – is often called the “fight-or-flight” system;
            • Controls body functions that are essential for survival;
            • Effects:
              • Increases heart rate
              • Increases BP
              • Bronchial dilation
              • Decreases peristalsis
              • Dilated pupils
            • Parasympathetic NS (craniosacral division)
              • is most active when the body is at rest and not threatened in any way;
              • Concerned with normal body functions, usually opposite the SNS;
      • BLOOD SUPPLY OF THE BRAIN:
        • the brain is supplied by a specialized form of blood vessels called the CIRCLE OF WILLIS;
        • Arteries that supply the brain:
          • internal carotid artery – branch of the common carotid artery;
          • vertebral artery – branch of the subclavian artery;
          • middle meningeal artery – branch of the external carotid artery;
    •