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Nervous system


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    • 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)
  • 3.
    • 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;
  • 4.
        • 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
  • 5.
      • the nervous system is made up of two principal types of cells:
          • Supporting Cells
          • Neurons
      • 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;
  • 6.
        • 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;
  • 7.
      • 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;
  • 8.
      • 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;
    • Clusters of neuron cell bodies in the CNS are called NUCLEI;
    • Small collections of cell bodies in the PNS are called GANGLIA;
  • 9.
    • 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;
  • 10.
    • 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;
  • 11.
    • 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;
  • 12.
      • 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
  • 13.
    • 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;
  • 14.
    • 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;
  • 15.
    • 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;
  • 16.
    • 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;
  • 17.
    • 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;
  • 18.
    • Parts of Brainstem:
    • Midbrain – contains the cerebral aqueduct of Sylvius;
      • contains nuclei that act as reflex centers involved with vision and hearing;
  • 19.
    • 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;
  • 20.
    • 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;
  • 21.
    • 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;
    • 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;
  • 23.
    • 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;
  • 24.
        • 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;
  • 25.
    • SUBARACHNOID SPACE (space between the arachnoid and pia mater)
  • 26.
      • 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;
  • 27.
      • 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;
  • 28.
    • 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;
  • 29.
    • 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;
  • 30.
      • 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;
  • 31.
      • 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
      • 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);
  • 32.
    • 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!”
  • 33.
      • 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;
  • 34.
    • 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
  • 35.
          • 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;
  • 36.
      • 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;
  • 37.