Nervous System Chapters 8 and 9

Homeostasis Review  Variables:  Set Point:  Normal Range:  Sensor:  Regulatory Center:  Effector:

System Functions  Sensory Input: Sensory receptors within the skin and internal organs respond to internal and external stimuli by generating nerve impulses that travel to the brain and spinal cord.  Integration: The brain and spinal cord sum up the impulses received from all over the body and send out nerve impulses.  Motor Output: The impulses from the brain and spinal cord go to the effectors, which are muscles and glands.

OrganizationOrganization

Nervous Tissue  All nervous tissue is composed of only two types of cells: ________________ and ____________________________.  Neurons vary in appearance, but all have 1) cell body, 2) dendrite, and 3) axon.  Neurolemmocyte (Schwann cell): specialized neuroglial cell of the PNS that creates myelin.

Types of Neurons  Motor: impulses from CNS to muscles or glands (mostly multipolar).  Sensory: impulses from sensory receptors to the CNS (many are unipolar).  Interneurons: impulses conducted within the CNS (often multipolar).

CNS  Gray matter: cell bodies and short nonmyelinated fibers.  White matter: contains myelinated axons that run together in bundles called tracts.  Meninges: membranes covering the brain and spinal cord. (dura mater (outermost), arachinod, pia mater (innermost)).  The subarachinod area is full of cerebrospinal fluid.

CNS: Spinal Cord  Extends from the base of the brain through the foramen magnum of the cranium.  It is protected by the vertebral column and is located in the vertebral foramen.  The spinal cord ends at L1.

CNS: Spinal Cord Anatomy  Central canal with gray matter surrounded by white matter.  The central canal contains cerebrospinal fluid.  Portions of sensory and motor neurons reside in the gray matter as do interneurons. The posterior root of a spinal nerve enters here and the anterior root (containing motor fibers) exits the gray matter.  Spinal nerves are created by the joining of these two roots (part of PNS).  White matter is made of ascending and descending tracts that take data to and from the brain. Because these tracts cross just after they enter or exit the brain, the right side of the brain controls the left side of the body and the left side of the brain controls the right side of the body.

CNS: Spinal Cord Function  Communication between the Brain and the PNS.  Example: hand touched  sensory fibers generate nerve impulses  passes through sensory neurons  spinal cord  ascending tract  brain.  Center for reflex arcs. A stimulus causes sensory receptors to generate nerve impulses through sensory nerves these go to interneurons that integrate the data and respond.

CNS - Brain  The brain is organized in ventricles. The Cerebrum is in the two lateral ventricles, the diencephalon is in the third ventricle, and the brain stem is in the fourth ventricle.  Cerebrum: largest portion; last to receive sensory input and integrate it before commanding voluntary motor response; coordinates other areas of the brain; and carries out higher thought processes, memory, language, speech, and learning.

More Brain  Diencephalon: hypothalamus, thalamus and the pineal gland. Thalamus receives all sensory input except smell. This area integrates this information and sends it to the appropriate area of the cerebrum.  Cerebellum: Receives sensory input from the eyes, ears, joints, and muscles about the position of body parts. It also receives information from the cerebral cortex as to where those parts should be located. Therefore it plays a role in posture, balance, and coordination.

Even More Brain  Brain stem: contains the midbrain, the pons, and the medulla oblongata. Midbrain – relay station for tracts Pons – contains bundles of axons traveling between the cerebellum and the rest of the CNS. Medulla Oblongata - contains a lot of reflex centers for controlling heartbeat, breathing, and vasoconstriction.

PNS  Composed of neurons and ganglia. Ganglia are swellings associated with nerves that contain collections of cell bodies.  Somatic division: serves the skin, skeleton, and tendons.  Autonomic division: regulates the activity of cardiac and smooth muscles and glands.

Types of PNS Nerves  Cranial: 12 pairs; many belong to the somatic division; includes the vagus nerve which has branches to most of the internal organs.  Spinal: 31 pairs; associated with the 3 regions of the vertebral column;

Somatic Division  Most actions are voluntary which means they originate in the cerebral cortex.  Others are reflexes: cranial (blinking) and spinal reflexes (hand on stove).

Autonomic Division  Sympathetic: most arise from the lower thoracic or lumbar region. Highly involved in the fight or flight reflex.  Parasympathetic: Craniosacral; promotes all the internal responses we associated with a relaxed state.  Commonalities: 1) they function automatically and usually involuntary, 2) they innervate all internal organs, and 3) they utilize 2 motor neurons and 1 ganglion for each impulse.

Nerve Impulses  Resting Potential: membrane is polarized (outside + inside -). The sodium potassium pumps are responsible for setting this up.  Action Potential: 1) depolarization (inside +); 2) repolarization (inside -).  If an axon is myelinated, the action potentials are stimulated between the nodes of Ranvier (faster potential) in non-myelinated it stimulates another part of the axomembrane.  All or None event. One way from cell body to axion terminal.

Transmission  Every axon terminates in an axon terminal. All of these lie close to a dendrite or the cell body of another neuron.  Pre-synaptic and Postsynaptic region. Between them is the Synaptic cleft.

Transmission  Transmission is carried out by molecules called neurotransmitters. These are stored in vesicles in the axon terminals.  Impulse reaches terminal  opens calcium channels  Calcium enters the terminal  vesicles move toward membrane for exocytosis  neurotransmitters are released and diffuse through synaptic cleft  neurotransmitters bind with receptors on postsynaptic membrane.  Depending on the neurotransmitter and receptor the response will be excitation or inhibition.

Integration  Neurons can have many dendrites and can synapse with many other neurons.  An excitatory NT produces a potential change called a signal. The signal drives the polarity of a neuron closer to an action potential. An inhibitory NT does the opposite.  Integration is the summing up of all of the excitatory and inhibitory signals. Which ever side wins determines if an Action Potential will be transmitted.