Nervous System Chapter 12 & 13
Fig 12-2 Organization of Nervous System A. Central Nervous System (CNS) - brain and spinal cord - integrating and command center of the nervous system B. Peripheral Nervous System (PNS) - part of nervous system that extends from the brain and spinal cord 1. cranial nerves : carry signals to and from the brain 2. spinal nerves: carry signals to and from the spinal cord
Pathways of CNS and PNS Somatic vs Autonomic – are categorized based on the efferent pathway SomaticAutonomic (“self governing”) -Voluntary -Involuntary -Carry impulse to skeletal muscles -Carry impulses to viseral organs and skin smooth, cardiac muscle and glands Parasympathetic – “resting & digesting” division. It over-sees digestion, elimination and glandular function (arise from brain and sacralregion) “rest and repair” Sympathetic – “fight, fright & flight” division. It prepares the body to cope with danger or excitement (arise from the thoracic and lumbar region) “fight or flight”
Neuron Functional Classification • Sensory neurons - or afferent neurons transmit impulses • toward the CNS from sensory receptors in the PNS. • (Sensory input/function) • Interneurons - or association neurons connect motor and • sensory neurons and are confined to the CNS. The processing • and interpreting of the sensory input to make decisions about • what should be done at the moment. • (Integrative function) • Motor neurons - or efferent neurons, carry impulses away • from the CNS to the effector organs, muscles or glands. • Most are multipolar. • (Motor output/function)
Example *Let’s say you are driving a car and you happen to come upon a red light (sensory input), your nervous system integrates this info (red light means “ and your foot goes for the brake (motor output). “
Nervous Tissue - made up of 2 main cells 1. Neurons / nerve cells: basic structural units of the nervous system and are specialized to react to physical and chemical changes in the environment. They conduct nerve impulses 2. Neuroglial cells / supporting cells: non- excitable cells that surround and wrap neurons (exp: Schwann cells)
Neuroglial Cells Glial cells - supporting cells of the CNS and PNS. They fill spaces, support neurons, provide structure, produce myelin, and carry on phagocytosis. Glia means “glue”
Neuroglial Cells Types of Glial Cells 1. Astrocytes - “star cells” are the most abundant. They are found between nervous tissue and blood vessels. Their function is to provide support, hold parts together, and regulate nutrients and ion concentrations. (BBB) *Responsible for scar tissue
Neuroglial Cells • Oligodendrocytes - they are arranged in rows along • nerve fibers and wrap their cell processes around the axons • of nerve fibers within the brain and spinal cord, producing • myelin sheaths. • http://www.myelin.org/ • 3. Microglia - are phagocytes of the CNS. They • engulf invading microorganisms and injured • or dead neurons. (smallest and least abundant)
Neuroglial Cells • Ependymal - form a simple epithelium that lines the • central cavity of the spinal cord and brain. Function in • producing and circulating fluid. (covers the ventricles • of the brain and the central canal of the spinal cord)
Neuroglial Cells • Schwann cells – found in the PNS, they provide • support for nerve fibers and sometimes form myelin • around them (neurilemma). • *Could be a possible treatment for nerve damage or even spinal cord injury.
THE NEURON Text : p348 Fig 12-4
Neuron Cell body - consists of a nucleus, nucleolus, cytoplasm, and various organelles. Neurofibrils - fine threads that extend into nerve fibers (cytoskeleton). Dendrites - nerve fibers that branch like the limb of a tree, function as receptive sites and conduct electrical signals toward the cell body. Nissel Bodies - lg clusters of RER and free ribosomes. They renew the membranes of the cell and the protein part of the cytosol which is needed for nerve transmission.
Neuron Neuron Axon - arises from the cone shaped region of the cell body called the axon hillock and then tapers to form a slender process that conducts nerve impulses away from the cell body. Schwann cells - tightly wrapped layers of cell membrane composed of a lipoprotein called myelin forming the myelin sheath around nerves found in the PNS. Neurilemma sheath surrounds the myelin sheath. Nodes of Ranvier - gaps in the myelin sheath between adjacent Schwann cells inc rate of impulse.
Fact: *tract – bundles of nerve fibers running through the CNS *nerves- bundles of nerve fibers running through the PNS *white matter – myelinated nerve fibers *gray matter – unmyelinated nerve fibers
P349 Fig 12-6 Neuron Structural Classification 1) Multipolar neurons - more than 2 processes or nerve fibers 2) Bipolar neurons - have 2 processes that extend from opposite sides of the cell body (ear, smell region of nose, retina of eye) 3) Unipolar neurons - have a short, single process that emerges from the cell body and divides like a “T” into 2 long branches
Bipolar Multipolar Unipolar
Propagation of Action Potential/ Nerve Impulse • Nerve cell is at resting membrane potential/polarized • due to the difference in ion concentration caused by • Na/K pump Nerve cell at rest has Na+ outside and K+ inside. RMP = -70 mV.
Propagation of Action Potential/ Nerve Impulse 2. Depolarized – stimulus causes Na+ ions to enter into the cell and RMP dec as the inside of the cell membrane becomes more (+) than the outside. Once threshold potential is reached (-59mV) the voltage gated Na+ channels open and the action potential/nerve impulse is propagated. The membrane potential rapidly changes to about +30mV
Propagation of Action Potential/ Nerve Impulse • Repolarization – at about +30 mV the voltage gated • Na+ channels close and the voltage gated K+ channels • open. K+ ions diffuse outward making the cell • membrane chgd again (back to RMP).
Propagation of Action Potential/ Nerve Impulse • Hyperpolarization- repolarization overshoots the • RMP when more K+ ions are released and • voltage moves to about -90 mV. This prevents • the neuron from receiving another stimulus, by • raising the threshold.
Propagation of Action Potential/Nerve Impulse 5. After hyperpolarization, the Na+/K+ pump eventually brings the membrane back to its resting state of -70 mV .
Nerve Impulse Harvard Action Potential Animation
Nerve Impulse • Read conduction of action potential on pg357 • Impulse Conduction - myelinated nerve fibers conduct • impulses at a faster rate then unmyelinated nerve fibers • greater diameter/surface area conducts/insulates better • gated ion channels are only found at the nodes…. • jumping vs walking (saltatory propagation) Unmyelinated = 1 m/s VS Myelinated = 100 m/s http://www.brainviews.com/abFiles/AniSalt.htm
Synapse and Synaptic Transmission Synapse - the junction between the axon of one neuron and the dendrite of another neuron or an axon and an effector organ. Presynaptic terminal / neuron - end of the axon postsynaptic membrane / neuron - the dendrite or the effector cell synaptic cleft - the space separating the presynaptic and postsynaptic neurons, or the gap in a synapse synaptic transmission - the process of an impulse cross- ing the gap at a synapse. Transmission across synapse
Synapse and Synaptic Transmission * Axons have several rounded structures called synaptic knobs that contain numerous membraneous sacs called synaptic vesicles that releaseneurotransmitters or molecules that transmit signals across a synapse. Fig 12-20 p359, Fig 12-21 p360 http://www.youtube.com/watch?v=LT3VKAr4roo&safe=active
Neurotransmitters Chemical substances that transmit signals/messages across a synapse A. Stimulatory - acetylcholine and norepinephrine cause increased postsynaptic membrane permeability to sodium ions. B. Inhibitory - dopamine, serotonin, and the amino acids GABA and glycine cause a decrease in membrane permeability to sodium ions.
Nerve Pathway Reflexes - rapid, automatic motor responses to stimuli. Reflex Arc - reflexes that are mediated by chains of neurons.
5 Basic Components of the Reflex Arc 1.Sensory receptor - the site where the stimulus acts (dendritic ending of a sensory neuron) 2. Afferent or sensory neuron - transmits a impulse from the receptor into the CNS. 3. Association / Interneuron - neurons located between sensory and motor neurons 4. Motor Neuron - conducts impulse from CNS to an effector neuron 5. Effector - the muscle or gland that responds to the efferent impulses by contracting or secreting. Fig 14-15 p430
General Anatomy of CNS A. Meninges - a group of 3 membranes that cover the brain and spinal cord. 1. Dura mater - outermost layer, it extends inward between lobes of the brain. 2. Arachnoid mater - a thin, weblike membrane that lacks blood vessels and is located between the dura and pia maters. 3. Pia mater - very thin and contains many nerves as well as blood vessels. p376 Fig 13-2
Spinal Cord Spinal cord - nerve column that extends from the brain into the vertebral canal and consists of 31 segments each giving rise to a pair of spinal nerves. The anterior median fissure and the posterior median sulcus divide the spinal cord into right and left halves…….Fig 13.6 p381 • Functions: • Conduct nerve impulses • Serve as a center for spinal reflexes
Spinal Cord 1. Gray matter - butterfly structure or “H” in center, it has posterior and anterior lateral horns. 2. White matter - surrounds the gray matter and is divided into 3 regions the anterior, lateral, and posterior funiculi which contain nerve tracts 3. Central canal - narrow canal that contains the cerebrospinal fluid. Nerve Tracts a) ascending tracts – conduct sensory impulses from body to the brain b) descending tracts – conduct motor impulses from brain to muscles and glands.
Posterior median sulcus Posterior funiculus Lateral funiculus Anterior Median fissure Anterior funiculus Spinal Reflexes – reflex arc passes through the spinal cord … pg 430, 432
Brain 3 Major parts -Cerebrum -Cerebellum -Brain Stem I. Cerebrum - largest, contains nerve centers associated with sensory and motor functions -cerebral hemispheres - 2 lg masses on either side -corpus callosum - connects the 2 hemispheres -convolutions or gyri - twisted ridges in the cerebrum -sulci - shallow groove -fissure- deep groove furrows
Brain *Lobes are named after the skull bones they lie under. 1) frontal lobe 2) parietal lobe (p391 Fig 13-13) 3) temporal lobe *Read about these!! 4) occipital lobe 5) insula - buried deep within the lateral fissure
Cerebrum p392 Fig 13-14, 13-15 -cerebral cortex - superficial gray matter that covers the cerebrum “conscious mind” -cerebral white matter - mass of white matter beneath the cerebral cortex. -basal/cerebral nuclei - several masses of gray matter deep in the white matter. Functions of Cerebrum 1. Interprets sensory impulses 2. Stores info and memory and uses it to reason 3. Determines a persons intelligence / personality
Cerebrum p393 13-16 Read over this section!! 1. Motor Areas - (frontal lobes) motor area of the right hemisphere controls muscles on the left side, concentration, drawing, problem solving, eye control, speech, concentration etc. Broca’s area - motor speech area, coordinates muscular actions of the mouth, tongue, and larynx Frontal Eye field - controls voluntary movements of the eyes and eyelids