The nervous system

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The nervous system
2011-09-17 23:31:27
nervous system 17 11

The nervous system
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  1. Nervous system
    Allows for communication between cells through sensory input, integration of data and motor output
  2. 2 nervous cell types
    neurons and neuroglia
  3. Sensory
    takes impulses from sensory receptor to CNS
  4. Interneurons
    receive information in the CNS and send it to a motor neuron
  5. Motor
    takes impulses from the CNS to an effector (i.e. gland or muscle fiber)
  6. (Neuron structure)

    Cell Body
    main cell where organelles and nuclei reside
  7. (Neuron structure)

    many, short extensions that carry impulses to a cell body
  8. (Neuron structure)

    Axon (nerve fiber)
    single, long extension that carries impulses away from the cell body
  9. The myelin sheath
    A lipid covering on long axons that acts to increase the speed of nerve impulse conduction, insulation and regeneration in the PNS
  10. Schwann cells
    neuroglia that make up the myelin sheath in the PNS
  11. Nodes of Ranvier
    gaps between myelination on the axons
  12. Saltatory conduction
    conduction of the nerve impulse from node to node
  13. (The nerve impulse)

    Resting potential
    when the axon is not conducting a nerve impulse
  14. (The nerve impulse)

    Action potential
    rapid change in the axon membrane that allows a nerve impulse to occur

    • •Sodium gates open letting Na+ in
    • •Depolarization occurs
    • •Interior of axon loses negative charge (+40mV)

    • •Potassium
    • gates open letting K+ out
    • •Repolarization occurs
    • •Interior of axon regains negative charge (-65mV)
    • •Wave of depolarization/repolarization travels down the axon
    • •Resting potential is restored by moving potassium inside and sodium outside
  15. The synapse
    • A small gap between the sending neuron (presynaptic membrane) and the receiving neuron (postsynaptic membrane)
    • •Transmission is accomplished across this gap by a neurotransmitter (e.g. ACh, dopamine and
    • serotonin)
    • •Neurotransmitters are stored in synaptic vesicles in the axon terminals
  16. How does transmission across the synapse occur?
    • •Nerve impulse reaches the axon terminal
    • •Calcium ions enter the axon terminal that stimulate the synaptic vesicles to fuse with
    • the presynaptic membrane
    • •Neurotransmitters are released and diffuse across the synapse and bind with the postsynaptic membrane to inhibit or excite the neuron
  17. Synaptic integration
    • •Integration is the summation of the inhibitory and excitatory signals received by a postsynaptic neuron
    • •This occurs because a neuron receives many signals
  18. The nervous divisions
    • –Central
    • nervous system (CNS): Brain and spinal cord

    • –Peripheral
    • nervous system (PNS): Nerves and ganglia (cell bodies)
  19. The central nervous system
    •Consists of the brain and spinal cord
  20. the brain and spinal cord protected
    • •Bones – skull and
    • vertebral column

    •Meninges – 3 protective membranes that wrap around CNS

    • •Cerebral
    • spinal fluid (CSF)
    • – space between meninges is filled with this
    • fluid that cushions and protects the CNS
  21. the brain and spinal cord made up of 2 types of nervous tissue:
    • •Gray
    • matter – contains cell
    • bodies and nonmyelinated fibers

    • •White
    • matter – contains myelinated axons
  22. The CNS: Spinal cord
    • •Extends
    • from the base of the brain and along the length of the vertebral canal formed
    • by the vertebrae

    • •Functions
    • to provide communication between the brain and most of the body

    • •Center
    • for reflex arcs

    • •Gray
    • matter in the center is a butterfly shape

    • •White
    • matter surrounds the gray matter
  23. (The CNS: Brain)

    Four major parts:



    4.Brain stem
  24. The brain: Cerebrum
    •Cerebral hemisphere

    •Cerebral cortex

    •Primary motor and sensory areas of the cortex

    •Association areas

    •Processing centers

    •Central white matter
  25. 1. The brain: Cerebrum – the lobes
    • •Cerebrum
    • – largest portion of the brain
  26. (Cerebrum)
    •Divided into 5 lobes/hemispheres:
    • •Frontal
    • lobe: primary motor area
    • and conscious thought

    • •Temporal
    • lobe: primary auditory,
    • smell and speech area

    • •Parietal
    • lobe: primary somatosensory and taste area

    • •Occipital
    • lobe – primary visual area
  27. (Cerebrum)

    the cerebral cortex
    thin, outer layer of gray matter

    -Primary motor area – voluntary skeletal muscle

    -Primary somatosensory area – sensory information from skeletal muscle and skin

    -Association areas – integration occurs here

    • -Processing centers – perform higher level analytical
    • functions including Wernicke’s and Broca’s areas both involved in speech
  28. 2. The brain: Diencephalon´╗┐
    •Includes the:

    • •Hypothalamus –
    • helps maintain homeostasis (hunger, sleep, thirst, body temperature and water balance) and controls pituitary gland

    • •Thalamus –
    • 2 masses of gray matter that receive all sensory input except smell; involved in memory and emotions

    • •Pineal gland –
    • secretes melatonin that controls our daily rhythms
  29. 3. The brain: Cerebellum
    •Receives and integrates sensory input from the eyes, ears, joints and muscles about the current position of the body
  30. Cerebellum Functions
    •Maintains posture

    •Coordinates voluntary movement

    • •Allows learning of new motor skills (i.e. playing the
    • piano or hitting a baseball)
  31. 4. The brain: The brain stem

    • •Midbrain –
    • relay station between the cerebrum and spinal cord or cerebellum; reflex center

    • •Pons – a bridge between
    • cerebellum and the CNS; regulate breathing rate; reflex center for head
    • movements

    • •Medulla oblongata –
    • reflex centers for regulating breathing, heartbeat and blood pressure

    • •Reticular formation – major component of the reticular activating system
    • (RAS) that regulates alertness
  32. The limbic system
    • •Joins primitive emotions (i.e. fear, pleasure) with higher functions such as
    • reasoning

    • •Can cause strong emotional reactions to situations but conscious thought can
    • override and direct our behavior


    •Amygdala – has emotional overtones

    •Hippocampus – important to learning and memory
  33. Higher mental functions
    •Learning – what happens when we recall and use past memories

    •Memory – ability to hold a thought or to recall past events

    • •Short-term memory – retention of
    • information for only a few minutes

    • •Long-term memory – retention of
    • information for more than a few minutes and include the following:

    •Episodic memory – persons and events

    •Semantic memory – number and words

    •Skill memory – performing skilled motor activities (i.e. riding a bike)

    •Language – depends on semantic memory
  34. The peripheral nervous system (PNS)
    •Includes cranial (12 pr) and spinal nerves (31 pr) and ganglia outside the CNS

    -Spinal nerves conduct impulses to and from the spinal cord

    -Cranial nerves conduct impulses to and from the brain

    • •Divided into 2
    • systems:


  35. The PNS: Somatic division
    •Serves the skin, skeletal muscles and tendons

    •Automatic responses are called reflexes
  36. The PNS: Autonomic division
    • •Regulates the
    • activity of involuntary muscles (cardiac and smooth) and glands

    •Divided into 2 divisions:

    –Sympathetic: coordinates the body for the “fight or flight” response by speeding up metabolism, heart rate and breathing while slowing down and regulating other functions

    –Parasympathetic: counters the sympathetic system by bringing up a relaxed state by slowing down metabolism, heart rate and breathing and returning other functions to normal
  37. Drugs and drug abuse
    Both pharmaceuticals and illegal drugs have several basic modes of action:

    •Promote the action of a neurotransmitter

    •Interfere with or decrease the action of a neurotransmitter

    •Replace or mimic a neurotransmitter or neuromodulator

    •Most drug abusers take drugs that affect dopamine and thus artificially affect this reward circuit to the point they ignore basic physical needs in favor of the drug

    •Drug abusers tend to show a physiological and psychological effect

    •Once a person is physically dependent they usually need more of the drug for the same effect because their body has become tolerant
  38. Drug abuse: Alcohol
    • •Alcohol – a depressant
    • directly absorbed from the stomach and small intestine

    •Most socially accepted form of drug use

    •About 80% of college-aged people drink

    •Alcohol denatures proteins, causes damage to tissues such as the brain and liver; chronic consumption can damage the frontal lobe

    •High blood alcohol levels can lead poor judgment, loss of coordination or even coma and death
  39. Drug abuse: Nicotine and Cocaine
    •Nicotine – stimulant derived from tobacco plant

    • -Causes neurons to release dopamine that helps lead to
    • dependence

    –Adversely affects a developing embryo or fetus

    –Increases heart rate and blood pressure

    –Psychological and physiological dependency

    •Cocaine – stimulant derived from a plant

    • –Results
    • in a rush sensation (5-30 minutes) and an increased sex drive

    –Results in hyperactivity and little desire for food and sleep

    –Extreme physical dependence with this drug

    –“Crack” is a street name for cocaine that is processed to a free base for smoking
  40. Drug abuse: methamphetamine
    •Powder form is called speed and crystal form is called meth or ice

    •A stimulant that reverses the effects of fatigue and is a mood elevator

    •High agitation is common after the rush and can lead to violent behavior

    •Causes psychological dependency and hallucinations

    •“Ecstasy” is the street name for a drug that has the same effects as meth without the hallucinations
  41. Drug abuse: Heroin
    •Heroin: depressant from the sap of the opium poppy plant

    •Leads to a feeling of euphoria and no pain because it is delivered to the brain and is converted into morphine

    •Side effects are nausea, vomiting and depression of the respiratory and circulatory systems

    •Can lead to HIV, hepatitis and other infections due to shared needles

    •Extreme dependency
  42. Drug abuse and its use: Marijuana
    •Marijuana: psychoactive drug derived from a hemp plant called Cannabis

    •Most often smoked as a “joint”

    •Mild euphoria and brain damage

    •Alterations to vision and judgment as well as impaired motor coordination with slurred speech

    •Heavy users may experience depression, anxiety, hallucinations, paranoia and psychotic symptoms
  43. Bioethical focus: Medical Marijuana
    •Banned in the US in1937 but recently has been legalized in a few states for medical use in seriously ill patients.

    –Should marijuana be available to more patients? Why or why not?

    –Should people in states where it is legal for medical purposes to be prosecuted?

    –How should the use of medical marijuana be regulated?