Comparison of Somatic Motor and Autonomic Motor Pathway
Nerve
Lobes of Cerebral Hemisphere
Ventricles of Brain
Spinal Cord 2
Spinal Cord 1
Synapse
Myelinated Sheath
Action Potential
Path of Nerve Impulse
Myelin Sheath
Motor Neuron
Sensory Neuron
Neuroglia
Central Nervous System, "real"
Central Nervous System Labeled
Central Nervous System Chart
I. Overview of the Nervous System
II. The Central Nervous System
III. The Limbic System and Higher Mental Functions
IV. The Peripheral Nervous System
V. Drug Abuse
I. Overview of the Nervous System
A. Two major divisions:
1a. Central Nervous System: Brain and Spinal Cord, located midline of body.
2a. Peripheral Nervous System: The nerves. Lie outside of the CNS.
3a. Three functions of the Nervous System:
1. Receives sensory input. "Sensory receptors in skin and other organs respond to external and internal stimuli by generating nerve impulses that travel by was of the PNS to the CNS."
2. CNS performs "integration"- it takes the input from all over the body and summarizes it.
3. CNS creates "motor output"- the nerve impulses from the CNS go to the muscles and glands by way of the PNS. (Mader 248)
(Insert central nervous system chart picture / www.ling.mq.edu.au http://www.ling.mq.edu.au/ling/units/sph302/neuroling)
(Insert central nervous system labeled picture / www.flickr.com http://www.flickr.com/photos/rbjaneite/2219438029/)
(Insert central nervous system "real" picture / www.flickr.com http://www.flickr.com/photos/57368254@N00/142842721/)
B. Nervous Tissue
1b. Contains two types of cells: Neurons (cells that transmit nerve impulses between the parts of the nervous system; these are the main cells of the nervous system)(Frolich PowerPoint Slide 9)and (Mader 249), and Neuroglia (support and nourish the neurons.)
(Insert Neuroglia picture / www.afh.bio.br / http://www.afh.bio.br/nervoso/nervoso2.asp)
- Neurons transmit the messages, while the axon carries the message.
- "Dendrites connect to other cells, usually neurons or muscle cells." A single cell can connect to thousands of others through these dendrites.
- Most neurons do not divide or die, so they last a lifetime! (Frolich PowerPoint Slides 2 and 9).
C. Neuron Structure: There are three types of neurons.
1c. Sensory Neuron: Takes nerve impulses (messages) from a sensory receptor (special structures that detect changes in the environment) to the CNS. (Mader 249) Sensory Neurons- action potential brings message to brain or spinal cord with sensory input information from sensory receptors. (Frolich PowerPoint Slide 20)
- They are bundled in the nerves.
- Bring in information from almost every tissue, organ, and body structure (except brain and spinal cord.) (Frolich PowerPoint Slide 12)
(Insert Sensory Neuron picture / science.kennesaw.edu http://science.kennesaw.edu/~jdirnber/Bio2108/Lecture/LecPhysio/PhysioNervous.html)
2c. Interneuron: Lies entirely within the CNS. Can receive information from the sensory neurons and from other interneurons in the CNS. Then, they sum up all the nerve impulses they have gotten from these neurons and communicate with motor neurons.
3c. Motor Neuron: Takes nerve impulses away from the CNS (brain or spinal cord) to an effector (muscle fiber or gland). (Mader 249)
- Also bundled in nerves.
- Bring information to every muscle and gland, including blood vessels. (Frolich PowerPoint Slide 12)
* All neurons use the same methods to transmit nerve impulses along neurons and across synapses. (Mader Text Website Chapter 13 Review)
- Effectors carry out our responses to environmental changes, internal or external._
(Insert Motor neuron picture / www.nicksnowden.net / http://www.nicksnowden.net/Module_4pages/ions_nerves_and_muscles.htm)
4c. All neurons have 3 parts:
1. Cell Body: Contains nucleus and other organelles.
2. Dendrites: Many short extensions that receive signals from sensory receptors or other neurons. These signals can result in nerve impulses are are then conducted by an axon.
3. Axon: Portion of a neuron that conducts nerve impulses. When present in nerves, it is called a nerve fiber.
D. Myelin Sheath: A protective covering on axons. (Mader 249)
- A single neuron has hundreds or thousands of axons,and each axon is surrounded by the myelin sheath. (Frolich PowerPoint Slide 10)
1d. In PNS, the myelin sheath is formed by a type of neuroglia called Schwann cells, which contain myelin (a lipid substance) in their plasma membranes. Myelin sheath develops when the Schwann cells wrap themselves around an axon many times. The sheath is broken in places because each neuroglia cell covers only a portion of the axon. These gaps are called nodes of Ranvier.
2d. Long axons have a myelin sheath, short do not.
3d. In the CNS, white matter is white because of the myelin sheath, and gray matter is gray because it does not have myelinated axons.
4d. In the PNS, myelin makes nerve fibers appear white and glistening, and also serves as insulation. Also plays important part in nerve regeneration. Serves as a passageway for new fiber growth when an axon is severed.
(Insert Myelin Sheath picture / Frolich PowerPoint Slide 11)
2d. In the CNS, oligodendrocytes cover the axons.
3d. Disorders: Multiple Sclerosis (an attack on the myelin by the body's immune system), and Leukodystrophies (caused by loss of myelin from axons.) (Mader 249)
E. Nerve Impulses: Convey information within the nervous system. 1e. voltmeter measures the potential difference between two sides of the axonal membrane, which allows us to study the nerve impulse.
(Insert nerve impulse picture / www.phschool.com http://www.phschool.com/atschool/science_activity_library/path_nerve_impulse.html)
2e. Resting Potential: The axon is NOT conducting an impulse. Voltmeter records a membrane potential of approx. -65mV (millivolts). This implies that the inside of the neuron is more negative than the outside. (Mader 250)
- Happens in thousands of a second, and constantly maintains resting state for all neurons and muscle cells so they are ready to “fire”." (Frolich PowerPoint Slide 13)
- During resting potential, there are more sodium ions (Na+)outside the axon than inside, and the concentration of potassium ions (K+) is greater inside the axon than outside.
- The sodium potassium pump is responsible for the unequal distribution of these ions, because it actively trnaports sodium out of and potassium into the axon across the membrane.
- Membrane is permeable to K+ ions but not Na+ ions, so there are always more positive ions outside the membrane than inside. (Mader 250)
3e. Action Potential: "Ability to sense environment, process information rapidly and respond requires rapid transmission of messages within body." (Frolich PowerPoint Slide 8)
4e. It is a rapid change in polarity across an axonal membrane as the nerve impulse occurs.
- Threshold: The level of depolarization that occurs from a stimulus to the axonal membrane. This is when the action potential occurs. Requires two types of gated channel proteins that open to allow Na+ and K+ to pass through the membrane. (Mader 250)
- "Gates” are actually protein structures in cell membrane. (Frolich PowerPoint Slide 15)
- When an action potential occurs, the gates of sodium channels open first, and Na+ flows into the axon. As Na+ moves inside the axon, the membrane potential goes from -65 mV to +40 mV. This is called depolarization because the charge insde the axon goes from netative to positive.
- Next, the gates of potassium channels open, and K+ flows outside the axon. As this occurs, the action potential changes from +40 mV back to -65 mV, and is called repolarization because the inside of the axon resumes a negative charge as the K+ exits.
- After an action potential has passed, the sodium potassium pump restores the resting potential by moving the K+ back to the inside and Na+ back to the outside. (Mader 250-251)
- "Voltage change from negative resting potential to positive action potential and back to negative resting potential can all happen within 3/1000 of a second." (Frolich PowerPoint Slide 17)
(Insert Action Potential picture / Frolich PowerPoint Slide 15)
F. Propagation of an Action Potential: Self-propagating: Each action potential generates another along the length of the axon.
1f. If an axon is unmyelinated, the action potential at one locale stimulates an adjacent part of the axon's membrane to produce an action potential.
- In myelinated axons, an action potential at one Ranvier node causes an action potential at the next node, and this type of conduction is called saltatory conduction, because the nerve impulse jumps from node to node. (Mader 251) Simply stated, "action potential can jump to nodes where cell membrane is exposed". "It saves energy (so entire membrane doesn’t depolarize) and makes action potential move faster". (Frolich PowerPoint Slide 16)
- In myelinated axons, the nerve impulse is more than 100 m / second, compared to 1.0 m/ second in thin, unmyelinated axons.
(Insert Myelinated Sheath picture / www.neuropathologyweb.org http://www.neuropathologyweb.org/chapter1/chapter1cOligodendroglia.html)
2f. Refractory Period: Occurs immediately after an impulse has passed by each successive portion of an axon. During this period, the sodium gates are unable to open, and therefore, the action potential cannot move backward and instead moved down an axon toward its branches. (Mader 251)
G. The Synapse
1g. Axon Terminal: The small swelling on the tips of axon branches. Each of these terminals lies close to either the dendrite or the cell body of another neuron. This region of close proximity is called a synapse.
2g. Synaptic cleft: At the synapse, the synaptic cleft separates the sending neuron from the receiving neuron.
3g. Neurotransmitters: Since nerve impulses are unable to jump the synaptic cleft, neurotransmitters carry the impulse across a synapse. They are stored in synaptic vesicles in the axon terminals.
- Three steps: 1st, Nerve impulses traveling along an axon reach an axon termimal. 2nd, Calcium ions enter the terminal and stimulate synaptic vesicles to merge with the sending membrane, and 3rd, neurotransmitter molecules are released into the synaptic cleft, and they spread across the cleft to the receiving membrane, where they bind with receptor proteins. This initiates a response. Once finished, the neurotransmitter is removed from the cleft.
4g. Receiving neuron can be excitation or inhibition: in excitation, the sodium gate opens and sodium diffuses into the receiving neuron. An excitatory neurotransmitter produces a potential change called a signal that drives the neuron closer to an action potential. In inhibition, potassium enters the receiving neuron. Produces a signal that drives the neuron farther from an action potential (Mader 252)
(Insert Synapse picture / www.epilepsy.com / http://www.epilepsy.com/epilepsy/brain.html)
5g. Neurotransmitter Molecules: Many drugs that affect the nervous system act by interfering with the action of neurotransmitters.
- Drugs can enhance or block the release of a neurotransmitter, mimic the action of it, block the receptor, or interfere with the removal of neurotranmitters from a synaptic cleft.
6g. Synaptic Integration: The summing up of excitatory and inhibitory signals in the dendrite and cell body of postsynaptic neuron. (Mader 253)
II. The Central Nervous System
A. The Spinal Cord and Brain:
- Protected by bone.
- Spinal cord is surrounded by vertebrae.
- Brain is enclosed in skull.
- Both are wrapped in protective membranes called meninges.
- Spaces between the meninges are filled with cerebrospinal fluid, to cushion and protect the CNS. This fluid is also found within the ventricles of the brain and in the central canal of the spinal cord.
- Brain has four ventricles, which are chamgers that connect with one another and produce and serve as a reservoir for cerebrospinal fluid.
1a. This is where sensory information is received and motor control is initiated.
2a. CNS is made up of two types of nervous tissue: gray matter (contains cell bodies and short, nonmyelinated fibers)and white matter (contains myelinated axons that run together in bundles called tracts.
B. The Spinal Cord: extends from base of brain through a large opening in skull (foramen magnum) and into the vertebral canal formed by openings in the vertebrae.
1b. Structure: Cross section shows a central canal, gray matter, and white matter. - Individual vertebra protects the spinal cord.
- Spinal nerves project from the cord between the vertebrae that make up the vertebral column.
- Intervertebral disks separate the vertabrae.
- Central canal contains cerebrospinal fluid, just like the meninges that protect the spinal cord.
- Gray matter: centrally located, shape of H. This is where parts of sensory neurons, interneurons, and motor neurons are found.
- Dorsal root has sensory vibers entering the gray matter.
- Ventral root has motor fibers exiting gray matter.
- Both roots join before the spinal nerve leaves the vertebral canal as a mixed nerve.
- White matter occurs in areas around the gray matter. Contains tracts that both take info to the brain, and tracts taking info away from brain.
- Left side of brain controls right side of body, and right side of brain controls left side of body. (Mader 254)
C. Functions of Spinal Cord: Provides communication between brain and peripheral nerves that leave the cord. Ex. Something touches your hand, sensory receptors generate nerve impulses that go through sensory fibers to the spinal cord and up ascending tracts to the brain.
1c. Gate Control Theory of Pain: Suggests that the tracts in the spinal cord have "gates", which control the flow of pain messages from the peripheral nerves to the brain. Endorphins can temporarily block pain messages.
2c. Brain initiates voluntarily control over our limbs. Motor impulses that originate in the brain pass down tracts to the spinal cord and out to our muscles by way of motor fibers.
3c. Spinal cord is center for thousands of reflex arcs.
- Stimulus causes sensory receptors to generate nerve impulses that travel in sensory axons to the spinal cord.
- Interneurons integrate the data that comes to them and relay signals to motor neurons.
- Motor axons respond to the stimulus by causing skeletal muscles to contract.
(Mader 255)
- Ex. Spinal cord reflex:
- Sensory neurons action potential bring in pain information from skin.
- Neurons of spinal cord process information, take decision.
- Motor neurons carry output to muscles to move limb away from pain.
(Frolich PowerPoint Slide 21)
(Insert Spinal Cord pictures / www.ee.umd.edu / http://www.ee.umd.edu/courses/enee719v.S2002/figures/funfigs.html) & ( http://www.uhseast.com/153912.cfm http://www.uhseast.com/153912.cfm)
D. The Brain
1d. 4 Ventricles: Two lateral ventricles (associated with cerebrum), the third ventricle (associated with diencephalon), and the fourth ventricle (associated with brain stem and cerebellum). (Mader 256)
(Insert Ventricles of Brain picture /universe-review.ca / http://universe-review.ca/option2.htm )
2d. The Cerebrum: (AKA telencephalon)makes up the largest portion of the brain in humans. Last to receive sensory input and carry out integration before commanding voluntary motor responses. Communicates with and coordinates activities of other parts of brain.
3d. Cerebral Hemispheres: Two halves of brain, called left and right cerebral hemispheres, divided by the longitudinal fissure.
- Each hemisphere is divided into lobes by sulcus. (Frontal lobe, parietal lobe, occipital lobe, temporal lobe... and each is associated with particular functions.)
4d. Cerebral Cortex: Thin layer of gray matter covering the cerebral hemispheres. Accounts for sensation, voluntary movement, and all thought processes when awake.
5d. Primary Motor and Sensory Areas of Cortex:
- Primary Motor Area: Frontal lobe, before central sulcus. Begins voluntary commands to skeletal muscles. Each part of body is controlled by a certain section.
- Primary Somatosensory Area: Just dorsal to central sulcus in parietal lobe. Sensory info from skin and skeletal muscles arrives here, where each part of body is represented sequentially.
(Insert Lobes of Cerebral Hemisphere picture / www.indiana.edu / http://www.indiana.edu/~p1013447/dictionary/cer_hemi.htm)
6d. Association Areas: Places where integration occurs.
7d. Processing Centers: In cortex. Receive info from other association areas and performs higher-level analytical functions.
- Prefrontal Area: Association area in frontal lobe, receives info from other association areas and uses it to reason and plan our actions. Integration in this area accounts for critical thinking and formulating appropriate behaviors.
- Wernicke's area and Broca's area: Two processing centers located in left cerbral cortex only. Wernicke's helps us understand written and spoken word and sends info to Broca's area. Broca's helps with grammatical function and directs primary motor area to stimulate appropriate muscles for speaking and writing.
8d. Central White Matter: Composes much of the rest of the cerebrum.
E. The Diencephalon: Region that encircles the third ventricle. Hypothalamus and thalamus are located here.
- Hypothalamus: Forms floor of third ventricle. An integrating center that helps maintain homeostasis by regulating sleep, hunger, thirst, body temp, and water balance. Controls pituitary gland and is the link between the nervous and endocrine systems.
- Thalamus: Two masses of gray matter that are in the sides and roof of third ventricle. Receives all sensory input except smell. Involved in arousal of cerebrum, and is involved with higher mental functions like memory and emotions.
F. The Cerebellum: Under occipital lobe of cerbrum, separated from brain stem by fourth ventricle.
- Made up of two portions, each composed of white matter.
- Receives sensory input from eyes, ears, joints, and muscles about position of body parts.
- Receives motor output from cerebral cortex about where parts should be located.
- After integration, cerebellum sends motor impulses by way of brain stem to skeletal muscles. Thus, maintains posture and balance. Ensures that muscles work together for voluntary movements.
G. The Brain Stem: Contains the midbrain, pons, and medulla oblongata.
1g. Midbrain: Relay station for tracts passing between cerebrum and spinal cord or cerebellum. - Reflex centers for visual, auditory, and tactile responses.
2g. Pons: "Bridge". Contains bundles of axons traveling between cerebellum and rest of CNS.
- Helps medulla oblongata regulate breathing rate and has reflex centers associated with head movements in response to stimuli.
3g. Medulla Oblongata: Has a number of reflex centers for regulating heartbeat, breathing, and blood pressure. Also contains the reflex centers for vomiting, coughing, sneezing, hiccuping, and swallowing.
- Lies superior to spinal cord.
H. Reticular Formation: Complex network of nuclei (masses of gray matter) and fibers that extend the length of brain stem. Receives sensory signals and sends them up to higher center, and motor signals, which it sends to spinal cord. (Mader 258-259)
III. The Limbic System and Higher Mental Functions: Intimately involved in our emotions and higher mental functions.
A. Linked structures in cerebrum that is a functional grouping rather than anatomical.
- Blends primitive emotions and higher mental functions.
1a. Amygdala: Within limbic system. Can cause experiences to have emotional overtones, and it creates the sensation of fear.
2a. Hippocampus: Plays crucial role in learning and memory. Information gateway during learning process.
B. Higher Mental Functions:
1b. Memory:
- Short-term memory: Prefrontal area. Lies dorsal to forehead.
- Long-term memory: Mixture of semantic memory (numbers, words, etc.) and episodic memory (persons, events, etc.)
- Skill memory: Involved in performing motor activities like riding a skateboard. All motor areas of cerebrum below the level of consciousness.
C. Long-Term Memory Storage and Retrieval: Long-term memory stores in bits and pieces throughout sensory association areas of cerebral cortex.
D. Long-Term Potentiation: Involved in memory storage. Occurs when synapses are used intensively for a short period of time, and they release more neurotransmitters. (Mader 260-261)
IV. The Peripheral Nervous System
A. Lies outside central nervous system, and contains the nerves. When they come from brain, they are cranial nerves. From spinal cord, they are spinal nerves.
- All nerves take impulses to and from the CNS. All are composed of axons, the long part of neurons.
(Insert Nerve picture / fig.cox.miami.edu / http://fig.cox.miami.edu/~lfarmer/BIL265)
1a. Humans have 12 pairs of cranial nerves attached to brain. Some are sensory, some are motor, and others are mixed nerves that have both sensory and motor fibers.
- Cranial nerves are most concerned with head, neck and facial regions.
2a. Spinal nerves: 31 pairs from either side of spinal cord.
- Roots separate the axons of sensory neurons from axons of motor neurons.
- Dorsal Root Ganglion: Cell body of a sensory neuron. Ganglion: Collection of cell bodies outside the CNS.
- All spinal nerves are mixed nerves, and each spinal nerve serves the particular region of the body.
B. Somatic System: These nerves serve the skin, skeletal muscles, and tendons.
- Some nerves take sensory info from external sensory receptors to the CNS and motor commands away from it to the skeletal muscles.
- In somatic system, some responses to stimulus are not voluntary, but automatic. These are called reflexes.
C. The Reflex Arc: The path of a reflex.
- A series of responses occur when interneurons carry nerve impulses to the brain.
- The brain makes you aware of the stimulus and directs other reactions to it. In fact, you don't even feel pain until the brain receives and interprets info.
D. Autonomic System: Also in PNS. Regulates the activity of cardiac and smooth muscles and glands.
- Divided into the sympathetic and parasympathetic divisions. Activation of these two systems generally causes opposite responses.
- Both have different functions, but also similarities: Both function automatically and in an involuntary manner, they innervate all internal organs, and they utilize two neurons and one ganglion for each impulse.
1d. Sympathetic Division: Most arise from the middle of the spinal cord and almost immediately terminate in ganglia that are near the cord.
- In this division, the preganglionic fiber is short, and the postganglionic fiber that makes contact with an organ is long.(Mader 264-265)
- Important in emergency situations: Speed up (“fight or flight”) response. (Frolich PowerPoint Slide 22)
2d. Parasympathetic Division: Includes a few cranial nerves and fibers that come from the bottom (sacral) portion of the spinal cord.
-Pregangliotic fiber is long, and the postganglionic fiber is short because the ganglia lie near or within the organ.
- Promotes all internal responses we associate with a relaxed state. (Mader 265) "Slow down (“meditative”) response". (Frolich PowerPoint Slide 22) (The "rest and digest" system.)
(Insert Comparison of Somatic Motor and Autonomic Motor Pathway picture / Frolich PowerPoint Slide 22)
E. Degenerative Brain Disorders
1e. Alzheimer Disease: Characterized by loss of memory. Usually occurs in those over 65. Abnormal neurons are present throughout the brain but mostly in hippocampus and amygdala. Neurons end up dying.
2e. Parkinson Disease: Gradual loss of memory control. Wide-eyed, unblinking expression, involuntary tremors of fingers, muscular rigidity, and a shuffle. (Mader 266)
V. Drug Abuse
A. Drugs affect nervous system in two general affects:
- Affecting the limbic system,
- Either promote or decrease the action of a particular neurotransmitter.
- Stimulants: increase likelihood of neuron excitation.
- Depressants: decrease likelihood of neuron excitation.
B. Drug Abuse: Taking a drug at a dose level and under circumstances that increase the potential for a harmful effect. Psychological and physical dependence.
C. Alcohol: Readily crosses cell membranes.
- Causes damage to several tissues and vital organs. Liver can become scarred and impaired. Can damage frontal lobe of brain, decrease overall brain size, and increase size of ventricles. Brain damage, coma and death can occur if blood alcohol level is extremely high.(Mader 267)
D. Nicotine: small molecule, stimulant. Rapidly deliverd to CNS, especially midbrain. Binds to neurons in CNS, it increases skeletal muscle activity, heart rate, and blood pressure. Highly addictive.
E. Cocaine: Stimulant that interferes with the "re-uptake of dopamine at synapses". Highly addictive. Results in sleeplessness, lack of appetite, increased sex drive, tremors, and "cocaine psychosis", which is like paranoid schizophrenia. Can result in cardiac and /or respiratory arrest, and death.
F. Methamphetamine: Synthetic. Stimulant. Reverses effects of fatigue, maintains wakefulness, and elevates the mood of the user. Can lead to amphetamine psychosis resulting in paranoia, hallucinations, aggressive behavior.
G. Heroin: From sap of opium poppy. Highly addictive depressent. Pain-killing effects. Depress breathing, block pain pathways, cloud mental function, and can cause nausea and vomiting.
H. Marijuana: Mild euphoria, alterationsin vision and judgment. Hallucinations, anxiety, depression, rapid flow of ideas, body image distortions, paranoia, and psychotic symptoms can result. (Mader 268-269)
No comments:
Post a Comment