Review Sheet -- Exam 3 Bio 2212 Dr. Adams

NERVOUS SYSTEM/NERVOUS TISSUE -- One of two control systems (the other is
        endocrine) of the body; functional cells -- neurons

Three main functions:
    1.  Perception/sensation -- afferent (sensory) neurons
    2.  Integration -- association (inter-) neurons
    3.  Effecting a response -- efferent (motor) neurons; stimulate effectors º muscles, glands

Overview of Nervous System:

I. Central nervous system (CNS) -- Brain and spinal cord
II. Peripheral nervous system (PNS) -- Nerves and associated ganglia
        A. Sensory Division
        B. Motor Division
                1. Somatic (Voluntary) nervous system
                2. Autonomic (Involuntary) nervous system
                        a. Sympathetic subdivision
                        b. Parasympathetic subdivision

Cells of the NS:
1. Supporting (Glial) Cells
        a. CNS -- astrocytes, microglia, ependymal cells (associated with choroid plexuses),
                oligodendrocytes (myelin sheath); know functions
        b. PNS -- satellite cells (associated with unipolar sensory neuron cell bodies in dorsal 
            root ganglia [huh? Don=t worry, you=ll learn this!!]), Schwann cells (myelin sheath)
2. Neurons -- amitotic and therefore extreme longevity; high metabolic rate
        Cell body (soma), dendrites, axon/nerve fiber (with hillock, collaterals,  
            terminals, synaptic knobs) ; know functions of each region

    Also know nuclei, ganglia, tracts, nerves

Myelin Sheath -- multiple layers of phospholipid membrane, wrapped around axon (from
    oligodendrocytes [CNS] or Schwann cells [PNS]); neurilemma; nodes of Ranvier. Know
     importance.

Classification of neurons: Structural classification
    1.  Multipolar (many processes off cell body): all association and motor neurons
    2.  Bipolar (one dendrite/axon off cell body): unusual sensory neurons (olfactory, optic)
    3.  Unipolar neurons (one process off cell body): most sensory neurons

Neurophysiology: understand resting membrane potential, action potential (AP), threshold,
        chemically-regulated ion channels, voltage-regulated ion channels (on axons only), 
        resistance, current, polarization (de-, re-, hyper-). An   action potential  for an axon is 
        an all-or-none phenomenon -- if threshold is reached, an AP is generated.

Concepts:

• Stimulus intensity -- amplitude of AP cannot change; stronger stimuli result in more 
  frequent AP=s
• Refractory periods -- absolute/relative; know this concept.
• Conduction velocities -- influenced by axon diameter (largerºfaster) and myelin 
  sheath (presenceºfaster, through saltatory conduction)

Synapses: presynaptic/postsynaptic neurons (neuro- muscular/glandular junctions)
        Structural classification -- axodendritic/axosomatic common.
        Functional classification -- electrical/chemical.

I.  Electrical: cells directly connected by gap junctions (rare, but know example).
II.  Chemical: presynaptic neuron releases neurotransmitters (NT=s) which influences 
        postynaptic neuron=s membrane ion permeability (see "Action Potentials" section 
        under Muscles and Muscle Tissues, previous review sheet)
    Termination of NT effects: diffusion away from synaptic cleft, degradation by 
        postsynaptic membrane enzymes (as for Ach by acetylcholinesterase), reuptake 
        by presynaptic neuron (as for norepinephrine)

Postsynaptic potentials and Synaptic integration: involves summation of graded 
        potentials (pgs. 411 - 412)
    Graded potentials:  Excitatory (depolarizing) and Inhibitory (hyperpolarizing) 
        postsynaptic potentials
                EPSP=s -- typically involves NT opening Na+ gates
                IPSP=s -- typically involves NT opening either K+ or Cl- gates

    Summation of these graded potentials may lead to generation of an action potential 
        at the axon hillock
            Temporal and/or 
            Spatial summation -- may involve more than one presynaptic neuron

    Potentiation: important in memory storage; synapses that are frequently used become 
        easier to use. May involve some unusual NT=s (NO, CO) as well as indirect NT 
            stimulation (secondary messenger systems) -- see below.

Neurotransmitters -- effects are ultimately determined by the postsynaptic receptors
        Neurons typically contain more than one NT, released at different stimulation frequencies.

Classification by structure: know some functions of each NT listed, and where located in NS.

1. Acetylcholine
2. Biogenic Amines: norepinenphrine (epinephrine), serotonin
3. Peptides: endorphins/enkephalins
4. Novel NT=s:  NO, CO

Classification by function: excitation/inhibition -- determined by receptors
       Direct (opens ion channels) vs. indirect (acts through secondary messengers); the 
indirect effects may not change membrane polarity, but do change the activity inside the 
postsynaptic neuron. This could include the production of new receptors at the postsynaptic 
neuron=s receptive surface so that it may ultimately respond to NT=s that it had not been 
capable of responding to before.

Basic concepts of Neural Integration -- Know facilitation/discharge zones, neuronal pools.

        Circuits: diverging (amplifying), converging (concentrating), reverberating; most neurons 
            are involved in more than one type of circuit.
        Processing: serial (such as that involved in reflexes), and parallel. Typically, information 
            passage is rarely, if ever, solely serial.
____________________

Cerebral Hemispheres
  Cerebral Cortex (gray matter) - has sensory, association and motor areas, chiefly 
        concerned with input/output from/to the opposite side of the body. In other words, 
        control is typically contralateral. But remember, no part of brain works in isolation.
    Motor Areas: Know function/location of Primary Motor Cortex (precentral gyrus), 
        Premotor Cortex (an association area for motor function; helps control numerous 
        activities as once, particularly skill memories); all in frontal lobe.
    Sensory Areas: Know general function of Primary Somatosensory Cortex (postcentral
         gyrus) and its association area, and the primary cortex and association areas for the
         special senses (vision, hearing, olfaction, taste); in parietal, occipital and temporal
        lobes. Remember, olfactory sense deeply tied into sense of taste as well as with the
        limbic system (emotional brain; see discussion of rhinencephalon on page 436, 449).
    Association Areas: Prefrontal Area (most complex connections of all, involved in
         thought, reasoning, etc.); language areas; visceral association area (conscious
         awareness of visceral sensations - involves insular cortex); don=t forget association
        areas already mentioned.
    Lateralization of function: "Dominant" side is that hemisphere more concerned with
         language; varies from individual to individual. The "language dominant" hemisphere, 
        typically the left, also usually the logical/mathematical side. Other hemisphere, usually 
        the right, is the visual-spatial/creative/emotive/artistic side. Handedness typically 
        opposite side of dominant hemisphere (remember, control is mostly contralateral), 
        but not a one-to-one correspondence.

  White Matter -- myelinated tracts; know commissures, association tracts, projection
        (pyramidal) tracts. SEE "Lab Practical Structures to Know."
  Basal nuclei: Buried nuclei (gray matter) in cerebral hemispheres. Functions overlap those 
        of cerebellum somewhat. Particularly concerned with smooth control of repetitious 
        behavior (walking, for instance). Parkinson=s disease due to problems with basal 
        nuclei; results in tremors, irregular control of muscle function.

Diencephalon [SEE "Lab Practical Structures to Know."]
  Thalamus -- Gateway to cerebral cortex; virtually all motor or sensory pathways synapse 
        in nuclei of the thalamus. This means thalamus plays an extremely important role in
        refining/filtering sensory input/motor output.
  Hypothalamus (a neuroendocrine organ) -- Nuclei involved in numerous activities: ANS control
        limbic system center, T_B regulation, thirst/hunger centers, circadian rhythms, endocrine
        system function. Mammilary bodies (olfactory relays); infundibulum with pituitary gland      
  Epithalamus -- pineal gland (releases melatonin); choroid plexus (roof of third ventricle)
        for producing cerebrospinal fluid (CSF)

Brain Stem [SEE "Lab Practical Structures to Know."]; see also reticular formation, below.
  Midbrain -- cerebral aqueduct; cerebral peduncles (anterior; mostly white tracts going 
        to/from cerebral hemispheres). Superior (visual reflex) and inferior (auditory reflex) 
        colliculi; nuclei for cranial nerves III & IV.
  Pons -- large tracts; nuclei for cranial nerves V - VII; a respiratory nucleus.
  Medulla (Oblongata) -- nuclei for cranial nerves VIII - XII; ANS control nuclei; decussation 
        of pyramids. Overlap with hypothalamic functions? Easily explained -- hypothalamus 
        relays its commands through medullary nuclei.

Cerebellum -- concerned with helping control somatic motor functioning. Compares what brain is
        telling the body to do with what body is actually doing and makes appropriate adjustments.
    There are connections (cerebellar peduncles) between all three brain stem regions and 
        the cerebellum. Commands from cerebrum descend to body but also cross through 
        middle peduncles to cerebellum. Proprioceptive information from muscles/joints 
        ascends to cerebrum and also through inferior peduncles. Cerebellum compares the 
        information (what brain told body to do/what body actually did) and sends any 
        necessary adjustment information through superior peduncles to cerebrum. Particularly 
        important after nerve injury when body/brain need to be retrained to new connections.

Functional brain systems: diffuse but interconnected parts
    I. Limbic (emotions) -- Hypothalamus involved (with connections to ANS, explains
psychosomatic illnesses). Amygdala (basal nucleus anatomically) and hippocampus also
involved -- both of these structures intimately tied also to making memories. Don=t forget
olfactory connections as well -- smell memories rarely neutral; rapidly formed and hard to 
forget. Several other structures involved, and not clear how feelings actually form.
    II. Reticular formation (arousal/consciousness, but also a filter) -- Several brain stem 
loose nuclear clusters involved in sending a basal, steady stream of impulses to extensive 
areas of cerebrum and is involved in alertness. Sleep inhibits this system partially (though 
you can be aroused from sleep) and damage may irreversably affect this system, resulting
in coma. Also helps filter out most unimportant sensory inputs.

Higher Mental Functions – Brain Wave patterns (electroencephalograms -- EEGs)
    alpha, beta, theta, delta -- know normal activities and abnormal conditions typified by 
        the different brain waves

Sleep Cycles -- NREM and REM sleep; see fig. 12.19
    Begins with inhibition of RAS
        REM sleep: typified by rapid brain and dream activity, and partial arousal of RAS
    Patterns of sleep -- sleep cycles (NREM followed by REM) average 90 minutes (but 
        vary widely); as night progresses, each cycle increasingly predominated by REM 
    Serotonin, implicated as a sleep NT, levels rise in brain during sleep
    Importance of sleep unclear; people deprived of REM quickly exhibit personality problems
    Need for sleep declines a bit with age, with a long level period after puberty to early old age

Consciousness (Alertness) -- encompasses a large number of brain activities, clearly more
    than simply not sleep; understand fainting, coma, brain death. Some generalities are:
        1. Consciousness involves simultaneous activity of several areas of the cerebral cortex
        2. Consciousness is totally interconnected (follows from #1)
        3. Consciousness is superimposed on numerous other types of neural activity

Memory -- storage and retrieval of information; three principles:
        1. Memory occurs in stages
        2. Memory traces (engrams?) are widely distributed in the brain
        3. The hippocampus, amygdala, etc. play important, unique roles in memory processing
    Stages of memory:
        Short-term memory (STM) -- working memory; can hold seven or eight bits of
            information. Performs an important filtering function, as irrelevant info is lost.
        Long-term memory (LTM) -- seems to have limitless capacity. Info must pass
            through STM to get here. Takes some effort to get info in, and even then it can be
            lost (though retrieval is often the problem as opposed to info loss).
        Mechanisms for transferring STM to LTM -- heightened emotional state, rehearsal
            (repetition, practice), association within preexisting framework, automatic memory
            (unusual and not something that can be controlled)
        Even using above mechanisms, continued practice consolidates the memory within the
            framework of preexisting memories
    Categories of memory:
        Fact memory -- relatively easy to get in, also easier to forget. Associative mechanisms 
            used frequently, and remembered typically in context
        Skill memory -- acquired only through practice; difficult to establish, but once established
            difficult to lose the ability. Context typically not stored with skill
    Brain structures involved in memory: prefrontal (and premotor cortex for skill memories),
            cortical sensory areas, amygdala and hippocampus, diencephalon (thalamus and hypo-
            thalamus), basal forebrain. Know basic suggested network (see figure 12.21 and text
            on pgs. 457 - 458). Hippocampus and amygdala are crucial -- damage to
            both results in anterograde amnesia




    Mechanisms of memory: during memory (engram) storage,
        1. Neuronal RNA content is altered, which is consistent with . . .
        2. Unique extracellular proteins are deposited at synapses involved in LTM
            which suggest stimulatory capabilities not previously possible
        3. Dendritic spines change in shape
        4. Presynaptic terminals increase in size and number . . .
            . . . all of which means new connections
    Long term potentiation involved, and probably uses NO -- know general mechanism

Protection of the brain -- [SEE "Lab Practical Structures to Know."]
  Meninges -- Dura, arachnoid and pia maters; subdural and subarachnoid space.
         Know arachnoid villi/dural sinuses and their role in draining CSF.
  CSF -- in ventricles; central canal (of spinal cord); sudural/subarachnoid spaces. Similar 
        to plasma, but higher in Na⁺/lower in K⁺; pH also very precisely controlled. Choroid 
        plexuses form it, get it from blood. Contents able to be controlled strictly because of . . .
  Blood Brain Barrier -- continuous capillaries/feet of astrocytes; leaky only in hypothalamus
        (because?); causes problem with drugs intended to treat disorders of the brain (can=t 
        cross barrier). Small, non-polar molecules can still pass through.

The SPINAL CORD B [SEE "Lab Practical Structures to Know."]
  Meninges/spaces as above; plus fat-filled epidural space. Since dura not attached to
        inside of vertebrae, allows for much greater flexibility.  Spinal cord ends at L₁ (or L₂); 
        allows for sampling of CSF below L₂/epidural during labor.
    Know conus medullaris, filum terminale, cauda equina
  Enlargements -- cervical and lumbar (why? B Limbs!)

Rest of structures as on lab practical sheet.

Functional concepts:
  Gray matter: 

1. Anterior horns contain somatic motor nuclei 
2. Lateral horns contain autonomic motor nuclei.
3. Posterior horns contain synapses from peripheral sensory neurons.

  Ventral roots of spinal nerves therefore contain motor axons
  Dorsal roots contain sensory axons, with unipolar cell bodies in dorsal root ganglion
        Roots combine to form mixed spinal nerves

  White matter:
        Ascending (sensory) and descending (motor) tracts within the funiculi
        Most tracts consist of multi-neuron pathways and cross at some point; left and right 
            tracts are symmetrical both anatomically and functionally.

THE PERIPHERAL NERVOUS SYSTEM
    Receptors, Nerves (equivalent to tracts in CNS), Ganglia (Nuclei in CNS), (Effectors)

The Sensory Receptors -- Classification
    I. Stimulus type: mechano- (presso-, baro-); thermo-; photo-; chemo-; nociceptors
    II. Location: extero-, interoreceptors. Special intero- type -- proprioceptors.
    III. Complexity: simple and complex (complex are special senses, covered in chap. 15).
        Simple receptors: free dendritic endings (for example, associated with Merkel=s
        cells) and encapsulated endings (for example, Pacinian corpuscles). These are
        involved with sensing a variety of stimuli, but some are completely predictable:
                For example, muscle spindles, Golgi tendon organs, and joint kinesthetic 
        receptors are all involved in proprioception, an awareness of where your body parts
        are in relation to each other and the environment.

Nerves -- structured like muscles; fibers are axons; include blood vessels
    Epineurium (around entire nerve), perineurium (wraps fascicles), endoneurium.

  Regeneration of nerves -- distal portions of cut axons degenerate. Schwann cells, with 
myelin sheath tube/endoneurium remains to redirect regrowth of axons (at rate of @
1.5 mm/day); help with regrowth by releasing Growth Factors. Regrowth not precise; 
must retrain nervous system to deal with new connections.
    [CNS -- much less regeneration, as associated oligodendrocytes (and associated myelin 
sheath also degenerates)]

Cranial Nerves -- See "Cranial Nerves"  handout, and pages 492 - 500.
    Note that a few are purely sensory. Also note trigeminal is main sensory nerve of face, 
        while facial is the main motor nerve of face.

Spinal Nerves -- 31 pairs, emanating between vertebrae through intervertebral foramina.
         Eight cervical pairs (top pair between C₁ and occipital; bottom pair between C₇/T₁)
        Twelve thoracic pairs and five lumbar pairs, with pair emanating inferior to same 
            numbered vertebra.
        Five sacral pairs and one coccygeal pair.

    Ventral/dorsal roots combine to form nerve (see above); almost immediately after roots 
join, nerve branches. The branches (rami) include a tiny meningeal ramus, which reenters
vertebral column to innervate blood vessels/meninges; a small dorsal ramus, which innervates
muscle/skin at appropriate level immediately along vertebrae in back; and a large ventral  
ramus, responsible for innervating most everything else in front.
    Besides T₂ - T₁₂, whose ventral rami follow costae (ribs) around toward front and 
innervate at those levels directly, most ventral rami of spinal nerves "criss-cross"  in complex 
nerve plexuses, with terminal nerves involving neurons from several different roots/rami





[For each plexus, you need to know nerves involved and a main nerve or two of each]
Plexuses:
    1.  Cervical -- involves C₁ - C₅; many (of course) innervate neck, and also back of head, 
        but phrenic also a major branch (motor of diaphragm). Why phrenic from here?
    2.  Brachial (don=t forget cervical enlargement) -- involves C₅ - T₁; many innervate 
        different sections (muscle/skin) of arm. Axillary, median, radial, ulnar should be 
        somewhat obvious.
  Lumbosacral
    3.  Lumbar -- involves L₁ - L₄; femoral (anterior thigh), etc.
    4.  Sacral -- involves L₄ - S₄; sciatic (paired nerve and "largest" nerve in body), gluteal 
        branches, pudendal, etc.

Joints (Hilton's Law) and Dermatomes

Reflex Activity -- Simple, mainly serial, processing, at level of spinal cord for many.
        Components: receptor, sensory neuron, integration center, motor neuron, effector
        Know monosynaptic/polysynaptic; ipsilateral/contralateral
        Can be somatic or visceral; reflexes are protective in function.

  Types: for each, know simple connections and main objective of each reflex
        Stretch and Deep Tendon reflexes; Flexor and associated Crossed-Extensor reflex; 
        Superficial reflexes; doctors check reflexes to test integrity of associated nerves.