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
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.
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)
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
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.
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;
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.
Be aware that a portion of the information you need to know for Chapters 12 & 13 is on the
"Lab Practical -- Structures to Know" Handouts
THE CENTRAL NERVOUS SYSTEM -- Brain and Spinal Cord
The BRAIN: regions include the cerebrum, diencephalon, brain stem, and cerebellum.
As your "Nervous System Structures -- To know" handout includes the names of the parts
you are to know, this review sheet will concentrate on functions.
Diencephalon [SEE "Lab Practical Structures to
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.
Cerebellum -- concerned with helping control somatic motor functioning. Compares what brain
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.
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
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
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]
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
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.