Download BIOL 2402 Lecture Outline Chapter 5

5.1
Chapter 5 - Central Nervous System
I. systems that protect the CNS
A. cerebrospinal fluid (CSF)
1. formed by selective transport across ependymal cells
2. volume is 125-150 ml and is replaced > 3 times/day
3. flow maintained by 10 mmHg pressure gradient between ventricles and
dural sinuses
4. path: ventricles  subarachnoid space (review from anatomy)
5. reabsorbed into blood in dural sinuses through arachnoid villi
6. functions are to:
a. “float” the brain
b. control brain tissue fluid composition
c. cushion brain during normal head movements
B. blood-brain barrier
1. role of capillary endothelial cells:
a. tight junctions
b. restriction of membrane transport
2. role of astrocytes
a. induce formation of tight junctions
b. help control transcellular transport
3. membrane transport restrictions
a. materials that diffuse cannot be restricted (O2, CO2, alcohol,
steroids, H2O)
b. materials that require carrier transport are restricted (glucose,
amino acids, and ions)
c. materials that cannot pass (many drugs, amino acids, and ions)
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5.2
4. functions of the blood-brain barrier
a. protects NS from chemical fluctuations
b. prevents entry of harmful substances and microbes
c. prevents entry of molecules that would act as neurotransmitters
5. some areas of the brain do not have a blood-brain barrier (part of
hypothalamus)
II. brain functions
A. cerebrum (cortex, tracts, basal nuclei)
1. functional areas of the cortex
 sensory areas
 motor areas
 association areas
a. spatial representation / somatotopy
 somatosensory cortex  primary motor cortex size of area and number of neurons for each body area is
proportional to precision and complexity of movement
of that part
b. linking of cortical regions
primary sensory areas
higher sensory areas
association areas
higher motor area
primary motor cortex
c. language
visual and auditory cortex parietal-occipital-temporal association cortex
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5.3
Wernicke’s area Broca’s area primary motor cortex -
B. cerebellum
1. vestibulocerebellum 2. spinocerebellum  receives input concerning desired action from motor cortex
 receives input concerning actual action from proprioceptors,
vestibular apparatus, eyes
 compares inputs and sends corrective signals to motor tracts
3. cerebrocerebellum -
C. integrated brain functions
1. sleep-wake cycles
a. how do we get to sleep?
alertness is maintained by constant reciprocal stimulation
between the cerebral cortex and the reticular
activating system
the RAS is constantly stimulated by sensory input and input
from the cerebrum
to get to sleep you have to interrupt that stimulation
this involves signals from the slow wave (NREM) “sleep-on”
neurons, which receive directions from the biological
clock (suprachiasmatic nucleus)
b. what happens while we are asleep?
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5.4
we alternate between periods of slow wave (non rapid eye
movement or NREM) sleep and paradoxical (rapid
eye movement or REM) sleep
each full cycle lasts about 90 minutes, and in each
successive cycle the amount of paradoxical/REM
sleep increases
paradoxical sleep involves low muscle tone, increased
cortical activity, and dreaming
switching between slow wave/NREM and paradoxical/REM
is controlled by paradoxical/REM “sleep-on” neurons
c. how do we wake up?
the RAS receives internal or external stimuli
it then sends excitatory signals to the cortex, which returns
to normal alertness and reciprocal stimulation with the
RAS
2. memory = "storage of acquired knowledge for later recall"
a. short term memory
characteristics:
 seconds to hours
 limited capacity
 may be consolidated into long term memory
mechanisms:
 temporary modifications of synaptic function  changes in ion channels in the axon terminals
 presynaptic facilitation (cAMP)
 long-term potentiation
glutamate
AMPA receptors – generate EPSPs
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5.5
NMDA receptors –
open Ca channels
second messenger formation
increases # AMPA receptors
release of nitric oxide (NO)
acts on presynaptic neuron to increase
neurotransmitter release
b. long term memory
characteristics:
 days to years
 unlimited capacity
mechanisms:
 permanent physical changes in the brain
 formation of new synapses between existing neurons
 increased dendritic surface area
 increase in neurotransmitter receptors
 changes in neurotransmitter synthesis
c.
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consolidation is affected by:
amount of rehearsal
pre-existing “hook” (association of new & old data)
level of excitement/importance of information
CREB/CREB2
d. memory is processed in the:
hippocampus and medial temporal lobe
short term memory and consolidation
declarative memory (facts)
requires conscious recall
cerebellum
motor skill memories (procedural)
subconscious recall
prefrontal cortex
working memory –processes new and retrieved information
temporary storage
problem solving, planning, organizing
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5.6
III. spinal reflexes
reflex = automatic, predictable, unlearned and rapid motor response to a stimulus
A. reflex arc pathway has 5 components:
1. receptor - monitors environment & produces action potentials
2. afferent pathway carries signals from receptor to CNS
3. integrating center = one or more synapses in CNS that process the
information from the receptor
4. efferent pathway carries impulses from CNS to effector
5. effector (organ) - produces reflex response (contraction or secretion)
a. somatic vs autonomic
b. ipsilateral vs contralateral
c. reciprocal innervation in somatic reflexes
B. stretch reflexes
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monitor amount of stretch in skeletal muscles
cause contraction in the muscle to counteract stretch
1. receptor
2. integrating center
3. effector
example:
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5.7
C. flexor/withdrawal reflex - protects body from damage
1. receptor
2. integrating center
3. effector
response:
D. crossed-extensor reflex
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may occur at same time as flexor reflex but never alone
shares afferent pathway and part of integrating center with flexor
reflex
1. receptor
2. integrating center
3. effector
response:
E. Golgi tendon - protects muscles from damage
1. receptor
2. integrating center
3. effector
response:
BIOL 2305/Strong/Spring 2007