ANP1106 Chapter 11 & 12: Nervous System (the Brain)

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ANP1106 C Dr. Jackie Carnegie & Dr. W Staines
Nervous System Ch 11 & 12 02.14.2017
Divided in two part anatomically:
1) Central Nervous System: brain and spinal cord; integrating and command center
2) Peripheral Nervous System: cranial and spinal nerves; communication btwn CNS and all parts of the body
a. Sensory division: somatic and visceral fibers; from receptors to CNS (afferent pathway); pain and
sensory receptors, also internal receptors for visceral organs
b. Motor division: motor nerve fibers from CNS to effectors (efferent pathway); to skeletal muscles,
target organs, glands, etc.
b1 Somatic ns: voluntary control of skeletal muscles (msg from CNS to skeletal muscles)
b2 Autonomic ns: involuntary, visceral motor, from CNS to cardiac and smooth muscle, glands
b2.1 Sympathetic division fight or flight response
b2.2 Parasympathetic division conserve energy at rest; housekeeping functions
Histology of Nervous Tissue Very cellular (cells are densely packed), minimal extracellular
matrix; 2 principal types of cells:
1) Supporting cells or neuroglia (6 types) neurons associate closely with smaller cells
In CNS (4 types):
a) Astrocytes star-shaped, most abundant; anchor neurons close to capillaries; roles in
nutrient exchange, antigen presentation, control of chemical environment (pick up
leaked K+ and recycle neurotransmitters)
b) Microglia protective, thinner branches, touch neurons to monitor well-being; can
transform into macrophages to engulf damaged neurons
c) Ependymal cells single layer of cells that line cavities of brain & spinal cord as
permeable barrier btwn CSF (cerebral spinal fluid) & fluid bathing cells of CNS, cilia
circulate CSF (ventricular sys) that cushions brain and spinal cord
d) Oligodendrocytes few branches, line up along thicker nerve fibers and wrap their processes tightly
around givers to provide myelin sheaths to the CNS neurons; neurons are shorter
than those in PNS, so one oligodendrocyte can make myelin sheaths for multiple
neurons in CNS
In PNS (2 types):
e) Satellite cells surround neuron cell bodies in ganglia; influence chemical
environment of these neurons (similar to what astrocytes do but in PNS)
f) Schwann cells form myelin sheaths around larger neurons in PNS, vital to
peripheral nerve cell regeneration; many Schwann cells on axons of neurons
2) Neurons conduct message via nerve impulses throughout body
Extreme longevity, amitotic a’t diide ad replace damaged neurons), high MR
(require constant supply of oxygen and glucose)
cell body protein and membrane-making machinery, part of receptive region;
dendrites type of neuron process, short on motor neurons, large SA on receptive regions, convey
incoming msgs via graded potential twd cell body; axon arise from hillock, conducting region, generate
impulse and transmits awy rom cell body, can be short or long; axon hillock cone-shaped part of cell
body, trigger zone for nerve impulse at junction of axon hillock and axon; terminal branches thousands
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of them at the end of axon; axonal terminals knob-like distal endings of terminal
branches, when impulse reaches here the neurotransmitters are released into EC space to
excite or inhibit neurons; myelin sheath white fatty protein protecting and electrically
insulating nerve fibers to increase speed of impulse; node of Ranvier - gaps btwn myelin
sheaths (btwn Schwaan cells), also where axon collaterals can branch
Structural Classification of neurons according to number of processes extending from cell body
Multipolar 3+ processes (1 axon and many dendrites); most abundant, major neuron
type in CNS to allow multiple paths to receive sensory info & coordinate motor info
o i.e Purkinje cell of cerebellum, pyramidal cell
Bipolar 2 processes (a dendrite and one axon on opposite sides of cell body); rare, found
in special organs (olfactory, mucosa, eye, ear)
Unipolar 1 process emerging from cell body that divides into T-shape for dendrites and axon; mainly in
PNS associated with sensory receptor; common in dorsal root ganglia of spinal cord and sensory ganglia of
cranial nerves
Functional Classification of Neurons according to direction the nerve impulse travels with respect to CNS
Sensory from sensory receptor toward CNS; primary, secondary, tertiary neurons
o Almost all primary sensory neurons are unipolar and their cells bodies are located in ganglia
outside CNS, except bipolar neurons in some special sense organs; often really long
o Higher order sensory neurons all multipolar and reside entirely within CNS conduction to
higher brain centers for interpretation
Motor carry impulse away from CNS to effector organs like muscle & glands; multipolar, most cell
bodies reside in CNS
Association (interneurons) btwn sensory and motor neurons, integration of info; multipolar, most
entirely within CNS, 99% of neurons of the body; variety of sizes and branching patterns
Central Nervous System Brain: complexity of wiring rather than size is what matters; damage to pathways of
communication in neurons
Regions and Organization:
1. cerebral hemispheres aware of movement; surfaces crease and fold into convolutions to increase
surface area for more neurons
2. diencephalon thalamus, hypothalamus, epithalamus not completely aware of something
3. brain stem midbrain, pons, medulla (corrective movements, automatic)
4. cerebellum
Basic pattern of CNS i.e Spinal cord has central cavity surrounded by gray matter (nonmyelinated
neuron cell bodies) and outer white matter (myelinated axons)
cerebrum and cerebellum have islands of gray matter (nuclei) within white matter as well as an outer
cortex of gray matter (outer bark of gray matter)
brain stem has additional regions of gray matter (basal nuclei) scattered within the white matter
Ventricles of Brain continuous with one another and with central cavity of spinal cord; filled with CSF and lined
with ependymal cells
paired lateral ventricles separated by narrow septum pellucidum
o each communicates with narrow 3rd ventricle in diencephalon via interventricular foramen
3rd ventricle is continuous with 4th ventricle (dorsal to pons) via cerebral aqueduct
through midbrain
4th ventricle continuous with central canal of spinal cord
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o 3 openings paired lateral apertures and median aperture connect
ventricles to subarachnoid space (fluid-filled space surrounding brain)
Cerebral Hemispheres superior part of brain, ~83% of brain mass; Lobes frontal,
parietal, occipital, temporal, and insula (deep in center of brain)
Gyri (ridges of folds) are separated by sulci (shallow grooves)
o longitudinal fissure divides the two hemispheres; transverse cerebral
fissure divides cerebral hemispheres from cerebellum below
o insular central sulcus separates frontal and parietal lobes;
precentral/postcentral gyrus are the bumps in front and behind central sulcus
o parieto-occipital sulcus separates parietal and occipital lobes; lateral sulcus separates temporal
lobe from frontal and parietal lobes
Cerebral Cortex allows us to perceive, communicate, remember, understand, appreciate, initiate voluntary
movements (conscious behaviour)
Composed of gray matter; cell bodies, dendrites, and unmyelinated axons; only 2-4 mm thick, but many
convolutions triple surface area
Brodmann areas numbered according to subtle differences in thickness, structure of contained neurons;
some areas link with particular functions (i.e area 17 where visual info needs to be brought to see), other
functions (memory and language) have overlapping domains, more diffusely organized
o 3 functional areas motor, sensory, and association; all are interneurons
o each hemisphere handles sensory and motor functions of collateral (opposite) side of body
stroke damage to area of right hemisphere paralyzes body muscles on left (only
voluntary movement lost; reflex contraction still possible)
o largely symmetrical but not 100% equal in function (lateralization specialization of cortical fncs)
o no functional area of cortex acts alone, all conscious behavior involves entire cortex in some way
a) motor areas: control voluntary movement, posterior part of frontal lobes
primary motor cortex precentral gyrus of frontal lobe of each hemisphere; pyramidal cells allow control
of skeletal muscles; long axons project to spinal cord as pyramidal/corticospinal tracts
o entire body represented spatially in primary motor cortex of each hemisphere (somatotopy)
o pyramidal cells that control foot movements are all in one place; areas that require most precise
motor control are in face, tongue, and hands have large regions
o motor innervation is contralateral (left hemisphere control right side of body)
o motor homunculus view of primary motor cortex = disproportionate miniman model
o individual pyramidal motor neurons control muscles that work together in a synergistic way to
perform a movement (impulse sent to more than one muscle)
no overlap btwn muscles involved in unrelated movements (i.e posture)
NOTE: Stroke damage to area of right hemisphere paralyzes body muscles on left only voluntary movement is
lost; reflexive contractions are still possible
premotor cortex anterior to precentral gyrus; helps plan movements by selecting and sequencing basic
motor movements into more complex tasks (i.e playing muscle instrument, keyboarding)
o coordinates movement of several muscle groups simultaneously/sequentially by sending
activating impulses to motor cortex; improves with practice
o control voluntary actions that depend on sensory feedback; i.e feeling for light switch in the dark
o damage to the area of premotor cortex will impair motor skill, but you can still perform the
movement (b/c primary motor cortex is fine), just have to reprogram the skill to another set of
premotor neurons with practice
Broca’s Area anterior-inferior part of premotor area; overlaps Brodmann areas 44 & 45; present in one
hemisphere only (usually left)
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