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Nervous system notes
Chapter 9
I.
Introduction
A.
Functions of the nervous system
1.
monitoring body==sensory
2.
processing info==integrative
3.
initiate a response==motor
4.
homeostasis==maintaining balanced internal environment
5.
organs=brain, spinal cord, nerves, sensory organs
II.
Divisions of the nervous system
A.
Central nervous system
1.
Brain and spinal cord
2.
All sensory impulses travel to here, all motor responses originate here
B.
Peripheral nervous system
1.
Organs
a.
Cranial nerves
b.
Spinal nerves
2.
Somatic
a.
Sensory organs of skin, head,
b.
Motor nerves to skeletal muscle
c.
Voluntary control
3.
Autonomic
a.
Motor nerves to visceral organs, blood vessels, glands
b.
Sympathetic--respond to stress
c.
Parasympathetic-normal functioning
III.
Nerve tissue
A.
Neuroglia-support cells
B.
1.
2.
Astrocytes--brain and s.c. =anchor for neurons, aid in
Impulse conduction
3.
Microglia-brain and s.c.==phagocytosis of dead tissue, microorganisms
4.
Oligodendrocyte-brain and s.c.==insulate cns w/ myelin sheath
5.
Ependymal cavities of cns==circulate cerebrospinal fluid
6.
Schwann-large nerves of pns==insulate pns
Neuron
1.
Structure--cell body, dendrites, axon
a.
Cell body=nucleus and other organelles
b.
Dendrites=branching extensions from cell body, conduct messages
toward cell body
c.
Axon=conducts impulses away from cell body, one per cell
d.
Myelinated vs. Unmyelinated
(1). Myelin sheath=fatty material that insulates and nourishes axon
(2).
(3).
IV.
(a).
Node of ranvier-gaps between schwann cells
White matter =presence of myelin sheath
Grey matter= lack of myelin sheath
2.
Types of neurons
a.
Structural differences
(1). Multipolar=many dendrites , one axon
(2). Bipolar=single dendrite, axon
(3). Unipolar=single nerve fiber, one to cns(axon) , one to pns
(dendrite), skin receptors
b.
Functional differences
(1). Sensory (afferent) from pns to cns, unipolar
(2). Association (interneurons), in cns link neurons, multipolar
(3). Motor (efferent), carry impulses away from cns multipolar
3.
Function
a.
Resting potential=separation of charges by a membrane
(1). Mainly na And k+ outside, na/k pump, cl-inside
(2). About -70 millivolts
b.
Action potential=rapid depolarization of plasma membrane followed by
repolarization as moving ions restore resting potential==nerve impulse
p.247
c.
Conduction of impulse=wave of ionic reversals as impulse travels
down neuron
(1). Myelin sheath==a.p. Jumps from node to node, saltatory
conduction, faster than unmyelinated (300m/s)
d.
All or none=like muscle fibers, stimulus must be a certain threshold
e.
Transmission cell to cell==synaptic end bulb, synaptic vesicles w/
neurotransmitters, cross synaptic cleft
f.
Excitatory vs. Inhibitory=depends on neurotransmitter, some increase
na permeability, others increase cl-
g.
Processing at the synapse=a.p. Depends on sum of excitatory and
inhibitory messages on the postsynaptic membrane
The cns
A.
Spinal cord
1.
Protective coverings
2.
Structure
a.
Grey matter
b.
White matter
3.
Functions
a.
Conduction pathways
b.
Reflex center
(1). Reflex arc
(2). Somatic and visceral reflexes
B.
The brain
1.
Protective coverings
2.
3.
4.
5.
6.
7.
8.
V.
Cerebrospinal fluid and the ventricles of the brain
a.
Ventricles
b.
Csf production and circulation
Cerebrum
Diencephalon
a.
Thalamus
b.
Hypothalamus
Mid brain
Pons
Medulla oblongata
Cerebellum
Peripheral nervous system
A.
Function-- communication link between cns and body
1.
Consists of nerves, sensory receptors, and ganglia
2.
Divided into somatic and autonomic systems
B.
Organs of the pns
1.
Nerves and ganglia
a.
Nerve--composed of bundles of nerve fibers surrounded by c.t. Sheath
(1). Epineurium
(2). Perineurium
(3). Endoneurium
b.
Types of nerves
(1). Afferent--sensory function
(2). Efferent--motor function
(3). Mixed
c.
Ganglia--cluster of neuron cell bodies outside of cns, surrounded by
c.t.
2.
Sensory receptors
a.
Structures specialized to respond to stimuli
b.
Many are endings of dendrites from sensory neurons
(1). Mechanoreceptors--touch, pressure, muscle length, hearing and
balance, blood pressure
(2). Nociceptors--pain
(3). Thremoreceptors
(4). Chemoreceptors--odor, blood o2, co2, h+, glucose, taste,
osmolarity
C.
Cranial nerves
1.
Nerves attached directly to brain, supply had and neck
2.
12 pairs, numbered I thru xii
a.
I. Olfactory--afferent, smell
b.
Ii. Optic--afferent, sight
c.
Iii. Oculomotor--efferent, eye movement
d.
Iv. Trochlear--mixed, eye movement
e.
V. Trigeminal--mixed, ophthalmic, maxillary, mandibular, movement
and sensation
f.
Vi. Abducens--mixed, retraction of eye
g.
Vii. Facial-- mixed, taste, glands, expression
h.
Vii.--vestibulocochlear--sensory, hearing, equilibrium
i.
Ix. Glossopharyngeal--mixed, taste, touch, glands
j.
X. Vagus--mixed, speech, swallowing, heart rate, visceral sensations
k.
Xi. Accessory--efferent--speech, swallowing, head and neck
D.
VI.
l.
Xii. Hypoglossal--motor, tongue
Spinal nerves
1.
Roots of spinal nerves--31 pairs
a.
Root--fibers between cord and point of origin
(intervertebral foramina)
b.
Dorsal root--sensory, posterior horn
c.
Ventral root--motor, anterior horn
2.
Rami--branches in spinal nerve
3.
Plexuses--network of nerves that branch and recombine
a.
Advantage: Damage to a single root does not lead to
a complete loss of sense or function of body part
Functional divisions of pns
A.
Somatic system (Conscious thought)
1.
Pathways and effectors
a.
One sensory neuron between receptor and cns
b.
One motor neuron between cns and skeletal muscle
c.
Ach Is only neurotransmitter
B.
Autonomic system (Unconscious reflexes)
1.
Autonomic motor pathways
a.
2 neurons, pre and postganglionic
b.
Unmyelinated after ganglia, innervate smooth and
cardiac muscle, glands etc.
(1). Either excite or inhibit action
c.
Sympathetic division
(1). Preganglionic enters sympathetic trunk
ganglia, branches to many postg. Neurons
(1:20)
(2). Responds to flight of fright or frolic
d.
Parasympathetic division
(1). Preg. Axons end in terminal ganglia near
visceral effectors, postg. Only travel a short
distance
2.
Autonomic functions
a.
Sympathetic and parasympathetic are Usually
antagonists
b.
Each uses a different neurotransmitter
c.
Sympathetic
(1). Increase h.r., blood glucose, blood to skeletal
muscle, away from digestive
d.
Parasympathetic
(1). Stimulate digestive tract, slows h.r., "rest
response"
3.
Autonomic regulation