Basic Information about the Nervous System

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The nervous system controls everything you do, including breathing, walking, thinking, and feeling. This system is made up of your brain, spinal cord, and all the nerves of your body.
1. nervous
The Nervous System
 Millions of interconnected neurons form the nervous
 Human nervous system two major parts: central
nervous system and peripheral nervous system
2. nervous
Nervous System Organization
Central Nervous System
 Brain
 Spinal cord
3. nervous
Nervous System Organization
 All neurons outside the Peripheral Nervous System
– 31 pairs spinal nerves
– 12 pairs of cranial
4. nervous
The Brain - 3 Major Areas
 Cerebrum (telencephalon, diencephalon,)
 Cerebellum
 Brainstem (midbrain, pons, medulla oblongata)
5. nervous
 Composed of Telencephalon (Cerebral
Cortex) and Diencephalon
 Cerebral Cortex is gray matter because
nerve fibers lack white myelin coating
7. nervous
Cerebral Cortex - 4 Major
 Parietal
 Frontal
 Temporal
 Occipital
8. nervous
Functions of the Cerebral
 Intellectual processes: thought, intelligence.
 Processes sensory information and integrates with past
experience to produce appropriate motor response.
9. nervous
Diencephalon - 2 Major Parts
 Thalamus
– Relays stimuli received from all sensory neurons to cortex
for interpretation
– Relays signals from the cerebral cortex to the proper area
for further processing
 Hypothalamus
– Monitors many parameters
 temperature, blood glucose levels, various hormone levels
– Helps maintain homeostasis
– Signals the pituitary via releasing factors
– Signals the lower neural centers
11. nervous
 Located behind the
 Helps monitor and
regulate movement
 Integrates postural
maintenance of
equilibrium, perception
of speed, and other
reflexes related to fine
tuning of movement.
12. nervous
 Composed of midbrain, pons, and medulla
 Maintains vegetative functioning
– Where is respiratory control center?
– Where is cardiovascular control center?
 Reflexes
13. nervous
Brain Stem
14. nervous
Spinal Cord
 Containsboth gray and white matter
 Gray matter is H-shape in core of cord
16. nervous
Gray Matter
 Regions of brain and spinal cord made up
primarily of cell bodies and dendrites of
nerve cells
 Interneurons in spinal cord
– small nerves which do not leave the spinal cord
 Terminal portion of axons
17. nervous
White Matter
 Contains tracts or pathways made up of
bundles of myelinated nerves
 Carry ascending and descending signals
– Ascending nerve tract from sensory receptors
through dorsal root, up cord to thalamus, to
cerebral cortex
– Pyramidal tract transmits impulses downward
eventually excites motoneurons control muscles.
– Extrapyramidal originate in brain stem descend to
control posture.
18. nervous
Descending Nerve Tracts
Descending: lateral, ventro-
Ascending: dorsal medial tracts
20. nervous
Peripheral Nervous System
 Thirty-one pairs of spinal
nerves & 12 pairs of
cranial nerves.
 Each spinal nerve is a
mixed nerve containing:
– Somatic afferent
– Visceral afferent
– Somatic efferent
– Visceral efferent
 Which is a motor fiber?
21. nervous
Somatic Nervous System
 Somatic afferent
(sensory): carry
sensations from periphery
to spinal cord. Includes
exteroceptive (pain,
temperature, touch) &
 Somatic efferent (motor):
communicate from spinal
cord to skeletal muscles.
22. nervous
Autonomic Nervous System
 Sympathetic
– responsible for increasing activity in most
systems (except GI)
– adrenergic fibers release epinephrine
 Parasympathetic
– responsible for slowing activity in most systems
(except GI)
– cholinergic fibers release acetylcholine
24. nervous
Autonomic Reflex
 Monosynaptic reflex
 Knee jerk response
25. nervous
Complex Reflexes
 Involve multiple
 Crossed extensor reflex
26. nervous
Motor Unit
 A single motor neuron and all of the muscle fibers which it
innervates. Represents functional unit of movement.
 Ratio of muscle fibers to nerve relates to muscle’s movement
27. nervous
 Two basic types
1. Motor
2. Sensory
 Three basic parts
1. Axons
2. Dendrites
3. Soma or Cell Bodies
28. nervous
Sensory Nerves
 Enter the spinal cord on
the dorsal side
 Cell bodies lie outside
the spinal cord in
Dorsal Root Ganglia
29. nervous
Motor Nerves
 Exit the spinal cord on the ventral side
 Cell bodies lie within grey matter of spinal
 Somatic
– innervates skeletal muscle
 Autonomic (visceral)
– innervates organs / smooth muscle
30. nervous
Neuron Part: Axons
 Carry impulses away from the cell body
31. nervous
 Schwann cells
wrapped around the
axon of some
– appear as multiple lipid-protein layers
– are actually a continuous cell
– increase the speed of action potential conduction
32. nervous
Nodes of Ranvier
 Gaps between Schwann Cells
– impulse jumps from node to node
– saltatory conduction
34. nervous
Neuron Parts:
Dendrites and Cell body
 Dendrite: receives stimuli and carry it to the
cell body
 Cell body: site of cellular activity
35. nervous
 Junction between the dendrites of one neuron
and the axon of a second neuron
 Nerves communicate by releasing chemical
messenger at synapse
36. nervous
Important neurotransmitters:
Nitric oxide
37. nervous
Motor Nerves - Size
 Alpha motor nerves
– Larger fibers
– Conduct impulses faster
– Innervate regular muscle fibers
 Gamma Motor nerves
– smaller fibers
– conduct impulses more slowly
– Innervate proprioceptors such as muscle spindles
38. nervous
Nerve Properties
Related to Function
 Irritability
– able to respond to stimuli
 Conductivity
– able to transmit electrical potential along the axon
39. nervous
Resting Membrane Potential
 Difference in charge between the inside and
outside of the cell
– sodium in greater concentration outside
– potassium in greater concentration inside
– anions in greater concentration inside
– membrane permeability greater for potassium
than sodium
– Na+ / K+ pump moves sodium out, potassium in
41. nervous
Generating Action Potentials
 Voltage gated ion channels
– sodium channels open --- sodium rushes in
– sodium channels close --- stops inward flow of
– potassium channels open --- potassium rushes out
 Net effect - Depolarization then
– electrical flow created by ionic flow, not electron
42. nervous
Na+ / K + Pump
 Membrane bound proteins
 Utilizes ATP
 Maintains resting membrane potential
 Establishes sodium & potassium
concentration gradients
44. nervous
Neuromuscular Junction
 Motor neuron cell body and dendrites in gray
matter of spinal cord
 Axons extend to muscle
 Axon’s terminal end contains a synaptic knob
 Synaptic knob has synaptic vesicles
containing acetylcholine
45. nervous
Axon leaves spinal
Extends to skeletal
Terminal branches
end in synaptic
46. nervous
Motor End Plate
 Area beneath the terminal branches of the
 Contains acetylcholine receptor complexes
 Acetylcholine binding opens the receptor
 Cholinesterase degrades acetylcholine into
acetate and choline
48. nervous
Tension Generating
 All or None Law
– when a neuron reaches threshold it generates an
action potential which is conducted the length of
the axon without any voltage change
– when the nerve fires, all the muscle fibers it
innervates contract
49. nervous
Summation of Local Graded
 Temporal Summation
– additive effect of
successive stimuli from
an axon
 Spatial Summation
– additive effect of
stimuli from various
50. nervous
Gradation of Force
 Force of muscle varies
from slight to maximal:
– Increase number of
motor units recruited
– Increase frequency of
motor unit discharge.
51. nervous
 Muscle Spindles
 Golgi Tendon Organs
 Pacinian Corpuscles
 Ruffini Endings
52. nervous
Muscle Spindles
 Encapsulated fibers
within the muscle belly
 Monitor changes in
muscle length
 Monitor the rate of
change in muscle
 Respond by causing
muscle contraction
53. nervous
Golgi Tendon Organs
 Encapsulated receptors
 Located at the
 Monitor tension within
the tendon
 Respond by causing the
muscle to relax
54. nervous
Pacinian Corpuscles &
Ruffini Endings
 Encapsulated receptors
 Located near joints, in muscle, tendon, and bone