Psychology 411 chapter 3 lecture notes, Structure of the Nervous System, part 3

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Psychology 411 chapter 3 lecture notes, Structure
of the Nervous System, part 3
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Metencephalon

• Metencephalon consists of the
• Pons, just ventral to the cerebellum
• Contains the core of the reticular formation
• The pons is involved in the control of states of
  sleep and arousal
• Cerebellum is involved in motor control, more
  particularly, the timing and sequencing of
  movements.

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The cerebellum
?The cerebellum is a part of the brain located
dorsal to the pons, consisting of two cerebellar
hemispheres, covered with cerebellar cortex
overlying white matter and deep cerebellar
nuclei. ?Damage to the cerebellum impairs
balance, standing, walking and the performance
of coordinated movements. The cerebellum receives
inputs from visual, auditory, somatosensory and
vestibular systems as well as inputs from the
cerebral cortex about individual muscle
movements. The cerebellum acts to integrate this
information with movements, producing a smoothed
sequence of movements. Damage to the cerebellum
can produce movements that are out of sequence
and incorrectly timed, being jerky, erratic and
exaggerated, somewhat resembling alcohol
intoxication.
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The cerebellum shown in relation to other
subcortical motor control structures.
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Cross section of lower brain and cerebellum
Cerebellum
Midbrain
Pons
Medulla
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Myelencephalon

• The myelencephalon consists of the
• Medulla oblongata
• The medulla is the most caudal portion of brain
  its lower border is the rostral end of the spinal
  cord
• The medulla contains part of the reticular
  formation
• The nuclei of the medulla control vital functions
  such as regulation of the cardiovascular system,
  breathing, vomiting, and skeletal muscle tone.
  Other reflexes such as coughing, sneezing and
  hiccuping are likely controlled here.

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The Spinal Cord
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?The spinal cord is a long structure, about the
diameter of ones little finger. The spinal
cord only extends about two-thirds of the length
of the vertebral column, ending in a bundle of
spinal roots composing what is called the cauda
equina (horses tail). The spinal cord is
covered by the meninges, with the pia
mater actually fusing to the spinal cord. Also
note that in the spinal cord the white matter is
the outer layer and the gray matter is the inner
layer, the opposite of the brain. ?The spinal
cords primary function is to convey
somatosensory information to the brain and to
distribute motor axons to various effector organ
such as muscles and gland. An effector is
a structure that responds to stimuli. The
somatosensory and motor fibers enter and exit the
spinal cord along its dorsolateral
and ventrolateral surfaces in 31 pairs of
ventral and dorsal roots.
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?The afferent (bearing toward the CNS)
somatosensory fibers enter the spinal cord via
the dorsal roots, with their cell bodies located
in the dorsal root ganglia. The efferent (bearing
away from the CNS) motor fibers exit the spinal
cord via the ventral roots. The ventral and
dorsal roots join together outside the spinal
cord to form the 31 pairs of spinal nerves, part
of the peripheral nervous system.
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The Peripheral Nervous System

• Somatic division of PNS is comprised by nerves
  that control muscle action and that carry sensory
  information back to the CNS
• Cranial nerves (12 pairs)
• Spinal nerves (31 pairs)
• Autonomic division of PNS governs smooth muscle
  and gland secretion
• Parasympathetic supports activities that
  increase energy stores
• Sympathetic arousal and the expenditure of
  energy

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The 12 cranial nerves innervate (supply axons) to
the face, scalp and neck for sensory functions,
(BLUE) or motor functions (RED) or both (Mixed)
shown with parallel blue and red lines. The 10th
cranial nerve, the vagus innervates various
internal organs.
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?To remember the 12 cranial nerves in order, this
mnemonic will help On 1. olfactory old
2. optic Olympuses 3. occulomotor towering
4. trochlear top 5. trigeminal a
6. abducens Finn 7. facial and
8. auditory German 9.
glossopharyngeal viewed 10. vagus some
11. spinal accessory hops. 12.
hypoglossal
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?The rest of the body is innervated by the 31
pairs of spinal nerves... 8
Cervical 12 Thoracic 5 Lumbar
5 Sacral 1 Coccygeal
The spinal nerves and the cranial nerves are a
part of the peripheral nervous system termed
the somatic nervous system. This nervous system
receives sensory information from the sensory
system organs and controls the responses of the
skeletal muscles. Another branch of the
peripheral nervous system is the autonomic
nervous system.
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The Autonomic Nervous System
The ANS has two divisions itself

• Sympathetic division
• Associated with energy expenditure
• Derives from thoracic and columbar levels of the
  spinal cord
• Parasympathetic division
• Associated with energy conservation
• Derives from cranial and sacral levels of the
  spinal cord

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?The autonomic nervous system (ANS) controls the
responses of smooth muscle in the skin, blood
vessels, the eyes, (pupil, lens) the GI tract,
and the urinary system as well as cardiac muscle.
The ANS controls various vegetative functions
of the internal organs. With just a few
exceptions, the major organs are innervated by
both divisions of the ANS, the sympathetic and
the parasympathetic nervous systems. Each
division will have a different and antagonistic
effect to the other. The sympathetic nervous
system will accelerate our heart rate whereas
the parasympathetic nervous system will slow our
hearts. The ANS is a key part of our bodys
fight or flight response and recovering from
such responses.
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Overview of the ANS
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Overview of the ANS
?The sympathetic nervous system has its ganglia
parallel to the spinal cord (the sympathetic
ganglion chain) with short preganglionic axons
but long postganglionic axons extending to the
target organs. ?The parasympathetic nervous
system has long preganglionic axons with its
ganglia distributed adjacent to target organs.
The postganglionic axons are short, extending to
the target organs.