Download Nervous system functions

The nervous system chapter 12, 13 and 14
The Nervous System
Central Nervous System (CNS)
Brain
Peripheral Nervous System (PNS)
Spinal Cord
Motor Neurons
Somatic Nervous System
Sympathetic
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Sensory Neurons
Autonomic Nervous System
Parasympathetic
Subjects we will cover
• Our approach will be to cover functional systems:
• Somatic nervous system – sensory and motor
• Autonomic nervous system
• Special senses
• All system will cover both the central and
peripheral nervous systems
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• Neurons in the nervous system link together to form
circuits with specific functions.
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http://www.thefullwiki.org/Nervous_System
Nervous system functions
• Motor functions
• Control contraction of skeletal muscles – somatic nervous
system
• Control contractions of smooth and cardiac muscle –
autonomic nervous system
• Control of glands function – autonomic nervous system
• Sensory and integrative functions
• Process incoming information to ensure appropriate motor
response
• More than 99% of the incoming information is classified
as irrelevant and unimportant
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3 Major levels of the CNS
• Spinal cord
• involved in walking movement, reflexes of both skeletal
muscles and the autonomic nervous system effectors
• Lower brain/subcortical level
• Subconscious activities of both the autonomic and somatic
nervous system. Involved in several emotional patterns
• Higher brain/cortical level
• Very large memory storage, place of higher functions like
thoughts, awareness
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Peripheral nervous system components
• Includes nerves and ganglia
• Most nerves are mixtures of afferent and efferent fibers
and somatic and autonomic (visceral) fibers
• Pure sensory (afferent) or motor (efferent) nerves are rare
• Peripheral nerves classified as cranial or spinal nerves
• Ganglia contain neuron cell bodies associated with
nerves
• Dorsal root ganglia (sensory, somatic) (Chapter 12)
• Autonomic ganglia (motor, visceral) (Chapter 14)
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CNS protection
• Bony protection by the skeleton – brain by skull
and spinal cord by vertebrae
• 3 layers of membrane collectively called meninges
that are found between the bone and the CNS
tissue
• Cerebro-spinal fluid – CSF - found in the
ventricles, central canal and subarachnoid space
• Blood brain barrier - BBB
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http://tle.westone.wa.gov.au/content/items/969144ed-0d3b-fa04-2e888b23de2a630c/1/human_bio_science_3b.zip/content/002_nervous_control/page_06.htm
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Choroid Plexuses and CSF
• Clusters of capillaries and the ependymal cells
http://www.sci.uidaho.edu/med532/choroid.htm
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CSF production
• The choroid plexus forms tissue fluid filters
• Have ion pumps that selectively pump ions from
the plasma into the ventricles.
• The ions pumps create osmotic pressure that
draws water to the CSF
• the choroid plexus of the lateral ventricles producing
the most.
• The rate of formation is approximately 0.35 ml/min or 500
ml/day; a rate which replaces the total volume of CSF
approximately 2-3 times over in 24 hours.
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CSF – cerebrospinal fluid functions
• Liquid cushion for brain and spinal cord
• Nourishes brain
• Removes waste
• Conducts chemical signals between parts of CNS
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Why are the capillaries in the BBB less permeable?
• Endothelial cells form tight junctions that prevent
solutes movement between cells
• Astrocytes
• Selective transport properties of the endothelial cells
• The BBB
• Helps maintain a stable environment for the brain
• Separates neurons from some bloodborne substances
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Blood-Brain Barrier: Functions
• Selective barrier that allows nutrients to pass freely
• Is ineffective against substances that can diffuse through plasma
membranes (ex. Ethanol, caffeine)
• Absent in some areas:
• Ex. - hormones generally do not penetrate the brain from the
blood, so in order to control the rate of hormone secretion
effectively, there are specialized sites where neurons can
"sample" the composition of the circulating blood. At these
sites, the blood-brain barrier is 'leaky‘ (pituitary gland)
• Capillaries of the choroid plexus
• The BBB can break down under certain conditions:
• hypertension, radiation, infection and brain trauma
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Spinal Cord
• Because the cord does
not reach the end of the
vertebral column, the
lumbar and sacral spinal
nerve roots angle
sharply downward and
travel inferiorly before
reaching their
intervertebral foramina
• This collection of nerve
roots at the inferior end
of the vertebral canal is
called the cauda equina
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Gray Matter: Organization
Dorsal root (sensory)
Dorsal root ganglion
Dorsal horn (interneurons)
Somatic
sensory
neuron
Visceral
sensory
neuron
Visceral
motor
neuron
Somatic
motor neuron
Spinal nerve
Ventral root
(motor)
Ventral horn
(motor neurons)
Interneurons receiving input from somatic sensory neurons
Interneurons receiving input from visceral sensory neurons
Visceral motor (autonomic) neurons
Somatic motor neurons
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Figure 12.32
White Matter in the Spinal Cord
• Composed of both myelinated and unmyelinated fibers that run
in three directions
• Ascending – to higher centers; sensory
• Descending – to lower levels from brain or higher places in
the cord; motor
• Transversely – from one side of the cord to the other
• Divided into three funiculi (columns) – posterior, lateral, and
anterior
• Each funiculus contains several fiber tracks with similar
destination and function
• Fiber tract names reveal their origin and destination
• Fiber tracts are composed of axons with similar functions
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Structure of a Nerve
• Nerve – cordlike organ of the
PNS consisting of peripheral
axons enclosed by connective
tissue
• Connective
include:
tissue
coverings
• Endoneurium
–
connective
tissue
surrounds axons
loose
that
• Perineurium
–
coarse
connective tissue that bundles
fibers into fascicles
• Epineurium – tough fibrous
sheath around a nerve
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Spinal Nerves: Rami
• The short spinal nerves branch into three or four mixed,
distal rami
• Small dorsal ramus
• Larger ventral ramus
• Tiny meningeal branch – innervate the meninges
and blood vessels within the vertebral canal
• Rami communicantes at the base of the ventral
rami in the thoracic region that contain autonomic
nerve fibers
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Nerve Plexuses
• All ventral rami except T2-T12 form nerve networks
called plexuses
• Plexuses are found in the cervical, brachial, lumbar,
and sacral regions
• Each resulting branch of a plexus contains fibers from
several spinal nerves
• Fibers travel to the periphery via several different
routes
• Each muscle receives a nerve supply from more than
one spinal nerve
• Damage to one spinal segment cannot completely
paralyze a muscle
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Plexus
Main spinal nerves Regions innervated
Major nerves
Cervical
C1-C5
Skin and muscles of head & Phrenic (diaphragm)
neck. Superior chest and
shoulder
Brachial
C5-C8, T1
Shoulder and upper limbs
Axillary
Musculocutaneous
Radial
Median
Ulnar
Lumbar
L1-L4
Antero-lateral abdominal
Femoral
wall, external genitalia, part
of lower limbs
Sacral
L4-L5, S1-S4
Buttocks, perineum, lower
limbs
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Sciatic