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HUMAN ANATOMY
LECTURE TEN
NERVOUS SYSTEM
FUNCTIONS
• Maintains homeostasis
• Sensory input - monitors and responds to
environmental changes
• Relates past and present experiences
• Control of skeletal muscles
• Higher mental functions - consciousness, memory,
thinking
ORGANIZATION
Components
• Brain, spinal cord, nerves, sensory receptors
Subdivisions
• Central Nervous System (CNS)
- brain
- spinal cord
• Peripheral Nervous System (PNS)
- sensory receptors
- nerves
PERIPHERAL NERVOUS SYSTEM
• Includes all neural tissue outside of the
CNS
• Delivers sensory information to CNS and
carries motor commands to peripheral
tissues and organs
Divisions of the PNS
(1) Sensory/Afferent - transmits info from
sensory receptors to
CNS
(2) Motor/Efferent - transmits impulses from
CNS to effector organs
(muscles and glands)
- further divided
MOTOR DIVISIONS OF THE PNS
Somatic Nervous System - from CNS to skeletal muscles
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Voluntary
Single neuron system
Contain SYNAPSES - junction of a nerve cell with another cell
Reflexes
Autonomic Nervous System - from CNS to smooth muscle,
cardiac muscle, and some glands
• Involuntary or subconscious control
• Two neuron system - (1) CNS to ganglion (2) ganglion to effector
• Divisions of the ANS:
Sympathetic - prepares body for stress
Parasympathetic - resting state (digestion, urination, etc)
AUTONOMIC NERVOUS SYSTEM
STRUCTURES WITHIN THE PNS
• Sensory Receptors - endings of neuron dendrites
- specialized to detect environmental stimulus (pain,
touch, temperature, pressure, sound, light, odor)
• Nerve - bundle of neurons and their sheaths
- connects CNS to sensory receptors, muscles, glands
Cranial Nerves - originate from brain (12 pairs)
Spinal Nerves - originate from spinal cord (31 pairs)
• Ganglion - collection of neuron cell bodies outside the CNS
• Plexus - extensive network of axons, sometimes cell bodies, located
outside the CNS
CELLS OF THE NERVOUS SYSTEM
Neurons (nerve cells)
• Receive stimuli and transmit
action potentials
• Consist of: cell body (soma)
dendrites - input
axons - output
Neuroglia (glial cells)
• Support and protect neurons
• Several different types
PARTS OF THE NEURON
Cell Body
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Contain nucleus, organelles for ATP and protein
synthesis, nissl bodies, cytoskeleton, cytoplasm
NISSL BODIES - concentrated areas of rough ER
AXON HILLOCK - site of axon attachment
Dendrite
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Receive sensory input and carries toward cell body
DENDRITIC SPINES - site of axon synapses
Axon
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Carries impulse away from cell body
COLLATERALS - side branches
AXOPLASM - axon cytoplasm
AXOLEMMA - specialized cell membrane
May be surrounded by a myelin sheath
AXON TERMINALS - presynaptic endings
TYPES OF NEURONS
Functional Classification
• Sensory/Afferent Neurons
- impulse travels from sensory receptor to CNS
- cell bodies located in peripheral sensory ganglia near spinal cord
- unipolar
Somatic Sensory Neurons - info from external environment
Visceral Sensory Neurons - info from internal environment
• Motor/Efferent Neurons
- impulse travels from CNS to effector (muscle or gland)
- multipolar
Somatic Motor Neurons - innervate skeletal muscles
- have conscious control over
Visceral Motor Neurons - innervate smooth and cardiac muscle, glands
- impulse travels along 2 VMN with synapse inbetween
(1st is preganglionic fiber, 2nd is postganglionic fiber)
• Interneurons
- located within CNS
- distribute sensory info and coordinate motor
activity
- connect afferent and efferent neurons
Structural Classification
A. Unipolar
- dendrite and axon are a single process
- cell body off to the side
- sensory neurons of PNS
B. Bipolar
- have separate dendrite and axon
- located in sensory organs (retina of
eye, nasal cavity)
C. Multipolar
- many dendrites and single axon
- neurons within CNS and efferent
neurons
NEUROGLIA
• Nonneuronal cells of CNS and PNS
• Differ between CNS and PNS
• Several different kinds
Astrocytes (CNS)
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Most numerous in CNS
Processes form feet that cover surfaces of
neurons and blood vessels
Many functions:
- blood-brain barrier: regulates
substances entering brain
- creates structure like a cytoskeleton
- guide neuronal development
- regulates composition of extracellular brain
fluid
Ependymal Cells (CNS)
• Line brain ventricles and spinal
cord (similar to epithelial cells)
• Some form CHOROID PLEXUS
- secrete cerebrospinal fluid
• Cilia help move CSF through brain
• Have long processes on basal
surface that extend into brain tissue
Microglia (CNS)
• Smallest and fewest in number
• Wander through nervous tissue - specialized to phagocytize
microorganisms, necrotic tissue, foreign substances
Oligodendrocytes (CNS)
• Have long processes that form myelin sheaths around neurons (white
matter)
• Each may wrap around several neurons
Schwann Cells or Neurolemmocytes (PNS)
• Wrap around a portion of an axon forming myelin sheath
• Shields axon from interstitial fluid
Satellite Cells (PNS)
• Surround cell bodies in ganglia
• Provide support and nutrients