Download in Somatic Nervous System

The Nervous System
Nervous System Organization
All animals must be able to respond to
environmental stimuli
-Sensory receptors = Detect stimulus
-Motor effectors = Respond to it
-The nervous system links the two
-Consists of neurons and supporting cells
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Nervous System Organization
Vertebrates have three types of neurons
-Sensory neurons (afferent neurons) carry
impulses to central nervous system (CNS)
-Motor neurons (efferent neurons) carry
impulses from CNS to effectors (muscles
and glands)
-Interneurons (association neurons)
provide more complex reflexes and
associative functions (learning and memory)
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Nervous System Organization
The CNS consists of the brain and spinal cord
The peripheral nervous system (PNS)
consists of sensory and motor neurons
-Somatic NS stimulates skeletal muscles
-Autonomic NS stimulates smooth and
cardiac muscles, as well as glands
-Sympathetic and parasympathetic NS
-Counterbalance each other
-Fight or flight (sympathetic)
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The Peripheral Nervous System
The PNS consists of nerves and ganglia
-Nerves are bundles
of axons bound by
connective tissue
-Ganglia are
aggregates of
neuron cell bodies
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Neuron
• Neuron is
composed of
dendrites, cell
body, and axon.
• Synapse
• Supporting
Cells--neuroglia
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Resting Membrane Potential
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•
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Sodium-potassium pump
Ion leakage channels
Graded potentials
Chemically and voltage gated ion channels
Depolarization and hyperpolarization.
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Action Potential
• Depolarization/hyperpol
arization
• Threshold potential
• Action potential
– Voltage-gated ion
channels open and
close.
• Saltatory conduction
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The Synapse
• Electrical and
chemical.
• Synaptic vesicles
• Neurotransmitters
• Receptor proteins.
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The Brain
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Drug Addiction
Nicotine binds directly to a specific receptor
on postsynaptic neurons of the brain
-Brain adjusts to prolonged exposure by
“turning down the volume” in two ways:
1. Making fewer nicotine receptors
2. Altering the sensitivity to stimulation by
neurotransmitters
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Nervous System Organization
The CNS consists of the brain and spinal cord
The Peripheral Nervous System (PNS) consists of
sensory and motor neurons
-Somatic NS stimulates skeletal muscles
-Autonomic NS stimulates smooth and cardiac
muscles, as well as glands
-Sympathetic and parasympathetic NS
-Counterbalance each other
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CNS
Brain and Spinal Cord
Motor Pathways
PNS
Sensory Pathways
Sensory neurons
registering external
stimuli
Sensory neurons
registering external
stimuli
Somatic nervous
system
(voluntary)
Sympathetic nervous
system
"fight or flight"
Autonomic nervous
system
(involuntary)
Parasympathetic nervous
system
"rest and repose"
central nervous system (CNS)
peripheral nervous system (PNS)
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Vertebrate Brains
All vertebrate brains have three basic divisions:
-Hindbrain or rhombencephalon
-Midbrain or mesencephalon
-Forebrain or prosencephalon
In fishes,
-Hindbrain = Largest portion
-Midbrain = Processes visual information
-Forebrain = Processes olfactory information
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Vertebrate Brains
The relative sizes of different brain regions have
changed as vertebrates evolved
Forebrain became the dominant
feature...Neuronal correlate to: learning,
association, emotions.
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Compare Brain Diagrams
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Vertebrate Brains
Forebrain is composed of 2 elements:
-Diencephalon
-Thalamus: Integration and relay center
-Hypothalamus: Participates in basic drives &
emotions; controls pituitary gland
-Telencephalon (“end brain”)
-Devoted largely to associative activity
-ALSO Called the CEREBRUM in mammals
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Cerebral Cortex is the outer
layer of the Cerebrum
Cerebral cortex
-Contains about 10% of all neurons in brain
-Highly convoluted surface
-Increases threefold the surface area
of the human brain
-Divided into three regions, each with a
specific function
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Cerebral Cortex 3 Regions
Increase in brain size in mammals reflects
the great enlargement of the cerebrum
Cerebral cortex
1Primary motor cortex: Movement control
2Primary somatosensory cortex: Sensory
control
3Association cortex: Higher mental functions
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Complex Functions of the Brain
Memory
-Appears dispersed across the brain
-Short-term memory is stored in the form of
transient neural excitations
-Long-term memory appears to involve
structural changes in neural connections
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Complex Functions of the Brain
Alzheimer disease is a condition where memory
and thought become dysfunctional
-Two causes have been proposed
1. Nerve cells are killed from the outside in
-External protein: b-amyloid
2. Nerve cells are killed from the inside out
-Internal proteins: tau (t)
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Spinal Cord
The spinal cord is a cable of neurons
extending from the brain down through the
backbone
-Enclosed and protected by the
vertebral column and the
meninges
-It serves as the body’s
“information highway”
-Relays messages between
the body and the brain
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The Peripheral Nervous System
The PNS consists of nerves and ganglia
-Nerves are bundles
of axons bound by
connective tissue
-Ganglia are
aggregates of
neuron cell bodies
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The Peripheral Nervous System
Sensory neurons:
-Axons enter the dorsal surface of the spinal
cord and form dorsal root of spinal nerve
-Cell bodies are grouped outside the spinal
cord in dorsal root ganglia
Motor neurons:
-Axons leave from the ventral surface and
form ventral root of spinal nerve
-Cell bodies are located in the spinal cord
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Cutaneous Spinal Reflex (in Somatic Nervous
System)
Use “SAME DAVE” Acronym
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The Peripheral Nervous System
PNS is divided into the:
Somatic System
&
Autonomic System
.
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Somatic System
In GENERAL, The Somatic System is
responsible for skeletal muscle voluntary
movements & reflexes.
Stretch receptor
Nerve fiber (muscle spindle)
Sensory
Stimulus
neuro
Dorsal root
ganglion
Monosynaptic
synapse
White
matter
Motor neuron
Gray
matter
Skeletal
muscle
Spinal cord
Quadriceps
muscle
(effector)
Response
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The Autonomic Nervous System
Composed of the sympathetic and
parasympathetic divisions, plus the
medulla oblongata
-Smooth or cardiac muscle or glands
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