The Nervous
System
Functions of the Nervous System
• 1. Monitors internal and external environment
• 2. Take in and analyzes information
• 3. Coordinates voluntary and involuntary
responses.
Organs of the Nervous System
• Brain and Spinal Chord (CNS)
• Sensory Receptors of Sense Organs (eyes, ears
etc)
• Nerves connect nervous system with other
systems
Divisions of the Nervous System
• 1. Central Nervous System
– Spinal Chord and Brain
– Processing coordination of stimulus and response
2. Peripheral Nervous System
- All neural tissue outside the CNS
- Delivers sensory information to the CNS and
carries motor commands to the effectors
Functions of the CNS
• Are to process and coordinate:
• - sensory data:
• From inside and outside the body
– Movement:
• Control activities of peripheral organs (e.g. skeletal
muscles)
– Higher functions of the brain
• Intelligence, memory, learning, emotion
Functions of the PNS
• 1. Deliver sensory information to the CNS
• 2. Carry commands to peripheral tissues and
systems
Nerves
• Also called peripheral nerves:
– Bundles of axon with connective tissues and blood
vessels
– Carry sensory information and motor commands
in PNS:
• Cranial nerves: connects to brain (12 pairs)
• Spinal nerves: attach to spinal chord (31 pairs)
Divisions of the PNS
• Afferent Division:
– Carries information from PNS to CNS
• Efferent Division:
– Carries motor commands from CNS to PNS
– Has somatic and autonomic components
The Efferent Division of the PNS
• Somatic Nervous System (SNS)
– Controls skeletal muscle contraction
• Voluntary muscle contractions
• Reflexes
• Autonomic Nervous System (ANS)
– Controls subconscious actions
• Contraction of smooth and cardiac muscle
• Glandular secretions
The Autonomic Nervous System Splits
• Parasympathetic Nervous System
• Sympathetic Nervous System
Neural Tissue
• Contains 2 kinds of cells
– Neurons
• Cells that send and receive signals
– Neuroglia
• Cells that support and protect nerves
Neurons
• The basic functional units of the nervous
system
• Parts of a neuron
– Cell body (Soma)
– Short, branched dendrites
– Long, single axon
Structure of a Neuron
Dendrites
• Highly branched
• Dendritic spines:
– Receive information from other neurons
– 80-90% of neuron surface area
The Axon
• Long
• Carries electrical signal (action potential) to
target
• Axon structure is critical to function
Nodes and Internodes
• Internodes
– Myelinated segments of axon
• Nodes
– Also called nodes of Ranvier
– Gaps between internodes
– Where axons may branch
The Synapse
• Area where a neuron communicates with another cell
Synapse
• Areas where a neuron communicates with
another cell
• Presynaptic Cell
– Neuron that sends message
• Postsynaptic Cell
– Cell that receives message
• Synaptic Cleft
– Gap that separates the presynaptic membrane
and the postsynaptic membrane
The Synaptic Knob
• Is expanded area of axon
• Contains synaptic vesicles of
neurotransmitters
– Chemical messengers
– Released at presynaptic membrane
– Affect receptors of postsynaptic membrane
Functional Classifications of Neurons
• Sensory Neurons
– Deliver information to CNS
• Motor Neurons
– Stimulate or inhibit peripheral tissues
• Interneurons
– Located between sensory and motor neurons
– Analyze inputs, coordinates outputs
Neuroglia
• Half the volume
of the nervous
system
• Many types of
neuroglia in the
CNS and PNS
Neuroglia Functions
• Line of central canal of spinal chord and
ventricles of brain
• Repair damaged neural tissue
• Processes contact between other neuron cell
bodies
Neuorglia
• Wrap around axons to form myelin sheaths
(Schwann Cells)
– Increases speed of action potentials
– Myelin insulates myelinated axons
– Makes nerves appear white (white matter)
White and Grey Matter
• White Matter
– Regions of CNS with many myelinated nerves
• Grey Matter
– Unmyelinated areas of CNS