Organization of the Nervous System
Anatomy & Physiology
Mrs. Halkuff
The nervous system is the master controlling and communicating system of the body.
The nervous system has 3 main functions:– Uses sensory receptors to monitor
changes inside and outside of the body. (Sensory Neurons)
– Intergration: Processes and interprets sensory input and makes decision.
– Motor output: Responds by muscles or glands. (Motor Neurons)
Organization of the Nervous System
1. Central Nervous System (CNS):
– Brain and spinal cord– Command center– Interprets incoming
sensory information– Make decisions based
on past experiences
Organization of the Nervous System
2. Peripheral Nervous System (PNS):
– Nerves that extend from the brain and spinal cord.
1. Sensory (Afferent) Division:Deliver impulses to the CNS from various parts of the body.
2. Motor (Efferent) Division: Carries impulses from the CNS to muscles and glands.
Neuron Dendrites: Increase the surface area for
receiving incoming information. Axon: Carries information from the cell body to
a neighboring neuron. Myelin Sheath: Insulating fat cells that
increase the rate of signal transmissions. Node of Ranvier: Bare axon; allows action
potential to jump from node to node. Axon Terminals: Release
chemicals called
neurotransmitters.
Supporting Cells: CNS 6 Cell Types Total: 4 CNS; 2 PNS Microglia: Destroy invading microorganisms that
could be harmful to the CNS. A type of macrophage.
Astrocytes: Most abundant; Anchors the neurons in place by attaching to capillaries. Also serve as a nutrient (blood supply) to neurons.
Ependymal Cell: Line the brain & spinal cord cavities (dorsal). Have cilia that help to circulate the cerebro-spinal fluid.
Oligodendrocytes: Wrap around axons of neurons to form myelin sheaths.
Supporting Cells: PNS Schwann Cells: Help form myelin
sheath; also engulf deteriorating cell debris & aid in regeneration.
Satellite Cells: Surround the cell bodies and regulate chemical environment.
Resting Potential A neuron sends messages electrochemically. Ions are Na & K (positive) A neuron is at rest when it is not sending a
signal and is in a negatively charged state. Even at rest, the neuron allows K to pass. Neuron pumps 3 Na ions out for every 2 K ions
it pumps in. At rest, there are more Na ions outside and
more K ions inside Resting & Action Potential
Action Potential Occurs when a neuron sends information down
the axon. Electrical activity created by a depolarizing
current. A stimulus must make the neuron reach its
threshold in order to fire an action potential. Stimulus causes Na channels to open and Na+
rushes into the neuron, depolarizing it. K rushes out of the cell, reversing the
depolarization.
Autonomic Nervous System Part of the PNS. Has 2 divisions: Sympathetic &
Parasympathetic Controls heart rate, digestion, respiration
rate, salivation, & perspiration.
Sympathetic
Neurons begin in the Thoracic & Lumbar region of the spinal cord
Functions in actions that require a quick response.
“Fight or Flight” response.
Parasympathetic Neurons begin in the cervical
& sacral regions of the spinal cord.
Functions in actions that do not require an immediate response.
“Rest & Digest” Constant opposition to
Sympathetic N.S. Sympathetic & Parasympatheti
c Clip
Reflexes Involuntary, rapid actions; usually for
survival. Most reflexes don’t have to travel to the
brain, as they need to happen quickly.– Reflex Arc:
1. Receptors are excited.
2. Signal travels along sensory neuron to spinal cord
3. Signal is passed onto a motor neuron
4. Muscle/Gland is stimulated.