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.