N E U R O N S A N D T H E N E R V O U S S Y S T E M

The Nervous System

Structure and Functions System

A physical organ system

The main cell of the Nervous System is:

The NEURON!

Organs of the nervous system form two subsystems

Central Nervous System (CNS)

Peripheral Nervous System (PNS)

The PNS delivers information to the CNS and carries messages from the CNS to other organs via NERVES

Nerves

Nerves

Collections of neurons that are joined together by connective tissue.

Responsible for transferring impulses (a message carried by neurons) from receptors to CNS and back to effectors.

CNS & PNS

The CNS is made up of:

The Brain

The Spinal Cord

The PNS is made up of

All nervous tissue outside of the CNS

Sensory Neurons

Motor Neurons (sensory & autonomic)

Central Nervous System (CNS)

Brain Spinal Cord

Peripheral Nervous System (PNS)

Sensory Neurons Motor Neurons

Somatic Nervous System

• Voluntary movements via skeletal muscles

Autonomic Nervous System

• Organs, Smooth muscles

Sympathetic

- “Fight-or-Flight” responses Parasympathetic

- maintenance

Break It DOWN! The Nervous System

Divisions of the Autonomic Nervous System

The Sympathetic division of the nervous system prepares the body for action

The Parasympathetic division returns the body to a resting state

Neurons

Made up of a cell body and branches called dendrites and axons

Dendrites receive messages from other neurons and send them to the cell body

Axons carry messages away from the cell body

A message carried by a neuron is called an impulse

Functions

Neurons have 3 functions: Reception, Conduction, Transmission

1. 3.

2.

Types of Neurons

1. Sensory Neurons Neurons located near receptor organs (skin, eyes, ears).

Function: receive incoming stimuli from the environment.

2. Motor Neurons Neurons located near effectors (muscles and glands)

Function: Carry impulses to effectors to initiate a response.

3. Interneurons Neurons that relay messages between other neurons such as sensory and motor neurons. (Found most often in Brain and Spinal chord).

Types of Neurons

e.g., skin

e.g., muscle

Gray’s Anatomy 38 1999

Sensory Vs. Motor Sensory Nerve Neurons that send signals from the senses, skin, muscles,

and internal organs to the CNS

Motor Nerve Neurons that transmit commands from the CNS to the

muscles, glands, and organs

The Withdrawal Reflex

Parts of a Neuron

Dendrite Fine hair-like extensions on the end of a neuron. Function: receive incoming stimuli.

Receive messages from other neurons and send them to the cell body

Cell Body or Soma The control center of the neuron. Function: Directs impulses from the

dendrites to the axon. Nucleus Control center of the Soma. Function: Tells the soma what to do.

Neuron Structure

Extra Extra!

Dendrite The bushy, branching extensions of a

neuron that receive messages and conduct impulses toward the cell body

Axon The extension of a neuron, ending in

branching terminal fibers, through which messages are sent to other neurons or to muscles or glands

Parts of a Neuron Continued

Axon Pathway for the nerve impulse (electrical message) from the soma to the opposite end of the neuron.

Carries messages away from the cell body

Myelin Sheath An insulating layer around an axon. Made up of Schwann cells.

Nodes of Ranvier Gaps between Schwann cells.

Function: Conduction of the impulse. (Situation where speed of an impulse is greatly increased by the message ‘jumping’ the gaps in an axon).

Myelin Sheath & Nodes of Ranvier

Myelin Sheath Fatty material made by glial cells Insulates the axon Allows for rapid movement of

electrical impulses along axon Multiple sclerosis is a breakdown of

myelin sheath Nodes of Ranvier: gaps in myelin sheath where

action potentials are transmitted Speed of neural impulse Ranges from 2 – 200+ mph

Neurons

Axon of another neuron

Cell Body Dendrites

Axon

Myelin Sheath

Dendrites of another neuron