Download neurons and the nervous system

The Nervous System
NEURONS AND 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)
Break It DOWN!
The Nervous System
Central Nervous System (CNS)
Brain
Peripheral Nervous System (PNS)
Spinal Cord
•
Motor Neurons
Somatic Nervous System
Voluntary movements via
skeletal muscles
Sympathetic
- “Fight-or-Flight” responses
•
Sensory Neurons
Autonomic Nervous System
Organs, Smooth muscles
Parasympathetic
- maintenance
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
1.
3.
2.
Neurons have 3 functions: Reception,
Conduction, Transmission
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
Sensory Vs. Motor
 Sensory Nerve
 Neurons that send signals from the senses, skin, muscles,
and internal organs to the CNS
e.g., skin
 Motor Nerve
 Neurons that transmit commands from the CNS to the
muscles, glands, and organs
e.g., muscle
Gray’s Anatomy 38 1999
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
Dendrites
Cell Body
Myelin
Sheath
Axon of another
neuron
Axon
Dendrites of
another neuron