Download Motor Neurons

Neurons and the
Nervous System
Nervous System
– Central nervous system (CNS):
• Brain
• Spinal cord
– Peripheral nervous system (PNS):
• Sensory neurons
• Motor neurons (somatic and
autonomic)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Nervous System
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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Divisions of the autonomic nervous system
The Nervous System
• A physical organ system like any
other
• The main cell of the nervous
system are:
–Neurons
The Neuron
• The basic functional
unit of the nervous
system.
• Function: Send
impulses to and from
the CNS and PNS
Neuron Structure
• Dendrite  Fine hair-like extensions
on the end of a neuron.
–Function: receive incoming stimuli.
• 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.
• Axon Pathway for the nerve impulse
(electrical message) from the soma to the
opposite end of the neuron.
• Myelin Sheath  An insulating layer
around an axon. Made up of Schwann
cells.
• Nodes of Ranvier  Gaps between
schwann cells.
– Conduction of the impulse. (Situation
where speed of an impulse is greatly
increased by the message ‘jumping’ the
gaps in an axon).
Types of Neurons
• There are 3 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 impules 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
Nerves
• Nerves  Collections of neurons
that are joined together by
connective tissue.
• Responsible for transferring
impulses from receptors to CNS
and back to effectors.
Three main types of neurons
• Sensory Neurons
• Interneurons
• Motor Neurons
Sensory vs. Motor
sensory nerve
e.g., skin
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
Gray’s Anatomy 38 1999
e.g., muscle
The Withdrawal Reflex
Neuron Anatomy and Neural
Communication
Neurons
Dendrites
Cell Body
Myelin
Sheath
Axon of another
neuron
Axon
Dendrites of
another neuron
Neural Anatomy
 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
Neural Anatomy and
communication
 Synapse
 junction between the axon tip of the sending
neuron and the dendrite or cell body of the
receiving neuron
 tiny gap at this junction is called the synaptic
gap or cleft
 Synapse movie
Specific Parts: The Neuron
Structure
Specific Parts: The Neuron
Function
1.
3.
2.
Neurons = 3 functions: Reception, Conduction, Transmission
Communication
• Impulse releases
neurotransmitter from
vesicles
• Neurotransmitter
enters synaptic gap
• Neurotransmitter
binds to receptors on
the receiving neuron
Myelin Sheath
– Fatty material made by glial cells
– Insulates the axon
– Allows for rapid movement of
electrical impulses along axon
– Nodes of Ranvier: gaps in myelin sheath
where action potentials are transmitted
– Multiple sclerosis is a breakdown of
myelin sheath
– Speed of neural impulse Ranges from 2 –
200+ mph
Myelinization clip
Myelin conduction clip
Neurotransmitters
 chemical messengers that travel across
the synaptic gaps between neurons
 when released by the sending neuron,
neurotransmitters travel across the
synapse and bind to receptor sites on
the receiving neuron, thereby
influencing whether it will generate a
neural impulse