Nervous system

Cassification by structure

Classification by function

• Sensory neurons are the nerve cells that are activated by sensory input from the environment (Most sensory neurons are pseudounipolar)

• Motor neurons connect to muscles, glands and organs throughout the body. These neurons transmit impulses from the spinal cord to skeletal and smooth muscles (such as those in your stomach), and so directly control all of our muscle movements.

• Interneurons are the ones in between - they connect spinal motor and sensory neurons.

Neuroglia

Nerve nets

• Diffuse mesh of nerve

cells that take part in
simple reflex
pathways.

• Nerve cells interact

with sensory and
contractile cells.

Radial

• Sea stars have a

nerve net connected
by radial nerves to a
central nerve ring.

Ganglia and cordons

• Bilateral symmetry.

• Ganglia are a group of

neuron

Ventral Cord

Synapse

Is the junction between two neurons, or between a
neuron and an effector organ (muscle or gland).
Each synapse consists of:
• Presynapticneuron-that sends an impulse to the

synapse.

• Axon–the nerve fiber extends from the

presynaptic neuron, that propagates the impulse
to the synapse

• Synaptic knobs -the round endings of the axon.

Organization of the

Nervous System

Somatic Nervous System

Autonomic Nervous System

HOMEOSTASIS

• Is a state of relative stability within the body.
• Is critical for survival, because the body can

only survive within a narrow range of
conditions.

• The nervous system regulates body structures

and processes to maintain homeostasis
despite fluctuations in the internal and
external environment.

• The human nervous system can regulate tens

of thousands of activities simultaneously.

HOMEOSTASIS

RESPONSES

Three main types of neurons, however, form the
basic impulse-transmission pathway of the
entire nervous system.
This pathway, depends on three overlapping
functions:
• sensory input
• Integration
• motor output.

Sensory

Sensory
input:

• Sensory neurons gather information from the sensory

receptors (senses) and transmit these impulses to the
central nervous system (brain and spinal cord).

Integration:

• Interneurons are found entirely within the central nervous

system. They act as a link between the sensory and motor
neurons. They process and integrate incoming sensory
information, and relay outgoing motor information.

Motor

Motor
output:

• Motor neurons transmit information from the central

nervous system to the muscles, glands, and other organs
(effectors).

The Reflex Arc

• Some neurons are organized to enable your body to

react rapidly in times of danger, even before you are
consciously aware of the threat. These sudden,
unlearned, involuntary responses to certain stimuli are
called reflexes.

• Reflex arcs are simple connections of neurons

that explain reflexive behaviors. They can be
used to model the basic organization of the
nervous system.

• A reflex arc moves directly to and from the

brain or spinal cord, before the brain centers
involved with voluntary control have time to
process the sensory information.

Task

• Do a graphic organizer with:

– Senses

• Feautres (structures)
• Sesory receptors

The Nerve Impulse

•Is an electrical signal that
travels along an axon. There is
an electrical difference
between the inside of the
axon and its surroundings.

•The action potential is the
result of ions moving in and
out of the cell. Specifically, it
involves potassium (K+)
and sodium (Na+) ions. The
ions are moved in and out of
the cell by potassium
channels, sodium channels
and the sodium-potassium
pump.

Na+K+Pump

Na+K+Pump