Download SBI4U Nervous System

SBI4U The Importance of
the Nervous System
How does your brain control your
body?
Importance of Nervous System
• Your nervous system is active all the time
• It gets information about the depth of your
breathing, pressure on your skin, temperature, light,
odours etc.
• It controls muscle movements such as blinking,
scratching your nose. Memory and language are
functions of the nervous system.
Vertebrate Nervous System
• The nervous system (NS)
has two main divisions:
– Central Nervous System
(CNS)
– Peripheral Nervous
System (PNS)
• The CNS consists of the
brain and the spinal cord
and acts as a coordinating
centre for incoming and
outgoing information
Nervous System (contd.)
• The PNS consists of nerves that carry
information between the organs of the body
and the CNS
• PNS is further subdivided into somatic
nervous system and autonomic nervous
system
Nervous System (contd.)
• Somatic NS controls the skeletal muscle, bones and
skin. Somatic nerves can be either sensory nerves
(relay info) or motor nerves (generate response).
• The Autonomic NS controls the internal organs of
the body. The two divisions of the ANS are :
– Sympathetic nervous system (fight or flight)
• Acetylcholine and norepinephrine
– Parasympathetic nervous system (rest and
digest)
• Acetylcholine only
What are their effects?
Organ
Sympathetic
Parasympathetic
Heart
↑ heart rate
↓ heart rate
Esophagus
↓ peristalsis
↑ persistalsis
Liver
↑Release of Glucose
Stores Glucose
Eyes
Dilates pupil
Constricts pupil
Bladder
Relaxes sphincter
Contracts sphincter
Skin
↑ blood flow
↓ blood flow
Adrenal Gland
Releases epinephrine
No effect
So you should have….
Nerve Cells
• Two different types of cells are found in the
Nervous System
– Glial cells
– Neurons
• Glial cells are non-conducting cells that are
used for structural support and metabolism of
neurons
• Neurons are the functional units of the
nervous system
Parts of a Neuron
• Dendrite: projection of cytoplasm,
carries impulses towards the cell
body
• Axon: extension of the cytoplasm
that carries nerve impulses away
from the cell body
• Myelin Sheath: insulated covering
over the axon
• Axon Terminal: contains synapses,
specialized structures where
neurotransmitter chemicals are
released in order to communicate
with target neurons
Types of Neurons
• 3 groups:
– Sensory neurons (aka afferent neurons): relay
info from the environment to CNS.
– Interneurons: link neurons, located in the brain
and spinal cord usually; short length
– Motor neurons (aka efferent neurons): relay
information to the effectors which produce
responses.
Reflex Arc
• Neural circuit through the spinal cord that
provides a framework for a reflex action.
• It begins with a receptor that relays the
stimuli to spinal cord. Interneurons in the
spinal cord receive information and relay it to
motor neurons which activate the effector
organs causing a response.
Sequence of Events
1. Stimulus causes signal in
sensory receptors
2. Message travels along sensory
neuron
3. Message reaches interneuron
4. Message goes to brain
5. Message travels in the motor
neuron
6. Message causes response
(muscle to contract)