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Chapter 15:Coordination
Part 1
The Nervous System
• Function to pass information between different parts of the body to
coordinate activities of the body
• Take in large amount of information from environment and allow organisms body to
respond to it
• Purpose of information transfer:
1. Coordinate regulation of substances within in an organism
• Ex. Maintain blood glucose concentration
2. Change the activity of apart of organism ins response to external stimulus
• Ex. Pulling hand away from hot stove
• Two types of information transfer to coordinate activity in organism:
1. Nerves
• Transmit info in form of electrical impulses
2. Chemical messengers
• “Hormones” that travel in blood to different parts of organism to cause a change
Organization of the Nervous System
• Components:
• Brain
• Nerves
• Spinal cord
• White matter  mostly axons
• Grey matter  mostly cell bodies; contain all
synapses
• Divisions by location:
• Central Nervous System (CNS)
• Brain and spinal
• Function: processing of information received
from PNS and coordinating a response
• Peripheral Nervous System (PNS)
• Nerves and receptors
• Function: transmits information going in and
going out of the body
Peripheral Nervous System Divisions
• Afferent/sensory component
• Brings info INTO brain
• Incoming signal
• Efferent/motor component
• Sends info/signal OUT of the brain
• Outgoing signal
• 2 types of efferent signals:
• Somatic Nervous system (SNS): voluntary
control
• Skeletal muscle
• Things under our control
• Autonomic Nervous System (ANS): involuntary
control
• Heart rate, blood pressure, pupil dilation, rate
of digestion, etc
• Things not under our conscious control
• Operate in TWO directions/Two Categories:
• Sympathetic Nervous System  Speed Up
• Parasympathetic nervous system  Slow
Down
Autonomic Nervous System Divisions
• Sympathetic
•
•
•
•
•
Speed everything up
“Gas pedal”
Speeds up body during stress
“Fight or Flight” response
Sympathetic-Speed-Stress (all S’s)
• Parasympathetic
• Slows everything down
• “Brake pedal”
• Slows body down during nonstress
• ‘Rest and digest” side of NS….no
need to be ramped up b/c no
stress in environment
• Two systems work
together…called ANTAGONISTIC
CONTROL
Nerve Cell Structure
• Some nerves bring info INTO brain (afferent signal)
• Some nerves bring info OUT of brain (efferent signal)
• Nerve cells can transmit signals very quickly from brain to receiving structure
• Nerve cells called NEURONS
• Function: highly specialized cells adapted for rapid transmission of electrical impulses
called ACTION POTENTIALS, from one part of the body to another part
• Three Different Types of Neurons:
• Sensory Neurons
• Transmits impulses from receptors TO CNS
• Intermediate Neurons
• Aka relay or connector neurons
• Transmit impulses from sensory neurons to motor neurons
• Motor Neurons
• Transmits impulses from the CNS to effectors (effectors carry out needed response…muscles and
glands)
3 main Parts of Neuron:
• Dendrite
•
•
•
•
Antennae takes in lots of signals coming in
Thin, cytoplasmic extensions from the cell body
Some short, many branches
Increases surface area for attachment to endings of other neurons
• Soma (cell body)
• Contains all organelles: mitochondria, ER, lots of ribosomes
• Processes information received from the Dendrites
• Axon
• Very long structure that sends the signal processed by the soma down to another cell down LONG distances
• Can be 3-4 ft long!
• Cytoplasm contains organelles (mitochondria)
• Thick areas surround axons SCHWANN CELLS
• Secrete MYELIN biological insulator that protects signal that travels along axon; prevents signal degradation; allows signal to
travel faster
• Spaces between Schwann cells on axon NODES OF RANVIER
• Important in propagation of signal down an axon
• AXON TERMINAL: end of axon
• Lots of mitochondria
• Many vesicles containing TRANSMITTER SUBSTANCES (chemicals called NEUROTRANSMITTERS)
• Important in passing impulses to effector cell
• SYNAPSE: composed of the parts of the two adjacent neurons and the SYNAPTIC CLEFT (gap between two neurons
that is about 20 nm wide)
Motor vs. Sensory vs. Intermediate Neuron
• All work together to bring about a response to a stimulus
Motor vs. Sensory vs. Intermediate Neuron Structure
Motor Neuron
• Cell body lies in spinal cord or brain
• Many dendrites coming off of cell
body
• Dendrites HIGHLY branched
• LONG axons
• Ends of axons contain lots of
mitochondria and transmitter
chemicals in vesicles
• Some are myelinated
• Cell body lies in the CNS
• May form synapse with relay neuron
Sensory Neuron
Intermediate Neuron
• Cell body lies within the spinal nerve
• Relay neurons
• One long axon with cell body that may • Found entirely in CNS
be near source of stimuli or in swelling
of a spinal nerve (GANGLION)
• Dendron is usually longer than the
axon
• Contains many dendrites
• Some are myelinated
• May form synapse with relay neuron
Schwann Cells
• Specialized support cell
• Wrap them selves around axons of MOTOR and
SENSORY neurons
• Encloses axons with many layers of its cell membrane
• Inner most layer of Schwann cell that actually encloses
axon is called the MYELIN SHEATH it secretes MYELINE
• Secretes Myelin
•
•
•
•
composed of lipids and protein
Helps insulate axons
Prevents signal degradation
Helps neve impulses travel faster
• Myelinated cat fiber = carry impulses up to 100 m/s
• Unmyelinated cat fiber = carry impulses only 5 m/s
• 1/3 of motor and sensory neurons are MYELINATED
• 2/3 of motor and sensory neurons are UNMYELINATED
• Nodes of Ranvier
• Areas of the axon NOT covered by the Schwann cells
• 2-3 um in diameter
• Found every 1-3 mm in human neurons (between
Schwann cells)
Reflex Arc
• Pathway along which impulses are
transmitted from a receptor to an
effector without involving conscious
regions of the brain
• Sensory neuron connects to motor
neurons through interneurons in
the central nervous system (either
brain or spinal cord)
• Sometimes interneurons NOT
involved
• Impulse passes directly from sensory
neuron to motor neuron
• Different types of reflex arcs
• Brain reflex arc
• Pupil dilation/constriction
• Spinal reflex arc
• Impulse is passed from neuron to
neuron inside spinal cord
Reflex Action
• When an effector responds to the
stimulus BEFORE there is any voluntary
response involving conscious regions
of the brain
• Example
• Receptor detects signal, impulse passed from
one neuron to the next in spinal cord, heading
to brain while attach same time impulses are
traveling along the motor neuron to the
effector and the effector responds first
• Fast automatic response to a stimulus
• Useful in response to danger signals
• Touching hot object
• Something flying at your head
Practice Paper 4 Question 2
Optional portion of question 2