Download Nervous System

Functions of the Nervous System
 1. Sensory Input: Internal and External Stimuli
 EX. Sight, vision, hearing, taste, smell, touch, pain,
body position, temperature.
 Also those stimuli processed at an unconscious level,
such as, blood pH & blood pressure,
 2. Integration: Central nervous system processes
sensory input and responds.
 It may store info as a memory.
 3.Control of Muscles and Glands: May control the
skeletal muscles to contract when stimulated. Controls
the major movements.
 Also controls the cardiac muscle, smooth muscle and
major glands.
 4. Homeostasis: The nervous system detects
interprets and responds to changes in our internal and
external environments.
 The nervous system can stimulate or inhibit the
activities of other systems to help maintain a constant
internal environment.
 5. Mental Activity: conscious thinking, memory &
emotions.
Parts of the Nervous System
 Central Nervous System or CNS: Consists of the
Brain and Spinal Cord.
 12 pairs of Cranial Nerves
 Originate from the brain
 31 pairs of spinal nerves.
 Originate from the spine.
Parts of the Nervous System
 Peripheral Nervous System or
PNS: Consists of sensory receptors
and nerves.
 Sensory Receptors detect the
senses such as pain, touch, heat,
light, sound, odors etc.
 They are located in the skin,
muscles, joints, internal organs
and sensory organs such as the
eyes and ears.
Pripheral Nervous System
 Divided into two parts:
 1. Sensory or Afferent Division:
 This sends signals from the sensory receptors to the
CNS.
 2. Motor or Efferent Division:
 This transmits signals from the CNS to the effector
organs, such as muscles or glands. The motor division
can be further divided into the somatic motor and
the Autonomic nervous system.
Somatic Motor Nervous System
 This system transmits action potential from the CNS
to the skeletal muscles.
Parts of the Nervous System
 Nerve Cell or Neuron: A bundle of axons and their
Sheaths. Nerves transmit electrical signals called
action potentials.
Parts of the Nervous System
 Cell Body or Soma: This is the large area of the
Neuron that contains the nucleus and the other
organelles.
 The nerve cells contain many Golgi Bodies and an
extensive network of Rough Endoplasmic
Reticulum.
Parts of the Nervous System
 Axon: A long cell process extending from the cell body
of the neuron. The trigger zone is the part of the
nerve cell where the axon begins and the action
potential is generated.
 Axons are often referred to
as nerve fibers.
The axon can branch off
Known as collateral axons,
or remain on single fiber.
Parts of the Nervous System
 Axons carry impulses from the cell body to other nerve
cells. The junction happens at the Axon Terminals or
Presynaptic Terminal.
 The junction between two nerve cells is called the
Synapse.
Parts of the Nervous System
 Dendrites: short, highly branched areas that receive
the action potential from other neurons.
 The action potential is carried by Neurotransmitters
across the
Synaptic Clef.
Myelin Sheath
 This is the covering of the Axon or the plasma
membrane of the Schwann Cells.
 The myelin protects the and electrically insulates the
neuron.
 Also allows the action potential to move faster & easier.
 These are White in color, so heavily myelated cells
appear as White Matter.
Nodes of Ranvier.
 The bare area of the Axon. Oligodenrocytes do cross
these areas but do not wrap around multiple times. .
Unmyelinated areas.
 Grey matter. The oligodendrocytes surounds each axon
but does not wrap around it multiple times.
Parts of the Nervous System
 Neurotransmitters: These are chemicals that cross
the synapse. They will either stimulate or inhibit the
postsynaptic cell.
 The action potential in the presynaptic terminal or
axon terminal cause a voltage increase allowing ions
such as Ca++ to enter the cell. This voltage jump causes
the release of the neurotransmitters.
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Some Types of Neurotransmitters.
 Acetylcholine: Excitatory Effect in the CNS, Inhibitory
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in the ANS. EX Myasthenia Gravis the inability for the
muscle to respond to the nervous system.
Serotonin: Inhibitory
Dopamine: Excitatory & Inhibitory
Norepinepherine: Excitatory
Gamma-Amino Butyric Acid (GABA): Inhibitory
See Page 286, 287,288 & 289
Types of Neurons
 Sensory or Afferent Neurons conduct action potentials
toward the CNS.
 Motor or Efferent Neurons conduct action portential
from the CNS toward the muscle or gland.
 Interneurons or Association Neurons: conduct action
potential from one neuron to another within the CNS.
Three major categories of neurons
 Multipolar Neurons: These have many dendrites and
one axon. Found in the CNS and most motor neurons.
 Bipolar Neurons: one Dendrite and one Axon. Found
in some sensory organs. Retina of the Eye and nasal
cavity.
 Unipolar Neurons: These have a single process that
extends from the cell body. the process divides into
two branches. One to the CNS the other to the
peripheral nervous system. Most sensory neurons are
this type.
Glial Cells of the CNS
 Nonneural cells or Glial Cells. These are about ½ of the
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Brains weight. And are major supporting cells of the
CNS.
Function:
1. To make a permeable barrier between blood and
neurons.
2. phagocytize foreign substances.
3. produce cerebrospinal fluid
4. produce myelin Sheaths around the axon.
Astrocytes
 Star shaped glial cells. These are major supporting cells
of the CNS.
 They regulate the extracellular composition of the
brain fluid, by forming a blood brain barrier, which
determines what substances can pass from the blood
into the nervous tissue of the brain.
Ependymal Cells
 These line the ventricles of the brain and central canal
of the spinal cord. They may be lines with cilia to help
move the cerbral spinal fluid though the brain cavities.
Microglia
 Glial cells that become mobile and phagocytic in
response to damage or inflammation, infection, trama
or stroke.
Oligodendrocytes
 These form the myelin sheaths.
 They can wrap many times areound the axon.