Nervous System Functions
1. Receiving sensory input
2. Integrating information
3. Controlling muscles and glands
4. Maintaining homeostasis
Neurons
receive stimuli, conduct action potentials, and
transmit signals to other neurons or effector
organs.
Glial cells
Main Divisions of Nervous System
supportive cells of the CNS and PNS, meaning
these cells do not conduct action potentials.
Instead, glial cells carry out different functions
that enhance neuron function and maintain
normal conditions within nervous tissue.
Central nervous system (CNS).
Neurons
5. Establishing and maintaining mental
activity
•
brain and spinal cord
Peripheral nervous system (PNS).
•
All the nervous tissue outside
the CNS
Sensory division.
Conducts action potentials from sensory
receptors to the CNS
Motor division.
Conducts action potentials to effector organs,
such as muscles and glands
A neuron (nerve cell) has a:
Cell body – which contains a single nucleus
Dendrite – which is a cytoplasmic extension
from the cell body, that usually receives
information from other neurons and transmits
the information to the cell body
Axon – which is a single long cell process that
leaves the cell body at the axon hillock and
conducts sensory signals to the CNS and motor
signals away from the CNS
Structural Types of Neurons
Somatic nervous system.
Transmits action potentials from the CNS to
skeletal muscles.
Autonomic nervous system.
Transmits action potentials from the CNS to
cardiac muscle, smooth muscle, and glands
Enteric nervous system.
A special nervous system found only in the
digestive tract.
Cells of the Nervous System
Multipolar neurons have many dendrites and a
single axon. Most of the neurons within the CNS
and nearly all motor neurons are multipolar.
Bipolar neurons have two processes: one
dendrite and one axon. Bipolar neurons are
located in some sensory organs, such as in the
retina of the eye and in the nasal cavity.
Pseudo-unipolar neurons have a single process
extending from the cell body, which divides into
two processes as short distance from the cell
body.
One process extends to the periphery, and the
other extends to the CNS.
The two extensions function as a single axon
with small, dendrite-like sensory receptors at
the periphery.
Gray matter consists of groups of neuron cell
bodies and their dendrites, where there is very
little myelin.
Glial Cells
White matter consists of bundles of parallel
axons with their myelin sheaths, which are
whitish in color.
Glial cells are the supportive cells of the CNS
and PNS.
Astrocytes serve as the major supporting cells
in the CNS.
Astrocytes can stimulate or inhibit the signaling
activity of nearby neurons and form the bloodbrain barrier.
Ependymal cells line the cavities in the brain
that contains cerebrospinal fluid.
Microglial cells act in an immune function in the
CNS by removing bacteria and cell debris.
Oligodendrocytes provide myelin to axons of
neurons in the CNS.
Schwann cells provide myelin to axons of
neurons in the PNS.
Myelin Sheath
Myelin sheaths are specialized layers that wrap
around the axons of some neurons, those
neurons are termed, myelinated.
Gaps in the myelin sheath, called nodes of
Ranvier, occur about every millimeter
Unmyelinated Neurons
Unmyelinated axons lack the myelin sheaths.
These axons rest in indentations of the
oligodendrocytes in the CNS and the Schwann
cells in the PNS.
Organization of Nervous Tissue
Nerve Cell Communication
Nerve cells are excitable.
The resting membrane potential can change in
response to a stimuli.
In nerve cells, this change is a means by which
the cell communicates with other cells.
The changes in membrane potential that nerve
cells use to communicate with other cells are
called action potentials
Gated Membrane Channels
The stimuli that cause action potentials activate
gated channels which are closed until opened
by specific signals.