Nervous System—Physiology of the Brain
Lecture 8
Today we’re going to continue our journey through the nervous system,
and we’re going to begin to focus on the components at a microscopic
level, as well as the physiology, not so much where things are and what
they look like, but really how they work and how all of this system
gets integrated.
T
he nervous system and endocrine system function to maintain
homeostasis. After considering how the nervous and endocrine
systems work together for this purpose, we’ll review the functions
of the nervous system and the varieties and functions of nervous tissue, as
well as the main divisions and subdivisions of the central and peripheral
nervous systems. We will distinguish afferent from efferent nerves, and we
will describe the functional categories of cranial and spinal nerves.
The nervous system sends electrical signals to individual cells. It does so
Lecture 8: Nervous System—Physiology of the Brain
very rapidly (in milliseconds). Duration of action is very short. The nervous
system targets speci c organs for action. Speci c receptor organs at the end of
each neuron receive these signals. The endocrine system secretes hormones.
It functions much more slowly than the nervous system (seconds to hours). It
is less speci c. It reaches all of the body’s cells via the bloodstream. Duration
of action is longer than the electrical signals.
The nervous and endocrine systems provide redundancy and different types
of action. Some actions, such as adrenaline production, can be performed by
either or both systems.
Functions of the nervous system
Nervous impulses travel in two directions, and each direction has a
separate set of nerves.
Efferent, or descending, nerves send impulses away from the brain.
These are also called motor nerves.
42
, Sensory impulses that ascend the nerves
[Dr. Wilder Pen eld] to the brain are called afferent impulses
could anesthetize the and move along afferent nerves.
scalp … open that up,
Efferent impulses produce action in
and then open up the distant organs.
brain case, the skull …
and expose the brain Afferent impulses deliver information
from peripheral nerves to the brain.
to cut through that
dura mater, the hard The integrative function analyzes
covering, and look information input from afferent
right at the brain. impulses, les these data, and stimulates
action in response to sensory input.
Kinds of nervous tissue and their functions
Neurons (“nerve cells”) initiate and relay electrical nervous impulses toward
and away from the brain. Neurons have three basic parts:
The cell body
Dendrites (“trees”), which receive incoming messages
Axons, which deliver outgoing messages
Nerves can have any arrangement of dendrites and axons, including one input
to many outputs (divergence), many inputs to one output (convergence), and
one input to one output.
Some axons are myelinated (insulated) for rapid impulse delivery. These
axons display saltatory (jumping) conduction. Other axons are unmyelinated.
Myelin sheaths develop as a baby grows; disease can interrupt this process.
Neuroglia (“nerve glue”) are connective nerves that hold the structure of the
nervous system together. These cells nurture the neurons. They are much
more numerous than the neurons and are regenerated over time. Because
43
Lecture 8
Today we’re going to continue our journey through the nervous system,
and we’re going to begin to focus on the components at a microscopic
level, as well as the physiology, not so much where things are and what
they look like, but really how they work and how all of this system
gets integrated.
T
he nervous system and endocrine system function to maintain
homeostasis. After considering how the nervous and endocrine
systems work together for this purpose, we’ll review the functions
of the nervous system and the varieties and functions of nervous tissue, as
well as the main divisions and subdivisions of the central and peripheral
nervous systems. We will distinguish afferent from efferent nerves, and we
will describe the functional categories of cranial and spinal nerves.
The nervous system sends electrical signals to individual cells. It does so
Lecture 8: Nervous System—Physiology of the Brain
very rapidly (in milliseconds). Duration of action is very short. The nervous
system targets speci c organs for action. Speci c receptor organs at the end of
each neuron receive these signals. The endocrine system secretes hormones.
It functions much more slowly than the nervous system (seconds to hours). It
is less speci c. It reaches all of the body’s cells via the bloodstream. Duration
of action is longer than the electrical signals.
The nervous and endocrine systems provide redundancy and different types
of action. Some actions, such as adrenaline production, can be performed by
either or both systems.
Functions of the nervous system
Nervous impulses travel in two directions, and each direction has a
separate set of nerves.
Efferent, or descending, nerves send impulses away from the brain.
These are also called motor nerves.
42
, Sensory impulses that ascend the nerves
[Dr. Wilder Pen eld] to the brain are called afferent impulses
could anesthetize the and move along afferent nerves.
scalp … open that up,
Efferent impulses produce action in
and then open up the distant organs.
brain case, the skull …
and expose the brain Afferent impulses deliver information
from peripheral nerves to the brain.
to cut through that
dura mater, the hard The integrative function analyzes
covering, and look information input from afferent
right at the brain. impulses, les these data, and stimulates
action in response to sensory input.
Kinds of nervous tissue and their functions
Neurons (“nerve cells”) initiate and relay electrical nervous impulses toward
and away from the brain. Neurons have three basic parts:
The cell body
Dendrites (“trees”), which receive incoming messages
Axons, which deliver outgoing messages
Nerves can have any arrangement of dendrites and axons, including one input
to many outputs (divergence), many inputs to one output (convergence), and
one input to one output.
Some axons are myelinated (insulated) for rapid impulse delivery. These
axons display saltatory (jumping) conduction. Other axons are unmyelinated.
Myelin sheaths develop as a baby grows; disease can interrupt this process.
Neuroglia (“nerve glue”) are connective nerves that hold the structure of the
nervous system together. These cells nurture the neurons. They are much
more numerous than the neurons and are regenerated over time. Because
43
