Download The nervous system

Anatomy & physiology: The nervous system
Major regions of the brain
A
A
Cerebrum
D
Medulla
B
Mid brain
E
Spinal cord
C
Pons
F
Cerebellum
The central nervous system consists of the brain and the spinal
cord.
The cerebrum controls the hgher thought processess. The
cerebellum co-ordinates subconscious movement of skeletal
muscles and contributes to muscle tone, posture and balance.
The brain stem (Mid brain, Pons and Medulla) regulates
heartbeat and breathing, plays a role in consciousness, is the
reflex centre for movement of the eyeballs, head and trunk and
transmits impulses between the brain and spinal cord.
B
A
C
F
E
D
Nervous tissue
Spinal cord
The spinal cord is composed of bundles of nerve fibres and
leaves the skull through the foramen magnum extending
to the level of the second lumbar vertebra. At this point,
it gives rise to numerous individual nerve roots, called the
cauda equina.
A
Spinal cord
D
Spinal nerve
B
Vertebral body
E
Vertebral process
C
Intervertebral disc
F
Meninges
A
Nervous tissue is composed of two main cell types: neurons
and glial cells. Neurons transmit nerve messages. Glial cells
are in direct contact with neurons and often surround them.
The neuron is the functional unit of the nervous system.
While variable in size and shape, all neurons have three
parts. Dendrites receive information from another cell and
transmit the message to the cell body. The cell body contains
the nucleus, mitochondria and other organelles. The axon
conducts messages away from the cell body.
F
B
E
Motor neurons have a long axon and short dendrites and
transmit messages from the central nervous system to the
muscles (or to glands).
C
D
Reference: The nervous system
Sensory neurons typically have a long dendrite and short
axon, and carry messages from sensory receptors to the
central nervous system.
Interneurons are found only in the central nervous system
where they connect neuron to neuron.
The Pre-hospital Volunteer
Autonomic nervous system
Reflex arc
A reflex arc is a nerve pathway which
produces a fast, simple automatic
response when it is stimulated. A reflex
involves only a few nerve cells, unlike
the slower but more complex responses
produced by the many processing nerve
cells of the brain.
The autonomic nervous system operates without conscious control and regulates
the function of the internal organs, glands and smooth muscle. It is divided into the
parasympathetic nervous division and the sympathetic division.
Examples of such reflexes include the
sudden withdrawal of a hand in response
to a painful stimulus, for example when
touching a very hot object or other
unpleasant stimulus, or the jerking of a
leg when the kneecap is tapped, such as
with a reflex hammer.
The sympathetic pathway is responsible for the body’s response to shock and stress.
This response is associated with the release of epinephrine from the adrenal glands.
Sympathetic responses include moving blood from the extremities to the vital
organs, increasing heart rate and respirations, increasing blood pressure, dilation of
the pupils and the reduction of digestive system activity.
Sensory cells (receptors) in the knee
send signals to the spinal cord along a
sensory nerve cell. Within the spine a
reflex arc switches the signals straight
back to the muscles of the leg (effectors)
via an intermediate nerve cell and then a
motor nerve cell; contraction of the leg
occurs, and the leg kicks upwards.
The parasympatetic responses are involved with relaxing the body, including
slowing the heart rate and respiratory rates, lowering the blood pressure,
constricting the pupils and increasing the digestive system activity.
Only three nerve cells are involved, and
the brain is only aware of the response
after it has taken place.
Meninges and CSF
The entire central nervous system is
enclosed by a set of three membranes
called the meninges.
The outer layer is the dura mater, an
inelastic fibrous membrane.
The arachnoid mater is the second layer
and gets its name because the blood
vessels and fibres it contains resembles a
spider’s web.
The innermost layer is the pia mater and
rests directly on the brain or spinal cord.
The Pre-hospital Volunteer
Cerebrospinal fluid (CSF), which is
manufactured in the ventricles of the
brain, flows in the subarachnoid space
(located between the pia mater and the
arachnoid mater).
The meninges and CSF form a fluid
filled sac that cushions and protects the
brain and spinal cord.
Obstruction of the flow of CSF results
in increased pressure within the
skull, swelling of the ventricles and
compression of the brain, a condition
known as hydrocephalus.
Reference: The nervous system