Download m5zn_e06294c55d2e0eb

The Nervous System
The nervous system enables the
body to react to continuous
changes in its internal and external
environments.
It also controls and integrates the
various activities of the body, such
as circulation and respiration
The Nervous System
 Structurally : divided into CNS + PNS
CNS:
PNS:
brain + spinal cord
12 pairs of cranial nerves
31 pairs of spinal nerves
(8 cervical + 12 thoracic + 5 lumbar +
5 sacral + 1 coccygeal)
 Functionally : * somatic NS (control
voluntary activities)
* autonomic NS (control
involuntary activities)
Central
nervous
system (CNS)
Brain
Spinal cord
Peripheral nervous
system (PNS)
Cranial
nerves
Ganglia
outside
CNS
Spinal
nerves
Figure 48.19
1 coccygeal
CENTRAL NERVOUS SYSTEM
The human brain
– Contains an estimated 100 billion nerve cells,
or neurons
Each neuron
– May communicate with thousands of other
neurons
These neurons are supported by
Neuroglia
CENTRAL NERVOUS SYSTEM
Basic nerve cell structure
3 main types of nerve cells
sensory
neurone
relay
neurone
motor
neurone
Sensory neurons
Carries impulses from receptors e.g pain
receptors in skin to the CNS( brain or spinal
cord)
Relay neuron
Carries impulses from sensory nerves to
motor nerves.
Motor neuron
Carries impulses from CNS to effector e.g.
muscle to bring about movement or gland to
bring about secretion of hormone e.g ADH
White matter
Reflex arc
Sensory
neurone
Receptors in skin
cells
Grey matter
Relay
neurone
Motor neurone
Effector
(muscle)
The three stages of information processing
Are illustrated in the knee-jerk reflex
2
Sensors detect
a sudden stretch in
the quadriceps.
Sensory neurons
convey the information
to the spinal cord.
3
Cell body of
sensory neuron
in dorsal
root ganglion
4
The sensory neurons communicate with
motor neurons that supply the quadriceps. The
motor neurons convey signals to the quadriceps,
causing it to contract and jerking the lower leg forward.
Gray matter
5
Sensory neurons
from the quadriceps
also communicate
with interneurons
in the spinal cord.
Quadriceps
muscle
The
reflex is
1
initiated by tapping
the tendon connected
to the quadriceps
8.4 (extensor) muscle.
White
matter
Hamstring
muscle
6
Spinal cord
(cross section)
Sensory neuron
Motor neuron
Interneuron
The interneurons
inhibit motor neurons
that supply the
hamstring (flexor)
muscle. This inhibition
prevents the hamstring
from contracting,
which would resist
the action of
the quadriceps.
Protecting the Brain
Meninges 2
THE BRAIN
The cerebrum has right and left cerebral
hemispheres
– That each consist of cerebral cortex overlying
white matter and basal nuclei
Left cerebral
hemisphere
Right cerebral
hemisphere
Corpus
callosum
Neocortex
Figure 48.26
Basal
nuclei
In humans, the largest and most
complex part of the brain
–Is the cerebral cortex, where
sensory information is analyzed,
motor commands are issued, and
language is generated
A thick band of axons, the corpus
callosum
– Provides communication between the
right and left cerebral cortices
The cerebral cortex controls voluntary
movement and cognitive functions
Each side of the cerebral cortex has four
lobes
– Frontal, parietal, temporal, and occipital
Frontal lobe
Parietal lobe
Speech
Frontal
association
area
Somatosensory
association
area
Taste
Reading
Speech
Hearing
Smell
Auditory
association
area
Visual
association
area
Vision
Figure 48.27
Temporal lobe
Occipital lobe
THE SPINAL CORD
THE SPINAL CORD
THE SPINAL CORD
PERIPHERAL NERVOUS
SYSTEM
consists of the cranial and spinal nerves
and their associated ganglia
Cranial Nerves:
- 12 pairs that leave the brain and pass
through foramina in the skull.
- All are distributed in the head and neck
except the Xth (vagus), which also
supplies structures in the thorax and
abdomen
PERIPHERAL NERVOUS
SYSTEM
Spinal Nerves:
- A total of 31 pairs leave the spinal cord
and pass through intervertebral foramina
in the vertebral column
-The spinal nerves are named according
to the region of the vertebral column with
which they are associated: 8 cervical, 12
thoracic, 5 lumbar, 5 sacral, and 1
coccygeal.
PERIPHERAL NERVOUS
SYSTEM
Spinal Nerves:
- Each spinal nerve is connected to the
spinal cord by two roots: the anterior root
and the posterior root.
The anterior root carrying nerve impulses
away from the central nervous system (
efferent fibers) go to skeletal muscle and
cause them to contract are called motor
fibers. Their cells of origin lie in the
anterior gray horn of the spinal cord.
PERIPHERAL NERVOUS
SYSTEM
Spinal Nerves:
-The posterior root carry impulses to the
central nervous system and are called
afferent fibers concerned with conveying
information about sensations of touch,
pain, temperature, and vibrations,
(sensory fibers). The cell bodies of these
nerve fibers are situated in a swelling on
the posterior root called the posterior root
ganglion
THORACIC SEGMENT
PLEXUSES
At the root of the limbs, the anterior rami
join one another to form complicated nerve
plexuses .
The cervical and brachial plexuses are
found at the root of the upper limbs,
The lumbar and sacral plexuses are found
at the root of the lower limbs.
AUTONOMIC NERVOUS SYSTEM
concerned with the innervation of
involuntary structures such as the heart,
smooth muscle, and glands
distributed throughout the central and
peripheral nervous system.
divided into two sympathetic and
parasympathetic and both parts have
afferent and efferent nerve fibers.
The hypothalamus of the brain controls the
autonomic nervous system
SYMPATHETIC ANS
It prepare the body for an emergency.
It accelerates the heart rate,
causes constriction of the peripheral
blood vessels
and raises the blood pressure.
redistribution of the blood so that it leaves
the areas of the skin and intestine and
becomes available to the brain, heart, and
skeletal muscle.
At the same time, it inhibits peristalsis of
the intestinal tract and closes the
sphincters.
PARASYMPATHETIC ANS
aim at conserving and restoring energy.
They slow the heart rate,
increase peristalsis of the intestine and
glandular activity,
and open the sphincters.
Segmental innervation of skin
The area of skin supplied by a single
spinal nerve, and therefore a single
segment of the spinal cord, is called a
dermatome.
On the trunk, adjacent dermatomes
overlap considerably;
Segmental Innervation of Muscle
Biceps brachii tendon reflex: C5 and 6
(flexion of the elbow joint by tapping the
biceps tendon)
Triceps tendon reflex: C6, 7, and 8
(extension of the elbow joint by tapping the
triceps tendon)
Brachioradialis tendon reflex: C5, 6, and 7
(supination of the radioulnar joints by
tapping the insertion of the brachioradialis
tendon)
Segmental Innervation of Muscle
Abdominal superficial reflexes (contraction
of underlying abdominal muscles by
stroking the skin): Upper abdominal skin
T6 to 7, middle abdominal skin T8 to 9,
and lower abdominal skin T10 to 12
Patellar tendon reflex (knee jerk): L2, 3,
and 4 (extension of the knee joint on
tapping the patellar tendon)
Achilles tendon reflex (ankle jerk): S1 and
S2 (plantar flexion of the ankle joint on
tapping the Achilles tendon)