Nervous System
Nervous System
Nervous System
1. Neurons
• receive stimuli, conduct action potentials, and
transmit signals to other neurons or effector
organs
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
Main Divisions of Nervous System1
information from other neurons and transmits
1. Central nervous system (CNS) the information to the cell body
• brain and spinal cord • Axon – which is a single long cell process that
leaves the cell body at the axon hillock and
2. Peripheral nervous system (PNS) conducts sensory signals to the CNS and motor
• All the nervous tissue outside the CNS signals away from 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
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. TYPES OF NEURONS
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 Oligodendrocytes
organs, such as in the retina of the eye and in the
-provide myelin to neurons in
nasal cavity.
the CNS.
Pseudo-unipolar neurons
Schwann cells
-have a single process extending from the cell
body, which divides into two processes as short -provide myelin to neurons in the
distance from the cell body.
PNS.
-One process extends to the periphery, and the
Satellite Cells
other extends to the CNS.
-found around the cell bodies of certin neurons in
-The two extensions function as a single axon
the PNS
with small, dendrite-like sensory receptors at the
periphery.
bodies and their dendrites, where there is very The sodium-potassium pump is required to
maintain the greater concentration of Na+
little myelin. outside the cell membrane and K+ inside.
Cortex – surface of the brain The pump actively transports K+ into the cell and
Nuclei -clusters of gray matter located Na+ out of the cell.
deeper within the brain
Ganglion – a cluster of neuron cell bodies It is estimated that the sodium-potassium pump
in the PNS consumes 25% of all the ATP in a typical cell and
White matter 70% of the ATP in a neuron.
-abundance of myelin sheath Depolarization
- consists of bundles of parallel axons with their – sodium goes inside
myelin sheaths, which are whitish in color. Repolarization
– potassium goes outside
Hyperpolarization
-the charge on the cell
membrane briefly becomes more negative
than the
resting membrane potential;
All or none fashion
-if threshold is reached, an action
potential occurs; if the threshold
is not reached, no action potential occurs.
Unmyelinated and Myelinated Axon Action
Potentials
-Action potentials are conducted slowly in Reflex
SYNAPSE (neuronal synapse) -is the neuronal pathway by which a reflex occurs
and has five basic components.
-a junction where the axon of one neuron
interacts with another neuron. 1. A sensory receptor
BRAIN
• Pinkish Gray Tissue
• Wrinkled like a wall nut
• Texture: Cold Oatmeal
• Weight: 3 lbs
-Contained in the cranial cavity
-Is the control center for many of the body’s
functions
-Consists of the:
– Cerebrum
– Brainstem
– Cerebellum
Cerebrum functions: understood, and sentence formation may
be inhibited or non- sensical.
Speech
Memory CEREBRUM
Logic
-Gray matter forms the cortex and nuclei of
Emotional response
Consciousness the cerebrum
Interpretation of sensation -White matter forms the cerebral medulla,
Consciousness
which consists of three types of tracts
FRONTAL LOBE PARIETAL LOBE
Comprehension sensory input, Association fibers connect areas of the
& reasoning such as touch, cortex within the same hemisphere
voluntary pain,temperature, Commissural fibers connect the cerebral
motor function balance, and taste hemispheres
motivation Proprioception Projection fibers connect the cerebrum to
Aggression other parts of the brain and the spinal
sense of smell
cord
mood
general
BRAINSTEM MIDBRAIN
-Size of a thumb in diameter and approximately Corpora quadrigemina – vision and
3” (7.5cm) hearing
Cerebral peduncles - are the major
-Pathway
descending motor pathway
- Autonomic behaviors necessary for survival Cerebral aqueduct- tiny canal that travels
through the midbrain that connects the 3rd
-Consist of the:
ventricle to the diencephalon to the 4th
– Medulla oblongata ventricle
– Pons
– Midbrain
-Connects the spinal cord and cerebellum to the
remainder of the brain
-Ten of the 12 pairs of cranial nerves arise from it
-Damage to small areas of the brainstem can
cause death, whereas damage to relatively large
areas of the cerebrum or cerebellum do not
MEDULLA OBLONGATA CEREBELLUM
– Continuous with the spinal cord and - Large, cauliflower like that project dorsally from
contains ascending and descending under the occipital lobe of the cerebrum.
Periosteal Layer- forms the -CSF production and flow maintains the normal
periosteum
pressure (70-100 mmH2O and normal volume
Meningeal Layer- outermost
( 100-160 ml )
covering of the brain and spinal
cord Major solutes of the CSF:
• The third ventricle is connected to the fourth Blood Supply to the Brain
ventricle in the pons by the cerebral aqueduct -The brain requires tremendous amounts of
blood to function normally
– High metabolic rate and brain cells cannot store – Dura mater – Arachnoid mater – Pia mater
high-energy molecules
• The epidural space is between the
– Only about 2% of body weight, but receives
periosteum of the vertebral canal and the
~15%-20% of the blood pumped by the heart
dura mater
-The blood-brain barrier is formed by the
endothelial cells of the capillaries in the brain. • The subarachnoid space is between the
– Limits what substances enter brain tissue arachnoid mater and the pia mater
SPINAL CORD
-Major communication link between the brain
and the PNS (spinal nerves)
-Participates in the integration of incoming
information and produces responses through
reflex mechanisms
-Gives rise to 31 pairs of spinal nerves
-Cervical and lumbosacral enlargements give rise
to the spinal nerves of the limbs
– Nerves from the end of the spinal cord form the
cauda equina
Spinal Cord Cross Section
-Extends from the Foramen magnum to the 1st or
2nd lumbar vertebra • The spinal cord consists of peripheral white
matter and central gray matter
-Protected by meninges
• White matter is organized into columns
(funiculi), which are subdivided into tracts
(fasciculi or pathways), which consist of
ascending and descending axons
• Gray matter is divided into horns
– The dorsal horns contain sensory
axons that synapse with
interneurons
– The ventral horns contain the
neuron cell bodies ofsomatic
motor neurons
– The lateral horns contain the
neuron cell bodies of autonomic
motor neurons
– The gray and white commissures
connect each half ofthe spinal cord
• Spinal nerves arise from the spinal cord in
Meninges of the Spinal Cord numerous rootlets
• Three meningeal layers surround the spinal • The rootlets combine to form a ventral root and
cord. From superficial to deep they are a dorsal root
-Mediated through the ANS and are responsible
for maintaining variables within their normal
ranges
– Blood pressure
– Blood carbon dioxide
– Water Intake
STRUCTURE OF NERVES
-Individual axons are surrounded by the
endoneurium
-Groups of axons (fascicles) are bound together
by the perineurium
-Fascicles form the nerve and are held together
The dorsal root contains sensory axons by the epineurium
The ventral root has motor axons
Spinal nerves have sensory and motor
axons
Reflexes
Stereotypic, unconscious, involuntary responses
to stimuli Maintain homeostasis
Two general types:
1. Somatic reflexes
Spinal Nerves
-Mediated through the somatic motor nervous
system and includes responses that • There are 31 pairs of spinal nerves
Fig. X.
XI.
XII.
VELVET- Vagus
A-Accessory
HAEVEN- Hypoglossal
The two types of general functions are
sensory and motor
– Sensory includes special senses and general
senses
– Motor includes somatic motor and
parasympathetic
• The five major plexuses are • Many reflexes are mediated through the brainstem
• The brainstem is considered nonfunctional when
– Cervical (C1-C4) – Reflexes at all levels of the brainstem are
nonfunctional
• Phrenic nerve – There is no spontaneous breathing (mediated
through the medulla oblongata)
– Brachial (C5-T1)