Download Spinal nerves

Chapter 12,13,14,15
Nervous Tissue, Spinal Cord and
Nerves, brain and cranial nerves, and
Autonomic
Lecture Outline
Structures of the Nervous
System - Overview
• Twelve pairs of cranial nerves emerge from the
base of the brain through foramina of the skull.
– A nerve is a bundle of hundreds or thousands of
axons, each of which courses along a defined path
and serves a specific region of the body.
• The spinal cord connects to the brain through
the foramen magnum of the skull and is
encircled by the bones of the vertebral column.
– Thirty-one pairs of spinal nerves emerge from the
spinal cord, each serving a specific region of the
body.
• Ganglia, located outside the brain and spinal
Functions of the Nervous
Systems
• The sensory function of the nervous
system is to sense changes in the internal
and external environment through sensory
receptors.
– Sensory (afferent) neurons serve this
function.
• The integrative function is to analyze the
sensory information, store some aspects,
and make decisions regarding appropriate
behaviors.
Nervous System Divisions
• Central nervous system (CNS)
– consists of the brain and spinal cord
• Peripheral nervous system (PNS)
– consists of cranial and spinal nerves that contain
both sensory and motor fibers
– connects CNS to muscles, glands & all sensory
receptors
Subdivisions of the PNS
• Somatic (voluntary) nervous system (SNS)
– neurons from cutaneous and special sensory
receptors to the CNS
– motor neurons to skeletal muscle tissue
• Autonomic (involuntary) nervous systems
– sensory neurons from visceral organs to CNS
– motor neurons to smooth & cardiac muscle and
glands
• sympathetic division (speeds up heart rate)
• parasympathetic division (slow down heart rate)
• Enteric nervous system (ENS)
– involuntary sensory & motor neurons control GI
Neurons
• Functional unit of nervous system
• Have capacity to produce action
potentials
– electrical excitability
• Cell body
– single nucleus with prominent nucleolus
– Nissl bodies (chromatophilic substance)
• rough ER & free ribosomes for protein
synthesis
– neurofilaments give cell shape and support
– microtubules move material inside cell
Dendrites
• Conducts impulses
towards the cell
body
• Typically short,
highly branched &
unmyelinated
• Surfaces
specialized for
contact with other
neurons
Axons
• Conduct impulses
away from cell
body
• Long, thin
cylindrical process
of cell
• Arises at axon
hillock
• Impulses arise
from initial
segment (trigger
zone)
Axonal Transport
• Cell body is location for most protein
synthesis
– neurotransmitters & repair proteins
• Axonal transport system moves substances
– slow axonal flow
• movement in one direction only -- away from cell body
• movement at 1-5 mm per day
– fast axonal flow
• moves organelles & materials along surface of
microtubules
• at 200-400 mm per day
• transports in either direction
Diversity in Neurons
• Both structural and functional features are
used to classify the various neurons in the
body.
• On the basis of the number of processes
extending from the cell body (structure),
neurons are classified as multipolar,
biopolar, and unipolar (Figure 12.4).
• Most neurons in the body are interneurons
and are often named for the histologist
who first described them or for an aspect
Functional Classification of Neurons
• Sensory (afferent) neurons
– transport sensory information from skin,
muscles, joints, sense organs & viscera
to CNS
• Motor (efferent) neurons
– send motor nerve impulses to muscles &
glands
• Interneurons (association) neurons
– connect sensory to motor neurons
Neuroglial Cells
•
•
•
•
Half of the volume of the CNS
Smaller cells than neurons
50X more numerous
Cells can divide
– rapid mitosis in tumor formation (gliomas)
• 4 cell types in CNS
– astrocytes, oligodendrocytes, microglia &
ependymal
• 2 cell types in PNS
Myelination
• A multilayered lipid and protein covering
called the myelin sheath and produced by
Schwann cells and oligodendrocytes
surrounds the axons of most neurons
(Figure 12.8a).
• The sheath electrically insulates the axon
and increases the speed of nerve impulse
conduction.
Axon Coverings in PNS
• All axons surrounded by a lipid
& protein covering (myelin
sheath) produced by Schwann
cells
• Neurilemma is cytoplasm &
nucleus
of Schwann cell
– gaps called nodes of Ranvier
• Myelinated fibers appear white
– jelly-roll like wrappings made of
lipoprotein = myelin
– acts as electrical insulator
– speeds conduction of nerve
impulses
Myelination in
PNS
• Schwann cells myelinate (wrap around) axons
in the PNS during fetal development
• Schwann cell cytoplasm & nucleus forms
outermost layer of neurolemma with inner
portion being the myelin sheath
Myelination in the CNS
• Oligodendrocytes myelinate axons in the
CNS
• Broad, flat cell processes wrap about CNS
axons, but the cell bodies do not surround
the axons
• No neurilemma is formed
• Little regrowth after injury is possible due to
the lack of a distinct tube or neurilemma
Gray
and
White
Matter
• White matter = myelinated processes (white in
color)
• Gray matter = nerve cell bodies, dendrites,
axon terminals, bundles of unmyelinated axons
and neuroglia (gray color)
– In the spinal cord = gray matter forms an H-shaped
inner core surrounded by white matter
– In the brain = a thin outer shell of gray matter
INTRODUCTION
• The spinal cord and spinal nerves mediate
reactions to environmental changes.
• The spinal cord has several functions.
• It processes reflexes.
• It is a conduction pathway for sensory and
motor nerve impulses.
• The size of the vertebral canal varies in
different regions of the vertebral column
and affects spinal cord injuries.
Meninges
• The meninges are three coverings that run
continuously around the spinal cord and
brain (Figures 13.1a, 14.4a).
– The outermost layer is the dura mater.
– The middle layer is the arachnoid.
– The innermost meninx is the pia mater, a thin,
transparent connective tissue layer that
adheres to the surface of the spinal cord and
brain
• Denticulate ligaments are thickenings of
Structures Covering the Spinal Cord
• Vertebrae
• Epidural space filled
with fat
• Dura mater
– dense irregular CT
tube
• Subdural space filled
with interstitial fluid
• Arachnoid = spider
web of collagen fibers
• Subarachnoid space =
CSF
Applications
• The subarachnoid space is between
the arachnoid mater and pia mater and
contains cerebrospinal fluid (CSF).
• Inflammation of the meninges is known
as meningitis.
• Removal of cerebrospinal fluid from the
subarachnoid space is called a spinal
tap (lumbar puncture). This procedure
is used to diagnose pathologies and to
introduce antibiotics, contrast media,
External Anatomy of the Spinal
Cord
• The spinal cord begins as a continuation
of the medulla oblongata and terminates
at about the second lumbar vertebra in
an adult (Figure 13.2).
– It contains cervical and lumbar
enlargements that serve as points of origin
for nerves to the extremities.
• The tapered portion of the spinal cord is
the conus medullaris, from which arise
the filum terminale and cauda equina.
Inferior End of
Spinal Cord
• Conus medullaris
– cone-shaped end of spinal cord
• Filum terminale
– thread-like extension of pia
mater
– stabilizes spinal cord in canal
• Caudae equinae (horse’s tail)
– dorsal & ventral roots of lowest
spinal nerves
• Spinal segment
– area of cord from which each
Spinal nerves
• The 31 pairs of spinal nerves are named
and numbered according to the region and
level of the spinal cord from which they
emerge (Figure 13.2).
– 8 pairs of cervical nerves,
– 12 pairs of thoracic nerves,
– 5 pairs of lumbar nerves,
– 5 pairs of sacral nerves, and
– 1 pair of coccygeal nerves.
• Spinal nerves are the paths of
Internal Anatomy of the Spinal
Cord
• The anterior median fissure and the
posterior median sulcus penetrate the
white matter of the spinal cord and divide it
into right and left sides (Figure 13.3b).
• The gray matter of the spinal cord is
shaped like the letter H or a butterfly and
is surround by white matter.
– The gray matter consists primarily of cell
bodies of neurons and neuroglia and
unmyelinated axons and dendrites of
Sensory and Motor Tracts
• Figure 13.12 shows the principal sensory
and motor tracts in the spinal cord. These
tracts are discussed in detail in Chapter 16
summarized in tables 16.3 and 16.4.
• Sensory (ascending) tracts conduct nerve
impulses toward the brain.
– the lateral and anterior spinothalamic tracts
and the posterior column tract.
• Motor (descending) tracts conduct
impulses down the cord.
Function of Spinal Tracts
• Spinothalamic tract
– pain, temperature, deep pressure & crude touch
• Posterior columns
– proprioception, discriminative touch, two-point
discrimination, pressure and vibration
• Direct pathways (corticospinal & corticobulbar)
– precise, voluntary movements
• Indirect pathways (rubrospinal,
vestibulospinal)
– programming automatic movements, posture &
muscle tone, equilibrium & coordination of visual
SPINAL NERVES
• Spinal nerves connect the CNS to sensory
receptors, muscles, and glands and are
part of the peripheral nervous system.
– The 31 pairs of spinal nerves are named and
numbered according to the region and level of
the spinal cord from which they emerge
(Figure 13.2).
– Roots of the lower lumbar, sacral, and
coccygeal nerves are not in line with their
corresponding vertebrae and thus form the
cauda equina (Figure 13.2).
A Nerve Plexus
• Joining of ventral rami of
spinal nerves to form
nerve networks or
plexuses
• Found in neck, arm, low
back & sacral regions
• No plexus in thoracic
region
– intercostal nn. innervate
intercostal spaces
– T7 to T12 supply
abdominal wall as well
INTRODUCTION
• The brain is the center for registering
sensations, correlating them with one
another and with stored information,
making decisions, and taking action.
• It is also the center for intellect, emotions,
behavior, and memory.
• It also directs our behavior towards others.
• In this chapter we will consider the
principal parts of the brain, how the brain
is protected and nourished, and how it is
Principal
Parts of
the Brain
• Cerebrum
• Diencephalon
– thalamus & hypothalamus
• Cerebellum
• Brainstem
– medulla, pons & midbrain
Blood Supply to Brain
• Arterial blood supply is branches from circle of
Willis on base of brain
• Vessels on surface of brain----penetrate tissue
• Uses 20% of our bodies oxygen & glucose needs
– blood flow to an area increases with activity in that area
– deprivation of O2 for 4 min does permanent injury
• at that time, lysosome release enzymes
• Blood-brain barrier (BBB)
– protects cells from some toxins and pathogens
• proteins & antibiotics can not pass but alcohol & anesthetics do
– tight junctions seal together epithelial cells, continuous
basement membrane, astrocyte processes covering
capillaries
BBB
• A blood-brain barrier (BBB) protects brain
cells from harmful substances and
pathogens by serving as a selective
barrier to prevent passage of many
substances from the blood to the brain.
• An injury to the brain due to trauma,
inflammation, or toxins causes a
breakdown of the BBB, permitting the
passage of normally restricted substances
into brain tissue.
Protective Covering of the Brain
• The brain is protected by the cranial bones
(Figure 7.4) and the cranial meninges
(Figure 14.2).
– The cranial meninges are continuous with the
spinal meninges and are named dura mater,
arachnoid, and pia mater.
– Three extensions of the dura mater separate
parts of the brain: the falx cerebri, falx
cerebelli, and the tentorium cerebelli.
Cerebrospinal Fluid (CSF)
• 80-150 ml (3-5oz)
• Clear liquid containing glucose,
proteins, & ions
• Functions
– mechanical protection
• floats brain & softens impact with bony walls
– chemical protection
• optimal ionic concentrations for action
potentials
– circulation
• nutrients and waste products to and from
Ventricles
• There are four CSF filled cavities within
the brain called ventricles (Figure 14.3).
– A lateral ventricle is located in each
hemisphere of the cerebrum. The lateral
ventricles are separated by the septum
pellucidum.
– The third ventricle is a narrow cavity along the
midline superior to the hypothalamus and
between the right and left halves of the
thalamus.
– The fourth ventricle is between the brain stem
Medulla Oblongata
•
•
•
•
•
Continuation of spinal cord
Ascending sensory tracts
Descending motor tracts
Nuclei of 5 cranial nerves
Cardiovascular center
– force & rate of heart beat
– diameter of blood vessels
• Respiratory center
– medullary rhythmicity area sets basic rhythm of
breathing
• Information in & out of cerebellum
• Reflex centers for coughing, sneezing,
Pons
• The pons is located superior to the
medulla. It connects the spinal cord with
the brain and links parts of the brain with
one another by way of tracts (Figures
14.1, 14.5).
– relays nerve impulses related to voluntary
skeletal movements from the cerebral cortex
to the cerebellum.
– contains the pneumotaxic and apneustic
areas, which help control respiration along
with the respiratory center in the medulla
Midbrain
• One inch in
length
• Extends from
pons to
diencephalon
• Cerebral
aqueduct
connects 3rd
ventricle
above to 4th
ventricle below
Cerebellum
• 2 cerebellar hemispheres and vermis (central area)
• Function
– correct voluntary muscle contraction and posture based
on sensory data from body about actual movements
– sense of equilibrium
Thalamus
• The thalamus is located superior to the
midbrain and contains nuclei that serve as
relay stations for all sensory impulses,
except smell, to the cerebral cortex (Figure
14.9).
– seven major groups of thalamic nuclei on
each side (Figure 14.9 c and d).
– They are the Anterior nucleus, medial nuclei,
lateral group, ventral group, intralaminar
nuclei, midline nucleus, and the reticular
nucleus.
• It also registers conscious recognition of
Hypothalamus
• The hypothalamus
– inferior to the thalamus, has four major
regions (mammillary, tuberal, supraoptic, and
preoptic)
– controls many body activities, and is one of
the major regulators of homeostasis (Figure
14.10).
• The hypothalamus has a great number of
functions.
– It controls the ANS.
– It produces hormones.
THE CEREBRUM
• The cerebrum is the largest part of the brain .
– The surface layer, the cerebral cortex, is 2-4 mm
thick and is composed of gray matter. The cortex
contains billions of neurons.
– The cortex contains gyri (convolutions), deep
grooves called fissures, and shallower sulci.
(Figure 14.11a)
• Beneath the cortex lies the cerebral white
matter, tracts that connect parts of the brain
with itself and other parts of the nervous
system.
• The cerebrum is nearly separated into right
•
Cerebrum
(Cerebral
Cerebral cortex Hemispheres)
is gray
matter
overlying white matter
– 2-4 mm thick containing
billions of cells
– grew quickly; formed
folds
(gyri) and grooves (sulci
or fissures)
• Longitudinal fissure
separates left & right
cerebral hemispheres
– Corpus callosum is a
Lobes
• Each cerebral hemisphere is further
subdivided into four lobes by sulci or
fissures (Figure 14.11 a,b)
– frontal, parietal, temporal, and occipital.
• A fifth part of the cerebrum, the insula, lies
deep to the parietal, frontal, and temporal
lobes and cannot be seen in an external
view of the brain.
White Matter
• The white matter is under the cortex and
consists of myelinated axons running in
three principal directions (Figure 14.12).
– Association fibers connect and transmit nerve
impulses between gyri in the same
hemisphere.
– Commissural fibers connect gyri in one
cerebral hemisphere to the corresponding gyri
in the opposite hemisphere.
– Projection fibers form ascending and
descending tracts that transmit impulses from
Sensory Areas
• The sensory areas of the cerebral cortex
are concerned with the reception and
interpretation of sensory impulses.
• Some important sensory areas include
– primary somatosensory area,
– primary visual area,
– primary auditory area, and
– primary gustatory area
INTRODUCTION
• The autonomic nervous system (ANS)
operates via reflex arcs.
• Operation of the ANS to maintain
homeostasis, however, depends on a
continual flow of sensory afferent input,
from receptors in organs, and efferent
motor output to the same effector organs.
• Structurally, the ANS includes autonomic
sensory neurons, integrating centers in the
CNS, and autonomic motor neurons.
SOMATIC AND AUTONOMIC
NERVOUS SYSTEMS
• The autonomic nervous system contains
both autonomic sensory and motor
neurons.
– Autonomic sensory neurons are associated
with interoceptors.
– Autonomic sensory input is not consciously
perceived.
• The ANS also receives sensory input from
somatic senses and special sensory
neurons.
SOMATIC vs AUTONOMIC
NERVOUS SYSTEMS
• All somatic motor pathways consist of a
single motor neuron
• Autonomic motor pathways consists of
two motor neurons in series
– The first autonomic neuron motor has its cell
body in the CNS and its myelinated axon
extends to an autonomic ganglion.
• It may extend to the adrenal medullae rather than
an autonomic ganglion
– The second autonomic motor neuron has its
cell body in an autonomic ganglion; its
Basic Anatomy of ANS
• Preganglionic neuron
– cell body in brain or spinal cord
– axon is myelinated type B fiber that extends
to autonomic ganglion
• Postganglionic neuron
– cell body lies outside the CNS in an
autonomic ganglion
AUTONOMIC NERVOUS
SYSTEM
• The output (efferent) part of the ANS is
divided into two principal parts:
– the sympathetic division
– the parasympathetic division
– Organs that receive impulses from both
sympathetic and parasympathetic fibers are
said to have dual innervation.
• Table 15.1 summarizes the similarities and
differences between the somatic and
autonomic nervous systems.
Divisions
of the ANS
• 2 major divisions
– parasympathetic
– sympathetic
• Dual innervation
– one speeds up
organ
– one slows down
organ
– Sympathetic NS
increases heart rate
– Parasympathetic
Dual Innervation, Autonomic
Ganglia
• Parasympathetic
• Sympathetic
(thoracolumbar)
division
– preganglionic cell
bodies in thoracic and
first 2 lumbar
segments of spinal
cord
• Ganglia
– trunk (chain) ganglia
near vertebral bodies
– prevertebral ganglia
(craniosacral)
division
– preganglionic cell
bodies in nuclei of
4 cranial nerves
and the sacral
spinal cord
• Ganglia
– terminal ganglia in
wall of organ
Postganglionic Neurons:
Sympathetic vs.
Parasympathetic
• Sympathetic preganglionic neurons pass
to the sympathetic trunk. They may
connect to postganglionic neurons in the
following ways. (Figure 17.5).
– May synapse with postganglionic neurons in
the ganglion it first reaches.
– May ascend or descend to a higher of lower
ganglion before synapsing with postganglionic
neurons.
– May continue, without synapsing, through the
sympathetic trunk ganglion to a prevertebral