Transcript Spinal Cord and Spinal Nerves

Chapter 12
Spinal Cord and Spinal Nerves
12-1
Spinal Meninges
• Connective tissue
membranes surrounding
spinal cord and brain
– Dura mater: continuous
with epineurium of the
spinal nerves----thick
– Arachnoid mater: thin
and wispy
– Pia mater: bound tightly
to surface of brain and
spinal cord.
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Cross Section of Spinal Cord
• Roots: spinal nerves
arise as rootlets then
combine to form
roots
– Dorsal (posterior)
root has a
ganglion
– Ventral (anterior)
– Two roots merge
laterally and form
the spinal nerve
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Organization of Neurons in the Spinal
Cord and Spinal Nerves
• Dorsal root
ganglion:
collections of
cell bodies of
unipolar
sensory neurons
forming dorsal
roots.
• Motor neuron cell bodies are in anterior and lateral horns of
spinal cord gray matter.
– Multipolar somatic motor neurons in anterior (motor) horn
– Autonomic neurons in lateral horn
• Axons of motor neurons form ventral roots and pass into spinal
nerves
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Reflex Arc
• Basic functional unit of nervous system and simplest portion
capable of receiving a stimulus and producing a response
• Automatic response to a stimulus that occurs without conscious
thought. Homeostatic.
• Components
– Action potentials
produced in
sensory receptors
transmitted to
– Sensory neuron.
To-Interneurons.
To-Motor neuron.
To– Effector organ
which responds
with a reflex
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Structure of Peripheral Nerves
• Consist of
– Axon bundles
– Schwann cells
– Connective tissue
• Endoneurium:
surrounds individual
neurons
• Perineurium:
surrounds axon groups
to form fascicles
• Epineurium: surrounds
the entire nerve
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Branches of Spinal Nerves
•Dorsal Ramus: innervate deep muscles of the trunk responsible for movements of
the vertebral column and the C.T. and skin near the midline of the back.
•Ventral Ramus: what they innervate depends upon which part of the spinal cord
is considered.
–Thoracic region: form intercostal nerves that innervate the intercostal
muscles and the skin over the thorax
–Remaining spinal nerve ventral rami (roots of the plexus): form five plexuses
(intermingling of nerves).
• Ventral rami of C1-C4= cervical
plexus
• Ventral rami of C5-T1= brachial
plexus
• Ventral rami of L1-L4= lumbar
plexus
• Ventral rami of L4-S4= sacral plexus
• Ventral rami of S4 and S5= coccygeal
plexus
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Chapter 13
Brain and Cranial Nerves
13-8
Brain and Cranial Nerves
• Brain
–
–
–
–
Part of CNS contained in cranial cavity
Control center for many of body’s functions
Much like a complex computer but more
Parts of the brain
• Brainstem: connects spinal cord to brain; integration of
reflexes necessary for survival
• Cerebellum: involved in control of locomotion, balance,
posture
• Diencephalon: thalamus, hypothalamus
• Cerebrum: conscious thought, control
• Cranial nerves: part of PNS arise directly from
brain. Two pairs arise from cerebrum; ten pairs
arise from brainstem
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Sagittal Section of Brain
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Brainstem: Medulla Oblongata
• Most inferior part
• Continuous with spinal cord; has both ascending and
descending nerve tracts
• Regulates: heart rate, blood vessel diameter, respiration,
swallowing, vomiting, hiccupping, coughing, and sneezing
Brainstem: Pons
• Superior to the medulla oblongata
– Sleep center
– Respiratory center coordinates with center in medulla
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Brainstem: Midbrain
• Also called mesencephalon
• Small and superior to pons
– Tectum: four nuclei that form mounds on dorsal surface of midbrain.
Corpora quadrigemina
• Each separate part is a colliculus
• Two superior colliculi involved in visual reflexes; receive information from
inferior colliculi, eyes, skin, cerebrum
• Two inferior colliculi involved in hearing
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Reticular Formation
• Group of nuclei scattered throughout
brainstem
• Controls cyclic activities such as sleepwake cycle (maintains alertness)
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Cerebellum
• Attached to brainstem posterior
to pons
• Cerebellar peduncles: fiber
tracts that communicate with
other parts of brain
– Superior: to midbrain
– Middle: to pons
– Inferior: to medulla oblongata
• Gray cortex and nuclei with
white matter (tracts) between
• Cortex folded in ridges called
folia; white matter resembles a
tree (arbor vitae)
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Cerebellar Functions
• Flocculonodular lobe: balance and eye
movements
• Vermis and medial portion of hemispheres:
posture, locomotion, fine motor
coordination leading to smooth, flowing
movements
• Lateral hemispheres, major portion: works
with cerebrum to plan, practice, learn
complex movements
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Diencephalon
• Located between
brainstem and
cerebrum
• Components:
thalamus,
subthalamus,
epithalamus,
hypothalamus
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Thalamus
• Two lateral portions connected by the
intermediate mass
• Surrounded by third ventricle
• Sensory information from spinal cord
synapses here before projecting to
cerebrum
– Medial geniculate nucleus: auditory
information
– Lateral geniculate nucleus: visual
information
– Ventral posterior nucleus: most
other types sensory information
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Hypothalamus
• Most inferior portion of diencephalon
• Mammilary bodies: bulges on ventral
surface; olfactory reflexes and emotional
responses to odors
• Infundibulum: stalk extending from floor;
connects hypothalamus to posterior pituitary
gland. Controls endocrine system.
• Receives input from viscera, taste receptors,
nipples, external genitalia, prefrontal cortex
• Efferent fibers to brainstem, spinal cord
(autonomic system), through infundibulum
to posterior pituitary, and to cranial nerves
controlling swallowing and shivering
• Important in regulation of mood, emotion,
sexual pleasure, satiation, rage, and fear
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Cerebrum
• Largest portion of brain
• Composed of right and left
hemispheres each of which has the
following lobes: frontal, parietal,
occipital, temporal
• Sulci and Fissures
– Longitudinal fissure: separates the two
hemispheres
– Lateral fissure: separates temporal lobe
from frontal and parietal lobes
– Central sulcus: separates frontal and
parietal lobes
• Cortex: outer surface
– Gyri are folds (increase surface area)
– Sulci are depressions
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Cerebrum, cont.
• Central sulcus: between the precentral gyrus (primary
motor cortex) and postcentral gyrus (primary somatic
sensory cortex)
• Frontal lobe: voluntary motor function, motivation,
aggression, sense of smell, mood
• Parietal lobe: reception and evaluation of sensory
information except smell, hearing, and vision
• Occipital lobe: reception and integration of visual input
• Temporal lobe: reception and evaluation for smell and
hearing; memory, abstract thought, judgment. Insula is
within.
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Meninges
• Connective tissue
membranes
– Dura mater:
superficial
– Arachnoid mater
– Pia mater: bound
tightly to brain
– Spaces
• Subdural: serous fluid
• Subarachnoid: CSF
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Ventricles
• Lateral ventricles: within cerebral hemispheres; separated by
septa pellucida
• Third ventricle: within diencephalon
• Interventricular foramina join lateral ventricles with third
• Fourth ventricle: associated
with pons and medulla
oblongata. Connected to third
ventricle by the cerebral
aqueduct, continuous with
the spinal cord.
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Cerebrospinal Fluid (CSF)
•
•
•
•
Similar to serum, but most protein removed
Bathes brain and spinal cord
Protective cushion around CNS
Choroid plexuses produce CSF which fills ventricles and
other parts of brain and spinal cord
– Composed of ependymal cells, their support tissue, and
associated blood vessels
– Blood-cerebrospinal fluid barrier
• Endothelial cells of capillaries attached by tight
junctions
• Substances do not pass between cells
• Substances must pass through cells
• Makes the barrier very selective
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Chapter 14
Integration of
Nervous System Functions
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Senses
• Means by which brain receives information about
environment and body.
• Sensation (perception): conscious awareness of stimuli
received by sensory receptors.
• Steps to sensation
– Stimuli originating either inside or outside of the body
must be detected by sensory receptors and converted
into action potentials, which are propagated to the CNS
by nerves.
– Within the CNS, nerve tracts convey action potentials
to the cerebral cortex and to other areas of the CNS.
– Action potentials reaching the cerebral cortex must be
translated so the person can be aware of the stimulus.
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Types of Senses
• General: distributed over large part of body. Receptor
generates an action potential called a generator
potential that then travels to the brain. Called primary
receptors.
– Somatic (information about the body and environment):
touch, pressure, temperature, proprioception, pain
– Visceral (information about internal organs): pain and
pressure
• Special senses: smell, taste, sight, hearing, balance.
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Types of Sensory Receptors
• Mechanoreceptors: compression, bending,
stretching of cells. Touch, pressure,
proprioception, hearing, and balance
• Chemoreceptors: chemicals become attached to
receptors on their membranes. Smell and taste
• Thermoreceptors: respond to changes in
temperature
• Photoreceptors: respond to light: vision
• Nociceptors: extreme mechanical, chemical, or
thermal stimuli. Pain
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Types of Receptors
Based on Location
• Exteroreceptors: associated with skin
• Visceroreceptors: associated with organs
• Proprioceptors: associated with joints,
tendons (proprioception is the sense of the
orientation of one's limbs in space)
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Sensory Nerve Endings in Skin
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Free Nerve Endings
• Simplest, most common sensory receptor
• Scattered through most of body;
visceroceptors are of this type.
• Type responsible for temperature sensation
– Cold: 10-15 times more numerous than warm
– Warm
– Pain: responds to extreme cold or heat
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Merkel (Tactile) Disks
• Associated with dome-shaped mounds of
thickened epidermis in hairy skin
• Light touch and superficial pressure
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Pacinian Corpuscles
• Deep cutaneous pressure; vibration
• When associated with joints, involved in
proprioception (proprioception is the sense of the
orientation of one's limbs in space)
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Meissner (Tactile) Corpuscles
•
•
•
•
•
Two-point discrimination
Ability to detect simultaneous stimulations at two points
on the skin.
Used to determined texture of objects.
Numerous and close together on tongue and fingertips
Light touch & light pressure
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Sensory and Association Areas
of the Cerebral Cortex
• Sensory
– Primary somatic sensory cortex (general sensory area): posterior to
the central sulcus. Postcentral gyrus.
– General sensory input: pain, pressure, temperature
– Taste area: inferior end of postcentral gyrus
– Olfactory cortex: inferior surface of frontal lobe
– Primary auditory cortex: superior part of temporal lobe
– Visual cortex: occipital lobe
• Association areas: process of recognition
– Somatic sensory: posterior to
primary somatic sensory cortex
– Visual association: anterior to
visual cortex: present visual
information compared to past
information
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Referred Pain
• Referred: sensation in
one region of body
that is not source of
stimulus. Organ pain
usually referred to the
skin. Both the organ
and that region of the
skin input to the same
spinal segment and
converge on the same
ascending neurons.
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Phantom and Chronic Pain
• Phantom: occurs in people who have appendage
amputated or structure removed such as a tooth.
Gate control theory of pain-- in uninjured limb,
pressure and touch sensation inhibits pain (thus
the success of massage in pain relief). These
sensations are lost with amputations and thus their
inhibitory effect.
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Control of Skeletal Muscles
• Motor system: maintains posture and balance; moves
limbs, trunk, head, eyes; facial expression, speech.
• Reflexes: movements that occur without conscious
thought
• Voluntary movements: consciously activated to
achieve a specific goal
• Two neurons: upper and lower
– Upper motor neurons: directly or through interneurons
connect to lower
– Lower motor neurons: axons leave the CNS, extend through
PNS to skeletal muscles. Cell bodies in anterior horns of
spinal cord and in cranial nerve nuclei of brainstem
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Motor Areas of the Cerebral Cortex
• Precentral gyrus (primary motor cortex,
primary motor area): 30% of upper motor
neurons. Another 30% in premotor area.
Control voluntary movements, especially
fine motor movements of hands
• Premotor area: anterior to primary motor
cortex. Motor functions organized before
initiation
• Prefrontal area: motivation, foresight to
plan and initiate movements, emotional
behavior, mood
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Direct Pathways
• Control muscle tone and
conscious fine, skilled
movements in the face and
distal limbs
• Direct synapse of upper motor
neurons of cerebral cortex with
lower motor neurons in
brainstem or spinal cord
• Tracts
– Corticospinal: direct
control of movements
below the head
– Corticobulbar: direct
control of movements in
head and neck
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Indirect Pathways
• Control conscious and unconscious muscle
movements in trunk and proximal limbs.
• Synapse in some intermediate nucleus
rather than directly with lower motor
neurons.
• Tracts
– Rubrospinal: upper neurons synapse in
red nucleus. Similar to comparator
function of cerebellum. Regulates fine
motor control of muscles in distal part
of upper limb.
– Vestibulospinal: influence neurons
innervating extensor muscles in trunk
and proximal portion of lower limbs;
help maintain upright posture.
– Reticulospinal: maintenance of
posture.
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Cerebellum
• Helps maintain muscle tone in postural
muscles, helps control balance during
movement, and coordinate eye movements
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Cerebellar Comparator Function
1. The motor cortex sends action potentials to lower motor neurons in
the spinal cord.
2. Action potentials from the motor cortex inform the cerebellum of the
intended movement.
3. Lower motor neurons in the spinal
cord send action potentials to
skeletal muscles, causing them to
contract.
4. Proprioceptive signals from the
skeletal muscles and joints to the
cerebellum convey information &
cerebellum helps accomplish fine
motor coordination of simple
movements. It compares the
intended movement with the actual
movement and the result is smooth
& coordinated movements. (ex:
touching your nose--------not rapid
complex movements)
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Speech
• Area normally in left cerebral cortex
• Wernicke's area: sensory speech- understanding what is heard
and thinking of what one will say.
• Broca's area: motor speech- sending messages to the appropriate
muscles to actually make the sounds.
o
• Sound is heard first in the 1 association area, then information
travels to Wernicke's area. Neuronal connections between
Wernicke's area and Broca's area.
• Aphasia: absent or defective speech or language comprehension.
Caused by lesion somewhere in the auditory/speech pathway.
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Right and Left Cerebral Cortex
• Right: controls muscular activity in and receives
sensory information from left side of body
• Left: controls muscular activity in and receives sensory
information from right side of body
• Sensory information of both hemispheres shared
through commissures: corpus callosum
• Language, and possibly other functions like artistic
activities, not shared equally
– Left: mathematics and speech
– Right: three-dimensional or spatial perception, recognition of
faces, musical ability
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Chapter 16
Autonomic Nervous System
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Peripheral Nervous System
• Peripheral nerves contain both motor and sensory
neurons
• Among the motor neurons, some of these are
somatic and innervate skeletal muscles while some
are autonomic and innervate smooth muscle,
cardiac muscle, and glands
• Sensory neurons are not subdivided into somatic
and autonomic since there is overlap in function;
e.g., pain receptors can stimulate both somatic and
autonomic reflexes
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Somatic and Autonomic Nervous Systems
Somatic
Autonomic
• Skeletal muscle
• Conscious and
unconscious movement
• Skeletal muscle contracts
• One synapse
• Acetylcholine
• Receptor molecules:
nicotinic
• Smooth and cardiac muscle
and glands
• Unconscious regulation
• Target tissues stimulated or
inhibited
• Two synapses
• Acetylcholine by
preganglionic neurons and
ACh or norepinephrine by
postganglionic neurons
• Receptor molecules: varies
with synapse and
neurotransmitter
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Autonomic Nervous System
• Divided into sympathetic and parasympathetic divisions as
well as the enteric nervous system
• Sympathetic and parasympathetic divisions often supply the
same organs but differ in a number of features
• The enteric nervous system
– Nerve plexuses within the wall of the digestive tract.
– Contributions from: sensory neurons between digestive tract
and CNS, ANS motor neurons between the CNS and the
digestive tract, and enteric neurons confined within the
plexuses
– Functions
•
•
•
•
Stimulate/inhibit smooth muscle contraction
Stimulate/inhibit gland secretions
Detect changes in content of lumen
Interneurons connect sensory and motor aspects of enteric
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Sympathetic (Thoracolumbar)
Division
• Preganglionic cell bodies in lateral
horns of spinal cord T1-L2:
thoracolumbar
• Preganglionic axons pass through
ventral roots to white rami
communicantes to the
retroperitoneal sympathetic chain
ganglia.
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Routes of Sympathetic Axons
1.
2.
Spinal nerves: preganglionic axons synapse (at the same or
different level) with postganglionic neurons within the
sympathetic chain. These postganglion neurons exit the
ganglia through the gray rami communicantes and re-enter
spinal nerves.
Sympathetic nerves: preganglionic axons synapse (at the
same or different level) with postganglionic neurons, which
exit the ganglia through sympathetic nerves
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Routes of Sympathetic Axons
3. Splanchnic nerves: preganglionic axons pass through the chain
ganglia without synapsing to form splanchnic nerves.
Preganglionic axons then synapse with postganglionic neurons in
collateral ganglia. Postganglionic neurons then send fibers to
target organs (viscera).
4. Innervation to adrenal gland: preganglionic axons synapse
with the cells of the adrenal medulla. Embryologically, adrenal
medulla is derived from same cells as postganglionic ANS cells.
Medullary cells secrete epinephrine and norepinephrine; act as
hormones promoting physical activity.
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Parasympathetic (Craniosacral)
Division
• Preganglionic cell bodies in
nuclei of brainstem or lateral
parts of spinal cord gray
matter from S2-S4
– Preganglionic axons from
brain pass to terminal ganglia
through cranial nerves III, VII,
IX and X
– Preganglionic axons from
sacral region pass through
pelvic splanchnic nerves to
terminal ganglia
• Terminal ganglia located
near organ innervated or
embedded in wall of organ
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Enteric Nervous System
• Consists of nerve plexuses within wall of
digestive tract
– Sources of neurons
• Sensory neurons that connect the digestive tract to
CNS
• ANS motor neurons that connect CNS to digestive
tract
• Enteric neurons that are confined to enteric plexuses
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Parasympathetic Division
•
Outflow is through cranial and pelvic splanchnic
nerves
1. Cranial nerves supplying the head and neck.
Preganglion axons extend to terminal ganglia in
head. Postganglionic neurons supply nearby
structures.
a.
Oculomotor nerve through ciliary ganglion. Ciliary
muscles and iris of the eye
b. Facial nerve through pterygopalatine ganglion supplies
lacrimal gland and mucosal glands of nasal cavity and
palate. Through submandibular ganglion, supplies
submandibular and sublingual salivary glands
c. Glossopharyngeal nerve through otic ganglion supplies
parotid salivary gland
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Sensory Neurons in Autonomic
Nerve Plexuses
• Parts of reflex arcs regulating organ
activities
• Transmit pain and pressure sensations from
organs to the CNS
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Physiology of ANS
• Neurotransmitters: primary substances produced
by neurons of ANS
– Acetylcholine released by cholinergic neurons
– Norepinephrine released by adrenergic neurons
• Certain cells have receptors that combine with
neurotransmitters causing a response in the cell
– Cholinergic: bind acetylcholine. Have two different
forms: nicotinic and muscarinic
• Nicotinic: all receptors on postganglionic neurons, all skeletal
muscles, adrenal glands
• Muscarinic: all receptors on parasympathetic effectors,
receptors of some sweat glands
– Adrenergic receptors bind norepinephrine/epinephrine
• Alpha and beta receptors.These are further subdivided into
categories. α1 and β1 usually have opposite affects than α2 and
β2
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Location of ANS Receptors
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16-64
Regulation of ANS
• Autonomic reflexes control most of activity of visceral
organs, glands, and blood vessels.
• Autonomic reflex activity influenced by hypothalamus
and higher brain centers, but it is the hypothalamus that
has overall control of the ANS.
• Sympathetic and parasympathetic divisions influence
activities of enteric nervous system through autonomic
reflexes. These involve the CNS. But, the enteric
nervous system can function independently of CNS
through local reflexes. E.g., when wall of digestive
tract is stretched, sensory neurons send information to
enteric plexus and then motor responses sent to smooth
muscle of gut wall and the muscle contracts.
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Autonomic Reflexes
a) Parasympathetic
reflex via vagus
lowers heart rate.
b) Sympathetic reflex via
cardiac accelerator
nerves (sympathetic)
cause heart rate to
increase.
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Enteric Nervous System:
Autonomic and Local Reflexes
• Regulation of activity of digestive tract
• Sensory neurons of enteric plexuses supply CNS
with information
• Autonomic neurons affect responses of smooth
muscle and glands
• Local reflex: does not involve CNS. Produces
involuntary, unconscious, stereotypical response
to stimulus. E.g., stretch of wall of digestive tract
causes contraction of smooth muscle of the wall.
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Influence of Brain
on Autonomic Functions
16-68
Functional Generalizations of ANS
• Dual innervation to most organs with sympathetic
and parasympathetic having the opposite effects.
• Either division alone or both working together can
coordinate activities of different structures.
• Sympathetic prepares body for physical activity or
flight-or-fight response. But also important at rest.
Blood vessel walls receive only sympathetic
stimulation, so at rest, sympathetic is responsible
for maintenance of blood pressure.
• In general, parasympathetic more important for
resting conditions: SLUDD: salivation,
lacrimation, urination, digestion, defecation
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Innervation of Organs by ANS
16-70
Responses to Exercise
(Fight or Flight Response)
• Increased heart rate and force of contraction
• Blood vessel dilation in skeletal and cardiac
muscles
• Dilation of air passageways
• Energy sources availability increased
– Glycogen to glucose
– Fat cells break down triglycerides
• Muscles generate heat, body temperature increases
• Sweat gland activity increases
• Decrease in nonessential organ activities
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