Chapter 13 Spinal Cord

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Spinal Cord
Reflexes
Peripheral Nervous
System
Spinal Cord
Anatomy
• Extends from the
foramen magnum of the
skull to the first or
second lumbar vertebra
• Provides a two-way
conduction pathway
from the brain to and
from the brain
• 31 pairs of spinal nerves
arise from the spinal
cord
• Cauda equina is a
collection of spinal
nerves at the inferior
end
Spinal Cord Anatomy
Spinal Cord Internal Anatomy
Spinal Cord Internal Anatomy
Spinal Cord Input/Output
Spinal Nerves
• 31 left-right pairs of spinal nerves emerge from the
cord at regular intervals (called segments). Except for
the first cervical pair the spinal nerves leave the
vertebral column from the intervertebral foramen
between adjoining vertebrae – the first pair leaves
between the skull and the first cervical vertebrae .
–Cervical – 8 pairs, C1-C8
–Thoracic – 12 pairs, T1-T12
–Lumbar – 5 pairs, L1-L5
–Sacral - 5 pairs, S1-S5
–Coccygeal – 1 nerve pair
Cervical Plexus
Brachial Plexus
Lumbar Plexus
Sacral plexus
Dermatomes
Sensory and Motor Tracts
Reflex Arc
Stretch Reflex
Tendon Reflex
Withdrawal Reflex
Crossed Extensor Reflex
Peripheral Nervous System (PNS)
Peripheral Nervous System - PNS
somatic (SNS)
sensory
motor
autonomic (ANS)
sensory
motor
parasympathetic
sympathetic
PNS: Autonomic Nervous System
• Motor subdivision of the PNS
– Consists only of motor nerves
• Also known as the involuntary nervous
system
– Regulates activities of cardiac and smooth
muscles and glands
• Two subdivisions
– Sympathetic division
– Parasympathetic division
PNS: Differences Between Somatic
and Autonomic Nervous Systems
Somatic Nervous
System
Autonomic Nervous
System
Nerves
One-neuron; it
originates in the CNS
and axons extend to
the skeletal muscles
served
Two-neuron system
consisting of
preganglionic and
postganglionic
neurons
Effector organ
Skeletal muscle
Smooth muscle,
cardiac muscle,
glands
Subdivisions
None
Sympathetic and
parasympathetic
Neurotransmitter
Acetylcholine
Acetylcholine,
epinephrine,
norepinephrine
PNS: Differences Between Somatic
and Autonomic Nervous Systems
Central
nervous system
Peripheral nervous system
Effector organs
Acetylcholine
Skeletal
muscle
Somatic nervous system
Acetylcholine
Autonomic
nervous
system
Sympathetic
division
Smooth muscle
(e.g., in stomach)
Norepinephrine
Ganglion
Acetylcholine
Epinephrine and
norepinephrine
Adrenal medulla
Acetylcholine
Blood
vessel
Glands
Cardiac
muscle
Parasympathetic
division
Ganglion
KEY:
Preganglionic
axons
(sympathetic)
Postganglionic
axons
(sympathetic)
Myelination
Preganglionic
axons
(parasympathetic)
Postganglionic
axons
(parasympathetic)
PNS: Parasympathetic Division
• Preganglionic neurons originate from the
craniosacral regions:
– The cranial nerves III, VII, IX, and X
– S2 through S4 regions of the spinal cord
• Due to site of preganglionic neuron
origination, the parasympathetic division is
also known as the craniosacral division
• Terminal ganglia are at the effector organs
• Neurotransmitter: acetylcholine
PNS: Sympathetic Division
• Preganglionic neurons originate from T1
through L2
• Ganglia are at the sympathetic trunk (near
the spinal cord)
• Short pre-ganglionic neuron and long postganglionic neuron transmit impulse from
CNS to the effector
• Neurotransmitters: norepinephrine and
epinephrine (effector organs)
Parasympathetic
Sympathetic
Eye
Eye
Brain stem
Salivary
glands
Heart
Skin
Cranial
nerves
Sympathetic
ganglia
Salivary
glands
Cervical
Lungs
Lungs
T1
Heart
Stomach
Thoracic
Stomach
Pancreas
Pancreas
L1
Liver and
gallbladder
Lumbar
Adrenal
gland
Bladder
Bladder
Pelvic
splanchnic
nerves
Genitals
Liver
and gallbladder
Genitals
Sacral nerves (S2 – S4)
PNS: Autonomic Functioning
• Sympathetic—“fight or flight”
– Response to unusual stimulus
– Takes over to increase activities
– Remember as the “E” division
• Exercise, excitement, emergency, and
embarrassment
• Parasympathetic—“housekeeping” activites
– Conserves energy
– Maintains daily necessary body functions
– Remember as the “D” division
• digestion, defecation, and diuresis
Peripheral Nervous System
Flow to the CNS
Flow out of the CNS
Peripheral Nervous System
Integration occurs at many locations
along the pathway.
stimulus - environmental change
sensation - awareness of stimulus
perception - interpretation of the
meaning of the stimulus
Sensory Modalities
General senses: somatic and visceral
Special senses
smell,hearing/equilibrium
taste, vision, and hearing
Classification of Sensory Receptors
• Structural classification
• Type of response to a stimulus
• Type of stimuli they detect
Structural Classification of
Receptors
Classification by Location
1. Exteroceptors
2. Interoceptors
3. Proprioceptors
Classification by Stimuli Detected
1. Mechanoreceptors
2. Thermoreceptors
3. Photoreceptors
4. Chemoreceptors
5. Nociceptors
6. Osmoreceptors
Adaptation
Adaptation - generator potential or receptor
potential decreases in amplitude during a
maintained stimulus.
Rapidly adapting - e.g. pressure, touch, smell
Slowly adapting - e.g. pain, body position
Somatic Sensations
Tactile
touch, pressure,vibration,
itch and tickle
Pain
fast and slow
Thermal
Proprioceptive
warm and cold
muscle spindles,
tendon organs, joint
receptors
Sensory Receptors
Pain Sensations
• Nocicceptors = pain receptors
• Free nerve endings found in every tissue of
body except the brain
• Stimulated by excessive distension, muscle
spasm & ischemia
• Tissue injury releases chemicals such as
kinins, or prostaglandins
• Little adaptation occurs
Types of Pain
• Fast Pain (acute)
– occurs rapidly after stimuli (0.1 sec)
– sharp pain like needle puncture or cut
– not felt in deeper tissues
• Slow Pain (chronic)
– begins more slowly & increases in intensity
– aching or throbbing pain of toothache
– in superficial and deep tissues
Referred Pain
• Visceral pain felt just deep to the skin overlying the
stimulated organ or in a surface far from the organ
• Skin area & organ are served by same segment of the
spinal cord.
Pain Relief - Analgesia
• Aspirin and ibuprofen block formation of
prostaglandins that stimulate nociceptors
• Novocaine blocks conduction of nerve
impulses along pain fibers
• Morphine lessens the perception of pain in
the brain
Receptors - Summary
Stages of Sleep
Nonrapid eye movement (NREM)
Rapid eye movement (REM)
Learning and Memory
• Learning is the ability to acquire
new information or skills through
instruction or experience.
• Memory is the process by which
information acquired through
learning is stored and retrieved.
• Immediate memory- recall for a few
seconds.
• Short-term memory- temporary ability to
recall.
• Long-term memory- more permanent.
• Memory consolidation.

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