Spinal Cord Reflexes Peripheral Nervous System
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Transcript of Spinal Cord Reflexes Peripheral Nervous System
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
• 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
Spinal Nerves
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 - PNSsomatic (SNS)
sensorymotor
autonomic (ANS)sensorymotor parasympathetic
sympathetic
Peripheral Nervous System (PNS)
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
Centralnervous system Peripheral nervous system Effector organs
Somatic nervous system
Sympatheticdivision
Autonomicnervoussystem
Parasympatheticdivision
KEY:Preganglionic axons(sympathetic)
Postganglionic axons(sympathetic)
Myelination Preganglionic axons(parasympathetic)
Postganglionic axons(parasympathetic)
Acetylcholine
Acetylcholine
Acetylcholine
Epinephrine andnorepinephrine
Bloodvessel
Adrenal medullaAcetylcholine
Ganglion
Ganglion
Norepinephrine
Skeletalmuscle
Smooth muscle(e.g., in stomach)
Glands
Cardiacmuscle
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 post-ganglionic neuron transmit impulse from CNS to the effector
• Neurotransmitters: norepinephrine and epinephrine (effector organs)
Parasympathetic
Eye
Salivaryglands
Heart
Lungs
Cervical
StomachThoracic
T1
Pancreas
Liver and gall-bladder
L1
Lumbar
Bladder
Genitals
Pelvic splanchnicnerves
Sacral nerves (S2 – S4)
Genitals
Bladder
Adrenalgland
Liverand gall-bladder
Pancreas
Stomach
Heart
Lungs
Sympathetic
Eye
Skin
Salivaryglands
Brain stem
Cranialnerves
Sympatheticganglia
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 SystemIntegration 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
1. Exteroceptors
2. Interoceptors
3. Proprioceptors
Classification by Location
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
Tactiletouch, pressure,vibration, itch and tickle
Proprioceptivemuscle spindles, tendon organs, joint receptors
Thermalwarm and cold
Painfast and slow
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
• 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.
Referred Pain
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
Nonrapid eye movement (NREM)
Rapid eye movement (REM)
Stages of Sleep
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.