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.