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151

Sponteneous elevation in intracellular calcium levels

Ca++ “sparks”

152

- Uses much less ATP
- Slow onset but prolonged time for contraction
“Latch” State: force of contraction maintained with low
energy expenditure (300x less than skeletal muscles) during tonic contraction
- Greater force of contraction (4-6 kg/cm2)
- May produce connective tissue (e.g. atherosclerosis)

Smooth Muscle

153

Cardiac Muscle Action Potential

Phase 0: Rapid Depolarization - Sodium Influx
Phase 1: Initial Repolarization - Partial efflux of K
Phase 2: Plateau - influx of Ca+2
Phase 3: Final repolarization - Complete potassium influx
Phase 4: Resting - slightly more than influx of K

154

Which are the one that increases Calcium?

1. L Type
2. Calcium ATPase
3. Calcium Sodium Antiport

155

♣ output from the CNS travels along two pathways that are anatomically and functionally distinct

Nervous System

156

α-motor neuron links CNS to skeletal muscles

Somatic Motor Neurons (SNS)

157

autonomic neurons links CNS to visceral organs

Autonomic Motor Neurons (ANS)

158

ANS and SNS are organized on the basis of the reflex arc, composed of:

afferent limb
integrating center
efferent limb

159

afferent fibers from visceral structures reach CNS via ___

autonomic pathways

160

visceral afferents are found in the:

CN 7, 8, 9 and 10 (VAGUS nerve is the most parasympathetic

161

Pathway: SINGLE NEURON PATHWAY
Neurons involved: ALPHA-MOTOR NEURONS (large diameter, myelinated, rapidly conducting
Effector: SKELETAL MUSCLE
Innervation of effector: skeletal muscle innervated by single neuron
Neurotransmitter: Ach only

Somatic Nervous Sytem

162

Effect of NT: release of Ach (contraction of skeletal muscle)
Location: NEUROMUSCULAR JUNCTION
Location of NT synthesis and storage: AXON TERMINAL
Postsynaptic receptors: NICOTINIC RECEPTOR (N1) at Motor End Plate (MEP)

Somatic Nervous System

163

Pathway: TWO WAY NEURON PATHWAY
Neurons involved: PREGANGLIONIC - small diameter, myelinated, slow conducting B fibers
POSTGANGLIONIC - small diameter, unmyelinated C fibers
Effector: VISCERAL stuctures
Innervation of effector: VISCERAL effectoe may be innervated by many postganglionic neurons
Neurotransmitter: Ach, NE, Epi, Dopamine

Autonomic Nervous System

164

Effect of NT: response may be INHIBITORY of EXCITATORY
Location: NEUROEFFECTOR JUNCTION
Location of NT synthesis and storage: BEADS or VARICOSITIES that line the branching networks of postganglionic neurons
Postsynaptic receptors: postsynaptic receptors widely distributed on the target tissues
no specialized region of receptors like the MEP

Autonomic Nervous System

165

- part of the nervous system responsible for homeostasis
- regulatory in function
- essentially motor
- without ANS, survival is possible but the ability to adapt to stressors from the environment will be severely compromised
- striking characteristics - rapidity and intensity with which it can change visceral functions

Autonomic Nervous System

166

- can increase HR to 2x normal within 3-5 secs.
- can double ABP in 10-15 secs.
- can cause sweating within secs. operates through visceral reflexes

Autonomic Nervous System

167

Most of the organs are parasympathetically innervated except for _____

Sweat glands, blood vessel

168

Classification of the ANS

Anatomic differences
Functional differences
Biochemical differences
Pharmacologic differences

169

Divisions of ANS Based on Anatomic Differences

- Sympathetic NS
- Parasympathetic NS
- Enteric Nervous System / Intramural Nerve Plexus of GIT

170

- “mini brain” because it contains all elements of nervous system
- sensory and motor neurons, and interneurons (plexuses)
- can function autonomously but normal GI function often requires communication between the CNS and the ENS
- confined within GIT walls
- two divisions:
Myenteric or Auerbach’s Plexus - contraction of smooth muscle
Meissner’s or Submucosal Plexus - secretion

Enteric Nervous System

171

- Thoracolumbar Outflow
- larger division
- prepares individual to cope with emergency
- ensures that the body can respond appropriately to a stressful or emergency situation
- concerned with mobilizing the person for “fight or flight”

Symphathetic Nervous Sytem

172

♣ mydriasis
♣ increased ABP
♣ vasoconstriction
♣ increased in skeletal muscle strength
♣ increased ventilation

Symphathetic Nervous Sytem

173

♣ decreased GIT activity
♣ elevation of plasma glucose and fatty acid levels
♣ increase in mental activity
♣ lowers threshold in the reticular formation
♣ redistribution of blood from skin and splanchnic regions towards skeletal muscle

Symphathetic Nervous Sytem

174

a neuroendocrine organ

Adrenal Medulla

175

2 reasons why adrenal medulla is considered to be part of the ANS

1. Nerve supply to AM is anatomically and biochemically identical to autonomic preganglionic nerve fibers

2. Adrenomedullary cells are embryologically, anatomically and functionally identical to postganglionic autonomic nerve fibers

176

2 reasons why adrenal medulla is considered a component of SNS and not PSNS

1. Origin of nerve supply of AM is thoracolumbar
2. Adrenomedullary cells secrete catecholamines
Epinephrine – 80%
Norepinephrine – 20%, the neurotransmitter of sympathetic nerves

177

- Craniosacral Outflow
- dominates in quiet, relaxed situation
- activity tends to conserve energy and restore the body’s resources (anabolic nervous system)

Parasympathetic Nervous System

178

- cranial outflow supplies the visceral structures in the head through CN 3, 7 and 9 and the structures in the thorax and upper abdomen through CN 10
- sacral outflow supplies pelvic viscera through pelvic branches of the 2nd to 4th spinal nerves

Parasympathetic Nervous System

179

Origin of preganglionic neuron: CRANIOSACRAL
Location of peripheral ganglia: TARGET ORGAN
Length of preganglionic fiber: LONG
Length of postganglionic fiber: SHORT
Degree of branching of preganglionic nerve: LESS BRANCHING

Parasympathetic Nervous System

180

Origin of preganglionic neuron: THORACOLUMBAR
Location of peripheral ganglia: PARAVERTEBRAL
Length of preganglionic fiber: SHORT
Length of postganglionic fiber: LONG
Degree of branching of preganglionic nerve: MORE BRANCHING

Sympathetic Nervous System