Describe the function of the autonomic nervous system
- Controls involuntary effectors - smooth, cardiac and glandular cells (endocrine and exocrine)
- Targets lungs, heart, digestive, urinary and reproductive systems, blood vessels, sweat glands, piloerector muscles.
- Critical for homeostasis.
Compare and contrast the structure and function of the somatic nervous system with that of the autonomic nervous system.
Somatic motor pathway begins in anterior horn and involves single efferent fiber that extends to effector
Autonomic pathway begins in lateral horn involves 2 efferent fibers, one from the spinal cord to ganglion and other going from ganglion to effector
Somatic always uses ACh NTM and is always excitatory
Autonomic uses ACh or NE and can be excitatory or inhibitory
Explain the functions of the autonomic nervous system.
- "E" division - embarrassment, emergency, excitement.
- Increases alertness, heart rate, blood pressure, pulmonary air flow, blood flow to skeletal / cardiac muscles.
- Fight or flight response - extreme
Compare and contrast the function and structure of the sympathetic and parasympathetic divisions of the autonomic nervous system.
Compare:Innervate same organs - sometimes cooperative effects, sometimes contrasting effects; sympathetic effects last longer than parasympathetic - Ach broken down quickly
- Sympathetic - E division, emergency/excitement, decreases blood to digestive, reproductive, skin;
- Parasympathetic - D-division (defecate, digestion, diuresis, sex) - calming effect on body, conserves energy, maintains daily necessary bodily functions
Compare: Body does not shift from one to another - always autonomic tone; degree of symp/para depends on needs of body
- Sympathetic - preganglionic somas in lateral horns, short preganglia nerves, long postganglionic. Preganglionic synapse enter sympathetic chain ganglion, three paths: a) synapse with postsynaptic neuron, b) travel up or down sympathetic chain ganglion to postganglionic neuron, c) pass through chain without synapse to form splanchnic nerve, into collageral ganglion - in to network of abdominal aortic complex.
Parasympathetic - preganglionic axons run to terminal ganglia - close to effector organs. Long preganglionic fibers, short post. No chain ganglion.Less neural divergence;
Describe the stimulation and release of hormones by the adrenal medulla.
Adrenal medulla - modified sympathetic ganglion (without neurons)
1) preganglionic fibers extend directly to adrenal medulla; inner portion (medulla), outer portion (adrenal cortex).
2) Stimulation releases 85% epinephrine, 15% norepinephrine - directly in to blood, not as neurotransmitters
Explain how the sympathetic and parasympathetic divisions can have contrasting effects on the same organs.
- Sympathetic - heart rate increase;
- para - decrease heart rate.
- Some organs respond differently to same division - para - bladder muscles contract; relax internal urethral sphincter.
- Most organs have enervation from both para and symp.
- Secrete different neurotransmitters, have different receptors.
Explain how a neurotransmitter can have different effects on different target cells.
- Cells with different receptors respond differently to same neurotransmitter.
- ACh secreted by both pre and post ganglionic fibers of para division = cholinergic
- A few postsynaptic fibers of symp division are cholinergic, most are adrenergic
- All preganglionic (para and symp) always cholinergic
P- ostganglionic - para - always cholinergic; symp - most adrenergic, a few cholinergic
Describe the two types of cholinergic receptors.
Muscarinic - all cardiac (inhibitory effects), smooth (excitatory), gland cells that respond to ACh; can be inhibitory or excitatory; turn on various 2nd messenger systems
Nicotinic - activate all skeletal muscles, cells of adrenal medulla, postsynaptic cells of terminal ganglia;
- target cells can be nicotinic or muscarinic; always excitatory
Describe the two types of adrenergic receptors.
α-adenergic receptors - excitatory effects - smooth muscle contraction in blood vessels, uterus; inhibit intestinal mobility (inhibit cAMP, activates Ca2+ as 2nd messenger)
β-adenergic receptors - inhibitory effects; relaxes smooth muscles of bronchioles for increased air flow; works through cAMP systems
Describe what happens to acetylcholine and noradrenalin after they are released from their receptors.
ACh - Broken down quickly by acetylcholinesterase
Noradrenalin - 1) reuptake by synaptic knob for reuse; 2) reuptake then broken down by MAO;
3) diffuses to adjacent tissues, broken down by COMT; 4) significant amounts pass through into blood, have prolonged effects on the body
Identify the other molecules released by postsynaptic fibers.
Neuropeptides - modulate ACh and NE effects
Enkephalin - substance P, neuropeptide Y, somatostatin, neurostensin, gonadotrophin-releasing hormone
Explain how the sympathetic and parasympathetic divisions can have cooperative effects on a target organ.
2 systems act on different effectors to produce an effect (e.g. saliva - para - increases production of watery, enzyme rich secretions, symp - increases mucous production)
Explain how the sympathetic and parasympathetic divisions can have opposing effects on a target organ.
Divisions have opposite effects.
Innervations of same effector cells bind to different receptors,
e.g. cardiac muscle. Not innervated equally; some only controlled by one.
e.g. sympathetic - adrenergic effect - pupil dilation; parasympathetic - cholinergic effect, pupil constricted
Explain how the autonomic nervous system controls blood flow through blood vessels.
Sympathetic control of vasomotor tone shifts blood from one organ to another
e.g. during exercise, heart and skeletal need more, away from digestive, urinary and reproductive. Not enough blood to supply organs equally, distribute as needed.
Describe the influence of the cerebral cortex on the visceral reflexes.
Limbic system of cerebral cortex: emotional responses, connections with hypothalamus; anger, fear, hunger, sexual, anxiety.
Pathway connecting sensory and mental with autonomic nervous system.
Describe the influence of the brainstem cortex on the visceral reflexes.
Contains centers for cardiac, vasomotor, salivation, swallowing, sweating, gastrointestinal secretion, bladder control, pupillary constriction / dilation
Describe the influence of the hypothalamus on the visceral reflexes.
Major control center; signals sent to reticular formation of brainstem and sympathetic motor neurons of brainstem