I. Neurons and neuroglia comprise the Nervous System – neurons initiate and conduct electrical signals within and between cells while neuroglia support and protect the neurons.
II. Symmetry
A. Radial symmetry –Jellyfish and sea anemones have a nervous system interconnected into a large web or nerve net/nerve ring, with neurons distributed throughout the body. Neurons carry information in any direction and a nerve impulse radiates out from stimulus site in every direction. There is no obvious integrative center nor are there afferent or efferent neurons.
B. Bilateral symmetry –most animals have an anterior/posterior end and a right/left side. Many species have a large cluster of neurons forming a brain for integration.
1. Show Centralization – integrating neurons in central area such as brain
2. Show Cephalization – important nervous and sensory structures are concentrated in the head
3. Arthropods have brain and chain of ganglia (clumps of neuron cell bodies) linked by axons
4. Vertebrates have a brain and spinal cord intermingled with neuron cell bodies, synapses….
III. Central Nervous System
A. Brain and Spinal Cord– integrative and control centers
B. Contains both gray and white matter
IV. Peripheral Nervous System
A. Afferent– Sensory information is carried toward the CNS
1. Somatic –from surface of body like touch
2. Visceral –from visceral – like stomach ache
B. Efferent– Motor information is carried away from the CNS
1. Somatic –travels via one motor neuron to skeletal muscles
2. Visceral –travels via two motor neurons (preganglionic and postganglionic) to smooth muscle, cardiac muscle, glands; AKA AUTONOMIC NERVOUS SYSTEM
a. Terminology:
1. Ganglia are groups of neuron cell bodies in the PNS
2. Dual innervation means that most structures in the ANS are innervated by both Parasympathetic and Sympathetic neurons
3. Responses are beyond voluntary control and thus considered to be involuntary responses
b. Subdivision of ANS includes Parasympathetic Nervous System– rest and digest
c. Subdivision of ANS includes Sympathetic Nervous System -fight of flight
d. Neurotransmitters of ANS
1. Acetylcholine – Cholinergic
a. Parasympathetic {pre/postganglionic fibers}
b. Preganglionic fiber – SNS
2. Norepinephrine – Adrenergic
a. Postganglionic fiber – SNS
3. Adrenal medulla –Releases norepinephrine and epinephrine to exaggerate the fight or flight response
e. Receptors for the neurotransmitters of ANS
a. Acetylcholine
1. Muscarinic [blocked by atropine]
2. Nicotinic [blocked by curare in somatic system]
b. Norepinephrine/epinephrine
1. Alpha
a. Alpha 1 are most common and have a stimulatory response [constricts muscles]
b. Responds to norepinephrine & epinephrine
2. Beta 1
a. Heart Stimulatory effect
b. Responds to norepinephrine & epinephrine
c. Propranolol – B1 blocker
3. Beta 2
a. Most common beta receptor
b. Generally inhibitory
c. Responds to only epinephrine
f. Functions of ANS
Heart – SNS increases rate and force of contraction, PNS decreases rate and force.
Airways – SNS dilates airways, PNS narrows airways
Digestive structures – SNS decreases secretions and peristalsis, PNS increases secretions and motility
Pupil – SNS dilates pupil, PNS constricts pupil
Sweat glands – SNS increases sweat secretion
Adrenal medulla – SNS causes release of epinephrine and norepinephrine from adrenal medulla
Urinary bladder – SNS causes wall to relax and sphincter to contract, PNS causes wall to contract and sphincter to relax
Cutaneous and abdominal blood vessels – SNS causes vasoconstriction
Skeletal muscle blood vessels – SNS causes vasodilation
g. Controls Hypothalamus in the brain