VII. NERVOUS SYSTEM
A. General function
1. Sensory/receptors
2. Integration – memory
3. Response, motor/effectors
B. Classification
1. Central Nervous System – Brain & Spinal Cord
2. Peripheral Nervous System
a. Afferent – Sensory information from periphery towards CNS
1. Somatic
2. Visceral
b. Efferent – Motor information from CNS to periphery
1. Somatic
2. Visceral = Autonomic Nervous System
a- Sympathetic Nervous System (fight or flight)
b-Parasympathetic Nervous System (rest & relaxation)
C. Neuron
1. Cell body– Organelle-containing part of cell
a. Ganglion – Group of cell bodies in PNS
b. Nucleus – Group of cell bodies in CNS
2. Cytoplasmic process
a. Axon= Fiber
1. Fiber tracts – CNS
2. Nerve – PNS
3. Sensory vs Motor vs Mixed
b. Dendrite – Receptor
3. Synapse – Junction between neurons
a. Telodendria – Ends of axon entering synapse
b. Neurotransmitters – Chemicals bridging synapse
D. Neuroglia – Provide mechanical and nutritive support to neurons
1. Ependymal cells – Line the neurocoel
2. Oligodendroglia – Produce Myelin in CNS; Myelin (white matter) speeds up nerve impulse transmission
3. Astrocytes – Maintain blood-brain-barrier
4. Microglia – Phagocytes
5. Schwann Cells – Produce myelin in PNS
E. Development
1. Neurulation
2. Neural tube
a. Germinal layer
b. Mantle layer – gray
c. Marginal layer – white – Cytoplasmic extensions, lack nuclei
3. Neuroblasts – Form neurons
4. Spongioblasts – Form neuroglia
5. Alar vs Basal plate – Dorsal and ventral gray matter
6. Neural crest cells
a. First order sensory neuron – Has cell bodies in sensory ganglia
b. Second order sensory neuron = association neuron – Within the CNS
c. Exceptions of the typical cell body of sensory neurons being in ganglia:
1. Cranial nerves I, II
2. Proprioception pathways of cranial nerves I – X
F. SPINAL CORD
1. Location & Function
2. Meninges
a. Meninx Primitiva – In fish
b. Leptomeninx – Inner membrane in higher vertebrates
c. Dura mater – Outer membrane in higher vertebrates
d. Pia mater – Mammals only, inner splitting of leptomeninx
e. Arachnoid & Subarachnoid space – Mammals only, outer layer splitting from leptomeninx. Subarachnoid space contains cerebrospinal Fluid, or CSF.
3. Gray matter – Contains nuclei, nonmyelinated neurons, center of spinal cord
4. White matter – Myelinated ascending and descending tracts in peripheral spinal cord
5. Spinal nerves
a. Metamerism
b. Cauda equina – Caudal-most set of spinal nerves resembling a horse’s tail
c. Occipitospinal nerves – Anamniote nerves innervating hypobranchial muscles
d. Spinal Nerves are Mixed nerves: Dorsal and Ventral root – Dorsal root containing sensory information/ Ventral root containing motor information
e. Dorsal and ventral ramus – After exiting the vertebrae, spinal nerves branch into a dorsal branch supplying epaxial muscles and a ventral branch supplying hypaxial muscles and the autonomic nervous system.
f. Plexuses – Networks of successive spinal nerves supplying limbs
G. BRAIN
1. Prosencephalon – “Forebrain”, embryonic
a. Telencephalon
1. Rhinencephalon
a. Olfactory bulbs
b. Olfactory tract
c. Olfactory lobe
2. Cerebral hemispheres
a. Paleostriatum – Primary region in fish, responsible for olfactory reflexes
b. Neostriatum – Beginning with reptiles, more nuclei, tracts, and neuroglia
c. Hyperstriatum – Primarily in birds for stereotypical behavior
d. Corpus striatum = basal nuclei – Remnants of Paleostriatum and neostriatum buried in mammalian brain, responsible for repetitive and stereotyped movements
e. Cortex – Starting in reptiles but up to billions of neurons that must be folded in skull to fit in mammals
1. Motor & Sensory – Responsible for voluntary movement and conscious sensations
2. Memory & Integration
3. 4 lobes – In mammals, named according to skull bones
3. Lateral ventricles – Ventricles are cavities in brain
a. CSF – Cerebrospinal Fluid
1. Formation – from blood vessels called choroid plexus
2. Function – Cushion, protection, nutrients
b. Diencephalon
1. Epithalamus
a. Pineal body – Light receptor in agnathans, endocrine (hormone producer) in gnathostomes.
b. Parapineal = parietal eye – Monitors photoperiods in some fish, lampreys, some tadpoles
c. Habenula – Olfactory reflexes in blood hounds, sharks
2. Thalamus
a. Sensory relay
b. Intermediate mass = interthalamic adhesion
3. Hypothalamus
a. Optic chiasma
b. Infundibular stalk/Posterior Pituitary
c. Function – Endocrine, regulates ANS, emotions, water balance, thermostat, hunger & satiety
4. Third ventricle
a. Interventricular foramen
b. Cerebral aqueduct
2. Mesencephalon – Midbrain of embryo, term used in adult as well
a. Optic lobes – Especially well developed in many birds
b. Auditory lobes – Auditory reflexes such as jumping when hearing loud sound
-Corpora Quadrigemina
c. Cerebral peduncles – Descending motor tracts from cortex
d. Cerebral aqueduct
3. Rhombencephalon – Embryonic hindbrain
a. Myelencephalon
1. Medulla oblongata
a. Pyramids – Crossing of motor and sensory tracts
b. Function – Vital reflexes such as breathing, connection between brain and spinal cord for ascending and descending pathways
b. Metencephalon
1. Cerebellum – Coordination and balance; quite large in birds and mammals
2. Pons – “Bridge” between different parts of brain
c. Fourth ventricle – Containing CSF
H. CRANIAL NERVES– see Cranial Nerves page
I. AUTONOMIC NERVOUS SYSTEM
1. Visceral efferent to smooth & cardiac muscle and glands
2. Involuntary
3. Sympathetic vs Parasympathetic
a. Functional differences – Sympathetic is “fight or flight” response; Parasympathetic is “rest and relaxation” response
b. Structural differences – Sympathetic nerves travel with spinal nerves in thoracolumbar region; Parasympathetic nerves travel independent of spinal nerves in sacral region and along with cranial nerves III, VII, IX, X
4. Preganglionic neurons – Exit CNS and synapse in peripheral ganglion
5. Postganglionic neurons – Travel from ganglion to effector
6. Autonomic ganglia
a. Paravertebral
1. Sympathetic trunk – Interconnecting chain of sympathetic ganglia traveling parallel to spinal cord allowing for divergence of pathways
2. White ramus communicans – Branching of preganglionic neuron away from spinal nerve in SNS
3. Gray ramus communicans – Branching of postganglionic neuron to rejoin spinal nerve in SNS
b. Collateral
1. Splanchnic nerve
2. Cardiac nerve
3. Head and abdomen
c. Terminal ganglia
7. Cholinergic – Releasing acetylcholine as neurotransmitter
8. Adrenergic – Releasing norepinephrine as neurotransmitter
9. Adrenal medulla – Is part of SNS and releases epinephrine and norepinephrine to prolong and exaggerate the fight or flight response