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Central Nervous System
• Brain
• Cerebrum
• Cerebellum
• Diencephalon
• Brain stem
• Spinal Cord
• Gray matter - cerebral cortex;
outer layer of the brain
• White matter - fibers beneath
cortex and corpus callosum
(fibers that connect the two
halves of cerebral cortex)
• Area of brain responsible for
higher-order behaviors
(learning, intelligence,
awareness, etc.)
Cerebrum
Cerebrum
• Gyri (gyrus): folds (rises) in cerebral hemispheres
• Sulci (sulcus): shallow grooves
• Divides the cerebral hemispheres into lobes
• Fissures: deep grooves separating the gyri
• Longitudinal fissure: prominent groove
that divides cerebrum into right and left
cerebral hemispheres
Cerebellum
• Located just caudal to cerebrum
• Area of brain responsible for coordinated movement,
balance, posture, and complex reflexes
Diencephalon
• Passageway between brain stem and cerebrum
• Structures associated with diencephalon:
• Thalamus, hypothalamus, and pituitary gland
Brain Stem
• Connection between brain and spinal cord
• Medulla oblongata
• Pons
• Midbrain
• Area of brain responsible for basic (subconscious,
autonomic) functions of the body
• HR
• Breathing, coughing, sneezing,
• BP
• Many of the cranial nerves originate from this area of brain
• Connective tissue layers
that surround brain and
spinal cord
• Contain blood vessels,
fluid, and fat
• Supply nutrients and
oxygen to the superficial
tissues of the brain and
spinal cord
• Provide some cushioning
and distribution of
nutrients for CNS
Meninges
Meninges
• Three layers:
1.Dura mater - tough, fibrous
2.Arachnoid - delicate, spiderweb-like
3.Pia mater - very thin; lies directly on surface of brain and
spinal cord
CSF—in subarachnoid space
(Contains CSF)
Cerebrospinal Fluid
• Fluid between Arachnoid and Pia mater and in canals and
ventricles inside brain and central canal of spinal cord
• Provides cushioning function
• May play role in regulation of autonomic functions such as
respiration and vomiting
Blood-Brain Barrier
• Separates the capillaries in the brain from the nervous tissue
• Capillary walls in the brain have no fenestrations; covered
by cell membranes of glial cells
• Prevents many drugs, proteins, ions, and other molecules
from readily passing from the blood into the brain
Cranial Nerves
• 12 nerve pairs in PNS that originate directly from brain
• Numbered in Roman numerals from I through XII (1 through 12)
• Each nerve may contain axons of motor neurons, axons of
sensory neurons, or combinations of both
Spinal Cord
• Medulla: central part of spinal cord
• Composed of gray matter
• A lot of nerve processing occurs here (not just in brain)
• Central canal – center of medulla
Spinal Cord
• Cortex: outer part of spinal cord
• White matter
• Myelinated and unmyelinated nerve fibers
• Surrounds the gray matter
Spinal Cord
• Dorsal and Ventral Nerve Roots emerge as Spinal Nerves from
between each pair of adjacent vertebrae
• Dorsal nerve roots contain sensory fibers
• Ventral nerve roots contain motor fibers
• Spinal nerve is a mix of sensory and motor neurons
Autonomic Nervous System
• Controls automatic functions at subconscious level
• Sympathetic nervous system - nerves emerge from thoracic and lumbar
vertebral regions (thoracolumbar system)
• Parasympathetic nervous system - nerves emerge from brain and
sacrum (cranial-sacral)
Table 13-3. Effects of Sympathetic and Parasympathetic Nervous
Systems
Sympathetic System
Parasympathetic System
Effect
Effect
Heart rate
Increases
Decreases
Force of heart contraction
Increases
No significant effect
Diameter of bronchioles
Increases (dilates)
Decreases (constricts)
Diameter of pupil
Increases (dilates)
Decreases (constricts)
GI motility, secretions,and blood flow
Decreases
Increases
Diameter of skin blood vessels
Decreases
No significant effect
Diameter of muscle blood vessels
Increases
No significant effect
Diameter of blood vessels to kidney
Decreases
No significant effect
Neurotransmitters and Receptors
• Sympathetic nervous system
• 1º neurotransmitter—norepinephrine
• Adrenergic neurons - neurons that release norepinephrine
• Epinephrine/norepinephrine also released from adrenal medulla
• To elicit an effect, effector organ must contain receptor for epi/norepi
Neurotransmitters and Receptors
• Smooth/Cardiac muscles may constrict or dilate in
response to epi/norepi
1. α1- adrenergic receptors – cause vasoconstriction of skin, GI
tract, and kidney [don’t need to digest, make urine, or bleed
profusely}
2. β1-adrenergic receptors - increase heart rate and force of
contraction
3. β2-adrenergic receptors - cause bronchodilation (relaxation)
Neurotransmitters and Receptors
• Parasympathetic nervous system
• 1º neurotransmitter—acetylcholine
• Cholinergic neurons - release acetylcholine
• 2 types:
• Nicotinic receptors
• Muscarinic receptors
Summary: receptor types
Reflexes
• Somatic reflexes - involve contraction of skeletal
muscles
• Autonomic reflexes - regulate smooth muscle,
cardiac muscle, and endocrine glands
• Contralateral reflex - starts on one side of body
and travels to opposite side
• Ipsilateral reflex - stimulus and response are on
same side of body
Reflex Arc
5 Components:
•
Sensory receptor—activated by stimulus
•
Sensory neuron—transports AP to gray matter of spinal cord or brain stem
(cranial n.) and synapses with other neurons
•
•
•
Interneuron—sensory info integrated with info from other sensory neurons
Motor Neuron—response is sent out via motor neuron
Target organ—effector cell
Stretch Reflex (tap knee)
• Monosynaptic (1) reflex arc;
ipsilateral reflex
• Involves 1 sensory neuron and 1 motor neuron
• Signals also sent to:
• Antagonistic m (inhibitory)
• Cerebellum/Cerebrum
Withdrawal Reflex (toe pinch)
• Also called flexor reflex; ipsilateral reflex
• Several interneuron synapses
• Several segments of spinal cord
• Results in:
• Contraction of muscles
• Before cerebrum is aware
• Inhibition of antagonist m
Crossed Extensor Reflex
• Contralateral reflex
• Withdrawal reflex initiated
• afferent sensory neuron synapses with
interneurons
• Causes contraction of opposite extensor
muscles
CNS Moderation of Reflexes
• Upper CNS (brain) normally produces an inhibitory
effect on the reflex arcs (muffled effect)
• With injury, intact reflex arcs caudal to spinal cord trauma
become hyperreflexive
• Trauma to a portion of the reflex arc results in either
hyporeflexive or absent reflexes