Central Nervous System

• Brain• Cerebrum• Cerebellum• Diencephalon • Brain stem

• Spinal Cord

Cerebrum• 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• 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

Meninges

• 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• 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 DecreasesForce of heart contraction Increases No significant effectDiameter of bronchioles Increases (dilates) Decreases (constricts)Diameter of pupil Increases (dilates) Decreases (constricts)GI motility, secretions,and blood flow Decreases IncreasesDiameter of skin blood vessels Decreases No significant effectDiameter of muscle blood vessels Increases No significant effectDiameter 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 Arc5 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