1. Chapter 7 – Nervous system
Ms. Harborth
Anatomy and physiology

2. Structural classification
Central nervous system (CNS) – consists of the brain and spinal cord. Command center
Peripheral nervous system (PNS) – part of body outside of CNS.
Spinal nerves – carry impulses to and from spinal cord
Cranial nerves – carry impulses to and from the brain

3. PNS
Sensory (afferent) – carries impulses FROM sensory organs TO the brain
Motor (efferent) – carries impulses FROM the brain TO effector organs, muscles, and glands.
Somatic nervous system – control skeletal muscles
Autonomic nervous system – regulates automatic events (smooth and cardiac muscle)
Sympathetic
Parasympathetic

4. Nervous tissue Supporting cells of CNS “neuroglia” Neurons
Astrocytes – barrier between neurons and capillaries
Microglia – phagocytes that “clean”
Ependymal cells – beat cilia to circulate cerebrospinal fluid
Oligodendrocytes – form myelin sheaths
Supporting cells of PNS:
Schwann cells – form myelin sheaths
Satellite cells – protective, cushioning cells
Neurons
Cell body (Nissl substance & neurofibrils)
Processes (fibers)
Myelin sheath, Schwann cells (PNS), nodes of Ranvier
Dendrites (toward cell body)
Axons (away from cell body)
Axonal terminals, neurotransmitters, synaptic cleft, synapse

5. Astrocyte
Ependymal cells
Oligodendrocyte
Microglial cell

7. Multiple sclerosis
Immune system gradually destroys myelin sheaths, converting to scleroses (hardened processes)

8. Vocab Nuclei – clusters of cell bodies in the CNS
Ganglia – small collections of cell bodies found in the PNS.
Tracts – bundles of nerve fibers in the CNS
Nerves – bundles of nerve fibers in the PNS
White matter – myelinated fibers in the CNS
Gray matter – unmyelinated fibers and cell bodies in the CNS

9. Classification of neurons
Functional (direction of nerve impulse)
Sensory (afferent) neurons – neurons carrying impulses from sensory receptors to the CNS. Cell bodies are found in ganglion outside of CNS.
Cutaneous sense organs, proprioceptors
Motor (efferent) neurons – neurons carrying impulses to viscera and/or muscles and glands. Cell bodies are in the CNS.
Association neurons (interneurons) – connect motor and sensory neurons in neural pathways.

10. Classification of neurons
Structural
Multipolar neuron – several processes extending from cell body.
All motor and association neurons
Bipolar neuron – axon and dendrite extend from cell body
Rare. Found in some special sense organs.
Unipolar neuron – short, single process that usually divides into proximal and distal fibers. Axon conducts nerve impulses both toward AND away from the cell body.
Sensory neurons found in PNS ganglia

11. Neuron physiology Nerve impulse – Irritability Conductivity animation
1. Inactive neuron is polarized (more negative inside)
2. Stimulus excites neuron, permeability increases
3. Depolarization Action Potential
4. Repolarization
Saltatory conduction – occurs on myelinated nerves FASTER
Cold and continuous pressure hinder conduction
Conductivity
When action potential reaches axonal endings, tiny vesicles fuse with axonal membranes, rupture, and releases neurotransmitters which start impulse in next neuron
Electrochemical event
animation

12. Neuron physiology Reflex Arc Autonomic reflexes Somatic reflexes
Regulate activity of smooth muscles, heart, and glands.
Ex: salivary reflex and pupillary reflex.
Somatic reflexes
Reflexes that stimulate skeletal muscles
Minimum of five elements:
Sensory receptor
Afferent neuron
Integration center
Efferent neuron
Effector organ

13. Central Nervous System
Embryonic development:
Neural tube develops
4th week – anterior end of neural tube expands and brain formation begins. Central canal of neural tube becomes 4 ventricles

14. Functional Anatomy of the Brain
Cerebral Hemispheres
Diencephalon
Cerebellum
Brain Stem

15. Cerebral Hemispheres Gyri: elevated ridges of tissue
Sulci: shallow grooves
Fissures: deeper grooves which separate large regions of the brain
Hemispheres separated by longitudinal fissure
Lobes are named for cranial bones that surrounding them

16. Cerebral Hemisphere Parietal lobe: posterior to central sulcus
Somatic sensory area – localizes and interprets impulses from sensory receptors. Sensory pathways cross (left -> right, right -> left)
Occipital lobe: visual area
Temporal lobe: auditory and olfactory area
Frontal lobe: Higher intellectual reasoning in anterior part
Primary motor area - Axons of motor neurons form pyramidal (corticospinal) tract which descends to spinal cord. Pathways are crossed.
Broca’s area – speech. Only found in one hemisphere
Speech area – junction of temporal, parietal, and occipital lobes. Sound out words. One hemisphere.
Gray matter (cerebral cortex): cell bodies of neurons
White matter: fiber tracts carrying impulses to or from the cortex
Corpus callosum: large fiber tract that connects cerebral hemispheres. Allows halves to communicate with one another.
Basal nuclei: “islands” of gray matter buried in white matter. Modify instructions sent to muscles.

20. Diencephalon Thalamus Hypothalamus Epithalamus
Encloses third ventricle
Relay station for sensory impulses
Hypothalamus
Regulation of temperature, water balance and metabolism. Regulates pituitary
Limbic system – “emotional-visceral brain”. Thirst, appetite, sex, pain, pleasure centers.
Mammillary bodies – reflex involved in olfaction
Epithalamus
Pineal body
Choroid plexus of third ventricle

21. Diencephalon

22. Brain stem Midbrain Pons Medulla oblongata Reticular formation
Cerebral aqueduct – canal that connects third ventricle of diencphalon to fourth ventricle below
Cerebral peduncles – convey ascending and descending impulses
Corpora quadrigemina – reflex centers for vision and hearing
Pons
Mostly fiber tracts, but does have some nuclei involved in controlling breathing
Medulla oblongata
Merges into spinal cord.
Regulate vital visceral activities. Controls heart rate, blood pressure, breathing, swallowing, and vomiting
Reticular formation
Neurons involved in motor control of the visceral organs. RAS (reticular activating system) plays a role in consciousness and awake/sleep cycles. Damage to this area results in coma.

23. Brain Stem

24. Cerebellum Two hemispheres
Timing for skeletal muscle activity and controls balance/equilibrium
Takes info from eyes, ears and muscles to coordinate movements in a smooth fashion

25. meninges
Three connective tissue membranes covering and protecting brain and spinal cord
Dura mater – outermost layer. Double-layered, forms periosteum and meningeal layer.
Arachnoid mater – span subarachnoid space to attach to innermost membrane
Subarachnoid space filled with cerebrospinal fluid. Arachnoid villi protrude through dura mater. Dural sinuses absorb fluid into blood through arachnoid villi.
Pia mater – delicate layer clings tightly to surface of brain and spinal cord.
Meningitis – inflammation of meninges

27. Cerebrospinal fluid (CSF)
similar to blood plasma.
continually formed from blood by choroid plexuses
continually moving.
Blood-brain barrier – any changes in fluid around brain could be detrimental. Barrier composed of the LEAST permeable capillaries in whole body. Water, glucose and essential amino acids can pass through.

28. Spinal Cord 17 inches long, thickness of a thumb
Extends from foramen magnum to 1st or 2nd lumbar vertebrae, right below ribs
Cauda equina

30. Peripheral Nervous System
Endoneurium
Perineurium
Fascicles
Epineurium
Nerves are classified by which direction they transmit
Mixed nerves
Afferent (sensory)
Efferent (motor)

31. Cranial nerves 12 pairs (table 7.1)
Serve head and neck (except vagus nerves – extend to thoracic and abdominal cavities)
I. Olfactory
II. Optic
III. Oculomotor
IV. Trochlear
V. Trigeminal
VI. Abducens
VII. Facial
VIII. Vestibulochochlear
IX. Glossopharyngeal
X. Vagus
XI. Accessory
XII. Hypoglossal

32. Spinal Nerves/ Nerve Plexuses
31 pairs of spinal nerves formed by combo of ventral and dorsal roots of spinal cord. Named for region of spinal cord from which they arise.
Each spinal nerve divides into dorsal and ventral rami
Dorsal rami serve skin and muscles of posterior body trunk
Ventral rami of T1 – T12 form intercostal nerves
Ventral rami of other spinal nerves form 4 plexuses (Table 7.2)

33. Autonomic nervous system
Motor subdivisions that control automatic activities (cardiac and smooth muscle, and glands)
Sympathetic and parasympathetic
Sympathetic – mobilizes body during extreme situation (fear, exercise, rage, etc.)
Parasympathetic – allows us to “unwind” and conserve energy