Chapter 10 & 11: The Nervous System

Nervous System

  • Central Nervous System (CNS)
  • Brain
  • Spinal Cord
  • Peripheral Nervous System (PNS)
  • Nerves that connect the CNS to the rest of the body

Functions of the Nervous System

  • Sensory Function
  • Sensory nerves gather information from the body and the environment
  • Integrative Function
  • Sensory information is processed or interpreted in the CNS
  • Motor Function
  • Motor nerves (PNS) carry information from the CNS to the muscles and glands

Nervous System (Cells)

  • Neuroglia (glial cells)
  • Nerve glue
  • Found in the CNS
  • Support, protect, insulate, nourish and care for neurons
  • Do not conduct nerve impulses
  • Astrocytes
  • Star shaped glial cells
  • Support neurons
  • Form a protective barrier around neurons of the CNS
  • Helps keep toxic substances from in blood from entering the nervous tissue of the CNS
  • Ependymal Cells
  • Line the inside cavities of the brain
  • Help produce cerebrospinal fluid
  • Neuron
  • Conducts nerve impulses (information) around the body
  • Found in the CNS and PNS
  • Variety of shapes and sizes
  • Dendrites
  • Receive information
  • Cell Body
  • Contains the nucleus and other organelles
  • Axon
  • Long extension that transmits information away from the cell body
  • Axon Terminals
  • Highly branched end of the axon that contains stored chemical neurotransmitters.

Axon

  • Myelin sheath
  • Surrounds most long nerve fibers (both CNS and PNS)
  • White fatty substance the helps insulate the axon
  • Myelinated: nerve fibers covered by myelin
  • Nodes of Ranvier
  • Evenly spaced along the axon
  • No myelin sheath
  • Formation of myelin sheath (PNS)
  • Schwann cells surround the axon
  • Neurilemma (nuclei and cytoplasm) of Schwann cells lie outside the myelin sheath
  • Formation of myelin sheath (CNS)
  • Oligodendrocytes are a form of glial cells
  • No neurilemma

3 Types of Neuron

  • Sensory Neuron
  • Afferent neurons
  • Carries information from body to CNS
  • Found in PNS and CNS
  • Interneuron
  • Found only in the CNS
  • Forms connections between sensory and motor neurons
  • Motor Neuron
  • Efferent neurons
  • Carries information from CNS to body
  • Found in PNS and CNS

White Matter & Grey Matter

  • White Matter
  • White because of myelin
  • Gathered together in tracts
  • Grey Matter
  • Primarily cell bodies, interneurons and unmyelinated fibers
  • Can appear is clusters
  • In PNS ganglia
  • In CNS nuclei

Action Potential

  • Also called the nerve impulse
  • Electrical signal that conveys information along a neuron
  • Polarization
  • Resting state
  • Inside negative, outside positive
  • Depolarization
  • Stimulated, charges switch
  • Inside positive, outside negative
  • Repolarization
  • Return to resting state
  • Inside negative, outside positive

Polarization

  • Resting state
  • Inside of the cell more negative than outside
  • High concentration of anions (-) inside the cell
  • Potassium (K+) leaks out of the cell leaving net negative charge in the cell
  • Excess anions trapped in cell cause polarization

Depolarization

  • Neuron is stimulated
  • Change in neuronal membrane allow sodium (Na+) to cross the membrane
  • Na+ in higher concentration outside so it diffuses into the cell
  • Causes positive charge inside the cell
  • Inward diffusion of Na+ causes depolarization

Repolarization

  • Quickly after depolarization neuronal membrane undergoes another change
  • Stops diffusion of Na+ into the cell
  • Allows K+ to diffuse out of cell
  • Positive charge leaves with K+
  • Negative anions left behind give negative charge
  • Na+ pumped out of cell eventually
  • Repolarization due to K+ diffusion, not Na+ being pumped out

Moving the Action Potential

  • Nerve impulse moves in a wave like motion along the axon from cell body to the axon terminals
  • Myelin does not allow the nerve impulse to form on that area
  • Nerve impulse can develop at nodes of Ranvier
  • Nerve impulse jumps from node to node (saltatory conduction)
  • Increases speed of conduction of nerve impulse

Synapse

  • Junction or space between two neurons
  • Once nerve impulse reaches axon terminal the information must be transmitted across the synapse to the next neuron

Parts of a Synapse

  • Synaptic cleft
  • The space between the axon terminal of one neuron and the dendrite of a second neuron
  • Neurotransmitters
  • Chemical substances stored in vesicles in the axon terminal
  • When released they diffuse across synaptic cleft and bind with receptors
  • Transmission molecule
  • Most common
  • Acetylcholine (Ach)
  • Norepinephrine
  • Inactivators
  • Inactivate or terminate the activity of neurotransmitters after they have completed their task
  • Acetylcholine terminated by Acetylcholinesterase
  • Receptors (receptor sites)
  • Sites on the membrane of a dendrite to which the neurotransmitters bind
  • Specific shape for specific neurotransmitter

Events at the Synapse

  • Nerve impulse travels along axon toward axon terminal and synapse
  • Nerve impulse cause neurotransmitter filled vesicles to fuse with axon terminal membrane
  • Vesicles open and release neurotransmitter into the synaptic cleft
  • Neurotransmitter diffuses across the synapse and binds to receptor sites on dendrite membrane
  • Causes change in membrane (depolarization) that allows the nerve impulse to develop in the dendrite
  • Nerve impulse travels toward cell body

The Brain

  • Cerebrum
  • Diencephalon
  • Brain Stem
  • Cerebellum

Cerebrum

  • Largest part of the brain
  • Right and left hemispheres joined together with the corpus callosum
  • Cerebral Cortex
  • Thin layer of gray matter on the exterior of the brain
  • Mostly cell bodies and interneurons
  • Higher mental tasks – learning, reasoning, language and memory
  • Most of the cerebrum composed of white matter
  • Below the cerebral cortex
  • Forms connections between parts of the brain and the spinal cord
  • Gyri (Gyrus)
  • Ridges or elevations
  • Sulci (Sulcus)
  • Groves that separate the gyri
  • Fissure
  • A deep sulcus

Frontal Lobe

  • Voluntary motor activity
  • Decussation: crossing of fibers that carry information from motor areas
  • Right side of brain controls left side of the body
  • Left side of the brain controls right side of the body
  • Broca’s area (left hemisphere) important in motor speech (movement of mouth and tongue)
  • Stroke in the left hemisphere that affects Broca’s area can cause expressive aphasia
  • Personality development
  • Emotional and behavioral expression
  • Learning and thinking

Parietal Lobe

  • Primary somatosensory area
  • Receives general sensory information from the body
  • Allows you to experience temperature, pain, touch and proprioception
  • Reading, speech and taste

Temporal Lobe

  • Primary auditory cortex
  • Sensory information from the ears
  • Olfactory area
  • Sensory information from the nose
  • Taste
  • Sensory information from the taste buds
  • Wernicke’s area (posterior temporal lobe)
  • Comprehension of language
  • A stroke in that affects this area may lead to receptive aphasia

Occipital Lobe

  • Visual cortex
  • Sensory information from the eye
  • Visual reflexes
  • Reading
  • Judging distances
  • Seeing in 3 dimensions

Parkinson’s Disease

  • Basal nuclei
  • Patches of gray matter scattered throughout the cerebral white matter
  • Help regulate body movement and facial expression
  • Primary neurotransmitter is dopamine
  • Deficiency of dopamine in the basal nuclei is Parkinson’s disease
  • Symptoms
  • Shuffling, uncoordinated gait, rigidity, slowness of speech, drooling and shaking
  • Treatment with dopamine or dopamine - like drugs

Diencephalon

  • Inferior to cerebrum and superior to the brain stem
  • Thalamus
  • Relay station for sensory fibers coming from the brain stem and going to the sensory areas of the cerebrum
  • Hypothalamus
  • Regulation of body temperature, water balance and metabolism
  • Helps regulate the autonomic (involuntary) nerves
  • Heart rate, blood pressure and respiration
  • Pituitary gland
  • Direct or indirect affect on bodies hormones

Brain Stem

  • Connects spinal cord and higher brain structures
  • Relays sensory and motor information
  • Midbrain
  • Nuclei that are reflex centers for vision and hearing
  • Pons
  • Regulation of breathing rate and rhythm
  • Medulla oblongata
  • Nuclei control heart rate, blood pressure and respiration
  • Called the vital center
  • Sensitive to narcotics
  • Overdose can cause depression of medulla oblongata and depression of breathing leading to death

Cerebellum

  • Coordination of voluntary muscle activity
  • Helps produce smooth coordinated muscle response
  • Damage causes jerky movement, staggering gait and difficulty maintaining balance

Spinal Cord

  • Extension of the brain stem
  • Tube-like structure found within the spinal cavity (vertebral column)
  • Diameter of the thumb and approximately 17 inches long
  • Extends from the foramen magnum to L1 vertebrae

Lumbar Puncture

  • Spinal cord ends at L1
  • Hollow needle inserted between L3 and L4
  • Sample of CSF withdrawn
  • No danger of hurting the spinal cord

Gray Matter

  • Located centrally in the spinal cord in the shape of a butterfly
  • Composed primarily of cell bodies and interneurons
  • Two projections
  • Dorsal horn
  • Ventral horn
  • Opening in the center of the spinal cord is the central canal

White Matter

  • Composed primarily of myelinated axons grouped into nerve tracts
  • Sensory tracts carry information from body toward the brain
  • Also called ascending tracts
  • Motor tracts carry information from the brain toward the body
  • Also called descending tracts

Protecting the CNS

  • Bone
  • Cranium and vertebral column
  • Meninges
  • Connective tissue surrounding the brain and spinal cord
  • Cerebrospinal Fluid (CSF)
  • Clear, plasma-like fluid
  • Blood-Brain Barrier
  • Cells associated with blood vessels supplying the brain and spinal cord control what substances enter the CNS from the blood

Spinal Cord Injury

  • Neurons of the brain and spinal cord do not regenerate
  • Spinal column is broken may lead to paralysis
  • Quadriplegia – paralysis of the trunk and all four extremities
  • High fracture (cervical and upper thoracic)
  • Paraplegia – paralysis from the waist down
  • Lower fracture (lumbar and lower thoracic)

Spinal Nerves

  • Two roots to each spinal nerve
  • Dorsal root
  • Sensory nerve fibers attach here
  • Dorsal root ganglia
  • Ventral root
  • Motor nerve fibers attach here
  • Dorsal and ventral root joined together to form a spinal nerve (mixed nerve)

Functions of the Spinal Cord

  • Sensory pathway
  • Pathway for sensory information traveling from the periphery to the brain
  • Motor pathway
  • Pathway for motor information traveling from the brain to the periphery
  • Reflex center
  • Bypass the brain
  • Spinal cord allows you to react in a quick reflex

Reflex

  • An involuntary response to a stimulus
  • Reflex arc
  • The nerve pathway involved in a reflex
  • First a receptor is stimulated
  • An afferent (sensory) neuron carries the information to the spinal cord
  • An efferent (motor) neuron carries the information to the effector organ
  • The effector organ responds with movement

Peripheral Nervous System (PNS)

  • All nerves and ganglia outside of the central nervous system (CNS)

Nerves

  • Many neurons bundled together with blood vessels and wrapped in connective tissue
  • Sensory nerves
  • Only contain sensory neurons
  • Motor nerves
  • only contain motor neurons
  • Mixed nerves (most nerves)
  • Contain both sensory and motor neurons

Classifying the PNS: Structure

  • Cranial Nerves
  • I Olfactory
  • II Optic
  • III Oculomotor
  • IV Trochlear
  • V Trigeminal
  • VI Abducens
  • VII Facial
  • VIII Vestibulocochlear
  • IX Glossopharyngeal
  • X Vagus
  • XI Accesory
  • XII Hypoglossal
  • Spinal Nerves
  • Nerve fibers converge into nerve plexuses
  • Cervical plexus
  • C1 – C4
  • Brachial plexus
  • C5 – C8, T1
  • Lumbosacral plexus
  • T12, L1 – L5, S1 to end

Dermatatome

  • Pictorial representation of where a spinal nerve innervates the skin
  • Named for the nerve
  • Used clinically to find which nerves are injured or impaired

Classifying the PNS: Function

  • Somatic Nervous System
  • Voluntary motor control
  • Afferent nerves
  • Efferent nerves
  • Autonomic Nervous System
  • Involuntary response of internal organs and glands
  • Sympathetic nervous system
  • Parasympathetic nervous system

Autonomic Nervous System

  • Divided into sympathetic and parasympathetic nervous systems
  • Most organs receive fibers from both systems
  • Effects of stimulus from each system are opposite of each other
  • Sympathetic Nervous System
  • Fight or Flight response
  • In times of stress or when threatened this system gets you ready to fight or flee
  • Parasympathetic Nervous System
  • Feed and Breed
  • Regulates the digestive system and important in reproductive function
  • Neuron 1
  • Cell body in the CNS
  • Axon of neuron 1 extends to the ganglion
  • Preganglionic fiber
  • Neuron 2
  • Cell body in ganglion
  • Axon of neuron 2 extends to the organ
  • Postganglionic fiber
  • Different neurotransmitters secreted from the postganglionic fibers in the sympathetic and parasympathetic systems

Sympathetic Nervous System

  • Exit the spinal cord at the thoracic and lumbar levels
  • Called the thoracolumbar outflow
  • Short distance to the ganglia
  • Chain of ganglia called the paravertebral ganglia or sympathetic chain ganglia
  • Neurotransmitter secreted by postganglionic fibers is norepinephrine or noradrenalin (adrenergic fibers)

Parasympathetic Nervous System

  • Exit spinal cord at level of the brain stem and sacrum
  • Called the craniosacral outflow
  • Preganglionic fibers are long
  • Ganglia are located near or within organs
  • Neurotransmitter secreted by postganglionic fibers is acetylcholine (cholinergic fibers)

Multiple Sclerosis

  • Progressive demyelination or neurons and destruction of the oligodendrocytes
  • Impairs sensory and motor activity

Peripheral Neuropathy

  • Loss of sensation to due nerve damage
  • Most severe in hands and feet
  • Common cause is diabetes mellitus
  • Loss of sensation can lead to injuries and amputations