6 Lesson 6.1: Overview of the Nervous System Lesson 6.2: Transmission of Nerve Impulses Lesson 6.3: Functional Anatomy of the Central Nervous System Lesson

6

Lesson 6.1: Overview of the Nervous System

Lesson 6.2: Transmission of Nerve Impulses

Lesson 6.3: Functional Anatomy of the Central Nervous System

Lesson 6.4: Functional Anatomy of the Peripheral Nervous System

Lesson 6.5: Injuries and Disorders of the Nervous System

The Nervous System

Lesson 6.1

Overview of the Nervous System

Chapter 6: The Nervous System

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

• The function of the nervous system is to coordinate all body systems! This is accomplished by the transmission of signals (electrochemical) from body parts to the brain and back to the body parts..

• The nervous system is composed of:• Neurons• Neuroglial cells (also known as neuroglia, glia, and glial

cells)• Blood vessels• Connective tissue


Two Major Divisions


• two major divisions– central nervous system (CNS) – consists of the brain

and spinal cord– peripheral nervous system (PNS) – consists of cranial

nerves and spinal nerves• sensory receptors• afferent (sensory) nerves – transmit nerve impulses from

the sensory receptors in the skin, muscles, and joints to the CNS

• efferent (motor) nerves – transmit nerve impulses from the CNS to the muscles and glands

Organization of the Nervous System


• somatic nervous system– voluntary – carries information to skeletal muscle

• autonomic nervous system– involuntary – carries information to smooth muscle,

cardiac muscle, and glands– sympathetic– parasympathetic

The Efferent Nerves


Sensory division Sensoryreceptors

Motor division

Somatic Nervous System

AutonomicNervous System

Skeletal muscle

Smooth muscleCardiac muscleGlands

Peripheral Nervous System(cranial and spinal nerves)

Central Nervous System(brain and spinal cord)brain cranial

nerves

spinalcord spinal

nerves


• neuroglia– also known as glial cells– support the neurons– protect the neurons

• neurons – transmit nerve impulses

Nervous Tissues


• central nervous system– astrocytes– microglia– ependymal– oligodendrocytes

Neuroglia


• Astrocytes – most numerous - positioned between neurons and capillaries – protect neurons from harmful substances in the blood

• Microglia – absorb and dispose of dead cells and bacteria

• Ependymal – form a protective covering around the spinal cord and central cavities within the brain

• Oligodendrocytes – produce myelin (fatty insulating material that surrounds nerve fibers)

Neuroglia - CNS


• peripheral nervous system– Schwann cells – form fatty myelin sheaths around nerve

fibers • insulation from myelin sheath speeds up

neurotransmission

• a bundle of myelinated nerve fibers (axons) = “white matter”

• a bundle of unmyelinated nerve fibers (cell bodies/dendrites) = “gray matter”

• nodes of Ranvier – uninsulated gaps between sections of myelin where the axon is exposed

– satellite cells – provide cushioning

Neuroglia - PNS


Neuroglia - PNS


• cell body (soma) - central portion of neuron - contains usual organelles

• neuron processes (two types) - extensions from cell body

• Dendrites – many per neuron; short & branched; receptive portion of neuron; carries impulse toward cell body

• Axon - one per neuron; long, thin process; carries impulses away from cell body; terminations of axon branch = axon terminals

Parts of a Neuron


Parts of a Neuron


• sensory neurons– send impulses toward CNS

• motor neurons– send impulses away from CNS

• interneurons– transport impulses between neurons

Neuron Types by Function


• Due to structural differences, neurons can be classified into three (3) major groups:

• Bipolar neurons – two extensions; one fused dendrite leads toward cell body and one axon leads away from cell body ex. Specialized parts of eyes, nose, & ears (sensory)

• Unipolar neurons – one process from cell body; forms central & peripheral process; only distal ends are dendrites ex. Some sensory neurons in the PNS

• Multipolar neurons – many extensions; many dendrites lead toward cell body and one axon leads away from cell body ex. All motor neurons and interneurons

Structural Types of Neurons


• bipolar

Neuron Structures

• multipolar• unipolar


Match these words with 1–4 below: sympathetic nervous system, myelin, synapse, axon.

1. high alert

2. transmits impulses away from cell body

3. fatty insulating material

4. gap between neurons

Review and Assessment

Lesson 6.2

Transmission of Nerve Impulses



Transmission of nerve impulses is an electrochemical process

Creation of an action potential is electrical Neurotransmitters released at the synapse is chemical

Transmission of Nerve Impulses


When a neuron is inactive or at rest: Potassium ions are inside the cell and sodium ions are

outside the cell membrane Inside of cell is more negatively charged than outside of

cell Difference in electrical charge inside and outside of cell

= cell membrane is polarized

Transmission of Nerve Impulse


Activation of a neuron: Stimulus causes the sodium channels to open Sodium ions enter the neuron causing the inside of the

membrane to become more positive = cell membrane is depolarized

Depolarization occurs only at the nodes of Ranvier Opening of sodium channels is like a domino effect

creating more sodium channels to open along the membrane = action potential (electrical impulse)

All-or-none concept – electrical charge of the action potential is always the same size and travels the full length of the axon



Action Potential

Direction of nerve impulse


Discharge of the action potential Membrane becomes permeable to potassium ions Potassium ions diffuse out of the cell Membrane is restored to its polarized state with a more

negative charge inside the cell = repolarization Refractory period = time between the completion of the

action potential and repolarization





Factors affecting speed of impulse transmission:– Faster in myelinated axons vs nonmyelinated axons

where the myelin sheath acts as an insulator • Saltatory conduction – action potentials jump over

myelinated regions of the axon– Faster in nonmyelinated axons with larger diameters vs.

nonmyelinated axons with smaller diameters– Faster in warmer temps because of an increase in ions

diffusion rates

Impulse Transmission


Transmission at synapses When an action potential reaches an

axon terminal, calcium

gates open and calcium

ions flow into the terminal Influx of calcium causes the

neurotransmitter vesicles

to release the neurotransmitter

into the synapse Neurotransmitters connect

to a receptor site on a joining

neuron or muscle fiber

Impulse Transmission


• Introduction to Anatomy and Physiology Student Site Video.html


2 types of neurotransmitters:– Excitatory neurotransmitter – acetylcholine – activates

muscle fibers– Inhibitory neurotransmitter – endorphins – inhibit nerve

cells from discharging more pain signals

Neurotransmitters


- simple, rapid, involuntary response to stimuli that follows a reflex arc involving both the PNS and CNS

2 types Somatic reflexes – involve the stimulation of skeletal

muscles – when touching a hot surface, nerve impulses travel from a sensory nerve to an interneuron in the spinal cord to a motor neuron, bypassing the brain

Reflex video.html Autonomic reflexes – send involuntary stimuli to the

cardiac muscles of the heart and the smooth muscles of the organs – digestion, elimination, sweating

Reflexes


Fill in the blanks with: reflexes, saltatory conduction, neurotransmitter, or action potential.

1. A(n) _______________ is an all or none response.

2. _______________ occurs only in myelinated axons.

3. _______________ are rapid, involuntary responses.

4. The axon terminal has tiny vesicles filled with _______________.


Lesson 6.3

Functional Anatomy of the Central

Nervous System



• cerebrum• diencephalon• brain stem• cerebellum• meninges• blood-brain barrier

The Brain


• cerebral cortex– gyrus– sulcus– fissure

• lobes– frontal– parietal– occipital– temporal

• primary motor cortex• primary somatic sensory cortex

Cerebrum


Cerebrum


• thalamus• hypothalamus• epithalamus

Diencephalon


• midbrain• pons• medulla oblongata

Brain Stem


• cerebellum• blood-brain barrier

The Brain

• meninges– dura mater– arachnoid mater– pia mater


Spinal Cord


True or False?

1. The gyri divide the brain into 4 regions.

2. The hypothalamus regulates blood pressure.

3. The meninges has 3 layers.

4. The cerebellum coordinates balance.

5. The pons is also called the interbrain.


Lesson 6.4

Functional Anatomy of the Peripheral Nervous System



• nerve structure• cranial nerves• spinal nerves and nerve plexuses• autonomic nervous system

Functional Anatomy of the Peripheral Nervous System


• endoneurium– covers axons

• perineurium– bundles fascicles

• epineurium – wraps nerves

Nerve Structure


Cranial Nerves


• 31 pairs• dorsal root• ventral root• dorsal ramus• ventral ramus• plexuses

Spinal Nerves and Nerve Plexuses


• preganglionic and postganglionic neurons• sympathetic nerves

– fight-or-flight action

• parasympathetic nerves– resting or digesting action

Autonomic Nervous System


Match these words with 1–4 below: efferent, ganglion, optic, perineurium.

1. wraps fascicles

2. motor

3. a cranial nerve

4. enlarged junction


Lesson 6.5

Injuries and Disorders of the Nervous System



• traumatic brain injury• cerebral palsy• spinal cord injury

Injuries to the Brain and Spinal Cord


• violent impact to head– mild– moderate– severe

Traumatic Brain Injury


• damage to brain– before birth– during birth– during infancy

• motor function impairment

Cerebral Palsy


• C1–C3: usually fatal• C1–C4: quadriplegia• C5–C7: paralysis of lower extremities• T1–L5: paraplegia

Spinal Cord Injuries

Corepics/Shutterstock.com


• meningitis• multiple sclerosis• epilepsy• Parkinson’s disease• dementia and Alzheimer’s disease

Common Diseases and Disorders of the CNS


Match these words with 1–4 below: quadriplegia, multiple sclerosis, dementia, cerebral palsy.

1. inflammation destroys myelin sheath

2. loss of memory and thinking

3. loss of function below the neck

4. may begin before birth


Documents

6 Lesson 6.1: Overview of the Nervous System Lesson 6.2: Transmission of Nerve Impulses Lesson 6.3: Functional Anatomy of the Central Nervous System Lesson