Nervous System

Nervous System

Objectives:1. Identify structures of the nervous system.2. Explain differences in the function of the

peripheral nervous system and the central nervous system.

D. Nervous Tissue

• Nervous tissue is:– found in the brain, spinal cord, and nerves. – made up of:

1. Neurons: nerve cells (bundles of axons)2. Neuroglial cells: helper cells

– “glia” = glue– Support and bind components of nervous tissue to each

other and to blood vessels– Function similarly to connective tissue in other organ

systems

Parts of a Neuron

Nervous System• Organs of this system are divided into 2 groups:

1. Central Nervous System (CNS)• Brain• Spinal cord

2. Peripheral Nervous System (PNS)• Composed of the nerves (peripheral nerves) that

connect the CNS to other body parts

• Functions of the nervous system:1. Sensory2. Integrative3. Motor

1. Sensory Function

• Sensory receptors at the ends of peripheral neurons:– Gather info by detecting changes inside and

outside the body.• Inside: temperature and oxygen concentration• Outside: light and sound intensities

– Convert info into nerve impulses (electrochemical changes) which are transmitted along peripheral nerves to the CNS

2. Integrative Function

• Nerve impulses are integrated (brought together) in the CNS.

• Allows us to make conscious or subconscious decisions.

3. Motor Function• Peripheral nerves carry impulses from the

CNS to effectors (responsive structures).• Effectors are NOT part of the nervous system,

but include muscles and glands.

Motor Function

• Motor functions can be divided into 2 groups:– Somatic nervous system• Consciously controlled (voluntary)• Controls skeletal muscle

– Autonomic nervous system:• Involuntary• Includes heart, smooth muscle, and various glands

Nervous System Function Recap

1. Detects changes inside and outside the body,

2. Makes decisions based on the information received, and

3. Stimulates muscles or glands to respond.

• What is the purpose of this process?????

Neuroglial Cells

• Functions:– Fill spaces– Provide structural frameworks– Produce myelin– Carry on phagocytosis

• Vary from CNS to PNS• Table: Type of Cell, Location, Function, Other

specific info

CNS Neuroglial Cells• Greatly outnumber neurons in the CNS

(think worker ants vs. Queen ant)1. Microglial cells– Scattered throughout CNS– Support neurons and phagocytize bacterial cells

and cellular debris2. Oligodendrocytes– Occur in rows along nerve fibers– Provide layers of myelin around axons within

brain and spinal cord

CNS Neuroglial Cells, continued….

3. Astrocytes– Found between neurons and blood vessels– Provide structural support, help regulate

nutrients and ions in tissues– Form scar tissue to fill spaces after CNS injuries

4. Ependymal cells– Form epithelial-like membrane in parts of the

brain (choroid plexuses)– Form inner linings that enclose ventricles in the

brain and central canal in the spinal cord

CNS Neuroglial Cells

PNS Neuroglial cells

1. Schwann cells: form myelin sheath around axons

Neurons

• Vary in size and structure, but have common features:

1. Cell Body2. Dendrites3. Axon

• Mature neurons do not divide, but neural stem cells can divide and form neurons or neuroglial cells.

1. Cell Body• Contains normal cellular structures (golgi

apparatus, mitochondria, cytoplasm, cell membrane, etc.)

• Neurofibrils – fine threads that extend into the axon

• Nissl bodies (chromatophilic substances)– Membranous sacs in the cytoplasm – Similar to rough ER– Ribosomes on Nissl bodies synthesize ______

2. Dendrites

• Usually short and highly branched (dendr = ?)• The main receptive surfaces for receiving

communication from axons of other neurons

3. Axons

• Arise from a slight elevation of the cell body, called the axonal hillock.

• Conduct nerve impulses away from the cell body

• Contains many mitochondria, microtubules, and neurofibrils

• Originates as a single structure, but may have branches, especially at the end to interact with receptive surfaces of other cells

PNS Axons

• Enclosed in myelin sheaths composed of many Schwann cells

• Myelin is a lipoprotein.• Neurilemma sheath surrounds the myelin

sheath• Nodes of Ranvier – narrow gaps in the myelin

sheath between the Schwann cells

Classification of Neurons

• Classification based on Structural differences:• Bipolar neurons• Unipolar neurons• Multipolar neurons

• Classification based on Functional differences:• Sensory neurons (afferent neurons)• Interneurons (association or internuncial neurons)• Motor neurons (efferent neurons)

Structural Differences• Sketch the neurons below. Notes on the next

3 slides:

Structural Differences, cont…..

1. Bipolar:– 2 processes• Axon• Dendrite

– Found in specialized parts of the eyes, nose, and ears


2. Unipolar:– 1 process divides into 2 branches, which

function as a single axon• 1 branch (peripheral process) associated with

dendrites• Other branch (central process) enters brain or spinal

cord


3. Multipolar:– Many processes arising from cell body:• 1 axon• Many dendrites

– Most neurons whose cell bodies lie in the brain or spinal cord are multipolar.

• Direction of impulse is ALWAYS from dendrites to axon.

Functional Differences

1. Sensory (afferent) neurons– From peripheral body parts to the brain or spinal

cord– Have specialized receptor ends at the tips of their

dendrites OR– Dendrites closely associated with receptor cells

in the skin or sensory organs.– Most are unipolar, but some are bipolar.

Functional Differences, cont…..2. Interneurons (association or internuncial

neurons)– Lie entirely in the brain or spinal cord– Multipolar and link other neurons– Transmit impulses from one part of the brain or

spinal cord to another3. Motor (efferent) neurons– Multipolar– Carry nerve impulses from brain or spinal cord

to effectors– Stimulate muscles or glands

Copy Diagram on Whiteboard

1. Identify the direction of nerve impulse.2. How can you tell the direction?3. Label all dendrites, cell bodies, and axons.4. Label each nerve as either sensory neuron,

interneuron, or motor neuron.5. Color code the CNS and PNS portions of the

pathway.

Reflex Arcs

• Nerve impulse pathways that are responsible for involuntary actions

• Look like the pathway you drew and labeled:Receptor toSensory neuron to (optional step) Interneurons in the CNS (a reflex

center) toMotor neurons to Effector

Reflexes

• Automatic subconscious responses to changes within or outside the body:– Maintain homoestasis: blood pressure, heart

rate, respirations, digestion, temperature– Automatic actions: swallowing, coughing,

sneezing, vomiting

2 Examples of Types of Reflexes (?)

1. Knee-jerk reflex (patellar tendon reflex)– Employs only 2 neurons: sensory neuron

communicating directly with a motor neuron2. Withdrawal reflex:– A response to painful stimuli– Sensory neuron takes impulse to interneurons

in the spinal cord reflex center, where it is transmitted to motor neurons.

– Other interneurons carry impulses to the brain for processing of the experience and pain.

Knee-jerk Reflex (Fig. 9.16)

Withdrawal Reflex (Fig. 9.17)

CNS Structures

1. Meninges2. Spinal cord3. Brain

Meninges

• Membranes between the bone and soft tissues of the nervous system

• Function: ?• 3 layers: Orange analogy

1. Dura mater2. Arachnoid mater3. Pia mater

– Meningitis (?)

Dura Mater

• Outermost layer• Contains many blood vessels and nerves• Attaches to the inside of the cranial cavity

and forms the internal periosteum (???) of the surrounding skull bones

• Forms partitions between lobes of the brain• Continues into vertebral canal• Terminates as a blind sac below the end of

the spinal cord

Arachnoid Mater

• Thin, weblike membrane located between dura and pia maters

• Lacks blood vessels• Spreads over brain and spinal cord, but does

not dip into grooves and depressions on their surfaces

Pia Mater

• Cerebrospinal fluid (CSF) – clear, watery fluid that fills space between arachnoid and pia maters

• Pia mater – very thin and contains many nerves and blood vessels that nourish cells of the brain and spinal cord

• Hugs surfaces and follows all irregular contours of brain and spinal cord

• Subdural hematoma (?)

Review

• List and describe the 3 layers of the meninges.

Spinal Cord

• Slender nerve column that passes downward from the brain into the vertebral canal

• Starts at the foramen magnum and ends between first and second lumbar vertebrae

Structure of Spinal Cord• 31 segments that each give rise to a pair of

spinal nerves

Functions of the Spinal Cord• What do you think would be the functions

of the spinal cord?1. Conducting nerve impulses2. Serving as a center for spinal reflexes• Nerve tracts (major nerve pathways) of the

spinal cord are made up of axons that provide 2-way communication between brain and body parts:

1. Ascending tracts - sensory information to brain2. Descending tracts – motor impulses from brain

Brain• About 100 billion multipolar neurons• 3 major portions:– Cerebrum• Largest part• Contains nerve centers associated with sensory and

motor functions• Provides higher mental functions, including memory

and reasoning– Cerebellum - includes centers that coordinate voluntary

movements– Brain stem – • Connects parts of the nervous system (???)• Regulates some visceral (???) activities

Cerebrum• Cerebral hemispheres: 2 large, mirror-image

halves• Corpus callosum: deep bridge of nerve fibers

that connect the cerebral hemispheres• Surface of the cerebrum has:– Ridges: convolutions– Grooves: • Shallow grooves: sulci (sulcus, singular) – separates

lobes• Deep Grooves: fissures

– Longitudinal fissure – separates cerebral hemispheres– Transverse fissure - separates cerebrum and cerebellum

Locations and Boundaries of the Lobes of the Cerebral Hemisphere

Lobe Location Boundaries

Use textbook, pp.227-228 to complete the table below.

Functional Regions of the Cerebrum

1. Complete graphic organizer.

2. Color-code and label diagram of association areas of the brain to correspond to your graphic organizer.

Hemisphere Dominance

• Right-Left Brain Test• The dominant hemisphere controls the

ability to use and understand language.• Which hemisphere do you think is dominant

in most of the population?• Broca’s area (???) in the dominant

hemisphere controls the muscles used in speaking.

Hemisphere FunctionsDominant Hemisphere Non-dominant Hemisphere

•Language-related activities: reading, writing, speaking

Nonverbal functions:1. Motor tasks requiring

orientation of body in space

•Complex intellectual functions requiring verbal, analytical, and computational skills

2. Recognition and understanding of musical patterns

3. Nonverbal visual experiences

Corpus Callosum (???) and Hemisphere Dominance

• What is it? Nerve fibers connecting the 2 cerebral hemispheres

• Functions:– Allows the dominant hemisphere to control the

motor cortex of the non-dominant hemisphere.– Transfers info received by the non-dominant

hemisphere to the dominant hemisphere for use in decision-making.

Ventricles and CSF

• Ventricles: – interconnected cavities within the cerebral

hemispheres and brain stem– contain CSF

• Choroid plexuses: tiny, reddish, cauliflower-like masses of specialized capillaries from the pia mater that secrete CSF into the ventricles

• Infections, tumors, blood clots can block the flow of CSF and increase intracranial pressure.

Ventricles and CSF

Diencephalon• Located between the cerebral hemispheres

and above the midbrain• Contains:– Thalamus– Hypothalamus– Optic tracts and optic chiasma – formed by

crossing of optic nerves– Infundibulum – attaches to pituitary gland– Posterior pituitary gland – hangs from floor of

hypothalamus– Pineal gland – attached to upper diencephalon

Diencephalon• Thalamus – receives all sensory input, EXCEPT smell,

and sends them to proper region of cerebral cortex• Hypothalamus – maintains homeostasis by regulating:

1. Heart rate2. Blood pressure3. Body temperature4. Water and electrolyte balance5. Hunger control and body weight6. Movements and secretions of stomach and intestines7. Neurosecretory substances that stimulate the pituitary

gland8. Sleep and wakefulness

Brain Stem• Connects _______ to _______.• Three sections:

1. Midbrain2. Pons3. Medulla oblongata

1. Midbrain – Between diencephalon and pons– Contains some visual and auditory reflex

centers

Brain Stem2. Pons– Rounded bulge on the underside of the brain

stem, between midbrain and medulla oblongata

– Relays impulses from medulla oblongata to cerebrum

– Transmits impulses from cerebrum to cerebellum

– Relays sensory impulses from peripheral nerves to higher brain centers

– Helps regulate breathing

Brain Stem3. Medulla oblongata– Extends from pons to foramen magnum– All ascending and descending nerve fibers

must pass though– Control of visceral activities:

1. Cardiac center – heart rate2. Vasomotor center – constriction and dilation of

blood vessels to control blood pressure3. Respiratory center – regulates rate, rhythm, and

depth of breathing

Cerebellum• Located below the

occipital lobes of the cerebrum and posterior to the pons and medulla oblongata

• Like cerebrum, has two hemispheres, connected by a structure called the vermis.

Cerebellum• Communicates with other parts of the CNS

by 3 nerve tracts (cerebellar peduncles):1. Inferior peduncles: receives sensory info about

position of body parts2. Middle peduncles: signals from cerebrum to

cerebellum about desired position of limbs3. Superior peduncles: takes correcting info from

cerebellum to midbrain

Functions of Cerebellum• Based on the previous slide, what do you

think are the main functions of the cerebellum?

• Answer: – Reflex center for integrating sensory info

concerning body positioning and coordination– Helps maintain posture

• What do you think damage to the cerebellum would cause?

Peripheral Nervous System

• Includes:1. Cranial nerves2. Spinal nerves

• Can also be divided into:1. Somatic nervous system – controls conscious

activities2. Autonomic nervous system – controls

unconscious activities

Cranial Nerves

• Where would these originate?• 12 pairs– 1st pair originates in the cerebrum– The rest originate from the brain stem

Cranial Nerves, continued…..1. Olfactory nerves (I)2. Optic nerves (II)3. Oculomotor nerves (III)4. Trochlear nerves (IV) – smallest; takes

impulses to a muscle that moves the eye5. Trigeminal nerves (V) – largest cranial nerves

1. Ophthalmic division – sensory info from eyes2. Maxillary division – sensory info from upper

mouth3. Mandibular division – sensory info from scalp

behind ears and lower mouth

Cranial Nerves, continued…..

6. Abducens nerves (VI) – small; motor impulses to move eye

7. Facial nerves (VII) – 1. Sensory associated with taste receptors2. Motor impulses to facial muscles and tear

glands and salivary glands8. Vestibulocochlear nerves (VIII) – inner ear

1. Vestibular branch – maintaining balance2. Cochlear branch - hearing


9. Glossopharyngeal nerves (IX) – tongue and pharynx; swallowing

10. Vagus nerves (X) – 1. Larynx muscles associated with speech and

swallowing2. Supplies muscles of the heart and smooth

muscles and glands in thorax and abdomen– Vasovagal response


11. Accessory nerves (XI) – originate in the medulla oblongata AND spinal cord, so has cranial AND spinal branches

1. Cranial branches – join a vagus nerve and carry impulses to muscles of soft palate, pharynx, and larynx

2. Spinal branches – motor impulses to trapezius and sternocleidomastoid muscles

12. Hypoglossal nerves (XII) – motor impulses to tongue

Spinal Nerves• Thirty-one pairs providing 2-way

communication between spinal cord and parts of upper and lower limbs, neck, and trunk

• Divided into:1. Cervical nerves2. Thoracic nerves3. Lumbar nerves4. Sacral nerves5. Coccygeal nerves– Naming and how many of each????

Autonomic Nervous System

• Two divisions:– Sympathetic division – prepares body for

stressful situations– Parasympathetic division• Most active under ordinary conditions• Counterbalances sympathetic division

Cranial Nerves Mnemonic Devices

• Naming:O! O! O! There’s The Abercrombie and Fitch.

Very Gorgeous and Very Adorable! Hot!

• Type of Nerve:Some Say Money Matters, But My Brother Says

Big Boobs Matter More.

• F:\Public\ULNAR NERVE

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Nervous System