Chapter 8 - The Nervous System

Question 1

Describe the main functions of the nervous system

Answer 1

1) to detect changes and feel sensations
2) to initiate appropriate responses to changes
3) to organize information for immediate use and store it for future use.

It is one of the regulating systems (endocrine system being the other)

Question 2

What makes up the Central Nervous system (CNS)?

Answer 2

The brain and the spinal cord

Question 3

What makes up the peripheral nervous system (PNS)

Answer 3

Cranial nerves and spinal nevers (includes nerves to and from skin and skeletal muscles)
-Also includes autonomic nervous system (ANS)

Question 4

Describe nerve cells

Answer 4

Also called neurons or nerve fibers.

• All have cell body (contains nucleus, essential for continued life of the neuron)
• Neuron cell bodies found in the CNS or close to it in the trunk of the bodies

Question 5

What do Dendrites do?

Answer 5

• Processess that transmit electrical impulses toward the cell body.
• One axon of a neutron transmits impulses away from the cell body
• Cell membrane of dendrites, cell body and axon carries the electrical nerve impulse

Question 6

What are Schwann ccells?

Answer 6

Axons and dendrites in the PNS are wrapped in Schawnn cells

• They grow to surround the neuron processes during embryonic development, enclosing them in several layers of Schwann membrane called the myelin sheath (which electrically insulates neurons from one another)
• beleive to produce a chemical growth factor that stimulates regeneration.

Question 7

What is the space between Schwann cells or segments of the myelin sheath?

Answer 7

Nodes of Ranvier - parts of the neuron cell membrane that depolarize when an electrical impulse is transmitted
-^ speed of transmission

Question 8

What is the neurolemma (or neurilemnaa)?

Answer 8

Nuclei and cytoplasm of Schwann cells which are wrapped around the outside of the myelin sheath

• Very important if nerves are damaged
• Allow for axons and dendrites to regenerate through the tunnels formed by the neurolemmas

Question 9

What are Oligodendrocytes

Answer 9

In CNS, myelin sheaths are formed by oligodendroytes
-Specialized cells (neuroglia) found only in the brain and spinal cord with no Schwann cells present (therefore no neurolemma/regeneration of neurons)

Question 10

What are microglia

Answer 10

Capable of movement and phagocytosis of pathogens and damaged tissues

Question 11

What is an astrocyte?

Answer 11

Literally translates to “star cell”
A glial cell, which in the embryo, provide a framework for the migrating neurons that will form the brain.
-Regulate localized blood flow within the brain.
-Can contribute to the blood-brain barrier (prevents potentially harmful waste products in the blood from diffusing into brain tissues)

Question 12

What are Ependyma

Answer 12

Line the ventricles of the brain and CNS of the spinal cord, many of the cells have cilia, and involved in the circulation of cerebrospinal fluid

Question 13

Describe the process of the nerve impulse

Answer 13

• Same as electrical impulse generated in muscle fibers
  1) A neuron not carrying an impulse is in a state of polarization (Na+ ions more abundant outside cell, K+ ions and negative ions more abundant inside the cell.
  2) Neuron has a positive charge on the outside of the cell membrane and a relative negative charge inside
  3) A stimulus (neurotransmitter), makes the membrane very permeable to Na+ ions, which rush in into the cell –> brings about depolarization (reversal of charges on the membrane)
  4) Outside now has a negative charge and inside has a positive charge
  5) Depolarization makes neuron membrane very permeable to K+ ions, which rush out of the cells –> restors postive charge outside and negative charge inside (Re-polarization)
  6) Sodiums and postium pumps return Na+ ions outside and K+ Iions inside, and the neuron is ready to respond to another stimulus and transmit another impulse.
• Very rapid process, especially if neurons are myelinated. (transmit at a speed of many meters per second - Salatory conduction)
• Enable the nervous system to communicate very rapidly with all parts of the body.

Question 14

How does Multiple Sclerosis (MS) work?

Answer 14

Demyeelinating disease - involves the deterioration of the myelin sheath of neurons in the CNS

• Without the sheath , the impulses of these neurons are short-circuited and dod not reach theirr proper destinations (neuron axons are damaged and gradually die)
• Autoimmune disorder (genetic and environmental factors)
• Onset age 20-40 typically. Can progress slowly or rapidly. Some MS patients have remissions (where sx diminish –>not predictable)

Question 15

What are Synapses?

Answer 15

• Ensure one-way transmission of impulses in a living person.
• The small gap or space between the axon of none neuron and the dendrites of cell body of the next neuron.
• Chemical neurotransmitter is released into the synapse by the arrival of an electrical nerve impulse, which diffuses across the synapse and combines with the specific receptor sites on te cell membrane of the postsynaptic neuron–> generates an electrical impulse that is then carried by neurons axon to the next synapse (and continues on) –? stopped by a chemical inactivator at the cell body or dendrite of the postsynaptic neuron to inactivate the neurotransmitter to prevent unwanted, continuous impulses.

Question 16

Define Hyperpolarization

Answer 16

The neuron membrane becomes even more positive outside as K+ ions leave the cell or C1 ions enter the cell, therefore the netron does not transmit an electrical impulse.
-Important for slowing of the heart

Question 17

What is Acetytlcholine?

Answer 17

Found at neuromuscular junctions in the CNS and in much of the PNS
-Makes post synaptic membrane more permeable to Na_ ions, which brings about depolarization of the post synaptic neuron.

Question 18

What is Cholinesterase?

Answer 18

The in activator of acetylcholine.

Question 19

Name a few examples of neurotransmitters

Answer 19

• Dopamine
• GABA
• Norepeinephrine
• Glutamate
• Serotonin
• All have their own chemical inactivator.
• Some neurotransmitters are reabsorbed into the neurons that secreted them (process called Reuptake, which terminates the effect of the transmitter).

Question 20

Name the three groups of neurons and how they work.

Answer 20

1) Sensory neurons (carry impulses from receptors to the CNS. Contain receptors that detect changes and generate impulses. CNS interprets theses impulses as sensation (somatic impulses from skin, skeletal muscles, joints; Visceral are receptors in internal organs)
2) Motor neurons - carry impulses from CNS to effectors ((muscles and glands). Muscles contract or relax, glands secrete or do not. (Somatic when linked to skeletal muscle, Visceral when linked to cardiac muscle, smooth muscle or visceral.
3) Interneurons - Found largely in the CNS, arrange to carry only sensory or motor impulses or integrate these functions

Question 21

What is a nerve (3 types)

Answer 21

A group of axons or dendrites of many neurons, with blood vessels and connective tissues.

1) sensory nerves are made of only sensory neurons (optic nerves for vision, olfactory nerves for smell)
2) Motor nerves are made of only motor neurons (autonomic nerves)
3) Mixed nerve contains both sensory and motor neurons (most peripheral nerves)

Question 22

What is a nerve tract

Answer 22

Refers to groups of neurons within the CNS. All neurons in a nerve tract are concerned with either sensory or motor activity –> often referred to as white matter.

Question 23

What does the spinal cord do?

Answer 23

Transmits impulses to and from the brain and is the integrating center for the spinal cord reflexes.

• Internal gray matter shaped like the letter H, consists of cell bodies of motor neurons and interneurons
• External white matter made of myelinated axons and dendrites of interneurons.
• Central canal contains cerebrospinal fluid and is continuous with cavities in the brain called ventricles.

Question 24

What do Ascending tracts (of the spinal cord) do?

Answer 24

Carry sensory impulses to the brain.

Question 25

What do Descending tracts (of the spinal cord) do?

Answer 25

Carry motor impulses away from the brain.

Question 26

How many pairs of spinal nerves are there?

Question 27

What doe the cervical nerves (of spinal cord) do?

Answer 27

• 8 of them - supply the back of the head, neck shoulders, arms and the diaphragm (phrenic nerves).

Question 28

What does the thoracic nerves do? (of the spinal cord)

Answer 28

• Most supply the trunk of the body.
• the first thoracic nerve also contributes to nerves in the arms

Question 29

What does the lumbar and scaral nerves do? (of the spinal cord)

Answer 29

Supply the hips, pelvic cavity and legs.\
-Hang below the end of the spinal cord (in order to reach their proper openings - called the cauda equina (horses tail)

Question 30

Describe how spinal nerves are composed?

Answer 30

• Each has 2 roots which are neurons entering or leaving the spinal cord
  1) Dorsal root - made of sensory neurons that carry impulses into the spinal cord. –> dorasal root ganglion (ganglion being a group of cell bodies outside the CNS) is an enlarged part of the dorsal root that contains cell bodies of the sensory neurons
  2) Ventral root - is the motor root. Made of axons of motor neurons carrying impulses from the spinal cord to the muscles or glansa

Question 31

Name the 7 major peripheral nerves

Answer 31

1) Phrenic (c3-C5) - Diaphragm
2) Radial (C5-C8, T1) - Skin and muscles of posterior arm, forearm and hand, thumb and first 2 fingers
3) Median (C5-C8, T1) - Skin and muscles of anterior arm, forearm and hand
4) Ulnar - C8, T1 (skin and muscles of medial arm, forearm and hand; little and ring finger
5) Intercostal - T2-T12 - Intercostal muscles, abdominal muscles; sklin of trunk
6) Femoral - L2-L4 - Skin and muscles of anterior thigh, medial leg and foot
7) Sciatic (L4-S3) - Skin and muscles of posterior thigh, leg and foot.

Question 32

What is Shingles?

Answer 32

Caused by Hepes varicella-zoster virus (chicken pox).

• When a person recovers from chickenpox, virus may remain dormant in the dorsal root ganglia of some spinal nerves. For most, immune system is able to prevent reactivation of the virus, but with increasing age, immune system is not as effective and may become active and cause shingles (zoster)
• Present in sensory neurons of the trunk. Damage seen in skin over the affected area (raised red lesions)
• Occasionally can affect the cranial nerve and cause facial paralysis (Bells Palsy) or extensive facial lesions or even blindness.
• Not a cure, but some antiviral meds lessen the duration of the illness.
• Vaccine exists, typically recommended for those over 60.

Question 33

What is a spinal cord reflex

Answer 33

An involuntary response to a stimuls - in spinal cord, those that do not depend directly on the brain (we do not have to think about them)

Question 34

What is a reflex Arc (5 parts)

Answer 34

A pathway that nerve impulses travel when a reflex is elicited.

1) Receptors - detect a change and generate impulses
2) Sensory neurons - transmit impulses from receptors to CNS
3) CNS - contains one or more synapses
4) _ Motor neurons - transmit impulses from CNS to the effector
5) Effector - performs its characteristic action
- Example:
- Patellar reflex (knee jerk),
- Flexor reflexes (painful stimulus or harmful, response is to pull away)

Question 35

How many neurons in the brain?

Answer 35

86 billion neurons, and ~ same number of glial cells, containing trillions of synapses all functioning and an integrated whole.

Question 36

What are ventricles?

Answer 36

4 cavvities within the brain: 2 lateral ventricles, the third ventricle and the fourth.

• Lined with ciliatated ependymal cells., filled with cerebrospinal fluid (CSF)
• Contain a capillary network (choroid plexus) which forms the CSF from blood plasma
• CSFS is the tissue fluid of the CNS

Question 37

What is the Medulla

Answer 37

Extends from the spinal cord to the pons and is anterior to the cerebellum.

• Think of vital sign as its function (cardiac centers regulate heart rate, vasomotor centers regulate diameter of blood vessels and blood pressure respiratory centers regulate breathy)
• Also has reflex centers (coughing, sneezing, swallowing, vomiting)

Question 38

What are Pons?

Answer 38

Pons bulges anteriorly from the upper part of the medulla
-2 respiratory centers that work with those in the medulla to produce and normal breath and rhythm.

Question 39

What is the midbrain?

Answer 39

Extends from pons to the hypothalamus and encloses the cerebral aqueduct (tunnel that connects 3rd and 4th ventricles)

• Visual and auditory reflexes (ability to read, turning your head to a sound)
• Also concerned with righting reflexes (those that keep the head upright and maintain balance)

Question 40

What is the Cerebellum?

Answer 40

Separated from the medulla and pons by the 4th ventricle, inferior to the Occipital lobes.
-Concerned with movement (coordination, regulation of muscle tone etc…) - All involuntary, functions below the level of conscious thought.

Question 41

What is the Hypothalamus and its functions (7)?

Answer 41

Located superior ot the pituitary gland and inferior to the thalamus, it is a small area of the brain with many functions

1) Production of antidiruretic hormone (ADH) and oxytocin - stored in posterior pituitary gland. ADH enables kidneys to reabsorb water back into the blood - maintains blood volume.
- Oxtytocin causes contractions of the uterus for labor
2) Production of releasing hormones - stimulates secretion of hormones by the anterior pituitary gland –> like Growth hormone
3) regulation of body temperature by promoting responses (sweating, or shivering)
4) Regulation of food intake - responds to changes in blood nutrient levels, chemicals secreted by fat cells and hormones secreted byt te gastrointestinal tract.
5) Integration of the functioning of the autonomic nervous system, which regulates the activity of organs (heart, blood vessels and intestines)
6) Stimulation of viscceral responses during emotional situations (^ heart rate when agnry, blush when embarrassed)
7) Regulation of body rhythms such as secretion of hormones, sleep cycles, changes in mood or mental alertness.

Question 42

What is the Thalamus

Answer 42

Located superior to hypothalamus and inferior to the cerebrum. 3rd ventricle is a narrow cavity that passes through both the thalamus and hypothalamus.

• Concerned with sensation - sensory impulses to the brain follow neuron pathways that 1st enter the thalamus, which groups the impulses before relaying them to the cerebrum (where sensations are felt)
• Some sensations(like pain) are believed to be felt by the thalamus, but cannot localize the sensation (doesnt know where it is coming from, this is done in the cerebrum)

Question 43

What is the Cerebrum

Answer 43

Largest part of the brain, consists of 2 hemispheres (right and left).

• Connected by corpus callosum - band of 200 million neurons that connects left and right hemisphere
• Surface of cerebrum is gray matter called the cerebral cortex (cell bodies of neurons that carry out functions of the cerebrum)
• Internal to grey matter is white matter, connects the lobes of cerebrum to one another.
• Cerebral cortex folded extensively (called convolutions, grooves between them are fissures - permits the presence of millions more neurons in te cerebral cortex (much more than animals d/t folding).

Question 44

Name the lobes of the cerebral cortex

Answer 44

1) Frontal Lobes
2) Parietal Lobes
3) Temporal Lobes
4) Occipital Lobes
- Cerebral cortex has neuroplasticity - it is capable of taking on or being molded into different shapes. The younger the person, the more plastic the brain - hence children are extraordinarily adaptable.,

Question 45

What do the frontal lobes do?

Answer 45

• Motor areas that generate impulses for voluntary movement (left area controls movement on right side of body, right area controls left side of body)
• Premotor areas - concerned with learned motor skills that require a sequence of movements (i.e. tying shoelaces)
• Prefrontal cortex - right behind the eyes, concern with keeping emotional
• Contributes to what makes us human
• Brocas motor speech area - controls movement of the mouth involved in speaking responses appropriate to the situation

Question 46

What do the Parietal lobes do?

Answer 46

General sensory areas that receive impulses from receptors in the skin and feel and interpret the cutaneous sensations. (left area for right side, right for left)

• Receptive impulses from stretch receptors in muscles for conscious muscle sense
• Taste areas overlap the parietal and temporal lobes, receiving impulses from taste buds.

Question 47

What do Temporal Lobes do?

Answer 47

Olfactory areas receive impulses from receptors in nasal cavities for sense of smell.

• Auditory areas receives impulses from receptors in the inner ear. Part concerned with meaning of words we hear, others for interpretation of sounds such as thunder.. A
• Also involved with the though that precedes speech

Question 48

What do the Occipital Lobes do?

Answer 48

Impulses from the retinas of the eyes travel optic nerves to the visual areas in the occiptal lobes - These areas “see”

Question 49

What is a Cerebrovascular aaccident (CVA)

Answer 49

CVA or stroke is damage to a blood vessel in the brain, resulting in lack of oxygen to that part of the brain. Thrombosis or hemorrhage.

• Thrombus (blood clot), often consequence of atherosclerosis - obstructs blood flow to the part of the brain supplied byt the artery. Sx depend on the area of brain affected. 80% of CVAs are thrombus.
• Hemorrhage - result of arteriosclerosis or aneurysm (bubble in the wall that may burst) of a cerebral artery - allows blood out into brain tissues, which destroys brain neurons by putting excessive pressure on them. Onset of this type is usually rapid.

Question 50

What is Aphasia

Answer 50

Damage to the speech areas or interpretation areas of the cerebrum that may impair one or more aspects of a persons ability to use language.

• May be consequence of CVA or physical trauma to the skull.
• If motor speech (brocas area) is damaged, the person is still able to understand written and spoken words and knows what they want to say, but cannot say it
• Auditory Aphasia - word deafness - caused by damage to interpretation area( can hear but cant comprehend what the words mean)
• Visual Aphasia (word blindness), can still see well but cannot make sense of written word (still understands spoken words)

Question 51

What are association areas?

Answer 51

Parts of the cerebral cortex not concerned with movement oor a particular sensation.
-They make us individuals, give personality, a sense of humor etc…
Memories involved the hippocampus, part of the temporal lobe and floor of the lateral ventricle.

Question 52

What is the Basal Ganglia

Answer 52

Paired masses of gray matter within the white matter of the cerebral hemispheres..

• Control certain subconscious aspects of voluntary movement, work with the cerebellum.
• Helps regulate muscle tone, coordinate accessory movements (walking, gesturing)
• Most common disorder of basal ganglia is Parkinsons disease.

Question 53

What is Parkinsons Disease

Answer 53

Disorder of the basal ganglia whose cause is unknown.

• Usually begins after age 60
• Neurons in the basal ganglia that produce the neuotransmitter dopamine begin to degenerate and dise, and a protein called alpha-synuclein begins to accumulate.
• Sx of tremors. Eventually all voluntary movements become slower and more difficult
• Cannot be tx by dopamine itself as it does not cross the blood-brain barrier.
• Can be tx temporarily with L-Dopa, looses effectiveness within a few years.

Question 54

What does the Corpus callosum do?

Answer 54

Band of nerve fibers that connects left and right cerebral hemispheres. Enables them to communicate.

• Person with musical training has a thicker corpus callosum then someone without.
• Important because for most, left hemisphere contains speech areas and right hemisphere does not. Corpus callosum lets the left hemisphere know what the right hemisphere is thinking about, and vice versa.

Question 55

What is Alzeimers disease?

Answer 55

Progressive incurable form of mental deterioration

• Affects ~5.5 Million people and is th cause of 100K deaths each year
• Onset usually after 65
• SX memory lapses, slight personality changes –> progresses to total loss of memory, reasoning ability and personality.
• difficult to dx, early stages resembles types of dementia. 1 possible test may be a lumbar puncture (small amount of amyloid present in CFS may be indicative)

Question 56

What are Meninges (3 layers)?

Answer 56

Connective tissue membranes that cover the brain and spinal cord; 3 layers

1) Dura mater (tough mother) - thick outermost layer, made of fibrous connective tissues, lines the skull and vertebral canal
2) Arachnoid Membrane (spider) is the middle layer made up of web=like strands of connective tissues
3) Pia mater (gentle mother), innermost thin membrane on the surface of the spinal cord and brain.
- Subarachnoid space - the space between anarchnoid a pia mater which contains CSF.

Question 57

What does the arachnoid villi do?

Answer 57

From the subarachnoid space, CSF is reabsorbed through arachnoid villi into the blood in the cranial venous sinuses. This CSF becomes blood plasma again.

Question 58

How many pairs of cranial nerves are there?

Answer 58

12 pairs that emerge from the brain stem.

• The impulses for the senses of smell, taste, sight, hearing and equilibrium are all carried by cranial nerves to their respective sensory areas in the brain.
  1) Olfactory (smell)
  2) Optic (sight)
  3) Oculomtor (movement of eyeball, constriction of pupil)
  4) Trochlear (Movement of eyeball)
  5) Trigeminal (sensation in fac e, scalp and teeth; chewing muscles)
  6) Abducens (movement of eyeball)
  7) Facial (sense of taste, contraction of facial msucles, saliva secretion)
  8) Acoustic (sense of hearing, equilibrium)
  9) Glossopharyngeal (sense of taste, sensory for cardiac, respiratory and BP reflexes, contraction of pharynx, secretion of saliva)
  10) Vagus (sensory in cardiac, respiratory and BP, sensory and motor to larynx (speaking), decreases in heart rate, contraction of alimentary tube, increases digestive secretions)
  11) Accessory (contraction of neck and shoulder muscles, motor to larynx)
  12) Hypoglossal (movement of the tongue)

Question 59

What is the autonomic nervous system? (ANS)

Answer 59

Part of the PNS - consists of motor portions of some cranial and spinal nerves.
Made up of visceral motor neurons to smooth muscles,cardiac muscle and glands (visceral effectors make them contract or relaxx, and will make glandes either increase or decrease secretions
2 divisions: sympathetic and parasympathetic

Question 60

What are autonomic pathways

Answer 60

Autonomic nerve pathways going from CNS to visceral effectors differ anatomically from somatic pathways that lead to skeletal muscle effectors.
-Somatic motor pathway is a one-neuron pathways, Autonomic pathway is a 2 neuron pathway.

-It consists of 2 motor neurons that synapse in a ganglion outside the CNS (pre and post ganglionic neurons)

Question 61

What is sympathetic division?

Answer 61

It tells us where the sympathetic preganglionic neurons originate.

• Cell bodies are in the thoracic segments and some of the lumbar segments of the spinal cord.
• Their axons extend to the sympathetic ganglia,
• Sympathetic division is dominant in stressful situations (anger, fear, anxiety, exercise)
• Fight or flight response

Question 62

What is a lumbar puncture?

Answer 62

Spinal tap - a diagnostic procedure that involves the removal of cerebrospinal fluid to determine its pressure and constituents.

• Needle usually inserted between 4th and 5th vertibrae.
• CSF has nml pressure of 70-200 mm H20. Abnml pressure indicates obstruction in circulation (by infection, tuor or injury)
• Most common reason for lumbar puncture is suspected meningitis (cause by bacteria) - CSF will appear cloudy rather than clear.

Question 63

What is parasympathetic division

Answer 63

Dominates in relaxed situations to promote normal function of several organ systems (digestion is efficient, increased secretions, nml heart beat)

Question 64

What are neurotransimitters

Answer 64

Enable nerve impulses to cross synapses.
-in autonomic pathways, 2 synapses (one between the preganglionic and postganglionic neurons, the other between the postganglionic neurons and the cells of the visceral effectors).

Question 65

How does aging affect the nervous system?

Answer 65

• Aging brain loses neurons (sall % of total neurons)
• Formation of snyaptic connections is believed to slow considerably
• Forgetfulness to be expected
• blood-brain barrier deteriorates with age - cells that contribute to making brain capillaries less permeable no longer divide as efficiently - may be factor in onset of dementia.
• Dry eyes and constipation may become problems.