Chapter 15: Feeling Jumpy: The Nervous System Summary

The nervous system

The nervous system forms the network for communication through all the parts of the body by the use of cells called neurons.

The functional types of cells in the nervous system include receptor cells for sensing impulses, conductor cells for impulse transmission, and effector cells (motor neurons) that enhance a response.

The function of the nervous system

• Orientation: this is the capability to produce nerve impulses due to environmental changes.
• Coordination: this is the ability to accept, filter, and transmit nerve impulses through certain channels.
• Conceptual thought: this involves the ability to store, record, and analyze nerve signals to enhance response.

Components of the nervous system

Neurons

This is the basic unit of nerve tissue. There are three types of neurons which include the following:

Motor neuron: They transmit nerve impulses from the spinal cord and brain to effector organs such as glands and muscles bringing about a response. They are multipolar in structure because of the star-shaped cells.

Sensory neuron: They are induced by physical stimuli to generate impulses and they transmit the signals to the spinal cord and brain. They are monopolar because they contain a single process.

Interneurons: They are activated by sensory neurons and transmit signals in the spinal cord and brain. They are multipolar in structure.

Nerves

• This is cable-like axon bundles that combine to form the peripheral nervous system.
• The three types of nerves include:
  • Afferent nerves contain a group of sensory nerve fibers that transmit impulses to the central nervous system from the receptors.
  • Efferent nerves contain motor neurons that move signals from the CNS to the effector organs.
  • Mixed nerves contain efferent and afferent nerve fibers.
• The composition of nerves include:
  • Axon –the nerve conducting part of the neuron.
  • Myelin sheath: this is the envelope that protects the fiber and promotes impulse transmission.
  • Endoneurium: a layer of connective tissue around nerve fibers.
  • Fasciculi: fiber bundles in a nerve.
  • Epineurium: it is the connective tissue that surrounds fiber bundles of neurons.

Impulses

Neurons have semipermeable electrically polarized membranes that receive impulses from the environment.

A stimulus can change fiber membrane permeability and causes depolarization by exchanging anions and cations. This change spreads all over the nerve fiber and generates a nerve impulse.

When a neuron is not relaying a signal, it is known to be at resting potential. When the nerve fiber is relaying an impulse is known to be at the action potential.

Synapses

Neurons never touch each other hence when a signal is transported along the axon, it meets a gap.

The gap is referred to as a synapse or synaptic cleft.

Organs and glial cells contain electric synapses that use gap junctions to relay signals between neurons.

• Activities that occur to relay a synapse across a synapse include the following:
  • Synaptic vesicles secrete acetylcholine transmitter that crosses the junction and raises the permeability of the membrane across the gap.
  • Cholinesterase enzyme degrades the transmitter into choline and acetyl which diffuse back.
  • Choline acetylase within synaptic vesicles combines acetyl and choline to form acetylcholine and waits for another impulse to be transmitted across the junction in the same process.

The brain and the central nervous system (CNS)

The central nervous system is made up of the brain and the spinal cord. The spinal cord proceeds down into the vertebral column tail.

The spinal cord is 18 inches long and terminates between the second and the first lumbar vertebrae.

The spinal cord

• It has an oval-like cylindrical structure with grooves running along its axis. It is encapsulated inside a fat cushion, cerebrospinal fluid, meninges, and blood vessels of different types.
• The three types of meninges (membranes) that cover the spinal cord include:
  •  dura meter (outer layer) is the most fibrous, toughest, and the hardest layer which also has collagenous elastic fibers.
  • The arachnoid (middle layer) produces the web-like network within the dura meter.
  • The pia meter is the thin inner layer located near the CNS.
• The solid material within the spinal cord includes gray matter  (has unmyelinated neurons and dendrites) and the white matter (has myelinated nerve fibers).

The brain

The parts of a brain include the following:

• Medulla oblongata: This is where the brain and the spinal cord meet and it is located under the left and right cerebellar brain hemispheres.
  • The medulla oblongata regulates body functions like respiration, cardiac functions, and reflex activities like wheezing and sneezing.
• Pons: The pons connects the cerebellum using the middle peduncle, superior peduncle of the cerebrum, and the inferior peduncle of the oblongata.
  • It also joins the cerebellar hemispheres.
  • It promotes muscle coordination on both body sides.
  • It regulates the first respiration stage.
• The midbrain: It is located between the diencephalon and the pons. It has the corpora quadrigemina which performs tactile and optical impulse correlation. It also regulates body posture, equilibrium, and muscle tone using superior colliculus reflex centers.
  • It contains a cerebral aqueduct that joins the thalamus third ventricle to the medulla oblongata the fourth ventricle.
• Cerebellum: It is also referred to as a small brain. It the second largest segment of the brain. It is located beneath the cerebrum rear part and above the medulla oblongata.
• Diencephalon: It is located between the cerebrum and the mesencephalon. It hosts brain structures like the epithalamus, subthalamus, thalamus, and hypothalamus. The hypothalamus coordinates sexual reflexes like water, fat metabolism, and body temperature.
• Cerebrum: It has the left and right hemispheres. It is the forebrain and sometimes known as the true brain. The cerebral cortex has the following lobes:
  • Frontal lobe: the seat for memory and intelligence.
  • Parietal lobe: helps in sensing touch, temperature, position, and movement.
  • Occipital lobe: It is involved in visual perception.
  • Temporal lobe: It is involved in perception and acoustical stimuli correlation.
• Medulla: It is made up of matter containing three fiber groups: projection fibers that transfer impulses to the cortex from the brain. Association fibers relay impulses to the cortex of one hemisphere from cortical cells. Commissural fibers join both cerebral hemispheres.
• Ventricles: ventricles are canals and cavities occupied with cerebral fluid. The ventricle lining is called the ependymal layer.

The peripheral nervous system (PNS)

The PNS is a network that transports messages into or from the spinal cord. It is composed of 31 spinal nerve pairs each coming from the neuromere, a spinal cord segment.

Among these, cervical nerves are eight, thoracic are twelve, lumbar is 5, sacral is 5, and the coccygeal nerve is one. 

The sensory neurons’ bodies are located in the dorsal root ganglion outside the spinal cord.

Spinal reflexes take place when a danger signal (like a burning heat sensation) is relayed by a sensory neuron through the dorsal root ganglion.

An interneuron passes the signal to the motor neuron that stimulates muscles to pull the burning part of the body from heat.

Autonomic nervous system

It is divided into the parasympathetic and sympathetic systems. It stimulates cardiac and smooth muscles and glands to perform vital autonomic roles like respiration, digestion, and blood circulation.

Autonomic functions are regulated by medulla oblongata, cerebral cortex, and hypothalamus.

The sympathetic system promotes flight or fights involuntary response of the body. The parasympathetic system contains autonomic fibers that leave the brain via the cranial nerves.

Sense receptors

• These are organs that respond to stimuli.
• Types of sense receptors include:
  • Exteroreceptors receive signals from the outer environment. They include terminal sensory nerves found in the mucous membranes and skin.
  • Interoreceptors receive signals in the internal environment.
  • Proprioceptors are terminal sensory nerves located in joints and muscles to give movement information and body position.
  • Teleceptors are terminal sensory nerves activated by distant object emanations. Are located in ears and eyes.

Ears

• Ears are the organs for hearing. They are divided into the following parts:
  • External ear: it is rounded and folded made up of cartilage and skin. The ear canal extends into the skull.
  • The middle ear: it has an air-filled cavity located in the skull covered with a mucous membrane. It communicates with the pharynx using the eustachian tube.
  • The internal ear:  It is the part where vibrations undergo translation. It also contains interconnected canals called the cochlea.

Revision

(J) Sensory transmitters that send impulses from receptors in the skin, muscles, and joints to the central nervous system

1. afferent nerves

(E) Branch of the nervous system that controls involuntary body functions

2. autonomic nervous system

(H) Part of an axon that contains a nucleus

3. cell body

(K) The brain and spinal cord

4. central nervous system (CNS)

(C) Branches of a neuron that collect stimuli and transport them to the cell body

5. dendrites

(M) Motor transmitters that carry impulses from the central nervous system out to the muscles and glands

6. efferent nerves

(L) The fatty bands of insulation surrounding axon fibers

7. myelin sheath

(D) The thin, membranous sheath enveloping a nerve fiber

8. neurilemma

(G) Non-neural tissue that forms the interstitial or supporting elements of the CNS; also known as glial cells

9. neuroglia

(A) The uninsulated gaps in the myelin sheath of a nerve fiber where the axon is exposed

10. nodes of Ranvier

(I) All parts of the nervous system external to the brain and spinal cord

11. peripheral nervous system (PNS)

(F) Branch of the nervous system that stimulates the skeletal muscles

12. somatic nervous system

(B) The intersection between a neuron and another neuron, a muscle, a gland, or a sensory receptor

13. synapse

(L) Section of the brain that coordinates body movements, including balance

1. cerebellum

(E) The largest part of the brain, consisting of the left and right hemispheres

2. cerebrum

(R) Area of the brain that includes the epithalamus, thalamus, metathalamus, and hypothalamus; also known as the interbrain

3. diencephalon

(G) The uppermost portion of the diencephalon, which includes the pineal gland and regulates sleep-cycle hormones

4. epithalamus

(A) The uniformly positioned, deep grooves in the brain

5. fissures

(S) Sections of the brain located behind the forehead

6. frontal lobes

(K) A portion of the diencephalon, which regulates functions such as metabolism, heart rate, and blood pressure

7. hypothalamus

(Q) The name for the four regions of the brain—frontal, parietal, occipital, and temporal

8. lobes

(O) The lower portion of the brain stem, which regulates heart rate, blood pressure, and breathing, and controls several reflexes

9. medulla oblongata

D) Three protective membranes that surround the brain and spinal cord

10. meninges(

M) Relay station for sensory and motor impulses; located on the superior end of the brain stem

11. midbrain(

(F) Sections of the brain located behind the parietal lobes; integrate sensory information from the skin, internal organs, muscles, and joints

12. occipital lobes

(I) Sections of the brain located behind the frontal lobes; integrate sensory information from the skin, internal organs, muscles, and joints

13. parietal lobes

(C) The section of the brain located below the midbrain that plays a role in regulating breathing

14. pons

(B) Outer region of the brain in the frontal lobes that sends neural impulses to the skeletal muscles

15. primary motor cortex

(J) Outer region of the brain in the parietal lobes that interprets sensory impulses received from the skin, internal organs, muscles, and joints

16. primary somatic sensory cortex

(N) A column of nerve tissue that extends from the brain stem to the beginning of the lumbar region of the spine

17. spinal cord

(H) The most inferior portions of the brain; responsible for speech, hearing, vision, memory, and emotion

18. temporal lobes

(P) The largest portion of the diencephalon, which communicates sensory and motor information between the body and the cerebral cortex

19. thalamus

What are the two major divisions of the nervous system?
Central nervous system and peripheral nervous system

Which body structures comprise the central nervous system(CNS)? What is the function of the CNS?
Brain and spinal cord. It is the communication and coordination system in the body. Receives messages from stimuli and the brain interprets the message. Then the brain responds by carrying out an activity.

Describe the structure and function of the peripheral nervous system(PNS).
12 pairs of cranial nerves and 31 one pairs of spinal nerves. Receives information from outside and relays commands from the CNS.

What is the difference between afferent nerves and efferent nerves?
Afferent nerves are skin or sense organs carry into the central nervous system. Efferent nerves are from the central nervous system out to muscles and glands

What are the two subdivisions of the efferent nerves? Name the function of each.
Somatic, voluntary to skeletal muscles and Autonomic, involuntary to heart and smooth muscle

What is the main function of neurons?
to transmit messages from one cell to the next

Why is it important for an axon to be covered with a myelin sheath?
It is important because the myelin sheath protects the axons and it makes the transmissions better

What are neurotransmitters?
Special chemicals, mainly epinephrine, norepinephrine, and acetylcholine.

Neurons are classified according to function. How many types are there, and what are their functions?
There are three types of neurons. Sensory neurons: skin or sense organs carry to brain/sc; Motor neurons: from brain/sc to muscles and glands; Associative: from sensory to motor neurons

How much does the adult brain weigh? How many neurons does it possess?
The adult brain weighs about 3 pounds. It possesses 100 billion neurons

What are the four major anatomic regions of the brain?
Cerebrum, diencephalon, cerebellum, and brain stem

The brain’s shape is not smooth. What are the names of the raised areas and the grooves between them?
Fissures gyrus and sulcus

What divides the brain into right and left hemispheres?
longitudinal fissure

What are the four main lobes of the cerebrum?
Frontal lobe, parietal lobe, occipital lobe, and temporal lobe

Describe the functions of the thalamus, hypothalamus.
Thalamus: relay station for incoming and outgoing nerve impulses; Hypothalamus: “brain” of the brain

What structures are in the brainstem and what are their functions?
Midbrain: reflex centers involved with vision and hearing; Pons: controls respiration; Medulla oblongata: heart rate, respiration rate and depth, swallowing and vomiting

What is the role of the cerebellum?
Communicates with the rest of the cns; maintenance of balance and muscle tone as well as coordination of muscle movements.

What are the membranes that protect the brain and spinal cord?
meninges

What are the functions of the spinal cord?
To carry messages from sensory neurons to the brain for interpretation. Returning messages carried by motor neurons to muscles and glands. Serves as a reflex center for the body

Which area of the brain controls the reflexes of coughing, sneezing, and vomiting?
Brain stem

How many pairs of cranial nerves are found in the human body?
12

How many pairs of spinal nerves are present in the body?
31

What are the four plexuses of the body?
Cervical, brachial, lumbar, and sacral plexus

Which nervous system sends impulses to the heart—the somatic or the autonomic system?
autonomic

List the two divisions of the autonomic nervous system.
Sympathetic and parasympathetic

genetic disorder impacting the cerebellum. Benefit most from having a routine
Autism

progressive paralysis, also known as Lou Gehrig’s disease
ALS

person has out of body experiences, sees himself going through parts of the day
Dissociative

mental, developmental, and physical retardation of fetus during pregnancy due to alcohol consumption
Fetal Alcohol

uncontrollable tics and yelling
Tourette

mental disorder altering behavior, emotions, and cognitive functions
Schizophrenia

intense headache involving the cranial nerves
Migraines

extreme mood swings of mania and depression
Bipolar

having limited attention, hyperactivity, and impulsivity
Attention Deficit Disorder

difficulty reading and writing related to the left temporal lobe genetic dysfunction
Dyslexia

progressive disease that slows the brain cells, producing involuntary movements.
Huntington’s

loss or impairment of motor function, usually seen during first 3-5 years of life
Cerebral Palsy

irregular sleep/wake cycle causing person to fall asleep randomly
Narcolepsy

in babies, portion of the spinal neural tube fails to close during development
Spina Bifida

type of autism with difficulty in social interactions
Asperger’s

the constant worry or fear that can be so overwhelming that is becomes disabling in some ways
Panic/Anxiety

feelings of intense sadness that keep you from functioning normally
Depression

progressive disease that destroys memory and other mental functions
Alzheimer’s

unreasonable thoughts and fears about life that form an obsession
Obsessive Compulsive Disorder

caused by the malfunction and death of vital neurons in the brain, results in tremors
Parkinson’s

rare genetic neurological disorder that only affects girls
Rett’s

immune system damages peripheral nervous system causing muscle weakness
Guillain-Barre

group of neurological disorders characterized by seizures
Epilepsy

damage to the myelin sheath of the brain and spinal cord
Multiple Sclerosis

a result of poor blood flow to the brain resulting in cell death
Stroke

Immediately after the ions have rushed inside the neuron the sodium potassium pump:
a. pumps sodium ions out
b. pumps acetylcholine into the nerve
c. deactivates the epinephrine
d. pumps oppositely charged ion inside to compensate for the charge imbalance
e. pumps potassium ions out
e

In order for the impulse to travel to another nerve it must jump across:
a. the synaptic cleft
b. the action potential
c. the sodium potassium pump
d. the concentration gradient
a

Next gates a bit down further down the neuron open and __
a. the sodium rushes into the neuron at this point
b. potassium ions rush out of the neuron at this point
c. potassium ions rush into the neuron at this point
d. the sodium rushes out of the neuron at this point
a

Which part of the brain works with the medulla to regulate breathing and sleep?
a. superior colliculus
b. pineal gland
c. pons
d. cerebellum
e. thalamus
c

Signals for written and oral speech must be received at the correct area of the brain before a child enters school for formal education.
a. False
b. True
b

Which subdivision of the autonomic nervous system is known as the “housekeeping division”?
a. sympathetic
b. parasympathetic
b

Which part of the brain is responsible sex, thirst, and hunger drives?
a. thalamus
b. hypothalamus
c. pons
d. cerebellum
b

Which of the three meneges is the toughest?
a. dura
b. arachnoid
c. pia
a

The neurotransmitter attached to this subdivision of the autonomic nervous system is acetylcholine?
a. parasympathetic
b. sympathetic
a

Which subdivision of the autonomic nervous system would do the following: -cause glucose to be released into blood stream -inhibit the production of saliva -dilate your pupils
a. parasympathetic
b. sympathetic
b

The most posterior part of the brain nearest to the spinal cord is the:
a. pons
b. inferior colliculus
c. cerebral peduncle
d. medulla
d

The sodium potassium pump moves _ out of the neuron and _ into the neuron.
a. potassium, sodium
b. sodium, potassium
b

Which division of the nervous system operates using two nerve connections?
a. autonomic
b. somatic
a