nervous system

Question 1

CNS

Answer 1

Central Nervous System (CNS)

Functions as a control center, processing incoming
information and responding accordingly.

The CNS includes the:
Brain (cerebral cortex, pons, medulla, cerebellum, hypothalamus, thalamus, basal ganglia, pituitary gland etc..) – encased within the cranial cavity
Spinal cord – starting at the foramen magnum & ending at the sacrum – located within the vertebral canal

Question 2

brain

Answer 2

BRAIN – one of the most important organs for survival (technically
you are still alive if you have brain waves).

As well as the cranial bones, the brain is also protected by cerebrospinal fluid (CSF) and specialized connective tissue membranes called “meninges”.

The cerebrum (largest part of the brain) is divided into 2 hemispheres (left and right).
The RIGHT side receives stimuli from and controls the LEFT side of the body (and vice versa). You will learn more about this (neuroanatomy) in 300 level.

Question 3

PNS

Answer 3

Peripheral Nervous System (PNS) – includes all the nervous tissue outside the CNS
may be further subdivided into the somatic, autonomic, & enteric nervous systems.

Question 4

somatic nervous system

Answer 4

a. Somatic nervous system (A.K.A. voluntary nervous system) which includes:
Motor neurons that control skeletal muscles.
Sensory neurons that convey information towards the CNS including somatic and special senses.
Also responsible for involuntary reflexes.

Question 5

Autonomic nervous system

Answer 5

(ANS) – this is involuntary and includes:
Sensory nerves that supply internal organs.
Motor neurons that supply smooth muscle and glands (and therefore the function of internal organs).

The ANS is further sub-divided into the
Parasympathetic & sympathetic nervous systems

Question 6

Autonomic nervous system

Answer 6

(ANS) – this is involuntary and includes:
Sensory nerves that supply internal organs.
Motor neurons that supply smooth muscle and glands (and therefore the function of internal organs).

The ANS is further sub-divided into the
Parasympathetic & sympathetic nervous systems

Question 7

Parasympathetic nervous system

Answer 7

– responsible
for “rest & digest” mode which is responsible for
bringing the body back to homeostasis
(normalization of body functions).

For example:
Decreased heart rate, constriction of pupils, bronchoconstriction and increased blood flow to internal organs (diverting it from the muscles).

Question 8

Sympathetic nervous system

Answer 8

– responsible for the “fight or flight response” – the autonomic increase of body functions necessary for our survival.

For example:
Increased heart rate, dilation of pupils, increased glucose from liver to supply brain and muscles.
Dilation of airways to supply body with oxygen.
Slowing down of digestive function (by diverting blood to our musculoskeletal system).

Question 9

Enteric nervous system

Answer 9

ENS) – functions
autonomously although may be regulated by other
ANS divisions. Related and intrinsic to the GI tract.
Sensory neurons – monitor chemical changes and stretching of the GI tract walls.
Motor – governs smooth muscle contractions and secretion of glands in the GI tract.

E.g. When food enters the stomach it causes its walls to stretch and also changes the pH of the gastric fluid. This is detected by the mechanoreceptors (stretch) and chemoreceptors (pH) which triggers an increase in stomach motility and gastric juice secretion (among many other things).

Question 10

3 key functions

Answer 10

a. Sensory function – detection of external or internal stimuli. 
E.g. Somebody tapping you on the shoulder (external)
E.g. Your heart beating rapidly in your chest (internal)
Utilizes afferent (sensory) neurons which carry the signal towards the central nervous system. I.e. You are AFFected by these nerves!

Question 11

Integrative function

Answer 11

(association) – processes the incoming signals from afferent neurons & decides what the appropriate response is.
Utilizes interneurons (in between) or association neurons
Can be a simple reflex (patella reflex) or something complex like deciding what flavor pizza to order.

Question 12

Motor

Answer 12

(output) – the command sent by the CNS in reply to the incoming stimulus. This is the part of the pathway that elicits the response (e.g. muscle contraction).
Utilizes efferent (motor) neurons to activate ‘effectors’ including muscles and glands. 
Can be voluntary/involuntary or somatic/autonomic.

Question 13

Recall 2 main cell types: Neurons & Neuroglia

Answer 13

1. Neurons – A.K.A. “nerve cell” – responsible for conduction of electrical signals in the nervous system and therefore control of bodily functions.
   Neurons have electrical excitability – can generate action potentials (nerve impulse).
   Nerve impulses travel along the membrane of neurons at an extremely rapid rate (1-100 meters per second!).

Question 14

Anatomy of a Neuron:

Answer 14

Dendrites – finger like projections extending from the neuronal body that receive input
Axons – long, thin, projections that conduct the nerve impulse.

Question 15

Axon hillock

Answer 15

is the area where the axon joins the neuronal body. The area within the axon hillock where APs are generated (triggered) is called the trigger zone.

Question 16

The cytoplasm of a nerve axon

Answer 16

is called the axoplasm.

Question 17

The membrane of a nerve axon is called

Answer 17

the axolemma.

Question 18

Axons and their collaterals all end at axon terminals.

The bulges at the end of the axon terminals are called

Answer 18

synaptic end bulbs. These contain vesicles that release NTs.

The segment of the axon closest to the axon hillock is referred to as the initial segment.

Question 19

Axon collaterals

Answer 19

are ‘side branches’ off the axon that allow a neuron to communicate with many others.

Question 20

Nissl bodies

Answer 20

are large granular bodies found within the nerve cell’s body which consist of rough endoplasmic reticulum

Question 21

Nerve cell body – contains

Answer 21

the nucleus and other usual organelles (i.e. mitochondria, lysosomes, Golgi etc.). Also contains nissl bodies (bundles of rough ER) which produce proteins specific to the neuron.

Question 22

Synapse

Answer 22

– the gap b/w 2 neurons. The bulging at the ends are called synaptic end bulbs which contain synaptic vesicles that store neurotransmitters (i.e. ACh).

Question 23

Axon Transport:
Some substances synthesized or recycled by the neuron cell body are needed in the axon. They move via two types of transport:

Slow axonal transport

Answer 23

Moves materials in one direction (cell body to axon).
Supplies new axoplasm to developing or regenerating axons.
Moves materials about 1-5mm per day.

Question 24

Fast axonal transport

Answer 24

Moves materials in both directions (to and from the cell body).
Includes substances needing to be broken down or recycled.
Capable of moving materials 200-400mm per day.

Question 25

Neurons by shape:

Answer 25

Unipolar – dendrites and one axon form one continuous process from which the nerve cell body emerges (mainly tactile sensory neurons).
Bipolar – 1 axon & 1 main dendrite. These neurons are found in the retina, olfactory area, & inner ear (mainly special sensory neurons).
Multipolar – multiple dendrites and one axon. These are the most common neuron in the brain and spinal cord.
Purkinje – found in the cerebellum and named after the histologist that first described them. (Do you remember Purkinje fibers in the heart?)
Pyramidal – have a pyramidal cell body and are found only in the cerebral cortex.

Question 26

Functionally neurons are classified according to the direction the nerve impulse travels (in relation to the CNS).

Answer 26

Sensory/afferent neurons (input) – conduct APs TOWARDS the CNS in response to some kind of stimulus (internal or external).

Interneurons/association neurons (integration) – processes incoming sensory signals and then activates appropriate motor neurons.

Motor/efferent neurons (output) – conduct APs AWAY from the CNS which results in activation of the effector organs (muscles or glands).

Question 27

Neuroglia –

Answer 27

main role is to support, nourish, & protect neurons (supportive role).

Smaller but much more numerous than neurons (therefore make up about half the volume of CNS).

Gliomas are brain tumors arising out of glial cells which are highly malignant (and therefore usually fatal).

Question 28

CNS: Neuroglia

1. Astrocytes

Answer 28

– the largest and most numerous of neuroglia. These star-shaped cells play various supportive functions for neurons including forming the blood brain barrier (BBB).
The BBB is a tightly sealed lining that helps maintain the selective permeability of the capillaries (prevents harmful substances from entering the CNS).

Question 29

2. Oligodendrocytes

Answer 29

– Form the myelin sheath around CNS axons which is important for the speed of AP conduction (more on this later).

Question 30

3. Microglia

Answer 30

– the phagocytes of the CNS (remove microbes and cellular debris formed during cellular development and also during nervous tissue repair).

Question 31

4. Ependymal

Answer 31

– arranged in a single layer along the ventricles of the brain and spinal canal where they produce and circulate cerebrospinal fluid (CSF) (the CNS’s version of synovial fluid).

Question 32

Neuroglia of the PNS:

1. Schwann

Answer 32

– Form the myelin sheaths of PNS neurons (similar to the oligodendrocytes of the CNS).

Question 33

2. Satellite

Answer 33

– surround the cell bodies of neurons in the PNS (structural support), helping to regulate the exchange of materials between the neuron and interstitial fluid.

Question 34

D. MYELINATION:

Answer 34

The insulation of axons by neuroglia (oligodendrocytes and Schwann cells) that allows for increased rate and efficiency of transmission of electrical impulses.
Neurolemma – the outermost layer of axons in the PNS (sheath made of Schwann cells). Therefore there is NOT neurolemma in the CNS.

Question 35

Nodes of Ranvier

Answer 35

– gaps in the insulation (myelination) which consist of concentrations of ion channels. This allows APs to ‘skip’ along the axons which increases the speed of conduction (more on this later).

Question 36

Ganglion

Answer 36

(pl: ganglia) – clusters of neuronal cell bodies located within the PNS (closely associated with spinal/cranial nerves)

Question 37

Nucleus

Answer 37

– a collection of neuronal cell bodies within the

CNS.

Question 38

Nerve

Answer 38

– bundle of axons in the PNS.

Question 39

Tract

Answer 39

– bundle of axons in the CNS.

Question 40

Grey & White Matter:

Answer 40

Within the brain and spinal cord some regions appear
white, while others appear grey.

Grey Matter – the material in the nervous system that 
contains:
cell bodies
dendrites
axon terminals
unmyelinated axons
neuroglia cells

Question 41

White matter

Answer 41

– composed mainly of myelinated
axons (which appear white).

Note the difference between white and gray matter in the body:
Brain => grey is superficial and white is deep.
Spinal cord => white is superficial and grey is deep.

Question 42

Multiple Sclerosis (MS)

Answer 42

– A progressive autoimmune condition which results in the degeneration of myelin sheaths in multiple locations in the CNS. This leads to the replacement of these sheaths with scar/fibrous/plaque that is hard – hence the term ‘sclerosis’.
Affects female Caucasions most commonly.
S & S include fatigue, visual disturbances, paraesthesia, heaviness of muscles (progressive weakness), and other neurological deficits.
This condition is idiopathic and may have periods of spontaneous remission. Likely caused by both genetic and environmental factors.

Question 43

Simple Reflex:

Answer 43

E.g. Accidentally placing your hand on a hot stove.

1. Sensory receptors in the skin detect the extremely high temperature.
2. Signals (APs) are sent via sensory (AFFERENT) neurons to the spinal cord. Here the sensory neurons synapse with interneurons which is where the INTEGRATION occurs.
3. Interneurons then synapse with motor (EFFERENT) neurons, which cause the muscles of the arm & hand to contract and pull away from the ‘noxious’ stimulus.

Question 44

Complex Reflex

Answer 44

(response) : E.g. Someone feels a spider on their arm…
1. Sensory receptors in the skin detect crawling sensation (light touch) and transmit this to your primary somatosensory cortex. Your eyes ‘see’ something with eight legs on your arm.
2. This information is disseminated to other regions of the brain in order to decide what the response should be (integration). Your response will vary depending on factors such as your past experiences (whether you’ve seen a spider), personal preferences (whether you like them) and whether you know about rare flesh eating diseases (necrotizing fasciitis) caused by spider bites (ETC.)!!
3. Voluntary efferent signals are sent to your skeletal muscles (e.g. to violently shake it off!) as well as involuntary activation of the sympathetic nervous system leading to the fight or flight response (but only if you’re scared of spiders!!!).