Human Physiology - Lecture 7: Neural Tissue

Question 1

Neurons:

Answer 1

functional units of neural tissue.

Question 2

Neuroglia:

Answer 2

supporting role

Question 3

Neural tissues

Answer 3

are the brain, spinal cord, complex sense organs (eyes, ear) and nerves

Question 4

Anatomical division of Nervous System

Hint: 4 types & 2 divisions.

Answer 4

Central nervous system (CNS): Brain, spinal cord
Peripheral nervous system (PNS): Neural tissue outside CNS.

Afferent division: bring sensory information to CNS (from skin receptors, eyes, ear,…)
Efferent division: carries commands from the CNS

Somatic nervous system: controls skeletal muscle (voluntary or involuntary).

Autonomic nervous system (ANS); regulates visceral smooth muscle. Also glands, heart,…

Question 5

The Structure of Neurons

Answer 5

Draw the Structure of Neurons

1. Soma
2. Perikaryon
3. Nucleus
4. Axon hillock
5. Axon
6. Teledendria
7. Neurofilaments & Neurotubules
8. Synaptic terminals; connect to postsynaptic cells

Question 6

Structural Classification of Neurons

A.B.U.M

Answer 6

1. Anaxonic neuron: No axon can be distinguish.
   Found in the brain
2. Bipolar neuron: 1 dendrite, 1 axon.
   In special sense organs, but they are rare.
3. Unipolar neuron: One axon with the cell body in the middle.
   Sensory neurons of the peripheral nervous system
4. Multipolar neuron: 2 or more dendrites and 1 axon.
   Most common in CNS; e.g., Motor neurons

Question 7

Functional Classification of Neurons

Hint: 3 Types sEPI, mSV, i

Answer 7

Sensory neurons deliver information from;
Exteroceptors: Sense the external environment

Interoceptors: Monitor function of internal organs

Proprioceptors: Monitor position and movement of muscles and joints

Motor neurons form the efferent division of the PNS

• Somatic motor neurons innervate skeletal muscles
• Visceral motor neurons innervated peripheral effectors (smooth muscle, cardiac muscle, glands,…)

Interneurons (association neurons) constitute the majority of neurons.

• Located entirely within the brain and spinal cord, but some in ganglia
• Distribute sensory information and coordinate motor activity
• Required to integrate complex responses

Question 8

How would you classify a neuron with 2 dendrites and 1 axon?

Answer 8

Multipolar neuron

Question 9

Neuroglia of the Central Nervous System

1. Ependymal cells

Answer 9

Ependymal cells:
- Line ventricles (brain) and central canal (spinal cord)

• Assist in producing, circulating, and monitoring cerebrospinal fluid

Question 10

2. Astrocytes:

Answer 10

Maintain blood–brain barrier
Regulate ion, nutrient, and dissolved- gas concentrations
Provide structural support
Absorb and recycle neurotransmitters
Form scar tissue after injury

Question 11

3. Oligodendrocytes

Answer 11

Myelinate CNS axons

Provide structural framework

Question 12

Microglia

Answer 12

Remove cell debris, wastes, and pathogens by phagocytosis

Question 13

Neuroglia of the Peripheral Nervous System

Answer 13

1. Satellite cells:

2. Schwann cells:

Question 14

Satellite cells:

Answer 14

Surround neuron cell bodies in ganglia

Regulate O2, CO2, nutrient, and neurotransmitter levels around neurons in ganglia

Question 15

Schwann cells:

Answer 15

Surround all axons in PNS
Responsible for myelination of peripheral axons
Participate in repair process after injury

Question 16

Draw and label Neuroglia of the Peripheral Nervous System

Answer 16

.

Question 17

Where could you find Schwann cells?

Answer 17

Axons of motor neurons

Question 18

Resting Membrane Potential

Answer 18

Basic concepts:
Plasma membrane is SELECTIVELY PERMEABLE

Ion movement across the plasma membrane is controlled by ion channels

The Membrane potential changes when charged ions move

Question 19

Study Guide For Membrane Potentials

Answer 19

• 80 mV —–> Hyperpolarized
• 70 mV —–> Resting membrane potential
• 60 mV —–> Depolarized

+30 mV —–> Depolarized

• Depolarization typically involves Na+ entering
• Repolarization typically involves K+ exiting

Question 20

How would a chemical that blocks membrane sodium channels affect a neuron’s ability to depolarize?

Answer 20

It would inhibit depolarization completely

Question 21

What effect would decreasing the concentration of extracellular potassium ions have on the transmembrane potential of a neuron?

Answer 21

hyperpolarization

Question 22

Types of Channels

Hint: 4 types

Answer 22

Leak or background channels: open most of the time
Gated channels: open and close in response to specific stimuli. They may be found in three different states:
Open or activated
Closed, but capable of opening
Inactivated, or incapable of opening
Types of gated channels:
Ligand or Chemically gated channels: e.g. those opened by acetylcholine
Voltage gated channels: respond to changes in transmembrane potential
Mechanically gated channels: respond to physical pressure.

Question 23

What stimulus would open a voltage-gated Magnesium channel?

Answer 23

A change in the transmembrane potential

Question 24

What stimulus would open a voltage-gated Magnesium channel?

Answer 24

A change in the transmembrane potential

Question 25

Graded or Local Potentials

Answer 25

A change in potential that decreases with distance The intensity of the graded potential is proportional to the stimulus Localized depolarization (Na channel opens) or hyperpolarization (K channel opens) Graded potentials occur in dendrites and the cell body (or soma), or the synaptic knob (or terminal). Also in many other cell types. Graded potentials are mediated by chemically (ligand) gated, or sometimes mechanically gated, ion channels

Question 26

All-or-None Principle

Answer 26

Threshold for an axon is -60 mV to -55 mV Below (e.g. -62 mV) will not trigger an action potential Above (e.g. -59 mV) will trigger it. Once triggered, the action potential will always be the same, regardless of the strength of the original input

Question 27

Generation of Action Potentials

Answer 27

Step 1: Depolarization to threshold Step 2: Activation of Na channels Step 3: Inactivation of Na channels and activation of K channels Step 4: Return to normal permeability

Question 28

What is the difference between a graded potential and an action potential?

Answer 28

A graded potential may or may not develop into an action potential, depending on the strength of the depolarization

Question 29

How will a drug that blocks voltage-gated potassium channels affect the ability of a neuron to generate action potentials?

Answer 29

The neuron will stay permanently depolarized

Question 29

Propagation of Action Potentials Types

Answer 29

Continuous propagation & Saltatory propagation

Question 30

Saltatory propagation

Answer 30

Saltatory propagation along myelinated axons is even faster; No need to depolarize/repolarize every section of the axon

Question 31

Continuous propagation

Answer 31

Continuous propagation along an unmyelinated axon is affected by axon diameter; The thicker the faster.

Question 32

At the end of a propagating action potential the membrane is in a refractory state . This is because…

Answer 32

Voltage-gated sodium channels are inactivated

Question 33

Draw and label the ``` a.Presynaptic membrane b Post synaptic membrane c. synaptic cleft d.synaptic vesicles d. teledendrion ```

Answer 33

...

Question 34

Types of synapses

Answer 34

Electrical synapses: involve gap junctions, like a syncytium! VERY RARE Chemical Synapses: The vast majority

Question 35

Chemical Synapses:

Answer 35

A neurotransmitter is involved. May or may not result in an action potential at the postsynaptic cell. A synapses can be excitatory, which produces depolarization, or inhibitory, resulting in hyperpolarization (opening of voltage-gated K+ channels, instead of Na channels).

Question 36

Cholinergic Synapses

Answer 36

Release of acetylcholine (ACh) Information flows across synaptic cleft Synaptic delay occurs as calcium influx and neurotransmitter release take appreciable amounts of time ACh broken down; Choline reabsorbed by presynaptic neurons and recycled. Synaptic fatigue occurs when stores of ACh are exhausted.

Question 37

What should be the effect of completely blocking all voltage-gated Ca2+ channels at the synapse?

Answer 37

The synapse will stop responding to action potentials.

Question 38

Neurotransmitters

Answer 38

Neurotransmitters act on receptors, which may have excitatory role or inhibitory role. Examples; Dopamine, Serotonin, GABA, Nitric oxide (gas), carbon monoxide (gas), are all neurotransmitter in brain. Most drugs mimic or affect neurotransmitter function

Question 39

One neuron may receive information (graded potentials) from thousands of synapses

Answer 39

Arrive at the soma | All get integrated into one response.

Question 40

Incoming information may be;

Answer 40

Excitatory Postsynaptic Potential (EPSP) Inhibitory Postsynaptic Potential (IPSP)

Question 41

All this graded potentials are integrated at the axon hillock

Answer 41

If a threshold is reached and action potential is fired through the neuron’s axon. The degree of sensory stimulation or strength of motor response is proportional to the frequency of action potentials.

Question 42

All this graded potentials are integrated at the axon hillock

Answer 42

If a threshold is reached and action potential is fired through the neuron’s axon. The degree of sensory stimulation or strength of motor response is proportional to the frequency of action potentials.

Question 43

How does a mechanoreceptor neuron communicate a strong pressure applied to the dermis?

Answer 43

By firing multiple action potentials within a short time.

Question 44

What should be the effect of partially blocking voltage-gated Ca2+ channels at the synapse?

Answer 44

The synapse will still work, but will begin secreting less neurotransmitter in response to action potentials