Neuro Physiology Flashcards Preview

Physiology 1 > Neuro Physiology > Flashcards

Flashcards in Neuro Physiology Deck (89):
1

The nervous system has 2 categories of cells

Neurons, Neuroglia

2

What is the major functional unit of the nervous system?

Neuron

3

Neurons are composed of (7)

1. Dendrites- receive info
2. Cell body, soma, perikaryon- contains organelles
3. Axon- carries info
4. Axon hillock or trigger zone- axon origin, originates AP
5. Presynaptic terminal- end of axon, transmit info
6. Myelin sheath- enhances speed of info transfer
7. Node of Ranvier- gaps in the insulating myelin sheath

4

How do neurons communicate?

Via synapses

5

Where does myelin originate from?

Oligodendrocytes of CNS
Schwann cells of PNS

6

Myelin formation

Schwann cell cytoplasm forms a ring inside and outside of the sheath

7

What does the myelin sheath facilitate and why?

Facilitates conduction because it is an electrical insulator - saltatory conduction

8

In saltatory conduction of the impulse, what jumps from node to node?

The action potential

9

Is depolarization faster or slower with myelin sheaths?

Faster

10

Conduction velocity in myelinated fibers is proportional to?

Diameter of the axon - Larger axons have longer internodes and faster conduction velocities

11

What are the 3 structures of neurons?

Multipolar, bipolar, unipolar

12

Multipolar neurons

-Numerous cell processes
-1 axon, many dendrites
-Motor neurons
-Most prevalent

13

Bipolar neurons

-2 processes: 1 axon, 1 dendrite
-Interneurons- interconnect neurons w/ brain and spinal cord

14

Unipolar neurons

-Single stem process that separates into 2 processes: peripheral and central
-Sensory neurons

15

Neurons classified according to function (3)

1. Motor or efferent (brain to target organs)
2. Sensory or afferent (receptors to brain)
3. Interneurons or associated neurons (connect motor and sensory)

16

Neuroglia or glial cells

-Smaller, no axons or dendrites
-Capacity to divide
-No action potentials
-Do not participate directly in synaptic interactions and electrical signaling

17

Function of glial cells

• Participate in the production of myelin sheaths of axons
• Modulate the growth of developing or damaged neurons
• Buffer extracellular concentrations of K and neurotransmitters
• Participate in the formation of contacts between neurons (synapses)
• Participate in certain immune responses of the nervous system

18

Where are glial cells found in the CNS?

-Microglial cells
-Astrocytes
-Oligodendrocytes
-Ependymal cells

19

Where are glial cells found in the PNS?

Schwann cells

20

Microglia cells

-Brain immune cells
-Phagocytosis
-Release nitric oxide to prevent viral replication
-Protect brain against injury and infection
-Play a role in the developing brain

21

Astrocytes

-Star shaped cells with numerous long processes
-50% of glial cell population in CNS
-Structural and metabolic support for neurons
-Release neurotrophic factors important for neuronal survival
-Mantain a neuron’s working environment- control neurotransmitter and ion levels

22

Oligodendrocytes

-Provide support to axons of neurons in the CNS
-Processes that extend to form myelin

23

Ependymal cells

-Cover the ventricles of the brain, central canal of the CNS, and choroid plexus in the 4th ventricle of the medulla oblongata
-Creating CSF

24

Schwann cells

-AKA neurolemmocytes
-Provide support to axons of the PNS

25

CNS

Brain and spinal cord
• The brain is surrounded by the skull
• The spinal cord is surrounded by a series of cervical, thoracic and lumbar vertebrae and ligaments

26

CNS subdivided into 7 regions

1. Spinal cord
2. Medulla oblongata
3. Pons
4. Cerebellum
5. Midbrain or Mesencephalon
6. Diencephalon
7. Telencephalon or cerebral hemispheres

27

What is the CNS protected by?

The meninges and CSF

28

3 Protective Layers of CNS

1. Pia mater- Innermost meningeal layer, lying next to the CNS
2. Arachnoid- Spiderweb appearence, traps CSF, subarachnoid space
3. Dura mater- Outermost meningeal layer, often fused with inner surface of the skull, thicker and protects CNS

29

Cerebrospinal Fluid (CSF)

-Clear, colorless fluid
-Produced in the ventricles of the brain
-Determinant of neuronal microenvironment
-Shock absorber for CNS

30

Where is CSF located?

• Subarachnoidspace
• Central canal of the spinal cord
• Ventricular system of the brain

31

PNS

-Composed by all neural tissue outside CNS
-Deliver sensory info to CNS
-Carries motor commands to peripheral tissues and systems

32

Peripheral nerve fiber

-Axon and myelin sheath together
-Surrounded by endoneurium CT

33

Fascicle

-Bundle of nerve fibers
-Surrounded by perineurium CT

34

Nerve (cranial or spinal)

-Bundle of fascicles
-Surrounded by epineurium CT

35

Describe the nucleus in the cell body of the nerve.

-Prominent nucleolus
-No centrioles
-Cannot divide

36

What is the name of the Rough ER in a nerve cell body?

Nissl substance or nissl body

37

What do dendrites do?

Integrate the incoming info and determine whether action potentials will be produced by the neuron

38

In some neurons, the dendrites are covered with small membranous protrusions called?

Dendritic spines
-Each spine can synapse with different axons

39

How can neurons be transmitted to one another?

Chemical or electrical synapses

40

Chemical synapses

-Most common form of synapses - unidirectional transmission
-Presynaptic neuron secretes a neurotransmitter that will act on receptor proteins in postsynaptic neuron
-Can be excitatory or inhibitory

41

What does the action of the neurotransmitter in the postsynaptic membrane depend on?

Receptor proteins

42

Cation channels

Opened by excitatory neurotransmitters
Induce depolarization

43

Anion channels

Opened by inhibitory neurotransmitters
Induce hyperpolarization

44

Ionotropic receptors

Neurotransmitter receptor that acts directly on ion-gated channels

45

Metabotropic receptors

Neurotransmitter receptor that acts through 2nd messengers, GPCR, cAMP pathway

46

Electrical synapses

• The cytoplasm of adjacent cells are directly connected by clusters of ion channels, gap junctions
• Bidirectional transmission
• Coexist and interact with chemical synapses

47

The potential difference across the membrane of resting neurons is about?

-70mV

48

What 3 things determine membrane potential?

• The movement of ions toward a dynamic equilibrium
• Differential permeability of the membrane to diffusion of ions
• Na K pump

49

Where does ATP for the pump come from?

Intracellular metabolism of glucose and O2

50

What are graded potentials?

Brief local changes in postsynaptic membranes are generated

51

T/F: The amplitude of the graded potential is directly proportional to the intensity of the stimulus applied at synaptic sites.

True
• Each synaptic site generate graded potentials
• They travel to reach the axon hillock or trigger zone

52

Where are graded potentials integrated to generate action potentials?

Trigger zone

53

In order to initiate an action potential, graded potentials must reach a level called?

Threshold potential or threshold voltage

54

Threshold potential

The minimum voltage change to trigger an action potential, -55mV

55

When will the action potential be triggered in graded potential?

Once the sum of graded potentials exceeds the threshold

56

What happens if the depolarization does not reach the threshold?

No action potential will occur

57

How do graded potentials modulate the postsynaptic neuron?

By shifting the resting membrane potential, toward or away from the threshold potential

58

Depolarization

Shift the membrane potential toward more positive
Ex. Glutamate

59

Excitatory Postsynaptic Potentials (EPSP)

Depolarizing graded potentials
Drives the membrane potential toward the threshold
Excitatory synapses

60

Hyperpolarization

Shift membrane potential toward more negative
Ex. GABA

61

Inhibitory Postsynaptic Potentials (IPSP)

Hyperpolarizing graded potentials
Inhibitory synapses

62

What are the 2 modes of summation?

Spatial summation and temporal summation

63

Spatial summation

-Graded potentials induced by different synapses summate in the postsynaptic neuron
-Simultaneous summation of inhibitory (IPSP) and excitatory (EPSP) graded potentials also occur

64

Temporal summation

Succesive discharges from a single presynaptic terminal summate in the post synaptic neuron

65

What are the 3 phases of the action potential?

-Resting phase
-Depolarization phase
-Repolarization phase

66

Absolute refractory period

-The time needed for the voltage-gated sodium channels to revert from the inactivated state to the resting state
-AP initiation is completely blocked

67

Relative refractory period

-Voltage-gated potassium channels are closed
-AP is inhibited, not blocked
-A strong stimuli can shift the membrane potential to the threshold and generate an AP

68

Describe saltatory conduction

-AP occurs only at Nodes of Ranvier
-Nodes of Ranvier are rich in ion channels
-APs jump from node to node
-Na influx depolarizes the membrane

69

How are the neuraxis and meninges drained?

By veins and sinuses

70

The ventricular system comprises 4 expanded regions forming ventricles, interconnecting foramen and tubes. What are they?

-Lateral ventricles: longitudinally in each hemisphere and connected with the 3rd ventricle
-Third ventricle: surrounding the interthalamic adhesion and connected with 4th ventricle
-Fourth ventricle: connected with the subarachnoid space

71

T/F: Only some of the CSF is formed at the choroid plexus of the ventricles.

False, most of the CSF

72

What is the choroid plexus?

A cauliflower-like growth of capillaries covered by a thin layer of ependymal cells (glial cell)

73

In the choroid plexus, what type of junctions join the ependymal cells?

Tight Junctions

74

What regulates the passage of ions and molecules across the ependymal cell barrier?

Membrane transporters and selective channels

75

List some functions of CSF.

• Cushion the brain, protect it against blows to the head
• Mantain a consistent extracellular microenviroment for the neurons and glia
• Effective waste control system that can remove potentially harmfull cellular metabolites
• Act as a brain distribution system for some peptide hormones and growth factors

76

Most of the CSF is absorbed from the subarachnoid space into the venous sinuses through what?

Arachnoid villi
-Small finger like projections of the arachnoid membrane that poke through the dura mater in the lumen of venous sinuses

77

T/F: Absorption of CSF tends to be pressure dependent and bidirectional.

False, unidirectional

78

What 2 barriers are located both at the choroid plexus and at the tissue capillary membranes in most areas of the brain?

Blood-CSF barrier
Blood-Brain barrier

79

Interaction between what is important for the maintenance of the BBB?

Endothelial cells and astrocytes

80

Which glucose transporter is used in the BBB?

GLUT-1

81

Primary or 1st order neurons

The primary afferent neuron that receive the signal and send information to CNS

82

Secondary or 2nd order neurons

Conduct impulses from spinal cord or brainstem to thalamus (cross over to opposite side before reaching thalamus)

83

Tertiary or 3rd order neurons

Conducts impulses from thalamus to primary somatosensory cortex

84

Somatosensory signals

-Originate from cutaneous areas, muscles and joints
-Respond to mechanical, chemical, thermal stimuli
-Produce sensation of touch, pressure vibration, pain and warm/ cold

85

Viscerosensory signals

-Originate from internal structures of the body
-Some are consciously detectable
-Stretching of stomach and bladder

86

What are the 3 types of sensory receptors classified by their structure?

1. Simple receptors
2. Complex receptors
3. Special senses receptors

87

Simple receptors

• No special modification – free nerve endings
• Not myelinated
• Most common type

88

Complex receptors

• Ensheated by connective tissue capsule
• Encapsulated portions of axon are not myelinated

89

Special senses receptors

• Specialized receptor cells