Chapter 12: Nervous Tissue

Question 1

The nervous system

Answer 1

Responsible for all our behaviours, memories, and movements.

It helps to maintain homeostasis

Question 2

3 basic functions of nervous system

Answer 2

1) Sensory function - sensory input from receptors detect changes inside/outside the body.

2) Integrative function - sensory input is interpreted and coordinated with an appropriate motor response.

3) Motor function - motor output is brought to an effector organ (such as a muscle or gland)

Question 3

2 divisions of the nervous system

Answer 3

1) Central nervous system - contains the brain and spinal cord

2) Peripheral nervous system - contains the cranial and spinal nerves, ganglia, and sensory receptors
Subdivisions:
a) sensory division
b) motor division

Question 4

Sensory division

Answer 4

Part of the PNS which delivers sensory information from various sensory receptors throughout the body to the CNS.

Carries info such as smell, hearing, vision, taste, touch, temp, pain…etc.

Question 5

Motor division

Answer 5

Part of the PNS where motor neurons pass down impulses from CNS to effectors (muscles/glands) in order to produce movements.

Subdivisions:
i) Somatic nervous system
ii) Autonomic nervous system

Question 6

Somatic nervous system

Answer 6

Part of the motor division of the PNS which is under voluntary control.

Motor neurons will conduct impulses from CNS to skeletal muscles.

Question 7

Autonomic nervous system

Answer 7

Part of the motor division of the PNS which is under involuntary control.

Motor neurons conduct impulses from CNS to smooth and cardiac muscles

Subdivisions:
Sympathetic - fight or flight
Parasympathetic - rest of digest

Question 8

Neurons

Answer 8

Nerve cells which are the functional units of the nervous system. They will generate action potentials (impulses). They cannot undergo mitosis.

Parts of a neuron:
Soma - hold the nucleus, organelles, nissl bodies, neurofibrils
Dendrites - carry info towards the cell body of the neuron
Axons - carry info away from cell body of the neuron

Question 9

Neuroglia

Answer 9

Supportive/protective cells that aid neurons.
They are smaller and more numerous than neurons, and are capable of mitosis.

6 types:
- astrocytes, oligodendrocytes, microglia, ependymal cells (CNS)
- Schwann cells, satellite cells (PNS)

Question 10

Axons

Answer 10

Can be
a) Myelinated - covered by layers of neuroglial membrane and have nodes of ranveir.
If in CNS = wrapped by oligodendrocytes
If in PNE = wrapped by schwann cells

b) Unmyelinated - surrounded by a thin Schwann cell membrane that enclosed several axons

Question 11

Grey matter

Answer 11

Consists of neuron cell bodies, dendrites, unmyelinated axons, axon terminals, neuroglia

Question 12

White matter

Answer 12

Consists of neuron processes, mainly myelinated axons (myelin sheath)

Question 13

Nucleus

Answer 13

Cluster of neuron cell bodies in the CNS

Question 14

Ganglion

Answer 14

Cluster of neuron cell bodies in the PNS

Question 15

Tract

Answer 15

Bundle of neuron processes in the CNS

Question 16

Nerve

Answer 16

Bundle of neuron processes the PNS

Question 17

Ion channels

Answer 17

Ions can diffuse down an electrochemical gradient through a channel protein. They travel from an area that is charged, to an area that is oppositely charged.

4 kinds:
- leakage channels
- ligand-gated channels
- mechanically-gated channels
- voltage-gated channels

Question 18

Leakage channels

Answer 18

The gates of the channel will randomly open and close

There are more K+ leakage channels than Na+ leakage channels in the cell membrane so more + leaks out causing a more negative charge inside the cell

Question 19

Ligand-gated channels

Answer 19

Channel will open and close in response to a certain chemical stimulus

Question 20

Mechanically-gated channels

Answer 20

Channel will open or close in response to a mechanical stimulus (such as vibration, touch, pressure)

Question 21

Voltage-gated channel

Answer 21

Channel will open in response to a change in membrane potential (voltage)

Question 22

Resting membrane potential

Answer 22

There is difference in electrical charge that exists across the cell membrane.

Resting membrane potential = -70mV,

Outside of the cell (extracellular fluid) there is a higher concentration of Na+, and Cl-
Inside the cell (intracellular fluid) there is a higher concentration of K+ and negative proteins.

Question 23

Na/K pump

Answer 23

The sodium potassium pump maintains the diffusion of Na+ and K+.

3Na+ bind to the pump and ATP donates its phosphate which will change the shape and expel the 3Na outside the cell. While it’s still open to the outside, 2K+ bind to the pump, the phosphate detaches which changes the shape of the pump, and the 2K+ and released into the cell.

Question 24

Why can’t equilibrium be reached in a neuron?

Answer 24

Neurons need the difference in ion concentration in order to generate a nerve impulse / action potential.

Question 25

Threshold stimulus

Answer 25

The smallest amount of stimulation or force that is needed to initiate a response.

Must get the membrane potential to -55mV to make an action potential

(Essentially it triggers an action potential)

Question 26

Steps of generating an action potential

Answer 26

1. Resting state
2. Depolarizing phase
3. Repolarizing phase
4. Hyperpolarizing phase (if necessary)
5. Refractory period

Question 27

Resting state

Answer 27

All the voltage gated Na+ K+ channels are closed. The membrane is at a resting membrane potential (-70mV).
There is a buildup of negative charges inside the cell.

Question 28

Depolarizing phase

Answer 28

The voltage-gated Na+ channels rapidly send in Na+ ions, which makes the inside less negative (depolarizes it).

The membrane potential went from -70mV to -55mV (threshold needed to make action potential) to +30mV.

Question 29

Repolarizing phase

Answer 29

The Na+ channels close and the K+ channels start to slowly open and it becomes repolarized as the K+ ions are expelled from the neuron, leaving the negative charges in it.

The membrane potential goes back to -70mV as the ion distributions of the resting state are restored

Question 30

Hyperpolarizing phase

Answer 30

(Doesn’t always happen)

When the K+ channels close too slowly, too much K+ could leave the neuron.

The membrane potential could get to -90mV, but will eventually get back to -70mV.

Question 31

Refractory period

Answer 31

A time period where a second action potential cannot be generated as it is resetting from the last one. Makes sure there is only 1 action potential going on at a time.

2 types:
Absolute refractory period - an action potential is not possible at all
Relative refractory period - a stronger stimulus is required to generate an action potential

Question 32

Conducting of an action potential

Answer 32

When the action potential goes towards the axon terminals.

2 types:
Continuous conduction - occurs along unmyelinated axons (much slower)
Saltatory conduction - occurs along myelinated axons (much faster).
The action potential jumps from node to node regenerating itself. (Depolarization happens at each node)

Question 33

Synapse

Answer 33

A junction between 2 neurons

Can be between a neuron and its effector
or
Between 2 neurons:
Axodentritic - axon terminal to dendrite
Axosomatic - axon terminal to soma
Axoaxonic - axon terminal to axon terminal
The first neuron is presynaptic, the second is postsynaptic. They are separated by the synaptic cleft.

Question 34

Transmission across synapses

Answer 34

An action potential can’t cross the synaptic cleft because there are ligand gates channels it must go through, so it must be converted to a chemical signal using neurotransmitters.

Question 35

Removal of the neurotransmitter

Answer 35

Can occur by:
1. Breakdown via enzymes in the synaptic cleft
2. Re-uptake into presynaptic neuron
3. Uptake into neighbouring neuroglia cells
4. Diffusion away from cleft

Question 36

Divergence

Answer 36

The presynaptic neuron may branch many times to synapse with many postsynaptic neurons

Question 37

Convergence

Answer 37

Many presynaptic neuron endings may synapse with a single postsynaptic neuron

Question 38

Astrocytes

Answer 38

The largest, most numerous neuroglial cells in the CNS

Function to maintain chemical environment around the neurons

Question 39

Microglial cell

Answer 39

Smaller neuroglial cells in the CNS

Function to clean up cellular debris / invaders of the neurons

Question 40

Ependymal cells

Answer 40

Bottom layer of neuroglial cells in the CNS

Function to produce cerebrospinal fluid and secrete it

Question 41

Oligodendrocytes

Answer 41

Round (alien-looking) neuroglial cells in the CNS

Function by wrapping themselves around neurons to speed up the conduction of nerve impulses (form myelin sheaths)

Question 42

Schwann cells

Answer 42

In the PNS

Wrap around part neuron to speed up nerve impulses

Question 43

Satellite cells

Answer 43

In the PNS

Function to help in structural support, and mediate the exchange of things passing in and out of the neuron.