The Nervous System

Question 1

Function of the nervous system?

Answer 1

Helps the body to communicate with each other. To relay messages from inside and out of the body to the brain and back again. Reacts to changes inside and out

Question 2

What is the two divisions of the Nervous System?

Answer 2

Central nervous system (CNS)

Peripheral nervous system (PNS)

Question 3

What are the two functional divisions (to and from the brain)

Answer 3

# Sensory (afferent) division, carrying forward to the brain
# Motor (efferent) division, carrying information away from CNS to the effector organs

Question 4

What does Sensory (afferent) division do? carrying forward

Answer 4

Afferent fibres convey impulses from skin,
Skeletal muscles, joints and visceral organs 
# Keeps CNS constantly informed what is going on inside and out of the body
# Visceral afferent fibers constantly transmitting messages from visceral organs

Question 5

What does the Motor(efferent) division do? away from CNS

Answer 5

# Transmits impulses from the CNS to effector organs
# These impulses activate muscles to contract, and glands to secrete

Question 6

What is the name of two divisions of the motor (efferent) division of PNS?

Answer 6

Somatic (voluntary)typically under conscious control of skeletal muscles,
Autonomic (involuntary)
#no direct conscious control
#regulates smooth muscle(lining of the stomach), cardiac muscles and glands
#two functional subdivisions: Sympathetic
Parasympathetic

Question 7

What are the two cell types of Nervous tissue?

And what do they do?

Answer 7

Neurons: Co-ordinates body function
Communicates via electrical signals(and release of neurotransmitters)
Neurolglia: (glial cells)
Supports cells (provide nourishment and protection)

Question 8

What are the two main Neuroglia cells called?

Answer 8

Oligodentrocytes (CNS)
Schann cells (PNS)

Question 9

What is Oligodendrocytes?

Answer 9

Process of Ensheathing CNS nerve fibers, forming insulating myelin sheaths

Question 10

What do Schwann cells do?

Answer 10

Surround peripheral fibres(PNS) and form myelin sheaths and protect the axon

Question 11

What is a Myelin Sheath?

What 2 types of cells make these sheaths?

Answer 11

Protein-lipid sheath around most long axons eg. like our plastic covered electrical wiring
Functions: protect and electrically insulate the axon
increase speed of nerve impulse transmission
Schwann cells: PNS
Oligodendrocytes: CNS

Question 12

Neurons (nerve cells)

what do they need to function, or need a continuous supply of?

Answer 12

They are the basic building block of the nervous system
# Neurons are shaped differently depending where they are in the body(located)
All have 100’s of finger like projections called Dentrites and long fibers called axons
#The have a high metabolic rate - they need a lot of energy
They depend on a continuous supply of oxygen and glucose
# The cell membrane also acts at part of the receptive region that receives information from other neurons
# The rough ER are called Nissl bodies
# Clusters of cell bodies are called
- nuclei in the CNS
- ganglia in the PNS

Question 13

How do Neurons communicate with each other?

Answer 13

The axon feathers out at the end and has a number of bump sites.
Where the bump site is near a dendrite, an chemical signal can cross
# The space between these two sites is call a Synapse
# The special chemical messages which jump from one neuron to another are called Neurotransmitters

Question 14

Describe the Autonomic Nervous System.
# What are the two sub divisions of the Autonomic Nervous System?

Answer 14

The autonomic nervous system is part of the peripheral nervous system. One of its main roles is to regulate glands and organs without any effort from our conscious minds.

The autonomic nervous system is made up of two parts: the sympathetic and the parasympathetic. These systems act on the body in opposite ways. Together, they coordinate a multitude of adjustments required for our changing personal needs as we move through our environment. For example, the size of our pupils is adjusted automatically to allow the correct amount of light into our eyes for optimum vision, our sweat glands are turned on when we get too hot and our salivary glands produce saliva when we eat food (or even think about it!).

Question 15

What is the Sonomic (voluntary) Nervous System?
# What are the roles it plays in the peripheral nervous system?

Answer 15

The somatic nervous system is also a part of the peripheral nervous system. One of its roles is to relay information from the eyes, ears, skin and muscle to the central nervous system (brain and spinal cord). It also obeys commands from the central nervous system and makes muscles contract or relax, allowing us to move.

Question 16

Describe Dendrites?

Answer 16

Are short tapering difusely branching extensions. Typically motor neurons have 100’s clustering close to the cell body. Virtually all organelles that occur in the cell body occur in dendrites.
They are the main receptive or input regions. They provide an enourmous surface area for receiving signals from other neurons.
In many brain areas the finer dendrites are highly specialised for information collection. The bristle thorny appendages having bulbous or spiky ends, which represent points of very almost touching contact (synapses) with other neurons.
Dendrites convey incoming messages towards the cell body. Not usually action potentials(nerve impulses) but are graded potentials

Question 17

What is White matter?

What is Gray matter?

Answer 17

# White matter; Dense collections of myelinated fibers
# Gray matter; Mostly neuron cell bodies and unmyelinated fibers.

Question 18

Prior the Action Potential of a Neuron, describe charges of the nerve cell?

Answer 18

When a neuron is not sending signals, the inside of the neuron has a negative charge relative to the positive charge outside the cell. Electrically charged chemicals known as ions maintain the balance of positive and negative charges. Calcium contains two positive charges, sodium and potassium contain one positive charge and chloride contains a negative charge.

Question 19

Describe the Sodium-ion pump?

Answer 19

When at rest, the cell membrane of the neuron allows certain ions to pass through while preventing or restricting the movement of other ions. In this state, sodium and potassium ions cannot easily pass through the membrane. Potassium ions, however, are able to freely cross the membrane. The negatively ions inside of the cell are unable to cross the barrier. The cell must activity transport ions in order to maintain its polarized state. This mechanism is known as the sodium-ion pump. For every two potassium ions that pass through the membrane, three sodium ions are pumped out.

Question 20

What happens during an Action Potential?

Answer 20

When an impulse is sent out from a cell body, the sodium channels open and the positive sodium cells surge into the cell. Once the cell reaches a certain threshold, an action potential will fire, sending the electrical signal down the axon. Action potentials either happen or they don’t; there is no such thing as a “partial” firing of a neuron. This principle is known as the all-or-none law.

Question 21

What happens after the Action Potential?

Answer 21

After the neuron has fired, there is a refractory period in which another action potential is not possible. During this time, the potassium channels reopen and the sodium channels close, gradually returning the neuron to its resting potential.

Question 22

What are the key steps for the Action Potential?

Answer 22

# Electrical currents across neuron membranes are caused by the rapid diffusion of ions
- this occurs through specific membrane channels 
ie. voltage gated ion channels
# Sequence of events following neuron stimulation is as follows
1.  Sodium ions (Na+) rapidly diffuse into the neuron
2.  Potassium ions (K+) then diffuse out the neuron

Question 23

Action Potential Stages

Answer 23

Resting membrane potential
- -70mV
- Only leakage of channels of Na+ and K+ are open
- All voltage gated Na+ and K+ are closed
# Depolarisation
- Process where polarisation goes towards zero
- this occurs when stimulus caused opening of voltage-gated Na+ channels
- This Na+ influx caused depolarisation. Positive feedback leads to opening of all Na+ channels, and a reversal of membrane polarity to +30mV(spike of the action potential)
- overall, depolarisation results in inside of the membrane becoming less negative than the resting potential
# Repolarisation
- When the inside becomes positive enough, Na+ channels shut. This stimulates slow voltage-sensitive K+ gates to open. This means that now K+ can now exit the cell
- K+ carries a positive charge, so then inside of cell becomes negative again (ie. -70mV)
# Hyperpolarisation
- Increase of membrane potential away from zero
- Inside of the membrane becomes more negative than the resting potential, because K+ channels are very slow to shut and some extra K+ leaks out
- reduces the probability of producing a nerve impulse, but the normal resting state re-established with help of Na+/K+ ATPase pump.

Question 24

Explain Absolute Refractory Period

Answer 24

Is the time from the opening of the Na+ channels until the resetting of the channels

• Ensured that each AP is an all in one event
• Enforces one-way transmission of nerve impulses